AlloVir (ALVR) 10-Q 3 Aug 23 2023 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2023	Jul. 28, 2023
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2023
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q2
Trading Symbol	ALVR
Entity Registrant Name	ALLOVIR, INC.
Entity Central Index Key	0001754068
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		113,868,112
Security12b Title	Common Stock, par value $0.0001 per share
Security Exchange Name	NASDAQ
Entity File Number	001-39409
Entity Incorporation State Country Code	DE
Entity Tax Identification Number	83-1971007
Entity Address Address Line1	1100 Winter Street
Entity Address City Or Town	Waltham
Entity Address State Or Province	MA
Entity Address Postal Zip Code	02451
City Area Code	617
Local Phone Number	433-2605
Document Quarterly Report	true
Document Transition Report	false

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 196,954	$ 106,092
Short-term investments	49,582	127,703
Interest receivable	106	157
Prepaid expenses and other current assets	4,737	7,100
Prepaid expenses to related party	1,533	2,000
Total current assets	252,912	243,052
Restricted cash	852	852
Other assets	684	612
Property and equipment, net	759	930
Operating lease right-of-use assets	27,485	31,633
Total assets	282,692	277,079
Current liabilities:
Accounts payable	5,164	3,004
Accrued expenses	16,728	13,985
Income tax payable	127	128
Operating lease liability, current	8,483	7,165
Amount due to related party	61	56
Total current liabilities	30,563	24,338
Operating lease liability, long term	23,016	28,222
Total liabilities	53,579	52,560
Stockholders’ equity:
Preferred stock, $0.0001 par value: 10,000,000 shares authorized at June 30, 2023 and December 31, 2022, respectively; 0 shares issued and outstanding at June 30, 2023 and December 31, 2022, respectively
Common stock, $0.0001 par value: 300,000,000 and 150,000,000 shares authorized at June 30, 2023 and December 31, 2022, respectively; 113,729,743 and 93,268,069 shares issued at June 30, 2023 and December 31, 2022, respectively; and 113,716,018 and 93,093,243 shares outstanding at June 30, 2023 and December 31, 2022, respectively	11	9
Additional paid-in capital	781,552	690,753
Accumulated other comprehensive loss	(225)	(468)
Accumulated deficit	(552,225)	(465,775)
Total stockholders’ equity	229,113	224,519
Total liabilities and stockholders’ equity	$ 282,692	$ 277,079

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED) (Parenthetical) - $ / shares	Jun. 30, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Preferred stock, par or stated value per share	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	300,000,000	150,000,000
Common stock, shares issued	113,729,743	93,268,069
Common stock, shares outstanding	113,716,018	93,093,243

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Operating expenses:
Research and development	$ 34,824	$ 31,379	$ 65,543	$ 60,446
General and administrative	12,480	13,245	24,992	27,371
Total operating expenses	47,304	44,624	90,535	87,817
Loss from operations	(47,304)	(44,624)	(90,535)	(87,817)
Total other income (loss), net:
Interest income	1,516	162	2,841	310
Other income (loss), net	521	(27)	1,244	(845)
Loss before income taxes	(45,267)	(44,489)	(86,450)	(88,352)
Income tax expense	0	150	0	150
Net loss	$ (45,267)	$ (44,639)	$ (86,450)	$ (88,502)
Net loss per share - basic	$ (0.48)	$ (0.69)	$ (0.92)	$ (1.38)
Net loss per share - diluted	$ (0.48)	$ (0.69)	$ (0.92)	$ (1.38)
Weighted-average common shares outstanding - basic	94,625,837	64,467,483	93,968,407	64,231,579
Weighted-average common shares outstanding - diluted	94,625,837	64,467,483	93,968,407	64,231,579
Comprehensive loss:
Net loss	$ (45,267)	$ (44,639)	$ (86,450)	$ (88,502)
Other comprehensive income (loss), net of tax:
Unrealized gain (loss) on available-for-sale securities	76	(94)	243	(289)
Total other comprehensive income (loss)	76	(94)	243	(289)
Comprehensive loss	$ (45,191)	$ (44,733)	$ (86,207)	$ (88,791)

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit
Balance at Dec. 31, 2021	$ 225,266	$ 7	$ 522,479	$ (155)	$ (297,065)
Balance, Shares at Dec. 31, 2021		63,565,886
Stock-based compensation	10,467		10,467
Issuance of common stock, upon vesting of restricted stock, Shares		698,241
Unrealized gain (loss) on available-for-sale securities	(195)			(195)
Net loss	(43,863)				(43,863)
Balance at Mar. 31, 2022	191,675	$ 7	532,946	(350)	(340,928)
Balance, Shares at Mar. 31, 2022		64,264,127
Balance at Dec. 31, 2021	225,266	$ 7	522,479	(155)	(297,065)
Balance, Shares at Dec. 31, 2021		63,565,886
Unrealized gain (loss) on available-for-sale securities	(289)
Net loss	(88,502)
Balance at Jun. 30, 2022	158,137	$ 7	544,141	(444)	(385,567)
Balance, Shares at Jun. 30, 2022		64,788,103
Balance at Mar. 31, 2022	191,675	$ 7	532,946	(350)	(340,928)
Balance, Shares at Mar. 31, 2022		64,264,127
Stock-based compensation	10,951		10,951
Issuance of common stock, upon vesting of restricted stock, Shares		450,619
Purchase of common stock under the 2020 Employee Stock Purchase Plan	244		244
Purchase of common stock under the 2020 employee stock purchase plan, Shares		73,357
Unrealized gain (loss) on available-for-sale securities	(94)			(94)
Net loss	(44,639)				(44,639)
Balance at Jun. 30, 2022	158,137	$ 7	544,141	(444)	(385,567)
Balance, Shares at Jun. 30, 2022		64,788,103
Balance at Dec. 31, 2022	224,519	$ 9	690,753	(468)	(465,775)
Balance, Shares at Dec. 31, 2022		93,093,243
Stock-based compensation	10,029		10,029
Issuance of common stock, upon vesting of restricted stock, Shares		334,747
Unrealized gain (loss) on available-for-sale securities	167			167
Net loss	(41,183)				(41,183)
Balance at Mar. 31, 2023	193,532	$ 9	700,782	(301)	(506,958)
Balance, Shares at Mar. 31, 2023		93,427,990
Balance at Dec. 31, 2022	224,519	$ 9	690,753	(468)	(465,775)
Balance, Shares at Dec. 31, 2022		93,093,243
Unrealized gain (loss) on available-for-sale securities	243
Net loss	(86,450)
Balance at Jun. 30, 2023	229,113	$ 11	781,552	(225)	(552,225)
Balance, Shares at Jun. 30, 2023		113,716,018
Balance at Mar. 31, 2023	193,532	$ 9	700,782	(301)	(506,958)
Balance, Shares at Mar. 31, 2023		93,427,990
Stock-based compensation	10,288		10,288
Issuance of common stock, upon vesting of restricted stock, Shares		179,092
Purchase of common stock under the 2020 Employee Stock Purchase Plan	315		315
Purchase of common stock under the 2020 employee stock purchase plan, Shares		108,936
Issuance of common stock in public offering, net of underwriting discounts, commissions and offering costs	70,169	$ 2	70,167
Issuance of common stock in public offering, net of underwriting discounts, commissions and offering costs, Shares		20,000,000
Unrealized gain (loss) on available-for-sale securities	76			76
Net loss	(45,267)				(45,267)
Balance at Jun. 30, 2023	$ 229,113	$ 11	$ 781,552	$ (225)	$ (552,225)
Balance, Shares at Jun. 30, 2023		113,716,018

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022
Cash flows from operating activities
Net loss	$ (86,450)	$ (88,502)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	171	552
Non-cash lease expense	233	720
(Accretion) amortization of short-term investment (discounts) premiums	(1,253)	49
Stock-based compensation expense	20,317	21,418
Changes in operating assets and liabilities:
Interest receivable	51	(41)
Prepaid expenses and other current assets and prepaid expenses to related party	2,856	1,423
Other assets	(72)	245
Income tax payable	(1)	(853)
Accounts payable, accrued expenses and amount due to related party	4,908	(10,365)
Net cash used in operating activities	(59,240)	(75,354)
Cash flows from investing activities
Purchase of short-term investments	(14,196)	(92,783)
Maturities of short-term investments	93,814	37,325
Net cash provided by (used in) investing activities	79,618	(55,458)
Cash flows from financing activities
Proceeds from issuance of common stock in public offering, net of underwriting discounts, commissions and offering costs	70,169
Proceeds from issuance of stock under the 2020 Employee Stock Purchase Plan	315	244
Net cash provided by financing activities	70,484	244
Net increase (decrease) in cash, cash equivalents, and restricted cash	90,862	(130,568)
Cash, cash equivalents, and restricted cash at beginning of period	106,944	202,513
Cash, cash equivalents, and restricted cash at end of period	197,806	71,945
Non-cash investing and financing activities
Unrealized gain (loss) on available-for-sale securities	243	(289)
Deferred offering costs included in accounts payable and accrued expenses	331
Reduction of right-of-use asset and operating lease liability due to modification and remeasurement		(5,506)
Supplemental disclosure of cash flows
Income taxes paid, net of refunds	350	1,003
Cash and cash equivalents	196,954	71,093
Restricted cash	852	852
Total cash, cash equivalents, and restricted cash	$ 197,806	$ 71,945

Nature of the Business

Nature of the Business	6 Months Ended
	Jun. 30, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of the Business	1. Nature of the Business AlloVir, Inc. (“AlloVir” or “the Company”, formerly known as ViraCyte, Inc.) is a leading late clinical-stage cell therapy company developing highly innovative allogeneic T cell therapies to treat and prevent devastating viral diseases. The Company’s innovative and proprietary virus-specific T cell, or VST, therapy platform allows AlloVir to generate off-the-shelf VSTs designed to restore immunity in patients with T cell deficiencies who are at risk from the life-threatening consequences of viral diseases. There is an urgent medical need for therapies to treat a large number of patients suffering from viral diseases who currently have limited or no treatment options. The Company is developing three innovative, allogeneic, off-the-shelf VST therapy candidates targeting 11 different devastating viruses. The Company's lead product, posoleucel (previously referred to as Viralym-M or ALVR105), is a multi-VST therapy that targets six viruses: adenovirus, or AdV, BK virus, or BKV, cytomegalovirus, or CMV, Epstein-Barr virus, or EBV, human herpesvirus 6, or HHV-6 and JC virus, or JCV. The Company believes that posoleucel has the potential to fundamentally transform the treatment landscape for transplant patients by substantially reducing or preventing disease morbidity and mortality, thereby dramatically improving patient outcomes. Posoleucel is being studied in three ongoing Phase 3 registrational trials for three distinct indications - the prevention of clinically significant infections from multiple viruses, the treatment of virus-associated hemorrhagic cystitis, or HC, and the treatment of AdV infections – all in allogeneic hematopoietic cell transplant, or HCT, patients who are at high risk for life-threatening viral infections from the six viruses targeted by posoleucel. The Company accelerated the multi-prevention study in recognition of the fact that prevention best addresses patients’ unmet medical needs. Data readouts from all three trials are expected in 2024. In addition to the ongoing Phase 3 registrational studies, posoleucel has been studied in a Phase 2 proof-of-concept, or POC, study for the treatment of BK viremia in kidney transplant patients. Positive topline results of this study were released in February 2023. This is the first study of posoleucel in solid organ transplant, or SOT, patients, and the results of this trial will inform next steps for this potential indication as well as the Company’s broader SOT strategy. The Company’s pipeline includes additional investigational VST therapies that may benefit high-risk individuals. ALVR106 is the Company’s second off-the-shelf, multi-VST product candidate targeting devastating respiratory diseases caused by human metapneumovirus, or hMPV, influenza, parainfluenza virus, or PIV and respiratory syncytial virus, or RSV. A Phase 1b/2 POC clinical study of ALVR106 has completed enrollment of patients in Part A of the trial. In the preclinical space, the Company is developing ALVR107 to treat hepatitis B, or HBV, infected cells and with the aim of curing chronic HBV infection. Preclinical and IND-enabling studies of ALVR107 to treat and cure HBV were completed in 2022 to support advancement into a POC study after completion of the posoleucel Phase 3 registrational studies. ElevateBio, LLC - Related Party On September 17, 2018, the Company executed a Series A2 Preferred Stock Purchase Agreement ("Series A2 Agreement"), with ElevateBio, LLC ("ElevateBio") and ElevateBio was a purchaser in our registered direct offering in July 2022. ElevateBio, through its diverse platform of technologies to support cell and gene therapy products and expertise, provides drug development and manufacturing services . As a result of ElevateBio’s purchase of our Series A2 Preferred Stock, which converted to common stock upon completion of our IPO, and as a result of ElevateBio’s participation in the July 2022 registered direct offering, ElevateBio acquired an ownership interest in the Company. The Chief Financial Officer of ElevateBio currently serves in a similar management role with AlloVir. In May 2021, Diana M. Brainard M.D. succeeded David Hallal, ElevateBio’s Chief Executive Officer, as the Company’s Chief Executive Officer. Mr. Hallal currently serves as Executive Chairman of the Company's board of directors. In addition to Mr. Hallal and Mr. Sinha, Morana Jovan-Embiricos, a director of the Company's board of directors, also serves as a director of the board of directors of ElevateBio. Going Concern In accordance with Accounting Standards Update (“ASU”) 2014-15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern (Subtopic 205-40) , the Company has evaluated whether there are conditions and 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 the condensed consolidated financial statements are issued. 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. The accompanying condensed 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. Through June 30, 2023, the Company has funded its operations primarily with proceeds received from the sale of common stock, research grants, and from the sale of preferred stock. The Company has incurred recurring losses since its inception, including net losses attributable to common stockholders of $ 45.3 million and $ 44.6 million for the three months ended June 30, 2023 and 2022, respectively, and $ 86.5 million and $ 88.5 million for the six months ended June 30, 2023 and 2022, respectively. In addition, at June 30, 2023, the Company had an accumulated deficit of $ 552.2 million. The Company expects to continue to generate operating losses for the foreseeable future. The Company believes that its $ 246.5 million of cash, cash equivalents and short-term investments held at June 30, 2023 is sufficient to fund planned operations for at least twelve months from the date that these condensed consolidated financial statements are issued. COVID-19 Considerations The development of product candidates could be disrupted and materially adversely affected in the future by a pandemic, epidemic or outbreak of an infectious disease, such as the recent COVID-19 pandemic. Although the immediate impacts of COVID-19 have receded, the COVID-19 pandemic impacted the global economy and the Company’s operations, including the interruption of preclinical and clinical trial activities and potential interruption to the Company’s supply chain. For example, the COVID-19 pandemic has delayed clinical trials. The Company will continue to assess business plans and the impact COVID-19, including any resurgences, may have on its ability to advance the testing, development and manufacturing of drug candidates, including as a result of adverse impacts on the research sites, service providers, vendors, or suppliers on whom the Company relies on, or to raise financing to support the development of our drug candidates. No assurances can be given that this analysis will enable the Company to avoid part or all of any impact from the spread of COVID-19 or its consequences, including downturns in business sentiment generally or this sector in particular. The Company cannot presently predict the scope of any potential business shutdowns or disruptions, but if the Company or any of the third parties on whom it relies on or with whom it conducts business, were to experience shutdowns or other business disruptions, the Company’s ability to conduct business in the manner and on the timelines presently planned could be materially and adversely impacted.

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2023
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies The Company’s significant accounting policies are disclosed in the audited consolidated financial statements for the year ended December 31, 2022, and notes thereto, which are included in the Company’s Annual Report on Form 10-K that was filed with the Securities and Exchange Commission, or the SEC, on February 15, 2023. Since the date of those financial statements, there have been no material changes to the Company’s significant accounting policies except as described below. Interim Financial Information The accompanying condensed consolidated balance sheet at June 30, 2023, and the condensed consolidated statements of operations and comprehensive loss, statements of changes in stockholders’ equity for the three and six months ended June 30, 2023 and 2022 and the condensed consolidated statements of cash flows for the six months ended June 30, 2023 and 2022 are unaudited. The condensed consolidated interim financial statements have been prepared on the same basis as the audited annual financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments necessary for the fair presentation of the Company’s financial position at June 30, 2023 and the results of its operations for the three and six months ended June 30, 2023 and 2022 and its cash flows for the six months ended June 30, 2023 and 2022. The financial data and other information disclosed in these notes related to the three and six months ended June 30, 2023 and 2022 are also unaudited. The results for the three and six months ended June 30, 2023 are not necessarily indicative of results to be expected for the year ending December 31, 2023 or for any other subsequent interim period. Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (“FASB”), or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the impact of recently issued standards that are not yet effective will not have a material impact on the Company’s consolidated financial statements upon adoption. Under the Jumpstart Our Business Startups Act of 2012, as amended (the “JOBS Act”), the Company meets the definition of an emerging growth company and has elected the extended transition period for complying with certain new or revised accounting standards pursuant to Section 107(b) of the JOBS Act. Since December 31, 2022 , there have been no new accounting pronouncements adopted by the Company or issued by FASB that are applicable to the Company, except as noted below. Recently Adopted Accounting Pronouncements In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments , or ASU 2016-13, which requires the measurement and recognition of expected credit losses for financial assets held at amortized cost. ASU 2016-13 replaces the existing incurred loss impairment model with an expected loss model. It also eliminates the concept of other-than-temporary impairment and requires credit losses related to available-for-sale debt securities to be recorded through an allowance for credit losses rather than as a reduction in the amortized cost basis of the securities. These changes may result in earlier recognition of credit losses. The Company adopted ASU 2016-13 on January 1, 2023 . The adoption of ASU 2016-13 did not have a material impact on the Company’s condensed consolidated financial statements. Recently Issued Accounting Pronouncements Not Yet Adopted None.

Short-Term Investments

Short-Term Investments	6 Months Ended
	Jun. 30, 2023
Investments, Debt and Equity Securities [Abstract]
Short-Term Investments	3. Short-Term Investments The following tables summarize the amortized cost and estimated fair value of the Company’s U.S. government treasury securities and marketable securities, which are considered to be available-for-sale investments and are included in short-term investments on the condensed consolidated balance sheets: June 30, 2023 (in thousands) Amortized Unrealized Unrealized Fair U.S. government treasury securities $ 42,172 $ — $ ( 70 ) $ 42,102 Marketable securities: Corporate and agency bonds 7,500 — ( 20 ) 7,480 Totals $ 49,672 $ — $ ( 90 ) $ 49,582 December 31, 2022 (in thousands) Amortized Unrealized Unrealized Fair U.S. government treasury securities $ 99,288 $ 1 $ ( 253 ) $ 99,036 Marketable securities: Corporate and agency bonds 28,748 3 ( 84 ) $ 28,667 Totals $ 128,036 $ 4 $ ( 337 ) $ 127,703 Certain short-term debt securities with original maturities of less than three months are included in cash and cash equivalents on the condensed consolidated balance sheets and are not included in the tables above. The Company holds debt securities of companies with high credit quality and has determined that there was no material change in the credit risk of any of its debt securities. At June 30, 2023 and December 31, 2022 , all investments had contractual maturities within one year.

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jun. 30, 2023
Fair Value Disclosures [Abstract]
Fair Value Measurements	4. Fair Value Measurements The following tables present information about the Company’s financial assets and liabilities measured at fair value on a recurring basis: June 30, 2023 (in thousands) Level 1 Level 2 Level 3 Total Cash equivalents: Money market fund $ 111,015 $ — $ — $ 111,015 Totals $ 111,015 $ — $ — $ 111,015 Short-term investments: U.S. government treasury securities $ 42,102 $ — $ — $ 42,102 Marketable securities: Corporate and agency bonds — 7,480 — 7,480 Totals $ 42,102 $ 7,480 $ — $ 49,582 December 31, 2022 (in thousands) Level 1 Level 2 Level 3 Total Cash equivalents: Money market fund $ 32,641 $ — $ — $ 32,641 Totals $ 32,641 $ — $ — $ 32,641 Short-term investments: U.S. government treasury securities $ 99,036 $ — $ — $ 99,036 Marketable securities: Corporate and agency bonds — 28,667 — $ 28,667 Totals $ 99,036 $ 28,667 $ — $ 127,703 During the six months ended June 30, 2023 and the year ended December 31, 2022, there were no transfers between levels. The Company classifies its money market fund and U.S. government treasury securities as Level 1 assets under the fair value hierarchy, as these assets have been valued using quoted market prices in active markets without any valuation adjustment. The Company classifies its marketable securities as Level 2 assets under the fair value hierarchy, as these assets have pricing inputs that are other than quoted prices in active markets, which are either directly or indirectly observable as of the reporting date, and fair value is determined using models or other valuation methodologies. The carrying amounts of prepaid expenses and other current assets, prepaid expenses to related party, accounts payable, amount due to related party and accrued expenses approximate their fair values due to the short-term nature of these assets and liabilities.

Leases

Leases	6 Months Ended
	Jun. 30, 2023
Leases [Abstract]
Leases	5. Leases Operating leases Development and Manufacturing Services Agreement ("DMS Agreement") with Third-Party Supplier In October 2022, the Company entered into a SOW under the DMS Agreement ("2022 SOW under the DMS Agreement") with a third-party supplier. The 2022 SOW under the DMS Agreement contained an embedded lease for a dedicated manufacturing suite for the manufacture of AlloVir’s products at the facility because the Company directs how and for what purpose the suite is used and obtains substantially all of the economic benefit of the suite. At inception of the lease, it was determined that, in exchange for this dedicated manufacturing suite, AlloVir will pay the supplier a monthly fixed suite utilization fee, fixed batch payments and other related fixed costs, totaling $ 16.3 million over the 2.25 year lease term ending in December 2024 . As part of the arrangement, there were also variable costs for materials, non-fixed batch payments, testing, storage, knowledge and tech transfer and other common area maintenance fees that were not included in the measurement of the lease. The lease of the facility was determined to be classified as an operating lease and commenced in October 2022, the point at which the suite was substantially complete and available for use by the Company. Accordingly, at inception, the Company recorded a ROU asset and lease liability of $ 14.7 million. Waltham Leases In September 2021, the Company entered into a lease agreement with BP Bay Colony LLC and a sublease with AMAG Pharmaceuticals Inc. for the lease of property in Waltham, Massachusetts (collectively, the "Waltham leases"). The space identified under the Waltham leases is intended for general office space, research and development, laboratory use, and light manufacturing. The Waltham leases are classified as operating leases and commenced in September 2021 . At the inception date, the Company recorded a ROU asset and lease liability of $ 6.0 million for the lease and a ROU asset and lease liability of $ 17.3 million for the sublease based on a July 30, 2030 end date for the Waltham leases. As part of the arrangement, there were also variable costs for common area maintenance fees that were not included in the measurement of the lease. The agreement also provides a $ 3.1 million tenant improvement allowance which is to be reimbursed by the landlord over the duration of the first two years of the Waltham leases. At June 30, 2023 , $ 0.9 million of the tenant improvement allowance has been used. The Company has the option to renew the leased space for an additional one time period of five years with written notice from the Company. At June 30, 2023 , the Company has no reasonable certainty that this option to extend will be exercised. Maturities of operating lease liabilities at June 30, 2023 are as follows (in thousands): 2023 (remaining 6 months) 5,110 2024 11,533 2025 3,229 2026 3,308 2027 3,386 Thereafter 9,681 Total lease payments 36,247 Less: interest ( 4,748 ) Total lease liability $ 31,499 Lease liability – current $ 8,483 Lease liability – long-term $ 23,016 Total lease costs were $ 2.6 million and $ 1.3 million for the three months ended June 30, 2023 and 2022 , respectively, and $ 5.1 million and $ 2.8 million for the six months ended June 30, 2023 and 2022 , respectively. Cash paid for operating leases was $ 2.8 million and $ 0.9 million for the three months ended June 30, 2023 and 2022 , respectively, and $ 4.9 million and $ 2.1 million for the six months ended June 30, 2023 and 2022 , respectively. The Company’s total variable lease costs, such as materials, non-fixed batch payments, testing, storage, knowledge and tech transfer, and other common area maintenance fees, related to the operating leases was $ 0.5 million and $ 0.9 million for the three months ended June 30, 2023 and 2022 , respectively, and $ 0.6 million and $ 2.2 million for the six months ended June 30, 2023 and 2022 , respectively. The weighted average remaining lease term was 6.55 years and 6.93 years at June 30, 2023 and December 31, 2022 , respectively. The weighted average discount rate was 6.10 % and 6.23 % at June 30, 2023 and December 31, 2022 , respectively.

Accrued Expenses

Accrued Expenses	6 Months Ended
	Jun. 30, 2023
Payables and Accruals [Abstract]
Accrued Expenses	6. Accrued Expenses Accrued expenses consisted of the following: (in thousands) June 30, December 31, Employee compensation and benefits $ 3,574 $ 6,416 Professional fees 960 559 Research and development 7,288 5,678 Process development and manufacturing costs 4,603 504 Other 303 828 Total accrued expenses $ 16,728 $ 13,985

Stockholder's Equity

Stockholder's Equity	6 Months Ended
	Jun. 30, 2023
Equity [Abstract]
Stockholder's Equity	7. Stockholder’s Equity On May 15, 2023, the Company filed a certificate of amendment to its amended and restated certificate of incorporation authorizing the Company to issue up to 300,000,000 shares of common stock at a par value of $ 0.0001 per share and 10,000,000 shares of preferred stock at a par value of $ 0.0001 per share. There were no shares of preferred stock issued or outstanding at June 30, 2023 and December 31, 2022. On June 21, 2023, the Company entered into an underwriting agreement with J.P. Morgan Securities LLC, Morgan Stanley & Co. LLC and BoFA Securities, Inc., as the representatives of the several underwriters (the “Underwriters”) relating to an underwritten public offering of 20,000,000 shares of its common stock at a public offering price of $ 3.75 per share, resulting in net proceeds of $ 70.2 million after deducting underwriting discounts and commissions of $ 4.5 million and offering costs of $ 0.3 million. Under the terms of the underwriting agreement, the Company granted the Underwriters an option, exercisable for 30 days, to purchase up to an additional 3,000,000 shares of its common stock at the same price per share as the shares, less underwriting discounts and commissions. On July 21, 2023 , the Underwriters option expired. The Company has reserved shares of common stock for issuance as follows: June 30, December 31, Options to purchase common stock 10,304,403 7,922,797 Unvested restricted stock 3,503,459 2,239,106 Stock available for grant under the 2020 Stock Option and Grant Plan 4,476,879 4,253,680 Stock available for issuance under the 2020 Employee Stock Purchase Plan 505,366 454,302 Total 18,790,107 14,869,885

Stock-Based Compensation

Stock-Based Compensation	6 Months Ended
	Jun. 30, 2023
Share-Based Payment Arrangement [Abstract]
Stock-Based Compensation	8. Stock-Based Compensation Stock-Based Compensation Expense Stock-based compensation expense was as follows: Three Months Ended Six Months Ended (in thousands) 2023 2022 2023 2022 Research and development $ 3,514 $ 3,892 $ 6,937 $ 7,232 General and administrative 6,774 7,059 13,380 14,186 Total stock-based compensation expense $ 10,288 $ 10,951 $ 20,317 $ 21,418 2018 Equity Incentive Plan At June 30, 2023 , there was an aggregate of 64,042 shares of common stock issuable upon the exercise of outstanding options under the 2018 Plan and 6,616,772 shares of restricted common stock granted under the 2018 plan. No shares remain available for future issuance under the 2018 Plan. Any options or awards outstanding under the 2018 Plan remain outstanding and effective. 2020 Stock Option and Grant Plan At June 30, 2023 , there was an aggregate of 10,240,361 shares of common stock issuable upon the exercise of outstanding options under the 2020 Plan and 5,150,960 shares of restricted common stock granted under the 2020 Plan. There is an aggregate of 4,476,879 shares reserved for future issuance under the 2020 Plan. Restricted Common Stock The following table summarizes restricted common stock activity for the six months ended June 30, 2023: Shares Weighted Unvested at January 1, 2023 2,239,106 $ 13.75 Granted 2,074,444 6.31 Forfeited ( 296,252 ) 11.78 Vested ( 513,839 ) 12.67 Unvested at June 30, 2023 3,503,459 $ 9.67 At June 30, 2023 , there was $ 30.3 million of unrecognized stock-based compensation cost related to the restricted stock, which is expected to be recognized over a weighted average period of 2.57 years. Stock Options The following table summarizes stock option activity (in thousands, except share and per share data): Shares Weighted Weighted Aggregate Options outstanding at January 1, 2023 7,922,797 $ 17.81 8.30 $ 786 Granted 3,400,892 6.60 — — Exercised — — — — Forfeited ( 1,019,286 ) 15.83 — — Options outstanding at June 30, 2023 10,304,403 $ 14.31 8.39 $ 19 Options vested and exercisable at June 30, 2023 3,751,655 $ 19.66 7.60 $ 19 The aggregate intrinsic value of options is calculated as the difference between the exercise price of the stock options and the fair value of the Company’s common stock for those stock options that had exercise prices lower than the fair value of the common stock as of the end of the period. The weighted-average grant date fair value of stock options granted during the six months ended June 30, 2023 and 2022 was $ 5.16 per share and $ 6.33 per share, respectively. At June 30, 2023 , there was $ 50.1 million of unrecognized stock-based compensation expense related to unvested stock options, which is being recognized over a period of 2.24 years. The fair value was estimated on the date of grant using the Black-Scholes option-pricing model, with the following weighted-average assumptions: Three Months Ended Six Months Ended Expected term (in years) 6.09 6.11 Expected volatility 93.95 % 94.49 % Risk-free interest rate 3.61 % 3.46 % Expected dividend yield — — Fair value of common stock $ 3.76 $ 6.60 2020 Employee Stock Purchase Plan The Company issued 108,936 shares of common stock under the 2020 Employee Stock Purchase Plan (the “ESPP”) during the six months ended June 30, 2023 at an average price per share of $ 2.89 . Cash received from purchases under the ESPP for the six months ended June 30, 2023 and 2022 were $ 0.3 million and $ 0.2 million, respectively. The Company recognized $ 0.1 million and $ 0.1 million of compensation expense for the ESPP during the three months ended June 30, 2023 and 2022 , respectively, and $ 0.3 million and $ 0.1 million of compensation expense for the ESPP during the six months ended June 30, 2023 and 2022, respectively. At June 30, 2023 , there was an aggregate of 505,366 shares reserved for future issuance under the ESPP.

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2023
Income Tax Disclosure [Abstract]
Income Taxes	9. Income Taxes The Company’s income tax provision is computed based on the federal statutory rate, the average state statutory rates, net of the related federal benefit, and foreign statutory rates. For the three and six months ended June 30, 2023 and 2022, the Company recorded income tax expense of $ 0 and $ 0.2 million, respectively. The Company’s estimate of the realizability of the deferred tax asset is dependent on estimates of projected future levels of taxable income. In consideration of historical losses and in analyzing future taxable income levels, the Company considered all evidence currently available, both positive and negative, and has not recognized deferred tax assets.

Net Loss per Share

Net Loss per Share	6 Months Ended
	Jun. 30, 2023
Earnings Per Share [Abstract]
Net Loss per Share	10. Net Loss per Share The following table summarizes the computation of basic and diluted net loss per share attributable to common stockholders of the Company: Three Months Ended Six Months Ended (in thousands, except share and per share data) 2023 2022 2023 2022 Numerator: Net loss – basic and diluted $ ( 45,267 ) $ ( 44,639 ) $ ( 86,450 ) $ ( 88,502 ) Denominator: Weighted-average common shares outstanding – basic and diluted 94,625,837 64,467,483 93,968,407 64,231,579 Net loss per share – basic and diluted $ ( 0.48 ) $ ( 0.69 ) $ ( 0.92 ) $ ( 1.38 ) Based on the amounts outstanding at June 30, 2023 and 2022, the Company excluded the following potential shares of common stock from the computation of diluted net loss per share attributable to common stockholders for the three and six months ended June 30, 2023 and 2022, because including them would have had an anti-dilutive effect. Therefore, the weighted-average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. June 30, 2023 2022 Options to purchase common stock 10,304,403 7,933,192 Unvested restricted stock 3,503,459 2,494,263

Related Party Transactions

Related Party Transactions	6 Months Ended
	Jun. 30, 2023
Related Party Transactions [Abstract]
Related Party Transactions	11. Related Party Transactions In March 2020, the Company entered into a Management and Administrative Services Agreement with ElevateBio Technologies, Inc. that provides for ongoing services to the Company in areas such as information technology, human resources and administration management, and facilities. The Company is billed monthly for such services at cost, with mark-up for profit on specific services, but including reasonable allocations of employee benefits, facilities and other direct or fairly allocated indirect costs that relate to the associates providing the services. The agreement has an initial term of five years and will automatically renew for successive one year terms, unless earlier terminated under the terms of the agreement. In May 2020, the Company entered into a Development and Manufacturing Services Agreement with ElevateBio BaseCamp, Inc. ("BaseCamp") pursuant to which BaseCamp provides products and services that are used in the Company's laboratory operations, including consulting services, project management services, quality control services and cGMP drug product manufacturing. The agreement will expire upon the later of (a) five years from the effective date of January 1, 2019 or (b) the completion of services under all work orders executed prior to the fifth anniversary of the effective date, unless earlier terminated under the terms of the agreement. In August 2022, the Company made a $ 2.0 million prepayment to BaseCamp for future services. The Company incurred $ 0.5 million and $ 0.8 million during the three months ended June 30, 2023 and 2022 , respectively, and $ 0.7 million and $ 2.0 million during the six months ended June 30, 2023 and 2022, respectively, related to services provided to the Company by ElevateBio and affiliates. At June 30, 2023 and December 31, 2022 , the Company owed ElevateBio and affiliates $ 0 and $ 0.1 million, respectively and had prepaid expenses with ElevateBio and affiliates of $ 1.5 million and $ 2.0 million, respectively. In March 2023, the Company entered into a services agreement with Marker Therapeutics, Inc. (“Marker”) pursuant to which Marker provides development services to the Company. Juan Vera, a current director and former executive officer of the Company, is co-founder, director and chief executive officer of Marker. The Company incurred $ 0.1 million during the three and six months ended June 30, 2023 under the agreement. At June 30, 2023 and December 31, 2022 , the Company owed Marker $ 0.1 million and $ 0 , respectively. Members of the Company’s management and board of directors received consulting fees totaling $ 0.1 million and $ 0.1 million during the three months ended June 30, 2023 and 2022 , respectively, and $ 0.2 million and $ 0.3 million during the six months ended June 30, 2023 and 2022 , respectively.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2023
Accounting Policies [Abstract]
Interim Financial Information	Interim Financial Information The accompanying condensed consolidated balance sheet at June 30, 2023, and the condensed consolidated statements of operations and comprehensive loss, statements of changes in stockholders’ equity for the three and six months ended June 30, 2023 and 2022 and the condensed consolidated statements of cash flows for the six months ended June 30, 2023 and 2022 are unaudited. The condensed consolidated interim financial statements have been prepared on the same basis as the audited annual financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments necessary for the fair presentation of the Company’s financial position at June 30, 2023 and the results of its operations for the three and six months ended June 30, 2023 and 2022 and its cash flows for the six months ended June 30, 2023 and 2022. The financial data and other information disclosed in these notes related to the three and six months ended June 30, 2023 and 2022 are also unaudited. The results for the three and six months ended June 30, 2023 are not necessarily indicative of results to be expected for the year ending December 31, 2023 or for any other subsequent interim period.
Recent Accounting Pronouncements	Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (“FASB”), or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the impact of recently issued standards that are not yet effective will not have a material impact on the Company’s consolidated financial statements upon adoption. Under the Jumpstart Our Business Startups Act of 2012, as amended (the “JOBS Act”), the Company meets the definition of an emerging growth company and has elected the extended transition period for complying with certain new or revised accounting standards pursuant to Section 107(b) of the JOBS Act. Since December 31, 2022 , there have been no new accounting pronouncements adopted by the Company or issued by FASB that are applicable to the Company, except as noted below.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments , or ASU 2016-13, which requires the measurement and recognition of expected credit losses for financial assets held at amortized cost. ASU 2016-13 replaces the existing incurred loss impairment model with an expected loss model. It also eliminates the concept of other-than-temporary impairment and requires credit losses related to available-for-sale debt securities to be recorded through an allowance for credit losses rather than as a reduction in the amortized cost basis of the securities. These changes may result in earlier recognition of credit losses. The Company adopted ASU 2016-13 on January 1, 2023 . The adoption of ASU 2016-13 did not have a material impact on the Company’s condensed consolidated financial statements.
Recently Issued Accounting Pronouncements Not Yet Adopted	Recently Issued Accounting Pronouncements Not Yet Adopted None.

Short-Term Investments (Tables)

Short-Term Investments (Tables)	6 Months Ended
	Jun. 30, 2023
Investments, Debt and Equity Securities [Abstract]
Summary of Amortized Cost and Estimated Fair Value of Marketable Securities	The following tables summarize the amortized cost and estimated fair value of the Company’s U.S. government treasury securities and marketable securities, which are considered to be available-for-sale investments and are included in short-term investments on the condensed consolidated balance sheets: June 30, 2023 (in thousands) Amortized Unrealized Unrealized Fair U.S. government treasury securities $ 42,172 $ — $ ( 70 ) $ 42,102 Marketable securities: Corporate and agency bonds 7,500 — ( 20 ) 7,480 Totals $ 49,672 $ — $ ( 90 ) $ 49,582 December 31, 2022 (in thousands) Amortized Unrealized Unrealized Fair U.S. government treasury securities $ 99,288 $ 1 $ ( 253 ) $ 99,036 Marketable securities: Corporate and agency bonds 28,748 3 ( 84 ) $ 28,667 Totals $ 128,036 $ 4 $ ( 337 ) $ 127,703

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jun. 30, 2023
Fair Value Disclosures [Abstract]
Summary of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis	The following tables present information about the Company’s financial assets and liabilities measured at fair value on a recurring basis: June 30, 2023 (in thousands) Level 1 Level 2 Level 3 Total Cash equivalents: Money market fund $ 111,015 $ — $ — $ 111,015 Totals $ 111,015 $ — $ — $ 111,015 Short-term investments: U.S. government treasury securities $ 42,102 $ — $ — $ 42,102 Marketable securities: Corporate and agency bonds — 7,480 — 7,480 Totals $ 42,102 $ 7,480 $ — $ 49,582 December 31, 2022 (in thousands) Level 1 Level 2 Level 3 Total Cash equivalents: Money market fund $ 32,641 $ — $ — $ 32,641 Totals $ 32,641 $ — $ — $ 32,641 Short-term investments: U.S. government treasury securities $ 99,036 $ — $ — $ 99,036 Marketable securities: Corporate and agency bonds — 28,667 — $ 28,667 Totals $ 99,036 $ 28,667 $ — $ 127,703

Leases (Tables)

Leases (Tables)	6 Months Ended
	Jun. 30, 2023
Leases [Abstract]
Summary of Maturities Operating Leases Liabilities	Maturities of operating lease liabilities at June 30, 2023 are as follows (in thousands): 2023 (remaining 6 months) 5,110 2024 11,533 2025 3,229 2026 3,308 2027 3,386 Thereafter 9,681 Total lease payments 36,247 Less: interest ( 4,748 ) Total lease liability $ 31,499 Lease liability – current $ 8,483 Lease liability – long-term $ 23,016

Accrued Expenses (Tables)

Accrued Expenses (Tables)	6 Months Ended
	Jun. 30, 2023
Payables and Accruals [Abstract]
Schedule of Accrued Expenses	Accrued expenses consisted of the following: (in thousands) June 30, December 31, Employee compensation and benefits $ 3,574 $ 6,416 Professional fees 960 559 Research and development 7,288 5,678 Process development and manufacturing costs 4,603 504 Other 303 828 Total accrued expenses $ 16,728 $ 13,985

Stockholder's Equity (Tables)

Stockholder's Equity (Tables)	6 Months Ended
	Jun. 30, 2023
Equity [Abstract]
Schedule of Reserved Shares of Common Stock for Issuance	The Company has reserved shares of common stock for issuance as follows: June 30, December 31, Options to purchase common stock 10,304,403 7,922,797 Unvested restricted stock 3,503,459 2,239,106 Stock available for grant under the 2020 Stock Option and Grant Plan 4,476,879 4,253,680 Stock available for issuance under the 2020 Employee Stock Purchase Plan 505,366 454,302 Total 18,790,107 14,869,885

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	6 Months Ended
	Jun. 30, 2023
Share-Based Payment Arrangement [Abstract]
Schedule of Stock-based Compensation Expense	Stock-based compensation expense was as follows: Three Months Ended Six Months Ended (in thousands) 2023 2022 2023 2022 Research and development $ 3,514 $ 3,892 $ 6,937 $ 7,232 General and administrative 6,774 7,059 13,380 14,186 Total stock-based compensation expense $ 10,288 $ 10,951 $ 20,317 $ 21,418
Summary of Restricted Common Stock Activity	The following table summarizes restricted common stock activity for the six months ended June 30, 2023: Shares Weighted Unvested at January 1, 2023 2,239,106 $ 13.75 Granted 2,074,444 6.31 Forfeited ( 296,252 ) 11.78 Vested ( 513,839 ) 12.67 Unvested at June 30, 2023 3,503,459 $ 9.67
Summary of Stock Option Activity	The following table summarizes stock option activity (in thousands, except share and per share data): Shares Weighted Weighted Aggregate Options outstanding at January 1, 2023 7,922,797 $ 17.81 8.30 $ 786 Granted 3,400,892 6.60 — — Exercised — — — — Forfeited ( 1,019,286 ) 15.83 — — Options outstanding at June 30, 2023 10,304,403 $ 14.31 8.39 $ 19 Options vested and exercisable at June 30, 2023 3,751,655 $ 19.66 7.60 $ 19
Schedule of Estimated Fair Value Weighted-Average Assumptions Using Black-Scholes Option-Pricing Model	The fair value was estimated on the date of grant using the Black-Scholes option-pricing model, with the following weighted-average assumptions: Three Months Ended Six Months Ended Expected term (in years) 6.09 6.11 Expected volatility 93.95 % 94.49 % Risk-free interest rate 3.61 % 3.46 % Expected dividend yield — — Fair value of common stock $ 3.76 $ 6.60

Net Loss per Share (Tables)

Net Loss per Share (Tables)	6 Months Ended
	Jun. 30, 2023
Earnings Per Share [Abstract]
Computation Of Basic And Diluted Net Loss Per Share Attributable To Common Stockholders	The following table summarizes the computation of basic and diluted net loss per share attributable to common stockholders of the Company: Three Months Ended Six Months Ended (in thousands, except share and per share data) 2023 2022 2023 2022 Numerator: Net loss – basic and diluted $ ( 45,267 ) $ ( 44,639 ) $ ( 86,450 ) $ ( 88,502 ) Denominator: Weighted-average common shares outstanding – basic and diluted 94,625,837 64,467,483 93,968,407 64,231,579 Net loss per share – basic and diluted $ ( 0.48 ) $ ( 0.69 ) $ ( 0.92 ) $ ( 1.38 )
Potential Dilutive Securities Excluded From Computation Of Diluted Net Loss Per Share Attributable To Common Stockholders	Based on the amounts outstanding at June 30, 2023 and 2022, the Company excluded the following potential shares of common stock from the computation of diluted net loss per share attributable to common stockholders for the three and six months ended June 30, 2023 and 2022, because including them would have had an anti-dilutive effect. Therefore, the weighted-average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. June 30, 2023 2022 Options to purchase common stock 10,304,403 7,933,192 Unvested restricted stock 3,503,459 2,494,263

Nature of the Business - Additi

Nature of the Business - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Net losses attributable to common stockholders	$ (45,267)	$ (41,183)	$ (44,639)	$ (43,863)	$ (86,450)	$ (88,502)
Accumulated deficit	(552,225)				(552,225)		$ (465,775)
Cash, cash equivalents and short-term investments	$ 246,500				$ 246,500

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Details) - ASU 2016-13	Jan. 01, 2023
Summary Of Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]	true
Change in Accounting Principle, Accounting Standards Update, Early Adoption [true false]	false
Change in Accounting Principle, Accounting Standards Update, Adoption Date	Jan. 01, 2023
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]	true

Short-Term Investments - Summar

Short-Term Investments - Summary of Amortized Cost and Estimated Fair Value of Marketable Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 49,672	$ 128,036
Unrealized Gains		4
Unrealized Losses	(90)	(337)
Fair Value	49,582	127,703
U.S. Government Treasury Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	42,172	99,288
Unrealized Gains		1
Unrealized Losses	(70)	(253)
Fair Value	42,102	99,036
Corporate and Agency Bonds
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	7,500	28,748
Unrealized Gains		3
Unrealized Losses	(20)	(84)
Fair Value	$ 7,480	$ 28,667

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Assets and Liabilities Measured at Fair Value On Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Cash equivalents:
Cash equivalents	$ 111,015	$ 32,641
Short-term investments:
Short-term investments	49,582	127,703
Money Market Fund
Cash equivalents:
Cash equivalents	111,015	32,641
U.S. Government Treasury Securities
Short-term investments:
Short-term investments	42,102	99,036
Corporate and Agency Bonds
Short-term investments:
Short-term investments	7,480	28,667
Level 1
Cash equivalents:
Cash equivalents	111,015	32,641
Short-term investments:
Short-term investments	42,102	99,036
Level 1 | Money Market Fund
Cash equivalents:
Cash equivalents	111,015	32,641
Level 1 | U.S. Government Treasury Securities
Short-term investments:
Short-term investments	42,102	99,036
Level 2
Short-term investments:
Short-term investments	7,480	28,667
Level 2 | Corporate and Agency Bonds
Short-term investments:
Short-term investments	$ 7,480	$ 28,667

Leases - Additional Information

Leases - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended		6 Months Ended
	Oct. 31, 2022	Sep. 30, 2021	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022
Leases [Line Items]
ROU asset			$ 27,485		$ 27,485		$ 31,633
Lease liability			31,499		31,499
Operating lease costs			2,600	$ 1,300	5,100	$ 2,800
Cash paid for operating lease			2,800	900	4,900	2,100
Variable lease costs			$ 500	$ 900	$ 600	$ 2,200
Operating lease, weighted average remaining lease term			6 years 6 months 18 days		6 years 6 months 18 days		6 years 11 months 4 days
Operating lease, weighted average discount rate, percent			6.10%		6.10%		6.23%
Waltham Leases
Leases [Line Items]
Expiration date		Jul. 30, 2030
Operating lease, existence of option to extend		true
Lease, option to extend					The Company has the option to renew the leased space for an additional one time period of five years with written notice from the Company. At June 30, 2023, the Company has no reasonable certainty that this option to extend will be exercised.
Tenant improvement allowance to be reimbursed		$ 3,100
Tenant improvement allowance, reimbursement period		2 years
Tenant improvement allowance			$ 900		$ 900
Lease commencement month and year		2021-09
Additional one time lease period		5 years
New Lease Agreement with BP Bay Colony LLC
Leases [Line Items]
ROU asset		$ 6,000
Lease liability		6,000
Sublease with AMAG Pharmaceuticals
Leases [Line Items]
ROU asset		17,300
Lease liability		$ 17,300
2022 SOW Under the DMS Agreement
Leases [Line Items]
Lease expiration month and year	2024-12
ROU asset	$ 14,700
Lease liability	14,700
Utilization fee	$ 16,300
Lessee operating lease, lease term including renewal option	2 years 3 months

Leases - Summary of Operating L

Leases - Summary of Operating Lease Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Leases [Abstract]
2023 (remaining 6 months)	$ 5,110
2024	11,533
2025	3,229
2026	3,308
2027	3,386
Thereafter	9,681
Total lease payments	36,247
Less: interest	(4,748)
Total lease liability	31,499
Lease liability - current	8,483	$ 7,165
Lease liability - long-term	$ 23,016	$ 28,222

Accrued Expenses - Schedule of

Accrued Expenses - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Payables and Accruals [Abstract]
Employee compensation and benefits	$ 3,574	$ 6,416
Professional fees	960	559
Research and development	7,288	5,678
Process development and manufacturing costs	4,603	504
Other	303	828
Total accrued expenses	$ 16,728	$ 13,985

Stockholders Equity - Additiona

Stockholders Equity - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	Jun. 21, 2023	Jun. 30, 2023	May 15, 2023	Dec. 31, 2022
Class Of Stock [Line Items]
Preferred stock, par or stated value per share		$ 0.0001	$ 0.0001	$ 0.0001
Preferred stock, shares authorized		10,000,000	10,000,000	10,000,000
Preferred stock, shares issued		0		0
Preferred stock, shares outstanding		0		0
Common stock, shares authorized		300,000,000	300,000,000	150,000,000
Common stock, par value		$ 0.0001	$ 0.0001	$ 0.0001
Underwriter | J.P. Morgan Securities LLC [Member]
Class Of Stock [Line Items]
Stock issued	20,000,000
Offering price per share	$ 3.75
Proceeds from issuance of common stock	$ 70.2
Underwriting discounts commissions	4.5
Offering costs	$ 0.3
Option to purchase additional number of shares	3,000,000
Expiration of option to purchase additional number of shares	Jul. 21, 2023

Stockholders Equity - Schedule

Stockholders Equity - Schedule of Reserved Shares of Common Stock for Issuance (Details) - shares	Jun. 30, 2023	Dec. 31, 2022
Class Of Stock [Line Items]
Reserved shares of common stock for issuance	18,790,107	14,869,885
2020 Employee Stock Purchase Plan
Class Of Stock [Line Items]
Reserved shares of common stock for issuance	505,366
Option To Purchase Common Stock
Class Of Stock [Line Items]
Reserved shares of common stock for issuance	10,304,403	7,922,797
Unvested Restricted Stock
Class Of Stock [Line Items]
Reserved shares of common stock for issuance	3,503,459	2,239,106
Stock Available For Grant | 2020 Stock Option and Grant Plan
Class Of Stock [Line Items]
Reserved shares of common stock for issuance	4,476,879	4,253,680
Stock Available For Issuance | 2020 Employee Stock Purchase Plan
Class Of Stock [Line Items]
Reserved shares of common stock for issuance	505,366	454,302

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 10,288	$ 10,951	$ 20,317	$ 21,418
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	3,514	3,892	6,937	7,232
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 6,774	$ 7,059	$ 13,380	$ 14,186

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Reserved shares of common stock for issuance	18,790,107		18,790,107		14,869,885
Stock-based compensation expense	$ 10,288	$ 10,951	$ 20,317	$ 21,418
Restricted Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares granted			2,074,444
Unrecognized stock-based compensation cost	30,300		$ 30,300
Weighted average period of cost expected to be recognized			2 years 6 months 25 days
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted average period of cost expected to be recognized			2 years 2 months 26 days
Weighted average grant-date fair value of stock options granted			$ 5.16	$ 6.33
Unrecognized stock-based compensation expenses	$ 50,100		$ 50,100
2018 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares of common stock issuable upon exercise of outstanding options	64,042		64,042
Reserved shares of common stock for issuance	0		0
2018 Equity Incentive Plan | Restricted Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares granted			6,616,772
2020 Stock Option and Grant Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock issuable upon exercise of outstanding options			10,240,361
2020 Stock Option and Grant Plan | Restricted Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares granted			5,150,960
2020 Stock Option and Grant Plan | Stock Available For Grant
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Reserved shares of common stock for issuance	4,476,879		4,476,879		4,253,680
2020 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Reserved shares of common stock for issuance	505,366		505,366
Purchase of common stock under the employee stock purchase plan			108,936
Share issued, average price per share	$ 2.89		$ 2.89
Cash received from purchases under the ESPP			$ 300	$ 200
Stock-based compensation expense	$ 100	$ 100	$ 300	$ 100

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Restricted Common Stock Activity (Details) - Restricted Common Stock	6 Months Ended
	Jun. 30, 2023 $ / shares shares
Number of Shares
Number of Shares, Unvested at January 1, 2023 | shares	2,239,106
Number of Shares, Granted | shares	2,074,444
Number of Shares, Forfeited | shares	(296,252)
Number of Shares, Vested | shares	(513,839)
Number of Shares, Unvested at June 30, 2023 | shares	3,503,459
Weighted Average Grant Date Fair Value
Weighted Average Grant Date Fair Value, Unvested at January 1, 2023 | $ / shares	$ 13.75
Weighted Average Grant Date Fair Value, Granted | $ / shares	6.31
Weighted Average Grant Date Fair Value, Forfeited | $ / shares	11.78
Weighted Average Grant Date Fair Value, Vested | $ / shares	12.67
Weighted Average Grant Date Fair Value, Unvested at June 30, 2023 | $ / shares	$ 9.67

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2023	Dec. 31, 2022
Share-Based Payment Arrangement [Abstract]
Number of Options Outstanding, Beginning Balance	7,922,797
Number of Options, Granted	3,400,892
Number of Options, Forfeited	(1,019,286)
Number of Options Outstanding, Ending Balance	10,304,403	7,922,797
Options vested and exercisable at June 30, 2023	3,751,655
Weighted Average Exercise Price, Options outstanding as of January 1, 2023	$ 17.81
Weighted Average Exercise Price, Granted	6.60
Weighted Average Exercise Price, Forfeited	15.83
Weighted Average Exercise Price, Options outstanding at June 30, 2023	14.31	$ 17.81
Weighted Average Exercise Price, Options vested and exercisable at June 30, 2023	$ 19.66
Weighted Average Contractual Life (in years), Options outstanding	8 years 4 months 20 days	8 years 3 months 18 days
Weighted Average Contractual Life (in years), Options vested and exercisable at June 30, 2023	7 years 7 months 6 days
Aggregate Intrinsic Value, Options outstanding at January 1, 2023	$ 786
Aggregate Intrinsic Value, Options outstanding at June 30, 2023	19	$ 786
Aggregate Intrinsic Value, Options vested and exercisable at June 30, 2023	$ 19

Stock-Based Compensation - Sc_2

Stock-Based Compensation - Schedule of Estimated Fair Value Weighted-Average Assumptions Using Black-Scholes Option-Pricing Model (Details) - $ / shares	3 Months Ended	6 Months Ended
	Jun. 30, 2023	Jun. 30, 2023
Share-Based Payment Arrangement [Abstract]
Expected term (in years)	6 years 1 month 2 days	6 years 1 month 9 days
Expected volatility	93.95%	94.49%
Risk-free interest rate	3.61%	3.46%
Expected dividend yield	0%	0%
Fair value of common stock	$ 3.76	$ 6.60

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Income Tax Disclosure [Abstract]
Income tax expense	$ 0	$ 150	$ 0	$ 150

Net Loss per Share - Computatio

Net Loss per Share - Computation Of Basic And Diluted Net Loss Per Share Attributable To Common Stockholders (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Numerator:
Net loss - basic and diluted	$ (45,267)	$ (44,639)	$ (86,450)	$ (88,502)
Denominator:
Weighted-average common shares outstanding - basic	94,625,837	64,467,483	93,968,407	64,231,579
Weighted-average common shares outstanding - diluted	94,625,837	64,467,483	93,968,407	64,231,579
Net loss per share - basic	$ (0.48)	$ (0.69)	$ (0.92)	$ (1.38)
Net loss per share - diluted	$ (0.48)	$ (0.69)	$ (0.92)	$ (1.38)

Net Loss per Share - Potential

Net Loss per Share - Potential Dilutive Securities Excluded From Computation Of Diluted Net Loss Per Share Attributable To Common Stockholders (Details) - shares	6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022
Options To Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	10,304,403	7,933,192
Unvested Restricted Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	3,503,459	2,494,263

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022	Aug. 31, 2022
Related Party Transaction [Line Items]
Amount due to related party	$ 61		$ 61		$ 56
Consulting fees to members of management and board of directors	100	$ 100	$ 200	$ 300
ElevateBio Technologies, Inc | Management and Administrative Services Agreement
Related Party Transaction [Line Items]
Lease expiration term			The agreement has an initial term of five years and will automatically renew for successive one year terms, unless earlier terminated under the terms of the agreement.
BaseCamp
Related Party Transaction [Line Items]
Prepaid expenses						$ 2,000
BaseCamp | DMS Agreement
Related Party Transaction [Line Items]
Lease expiration term			The agreement will expire upon the later of (a) five years from the effective date of January 1, 2019 or (b) the completion of services under all work orders executed prior to the fifth anniversary of the effective date, unless earlier terminated under the terms of the agreement.
ElevateBio and Affiliates
Related Party Transaction [Line Items]
Prepaid expenses	1,500		$ 1,500		2,000
Expenses related to services with related party	500	$ 800	700	$ 2,000
Amount due to related party	0		0		100
Marker Therapeutics, Inc.
Related Party Transaction [Line Items]
Amount due to related party	100		100		$ 0
Costs incurred under agreement	$ 100		$ 100