0001628280-26-045886 | 10-K | XBRL Viewer

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Income taxes - Net loss before income taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest [Abstract]
United States	$ (66,042)	$ (25,870)
United Kingdom	(248,449)	(220,959)
Total	$ (314,491)	$ (246,829)

- Definition

Amount after tax of income (loss) from continuing operations attributable to the parent.

+ References

+ Details

Fair value of financial assets and liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Mar. 31, 2025
Fair value of financial assets and liabilities
Short-term investments:	$ 180,138	$ 462,564
Money market funds
Fair value of financial assets and liabilities
Cash equivalents:	104,275	89,879
US Government Agency bonds
Fair value of financial assets and liabilities
Cash equivalents:	15,998
Short-term investments:	3,984	84,804
US Treasury bonds
Fair value of financial assets and liabilities
Short-term investments:	55,881	287,881
Level 1
Fair value of financial assets and liabilities
Short-term investments:	0	0
Level 1 \| Money market funds
Fair value of financial assets and liabilities
Cash equivalents:	0	0
Level 1 \| US Government Agency bonds
Fair value of financial assets and liabilities
Cash equivalents:	0
Short-term investments:	0	0
Level 1 \| US Treasury bonds
Fair value of financial assets and liabilities
Short-term investments:	0	0
Level 2
Fair value of financial assets and liabilities
Short-term investments:	180,138	462,564
Level 2 \| Money market funds
Fair value of financial assets and liabilities
Cash equivalents:	104,275	89,879
Level 2 \| US Government Agency bonds
Fair value of financial assets and liabilities
Cash equivalents:	15,998
Short-term investments:	3,984	84,804
Level 2 \| US Treasury bonds
Fair value of financial assets and liabilities
Short-term investments:	55,881	287,881
Level 3
Fair value of financial assets and liabilities
Short-term investments:	0	0
Level 3 \| Money market funds
Fair value of financial assets and liabilities
Cash equivalents:	0	0
Level 3 \| US Government Agency bonds
Fair value of financial assets and liabilities
Cash equivalents:	0
Short-term investments:	0	0
Level 3 \| US Treasury bonds
Fair value of financial assets and liabilities
Short-term investments:	$ 0	$ 0

- Definition

Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

+ References + Details

Nature of the business	12 Months Ended
Nature of the business	Mar. 31, 2026
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of the business	Nature of the business Replimune Group, Inc. (the “Company”) is a clinical-stage biotechnology company committed to applying our leading expertise in the field of oncolytic immunotherapy to transform the lives of cancer patients through our novel oncolytic immunotherapies. Replimune Group, Inc., whose predecessor was founded in 2015, is the parent company of its wholly owned, direct and indirect subsidiaries: Replimune Limited (“Replimune UK”); Replimune, Inc. (“Replimune US”); Replimune Securities Corporation; and Replimune (Ireland) Limited. The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, development by competitors of new technological innovations, dependence on key personnel, protection of proprietary technology, compliance with government regulations and the ability to secure additional capital to fund operations. Product candidates currently under development will require significant additional research and development efforts, including preclinical and clinical testing and regulatory approval, prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel and infrastructure and extensive compliance and reporting capabilities. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales. Basis of presentation The accompanying consolidated financial statements have been prepared on the basis of continuity of operations, realization of assets and the satisfaction of liabilities and commitments in the ordinary course of business. The Company has incurred recurring losses since its inception, including net losses of $313.9 million and $247.3 million for the years ended March 31, 2026 and 2025, respectively. In addition, as of March 31, 2026, the Company had an accumulated deficit of $1,262.5 million. In accordance with ASC 205-40, Presentation of Financial Statements—Going Concern, management has evaluated whether there are conditions or events, considered in the aggregate, that raise substantial doubt about the Company's ability to continue as a going concern within one year after the date these consolidated financial statements are issued. Based on its current operating plan, the Company expects to continue to generate operating losses for the foreseeable future and that its existing cash, cash equivalents and short-term investments will be sufficient to fund its operating expenses and capital expenditure requirements only into the first calendar quarter of 2027, which is less than one year from the date these consolidated financial statements are issued. The Company does not have any committed source of additional funding and will be required to obtain additional financing to fund its operations beyond that date. These conditions raise substantial doubt about the Company's ability to continue as a going concern. The Company is collaborating with the FDA regarding a path forward for RP1 and, if the BLA is approved, the Company will determine the best source of capital, which may be raising additional capital through public or private equity offerings (including under our at-the-market facilities), although there can be no guarantee that the Company will be able to raise such capital on acceptable terms, or at all. If the BLA is not approved, the Company will likely need to (i) execute a considerable restructuring and workforce reduction to reduce our cash burn, (ii) reconsider our product development efforts and strategies and (iii) pursue collaborations, strategic alliances, licensing arrangements, business combination, merger or acquisition, or other strategic business development activities to continue operations. In either scenario, our plans are subject to risks and uncertainties, including factors outside our control. Accordingly, we have not been able to conclude that these plans are probable of being effectively implemented and, as such, they do not alleviate the substantial doubt about our ability to continue as a going concern.

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Cash flows from operating activities:
Net loss	$ (313,940)	$ (247,297)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	32,272	35,044
Depreciation and amortization	3,332	3,502
Operating lease, right-of-use-asset amortization	771	683
Finance lease, right-of-use-asset amortization	2,428	2,428
Net amortization of premiums and discounts on short-term investments	(2,545)	(8,947)
Impairment on property, plant and equipment	188	0
Noncash interest expense	1,933	1,568
Unrealized foreign currency transaction gains	(942)	(201)
Changes in operating assets and liabilities:
Research and development incentives receivable	451	1,303
Prepaid expenses and other current assets	(232)	(252)
Other non-current assets	0	(1,200)
Accounts payable	(4,939)	9,941
Accrued expenses and other current liabilities	2,184	11,743
Operating lease liabilities	(818)	(720)
Other non-current liabilities	(487)	155
Net cash used in operating activities	(280,344)	(192,250)
Cash flows from investing activities:
Purchases of property, plant and equipment and software capitalization	(4,223)	(6,687)
Purchase of short-term investments	(77,894)	(403,586)
Proceeds from sales and maturities of short-term investments	392,960	386,477
Net cash provided by (used in) investing activities	310,843	(23,796)
Cash flows from financing activities:
Proceeds from issuance of prefunded warrants to purchase common stock, net of underwriting fees and offering costs	0	97,000
Proceeds from long-term debt	35,000	0
Principal payment of finance lease obligation	(736)	(599)
Proceeds from exercise of stock options and pre-funded warrants	883	267
Net cash provided by financing activities	66,294	252,396
Effect of exchange rate changes on cash, cash equivalents and restricted cash	1,112	315
Net increase in cash, cash equivalents and restricted cash	97,905	36,665
Cash, cash equivalents and restricted cash at beginning of period	112,822	76,157
Cash, cash equivalents and restricted cash at end of period	210,727	112,822
Supplemental disclosure of cash flow information:
Cash paid during the period for interest	4,688	4,198
Cash received (paid) for income taxes, net	5	(105)
Supplemental disclosure of non-cash investing and financing activities:
Purchases of property and equipment included in accounts payable and accrued expenses	80	171
Common stock
Cash flows from financing activities:
Proceeds from issuance of common stock, net of offering costs	0	155,728
ATM Offering
Cash flows from financing activities:
Proceeds from issuance of common stock, net of offering costs	$ 31,147	$ 0

Segment Information (Details) $ in Thousands	12 Months Ended
Segment Information (Details) $ in Thousands	Mar. 31, 2026 USD ($) segment	Mar. 31, 2025 USD ($)
Segment Reporting [Abstract]
Number of operating segments \| segment	1
Number of reportable segments \| segment	1
Operating expenses:
Selling, general and administrative	$ 98,735	$ 72,180
Total operating expenses	319,919	261,627
Loss from operations	(319,919)	(261,627)
Other income (expense), net	5,428	14,798
Loss before income taxes	(314,491)	(246,829)
Income tax (benefit) provision	(551)	468
Net loss	(313,940)	(247,297)
Reportable Segment
Operating expenses:
Unallocated research and development expenses	132,786	125,580
Selling, general and administrative	98,735	72,180
Total operating expenses	319,919	261,627
Loss from operations	(319,919)	(261,627)
Other income (expense), net	5,428	14,798
Loss before income taxes	(314,491)	(246,829)
Income tax (benefit) provision	(551)	468
Net loss	(313,940)	(247,297)
IGNYTE \| Reportable Segment
Operating expenses:
RP1 program costs by study:	9,541	14,620
ARTACUS \| Reportable Segment
Operating expenses:
RP1 program costs by study:	5,884	6,934
CERPASS \| Reportable Segment
Operating expenses:
RP1 program costs by study:	4,559	7,276
IGNYTE-3 \| Reportable Segment
Operating expenses:
RP1 program costs by study:	21,264	7,183
Other RP1 study costs \| Reportable Segment
Operating expenses:
RP1 program costs by study:	18,523	10,863
RP2 \| Reportable Segment
Operating expenses:
RP1 program costs by study:	25,953	12,043
RP3 \| Reportable Segment
Operating expenses:
RP1 program costs by study:	$ 2,674	$ 4,948

Net loss per share - Computation of Net Loss per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Numerator:
Net loss	$ (313,940)	$ (247,297)
Denominator:
Weighted average common shares outstanding, basic (in shares)	92,803,711	80,564,147
Weighted average common shares outstanding, diluted (in shares)	92,803,711	80,564,147
Net loss per common share, basic (in dollars per share)	$ (3.38)	$ (3.07)
Net loss per common share, diluted (in dollars per share)	$ (3.38)	$ (3.07)

- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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- Definition

The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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- Definition

Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities; of income (loss) available to common shareholders.

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+ Details

Commitments and contingencies - Balance sheet disclosures (Details) $ in Thousands	Mar. 31, 2026 USD ($)
Operating leases
2027	$ 1,160
2028	1,106
2029	1,021
2030	587
2031	369
Thereafter	0
Total lease payments	4,243
Less: interest	757
Total lease liabilities	3,486
Finance lease
2027	2,883
2028	2,969
2029	3,058
2030	3,096
2031	3,096
Thereafter	25,803
Total lease payments	40,905
Less: interest	16,113
Total lease liabilities	24,792
Total
2027	4,043
2028	4,075
2029	4,079
2030	3,683
2031	3,465
Thereafter	25,803
Total lease payments	45,148
Less: interest	16,870
Total lease liabilities	$ 28,278

Income taxes - Reconciliation of the U.S federal statutory income tax rate including percent (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Amount
Pre tax loss	$ (314,491)	$ (246,829)
U.S. Federal statutory tax rate	(66,043)
State and local income taxes, net of federal benefit	(2,516)
Federal R&D credit	(15,381)
Other	(788)
Stock compensation	2,204
Changes in unrecognized tax benefits	9,537
Total	$ (551)	$ 468
Percent
U.S. Federal statutory tax rate	21.00%	21.00%
State and local income taxes, net of federal benefit	0.80%	0.50%
Change in valuation allowance		(24.30%)
Statutory tax rate difference between U.K. and U.S.		3.60%
Other		(1.00%)
Federal R&D credit	4.90%	1.60%
Other	0.30%
Stock compensation	(0.70%)	(1.20%)
Changes in unrecognized tax benefits	(3.00%)
Total	0.20%	0.20%
United Kingdom
Amount
Change in valuation allowance	$ 63,295
Statutory tax rate difference between U.K. and U.S.	(9,938)
Other	$ (1,186)
Percent
Change in valuation allowance	(20.10%)
Statutory tax rate difference between U.K. and U.S.	3.20%
Other	0.40%
United States
Amount
Change in valuation allowance	$ 20,265
Percent
Change in valuation allowance	(6.40%)

Short-term investments (Details) - USD ($) $ in Thousands	12 Months Ended
Short-term investments (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Mar. 31, 2025
Short-term investments
Amortized cost	$ 59,857	$ 372,377
Gross unrealized gains	9	349
Gross unrealized losses	(1)	(41)
Credit Losses	0	0
Fair value	59,865	372,685
US Government Agency bonds
Short-term investments
Amortized cost	3,985	84,807
Gross unrealized gains	0	15
Gross unrealized losses	(1)	(18)
Credit Losses	0	0
Fair value	3,984	84,804
US Treasury bonds
Short-term investments
Amortized cost	55,872	287,570
Gross unrealized gains	9	334
Gross unrealized losses	0	(23)
Credit Losses	0	0
Fair value	$ 55,881	$ 287,881

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Accrued expenses and other current liabilities

12 Months Ended

Mar. 31, 2026

Accrued Liabilities and Other Liabilities [Abstract]

Accrued expenses and other current liabilities

Accrued expenses and other current liabilities consisted of the following:


	March 31, 2026		March 31, 2025
Accrued research and development costs	$	26,740	$	19,606
Accrued compensation and benefits costs	17,483		20,080
Accrued professional fees	537		161
Other	2,756		6,069
	$	47,516	$	45,916

Segment Information

12 Months Ended

Mar. 31, 2026

Segment Reporting [Abstract]

Segment Information

The Company manages its operations on a consolidated basis as a single operating and reportable segment with a focus on developing and commercializing novel oncolytic immunotherapies in order to treat cancer. The Company defines its segments on the basis of the way in which internally reported financial information is regularly reviewed to analyze financial performance and make operating decisions. The Company’s Chief Operating Decision Maker ("CODM") is Sushil Patel, the Chief Executive Officer. The CODM reviews consolidated operating results, and uses the Company's consolidated net income (loss), in order to monitor actual results as compared to the budget, and to determine how best to allocate the Company's operating and capital resources, specifically as it relates to the Company's development programs.

The following table presents selected financial information with respect to the Company's single operating segment, including significant segment expenses by program, for the years ended March 31, 2026 and 2025:


	Year Ended March 31,
	2026		2025
Operating expenses:	(Amounts in thousands)
Direct research and development expenses by program:
RP1 program costs by study:
IGNYTE	9,541		14,620
ARTACUS	5,884		6,934
CERPASS	4,559		7,276
IGNYTE-3	21,264		7,183
Other RP1 study costs	18,523		10,863
RP2	25,953		12,043
RP3	2,674		4,948
Unallocated research and development expenses1:	132,786		125,580
Selling, general and administrative	98,735		72,180
Total operating expenses	319,919		261,627
Loss from operations	(319,919)		(261,627)
Other income (expense), net	5,428		$	14,798
Loss before income taxes	$	(314,491)	$	(246,829)
Income tax provision	(551)		468
Net loss	(313,940)		(247,297)

1 Includes personnel-related costs and other costs

- Definition

The entire disclosure for reporting segments including data and tables. Reportable segments include those that meet any of the following quantitative thresholds a) it's reported revenue, including sales to external customers and intersegment sales or transfers is 10 percent or more of the combined revenue, internal and external, of all operating segments b) the absolute amount of its reported profit or loss is 10 percent or more of the greater, in absolute amount of 1) the combined reported profit of all operating segments that did not report a loss or 2) the combined reported loss of all operating segments that did report a loss c) its assets are 10 percent or more of the combined assets of all operating segments.

+ References

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+ Details

Summary of significant accounting policies (Policies)

12 Months Ended

Mar. 31, 2026

Accounting Policies [Abstract]

Principles of consolidation

The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America, or GAAP, and include the accounts of the Company and its direct and indirect wholly owned subsidiaries, Replimune UK, Replimune US, Replimune Securities Corporation and Replimune (Ireland) Limited after elimination of all intercompany accounts and transactions.

Use of estimates

The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of expenses during the reporting periods. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, the accrual for research and development expenses and the valuation of stock-based awards. The Company bases its estimates on historical experience, known trends and other market-specific or other relevant factors that it believes to be reasonable under the circumstances.

Foreign currency and currency translation

The functional currency for the Company’s wholly owned foreign subsidiary, Replimune UK, is the British pound. Assets and liabilities of Replimune UK are translated into United States dollars at the exchange rate in effect on the balance sheet date. Revenues and expenses are translated at the average exchange rate in effect during the period. Unrealized translation gains and losses are recorded as a cumulative translation adjustment, which is included in the consolidated statements of stockholders’ equity as a component of accumulated other comprehensive income (loss). Adjustments that arise from exchange rate changes on transactions denominated in a currency other than the local currency are included in other income (expense), net in the consolidated statements of operations as incurred.

Concentrations of credit risk and of significant suppliers

Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash and cash equivalents as well as short-term investments. The Company deposits its cash in financial institutions in amounts that may exceed federally insured limits. We limit our exposure to credit risk by placing investments with high credit quality financial institutions, diversifying our investment portfolio and placing investments with maturities that maintain safety and liquidity. To date, the Company has not experienced any losses on such accounts.

The Company relies, and expects to continue to rely, on a small number of vendors to manufacture and supply raw materials and supply services for its development programs. These programs could be adversely affected by a significant interruption in these services or the availability of raw materials.

Cash and cash equivalents

The Company considers all highly liquid investments with original maturities of three months or less at date of purchase to be cash equivalents.

Restricted cash

The Company holds restricted cash in segregated bank accounts in connection with a letter of credit.

Short-term investments

The Company’s short-term debt security investments are classified as available-for-sale and are carried at fair value, with the unrealized gains and non-credit related losses reported as a component of accumulated other comprehensive income (loss) and included in stockholders’ equity. Realized gains and losses and declines in value determined to be other than temporary are based on the specific identification method and are included as a component of other income (expense), net in the consolidated statements of operations.

For available-for-sale debt securities in an unrealized loss position, we first assess whether we intend to sell, or if it is more likely than not that we will be required to sell, the security before recovery of its amortized cost basis. If either of the criteria regarding intent or requirement to sell is met, the security’s amortized cost basis is written down to fair value through a charge to investment income. For available-for-sale debt securities that do not meet the aforementioned criteria, we evaluate whether the decline in fair value has resulted from credit losses or other factors. In making this assessment, the Company considers such

factors as, among other things, the severity of the impairment, any changes in interest rates, how long the market value of the investment has been less than its original cost, the Company’s ability and intent to retain the short-term debt security investment for a period of time sufficient to allow for any anticipated recovery in fair value and market conditions in general. The credit-related portion of unrealized losses, and any subsequent improvements, are recorded in investment income through an allowance account. Any impairment that has not been recorded through an allowance for credit losses is included in other comprehensive loss on the statements of comprehensive loss.

No credit-related losses or impairments have been recognized on the Company's investments in available-for-sale debt securities during the years ended March 31, 2026 or 2025.

The Company’s short-term investments as of March 31, 2026 and 2025 had maturities of less than one year. The Company has classified its investments with maturities beyond one year as short term, based on their highly liquid nature and because they represent the investment of cash that is available for current operations.

Property, plant and equipment

Property, plant and equipment are stated at cost, less accumulated depreciation and amortization. Depreciation and amortization expense is recognized using the straight-line method over the estimated useful lives of the respective assets as follows:


			Estimated Useful life
Office equipment			5 years
Computer equipment			3 years
Plant, manufacturing and laboratory equipment			5 years
Capitalized software			3 to 5 years
Leasehold improvements			Lesser of lease term or 10 years

Costs for capital assets not yet placed into service are capitalized as construction-in-progress and depreciated in accordance with the above guidelines once placed into service. Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is included in loss from operations. Expenditures for repairs and maintenance are charged to expense as incurred.

Capitalized software as a service costs represent implementation costs incurred during the application development stage and are included in "property, plant and equipment, net" on the Company's consolidated balance sheet. Such costs are amortized on a straight-line basis over the term of the associated arrangement plus any reasonably certain renewal period. Costs incurred during the preliminary project stage and the post-implementation-operation stage are expensed as incurred.

Inventory

Prior to the regulatory approval of the Company’s product candidates, the Company incurs expenses for the manufacture of drug product that could potentially be available to support the commercial launch of those products. Until the date at which regulatory approval has been received or is otherwise considered probable, the Company records all such costs as research and development expenses. There were no capitalized inventory costs recorded as of March 31, 2026 and 2025.

Impairment of long-lived assets

Long-lived assets consist of property, plant and equipment, right-of-use-asset - operating leases, and right-of-use-asset - finance leases. Long-lived assets to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset group for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset group to its carrying value. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of an asset group are less than its carrying amount. The impairment loss would be based on the excess of the

carrying value of the impaired asset group over its fair value, determined based on discounted cash flows. To date, the Company has recorded immaterial impairment losses on long-lived assets.

Fair value measurements

Certain assets and liabilities of the Company are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable:

•Level 1 — Quoted prices in active markets for identical assets or liabilities.

•Level 2 — Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data.

•Level 3 — Unobservable inputs that are supported by little or no market activity that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques.

The Company’s short-term investments and cash equivalents are carried at fair value, determined according to the fair value hierarchy described above (see Note 3). The carrying values of research and development incentives receivable, prepaid expenses and other current assets, accounts payable and accrued expenses and other current liabilities approximate their fair values due to the short-term nature of these assets and liabilities. Furthermore, the carrying value of the Company’s long-term debt approximates its fair value at each balance sheet date due to its variable interest rate, which approximates a market interest rate.

Debt issuance costs

Debt issuance costs consist of payments made to secure commitments under certain debt financing arrangements. These amounts are recognized as interest expense over the period of the financing arrangement using the effective interest method. If the financing arrangement is canceled or forfeited, or if the utility of the arrangement to the Company is otherwise compromised, these costs are recognized as interest expense immediately. The Company’s consolidated financial statements present debt issuance costs related to a recognized debt liability as a direct reduction from the carrying amount of that debt liability.

Segment information

The Company manages its operations on a consolidated basis as a single operating segment for the purposes of assessing performance and making operating decisions. The Company’s current focus is on developing oncolytic immunotherapies for the treatment of cancer.

Research and development costs

Research and development costs are expensed as incurred. Research and development expenses consist of costs incurred in performing research and development activities, including salaries, stock-based compensation and benefits, facilities costs and laboratory supplies, depreciation and external costs of outside vendors engaged to conduct preclinical development, clinical development activities and clinical trials as well as to manufacture clinical trial materials. Non-refundable prepayments for goods or services that will be used or rendered for future research and development activities are deferred and capitalized. Such amounts are recognized as an expense as the goods are delivered or the related services are performed, or until it is no longer expected that the goods will be delivered or the services rendered. Upfront payments for materials and supplies acquired for particular research and development activities that have no alternative future use in other research and development projects or otherwise, and therefore have no separate economic value, are expensed as research and development costs at the time the costs are incurred.

Research contract costs and accruals

The Company has entered into various research and development-related contracts with companies both inside and outside of the United States. These agreements are generally cancellable, and related costs are recorded as research and development expenses as incurred. The Company records accruals for estimated ongoing research costs. Accrual estimates are based on a number of factors, including management’s assessment of progress towards completion of the research and development activities, invoicing to date under the contracts, communication from the research organization or other companies of any actual costs incurred during the period that have not yet been invoiced, and the costs included in the contracts. When billing terms under these contracts do not coincide with the timing of when the work is performed, management is required to make estimates of outstanding obligations to those third parties as of the end of the reporting period. Significant judgments and estimates are made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual costs.

Patent costs

All patent-related costs incurred in connection with filing and prosecuting patent applications are expensed as incurred due to the uncertainty about the recovery of the expenditure. Amounts incurred are classified as selling, general and administrative expenses.

Stock-based compensation

The Company accounts for share-based payment awards granted to employees, consultants, and non-employees and directors using the fair value of the award on the grant date and compensation expense is recognized for those awards over the requisite service period, which is generally the vesting period of the respective award. To date, the Company has issued stock-based awards in the form of restricted stock units, or RSUs, performance stock units, or PSUs, and stock option grants. Forfeitures for all awards are accounted for as they occur.

The grant date fair value for RSUs and PSUs is based on the closing price of the Company's common stock on the date of grant. The Company’s RSUs have service-based vesting conditions and the related expense for these awards is recorded using the straight-line method. The Company's PSUs have performance-based vesting conditions and expense is recognized when the achievement of the performance condition is probable.

The grant date fair value of each stock option grant is estimated using the Black-Scholes option-pricing model, which requires inputs based on certain subjective assumptions, including the expected stock price volatility, the expected term of the option, the risk-free interest rate for a period that approximates the expected term of the option, and the Company’s expected dividend yield (see Note 10). Expense for these awards is recorded using the straight-line method over the vesting period of the respective award.

The Company classifies stock-based compensation expense in its consolidated statements of operations in the same manner in which the award recipient’s payroll costs are classified or in which the award recipient’s service payments are classified.

Research and development incentives and receivable

The Company, through its subsidiary in the United Kingdom, receives reimbursements of certain research and development expenditures as part of a United Kingdom government’s research and development tax reliefs program. Under the program, a percentage of qualifying research and development expenses incurred by the Company’s subsidiary in the United Kingdom are reimbursed up to 16.2%.

Management has assessed the Company’s research and development activities and expenditures to determine which activities and expenditures are likely to be eligible under the research and development incentive program described above. At each period end, management estimates the reimbursement available to the Company based on available information at the time.

The Company recognizes income from the research and development incentives when the relevant expenditure has been incurred, the associated conditions have been satisfied and there is reasonable assurance that the reimbursement will be received. The Company records these research and development incentives as other income. The research and development incentives receivable represents an amount due in connection with the above program.

Comprehensive loss

Comprehensive loss includes net loss as well as other changes in stockholders’ equity that result from transactions and economic events other than those with stockholders.

Income taxes

The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the consolidated financial statements or in the Company’s tax returns. Deferred tax assets and liabilities are determined on the basis of the differences between the consolidated financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax provision. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies.

The Company accounts for uncertainty in income taxes recognized in the consolidated financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more-likely-than-not to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the consolidated financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties.

Net income (loss) per share

Basic net income (loss) per common share is computed by dividing the net income (loss) by the weighted average number of shares of common stock outstanding for the period. Diluted net income (loss) per common share is computed by dividing the diluted net income (loss) by the weighted average number of shares of common stock outstanding for the period, including potential dilutive common shares assuming the dilutive effect of common stock equivalents.

In periods in which the Company reports a net loss, diluted net loss per share is the same as basic net loss per share, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive.

Recently Adopted Accounting Pronouncements and Recently Issued Accounting Pronouncements

Recently Adopted Accounting Pronouncements

In December 2023, the Financial Accounting Standards Board issued Accounting Standards Update ("ASU") No. 2023-09, “Income Taxes (Topic 740): Improvements to Income Tax Disclosures.” This ASU primarily focuses on the rate reconciliation and income taxes paid. ASU No. 2023-09 requires a public business entity (PBE) to disclose, on an annual basis, a tabular rate reconciliation using both percentages and currency amounts, broken out into specified categories with certain reconciling items further broken out by nature and jurisdiction to the extent those items exceed a specified threshold. In addition, all entities are required to disclose income taxes paid, net of refunds received disaggregated by federal, state/local, and foreign and by jurisdiction if the amount is at least 5% of total income tax payments, net of refunds received. For PBEs, the new standard is effective for annual periods beginning after December 15, 2024, with early adoption permitted. An entity may apply the amendments in this ASU prospectively by providing the revised disclosures for the first period ending December 31, 2025 or later, and continuing to provide the pre-ASU disclosures for the prior periods, or may apply the amendments retrospectively by providing the revised disclosures for all period presented. For the year ended March 31, 2026, the Company adopted this

guidance in the current year on a prospective basis. As this accounting standard only impacts disclosures, it did not have an impact on the Company's consolidated financial results. Refer below to Note 15 - Income taxes for disclosure updates as a result of this ASU.

Recently Issued Accounting Pronouncements

In November 2024, the FASB issued ASU-2024-03, Income Statement-Reporting Comprehensive Income-Expense Disaggregation Disclosures (Topic 220): Disaggregation of Income Statement Expenses. The ASU requires more detailed information about specified categories of expenses (purchases of inventory, employee compensation, depreciation, amortization, and depletion) included in certain expense captions presented on the face of the income statement. This ASU is effective for fiscal years beginning after December 15, 2026, and for interim periods within fiscal years beginning after December 15, 2027. Early adoption is permitted. The amendments may be applied either (1) prospectively to financial statements issued for reporting periods after the effective date of this ASU or (2) retrospectively to all prior periods presented in the financial statements. The Company is currently evaluating the impact of adopting this ASU on its consolidated financial statements and related disclosures.

In September 2025, the FASB issued ASU 2025-06, "Intangibles-Goodwill and Other-Internal-Use Software (Subtopic 350-40) Targeted Improvements to the Accounting for Internal-Use Software (ASU 2025-06)", which is intended to simplify the capitalization guidance for internal-use software by removing references to project stages and clarifying when the capitalizing of eligible costs is required. The new guidance is effective for annual periods beginning after December 15, 2027, and interim periods within those fiscal years, with early adoption permitted. ASU 2025-06 may be applied retrospectively or prospectively. The Company is in the process of evaluating the impact of this new guidance on its consolidated financial statements and related disclosures.

Segment Information (Tables)

12 Months Ended

Mar. 31, 2026

Segment Reporting [Abstract]

Schedule of Financial Information Including Significant Segment Expenses by Program


	Year Ended March 31,
	2026		2025
Operating expenses:	(Amounts in thousands)
Direct research and development expenses by program:
RP1 program costs by study:
IGNYTE	9,541		14,620
ARTACUS	5,884		6,934
CERPASS	4,559		7,276
IGNYTE-3	21,264		7,183
Other RP1 study costs	18,523		10,863
RP2	25,953		12,043
RP3	2,674		4,948
Unallocated research and development expenses1:	132,786		125,580
Selling, general and administrative	98,735		72,180
Total operating expenses	319,919		261,627
Loss from operations	(319,919)		(261,627)
Other income (expense), net	5,428		$	14,798
Loss before income taxes	$	(314,491)	$	(246,829)
Income tax provision	(551)		468
Net loss	(313,940)		(247,297)

1 Includes personnel-related costs and other costs

Accrued expenses and other current liabilities (Tables)

12 Months Ended

Mar. 31, 2026

Accrued Liabilities and Other Liabilities [Abstract]

Schedule of accrued expenses and other current liabilities

Accrued expenses and other current liabilities consisted of the following:


	March 31, 2026		March 31, 2025
Accrued research and development costs	$	26,740	$	19,606
Accrued compensation and benefits costs	17,483		20,080
Accrued professional fees	537		161
Other	2,756		6,069
	$	47,516	$	45,916

Commitments and contingencies (Tables)

12 Months Ended

Mar. 31, 2026

Commitments and Contingencies Disclosure [Abstract]

Schedule of variable lease components

The table below presents the lease-related costs which are included in the consolidated statements of operations for the years ended as of March 31, 2026 and 2025:


	Year ended March 31,
	2026		2025
Lease cost
Finance lease costs:
Amortization of right-of-use asset	$	2,428	$	2,428
Interest on lease liabilities	2,063		2,118
Operating lease costs	1,156		1,129
Total lease cost	$	5,647	$	5,675

The following table summarizes the classification of lease costs in the consolidated statement of operations for the years ended March 31, 2026 and 2025 as follows:


	Year ended March 31,
	2026		2025
Finance Lease Costs
Research and development	$	2,428	$	2,428
Other expense	2,063		2,118
Operating Lease Costs
Research and development	887		877
Selling, general and administrative	269		252
Total lease cost	$	5,647	$	5,675

The following table provides lease disclosure as of and for the years ended March 31, 2026 and 2025:


	March 31, 2026			March 31, 2025
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$	1,203		$	1,167
Operating cash flows from finance leases	$	2,063		$	2,118
Financing cash flows from finance leases	$	736		$	599
Weighted-average remaining lease term – operating leases	3.8 years			4.7 years
Weighted-average remaining lease term – finance leases	13.3 years			14.3 years
Weighted-average discount rate – operating leases	10.4		%	10.4		%
Weighted-average discount rate – finance leases	8.3		%	8.3		%

Summary of the maturity of company's lease liabilities

The following table summarizes the maturity of the Company’s lease liabilities on an undiscounted cash flow basis and a reconciliation to the operating and finance lease liabilities recognized on our balance sheet as of March 31, 2026:


	March 31, 2026
	Operating leases		Finance lease		Total
2027	$	1,160	$	2,883	$	4,043
2028	1,106		2,969		4,075
2029	1,021		3,058		4,079
2030	587		3,096		3,683
2031	369		3,096		3,465
Thereafter	—		25,803		25,803
Total lease payments	4,243		40,905		45,148
Less: interest	757		16,113		16,870
Total lease liabilities	$	3,486	$	24,792	$	28,278

Schedule of additional information related to leases

The following table provides lease disclosure as of and for the years ended March 31, 2026 and 2025:


	March 31, 2026			March 31, 2025
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$	1,203		$	1,167
Operating cash flows from finance leases	$	2,063		$	2,118
Financing cash flows from finance leases	$	736		$	599
Weighted-average remaining lease term – operating leases	3.8 years			4.7 years
Weighted-average remaining lease term – finance leases	13.3 years			14.3 years
Weighted-average discount rate – operating leases	10.4		%	10.4		%
Weighted-average discount rate – finance leases	8.3		%	8.3		%

Stockholders’ Equity (Tables)

12 Months Ended

Mar. 31, 2026

Stockholders' Equity Note [Abstract]

Schedule of stockholders equity

The Company had reserved for common stock for the exercise of outstanding stock options and the vesting of restricted share units, the number of shares remaining available for grant under the Company’s 2018 Omnibus Incentive Compensation Plan and the Company’s Employee Stock Purchase Plan (see Note 10) and the exercise of the outstanding warrants to purchase shares of common stock as follows:


	March 31, 2026	March 31, 2025
Stock options, issued and outstanding	11,785,458	10,214,878
Restricted and performance stock units	5,508,882	3,611,774
Stock options and restricted stock units, future issuance	1,569,457	2,119,283
Employee stock purchase plan, available for future grants	4,102,399	3,405,175
Pre-IPO warrants to purchase common stock	—	497,344
Pre-funded warrants	14,058,153	14,058,153
Total shares of common stock reserved for future issuance	37,024,349	33,906,607

Long-term debt (Tables)

12 Months Ended

Mar. 31, 2026

Debt Disclosure [Abstract]

Schedule of long-term debt

The summary of obligations under the term loan as of March 31, 2026 and 2025 consisted of the following (in thousands):


	March 31, 2026		March 31, 2025
Principal loan balance	$	82,252	$	46,450
Facility charge and diligence fee	(120)		(201)
Unamortized issuance costs	(536)		(901)
Accumulated end of term fee	1,712		1,029
Long term debt, net	$	83,308	$	46,377

Schedule of maturities of long-term debt

The annual principal payments by fiscal year due under the Loan Agreement as of March 31, 2026 were as follows:


	March 31, 2026
2027	$	—
2028	84,150
Total	$	84,150

- Definition

Tabular disclosure of long-debt instruments or arrangements, including identification, terms, features, collateral requirements and other information necessary to a fair presentation. These are debt arrangements that originally required repayment more than twelve months after issuance or greater than the normal operating cycle of the entity, if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-SubTopic 10
-Topic 210
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 942
-SubTopic 235
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477314/942-235-S99-2

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S50
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480738/235-10-S50-4

Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-04(a))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480678/235-10-S99-3

Reference 5: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 69B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481568/470-20-55-69B

Reference 6: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 69E
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481568/470-20-55-69E

Reference 7: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 835
-SubTopic 30
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482925/835-30-45-2

Reference 8: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-3

Reference 9: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477734/942-470-50-3

Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-8

Reference 11: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-6

Reference 12: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-7

+ Details

Income taxes - Components of deferred tax assets and liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2024
Deferred tax assets:
Net operating loss carryforwards	$ 267,196	$ 192,909
Research and development credits	15,144	2,676
Property, plant and equipment	4,735	4,596
Capitalized start-up costs	873	1,014
Stock compensation	20,297	16,478
Accrued expenses	5,595	6,397
Lease liability	6,931	7,318
Other	120	0
Total deferred tax assets	320,891	231,388
Valuation allowance	(312,035)	(221,629)	$ (161,890)
Net deferred tax assets	8,856	9,759
Deferred tax liabilities:
Right of use asset	(8,856)	(9,698)
Other	0	(61)
Total deferred tax liabilities	(8,856)	(9,759)
Net deferred tax assets (liabilities)	$ 0	$ 0

Summary of significant accounting policies

12 Months Ended

Mar. 31, 2026

Accounting Policies [Abstract]

Summary of significant accounting policies

Principles of consolidation

Use of estimates

Foreign currency and currency translation

Concentrations of credit risk and of significant suppliers

Cash and cash equivalents

The Company considers all highly liquid investments with original maturities of three months or less at date of purchase to be cash equivalents. Cash equivalents consisted of money market funds as of March 31, 2026 and 2025, respectively. As of March 31, 2026 and 2025, the amount of cash equivalents included in cash and cash equivalents totaled $120.3 million and $89.9 million, respectively.

Restricted cash

The Company holds restricted cash in segregated bank accounts in connection with a letter of credit. As of March 31, 2026 and 2025, restricted cash consisted of $1.7 million, respectively, held for the benefit of the landlords in connection with our leases and for the Company's credit card program in the United Kingdom. These amounts have been classified as non-current assets on the Company’s consolidated balance sheets.

Short-term investments

No credit-related losses or impairments have been recognized on the Company's investments in available-for-sale debt securities during the years ended March 31, 2026 or 2025.

Property, plant and equipment


			Estimated Useful life
Office equipment			5 years
Computer equipment			3 years
Plant, manufacturing and laboratory equipment			5 years
Capitalized software			3 to 5 years
Leasehold improvements			Lesser of lease term or 10 years

Inventory

Impairment of long-lived assets

carrying value of the impaired asset group over its fair value, determined based on discounted cash flows. To date, the Company has recorded immaterial impairment losses on long-lived assets.

Fair value measurements

•Level 1 — Quoted prices in active markets for identical assets or liabilities.

Debt issuance costs

Segment information

Research and development costs

Research contract costs and accruals

Patent costs

Stock-based compensation

Research and development incentives and receivable

from research and development incentives of $1.6 million and $1.8 million during the years ended March 31, 2026 and 2025, respectively, in the consolidated statements of operations and a research and development incentives receivable of $1.6 million and $3.7 million as of March 31, 2026 and 2025, respectively, on the consolidated balance sheets.

Comprehensive loss

Comprehensive loss includes net loss as well as other changes in stockholders’ equity that result from transactions and economic events other than those with stockholders. For the year ended March 31, 2026, comprehensive loss included $0.3 million of unrealized losses on short-term investments, as well as $0.3 million of foreign currency translation gains. For the year ended March 31, 2025, comprehensive loss included $0.4 million of unrealized gains on short-term investments and $0.2 million of foreign currency translation gains.

Income taxes

Net income (loss) per share

Recently Adopted Accounting Pronouncements

Recently Issued Accounting Pronouncements

Fair value of financial assets and liabilities (Tables)

12 Months Ended

Mar. 31, 2026

Fair Value Disclosures [Abstract]

Schedule of company's financial assets and liabilities measured at fair value on a recurring basis

The following tables present information about the Company’s financial assets and liabilities measured at fair value on a recurring basis:


	Fair Value Measurements as of March 31, 2026 Using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	—	$	104,275	$	—	$	104,275
US Government Agency bonds	—		15,998		—		15,998
Short-term investments:
US Government Agency bonds	—		3,984		—		3,984
US Treasury bonds	—		55,881		—		55,881
	$	—	$	180,138	$	—	$	180,138


	Fair Value Measurements as of March 31, 2025 Using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	—	$	89,879	$	—	$	89,879
Short-term investments:
US Government Agency bonds	—		84,804		—		84,804
US Treasury bonds	—		287,881		—		287,881
	$	—	$	462,564	$	—	$	462,564

Income taxes (Tables)

12 Months Ended

Mar. 31, 2026

Income Tax Disclosure [Abstract]

Schedule of net loss before income taxes

Loss before income taxes for the years ended March 31, 2026 and 2025 were as follows:


	Year ended March 31,
	2026		2025
United States	(66,042)		(25,870)
United Kingdom	(248,449)		(220,959)
Total	$	(314,491)	$	(246,829)

Schedule of components of income tax expense (benefit)

Income tax (benefit) expense consisted of the following:


	Year ended March 31,
	2026		2025
Current income tax (benefit) provision:
Federal	$	(313)	$	468
State	(238)		—
Foreign (United Kingdom)	—		—
Total current income tax (benefit) provision:	$	(551)	$	468

Schedule of reconciliation of the U.S federal statutory income tax rate

A reconciliation of taxes at the U.S. federal statutory income tax rate to the Company’s benefit from income taxes for the year ended March 31, 2026 in accordance with the guidance upon adoption of ASU 2023-09 is as follows:


	Year Ended March 31,
	2026
	Amount		Percent
Pre tax loss	$	(314,491)

U.S. Federal statutory tax rate	(66,043)		21.0	%
State and local income taxes, net of federal benefit	(2,516)		0.8	%
Foreign tax effects:
United Kingdom
Change in valuation allowance	63,295		(20.1)	%
Statutory tax rate difference between U.K. and U.S.	(9,938)		3.2	%
Other	(1,186)		0.4	%



Tax credits:
Federal R&D credit	(15,381)		4.9	%
Change in valuation allowance	20,265		(6.4)	%
Nontaxable or nondeductible items:
Other	(788)		0.3	%
Stock compensation	2,204		(0.7)	%
Changes in unrecognized tax benefits	9,537		(3.0)	%

Total	$	(551)	0.2	%

The Company's effective tax rate includes the effects of state and local income taxes, net of the federal income tax benefit, which are primarily attributable to Massachusetts, where the Company has significant business activities. Massachusetts has a higher effective tax rate compared to other jurisdictions where the Company operates, and together, accounts for more than half of the Company's total state tax benefit.

The reconciliation of taxes at the federal statutory rate to our provision for (benefit from) income taxes for the year ended March 31, 2025 in accordance with the guidance prior to the adoption of ASU 2023-09 was as follows:


	Year Ended March 31,
	2025
U.S. federal statutory income tax rate	(21.0)	%
State taxes, net of federal benefit	(0.5)	%
Research and development	(1.6)	%
Stock compensation	1.2	%
Foreign tax rate differential	(3.6)	%
Change in tax rates	0.4	%
Change in valuation allowance	24.3	%
Other	1.0	%
	0.2	%

Schedule of components of deferred tax assets and liabilities

The components of the Company’s deferred tax assets as of March 31, 2026 and 2025 were as follows:


	Year Ended March 31,
	2026		2025
Deferred tax assets:
Net operating loss carryforwards	$	267,196	$	192,909
Research and development credits	15,144		2,676
Property, plant and equipment	4,735		4,596
Capitalized start-up costs	873		1,014
Stock compensation	20,297		16,478
Accrued expenses	5,595		6,397
Lease liability	6,931		7,318
Other	120		—
Total deferred tax assets	320,891		231,388
Valuation allowance	(312,035)		(221,629)
Net deferred tax assets	8,856		9,759

Deferred tax liabilities:
Right of use asset	(8,856)		(9,698)
Other	—		(61)
Total deferred tax liabilities	(8,856)		(9,759)
Net deferred tax assets (liabilities)	$	—	$	—

Schedule of changes in the valuation allowance for deferred tax assets

Changes in the valuation allowance for deferred tax assets during the years ended March 31, 2026 and 2025 related primarily to the increase in net operating loss carryforwards were as follows:


	Year Ended March 31,
	2026		2025
Valuation allowance as of beginning of year	$	221,629	$	161,890
Increases recorded to income tax provision	90,329		59,848
(Decreases) increases recorded to equity	77		(109)
Valuation allowance as of end of year	$	312,035	$	221,629

Schedule of unrecognized tax benefits

Changes in the Company's gross unrecognized tax benefits from uncertain tax positions, excluding interest and penalties, consisted of the following:


	Year Ended March 31,
	2026		2025
Unrecognized tax benefits - beginning of year	$	10,443	$	8,667
Increases for tax positions taken during current years	4,874		921
Increases (decreases) for tax positions taken during prior years	5,252		855
Unrecognized tax benefits - end of year	$	20,569	$	10,443

Schedule of cash flow, supplemental disclosures

The following summarizes the Company's income taxes paid, net of refunds received, for the year presented below:


	Year Ended March 31,
	2026
Federal	$	130
State
Massachusetts	(135)
Foreign	—
Total	$	(5)

Summary of significant accounting policies - Schedule of property, plant and equipment, net (Details)	Mar. 31, 2026
Office equipment
Property, plant and equipment, net
Property, plant and equipment, useful life (in years)	5 years
Computer equipment
Property, plant and equipment, net
Property, plant and equipment, useful life (in years)	3 years
Plant, manufacturing and laboratory equipment
Property, plant and equipment, net
Property, plant and equipment, useful life (in years)	5 years
Capitalized software \| Minimum
Property, plant and equipment, net
Property, plant and equipment, useful life (in years)	3 years
Capitalized software \| Maximum
Property, plant and equipment, net
Property, plant and equipment, useful life (in years)	5 years
Leasehold improvements
Property, plant and equipment, net
Property, plant and equipment, useful life (in years)	10 years

Cybersecurity Risk Management and Strategy Disclosure	12 Months Ended
Cybersecurity Risk Management and Strategy Disclosure	Mar. 31, 2026
Cybersecurity Risk Management, Strategy, and Governance [Line Items]
Cybersecurity Risk Management Processes for Assessing, Identifying, and Managing Threats [Text Block]	We have policies, procedures, and processes for assessing, identifying, and managing cybersecurity risks, which are built into our overall information technology function and information about cybersecurity risks, and our risk management processes is collected, analyzed and considered as part of our overall risk management program. Such policies, procedures, and processes are designed to help protect our information assets and operations from internal and external cyber threats as well as secure our networks and systems. Such processes include procedural and technical safeguards, response plans, regular vulnerability and penetration tests on our systems and product applications, incident simulations, and routine review of our policies and procedures to identify risks and improve our practices. Our security incident response plan is designed to help coordinate our response to, and recovery from, cybersecurity incidents, and includes processes to assess the severity of, escalate, contain, investigate, and remediate incidents as well as to comply with applicable legal obligations. We maintain cyber insurance coverage; however, such insurance may not be sufficient in type or amount to cover us against claims related to security breaches, cyber-attacks, and other related breaches. We engage certain external parties, including cybersecurity assessors, consultants and auditors, to enhance our cybersecurity processes and strategies. In addition, depending on the nature of the services provided, the sensitivity and quantity of information processed, and the identity of the service provider, we evaluate the security and risk posture with respect to our third party service providers according to the perceived level of risk and in accordance based on industry standard best practices.
Cybersecurity Risk Management Processes Integrated [Flag]	true
Cybersecurity Risk Management Processes Integrated [Text Block]	We have policies, procedures, and processes for assessing, identifying, and managing cybersecurity risks, which are built into our overall information technology function and information about cybersecurity risks, and our risk management processes is collected, analyzed and considered as part of our overall risk management program. Such policies, procedures, and processes are designed to help protect our information assets and operations from internal and external cyber threats as well as secure our networks and systems. Such processes include procedural and technical safeguards, response plans, regular vulnerability and penetration tests on our systems and product applications, incident simulations, and routine review of our policies and procedures to identify risks and improve our practices. Our security incident response plan is designed to help coordinate our response to, and recovery from, cybersecurity incidents, and includes processes to assess the severity of, escalate, contain, investigate, and remediate incidents as well as to comply with applicable legal obligations. We maintain cyber insurance coverage; however, such insurance may not be sufficient in type or amount to cover us against claims related to security breaches, cyber-attacks, and other related breaches.
Cybersecurity Risk Management Third Party Engaged [Flag]	true
Cybersecurity Risk Third Party Oversight and Identification Processes [Flag]	true
Cybersecurity Risk Materially Affected or Reasonably Likely to Materially Affect Registrant [Flag]	false
Cybersecurity Risk Board of Directors Oversight [Text Block]	Our audit committee of the Board of Directors provides direct oversight over cybersecurity risk and provides applicable updates to the Board of Directors regarding such oversight. Members of management responsible for data privacy, technology, and information security risks join our audit committee meetings from time to time to discuss these risks, risk management activities, incident response plans, best practices, the effectiveness of our security measures, and other related matters.
Cybersecurity Risk Board Committee or Subcommittee Responsible for Oversight [Text Block]	Our audit committee of the Board of Directors provides direct oversight over cybersecurity risk and provides applicable updates to the Board of Directors regarding such oversight.
Cybersecurity Risk Process for Informing Board Committee or Subcommittee Responsible for Oversight [Text Block]	Our audit committee of the Board of Directors provides direct oversight over cybersecurity risk and provides applicable updates to the Board of Directors regarding such oversight. Members of management responsible for data privacy, technology, and information security risks join our audit committee meetings from time to time to discuss these risks, risk management activities, incident response plans, best practices, the effectiveness of our security measures, and other related matters. Our Vice President of IT, who reports to our Chief Financial Officer, leads the operational oversight of company-wide cybersecurity strategy, policy, standards, and processes and works across relevant departments to assess and help prepare us and our employees to address cybersecurity risks. Specific cybersecurity related responsibilities include overseeing our processes and strategies for the detection, mitigation, and remediation of cybersecurity incidents. Our Vice President of IT has extensive experience assessing and managing cybersecurity and risk programs having served in relevant positions of increasing responsibility for over 25 years at several private and public companies. In an effort to deter and detect cyber threats, we provide all employees with routine response and prevention training, which covers timely and relevant topics, including social engineering, phishing, password protection, confidential data protection, asset use, and mobile security, and educates employees on the importance of reporting all incidents promptly. We also use technology-based tools to mitigate cybersecurity threats and risks and to bolster our employee-based cybersecurity programs.
Cybersecurity Risk Role of Management [Text Block]	Members of management responsible for data privacy, technology, and information security risks join our audit committee meetings from time to time to discuss these risks, risk management activities, incident response plans, best practices, the effectiveness of our security measures, and other related matters. Our Vice President of IT, who reports to our Chief Financial Officer, leads the operational oversight of company-wide cybersecurity strategy, policy, standards, and processes and works across relevant departments to assess and help prepare us and our employees to address cybersecurity risks. Specific cybersecurity related responsibilities include overseeing our processes and strategies for the detection, mitigation, and remediation of cybersecurity incidents. Our Vice President of IT has extensive experience assessing and managing cybersecurity and risk programs having served in relevant positions of increasing responsibility for over 25 years at several private and public companies. In an effort to deter and detect cyber threats, we provide all employees with routine response and prevention training, which covers timely and relevant topics, including social engineering, phishing, password protection, confidential data protection, asset use, and mobile security, and educates employees on the importance of reporting all incidents promptly. We also use technology-based tools to mitigate cybersecurity threats and risks and to bolster our employee-based cybersecurity programs.
Cybersecurity Risk Management Positions or Committees Responsible [Flag]	true
Cybersecurity Risk Management Positions or Committees Responsible [Text Block]	Our Vice President of IT, who reports to our Chief Financial Officer, leads the operational oversight of company-wide cybersecurity strategy, policy, standards, and processes and works across relevant departments to assess and help prepare us and our employees to address cybersecurity risks. Specific cybersecurity related responsibilities include overseeing our processes and strategies for the detection, mitigation, and remediation of cybersecurity incidents.
Cybersecurity Risk Management Expertise of Management Responsible [Text Block]	Our Vice President of IT has extensive experience assessing and managing cybersecurity and risk programs having served in relevant positions of increasing responsibility for over 25 years at several private and public companies.
Cybersecurity Risk Process for Informing Management or Committees Responsible [Text Block]	Our audit committee of the Board of Directors provides direct oversight over cybersecurity risk and provides applicable updates to the Board of Directors regarding such oversight. Members of management responsible for data privacy, technology, and information security risks join our audit committee meetings from time to time to discuss these risks, risk management activities, incident response plans, best practices, the effectiveness of our security measures, and other related matters. Our Vice President of IT, who reports to our Chief Financial Officer, leads the operational oversight of company-wide cybersecurity strategy, policy, standards, and processes and works across relevant departments to assess and help prepare us and our employees to address cybersecurity risks. Specific cybersecurity related responsibilities include overseeing our processes and strategies for the detection, mitigation, and remediation of cybersecurity incidents. Our Vice President of IT has extensive experience assessing and managing cybersecurity and risk programs having served in relevant positions of increasing responsibility for over 25 years at several private and public companies. In an effort to deter and detect cyber threats, we provide all employees with routine response and prevention training, which covers timely and relevant topics, including social engineering, phishing, password protection, confidential data protection, asset use, and mobile security, and educates employees on the importance of reporting all incidents promptly. We also use technology-based tools to mitigate cybersecurity threats and risks and to bolster our employee-based cybersecurity programs.
Cybersecurity Risk Management Positions or Committees Responsible Report to Board [Flag]	true

Stock-based compensation - Summary of RSU Activity (Details) - Restricted and performance stock units	12 Months Ended
	Mar. 31, 2026 $ / shares shares
Number of Shares
Outstanding as of March 31, 2025 (in shares) \| shares	3,611,774
Granted (in shares) \| shares	3,499,956
Vested (in shares) \| shares	(1,003,362)
Cancelled (in shares) \| shares	(599,486)
Outstanding as of March 31, 2026 (in shares) \| shares	5,508,882
Weighted Average Grant Date Fair Value
Outstanding as of March 31, 2025 (in dollars per share) \| $ / shares	$ 12.40
Granted (in dollars per share) \| $ / shares	8.81
Vested (in dollars per share) \| $ / shares	15.94
Cancelled (in dollars per share) \| $ / shares	10.44
Outstanding as of March 31, 2026 (in dollars per share) \| $ / shares	$ 9.69

Significant agreements (Details)	1 Months Ended	12 Months Ended
Significant agreements (Details)	Jan. 31, 2020 patient	Mar. 31, 2026 USD ($)	Mar. 31, 2025 USD ($)
Significant agreements
Research and development		$ 221,184,000	$ 189,447,000
Prepaid expenses and other current assets		$ 8,611,000	8,351,000
Bristol-Myers Squibb Company
Significant agreements
Number of patients \| patient	125
Roche
Significant agreements
Termination period		60 days
Prepaid expenses and other current assets		$ 0	0
Roche \| Collaborative Arrangement, Transaction with Party to Collaborative Arrangement
Significant agreements
Research and development		0	0
Proceeds from collaborators		$ 0	$ 1,800,000

Geographic information

12 Months Ended

Mar. 31, 2026

Segments, Geographical Areas [Abstract]

Geographic information

The Company operates in two geographic regions: the United States (Massachusetts) and the United Kingdom (Oxfordshire). Information about the Company’s long-lived assets held in different geographic regions is presented in the tables below:


	March 31, 2026		March 31, 2025
United States	$	12,174	$	12,820
United Kingdom	800		919
	$	12,974	$	13,739

Net loss per share (Tables)

12 Months Ended

Mar. 31, 2026

Earnings Per Share [Abstract]

Schedule of calculation of basic and diluted net loss per share attributable to common stockholders

The following table sets forth the computation of the Company’s basic and diluted net loss per share attributable to common stockholders (in thousands, except per share amounts):


	Year ended March 31,
	2026		2025
Numerator:
Net loss	$	(313,940)	$	(247,297)
Denominator:
Weighted average common shares outstanding, basic and diluted	92,803,711		80,564,147
Net loss per share, basic and diluted	$	(3.38)	$	(3.07)

Schedule of anti-dilutive securities excluded from the computation of diluted net loss per share attributable to common shareholders

The Company excluded the following potential common shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share for the periods indicated because including them would have had an anti-dilutive effect:


	Year ended March 31,
	2026	2025
Options to purchase common stock	11,785,458	10,214,878
Unvested restricted and performance stock units	5,508,882	3,611,774
Warrants to purchase common stock	—	497,344
	17,294,340	14,323,996

Net loss per share - Narrative (Details) - shares	Mar. 31, 2026	Mar. 31, 2025
Pre-funded warrants
Diluted net loss per share attributable to common stockholders
Common stock, authorized (in shares)	14,058,153	14,058,153

Accrued expenses and other current liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Mar. 31, 2025
Accrued Liabilities and Other Liabilities [Abstract]
Accrued research and development costs	$ 26,740	$ 19,606
Accrued compensation and benefits costs	17,483	20,080
Accrued professional fees	537	161
Other	2,756	6,069
Total accrued expenses and other current liabilities	$ 47,516	$ 45,916

Pre-funded Warrants

12 Months Ended

Mar. 31, 2026

Equity [Abstract]

Pre-funded Warrants

Stockholders’ Equity

Common stock

As of March 31, 2026 and 2025, the Company’s certificate of incorporation, as amended and restated, authorized the Company to issue up to 150,000,000 shares of common stock, par value $0.001 per share.


	March 31, 2026	March 31, 2025
Stock options, issued and outstanding	11,785,458	10,214,878
Restricted and performance stock units	5,508,882	3,611,774
Stock options and restricted stock units, future issuance	1,569,457	2,119,283
Employee stock purchase plan, available for future grants	4,102,399	3,405,175
Pre-IPO warrants to purchase common stock	—	497,344
Pre-funded warrants	14,058,153	14,058,153
Total shares of common stock reserved for future issuance	37,024,349	33,906,607

Undesignated preferred stock

As of March 31, 2026 and 2025, the Company’s certificate of incorporation, as amended and restated, authorized the Company to issue up to 10,000,000 shares of undesignated preferred stock, par value $0.001 per share. There were no undesignated preferred shares issued or outstanding as of March 31, 2026 and 2025.

ATM program

On August 3, 2023, the Company and Leerink Partners LLC (the "Current Agent") entered into a sales agreement, which was subsequently amended on May 16, 2024, November 25, 2024 and May 22, 2025 (as so amended, the "2023 Sales Agreement"). Under the 2023 Sales Agreement, the Company may sell, from time to time, at its option, up to an aggregate of $100.0 million of share of the Company's common stock, $0.001 par value shares (the "Shares"), through the Current Agent, as the Company's sales agent.

Any Shares to be offered and sold under the 2023 Sales Agreement will be issued and sold (i) by methods deemed to be an “at the market offering” (“ATM”) as defined in Rule 415(a)(4) promulgated under the Securities Act of 1933, as amended, or if authorized by the Company, in negotiated transactions or block trades, and (ii) pursuant to a registration statement on Form S-3 filed by the Company with the Securities and Exchange Commission on November 6, 2025, which became effective in accordance with the provisions of Section 8(a) of the Securities Act of 1933, as may be amended from time to time, for an offering of various securities, including shares of the Company’s common stock, preferred stock, debt securities, warrants and/or units for sale to the public in one or more public offerings.

Subject to the terms of the 2023 Sales Agreement, the Current Agent will use reasonable efforts to sell the Shares from time to time, based upon the Company’s instructions (including any price, time or size limits or other customary parameters or conditions the Company may impose). The Company will pay the Current Agent a commission of up to 3.0% of the gross proceeds from the sale of the Shares. The Company has also agreed to provide the Current Agent with customary indemnification rights.

During the year ended March 31, 2026, pursuant to the 2023 Sales Agreement, the Company issued and sold an aggregate of 4,019,975 shares of its common stock, resulting in net proceeds of $31.1 million, with $67.9 million left to sell under the Agreement. During the year ended March 31, 2025, the Company did not issue or sell any shares under the 2023 Sales Agreement. The Company cannot provide any assurances that it will issue any additional Shares pursuant to the 2023 Sales Agreement.

Equity offerings

On June 14, 2024, the Company completed a private placement transaction (the "Private Placement") pursuant to which the Company sold (a) 5,668,937 shares of the Company's common stock, at an offering price of $8.82, and (b) in lieu of common stock to certain investors, pre-funded warrants to purchase 5,669,578 shares of the Company's common stock at an offering price of $8.819 per warrant (the "June 2024 Pre-Funded Warrants"). The Company received aggregate net proceeds in the Private Placement of approximately $96.7 million after deducting placement agent fees and other offering expenses payable by the Company of approximately $3.3 million.

On November 25, 2024, the Company completed a public offering of (a) 8,538,377 shares of the Company’s common stock, inclusive of the Underwriters fully exercised 30-day option to purchase up to 1,615,377 additional shares of the Company's common stock at a public offering price of $13.00 per share, and (b) pre-funded warrants to purchase 3,846,184 shares of the Company’s common stock at a public offering price of $12.9999 per warrant (the "December 2024 Pre-Funded Warrants"). The Company received aggregate net proceeds of approximately $156.0 million after deducting fees and expenses of approximately $5.0 million.

Pre-funded Warrants

The Company's pre-funded warrants are exercisable at any time after the date of issuance. Unless otherwise modified by a holder of a pre-funded warrant, no holder may exercise a pre-funded warrant (i) if such holder, together with its affiliates, would beneficially own more than 9.99% (or, in the case of the December 2024 Pre-Funded Warrants, 4.99%) of the number of shares of our common stock outstanding immediately after giving effect to such exercise, or (ii) if the combined voting power of our securities beneficially owned by such holder, together with its affiliates, would exceed 9.99% (or, in the case of the December 2024 Pre-Funded Warrants, 4.99%) of the combined voting power of all of our securities then outstanding immediately after giving effect to the exercise of such pre-funded warrants, as such percentage ownership is determined in accordance with the terms of the pre-funded warrants. A holder of the June 2024 Pre-funded Warrants may increase or decrease this percentage to any other percentage not in excess of 9.99%, whereas a holder of the Company's other Pre-funded Warrants, may increase or decrease this percentage up to 19.99%, in each case, by providing at least 61 days’ prior notice to the Company.

The 14,058,153 shares of the Company's common stock underlying the pre-funded warrants issued by the Company are not included in the number of issued and outstanding shares of the Company’s common stock outstanding as reported on the consolidated balance sheet, though they are included in the Company's annual pool increase calculation as well as the weighted average outstanding common stock in the calculation of basic and diluted net loss per share, as noted below in Note 11.

During the year ended March 31, 2026, one pre-IPO warrant holder exercised 248,672 of the Company's pre-funded warrants for an exercise price of $1.01 per pre-funded warrant. In addition, a second holder of the Company's pre-IPO warrants exercised 248,672 of the Company's pre-funded warrants for an exercise price of $1.01 per pre-funded warrant. As a result of the exercises, the Company issued 497,344 shares of Common Stock in exchange thereof. During the year ended March 31, 2025, a holder of the Company's pre-funded warrants exercised 739,225 of its pre-funded warrants for an exercise price of $0.001 per pre-funded warrant and the Company issued 739,225 shares of Common Stock in exchange thereof.

- Definition

The entire disclosure for equity.

+ References

+ Details

Nature of the business (Details) - USD ($) $ in Thousands	12 Months Ended
Nature of the business (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Mar. 31, 2025
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Net loss	$ 313,940	$ 247,297
Accumulated deficit	$ 1,262,519	$ 948,579

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

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+ Details

- Definition

Amount of accumulated undistributed earnings (deficit).

+ References + Details

Stock-based compensation - Additional information (Details) - USD ($) $ / shares in Units, $ in Millions			12 Months Ended
	Apr. 01, 2025	Jul. 09, 2018	Mar. 31, 2026	Mar. 31, 2025
Stock-Based Compensation
Unrecognized compensation cost related to unvested common stock options			$ 19.0
Expenses expected to be recognized over a weighted average remaining period			2 years 6 months
Weighted average grant-date fair value (in dollars per share)			$ 5.84	$ 5.91
Intrinsic value of stock options exercised			$ 0.6	$ 0.5
Weighted average grant date fair value			30.8	19.0
Total fair value of shares vested			16.0	$ 13.5
Unrecognized compensation cost			$ 36.3
Stock options
Stock-Based Compensation
Exercise price for persons holding ten percent of voting power (as a percent)			100.00%
Exercise price for persons holding more than ten percent of voting power (as a percent)			110.00%
Share based payment award expiration period			10 years
Share based payment award vesting period			4 years
Stock options \| Maximum
Stock-Based Compensation
Expiration period for persons holding ten percent of voting power			5 years
Stock options \| Minimum
Stock-Based Compensation
Expiration period for persons holding more than ten percent of voting power			10 years
RSUs
Stock-Based Compensation
Share based payment award vesting period			4 years
RSUs \| Share-based Payment Arrangement, Tranche One
Stock-Based Compensation
Share based payment award vesting period			1 year
PSUs
Stock-Based Compensation
Granted (in shares)			0	246,110
Expenses expected to be recognized over a weighted average remaining period			2 years 1 month 6 days
Unrecognized compensation cost			$ 4.1
Pre-funded warrants
Stock-Based Compensation
Common stock, authorized (in shares)			14,058,153	14,058,153
2017 Plan
Stock-Based Compensation
Number of shares available for grant (in shares)		2,520,247
2018 Plan
Stock-Based Compensation
Shares authorized (in shares)		3,617,968
Number of shares available for grant (in shares)			1,569,457
Share based payment award percentage of outstanding shares		4.00%
Additional shares authorized (in shares)	3,645,727
ESPP
Stock-Based Compensation
Share based payment award percentage of outstanding shares		1.00%
Additional shares authorized (in shares)	697,224	697,224
Common stock reserved for issuance (in shares)	4,102,399	348,612
Out Of Plan Inducement Grants \| RSUs
Stock-Based Compensation
Granted (in shares)			333,130	404,030
Out Of Plan Inducement Grants \| Nonqualified Stock Options
Stock-Based Compensation
Granted (in shares)			202,945	267,835

Stockholders’ Equity - Common Stock and Undesignated Preferred Stock (Details) - $ / shares	Mar. 31, 2026	Mar. 31, 2025
Stockholders' Equity Note [Abstract]
Common stock, authorized (in shares)	150,000,000	150,000,000
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Undesignated preferred stock, authorized (in shares)	10,000,000	10,000,000
Undesignated preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Undesignated preferred shares issued (in shares)	0	0
Undesignated preferred shares outstanding	0	0

Pre-funded Warrants (Details) - $ / shares		1 Months Ended	12 Months Ended
Pre-funded Warrants (Details) - $ / shares	Nov. 25, 2024	Oct. 31, 2020	Mar. 31, 2026	Mar. 31, 2025	Jun. 14, 2024
Common stock
Class of Warrant or Right [Line Items]
Shares issued during period (in shares)			497,344	739,225
Pre-funded warrants
Class of Warrant or Right [Line Items]
Number of stock warrants issued (in shares)			248,672	739,225
Exercise price (in dollars per share)			$ 1.01	$ 0.001
Pre-funded warrants
Class of Warrant or Right [Line Items]
Maximum percentage of holding for exercise warrants (as a percent)		9.99%
Maximum percentage of increase (decrease) of holding for exercise warrants (as a percent)		19.99%
Prior notice period to change percentage of holding (in days)		61 days
Issuance of pre-funded warrants (in shares)			14,058,153	14,058,153
2024 Pre-funded Warrants
Class of Warrant or Right [Line Items]
Maximum percentage of holding for exercise warrants (as a percent)	4.99%
Issuance of pre-funded warrants (in shares)	3,846,184				5,669,578

Long-term debt - Schedule of Debt (Details) - Secured Debt - Term Loan Facility - Line of Credit - USD ($) $ in Thousands	Mar. 31, 2026	Mar. 31, 2025
Debt Instrument [Line Items]
Principal loan balance	$ 82,252	$ 46,450
Facility charge and diligence fee	(120)	(201)
Unamortized issuance costs	(536)	(901)
Accumulated end of term fee	1,712	1,029
Long term debt, net	$ 83,308	$ 46,377

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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+ Details

- Definition

Amount, after deduction of unamortized premium (discount) and debt issuance cost, of long-term debt. Excludes lease obligation.

+ References

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+ Details

Stockholders' Equity

12 Months Ended

Mar. 31, 2026

Stockholders' Equity Note [Abstract]

Stockholders’ Equity

Common stock


	March 31, 2026	March 31, 2025
Stock options, issued and outstanding	11,785,458	10,214,878
Restricted and performance stock units	5,508,882	3,611,774
Stock options and restricted stock units, future issuance	1,569,457	2,119,283
Employee stock purchase plan, available for future grants	4,102,399	3,405,175
Pre-IPO warrants to purchase common stock	—	497,344
Pre-funded warrants	14,058,153	14,058,153
Total shares of common stock reserved for future issuance	37,024,349	33,906,607

Undesignated preferred stock

ATM program

Equity offerings

Pre-funded Warrants

- Definition

The entire disclosure for equity.

+ References

+ Details

Cover - USD ($) $ in Millions	12 Months Ended
Cover - USD ($) $ in Millions	Mar. 31, 2026	Jun. 25, 2026	Sep. 30, 2025
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Mar. 31, 2026
Current Fiscal Year End Date	--03-31
Document Transition Report	false
Entity File Number	001-38596
Entity Registrant Name	REPLIMUNE GROUP, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	82-2082553
Entity Address, Address Line One	500 Unicorn Park Drive
Entity Address, Address Line Two	Suite 303
Entity Address, City or Town	Woburn
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	01801
City Area Code	781
Local Phone Number	222-9600
Title of 12(b) Security	Common Stock, par value $0.001 per share
Trading Symbol	REPL
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Auditor Attestation Flag	false
Document Financial Statement Error Correction [Flag]	false
Entity Shell Company	false
Entity Public Float			$ 234.5
Entity Common Stock, Shares Outstanding		83,945,161
Documents Incorporated by Reference	The registrant intends to file a definitive proxy statement pursuant to Regulation 14A within 120 days of the end of the fiscal year ended March 31, 2026. Portions of such definitive proxy statement are incorporated by reference into Part III of this Annual Report on Form 10-K.
Entity Central Index Key	0001737953
Amendment Flag	false
Document Fiscal Year Focus	2026
Document Fiscal Period Focus	FY

Property, plant and equipment, net (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Property, plant and equipment, net
Total property, plant and equipment	$ 29,705	$ 27,138
Less: Accumulated depreciation and amortization	(16,731)	(13,399)
Property, plant and equipment , net	12,974	13,739
Depreciation and amortization expense	3,332	3,502
Office equipment
Property, plant and equipment, net
Total property, plant and equipment	1,897	1,812
Computer equipment
Property, plant and equipment, net
Total property, plant and equipment	2,441	2,206
Plant, manufacturing and laboratory equipment
Property, plant and equipment, net
Total property, plant and equipment	12,325	10,877
Leasehold improvements
Property, plant and equipment, net
Total property, plant and equipment	2,504	2,504
Capitalized software
Property, plant and equipment, net
Total property, plant and equipment	9,736	8,089
Construction in progress
Property, plant and equipment, net
Total property, plant and equipment	$ 802	$ 1,650

Net loss per share

12 Months Ended

Mar. 31, 2026

Earnings Per Share [Abstract]

Net loss per share

The following table sets forth the computation of the Company’s basic and diluted net loss per share attributable to common stockholders (in thousands, except per share amounts):


	Year ended March 31,
	2026		2025
Numerator:
Net loss	$	(313,940)	$	(247,297)
Denominator:
Weighted average common shares outstanding, basic and diluted	92,803,711		80,564,147
Net loss per share, basic and diluted	$	(3.38)	$	(3.07)

The 14,058,153 shares of the Company's common stock issuable upon exercise of Pre-Funded Warrants described in Note 9 to these consolidated financial statements are included as outstanding common stock in the calculation of basic and diluted net loss per share.

The Company’s potentially dilutive securities, which include stock options, unvested restricted and performance stock units and warrants to purchase shares of common stock that resulted from the conversion of warrants to purchase shares of seed preferred stock existing before the Company's IPO, have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted average number of common shares outstanding used to calculate both basic and diluted net loss per share is the same. The Company excluded the following potential common shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share for the periods indicated because including them would have had an anti-dilutive effect:


	Year ended March 31,
	2026	2025
Options to purchase common stock	11,785,458	10,214,878
Unvested restricted and performance stock units	5,508,882	3,611,774
Warrants to purchase common stock	—	497,344
	17,294,340	14,323,996

Income taxes - Schedule of income taxes paid, net of refunds received (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Income Tax Paid, by Individual Jurisdiction [Line Items]
Federal	$ 130
Foreign	0
Total	(5)	$ 105
Massachusetts
Income Tax Paid, by Individual Jurisdiction [Line Items]
State	$ (135)

Long-term debt - Narrative (Details)				12 Months Ended
Long-term debt - Narrative (Details)	Jan. 29, 2026 USD ($)	Jun. 28, 2023 USD ($)	Oct. 06, 2022 USD ($) advance	Mar. 31, 2026 USD ($)	Mar. 31, 2025 USD ($)	Dec. 22, 2023 USD ($)
Debt Instrument [Line Items]
Unrestricted cash percentage				35.00%
Interest expense				$ 6,796,000	$ 5,775,000
End of term charge				4,000,000.0
Secured Debt \| Term Loan Facility \| Line of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 200,000,000.0		$ 200,000,000.0
Variable rate (as a percent)	8.50%
Additional rate (as a percent)	1.75%
Maximum amount outstanding for covenant			$ 100,000,000.0
Stated interest rate (as a percent)			1.50%
Prepayment fee, first 12 months (as a percent)			3.00%
Prepayment fee, after first 12 months before 36 months (as a percent)			2.00%
Prepayment fee, after 36 months (as a percent)			1.00%
Minimum market capitalization			$ 1,200,000,000
Minimum restricted cash (as a percent)			50.00%
Minimum unrestricted cash (as a percent)			85.00%
Facility charge			$ 500,000
Payment of issuance costs			$ 1,500,000
Repayment fee (as a percent)			4.95%
Accrued for final payment on debt				1,700,000	1,000,000.0
Unamortized deferred financing costs				500,000	900,000
Interest expense				$ 6,800,000	$ 5,800,000
Secured Debt \| Term Loan Facility, Tranche One \| Line of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity			$ 30,000,000.0
Secured Debt \| Term Loan Facility, Tranche Two \| Line of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity			30,000,000.0			$ 15,000,000.0
Secured Debt \| Term Loan Facility, Tranche Three \| Line of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 35,000,000.0		115,000,000.0
Secured Debt \| Term Loan Facility, Tranche Four \| Line of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity			$ 25,000,000.0
Number of term loan advances \| advance			2
Secured Debt \| Term Loan Facility, Tranche Five \| Line of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity			$ 25,000,000.0
Number of term loan advances \| advance			2
Secured Debt \| Term Loan Facility, Tranche One and Two \| Line of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity			$ 60,000,000.0
Decrease in borrowing capacity		$ 30,000,000.0

Income taxes

12 Months Ended

Mar. 31, 2026

Income Tax Disclosure [Abstract]

Income taxes

Loss before income taxes for the years ended March 31, 2026 and 2025 were as follows:


	Year ended March 31,
	2026		2025
United States	(66,042)		(25,870)
United Kingdom	(248,449)		(220,959)
Total	$	(314,491)	$	(246,829)

Income tax (benefit) expense consisted of the following:


	Year ended March 31,
	2026		2025
Current income tax (benefit) provision:
Federal	$	(313)	$	468
State	(238)		—
Foreign (United Kingdom)	—		—
Total current income tax (benefit) provision:	$	(551)	$	468

During the year ended March 31, 2026 and 2025, the Company recorded an income tax benefit of $0.6 million and a provision of $0.5 million, respectively.

Future realization of the tax benefits of existing temporary differences and net operating loss carryforwards ultimately depends on the existence of sufficient taxable income within the carryforward period. As of March 31, 2026 and 2025, the Company performed an evaluation to determine whether a valuation allowance was needed. The Company considered all available evidence, both positive and negative, which included the results of operations for the current and preceding years. It was determined that it was not possible to reasonably quantify future taxable income and determined that it is more likely than not that all of the deferred tax assets will not be realized. Accordingly, a full valuation allowance was maintained as of March 31, 2026 and 2025.


	Year Ended March 31,
	2026
	Amount		Percent
Pre tax loss	$	(314,491)

U.S. Federal statutory tax rate	(66,043)		21.0	%
State and local income taxes, net of federal benefit	(2,516)		0.8	%
Foreign tax effects:
United Kingdom
Change in valuation allowance	63,295		(20.1)	%
Statutory tax rate difference between U.K. and U.S.	(9,938)		3.2	%
Other	(1,186)		0.4	%



Tax credits:
Federal R&D credit	(15,381)		4.9	%
Change in valuation allowance	20,265		(6.4)	%
Nontaxable or nondeductible items:
Other	(788)		0.3	%
Stock compensation	2,204		(0.7)	%
Changes in unrecognized tax benefits	9,537		(3.0)	%

Total	$	(551)	0.2	%


	Year Ended March 31,
	2025
U.S. federal statutory income tax rate	(21.0)	%
State taxes, net of federal benefit	(0.5)	%
Research and development	(1.6)	%
Stock compensation	1.2	%
Foreign tax rate differential	(3.6)	%
Change in tax rates	0.4	%
Change in valuation allowance	24.3	%
Other	1.0	%
	0.2	%

The components of the Company’s deferred tax assets as of March 31, 2026 and 2025 were as follows:


	Year Ended March 31,
	2026		2025
Deferred tax assets:
Net operating loss carryforwards	$	267,196	$	192,909
Research and development credits	15,144		2,676
Property, plant and equipment	4,735		4,596
Capitalized start-up costs	873		1,014
Stock compensation	20,297		16,478
Accrued expenses	5,595		6,397
Lease liability	6,931		7,318
Other	120		—
Total deferred tax assets	320,891		231,388
Valuation allowance	(312,035)		(221,629)
Net deferred tax assets	8,856		9,759

Deferred tax liabilities:
Right of use asset	(8,856)		(9,698)
Other	—		(61)
Total deferred tax liabilities	(8,856)		(9,759)
Net deferred tax assets (liabilities)	$	—	$	—

As of March 31, 2026, the Company had U.S. federal operating loss carryforwards of approximately $62.7 million, which can be carried forward indefinitely subject to 80% limitation of taxable income when utilized. As of March 31, 2026, the Company had U.S. state net operating loss carryforwards of $102.4 million, which will begin to expire in 2038. As of March 31, 2026, the Company had U.K. net operating loss carryforwards of approximately $987.2 million, which can be carried forward indefinitely. Such U.S. federal and state, as well as U.K., net operating loss carryforwards are based on tax returns filed and does not reflect uncertain tax positions in the U.S. and offsetting positions in the U.K. related to the transfer pricing arrangement between the U.S. and the U.K.

As of March 31, 2026, the Company had U.S. federal research and development credit carryforwards of approximately $21.0 million, which begin to expire in 2040. Additionally, the Company has state research and development credit carryforwards of approximately $9.0 million, which will begin to expire in 2036.

Utilization of the U.S. federal and state net operating loss as well as research and development credit carryforwards may be subject to a substantial annual limitation under Section 382 of the Internal Revenue Code of 1986, as amended, and corresponding provisions of state law, due to ownership changes that have occurred previously or that could occur in the future. These ownership changes may limit the amount of net operating loss carryforwards that can be utilized annually to offset future taxable income and tax liabilities, respectively. The Company has completed a study and determined that an ownership change occurred on July 19, 2018. Due to the ownership change, the utilization of certain net operating loss carryforwards to offset future taxable income and is limited under IRC Section 382; however, none of the net operating losses are expected to expire unutilized.

Changes in the valuation allowance for deferred tax assets during the years ended March 31, 2026 and 2025 related primarily to the increase in net operating loss carryforwards were as follows:


	Year Ended March 31,
	2026		2025
Valuation allowance as of beginning of year	$	221,629	$	161,890
Increases recorded to income tax provision	90,329		59,848
(Decreases) increases recorded to equity	77		(109)
Valuation allowance as of end of year	$	312,035	$	221,629

Changes in the Company's gross unrecognized tax benefits from uncertain tax positions, excluding interest and penalties, consisted of the following:


	Year Ended March 31,
	2026		2025
Unrecognized tax benefits - beginning of year	$	10,443	$	8,667
Increases for tax positions taken during current years	4,874		921
Increases (decreases) for tax positions taken during prior years	5,252		855
Unrecognized tax benefits - end of year	$	20,569	$	10,443

The Company's unrecognized tax benefits primarily relate to the Company's transfer pricing arrangement between the U.S. and the U.K. and the impacts to the Company’s net operating loss as well as research and development credit carryforwards.

The Company's unrecognized tax benefits, if recognized, would not have a material impact to the Company's effective tax rate and income tax provision due to the Company's full valuation allowance.

As of March 31, 2026 and 2025, the Company had not accrued interest or penalties related to uncertain income tax positions.

The Company files U.S. federal and state as well as U.K. income tax returns. In the normal course of business, the Company is subject to examination by U.S. federal and state as well as U.K. jurisdictions, where applicable. There are currently no pending income tax examinations. The Company is open to future U.S. federal income tax examination from 2022 to the present and in the U.K. from 2024 to the present. Although, carryforward attributes from earlier years may still be adjusted upon examination if they either have been used in an open year or will be used in a future period.

As of March 31, 2026 and 2025, income taxes on outside basis differences, primarily related to undistributed earnings, of the Company’s subsidiary have not been provided for as the Company intends to indefinitely reinvest its outside basis differences, and the undistributed earnings were in a cumulative and overall deficit.

The following summarizes the Company's income taxes paid, net of refunds received, for the year presented below:


	Year Ended March 31,
	2026
Federal	$	130
State
Massachusetts	(135)
Foreign	—
Total	$	(5)

- Definition

The entire disclosure for income tax.

+ References

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+ Details

Geographic information (Tables)

12 Months Ended

Mar. 31, 2026

Segments, Geographical Areas [Abstract]

Schedule of company's long-lived assets held in different geographic regions


	March 31, 2026		March 31, 2025
United States	$	12,174	$	12,820
United Kingdom	800		919
	$	12,974	$	13,739

Summary of significant accounting policies - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Summary of significant accounting policies
Cash equivalents	$ 120,300	$ 89,900
Restricted cash	1,703	1,703
Research and development incentives	1,604	1,773
Research and development incentives receivable, current	1,619	3,725
Unrealized gains (loss) on short-term investments	(300)	419
Foreign currency translation gain (loss)	$ 255	174
Minimum percentage of benefit recognized is being realized upon ultimate settlement	50.00%
Maximum \| United Kingdom
Summary of significant accounting policies
Percentage of qualifying research and development expenses reimbursed by government	16.20%
Operating Lease
Summary of significant accounting policies
Restricted cash	$ 1,700	$ 1,700

Significant agreements	12 Months Ended
Significant agreements	Mar. 31, 2026
Significant agreements
Significant agreements	Significant agreements Agreement with Bristol-Myers Squibb Company In February 2018, the Company entered into an agreement with Bristol-Myers Squibb Company (“BMS”). Pursuant to the agreement, BMS will provide to the Company, at no cost, a compound for use in the Company’s ongoing clinical trial of RP1. Under the agreement, the Company will sponsor, fund and conduct the clinical trial in accordance with an agreed-upon protocol. BMS granted the Company a non-exclusive, non-transferrable, royalty-free license (with a right to sublicense) under its intellectual property to its compound in the clinical trial and agreed to supply its compound, at no cost to the Company, for use in the clinical trial. In January 2020, this agreement was expanded to cover an additional cohort of 125 patients with anti-PD-1 failed melanoma. Unless earlier terminated, the agreement will remain in effect until (i) the completion of the clinical trial, (ii) all related clinical trial data have been delivered to both parties and (iii) the completion of any statistical analyses and bioanalyses contemplated by the clinical trial protocol or any analysis otherwise agreed upon by the parties. The agreement may be terminated by either party (x) in the event of an uncured material breach by the other party, (y) in the event the other party is insolvent or in bankruptcy proceedings or (z) for safety reasons. Upon termination, the licenses granted to the Company to use BMS’s nivolumab in the clinical trial will terminate. In April 2019, the Company entered into a separate agreement with BMS on terms similar to the terms set forth in the agreement described above, pursuant to which BMS will provide to the Company, at no cost, nivolumab for use in the Company’s Phase 1 clinical trial of RP2 in combination with nivolumab. Roche In December 2022, the Company entered into a Master Clinical Trial Collaboration and Supply Agreement with Roche in relation to the Company's RP2 and RP3 programs in colorectal cancer, or CRC, and hepatocellular carcinoma, or HCC. Under the agreement, the companies intended to collaborate in 30 patient cohort signal finding studies in third-line, or 3L, CRC and in first- and second-line, or 1L and 2L, respectively, HCC. Following the Company's re-prioritization of its product development portfolio in December 2023, the Company agreed with Roche to terminate the CRC collaboration and pursue the 2L cohort in HCC with RP2 only. Roche has continued to supply its currently approved drugs, atezolizumab and bevacizumab for the 2L cohort in HCC but is not sharing costs following the Company's re-prioritization. Under the terms of the initial agreement the Company retained the responsibility of operating the clinical trials as well as retaining all the rights to the development and commercialization of its product candidates. The agreement may be terminated by either party upon sixty days prior written notice to the other party. The agreement with Roche is accounted for under ASC 808, Collaborative Arrangements (“ASC 808”), as both parties are active participants and each party pays its own compound costs and shares equally in development costs in accordance with and up to the amount in the agreed upon first study plan. The Company accounts for costs incurred as part of the study, including costs to supply compounds for use in the study, as research and development expenses within the consolidated statement of operations. The Company recognizes any amounts received from Roche in connection with this agreement as an offset to research and development expense within the consolidated statement of operations. During the years ended March 31, 2026 and 2025, the Company did not make any payments to Roche under the terms of the agreement. The Company did not record any offset to research and development expenses during the year ended March 31, 2026 and 2025. The Company did not receive any payments under the terms of the agreement from Roche during the year ended March 31, 2026, and the Company received $1.8 million under the terms of the agreement for the year ended March 31, 2025. As of March 31, 2026 and 2025, the Company had no receivables recorded from Roche in connection with this agreement. Amgen In August 2023 the Company entered into a Settlement Agreement with Amgen and mutually agreed to terminate the Company's challenges to Amgen's patents. In connection with the Settlement Agreement, the Company entered into a License and Covenant Agreement with Amgen in which the Company agreed to pay Amgen low single-digit royalty payments on net sales of its products that, but for the license, could be found to infringe a valid Amgen patent on a country-by-country and product-by-product basis.

Summary of significant accounting policies (Tables)

12 Months Ended

Mar. 31, 2026

Accounting Policies [Abstract]

Schedule of property, plant and equipment, net

Depreciation and amortization expense is recognized using the straight-line method over the estimated useful lives of the respective assets as follows:


			Estimated Useful life
Office equipment			5 years
Computer equipment			3 years
Plant, manufacturing and laboratory equipment			5 years
Capitalized software			3 to 5 years
Leasehold improvements			Lesser of lease term or 10 years

Property, plant and equipment, net consisted of the following:


	March 31, 2026		March 31, 2025

Office equipment	$	1,897	$	1,812
Computer equipment	2,441		2,206
Plant, manufacturing and laboratory equipment	12,325		10,877
Leasehold improvements	2,504		2,504
Capitalized software	9,736		8,089
Construction in progress	802		1,650
	29,705		27,138
Less: Accumulated depreciation and amortization	(16,731)		(13,399)
	$	12,974	$	13,739

Short-term investments

12 Months Ended

Mar. 31, 2026

Short-Term Investments [Abstract]

Short-term investments

As of March 31, 2026 and 2025, the Company's available-for-sale investments by type, consisted of the following:


	March 31, 2026
	Amortized cost		Gross unrealized gains		Gross unrealized losses		Credit Losses		Fair value
US Government agency bonds	$	3,985	$	—	$	(1)	$	—	$	3,984
US Treasury bonds	55,872		9		$	—	$	—	55,881
	$	59,857	$	9	$	(1)	$	—	$	59,865


	March 31, 2025
	Amortized cost		Gross unrealized gains		Gross unrealized losses		Credit Losses		Fair value
US Government agency bonds	$	84,807	$	15	$	(18)	$	—	$	84,804
US Treasury bonds	287,570		334		(23)		—		287,881
	$	372,377	$	349	$	(41)	$	—	$	372,685

As of March 31, 2026 and 2025, available-for-sale securities consisted of investments that mature within one year.

Net loss per share - Computation of diluted net loss per share attributable to common stockholders (Details) - shares	12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Diluted net loss per share attributable to common stockholders
Antidilutive securities excluded from computation of diluted weighted average shares outstanding (in shares)	17,294,340	14,323,996
Options to purchase common stock
Diluted net loss per share attributable to common stockholders
Antidilutive securities excluded from computation of diluted weighted average shares outstanding (in shares)	11,785,458	10,214,878
Unvested restricted and performance stock units
Diluted net loss per share attributable to common stockholders
Antidilutive securities excluded from computation of diluted weighted average shares outstanding (in shares)	5,508,882	3,611,774
Warrants to purchase common stock
Diluted net loss per share attributable to common stockholders
Antidilutive securities excluded from computation of diluted weighted average shares outstanding (in shares)	0	497,344

Geographic information (Details) $ in Thousands	12 Months Ended
Geographic information (Details) $ in Thousands	Mar. 31, 2026 USD ($) region	Mar. 31, 2025 USD ($)
Segments, Geographical Areas [Abstract]
Number of operating geographic regions \| region	2
Geographic information
Long-lived assets	$ 12,974	$ 13,739
United States
Geographic information
Long-lived assets	12,174	12,820
United Kingdom
Geographic information
Long-lived assets	$ 800	$ 919

Long-term debt -Schedule of Maturity of Debt (Details) - Secured Debt - Term Loan Facility - Line of Credit $ in Thousands	Mar. 31, 2026 USD ($)
Debt Instrument [Line Items]
2027	$ 0
2028	84,150
Total	$ 84,150

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

+ Details

Commitments and contingencies - Narrative (Details) - USD ($) $ in Millions	Mar. 31, 2026	Mar. 31, 2025
Lessee, Lease, Description [Line Items]
Minimum payments committed to manufacturing organization	$ 0.8	$ 0.8
Minimum
Lessee, Lease, Description [Line Items]
Lease term (in years)	5 years
Lease term (in years)	5 years
Maximum
Lessee, Lease, Description [Line Items]
Lease term (in years)	15 years
Lease term (in years)	15 years

Stockholders' Equity - Schedule of Pre-funded Warrants (Details) - shares	Mar. 31, 2026	Mar. 31, 2025
Stock options, issued and outstanding
Class of Warrant or Right [Line Items]
Issuance of pre-funded warrants (in shares)	11,785,458	10,214,878
Restricted and performance stock units
Class of Warrant or Right [Line Items]
Issuance of pre-funded warrants (in shares)	5,508,882	3,611,774
Stock options and restricted stock units, future issuance
Class of Warrant or Right [Line Items]
Issuance of pre-funded warrants (in shares)	1,569,457	2,119,283
Employee stock purchase plan, available for future grants
Class of Warrant or Right [Line Items]
Issuance of pre-funded warrants (in shares)	4,102,399	3,405,175
Pre-IPO warrants to purchase common stock
Class of Warrant or Right [Line Items]
Issuance of pre-funded warrants (in shares)	0	497,344
Pre-funded warrants
Class of Warrant or Right [Line Items]
Issuance of pre-funded warrants (in shares)	14,058,153	14,058,153
Total shares of common stock reserved for future issuance
Class of Warrant or Right [Line Items]
Issuance of pre-funded warrants (in shares)	37,024,349	33,906,607

Stockholders' Equity - ATM Program (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
	Aug. 03, 2023	Mar. 31, 2026	Mar. 31, 2025
Class of Warrant or Right [Line Items]
Common stock, par value (in dollars per share)		$ 0.001	$ 0.001
Net proceeds		$ 31,147	$ 155,728
ATM Program
Class of Warrant or Right [Line Items]
Percentage of commission	3.00%
Common stock
Class of Warrant or Right [Line Items]
Shares issued during period (in shares)		4,019,975	14,207,314
Net proceeds		$ 4	$ 14
Common stock \| ATM Program
Class of Warrant or Right [Line Items]
Maximum received on transaction	$ 100,000
Common stock, par value (in dollars per share)	$ 0.001
Shares issued during period (in shares)		4,019,975
Net proceeds		$ 31,100
Maximum amount left to sell		$ 67,900

- Definition

Equity impact of the value of new stock issued during the period. Includes shares issued in an initial public offering or a secondary public offering.

+ References + Details

Audit Information	12 Months Ended
Audit Information	Mar. 31, 2026
Auditor Information [Abstract]
Auditor Firm ID	238
Auditor Name	PricewaterhouseCoopers LLP
Auditor Location	Florham Park, New Jersey

Stock-based compensation - Classification of expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Share-Based Compensation
Stock-based compensation expense	$ 32,272	$ 35,044
Stock options
Share-Based Compensation
Stock-based compensation expense	15,312	19,885
Restricted and performance stock units
Share-Based Compensation
Stock-based compensation expense	16,960	15,159
Research and development
Share-Based Compensation
Stock-based compensation expense	16,734	18,439
Selling, general and administrative
Share-Based Compensation
Stock-based compensation expense	$ 15,538	$ 16,605

Commitments and contingencies - Income Statement Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Lessee, Lease, Description [Line Items]
Finance Lease Costs	$ 2,428	$ 2,428
Operating Lease Costs	1,156	1,129
Total lease cost	5,647	5,675
Research and development
Lessee, Lease, Description [Line Items]
Finance Lease Costs	2,428	2,428
Operating Lease Costs	887	877
Total lease cost	5,647	5,675
Other expense
Lessee, Lease, Description [Line Items]
Finance Lease Costs	2,063	2,118
Selling, general and administrative
Lessee, Lease, Description [Line Items]
Operating Lease Costs	$ 269	$ 252

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Mar. 31, 2026	Mar. 31, 2025
Stockholders' Equity Attributable to Parent [Abstract]
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, authorized (in shares)	150,000,000	150,000,000
Common stock, issued (in shares)	82,716,923	77,085,024
Common stock, outstanding (in shares)	82,716,923	77,085,024

Long-term debt

12 Months Ended

Mar. 31, 2026

Debt Disclosure [Abstract]

Long-term debt

Hercules Loan Agreement

On October 6, 2022, the Company entered into a Loan and Security Agreement (the “Loan Agreement”), with Hercules Capital, Inc., as administrative agent, collateral agent and as a lender (“Hercules”). Pursuant to the Loan Agreement, the Company can borrow term loans in an aggregate maximum principal amount of up to $200.0 million under multiple tranches (the “Term Loan Facility”). Under the Loan Agreement, the Company borrowed an initial amount of $30.0 million on the closing date, and at the Company's sole option, could have drawn, but did not draw down, an additional $30.0 million on or prior to September 30, 2023. The Company can also draw as additional term loan advances in an aggregate principal amount of up to $115.0 million during the term of the Term Loan Facility subject to achievement of specified performance milestones, and two additional term loan advances up to an aggregate principal amount of $25.0 million subject to certain terms and conditions, on or prior to the end of the interest-only period. The Company intends to use the proceeds of the Term Loan Facility for working capital and general corporate purposes.

The Loan Agreement was subsequently amended (the "Amendment") on June 28, 2023 pursuant to which the Company agreed to draw an initial term loan advance in an aggregate principal amount not less than $30.0 million, provided that the aggregate amount of the term loan advances made under tranche 1 do not exceed $30.0 million, which reflects a decrease of $30.0 million from the $60.0 million in the original Loan Agreement for tranche 1. The total amount of the Loan Agreement, as well as the outstanding balance of the loan, was unchanged, but the option to borrow additional funds were redistributed from tranche 1 to tranche 2.

A second amendment was made to the Loan Agreement (the "Second Amendment") on December 22, 2023 pursuant to which the Company agreed to draw a term loan advance in an aggregate principal amount not less than $15.0 million, provided that the aggregate amount of the term loan advances made under tranche 2 do not exceed $15.0 million on or prior to December 31, 2023. The Second Amendment re-allocated the total future consideration of the Loan Agreement to the future tranches extending through September 2026, subject to the terms and conditions of the Loan Agreement. The Second Amendment did not change the total aggregate maximum principal amount to be drawn under the Loan Agreement, which remained up to $200.0 million. Upon closing of the Second Amendment on December 22, 2023, the Company drew down the tranche 2 amount of $15.0 million.

A third amendment was made to the Loan Agreement (the "Third Amendment") on January 29, 2026 (the "Third Amendment Closing Date") pursuant to which the Company drew down the tranche 3 loan advance amount of $35.0 million. The Third Amendment maintains a $200.0 million maximum principal amount and re-allocates the future tranches extending through December 2027, subject to the terms and conditions of the Loan Agreement.

In addition, the Third Amendment extends the amortization date, with a balloon payment, inclusive of accrued interest and principal due on the maturity date of October 1, 2027. The Third Amendment provides that if the Company receives FDA approval prior to October 1, 2027, the amortization and maturity date shall be extended to October 1, 2029. Borrowings under the Loan Agreement are repayable in monthly interest-only payments through September 2027, with the outstanding principal balance of the Term Loan Facility bearing interest payable in cash at a floating rate per annum equal to the greater of (i) 8.50% and (ii) the Prime Rate plus 1.75%.

The principal balance of the Term Loan Facility will also bear “payment-in-kind” interest at the rate of 1.50% (“PIK Interest”), which PIK Interest will be added to the outstanding principal balance of the Term Loan Facility on each interest payment date.

At the Company's option, the Company may prepay all or a portion of the outstanding borrowings, subject to a prepayment fee of 3.0% of the principal amount if prepayment occurs during the 12 months following the Third Amendment Closing Date, 2.0% after 12 months following the Third Amendment Closing Date but prior to 36 months following the Closing Date, and 1.0% thereafter.

The Loan Agreement contains customary facility fees, events of default and representations, warranties and affirmative and negative covenants, including a financial covenant requiring the Company to maintain unrestricted cash in an amount not less than 35% of the aggregate outstanding secured obligations under the Loan Agreement in accounts subject to a control agreement in favor of the Agent (the “Unrestricted Cash”) at all times commencing on January 1, 2024. In addition, the Loan Agreement, as amended, also contains a financial covenant that beginning on the later of (i) July 1, 2026 and (ii) the date on which the aggregate outstanding principal amount of the Term Loan Facility is equal to or greater than $100.0 million, the Company is required to satisfy one of the following requirements: (1) achieve a minimum amount of trailing three-month net product revenue tested on a monthly basis, (2) maintain a market capitalization in excess of $1.2 billion and Unrestricted Cash in an amount no less than 50% of the outstanding amount under the Term Loan Facility, or (3) maintain Unrestricted Cash in an amount no less than 85% of the outstanding amount under the Term Loan Facility.

The Company paid a $0.5 million facility charge and incurred debt issuance costs of $1.5 million upon closing of the Loan Agreement. The Loan Agreement also provides for a final payment, payable upon maturity or the repayment of the obligations in full or in part (on a pro rata basis), equal to 4.95% of the aggregate principal amount of Term Loans advanced to the Borrower and repaid on such date, which is being accrued on the Company's consolidated balance sheet. As of March 31, 2026 and 2025, the amount accrued for the final payment was $1.7 million and $1.0 million, respectively.

Unamortized debt issuance costs are recorded as a reduction of the carrying amount on the term loan and amortized as interest expense using the effective-interest method. In addition, unamortized deferred financing costs of $0.5 million and $0.9 million were recorded in other assets as of March 31, 2026 and 2025, respectively, related to the Company's right to borrow additional amounts from Hercules in the future and amortized to interest expense over the relevant draw period on a straight-line basis. Interest expense for the twelve months ended March 31, 2026 and 2025 was $6.8 million and $5.8 million, respectively.

The summary of obligations under the term loan as of March 31, 2026 and 2025 consisted of the following (in thousands):


	March 31, 2026		March 31, 2025
Principal loan balance	$	82,252	$	46,450
Facility charge and diligence fee	(120)		(201)
Unamortized issuance costs	(536)		(901)
Accumulated end of term fee	1,712		1,029
Long term debt, net	$	83,308	$	46,377

The annual principal payments by fiscal year due under the Loan Agreement as of March 31, 2026 were as follows:


	March 31, 2026
2027	$	—
2028	84,150
Total	$	84,150

The table of future payments of long-term debt excludes the end of term charge of $4.0 million, which is due upon the maturity of the loan.

- Definition

The entire disclosure for information about short-term and long-term debt arrangements, which includes amounts of borrowings under each line of credit, note payable, commercial paper issue, bonds indenture, debenture issue, own-share lending arrangements and any other contractual agreement to repay funds, and about the underlying arrangements, rationale for a classification as long-term, including repayment terms, interest rates, collateral provided, restrictions on use of assets and activities, whether or not in compliance with debt covenants, and other matters important to users of the financial statements, such as the effects of refinancing and noncompliance with debt covenants.

+ References

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+ Details

Income taxes - Schedule of components of income tax expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Current income tax (benefit) provision:
Federal	$ (313)	$ 468
State	(238)	0
Foreign (United Kingdom)	0	0
Total	$ (551)	$ 468

- Definition

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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+ Details

Income taxes - Valuation allowance for deferred tax assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Deferred Tax Assets, Valuation Allowance [Roll Forward]
Valuation allowance as of beginning of year	$ 221,629	$ 161,890
Increases recorded to income tax provision	90,329	59,848
(Decreases) increases recorded to equity	77	(109)
Valuation allowance as of end of year	$ 312,035	$ 221,629

Property, plant and equipment, net

12 Months Ended

Mar. 31, 2026

Property, Plant and Equipment [Abstract]

Property, plant and equipment, net

Property, plant and equipment, net consisted of the following:


	March 31, 2026		March 31, 2025

Office equipment	$	1,897	$	1,812
Computer equipment	2,441		2,206
Plant, manufacturing and laboratory equipment	12,325		10,877
Leasehold improvements	2,504		2,504
Capitalized software	9,736		8,089
Construction in progress	802		1,650
	29,705		27,138
Less: Accumulated depreciation and amortization	(16,731)		(13,399)
	$	12,974	$	13,739

Depreciation and amortization expense was $3.3 million and $3.5 million for the years ended March 31, 2026 and 2025, respectively, and recorded within research and development and selling, general and administrative expenses in the consolidated statement of operations.

Benefit plans	12 Months Ended
Benefit plans	Mar. 31, 2026
Retirement Benefits [Abstract]
Benefit plans	Benefit plans The Company established a defined-contribution savings plan under Section 401(k) of the Code (the “401(k) Plan”). The 401(k) Plan covers substantially all employees who meet minimum age and service requirements and allows participants to defer a portion of their annual compensation on a pre-tax basis. Matching contributions to the 401(k) Plan may be made at the discretion of the Company’s board of directors. During the years ended March 31, 2026 and 2025, the Company made contributions totaling $3.7 million and $2.4 million, respectively, to the 401(k) Plan. We provide a pension contribution plan for our employees in the United Kingdom, pursuant to which we match our employees’ contributions each year in amounts up to 8% of their annual base salary.

- Definition

The entire disclosure for retirement benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (o)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480506/715-20-50-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
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-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (p)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480506/715-20-50-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
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-Paragraph 1
-Subparagraph (q)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480506/715-20-50-1

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 60
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480266/715-60-50-3

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
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-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Publisher FASB
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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Reference 7: http://www.xbrl.org/2003/role/exampleRef
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
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Reference 11: http://www.xbrl.org/2003/role/disclosureRef
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Reference 12: http://www.xbrl.org/2003/role/disclosureRef
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
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Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
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-URI https://asc.fasb.org/1943274/2147480506/715-20-50-1

+ Details

Stock-based compensation - Stock option activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Number of Shares
Outstanding at beginning of the period (in shares)	10,214,878
Granted (in shares)	2,201,239
Exercised (in shares)	(111,218)
Cancelled (in shares)	(519,441)
Outstanding at end of the period (in shares)	11,785,458	10,214,878
Options exercisable (in shares)	8,222,796
Options vested and expected to vest (in shares)	11,785,458
Weighted Average Exercise Price
Outstanding at beginning of the period (in dollars per share)	$ 15.22
Granted (in dollars per share)	8.41
Exercised (in dollars per share)	3.43
Cancelled (in dollars per share)	13.97
Outstanding at end of the period (in dollars per share)	14.12	$ 15.22
Options exercisable (in dollars per share)	16.01
Options vested and expected to vest (in dollars per share)	$ 14.12
Weighted Average Contractual Term (Years)
Outstanding (years)	5 years 7 months 17 days	6 years 2 months 26 days
Options exercisable (years)	4 years 4 months 24 days
Options vested and expected to vest (years)	5 years 7 months 17 days
Aggregate Intrinsic Value
Outstanding	$ 4,323	$ 10,652
Options exercisable	4,282
Options vested and expected to vest	$ 4,323

Stock-based compensation (Tables)

12 Months Ended

Mar. 31, 2026

Share-Based Payment Arrangement [Abstract]

Schedule of stock-based compensation expense

The following table summarizes the classification of stock-based compensation expense in the consolidated statements of operations for the years ended March 31, 2026 and 2025 as follows:


	Year ended March 31,
	2026		2025
Research and development	$	16,734	$	18,439
Selling, general and administrative	15,538		16,605
	$	32,272	$	35,044

The following table summarizes stock-based compensation expense by award type for the years ended March 31, 2026 and 2025 as follows:


	Year ended March 31,
	2026		2025
Stock options	$	15,312	$	19,885
Restricted and performance stock units	16,960		15,159
	$	32,272	$	35,044

Schedule of assumptions used to determine the grant-date fair value of stock options granted

The following table presents, on a weighted-average basis, the assumptions that the Company used to determine the grant-date fair value of stock options granted to employees and directors:


	Year ended March 31,
	2026		2025
Risk-free interest rate	3.97	%	4.35	%
Expected term (in years)	6.0		6.0
Expected volatility	77.2	%	76.3	%
Expected dividend yield	0	%	0	%

Summary of stock option activity

A summary of stock option activity under the Company’s equity incentive plans for the year ended March 31, 2026 is as follows:


	Number of Shares	Weighted Average Exercise Price		Weighted Average Contractual Term (Years)	Aggregate Intrinsic Value
Outstanding as of March 31, 2025	10,214,878	$	15.22	6.24	$	10,652
Granted	2,201,239	8.41
Exercised	(111,218)	3.43
Cancelled	(519,441)	13.97
Outstanding as of March 31, 2026	11,785,458	14.12		5.63	$	4,323
Options exercisable as of March 31, 2026	8,222,796	$	16.01	4.40	$	4,282
Options vested and expected to vest as of March 31, 2026	11,785,458	$	14.12	5.63	$	4,323

Schedule of share-based payment arrangement, restricted stock and restricted stock unit, activity

A summary of the changes in the Company’s RSUs and PSUs during the year ended March 31, 2026 is as follows:


	Number of Shares	Weighted Average Grant Date Fair Value
Outstanding as of March 31, 2025	3,611,774	$	12.40
Granted	3,499,956	8.81
Vested	(1,003,362)	15.94
Cancelled	(599,486)	10.44
Outstanding as of March 31, 2026	5,508,882	$	9.69

Property, plant and equipment, net (Tables)

12 Months Ended

Mar. 31, 2026

Property, Plant and Equipment [Abstract]

Schedule of property, plant and equipment, net

Depreciation and amortization expense is recognized using the straight-line method over the estimated useful lives of the respective assets as follows:


			Estimated Useful life
Office equipment			5 years
Computer equipment			3 years
Plant, manufacturing and laboratory equipment			5 years
Capitalized software			3 to 5 years
Leasehold improvements			Lesser of lease term or 10 years

Property, plant and equipment, net consisted of the following:


	March 31, 2026		March 31, 2025

Office equipment	$	1,897	$	1,812
Computer equipment	2,441		2,206
Plant, manufacturing and laboratory equipment	12,325		10,877
Leasehold improvements	2,504		2,504
Capitalized software	9,736		8,089
Construction in progress	802		1,650
	29,705		27,138
Less: Accumulated depreciation and amortization	(16,731)		(13,399)
	$	12,974	$	13,739

Income taxes - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
Income taxes - Narrative (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Mar. 31, 2025
Operating Loss Carryforwards [Line Items]
Income tax (benefit) provision	$ (551)	$ 468
Domestic Tax Jurisdiction
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	62,700
Research and development credit carryforwards	21,000
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	102,400
Research and development credit carryforwards	9,000
Foreign Tax Authority
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 987,200

- Definition

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References

+ Details

Stock-based compensation - Assumptions to determine grant-date fair value of stock options (Details) - Stock options	12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Stock-based Compensation
Risk-free interest rate	3.97%	4.35%
Expected term (in years)	6 years	6 years
Expected volatility	77.20%	76.30%
Expected dividend yield	0.00%	0.00%

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (f)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
-Section 35
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-URI https://asc.fasb.org/1943274/2147480483/718-10-35-1D

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org/1943274/2147480483/718-10-35-3

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
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Reference 14: http://www.xbrl.org/2003/role/disclosureRef
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Reference 15: http://www.xbrl.org/2003/role/disclosureRef
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Reference 19: http://www.xbrl.org/2003/role/disclosureRef
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Reference 25: http://www.xbrl.org/2003/role/disclosureRef
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Reference 26: http://www.xbrl.org/2003/role/disclosureRef
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Reference 27: http://www.xbrl.org/2003/role/disclosureRef
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Reference 28: http://www.xbrl.org/2003/role/disclosureRef
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Reference 29: http://www.xbrl.org/2003/role/disclosureRef
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Reference 30: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

Income taxes - Unrecognized tax benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Unrecognized Tax Benefits [Roll Forward]
Unrecognized tax benefits - beginning of year	$ 10,443	$ 8,667
Increases for tax positions taken during current years	4,874	921
Increases (decreases) for tax positions taken during prior years	5,252	855
Unrecognized tax benefits - end of year	$ 20,569	$ 10,443

Fair value of financial assets and liabilities

12 Months Ended

Mar. 31, 2026

Fair Value Disclosures [Abstract]

Fair value of financial assets and liabilities

The following tables present information about the Company’s financial assets and liabilities measured at fair value on a recurring basis:


	Fair Value Measurements as of March 31, 2026 Using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	—	$	104,275	$	—	$	104,275
US Government Agency bonds	—		15,998		—		15,998
Short-term investments:
US Government Agency bonds	—		3,984		—		3,984
US Treasury bonds	—		55,881		—		55,881
	$	—	$	180,138	$	—	$	180,138


	Fair Value Measurements as of March 31, 2025 Using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	—	$	89,879	$	—	$	89,879
Short-term investments:
US Government Agency bonds	—		84,804		—		84,804
US Treasury bonds	—		287,881		—		287,881
	$	—	$	462,564	$	—	$	462,564

The underlying securities held in the money market funds held by the Company are all government backed securities. During the years ended March 31, 2026 and 2025, there were no transfers between levels.

Valuation of cash equivalents and short-term investments

Money market funds, U.S. Treasury bonds and U.S. Government Agency bonds were valued by the Company using quoted prices in active markets for similar securities, which represent a Level 2 measurement within the fair value hierarchy. Cash equivalents consisted of both money market funds and U.S. Government Agency bonds at March 31, 2026 and money market funds at March 31, 2025.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (bbb)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 820
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Reference 3: http://www.xbrl.org/2003/role/exampleRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
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-Name Accounting Standards Codification
-Section 50
-Paragraph 2E
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2E

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6A
-Subparagraph (h)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-6A

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-6A

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
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-Name Accounting Standards Codification
-Section 50
-Paragraph 6A
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-6A

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
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-Name Accounting Standards Codification
-Section 50
-Paragraph 6A
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-6A

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (h)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 940
-SubTopic 820
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478119/940-820-50-1

+ Details

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common stock	Additional paid-in capital	Accumulated deficit	Accumulated other comprehensive income
Balance (in shares) at Mar. 31, 2024		61,415,105
Balance at Mar. 31, 2024	$ 374,508	$ 61	$ 1,070,874	$ (701,282)	$ 4,855
Increase (decrease) in Stockholders' Equity
Issuance of prefunded warrants to purchase common stock, net of issuance costs	97,000		97,000
Issuance of common stock, net of issuance costs and underwriter fees and net of offering costs (in shares)		14,207,314
Issuance of common stock, net of issuance costs and underwriter fees and net of offering costs	155,728	$ 14	155,714
Foreign currency translation adjustment	174				174
Unrealized gains (loss) on short-term investments	419				419
Exercise of pre-funded warrants (in shares)		739,225
Exercise of pre-funded warrants	0	$ 1	(1)
Exercise of stock options (in shares)		84,261
Exercise of stock options	267		267
Vesting of RSUs (in shares)		639,119
Vesting of RSUs	0	$ 1	(1)
Stock-based compensation expense	35,044		35,044
Net loss	(247,297)			(247,297)
Balance (in shares) at Mar. 31, 2025		77,085,024
Balance at Mar. 31, 2025	415,843	$ 77	1,358,897	(948,579)	5,448
Increase (decrease) in Stockholders' Equity
Issuance of common stock, net of issuance costs and underwriter fees and net of offering costs (in shares)		4,019,975
Issuance of common stock, net of issuance costs and underwriter fees and net of offering costs	31,147	$ 4	31,143
Foreign currency translation adjustment	255				255
Unrealized gains (loss) on short-term investments	(300)				(300)
Exercise of pre-funded warrants (in shares)		497,344
Exercise of pre-funded warrants	$ 501		501
Exercise of stock options (in shares)	111,218	111,218
Exercise of stock options	$ 380		380
Vesting of RSUs (in shares)		1,003,362
Vesting of RSUs	2	$ 1	1
Stock-based compensation expense	32,272		32,272
Net loss	(313,940)			(313,940)
Balance (in shares) at Mar. 31, 2026		82,716,923
Balance at Mar. 31, 2026	$ 166,160	$ 82	$ 1,423,194	$ (1,262,519)	$ 5,403

CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Statement of Comprehensive Income [Abstract]
Net Loss	$ (313,940)	$ (247,297)
Other comprehensive loss:
Foreign currency translation gain (loss)	255	174
Net unrealized (loss) gain on short-term investments	(300)	419
Comprehensive loss	$ (313,985)	$ (246,704)

- Definition

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.

+ References + Details

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

+ Details

Benefit plans (Details) - USD ($) $ in Millions	12 Months Ended
Benefit plans (Details) - USD ($) $ in Millions	Mar. 31, 2026	Mar. 31, 2025
401(k) Plan
Defined Contribution Plan Disclosure [Line Items]
Contributions to the plan	$ 3.7	$ 2.4
Pension Plan
Defined Contribution Plan Disclosure [Line Items]
Maximum percentage of contribution by employee of their annual base salary (as a percent)	8.00%

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2026	Mar. 31, 2025
Current assets:
Cash and cash equivalents	$ 209,024	$ 111,119
Short-term investments	59,865	372,685
Research and development incentives receivable	1,619	3,725
Prepaid expenses and other current assets	8,611	8,351
Total current assets	279,119	495,880
Property, plant and equipment, net	12,974	13,739
Restricted cash	1,703	1,703
Other non-current assets	2,942	1,200
Right-of-use asset – operating leases	3,270	3,998
Right-of-use asset – finance leases	32,380	34,808
Total assets	332,388	551,328
Current liabilities:
Accounts payable	6,671	12,463
Accrued expenses and other current liabilities	47,516	45,916
Operating lease liabilities, current	1,158	1,184
Finance lease liabilities, current	2,883	2,799
Total current liabilities	58,228	62,362
Operating lease liabilities, non-current	2,328	3,076
Finance lease liabilities, non-current	21,909	22,729
Long term debt, net of discount	83,308	46,377
Other liabilities, non-current	455	941
Total liabilities	166,228	135,485
Commitments and contingencies (Note 13)
Stockholders’ equity:
Common stock, $0.001 par value; 150,000,000 shares authorized as of March 31, 2026 and March 31, 2025; 82,716,923 and 77,085,024 shares issued and outstanding as of March 31, 2026 and March 31, 2025, respectively	82	77
Additional paid-in capital	1,423,194	1,358,897
Accumulated deficit	(1,262,519)	(948,579)
Accumulated other comprehensive income	5,403	5,448
Total stockholders’ equity	166,160	415,843
Total liabilities and stockholders’ equity	$ 332,388	$ 551,328

Insider Trading Policies and Procedures	12 Months Ended
Insider Trading Policies and Procedures	Mar. 31, 2026
Insider Trading Policies and Procedures [Line Items]
Insider Trading Policies and Procedures Adopted	true

Subsequent events	12 Months Ended
Subsequent events	Mar. 31, 2026
Subsequent Events [Abstract]
Subsequent events	Subsequent events On April 10, 2026 the Company received a CRL from the FDA for the BLA for RP1 in combination with nivolumab for the treatment of advanced melanoma. As a result of the CRL, the Company announced its plan for a restructuring, which included a reduction of its workforce by approximately 55%. As a result of this reduction in force, the Company estimates that it will record a charge in the range of $9.8 million to $10.3 million during the three months ended June 30, 2026, related to employee termination benefits, including severance, all of which is anticipated to result in cash expenditures. Communication has been made to all impacted employees under this restructuring plan. The Company expects the reduction in force to be substantially complete by the end of the first quarter of fiscal 2027.

Stock-based compensation

12 Months Ended

Mar. 31, 2026

Share-Based Payment Arrangement [Abstract]

Stock-based compensation

Stock-based compensation expense

The following table summarizes the classification of stock-based compensation expense in the consolidated statements of operations for the years ended March 31, 2026 and 2025 as follows:


	Year ended March 31,
	2026		2025
Research and development	$	16,734	$	18,439
Selling, general and administrative	15,538		16,605
	$	32,272	$	35,044

The following table summarizes stock-based compensation expense by award type for the years ended March 31, 2026 and 2025 as follows:


	Year ended March 31,
	2026		2025
Stock options	$	15,312	$	19,885
Restricted and performance stock units	16,960		15,159
	$	32,272	$	35,044

2018 Omnibus Incentive Compensation Plan

On July 9, 2018, the Company’s board of directors adopted, and the Company’s stockholders approved the 2018 Omnibus Incentive Compensation Plan (the “2018 Plan”), which became effective immediately prior to the effectiveness of the registration statement for the Company’s initial public offering. The 2018 Plan provides for the issuance of incentive stock options, non-qualified stock options, stock awards, stock units, stock appreciation rights and other stock-based awards. The number of shares initially reserved for issuance under the 2018 Plan is 3,617,968 shares. If any options or stock appreciation rights, including outstanding options and stock appreciation rights granted under the 2017 Plan (up to 2,520,247 shares), terminate, expire, or are canceled, forfeited, exchanged, or surrendered without having been exercised, or if any stock awards, stock units or other stock-based awards, including outstanding awards granted under the 2017 Plan, are forfeited, terminated, or otherwise not paid in full in shares of common stock, the shares of the Company’s common stock subject to such grants will be available for purposes of our 2018 Plan. The number of shares reserved for issuance under the 2018 Plan will increase automatically on the first day of each April equal to 4.0% of the total number of shares of Company stock outstanding on the last trading day in the immediately preceding fiscal year, which includes for these purposes, the 14,058,153 shares issuable upon exercise of those pre-funded warrants described in Note 9 to these consolidated financial statements, or such lesser amount as determined by the Board. On April 1, 2025, the number of shares reserved for issuance under the 2018 Plan automatically increased by 3,645,727 shares pursuant to the terms of the 2018 Plan and based on total number of shares of Company stock outstanding on March 31, 2025. As of March 31, 2026, 1,569,457 shares remained available for future grants under the 2018 Plan.

The 2018 Plan is administered by the board of directors or, at the discretion of the board of directors, by a committee of the board of directors. However, the board of directors shall administer and approve all grants made to non-employee directors. The exercise prices, vesting and other restrictions are determined at the discretion of the board of directors, except that the exercise price per share of incentive stock options may not be less than 100% of the fair market value of the common stock on the date of grant (or 110% of fair value in the case of an award granted to employees who hold more than 10% of the total combined voting power of all classes of stock at the time of grant) and the term of stock options may not be greater than five years for an incentive stock option granted to a 10% stockholder and greater than ten years for all other options granted. Stock options awarded under both plans expire ten years after the grant date, unless the board of directors sets a shorter term. Vesting periods for both plans are determined at the discretion of the board of directors. Incentive stock options granted to employees and non-statutory options granted to employees, officers, members of the board of directors, advisors, and consultants of the Company typically vest over four years. In 2021 the board of directors initiated the award of RSUs, under the 2018 Plan in addition to stock option awards available as part of the Company’s equity incentive for employees, officers, advisors and consultants of the Company. The RSUs typically vest over four approximately equal annual installments with the first such installment occurring on a designated vesting date that is approximately on the one year anniversary date of the date of grant and the subsequent installments occurring on the subsequent three annual anniversaries of the designated vesting date.

In 2024, the Board of Directors approved the award of performance stock units ("PSUs"), under the 2018 Plan in addition to the aforementioned stock option awards and RSUs available as part of the Company’s equity incentive for employees, officers, advisors and consultants of the Company, subject to non-market performance and service conditions. The grant date fair value for the PSUs is determined based on the market price of the Company's common stock on the grant date and expense is recognized over the requisite service period if and when the achievement of such performance condition is determined to be probable by the Company. The PSUs will become vested, if at all, upon the achievement of the approval of the Company's first Biologics License Application ("BLA") for RP1 by the Food and Drug Administration ("FDA") no later than June 30, 2026. The timing of recognition of this stock-based compensation expense is subject to our judgment as to when the performance conditions are considered probable of being achieved. The Company did not grant any PSUs under the 2018 Plan during the

year ended March 31, 2026. The Company granted 246,110 PSUs under the 2018 Plan during the year ended March 31, 2025. If the Company does not achieve the approval of the Company's first BLA for RP1 before the expiration of June 30, 2026 then no PSU will be earned or vested. The Company reassesses the probability of achieving the performance condition at each reporting period. As of March 31, 2026, the Company has not recognized any expense related to PSUs.

Employee Stock Purchase Plan

On July 9, 2018, the Company’s board of directors adopted and the Company’s stockholders approved the Employee Stock Purchase Plan (the “ESPP”), which became effective immediately prior to the effectiveness of the registration statement for the Company’s IPO. The total shares of common stock initially reserved for issuance under the ESPP is limited to 348,612 shares. In addition, as of the first trading day of each fiscal year during the term of the ESPP (excluding any extensions), an additional number of shares of the Company’s common stock equal to 1% of the total number of shares outstanding on the last trading day in the immediately preceding fiscal year, which includes for these purposes, the 14,058,153 shares issuable upon exercise of those pre-funded warrants described in Note 9 to these consolidated financial statements, or 697,224 shares, whichever is less (or such lesser amount as determined by the Company’s board of directors) will be added to the number of shares authorized under the ESPP. In accordance with the terms of the ESPP, on April 1, 2025, the number of shares reserved for issuance under the ESPP automatically increased by 697,224, for a total of 4,102,399 shares reserved for the ESPP. If the total number of shares of common stock to be purchased pursuant to outstanding purchase rights on any particular date exceed the number of shares then available for issuance under the ESPP, then the plan administrator will allocate the available shares pro-rata and refund any excess payroll deductions or other contributions to participants. The Company’s ESPP is not currently active.

Out-of-Plan Inducement Grant

From time to time, the Company grants equity awards to newly hired employees and executives as a material inducement to enter into employment with the Company. The grants constitute "employment inducement grants" in accordance with Rule 5635(c)(4) of the Nasdaq Listing Rules and have been issued outside of the 2018 Plan and each of the other stock incentive plans described above. The inducement grants typically include nonqualified stock options to purchase shares of the Company's common stock, as well as restricted stock unit grants representing shares of the Company's common stock. These stock option and restricted stock unit inducement grants have terms and conditions consistent with those set forth under the 2018 Plan and vest under the same respective vesting schedules as stock option and restricted stock unit awards granted under the 2018 Plan. The inducement grants are included in the stock option and RSU award tables below. During the years ended March 31, 2026 and 2025, the Company granted 202,945 and 267,835 nonqualified stock options to purchase shares of the Company's common stock, respectively, and 333,130 and 404,030 restricted stock units, respectively, under employment inducement grants.

Stock option valuation

The fair value of stock option grants is estimated using the Black-Scholes option-pricing model, which requires inputs based on certain subjective assumptions including the expected stock price volatility, the expected term of the option, the risk-free interest rate determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for a period that approximates the expected term of the option, and our expected dividend yield. The expected stock volatility is based on Replimune's historical share price volatility. The expected term of stock options granted to non-employees is equal to the contractual term of the option award. Expected dividend yield is based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future. For options with service-based vesting conditions, the expected term of the Company's stock options has been determined utilizing the "simplified" method for awards that qualify as "plain-vanilla" options.

Forfeitures are accounted for as they occur. The fair value of each RSU and PSU is estimated on the date of grant based on the fair value of our common stock on that same date.

The following table presents, on a weighted-average basis, the assumptions that the Company used to determine the grant-date fair value of stock options granted to employees and directors:


	Year ended March 31,
	2026		2025
Risk-free interest rate	3.97	%	4.35	%
Expected term (in years)	6.0		6.0
Expected volatility	77.2	%	76.3	%
Expected dividend yield	0	%	0	%

Stock options

A summary of stock option activity under the Company’s equity incentive plans for the year ended March 31, 2026 is as follows:


	Number of Shares	Weighted Average Exercise Price		Weighted Average Contractual Term (Years)	Aggregate Intrinsic Value
Outstanding as of March 31, 2025	10,214,878	$	15.22	6.24	$	10,652
Granted	2,201,239	8.41
Exercised	(111,218)	3.43
Cancelled	(519,441)	13.97
Outstanding as of March 31, 2026	11,785,458	14.12		5.63	$	4,323
Options exercisable as of March 31, 2026	8,222,796	$	16.01	4.40	$	4,282
Options vested and expected to vest as of March 31, 2026	11,785,458	$	14.12	5.63	$	4,323

As of March 31, 2026, there was $19.0 million of unrecognized compensation cost related to unvested common stock options, which is expected to be recognized over a weighted average period of 2.5 years.

The weighted average grant-date fair value of stock options granted during the years ended March 31, 2026 and 2025 was $5.84 and $5.91, respectively. The aggregate intrinsic value of stock options exercised during the years ended March 31, 2026 and 2025 was $0.6 million and $0.5 million, respectively.

Restricted and performance stock units

A summary of the changes in the Company’s RSUs and PSUs during the year ended March 31, 2026 is as follows:


	Number of Shares	Weighted Average Grant Date Fair Value
Outstanding as of March 31, 2025	3,611,774	$	12.40
Granted	3,499,956	8.81
Vested	(1,003,362)	15.94
Cancelled	(599,486)	10.44
Outstanding as of March 31, 2026	5,508,882	$	9.69

During the years ended March 31, 2026 and 2025, the weighted average grant date fair value of awards granted is $30.8 million and $19.0 million, respectively. In addition, the total fair value of shares vested during the years ended March 31, 2026 and 2025 is $16.0 million and $13.5 million, respectively.

As of March 31, 2026, there was $36.3 million of total unrecognized compensation cost related to unvested restricted stock units which vest over time, which primarily will be recognized over a weighted-average period of 2.1 years. In addition, the

Company has unrecognized expense of approximately $4.1 million related to performance based awards with vesting tied to the achievement of a company milestone.

Insider Trading Arrangements	3 Months Ended
Insider Trading Arrangements	Mar. 31, 2026
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Operating expenses:
Research and development	$ 221,184	$ 189,447
Selling, general and administrative	98,735	72,180
Total operating expenses	319,919	261,627
Loss from operations	(319,919)	(261,627)
Other income (expense):
Research and development incentives	1,604	1,773
Investment income	13,625	21,120
Interest expense on finance lease liability	(2,063)	(2,118)
Interest expense on debt obligations	(6,796)	(5,775)
Other expense	(942)	(202)
Total other income, net	5,428	14,798
Loss before income taxes	(314,491)	(246,829)
Income tax (benefit) provision	(551)	468
Net loss	$ (313,940)	$ (247,297)
Net loss per common share, basic (in dollars per share)	$ (3.38)	$ (3.07)
Net loss per common share, diluted (in dollars per share)	$ (3.38)	$ (3.07)
Weighted average common shares outstanding, basic (in shares)	92,803,711	80,564,147
Weighted average common shares outstanding, diluted (in shares)	92,803,711	80,564,147

Income taxes - Reconciliation of the U.S federal statutory income tax rate (Details)	12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Percent
U.S. federal statutory income tax rate	(21.00%)	(21.00%)
State taxes, net of federal benefit	(0.80%)	(0.50%)
Research and development	(4.90%)	(1.60%)
Stock compensation	0.70%	1.20%
Foreign tax rate differential		(3.60%)
Change in tax rates		0.40%
Change in valuation allowance		24.30%
Other		1.00%
Total	0.20%	0.20%

Subsequent events (Details) - Subsequent Event $ in Millions	Apr. 10, 2026 USD ($)
Subsequent Event [Line Items]
Restructuring and related cost, number of positions eliminated, period percent	55.00%
Minimum \| One-time Termination Benefits
Subsequent Event [Line Items]
Restructuring and related cost, expected cost	$ 9.8
Maximum
Subsequent Event [Line Items]
Restructuring and related cost, expected cost	$ 10.3

Short-term investments (Tables)

12 Months Ended

Mar. 31, 2026

Short-Term Investments [Abstract]

Schedule of short-term investments

As of March 31, 2026 and 2025, the Company's available-for-sale investments by type, consisted of the following:


	March 31, 2026
	Amortized cost		Gross unrealized gains		Gross unrealized losses		Credit Losses		Fair value
US Government agency bonds	$	3,985	$	—	$	(1)	$	—	$	3,984
US Treasury bonds	55,872		9		$	—	$	—	55,881
	$	59,857	$	9	$	(1)	$	—	$	59,865


	March 31, 2025
	Amortized cost		Gross unrealized gains		Gross unrealized losses		Credit Losses		Fair value
US Government agency bonds	$	84,807	$	15	$	(18)	$	—	$	84,804
US Treasury bonds	287,570		334		(23)		—		287,881
	$	372,377	$	349	$	(41)	$	—	$	372,685

- Definition

Tabular disclosure of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-9

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-3

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

Reference 6: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (aa)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

Reference 7: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (aaa)
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Reference 8: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

Reference 9: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
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-Name Accounting Standards Codification
-Section 50
-Paragraph 3
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-3

Reference 10: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
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-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-3

Reference 11: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
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-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-3

Reference 12: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-3

+ Details

Commitments and contingencies - Other information (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$ 1,203	$ 1,167
Operating cash flows from finance leases	2,063	2,118
Financing cash flows from finance leases	$ 736	$ 599
Weighted-average remaining lease term – operating leases	3 years 9 months 18 days	4 years 8 months 12 days
Weighted-average remaining lease term – finance leases	13 years 3 months 18 days	14 years 3 months 18 days
Weighted-average discount rate – operating leases	10.40%	10.40%
Weighted-average discount rate – finance leases	8.30%	8.30%

Stockholders' Equity - Equity offerings (Details) - USD ($) $ / shares in Units, $ in Millions	Nov. 25, 2024	Jun. 14, 2024
Class of Warrant or Right [Line Items]
Number of shares issued (in shares)	8,538,377	5,668,937
Sale of stock, price per share (in dollars per share)	$ 13.00	$ 8.82
Net proceeds	$ 156.0	$ 96.7
2024 Pre-funded Warrants
Class of Warrant or Right [Line Items]
Issuance of pre-funded warrants (in shares)	3,846,184	5,669,578
Share price (in dollars per share)	$ 12.9999	$ 8.819
Underwriting discounts, commissions and other offering expenses	$ 5.0	$ 3.3
Underwriter rights
Class of Warrant or Right [Line Items]
Issuance of pre-funded warrants (in shares)	1,615,377

Commitments and contingencies - Components of lease expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Finance lease costs:
Amortization of right-of-use asset	$ 2,428	$ 2,428
Interest on lease liabilities	2,063	2,118
Operating lease costs	1,156	1,129
Total lease cost	$ 5,647	$ 5,675

Commitments and contingencies

12 Months Ended

Mar. 31, 2026

Commitments and Contingencies Disclosure [Abstract]

Commitments and contingencies

Leases

The Company leases real estate assets and equipment, and the determination if an arrangement is a lease occurs at inception. For leases with terms greater than 12 months, the Company records a related right-of-use (“ROU”) asset and lease liability at the present value of lease payments over the term. Many leases include fixed rental escalation clauses, renewal options and/or termination options that are factored into the determination of lease payments when appropriate. The Company’s leases do not provide an implicit rate, and thus the Company estimated the incremental borrowing rate in calculating the present value of the lease payments. The Company has elected not to record a ROU asset and lease obligation for short-term leases (with terms less than 12 months) or separate non-lease components from associated lease components for its real estate lease assets. As a result, all contract consideration is allocated to the single lease component.

The Company’s leases have remaining lease terms of five years to fifteen years. Some of the Company's leases include one or more options to renew with renewal terms that can extend the lease for additional years, or options to terminate the leases, both at the Company’s discretion. The Company’s lease terms include options to extend or terminate leases when the Company concludes it is reasonably certain that it would exercise those options. Lease expense for minimum lease payments is recognized on a straight-line basis based on the fixed components of a lease arrangement. The Company amortizes this expense

over the term of the lease beginning with the date of initial possession, which is the date the Company can enter the leased space and begin to make improvements in preparation for its intended use. Variable lease components represent amounts that are not fixed in nature and are not tied to an index or rate, and are recognized as incurred.

The table below presents the lease-related costs which are included in the consolidated statements of operations for the years ended as of March 31, 2026 and 2025:


	Year ended March 31,
	2026		2025
Lease cost
Finance lease costs:
Amortization of right-of-use asset	$	2,428	$	2,428
Interest on lease liabilities	2,063		2,118
Operating lease costs	1,156		1,129
Total lease cost	$	5,647	$	5,675

The following table summarizes the classification of lease costs in the consolidated statement of operations for the years ended March 31, 2026 and 2025 as follows:


	Year ended March 31,
	2026		2025
Finance Lease Costs
Research and development	$	2,428	$	2,428
Other expense	2,063		2,118
Operating Lease Costs
Research and development	887		877
Selling, general and administrative	269		252
Total lease cost	$	5,647	$	5,675


	March 31, 2026
	Operating leases		Finance lease		Total
2027	$	1,160	$	2,883	$	4,043
2028	1,106		2,969		4,075
2029	1,021		3,058		4,079
2030	587		3,096		3,683
2031	369		3,096		3,465
Thereafter	—		25,803		25,803
Total lease payments	4,243		40,905		45,148
Less: interest	757		16,113		16,870
Total lease liabilities	$	3,486	$	24,792	$	28,278

The following table provides lease disclosure as of and for the years ended March 31, 2026 and 2025:


	March 31, 2026			March 31, 2025
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$	1,203		$	1,167
Operating cash flows from finance leases	$	2,063		$	2,118
Financing cash flows from finance leases	$	736		$	599
Weighted-average remaining lease term – operating leases	3.8 years			4.7 years
Weighted-average remaining lease term – finance leases	13.3 years			14.3 years
Weighted-average discount rate – operating leases	10.4		%	10.4		%
Weighted-average discount rate – finance leases	8.3		%	8.3		%

The variable lease costs and short-term lease costs were insignificant for the years ended March 31, 2026 and 2025, respectively.

Manufacturing commitments

The Company has entered into an agreement with a contract manufacturing organization to provide clinical trial products. As of March 31, 2026 and 2025, the Company had committed to minimum payments under these arrangements totaling $0.8 million and $0.8 million.

Indemnification agreements

In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, business partners and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of its executive management team and its board of directors that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs as a result of such indemnifications. The Company is not aware of any claims under indemnification arrangements, and therefore it has not accrued any liabilities related to such obligations in its consolidated financial statements as of March 31, 2026 or 2025.

Legal proceedings

From time to time, the Company may become involved in legal proceedings arising in the ordinary course of business. The Company records a liability for such matters when it is probable that future losses will be incurred and that such losses can be reasonably estimated. Significant judgment is required to determine both probability and the estimated amount.

On July 24, 2025, a class action complaint alleging violations of the federal securities laws was filed against the Company and its directors and certain officers in the United States District Court for the District of Massachusetts, or the District of Massachusetts. The complaint, captioned Jboor v. Replimune Group, Inc. et al., Case No. 1:25-cv-12085-JEK, was filed shortly after the Company announced it received a complete response letter from the FDA for its RP1 BLA for the treatment of advanced melanoma on July 22, 2025 and the subsequent decline in the trading price of the Company's common stock. The Court has appointed a lead plaintiff, or the Lead Plaintiff. On January 13, 2026, Lead Plaintiff filed an amended complaint. The Company and the other defendants deny any wrongdoing and continue to vigorously defend this action.

Following the class action complaint, three shareholders filed separate derivative actions on behalf of the Company in the District of Massachusetts captioned Chea v. Patel et al., Case No. 1:25-cv-12316-JEK, Wright v. Patel et al., Case No. 1:25-cv-12401-WGY, and Vochten v. Patel et al., Case No. 1:25-cv-12484-JEK. The plaintiffs allege substantially similar facts as the class action complaint and assert that the Company’s directors and officers breached their fiduciary duties. The parties have consolidated the derivative actions and agreed to a stay pending further developments in the class action.

On September 10, 2025, the Company received a letter from a shareholder demanding that the Company's board of directors take action to address alleged wrongdoing by certain directors and officers. The demand letter alleged substantially similar facts as the class action and derivative action complaints. The board of directors determined to defer action on the demand pending further developments in the class action.

On September 29, 2025, the SEC informed the Company that it was conducting an investigation and requested that the Company produce certain documents and communications connected with the RP1 BLA. The investigation is reviewing essentially the same subject matter raised in the litigation following the CRL. On June 24, 2026, the SEC informed the Company that it has concluded its investigation of the Company and that it is not recommending an enforcement action be taken against the Company.

Following the second CRL issued by the FDA on April 10, 2026 for the Company's RP1 BLA for the treatment of advanced melanoma, the Lead Plaintiff filed a second amended complaint in the class action that addresses the second CRL. The Company’s and the other defendants’ response is due July 20, 2026.

As the matters noted above are preliminary, the Company is unable to determine whether any loss will ultimately occur and cannot reasonably estimate the range of expected exposure. Therefore, the Company has not recorded any liability in the condensed consolidated financial statements as of and for the year ended March 31, 2026.