0000950170-21-003160 | 10-Q | XBRL Viewer

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Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2021	Oct. 29, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
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		65,140,831
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	139 Main Street
Entity Address, Address Line Two	Suite 500
Entity Address City Or Town	Cambridge
Entity Address State Or Province	MA
Entity Address Postal Zip Code	02142
City Area Code	617
Local Phone Number	433-2605
Document Quarterly Report	true
Document Transition Report	false

CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED) - USD ($)	Sep. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 243,187,000	$ 122,661,000
Short-term investments	32,654,000	233,663,000
Accrued interest	151,000	450,000
Prepaid expenses and other current assets	5,880,000	4,543,000
Total current assets	281,872,000	361,317,000
Restricted cash	852,000
Other assets	1,206,000
Property and equipment, net	1,113,000	812,000
Operating lease right-of-use assets	31,487,000	8,692,000
Total assets	316,530,000	370,821,000
Current liabilities:
Accounts payable	133,000	963,000
Accrued expenses	15,798,000	7,530,000
Operating lease liability, current	6,297,000	3,229,000
Amount due to related party	1,945,000	572,000
Total current liabilities	24,173,000	12,294,000
Operating lease liability, long term	25,053,000	5,463,000
Total liabilities	49,226,000	17,757,000
Stockholders’ equity:
Preferred stock, $0.0001 par value: 10,000,000 shares authorized at June 30, 2021 and December 31, 2020, respectively; 0 shares issued and outstanding at June 30, 2021 and December 31, 2020, respectively
Common stock, $0.0001 par value: 150,000,000 shares authorized at September 30, 2021 and December 31, 2020, respectively; 65,142,679 and 65,106,873 shares issued at September 30, 2021 and December 31, 2020, respectively; and 63,177,928 and 61,931,255 shares outstanding at September 30, 2021 and December 31, 2020, respectively	7,000	7,000
Additional paid-in capital	506,554,000	478,272,000
Accumulated other comprehensive loss	(133,000)	(112,000)
Accumulated deficit	(239,124,000)	(125,103,000)
Total stockholders’ equity	267,304,000	353,064,000
Total liabilities and stockholders’ equity	$ 316,530,000	$ 370,821,000

CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED) (Parenthetical) - $ / shares	Sep. 30, 2021	Dec. 31, 2020
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	150,000,000	150,000,000
Common stock, shares issued	65,142,679	65,106,873
Common stock, shares outstanding	63,177,928	61,931,255

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Operating expenses:
Research and development	$ 33,062	$ 17,182	$ 79,132	$ 32,906
General and administrative	12,442	6,718	34,890	12,987
Total operating expenses	45,504	23,900	114,022	45,893
Loss from operations	(45,504)	(23,900)	(114,022)	(45,893)
Total other income (loss), net:
Interest income	253	112	1,233	735
Other (loss) income, net	(259)	174	(1,232)	573
Net loss	$ (45,510)	$ (23,614)	$ (114,021)	$ (44,585)
Net loss per share — basic and diluted	$ (0.72)	$ (0.58)	$ (1.82)	$ (2.93)
Weighted-average common shares outstanding — basic and diluted	62,962,434	40,465,705	62,588,898	15,195,000
Comprehensive loss:
Net loss	$ (45,510)	$ (23,614)	$ (114,021)	$ (44,585)
Other comprehensive (loss) income, net of tax:
Unrealized (loss) gain on available-for-sale securities	(3)	(125)	23	(83)
Foreign currency translation adjustment	(105)	(26)	(44)	(26)
Total other comprehensive (loss)	(108)	(151)	(21)	(109)
Comprehensive loss	$ (45,618)	$ (23,765)	$ (114,042)	$ (44,694)

CONDENSED CONSOLIDATED STATEMENTS OF CONVERTIBLE PREFERRED STOCK AND CHANGES IN STOCKHOLDERS' EQUITY (DEFICIT) (UNAUDITED) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Series B Preferred Stock	Series A Preferred Stock
Balance at Dec. 31, 2019	$ (51,503)		$ 3,748	$ 68	$ (55,319)
Temporary equity, Balance, Shares at Dec. 31, 2019						14,877,697	44,520,653
Temporary equity, Balance at Dec. 31, 2019						$ 120,923	$ 52,204
Balance, Shares at Dec. 31, 2019		2,099,740
Issuance of common stock, upon vesting of restricted stock, Shares		292,644
Unrealized (loss) gain on available-for-sale securities	176			176
Stock-based compensation	646		646
Net loss	(9,339)				(9,339)
Balance at Mar. 31, 2020	(60,020)		4,394	244	(64,658)
Temporary equity, Balance, Shares at Mar. 31, 2020						14,877,697	44,520,653
Temporary equity, Balance at Mar. 31, 2020						$ 120,923	$ 52,204
Balance, Shares at Mar. 31, 2020		2,392,384
Balance at Dec. 31, 2019	(51,503)		3,748	68	(55,319)
Temporary equity, Balance, Shares at Dec. 31, 2019						14,877,697	44,520,653
Temporary equity, Balance at Dec. 31, 2019						$ 120,923	$ 52,204
Balance, Shares at Dec. 31, 2019		2,099,740
Unrealized (loss) gain on available-for-sale securities	(83)
Unrealized loss on foreign currency translation adjustment	(26)
Net loss	(44,585)
Balance at Sep. 30, 2020	373,903	$ 7	473,841	(41)	(99,904)
Balance, Shares at Sep. 30, 2020		61,659,533
Balance at Mar. 31, 2020	(60,020)		4,394	244	(64,658)
Temporary equity, Balance, Shares at Mar. 31, 2020						14,877,697	44,520,653
Temporary equity, Balance at Mar. 31, 2020						$ 120,923	$ 52,204
Balance, Shares at Mar. 31, 2020		2,392,384
Issuance of common stock, upon vesting of restricted stock, Shares		409,475
Unrealized (loss) gain on available-for-sale securities	(134)			(134)
Stock-based compensation	492		492
Net loss	(11,632)				(11,632)
Balance at Jun. 30, 2020	(71,294)		4,886	110	(76,290)
Temporary equity, Balance, Shares at Jun. 30, 2020						14,877,697	44,520,653
Temporary equity, Balance at Jun. 30, 2020						$ 120,923	$ 52,204
Balance, Shares at Jun. 30, 2020		2,801,859
Issuance of common stock, upon vesting of restricted stock, Shares		311,035
Initial public offering, net of underwriting discounts, commissions and offering costs	291,975	$ 2	291,973
Initial public offering, net of underwriting discounts, commissions and offering costs, Shares		18,687,500
Conversion of convertible preferred stock into common stock upon initial public offering	173,127	$ 5	173,122
Conversion of convertible preferred stock into common stock upon initial public offering, Shares		39,859,139
Temporary equity conversion of convertible preferred stock into common stock upon initial public offering						$ (120,923)	$ (52,204)
Temporary equity conversion of convertible preferred stock into common stock upon initial public offering, Shares						(14,877,697)	(44,520,653)
Unrealized (loss) gain on available-for-sale securities	(125)			(125)
Unrealized loss on foreign currency translation adjustment	(26)			(26)
Stock-based compensation	3,860		3,860
Net loss	(23,614)				(23,614)
Balance at Sep. 30, 2020	373,903	$ 7	473,841	(41)	(99,904)
Balance, Shares at Sep. 30, 2020		61,659,533
Balance at Dec. 31, 2020	353,064	$ 7	478,272	(112)	(125,103)
Balance, Shares at Dec. 31, 2020		61,931,255
Issuance of common stock, upon vesting of restricted stock, Shares		519,839
Unrealized (loss) gain on available-for-sale securities	42			42
Unrealized loss on foreign currency translation adjustment	83			83
Stock-based compensation	8,103		8,103
Net loss	(30,923)				(30,923)
Balance at Mar. 31, 2021	330,369	$ 7	486,375	13	(156,026)
Balance, Shares at Mar. 31, 2021		62,451,094
Balance at Dec. 31, 2020	$ 353,064	$ 7	478,272	(112)	(125,103)
Balance, Shares at Dec. 31, 2020		61,931,255
Issuance of common stock, upon exercise of stock options, Shares	9,425
Unrealized (loss) gain on available-for-sale securities	$ 23
Unrealized loss on foreign currency translation adjustment	(44)
Net loss	(114,021)
Balance at Sep. 30, 2021	267,304	$ 7	506,554	(133)	(239,124)
Balance, Shares at Sep. 30, 2021		63,177,928
Balance at Mar. 31, 2021	330,369	$ 7	486,375	13	(156,026)
Balance, Shares at Mar. 31, 2021		62,451,094
Issuance of common stock, upon vesting of restricted stock, Shares		340,949
Unrealized (loss) gain on available-for-sale securities	(16)			(16)
Unrealized loss on foreign currency translation adjustment	(22)			(22)
Stock-based compensation	9,726		9,726
Net loss	(37,588)				(37,588)
Balance at Jun. 30, 2021	302,469	$ 7	496,101	(25)	(193,614)
Balance, Shares at Jun. 30, 2021		62,792,043
Issuance of common stock, upon vesting of restricted stock, Shares		376,460
Issuance of common stock, upon exercise of stock options	167		167
Issuance of common stock, upon exercise of stock options, Shares		9,425
Unrealized (loss) gain on available-for-sale securities	(3)			(3)
Unrealized loss on foreign currency translation adjustment	(105)			(105)
Stock-based compensation	10,286		10,286
Net loss	(45,510)				(45,510)
Balance at Sep. 30, 2021	$ 267,304	$ 7	$ 506,554	$ (133)	$ (239,124)
Balance, Shares at Sep. 30, 2021		63,177,928

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash flows from operating activities
Net loss	$ (114,021)	$ (44,585)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	95	55
Non-cash lease expense	468
Amortization and accretion of discounts on short-term investments	1,130	92
Stock compensation expense	28,115	4,998
Changes in operating assets and liabilities:
Unbilled grant receivables		129
Accrued interest	299	(160)
Prepaid expenses and other current assets	(1,943)	(4,542)
Other assets	(1,206)
Accounts payable, accrued expenses and amount due to related party	8,812	4,295
Net cash used in operating activities	(78,251)	(39,718)
Cash flows from investing activities
Purchase of property and equipment	(396)
Purchase of short-term investments	(30,098)	(242,419)
Maturities of short-term investments	230,000	71,000
Net cash provided by (used in) investing activities	199,506	(171,419)
Cash flows from financing activities
Payment of initial public offering costs		(3,120)
Proceeds from issuance of common stock upon initial public offering, net of underwriting discounts of $22,238		295,449
Proceeds from exercise of stock options	167
Net cash provided by financing activities	167	292,329
Effect of exchange rate changes on cash, cash equivalents, and restricted cash	(44)	(26)
Net increase in cash, cash equivalents, and restricted cash	121,378	81,166
Cash, cash equivalents, and restricted cash at beginning of period	122,661	61,084
Cash, cash equivalents, and restricted cash at end of period	244,039	142,250
Non-cash investing and financing activities
Unrealized gain on available-for-sale securities	23	(83)
Right-of-use assets obtained in exchange for operating lease liability	26,386
Deferred offering costs included in accounts payable and accrued expenses		356
Conversion of preferred stock to common stock upon initial public offering		173,127
Cash and cash equivalents	243,187	142,250
Restricted cash	852
Total cash, cash equivalents, and restricted cash	$ 244,039	$ 142,250

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) (UNAUDITED) $ in Thousands	9 Months Ended
	Sep. 30, 2020 USD ($)
Statement Of Cash Flows [Abstract]
Underwriting discounts, amount	$ 22,238

Nature of the Business

9 Months Ended

Sep. 30, 2021

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. To date, the Company has generated five innovative, allogeneic, off-the-shelf VST therapy candidates targeting 13 different devastating viruses. The most advanced is posoleucel (previously referred to as Viralym-M or ALVR105), for which the Company has an ongoing pivotal trial for the treatment of virus-associated hemorrhagic cystitis and ongoing proof-of-concept, or POC, clinical trials for multi-virus prevention in HSCT and BKV in kidney transplant.

The Company’s lead product candidate, posoleucel, is a multi-VST-cell therapy that targets six viruses: BK virus, JC virus, cytomegalovirus, adenovirus, Epstein-Barr virus and human herpesvirus 6. We are prioritizing prevention and treatment programs with the largest potential to transform transplant patient care and outcomes. We are focusing on key areas where there are limited or no options, including the treatment or prevention of life-threatening viral diseases caused by six devastating viruses with a single therapy. Based on progress and preliminary data, we are prioritizing our multi-virus prevention program in allogeneic HSCT patients; the aim is to improve clinical outcomes by intervening before viral infections occur and to prevent end organ damage. If proven safe and effective, this approach has the potential to be transformative as, if successful, the use of posoleucel could supplant the need for potentially toxic treatments for CMV and other viruses in HSCT patients. Given the potential advantages of the prevention approach, we therefore have elected to delay the initiation of the planned Phase 3 CMV treatment trial in allogeneic HSCT patients, in order to focus resources on our highest priority studies. We also have elected to delay the initiation of a POC clinical trial for posoleucel to treat CMV in solid organ transplant (SOT) patients, given the potential read through of our ongoing multi-virus prevention study. Similarly, additional safety and efficacy data in kidney transplant patients with BK viremia will inform the potential benefit of exploring a multi-virus prevention approach in SOT patients. In addition to our ongoing programs, we plan to initiate a Phase 3 study by the end of 2021 evaluating posoleucel for the treatment of adenovirus (AdV) in adult and pediatric allogeneic HSCT recipients. ALVR106 is the Company’s second multi-virus-targeted off-the-shelf VST product candidate targeting devastating respiratory diseases caused by respiratory syncytial virus, or RSV, influenza, parainfluenza virus, or PIV, and human metapneumovirus, or hMPV. An Investigational New Drug, or IND, application with the FDA for ALVR106 was cleared in the fourth quarter of 2020 and the Company plans to initiate a Phase 1/2 clinical study in autologous and allogeneic HSCT patients with respiratory viral diseases in the fourth quarter of 2021. Pursuant to the sponsored research agreement with Baylor College of Medicine (“BCM”), BCM initiated a proof-of-concept trial for ALVR109, an allogeneic, off-the-shelf VST therapy designed to target SARS-CoV-2, the virus that causes the severe and life-threatening viral disease, COVID-19. ALVR109 is being studied to arrest the progression of COVID-19 by eradicating SARS-CoV-2 virus-infected cells. BCM initiated the POC clinical trial in the fourth quarter of 2020 and early clinical data on the activity, tolerability and persistence of ALVR109 were reported in September 2021. With efficacy of available vaccine and therapies to prevent serious disease, we do not see a role for our COVID-19 therapy in a broad population. However, depending on the evolution of the SARS-CoV-2 virus, there may be a future role to treat immunocompromised patients who aren’t adequately served by available vaccines and therapies. We continue to make ALVR109 available to physicians in response to appropriate compassionate use requests, and we are monitoring the evolution of the SARS-CoV-2 virus and the COVID-19 pandemic to guide the next steps for this program in the context of our broader R&D portfolio and priorities. In the preclinical space, the Company is advancing ALVR107 designed to target hepatitis B, or HBV, infected cells and cure chronic HBV infection and plan to complete preclinical IND enabling studies for ALVR107 in the fourth quarter of 2021. Lastly, we have paused our preclinical work on ALVR108 to treat human herpesvirus-8, or HHV-8, associated diseases including Kaposi Sarcoma, or KS, primary effusion lymphoma, or PEL, and multicentric Castleman’s disease, or MCD given the declining incidence of HHV-8 associated diseases.

The Company was formed on August 16, 2013 as a Delaware limited liability company (“LLC”) under the name AdCyte LLC and on July 29, 2014 the Company changed its name to ViraCyte LLC. On September 17, 2018, the Company converted from a Delaware LLC to a Delaware corporation (“LLC Conversion”) and changed its name to ViraCyte, Inc. On May 22, 2019, the Company changed its name to AlloVir, Inc. The Company has principal offices in Houston, Texas and Cambridge, Massachusetts.

On August 8, 2019, AlloVir formed AlloVir International Designated Activity Company (“AlloVir International”), a wholly-owned subsidiary established in Ireland.

On October 9, 2019, AlloVir Securities Corporation was incorporated as a Massachusetts Security Corporation, a wholly-owned subsidiary of AlloVir.

On November 10, 2019, AlloVir International formed AlloVir Italia S.R.L. (“AlloVir Italia”), a wholly-owned subsidiary in Italy.

On August 3, 2020, the Company completed an initial public offering (“IPO”) in which the Company issued and sold 18,687,500 shares of its common stock, at a public offering price of $17.00 per share, resulting in gross proceeds of $317.7 million. The Company received $292.0 million in net proceeds after deducting underwriting discounts and commissions and offering costs.

Upon the closing of the IPO, all of the then-outstanding shares of convertible preferred stock automatically converted into 39,859,139 shares of common stock at the applicable conversion ratio then in effect. Subsequent to the closing of the IPO, there were no shares of convertible preferred stock outstanding.

On July 20, 2021 AlloVir Inc formed AlloVir U.S., Inc. (“AlloVir U.S.”), a wholly-owned subsidiary of AlloVir.

ElevateBio, LLC

On September 17, 2018, the Company executed a Series A2 Preferred Stock Purchase Agreement (“Series A2 Agreement”) with ElevateBio, LLC, a Delaware LLC (“ElevateBio”) concurrent with the LLC Conversion. ElevateBio was formed on November 29, 2017 and is headquartered in Cambridge, Massachusetts with a focus on the development of a portfolio of novel cell therapy programs acquired through business development activities with biotechnology companies. ElevateBio is structured as a holding company, comprised of asset-specific subsidiaries focused on the development of pipeline assets, as well as a manufacturing subsidiary with the expertise to provide drug development and manufacturing services. As a result of the purchase of the Company’s Series A2 Preferred Stock, ElevateBio acquired an ownership interest in the Company. The Chief Executive Officer, Chief Financial Officer, and other executives of ElevateBio have previously or currently serve in similar management roles 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 and principal executive officer.

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 September 30, 2021, 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 $45.5 million and $23.6 million for the three months ended September 30, 2021 and 2020, respectively, and $114.0 million and $44.6 million for the nine months ended September 30, 2021 and 2020, respectively. In addition, at September 30, 2021, the Company had an accumulated deficit of $239.1 million. The Company expects to continue to generate operating losses for the foreseeable future.

The Company believes that its $243.2 million of cash and cash equivalents and $32.7 million of short-term investments held at September 30, 2021, are sufficient to fund planned operations for at least twelve months from the date that these condensed consolidated financial statements are available to be 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. The spread of COVID-19 has impacted the global economy and has impacted 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. If the disruption due to the COVID-19 pandemic continues, planned pivotal clinical trials also could be delayed due to government orders and site policies on account of the pandemic, and some patients may be unwilling or unable to travel to study sites, enroll in trials or be unable to comply with clinical trial protocols if quarantines impede patient movement or interrupt healthcare services, which would delay the Company’s ability to conduct preclinical studies and clinical trials or release clinical trial results and could delay the Company’s ability to obtain regulatory approval and commercialize product candidates. Furthermore, COVID-19 could affect the Company’s employees or the employees of

research sites and service providers on whom the Company relies on as well as those of companies with which the Company does business, including suppliers and contract manufacturing organizations or CMOs, thereby disrupting business operations. Quarantines and travel restrictions imposed by governments in the jurisdictions in which the Company and the companies with which it does business operate could materially impact the ability of employees to access preclinical and clinical sites, laboratories, manufacturing sites and offices. For the health and safety of our employees, the Company has implemented work-at-home policies and we have generally restricted on site staff to only those employees who are fully vaccinated or essential to the development and research of product candidates; accordingly, the Company may experience limitations in employee resources. The outbreak and any other preventative or protective actions that the Company, its suppliers or other third parties with which it has business relationships, or governments may take in respect of the COVID-19 pandemic, could disrupt, delay or otherwise adversely impact the business.

The Company is still assessing business plans and the impact the COVID-19 pandemic 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 and severity 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 Accounting Policies

9 Months Ended

Sep. 30, 2021

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Interim Financial Information

The accompanying condensed consolidated balance sheet at September 30, 2021, and the condensed consolidated statements of operations and comprehensive loss, statements of convertible preferred stock and changes in stockholders’ equity (deficit) for the three and nine months ended September 30, 2021 and 2020 and condensed consolidated statements of cash flows for the nine months ended September 30, 2021 and 2020 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 September 30, 2021 and the results of its operations for the three and nine months ended September 30, 2021 and 2020 and its cash flows for the nine months ended September 30, 2021 and 2020. The financial data and other information disclosed in these notes related to the three and nine months ended September 30, 2021 and 2020 are also unaudited. The results for the three and nine months ended September 30, 2021 are not necessarily indicative of results to be expected for the year ending December 31, 2021 or for any other subsequent interim period.

Restricted Cash

Cash accounts with any type of restriction are classified as restricted cash. The Company has restricted cash deposits with a bank, which serve as collateral for a letter of credit issued to the landlord of the Company’s leased Waltham facility for a security deposit. The Company classified this amount as restricted cash in the accompanying condensed consolidated balance sheet at September 30, 2021. There was no restricted cash balance at September 30, 2020.

Cloud Computing Arrangements

The Company capitalizes certain implementation costs for internal-use software incurred in a cloud computing agreement that is a service contract. Eligible costs associated with cloud computing arrangements, such as the implementation costs incurred to develop or obtain software business applications used in the normal course of business, are capitalized in accordance with ASC 350. Capitalization ceases at the point the software is substantially complete and ready for its intended use, and after all substantial testing is completed. Amortization is recorded on a straight-line basis over the expected useful life of three years of the internal-use software cost in the same line item in the statement of operations and comprehensive loss as the expense for fees for the associated cloud computing arrangement. No amortization expense associated with the Company's cloud computing arrangements has been recognized during the three and nine months ended September 30, 2021 and 2020.

Functional Currency

As a result of certain intercompany transactions in September 2021, the Company has determined that the functional currency for AlloVir International and AlloVir Italia is the U.S. Dollar (“USD”). Prior to this determination, the functional currency of AlloVir International was the Euro; however, due to the immateriality of the transactions that occurred at AlloVir International and AlloVir Italia previously, the impact of the determination for the transition from Euro to USD is not material and is not considered a change in accounting principle for reporting purposes. Reporting currency has been and remains the USD.

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, 2020, 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 December 2019, the FASB issued ASU 2019-12 – Income Taxes (Topic 740) (“ASU 2019-12”), which removes certain exceptions from the guidance and simplifies the accounting for income taxes in certain areas. The Company adopted ASU 2019-12 on January 1, 2021. There was no material impact to the Company’s consolidated financial statements as a result of adopting this new standard.

Recently Issued Accounting Pronouncements Not Yet Adopted

In June 2016, the FASB issued ASU 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (“ASU 2016-13”). ASU 2016-13 significantly changes the impairment model for most financial assets and certain other instruments. ASU 2016-13 will require immediate recognition of estimated credit losses expected to occur over the remaining life of many financial assets, which will generally result in earlier recognition of allowances for credit losses on loans and other financial instruments. ASU 2016-13 is effective for the Company’s fiscal year beginning after December 15, 2022 and subsequent interim periods. The adoption of this standard is not expected to have a material impact on the Company’s consolidated financial statements and related disclosures.

Short-Term Investments

9 Months Ended

Sep. 30, 2021

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 marketable securities, which are considered to be available-for-sale investments and were included in short-term investments on the condensed consolidated balance sheets:


	September 30, 2021
(in thousands)	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
U.S. government treasury securities	$	32,654	$	-	$	-	$	32,654
Totals	$	32,654	$	-	$	-	$	32,654


	December 31, 2020
(in thousands)	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
U.S. government treasury securities	$	233,687	$	-	$	(24	)	$	233,663
Totals	$	233,687	$	-	$	(24	)	$	233,663

Certain short-term debt securities with original maturities of less than 90 days are included in cash and cash equivalents on the condensed consolidated balance sheets and are not included in the tables above. At September 30, 2021 and December 31, 2020, all investments had contractual maturities within one year.

Fair Value Measurements

9 Months Ended

Sep. 30, 2021

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:


	September 30, 2021
(in thousands)	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market fund	$	208,841	$	-	$	-	$	208,841
Totals	$	208,841	$	-	$	-	$	208,841
Short-term investments:
U.S. government treasury securities	$	32,654	$	-	$	-	$	32,654
Totals	$	32,654	$	-	$	-	$	32,654


	December 31, 2020
(in thousands)	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market fund	$	55,505	$	-	$	-	$	55,505
U.S. government treasury securities		39,998		-		-		39,998
Totals	$	95,503	$	-	$	-	$	95,503
Short-term investments:
U.S. government treasury securities	$	233,663	$	-	$	-	$	233,663
Totals	$	233,663	$	-	$	-	$	233,663

During the nine months ended September 30, 2021 and the year ended December 31, 2020, 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 carrying amounts of prepaid expenses and other current assets, 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.

- 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 + Details

Leases

9 Months Ended

Sep. 30, 2021

Leases [Abstract]

Leases

5. Leases

Short-term leases

The Company leases an office space in Houston, Texas under an operating lease that expires in March 2022. The Company also sub-leases, on a month-to-month basis, a portion of ElevateBio's office space in Cambridge, Massachusetts. During the three months ended September 30, 2021 and 2020, total short-term lease expense recognized was $0.4 million (of which approximately $16 thousand relates to non-lease costs, such as utilities and cleaning), and $0.1 million (of which approximately $17 thousand relates to non-lease costs such as utilities and cleaning), respectively. During the nine months ended September 30, 2021 and 2020, total short-term lease expense recognized was $0.6 million (of which approximately $49 thousand relates to non-lease costs, such as utilities and cleaning), and $0.3 million (of which approximately $45 thousand relates to non-lease costs such as utilities and cleaning), respectively.

In April 2021, the Company entered into a Statement of Work (“SOW”) with a third-party supplier under the Development and Manufacturing Services Agreement (“DMS Agreement”) made effective in July 2019. This SOW is to lease a dedicated manufacturing suite for the manufacture of AlloVir’s products at the facility. On July 30, 2021, the Company provided a notification to reduce capacity to the third-party supplier which terminates this lease agreement in the first quarter of 2022. During the three and nine months ended September 30, 2021, total lease expense recognized under this SOW was $0.5 million and $0.7 million, respectively.

Operating leases

Operating lease liabilities and their corresponding right-of-use (“ROU”) assets are recorded based on the present value of future lease payments over the expected remaining lease term. The Company has elected to account for the lease and non-lease components together for existing classes of underlying assets. ROU assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. ROU assets and liabilities are recognized at the lease commencement date based on the present value of the lease payments over the lease term. The Company uses an incremental borrowing rate based on information available at the commencement date in determining the present value of lease payments. The incremental borrowing rate represents the rate of interest that a lessee would have to pay to borrow on a collateralized basis over a similar term at an amount equal to the lease payments in a similar economic environment. The Company estimates this rate based on prevailing market conditions, comparable company and credit analysis, the impact of collateralization, and the term of each of the Company’s lease agreements.

In March 2019, the Company entered into an interim services agreement which ultimately led to a DMS Agreement with a third-party supplier in July 2019. The DMS Agreement specifies a dedicated manufacturing suite for the manufacture of AlloVir’s products at the facility. The DMS Agreement will expire upon the later of: 1) two years from the Effective Date, or July 2021, and 2) the

completion of services under all SOWs. The term may be extended by agreement of the parties for additional two-year periods upon written notice to the supplier at least 30 days prior to expiration of the then-current term. The DMS Agreement (or any individual SOW) may be terminated earlier by AlloVir at any time by providing 190 days’ notice. The Company has extended the DMS Agreement, and estimates that early termination is not reasonably certain to occur. The total estimated lease term of 4.25 years expires in July 2023. In March 2019, at the inception of this lease, the Company recorded a ROU asset and lease liability of $6.9 million. In September 2019, the Company executed a SOW for another dedicated manufacturing suite under the DMS Agreement with substantially the same terms as the original SOW. The SOW calls for a fixed monthly payment through July 2023, with additional two-year renewal options. The use of this manufacturing suite qualifies as a lease under ASC 842, as it includes an identified asset for exclusive use by the Company at its direction.

In May 2020, the Company entered into a new Development and Manufacturing Services Agreement (“2020 DMS Agreement”) with ElevateBio BaseCamp, Inc. and signed a SOW in November 2020. The 2020 DMS Agreement and related SOW 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 for and obtains substantially all of the economic benefit of the suite. In exchange for this dedicated manufacturing suite, AlloVir will pay the supplier a monthly fixed suite utilization fee, and other related fixed costs, totaling $3.2 million over the two-year lease term (one year lease with a one-year renewal option), that covers costs associated with reserving capacity for AlloVir, as well as cleaning services, utilities, handling and maintenance of the manufacturing suite. The Company estimates that the exercise of the one-year renewal option is reasonably certain to occur, and the Company is reasonably certain that it will not exercise its early termination right, providing for a total estimated lease term of two years expiring in January 2023. As part of the arrangement, there were also variable costs for materials, non-fixed batch payments, 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 February 2021, the point at which the new facility area was substantially complete and available for use by the Company. Accordingly, at inception, the Company recorded a ROU asset of $3.1 million and a lease liability of $2.5 million. The Company prepaid $0.6 million of the suite utilization fee, which was reclassified from prepaid expense to the ROU asset upon lease commencement.

In September 2021, the Company entered into a new 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 have been classified as operating leases and commenced in September 2021. At the inception date, the Company has recorded an 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 Company has the option to renew the leased space for an additional one time period of five years with written notice from the Company. As of September 30, 2021, the Company has no reasonable certainty that this option to extend will be exercised.

Maturities of operating lease liabilities at September 30, 2021 are as follows (in thousands):


2021 (remaining 3 months)	$	2,260
2022		7,167
2023		5,273
2024		3,177
2025		3,255
Thereafter		16,582
Total lease payments		37,714
Less: interest (3.40% - 5.75%)		(6,364	)
Total lease liability	$	31,350
Lease liability – current		6,297
Lease liability – long-term		25,053

Total lease costs were $2.0 million and $0.9 million for the three months ended September 30, 2021 and 2020, respectively, and $4.4 million and $2.7 million for the nine months ended September 30, 2021 and 2020, respectively. Cash paid for operating leases was $1.3 million and $0.9 million for the three months ended September 30, 2021 and 2020, respectively, and $3.6 million and $2.7 million for the nine months ended September 30, 2021 and 2020, respectively. The Company’s total variable lease costs, such as materials, batch payments, storage, knowledge and tech transfer, and other common area maintenance fees, related to the operating leases was $5.3 million and $1.2 million for the three months ended September 30, 2021 and 2020, respectively, and $9.1 million and $3.7 million

for the nine months ended September 30, 2021 and 2020, respectively. The weighted average remaining lease term is 7.26 years at September 30, 2021. The weighted average discount rate is 4.95% at September 30, 2021.

Accrued Expenses

9 Months Ended

Sep. 30, 2021

Payables And Accruals [Abstract]

Accrued Expenses

6. Accrued Expenses

Accrued expenses consisted of the following:


(in thousands)	September 30, 2021		December 31, 2020
Employee compensation and benefits	$	4,198	$	3,314
Professional fees		755		696
Research and development		10,436		3,347
Other		409		173
Total accrued expenses	$	15,798	$	7,530

Sponsored Research, Collaboration and License Agreements

9 Months Ended

Sep. 30, 2021

Research And Development [Abstract]

Sponsored Research, Collaboration and License Agreements

7. Sponsored Research, Collaboration and License Agreements

Amended and Restated Exclusive License Agreement with BCM

In June 2017, the Company signed a License Agreement (the “License Agreement”) with BCM, whereby the Company acquired a royalty-bearing, worldwide, exclusive license to BCM’s rights in Subject Technology and related patent rights in the field of viral infection. In May 2020, the Company amended and restated the License Agreement (the “A&R License Agreement”), pursuant to which the Company obtained (a) an exclusive worldwide license, with the right to sublicense, under certain patent rights and other intellectual property rights of BCM, to make, have made, use, market, sell, offer to sell, lease, import and export products in a particular field, except that such license is non-exclusive within a particular subfield, and in addition with respect to certain patent rights such license is limited to two particular subfields, and (b) an exclusive, worldwide sublicense, with the right to further sublicense, under all patent rights and other intellectual property rights that are exclusively licensed to BCM by a certain third party licensor, to make, have made, use, market, sell, offer to sell, lease, import and export products in the same field. The Company’s rights are subject to the rights of the U.S. government and certain rights retained by BCM.

Unless earlier terminated, the A&R License Agreement will expire on a country-by-country basis with respect to a product upon the later of (a) the expiration of the last to expire valid claim of a patent or patent application covering such product in such country or (b) 10 years after the first commercial sale of such product in such country. The Company may terminate the A&R License Agreement in its entirety at any time for convenience upon a certain number of days’ written notice. BCM may terminate the A&R License Agreement in its entirety for the Company’s uncured material default.

BCM maintains control of all filing, prosecution and maintenance of its patent rights licensed by the Company, and the Company is responsible for all related costs and expenses during the term of the agreement. The Company also reimbursed BCM for costs and expenses (including reasonable legal fees and expenses) incurred prior to the effective date of the agreement with respect to the filing, prosecution and maintenance of the patent rights licensed by the Company. If BCM licenses the patent rights licensed by the Company to third parties for additional fields of use, the Company’s responsibility for patent related costs and expenses will be reduced on a pro-rata basis.

Under the A&R License Agreement, the Company must use commercially reasonable efforts to develop and commercialize one or more products in certain countries. As partial consideration for the rights conveyed by BCM under the original agreement executed in June 2017, the Company paid BCM a non-refundable license fee of $250,000. During the term of the A&R License Agreement, the Company is obligated to pay BCM a non-refundable annual license maintenance fee, but beginning with the fifth year after the original agreement date, license maintenance fees are fully creditable against royalty revenue due in the applicable year. The Company is required to pay certain milestone payments upon the achievement of specified clinical, regulatory, and sales milestones. In the event that the Company is able to successfully develop, launch and commercialize a product under the A&R License Agreement, total milestone payments could exceed $40.0 million. BCM is also eligible to receive tiered royalties at percentage rates ranging from less than 1% to the low single-digits, on net sales of any products that are commercialized by the Company or its sublicensees that incorporate, utilize or are made with the use of, the intellectual property licensed by the Company. To the extent the Company sublicenses its license rights under the A&R License Agreement, BCM would be eligible to receive tiered sublicense income at percentage rates in the mid-single to low double-digits.

In November 2020, the Company also entered into the First Amendment (the “License Amendment”) to the A&R License Agreement. Under the License Amendment, the Company assumed responsibility from BCM for the filing, prosecution and maintenance of the patent rights licensed by the Company from BCM under the A&R License Agreement that are in common with the License

Agreement. Further, BCM also transferred to the Company the right of enforcement against third parties for any suspected infringement of any claims in such patent rights or misuse, misappropriation, theft or breach of confidence of other proprietary rights.

Exclusive License Agreement with BCM

In November 2020, the Company signed a second License Agreement (the “Second License Agreement) with BCM, whereby the Company acquired a royalty-bearing, worldwide, exclusive license to BCM’s rights in Subject Technology and related patent rights outside the field of viral infection (all fields other than those covered by the A&R License Agreement).

Unless earlier terminated, the Second License Agreement will expire on a country-by-country basis with respect to a product upon the later of (a) the expiration of the last to expire valid claim of a patent or patent application covering such product in such country or (b) 10 years after the first commercial sale of such product in such country, provided that the Second License Agreement shall not expire later than March 25, 2040. The Company may terminate the Second License Agreement in its entirety at any time for convenience upon a certain number of days’ written notice. BCM may terminate the Second License Agreement in its entirety for the Company’s uncured material default.

Under the Second License Agreement, BCM transferred to the Company control of all filing, prosecution and maintenance of the patent rights licensed by the Company, and the Company is responsible for all related costs and expenses during the term of the Second License Agreement. BCM also transferred to the Company the right of enforcement against third parties for any suspected infringement of any claims in the patent rights or misuse, misappropriation, theft or breach of confidence of other proprietary rights. The Company also reimbursed BCM for costs and expenses (including reasonable legal fees and expenses) incurred prior to the effective date of the Second License Agreement with respect to the filing, prosecution and maintenance of the patent rights licensed by the Company, to the extent not already paid by the Company under the A&R License Agreement.

Under the Second License Agreement, the Company must use commercially reasonable efforts to develop and commercialize one or more products in certain countries. As partial consideration for the rights conveyed by BCM under the Second License Agreement, the Company paid BCM a non-refundable license fee of $125,000. During the term of the Second License Agreement, the Company is obligated to pay BCM a non-refundable annual license maintenance fee of (a) $20,000 for the first through fourth anniversary of the effective date of the Second License Agreement, and (b) $40,000 for the fifth anniversary of the effective date and continuing thereafter, but beginning with the fifth year, license maintenance fees are fully creditable against royalty revenue due in the applicable year. The Company is required to pay certain milestone payments upon the achievement of specified clinical, regulatory, and sales milestones. In the event that the Company is able to successfully develop, launch and commercialize multiple products under the Second License Agreement, total milestone payments could exceed $30.0 million. BCM is also eligible to receive tiered royalties at percentage rates ranging from less than 1% to the low single-digits, on net sales of any products that are commercialized by the Company or its sublicensees that incorporate, utilize or are made with the use of, the intellectual property licensed by the Company. To the extent the Company sublicenses its license rights under the Second License Agreement, BCM would be eligible to receive tiered sublicense income at percentage rates in the mid-single to low double-digits.

Sponsored Research Agreement with BCM

In June 2019, the Company entered into a sponsored research agreement (“SRA-2”) with BCM, under which the Company agreed to pay BCM for performing certain research activities related to virus specific T-cell manufacturing for a one-year period, renewable for an additional one-year term upon written consent of both parties. SRA-2 requires the Company to make payments to BCM totaling $1.0 million, payable in four equal installments. SRA-2 was amended in March 2020 to include the discovery and development of allogeneic, off-the-shelf, virus specific T-cell therapies to combat SARS-CoV-2, the virus that causes COVID-19. In June 2020, a second amendment was entered into resulting in a no cost extension through November 30, 2020, upon which the agreement terminated.

Collaboration Agreement with BCM

In November 2020, the Company also entered into a Research Collaboration Agreement (the “Research Agreement”) with BCM, under which the Company agreed to pay BCM for performing certain research activities under the direction of Dr. Ann Leen commencing on January 1, 2021 and continuing for a three-year period thereafter. The Research Agreement requires the Company to make payments to BCM totaling approximately $2.0 million per year, for a total of approximately $6.0 million over the term of the Research Agreement.

Collectively under the agreements above and for services provided by BCM the Company paid $0.7 million and $0.1 million during the three months ended September 30, 2021 and 2020, respectively, and $2.8 million and $0.9 million during the nine months ended September 30, 2021 and 2020, respectively. These costs are classified in research and development expense in the condensed consolidated statements of operations and comprehensive loss. The Company has also triggered three milestone events during the nine months ended September 30, 2021 and has accounted for $0.2 million in accrued milestone expenses which are classified under accrued expenses in the condensed consolidated balance sheet.

CPRIT Grant

In August 2017, the Company was awarded a $9.0 million grant (the “CPRIT Grant”) from the Cancer Research and Prevention Institute of Texas (“CPRIT”) to perform a phase IIB clinical trial to establish the safety and effectiveness of posoleucel, in adults and children with a common, very severe virus infection (BK Virus) after stem cell transplant. The grant period was three years beginning September 1, 2017 through August 31, 2020. This grant had a matching requirement where the Company was obligated to match 50% of the grant funds used on the project. In addition, the grant included other compliance requirements including the obligation for the Company to operate with a principal place of business in Texas. There were no costs incurred to obtain or fulfill the contract. In November 2019, the Company provided CPRIT with written notice of its intent to terminate the grant. In December 2019, the Company returned $2.6 million of grant funds received, including interest relating to these funds in the amount of $0.1 million, and decreased its deferred revenue balance to zero. The Company received acknowledgment of the termination from CPRIT in January 2020. The CPRIT Grant also required that the Company grant CPRIT a non-commercial license to technology developed under the grant and pay CPRIT a share of revenue on sales of commercial products developed using CPRIT funds equal to low single digits of revenue until such time as CPRIT has been paid an aggregate amount equal to 400% of the grant award proceeds. No royalty payments were made under this license agreement during the nine months ended September 30, 2021 and 2020, respectively.

Funding Arrangements

9 Months Ended

Sep. 30, 2021

Research And Development [Abstract]

Funding Arrangements

8. Funding Arrangements

SBIR Grant

In June 2017, the Company was awarded a Small Business Innovation Research (“SBIR”) grant by the National Institute of Health (“NIH”) in the amount of $3.0 million. This grant was effective from September 15, 2017 to June 30, 2020 and in April 2020, the Company received an extension through June 30, 2021. The grant was funded on an ongoing basis based on periodic reports of qualifying expenditures reported by the Company to NIH. Under this grant, the Company received proceeds of $0.0 and $0.4 million during the three months ended September 30, 2021 and 2020, respectively. During the nine months ended September 30, 2021 and 2020, the Company received proceeds of $0.0 million and $0.7 million, respectively. The Company recognized income of approximately $0.0 million and $0.2 million on expenses incurred during the three months ended September 30, 2021 and 2020, respectively, and $0.0 and $0.6 million during the nine months ended September 30, 2021 and 2020, respectively. At December 31, 2020, the Company had received the full amount awarded under the SBIR grant. The grant was not extended past June 30, 2021 and the Company notified the NIH of grant completion in July 2021.

The SBIR grant does not fall within the scope of ASC 606 as NIH does not meet the definition of a customer, and the grant from NIH was given for the benefit of public health rather than for monetary compensation. Accordingly, funding received under this grant is recognized in “Other income (loss), net” in the condensed consolidated statements of operations and comprehensive loss.

Stockholder's Equity

9 Months Ended

Sep. 30, 2021

Equity [Abstract]

Stockholder's Equity

9. Stockholder’s Equity

On August 3, 2020, in connection with the closing of the Company’s IPO, the Company filed its amended and restated certificate of incorporation, which authorizes the Company to issue up to 10,000,000 shares of preferred stock, $0.0001 par value per share. There were no shares of preferred stock issued or outstanding at September 30, 2021 and December 31, 2020.

At September 30, 2021 and December 31, 2020, the Company’s amended and restated certificate of incorporation authorized the Company to issue 150,000,000 shares of common stock at a par value of $0.0001 per share. In conjunction with the Company's IPO closing on August 3, 2020, the Company issued and sold 18,687,500 shares of its common stock, including 2,437,500 shares pursuant to the full exercise of the underwriters' option to purchase additional shares, at a public offering price of $17.00 per share, for aggregate net proceeds of $292.0 million after deducting underwriting discounts and commissions and offering costs. In connection with the Company’s IPO, all outstanding shares of preferred stock converted into 39,859,139 shares of common stock.

The Company has reserved shares of common stock for issuance as follows:


	September 30, 2021		December 31, 2020
Unvested restricted stock		3,126,635		3,410,979
Options to purchase common stock		6,028,476		3,972,909
Stock available for grant under the 2020 Stock Option and Grant Plan		4,068,527		3,895,961
Total		13,223,638		11,279,849

Stock-Based Compensation

9 Months Ended

Sep. 30, 2021

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

10. Stock-Based Compensation

2018 Equity Incentive Plan

The Company’s 2018 Plan provided for the Company to issue restricted stock, restricted stock units, incentive stock options, and non-statutory stock options and other stock-based awards to employees, officers, members of the Board, consultants and advisors of the Company. The 2018 Plan was most recently amended in July 2020. The awards granted under this plan generally vest over a four-year period and have a 10-year contractual term.

At September 30, 2021, the Company had granted 6,715,415 shares of common stock under the 2018 Plan, including an aggregate of 64,042 shares of common stock issuable upon the exercise of outstanding options under the 2018 Plan. Of the awards granted, 20,128 awards and 30,280 awards have been forfeited or cancelled during the three and nine months ended September 30, 2021, respectively. No shares remained 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

On July 2, 2020, the Company’s Board of Directors adopted and in July 2020 the stockholders approved the 2020 Stock Option and Grant Plan (the “2020 Plan”) which became effective on July 28, 2020, the date immediately prior to the date on which the registration statement related to the IPO was declared effective, and as a result no further awards will be made under the 2018 Plan thereafter. Initially, the aggregate number of shares of our common stock that may be issued pursuant to stock awards under the 2020 Plan was 8,008,734 shares. The number of shares of our common stock reserved for issuance under the 2020 Plan shall be cumulatively increased on January 1, 2021 and each January 1 thereafter by 5% of the total number of shares of our common stock outstanding on December 31 of the preceding calendar year or a lesser number of shares determined by our board of directors. Unless our board of directors elects not to increase the number of shares available for future grant each year, our stockholders may experience additional dilution, which could cause our stock price to fall. Accordingly, on January 1, 2021, 3,255,343 shares were added to the number of available shares under the 2020 Plan. The awards granted under this plan generally vest over a four-year period and have a 10-year contractual term.

At September 30, 2021, there were an aggregate of 5,964,434
shares of common stock issuable upon the exercise of outstanding options under the 2020 Plan and 1,298,620 shares of restricted common stock granted under the 2020 Plan. Additionally, there were an aggregate of 4,068,527 shares reserved for future issuance under the 2020 Plan.

Restricted Common Stock

The following table summarizes restricted common stock activity for the nine months ended September 30, 2021:


	Shares			Weighted Average Grant Date Fair Value
Unvested at January 1, 2021		3,410,979		$	3.55
Granted		1,047,613			34.76
Forfeited		(94,709	)		25.44
Vested		(1,237,248	)		2.44
Unvested at September 30, 2021		3,126,635		$	13.79

At September 30, 2021, there was $36.1 million of unrecognized stock-based compensation cost related to the restricted stock, which is expected to be recognized over a weighted average period of 3.15 years.

Stock Options

The following table summarizes stock option activity (in thousands, except share and per share data):


	Shares			Weighted Average Exercise Price		Weighted Average Contractual Life (in years)		Aggregate Intrinsic Value
Options outstanding at January 1, 2021		3,972,909		$	17.84		9.58	$	81,822
Granted		2,264,138			33.09		—		—
Exercised		(9,425	)		17.00		—		71
Forfeited		(199,146	)		25.29		—		948
Options outstanding at September 30, 2021		6,028,476		$	23.33		9.07	$	31,564
Options vested and exercisable at September 30, 2021		1,063,653		$	17.09		8.81	$	8,800

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 the Company’s stock options granted during the nine months ended September 30, 2021 was $25.30. At September 30, 2021, there was $81.7 million of unrecognized stock-based compensation expense related to unvested stock options, which is being recognized over a period of 3.07 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 September 30, 2021			Nine Months Ended September 30, 2021
Expected term (in years)		6.09			6.06
Expected volatility		93.76	%		95.00	%
Risk-free interest rate		0.97	%		0.84	%
Expected dividend yield		—			—
Fair value of common stock	$	20.05		$	33.09

Stock-Based Compensation Expense

Stock-based compensation expense was as follows:


	Three Months Ended September 30,				Nine Months Ended September 30,
(in thousands)	2021		2020		2021		2020
Research and development	$	4,010	$	3,092	$	11,274	$	3,400
General and administrative		6,276		768		16,841		1,598
Total stock-based compensation expense	$	10,286	$	3,860	$	28,115	$	4,998

2020 Employee Stock Purchase Plan

In July 2020, the 2020 Employee Stock Purchase Plan (the “2020 ESPP”) was also adopted by the Board of Directors and approved by the stockholders. The purpose of the 2020 ESPP is to provide eligible employees of the Company and other designated companies, with opportunities to purchase shares of the Company’s common stock, par value $0.0001 per share. 611,354 shares of common stock in the aggregate have been approved and reserved for this purpose, plus on January 1, 2021 and each January 1 thereafter until January 1, 2030, the number of shares of common stock reserved and available for issuance under the Plan shall be cumulatively increased by the least of (i) 1,222,707 shares of common stock, (ii) 1% of the number of shares of common stock issued and outstanding on the immediately preceding December 31, and (iii) such number of shares of common stock as determined by the Administrator. The Board of Directors elected not to increase the number of available shares as of January 1, 2021.

Income Taxes

9 Months Ended

Sep. 30, 2021

Income Tax Disclosure [Abstract]

Income Taxes

11. Income Taxes

The Company’s income tax provision is computed based on the federal statutory rate and the average state statutory rates, net of the related federal benefit. For the three and nine months ended September 30, 2021 and 2020, the Company did not record a current or deferred income tax expense or benefit due to current and historical losses incurred by the Company. The Company’s losses before income taxes consist primarily of losses from domestic operations.

The Company’s estimate of the realizability of the deferred tax asset is dependent on estimates of projected future levels of taxable income. In analyzing future taxable income levels, the Company considered all evidence currently available, both positive and negative.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References + Details

Net Loss per Share

9 Months Ended

Sep. 30, 2021

Earnings Per Share [Abstract]

Net Loss per Share

12. 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 September 30,						Nine Months Ended September 30,
(in thousands, except share and per share data)	2021			2020			2021			2020
Numerator:
Net loss – basic and diluted	$	(45,510	)	$	(23,614	)	$	(114,021	)	$	(44,585	)
Denominator:
Weighted-average common shares outstanding – basic and diluted		62,962,434			40,465,705			62,588,898			15,195,000
Net loss per share – basic and diluted	$	(0.72	)	$	(0.58	)	$	(1.82	)	$	(2.93	)

Based on the amounts outstanding at September 30, 2021 and 2020, 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 nine months ended September 30, 2021 and 2020, 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.


	September 30,
	2021		2020
Options to purchase common stock		6,028,476		3,661,905
Unvested restricted stock		3,126,635		3,554,488

Related Party Transactions

9 Months Ended

Sep. 30, 2021

Related Party Transactions

13. Related Party Transactions

The Company entered into an agreement with ElevateBio that provides for ongoing services to the Company in areas such as accounting operations, public relations, information technology, human resources and administration management, finance and risk management, marketing services, facilities, procurement and travel and corporate development and strategy (the “Shared Services Agreement”). The Company was billed quarterly 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 Company also subleases office space, which includes payment for common area charges. The Company also has a SOW to receive manufacturing and project management consulting services from ElevateBio. The Company incurred $0.6 million and $2.3 million during the three months ended September 30, 2021 and 2020, respectively, and $4.1 million and $4.8 million of expenses during the nine months ended September 30, 2021 and 2020, respectively, related to services provided to the Company by ElevateBio and affiliates. The Company owed ElevateBio $1.9 million and $0.6 million at September 30, 2021 and December 31, 2020, respectively, which is recorded in “Amount due to related party” on the condensed consolidated balance sheets.

Members of the Company’s management received a total of $0.1 million in consulting fees during the three months ended September 30, 2021 and 2020 and $0.3 million and $0.5 million during the nine months ended September 30, 2021 and 2020, respectively.

Summary of Significant Accounting Policies (Policies)	9 Months Ended
Summary of Significant Accounting Policies (Policies)	Sep. 30, 2021
Accounting Policies [Abstract]
Interim Financial Information	Interim Financial Information The accompanying condensed consolidated balance sheet at September 30, 2021, and the condensed consolidated statements of operations and comprehensive loss, statements of convertible preferred stock and changes in stockholders’ equity (deficit) for the three and nine months ended September 30, 2021 and 2020 and condensed consolidated statements of cash flows for the nine months ended September 30, 2021 and 2020 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 September 30, 2021 and the results of its operations for the three and nine months ended September 30, 2021 and 2020 and its cash flows for the nine months ended September 30, 2021 and 2020. The financial data and other information disclosed in these notes related to the three and nine months ended September 30, 2021 and 2020 are also unaudited. The results for the three and nine months ended September 30, 2021 are not necessarily indicative of results to be expected for the year ending December 31, 2021 or for any other subsequent interim period.
Restricted Cash	Restricted Cash Cash accounts with any type of restriction are classified as restricted cash. The Company has restricted cash deposits with a bank, which serve as collateral for a letter of credit issued to the landlord of the Company’s leased Waltham facility for a security deposit. The Company classified this amount as restricted cash in the accompanying condensed consolidated balance sheet at September 30, 2021. There was no restricted cash balance at September 30, 2020.
Cloud Computing Arrangements	Cloud Computing Arrangements The Company capitalizes certain implementation costs for internal-use software incurred in a cloud computing agreement that is a service contract. Eligible costs associated with cloud computing arrangements, such as the implementation costs incurred to develop or obtain software business applications used in the normal course of business, are capitalized in accordance with ASC 350. Capitalization ceases at the point the software is substantially complete and ready for its intended use, and after all substantial testing is completed. Amortization is recorded on a straight-line basis over the expected useful life of three years of the internal-use software cost in the same line item in the statement of operations and comprehensive loss as the expense for fees for the associated cloud computing arrangement. No amortization expense associated with the Company's cloud computing arrangements has been recognized during the three and nine months ended September 30, 2021 and 2020.
Functional Currency	Functional CurrencyAs a result of certain intercompany transactions in September 2021, the Company has determined that the functional currency for AlloVir International and AlloVir Italia is the U.S. Dollar (“USD”). Prior to this determination, the functional currency of AlloVir International was the Euro; however, due to the immateriality of the transactions that occurred at AlloVir International and AlloVir Italia previously, the impact of the determination for the transition from Euro to USD is not material and is not considered a change in accounting principle for reporting purposes. Reporting currency has been and remains the USD.
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, 2020, 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 December 2019, the FASB issued ASU 2019-12 – Income Taxes (Topic 740) (“ASU 2019-12”), which removes certain exceptions from the guidance and simplifies the accounting for income taxes in certain areas. The Company adopted ASU 2019-12 on January 1, 2021. There was no material impact to the Company’s consolidated financial statements as a result of adopting this new standard.
Recently Issued Accounting Pronouncements Not Yet Adopted	Recently Issued Accounting Pronouncements Not Yet Adopted In June 2016, the FASB issued ASU 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (“ASU 2016-13”). ASU 2016-13 significantly changes the impairment model for most financial assets and certain other instruments. ASU 2016-13 will require immediate recognition of estimated credit losses expected to occur over the remaining life of many financial assets, which will generally result in earlier recognition of allowances for credit losses on loans and other financial instruments. ASU 2016-13 is effective for the Company’s fiscal year beginning after December 15, 2022 and subsequent interim periods. The adoption of this standard is not expected to have a material impact on the Company’s consolidated financial statements and related disclosures.

Short-Term Investments (Tables)

9 Months Ended

Sep. 30, 2021

Investments Debt And Equity Securities [Abstract]

Summary of Amortized Cost and Estimated Fair Value of Marketable Securities


	September 30, 2021
(in thousands)	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
U.S. government treasury securities	$	32,654	$	-	$	-	$	32,654
Totals	$	32,654	$	-	$	-	$	32,654


	December 31, 2020
(in thousands)	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
U.S. government treasury securities	$	233,687	$	-	$	(24	)	$	233,663
Totals	$	233,687	$	-	$	(24	)	$	233,663

Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2021

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:


	September 30, 2021
(in thousands)	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market fund	$	208,841	$	-	$	-	$	208,841
Totals	$	208,841	$	-	$	-	$	208,841
Short-term investments:
U.S. government treasury securities	$	32,654	$	-	$	-	$	32,654
Totals	$	32,654	$	-	$	-	$	32,654


	December 31, 2020
(in thousands)	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market fund	$	55,505	$	-	$	-	$	55,505
U.S. government treasury securities		39,998		-		-		39,998
Totals	$	95,503	$	-	$	-	$	95,503
Short-term investments:
U.S. government treasury securities	$	233,663	$	-	$	-	$	233,663
Totals	$	233,663	$	-	$	-	$	233,663

Leases (Tables)

9 Months Ended

Sep. 30, 2021

Leases [Abstract]

Summary of Maturities Operating Leases Liabilities

Maturities of operating lease liabilities at September 30, 2021 are as follows (in thousands):


2021 (remaining 3 months)	$	2,260
2022		7,167
2023		5,273
2024		3,177
2025		3,255
Thereafter		16,582
Total lease payments		37,714
Less: interest (3.40% - 5.75%)		(6,364	)
Total lease liability	$	31,350
Lease liability – current		6,297
Lease liability – long-term		25,053

Accrued Expenses (Tables)

9 Months Ended

Sep. 30, 2021

Payables And Accruals [Abstract]

Schedule of Accrued Expenses

Accrued expenses consisted of the following:


(in thousands)	September 30, 2021		December 31, 2020
Employee compensation and benefits	$	4,198	$	3,314
Professional fees		755		696
Research and development		10,436		3,347
Other		409		173
Total accrued expenses	$	15,798	$	7,530

Stockholder's Equity (Tables)

9 Months Ended

Sep. 30, 2021

Equity [Abstract]

Schedule of Reserved Shares of Common Stock for Issuance

The Company has reserved shares of common stock for issuance as follows:


	September 30, 2021		December 31, 2020
Unvested restricted stock		3,126,635		3,410,979
Options to purchase common stock		6,028,476		3,972,909
Stock available for grant under the 2020 Stock Option and Grant Plan		4,068,527		3,895,961
Total		13,223,638		11,279,849

Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2021

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Restricted Common Stock Activity

The following table summarizes restricted common stock activity for the nine months ended September 30, 2021:


	Shares			Weighted Average Grant Date Fair Value
Unvested at January 1, 2021		3,410,979		$	3.55
Granted		1,047,613			34.76
Forfeited		(94,709	)		25.44
Vested		(1,237,248	)		2.44
Unvested at September 30, 2021		3,126,635		$	13.79

Summary of Stock Option Activity

The following table summarizes stock option activity (in thousands, except share and per share data):


	Shares			Weighted Average Exercise Price		Weighted Average Contractual Life (in years)		Aggregate Intrinsic Value
Options outstanding at January 1, 2021		3,972,909		$	17.84		9.58	$	81,822
Granted		2,264,138			33.09		—		—
Exercised		(9,425	)		17.00		—		71
Forfeited		(199,146	)		25.29		—		948
Options outstanding at September 30, 2021		6,028,476		$	23.33		9.07	$	31,564
Options vested and exercisable at September 30, 2021		1,063,653		$	17.09		8.81	$	8,800

Schedule of Estimated Fair Value 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 September 30, 2021			Nine Months Ended September 30, 2021
Expected term (in years)		6.09			6.06
Expected volatility		93.76	%		95.00	%
Risk-free interest rate		0.97	%		0.84	%
Expected dividend yield		—			—
Fair value of common stock	$	20.05		$	33.09

Schedule of Stock-based Compensation Expense

Stock-based compensation expense was as follows:


	Three Months Ended September 30,				Nine Months Ended September 30,
(in thousands)	2021		2020		2021		2020
Research and development	$	4,010	$	3,092	$	11,274	$	3,400
General and administrative		6,276		768		16,841		1,598
Total stock-based compensation expense	$	10,286	$	3,860	$	28,115	$	4,998

Net Loss per Share (Tables)

9 Months Ended

Sep. 30, 2021

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 September 30,						Nine Months Ended September 30,
(in thousands, except share and per share data)	2021			2020			2021			2020
Numerator:
Net loss – basic and diluted	$	(45,510	)	$	(23,614	)	$	(114,021	)	$	(44,585	)
Denominator:
Weighted-average common shares outstanding – basic and diluted		62,962,434			40,465,705			62,588,898			15,195,000
Net loss per share – basic and diluted	$	(0.72	)	$	(0.58	)	$	(1.82	)	$	(2.93	)

Potential Dilutive Securities Excluded From Computation Of Diluted Net Loss Per Share Attributable To Common Stockholders


	September 30,
	2021		2020
Options to purchase common stock		6,028,476		3,661,905
Unvested restricted stock		3,126,635		3,554,488

Nature of the Business - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended						9 Months Ended
	Aug. 03, 2020	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Aug. 04, 2020
Net proceeds from issuance initial public offering	$ 292,000								$ 295,449
Net losses attributable to common stockholders		$ (45,510)	$ (37,588)	$ (30,923)	$ (23,614)	$ (11,632)	$ (9,339)	$ (114,021)	(44,585)
Accumulated deficit		(239,124)						(239,124)		$ (125,103)
Cash and cash equivalents		243,187			$ 142,250			243,187	$ 142,250	122,661
Short-term investments		$ 32,654						$ 32,654		$ 233,663
Convertible Preferred Stock
Preferred stock, shares outstanding											0
Common Stock
Common stock issued and sold					18,687,500
Stock issued upon conversion of preferred stock					39,859,139
IPO
Common stock issued and sold	18,687,500
Public offering price per share	$ 17.00
Gross proceeds from issuance of common stock	$ 317,700
Stock issued upon conversion of preferred stock	39,859,139
IPO \| Common Stock
Stock issued upon conversion of preferred stock	39,859,139

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Summary Of Significant Accounting Policies [Line Items]
Amortization expense for cloud computing arrangements	$ 0	$ 0	$ 0	$ 0
Restricted cash	$ 852,000	$ 0	$ 852,000	$ 0
ASU 2019-02
Summary Of Significant Accounting Policies [Line Items]
Change In Accounting Principle Accounting Standards Update Adopted	true		true
Change In Accounting Principle Accounting Standards Update Adoption Date	Jan. 01, 2021		Jan. 01, 2021
Change In Accounting Principle Accounting Standards Update Immaterial Effect	true		true

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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 15: http://www.xbrl.org/2003/role/disclosureRef
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Reference 17: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Short-Term Investments - Summary of Amortized Cost and Estimated Fair Value of Marketable Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 32,654	$ 233,687
Unrealized Losses		(24)
Fair Value	32,654	233,663
U.S. Government Treasury Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	32,654	233,687
Unrealized Losses		(24)
Fair Value	$ 32,654	$ 233,663

Fair Value Measurements - Summary of Financial Assets and Liabilities Measured at Fair Value On Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Cash equivalents:
Cash equivalents	$ 208,841	$ 95,503
Short-term investments:
Short-term investments	32,654	233,663
Money Market Fund
Cash equivalents:
Cash equivalents	208,841	55,505
U.S. Government Treasury Securities
Cash equivalents:
Cash equivalents		39,998
U.S. Government Treasury Securities
Short-term investments:
Short-term investments	32,654	233,663
Level 1
Cash equivalents:
Cash equivalents	208,841	95,503
Short-term investments:
Short-term investments	32,654	233,663
Level 1 \| Money Market Fund
Cash equivalents:
Cash equivalents	208,841	55,505
Level 1 \| U.S. Government Treasury Securities
Cash equivalents:
Cash equivalents		39,998
Level 1 \| U.S. Government Treasury Securities
Short-term investments:
Short-term investments	$ 32,654	$ 233,663

Leases - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended				3 Months Ended		9 Months Ended
	Sep. 30, 2021	Apr. 30, 2021	Feb. 28, 2021	Jul. 31, 2019	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Sep. 30, 2019
Leases [Line Items]
Lease expiration month and year							2022-03
Short-term lease expenses					$ 400	$ 100	$ 600	$ 300
Non-lease costs					16	17	49	45
ROU asset	$ 31,487				31,487		31,487		$ 8,692
Lease liability	$ 31,350				31,350		31,350
Operating lease costs					2,000	900	4,400	2,700
Cash paid for operating lease					1,300	900	3,600	2,700
Variable lease costs					$ 5,300	$ 1,200	$ 9,100	$ 3,700
Operating lease, weighted average remaining lease term	7 years 3 months 3 days				7 years 3 months 3 days		7 years 3 months 3 days
Operating lease, weighted average discount rate, percent	4.95%				4.95%		4.95%
DMS Agreement
Leases [Line Items]
Lease expiration month and year				2021-07
Lease expense recognized					$ 500		$ 700
Lease effective date		2021-04		2019-07
Term of agreement				2 years
Lease termination description							On July 30, 2021, the Company provided a notification to reduce capacity to the third-party supplier which terminates this lease agreement in the first quarter of 2022.
Operating lease, existence of option to extend				true
Lease, option to extend				The term may be extended by agreement of the parties for additional two-year periods upon written notice to the supplier at least 30 days prior to expiration of the then-current term.
Operating lease, existence of option to terminate				true
Lease, option to terminate				The DMS Agreement (or any individual SOW) may be terminated earlier by AlloVir at any time by providing 190 days’ notice.
Lease renewal term										2 years
Estimated lease term				4 years 3 months
Estimated lease expiring month and year				2023-07
ROU asset				$ 6,900
Lease liability				$ 6,900
2020 DMS Agreement
Leases [Line Items]
Term of agreement			1 year
Lease renewal term			1 year
Estimated lease term			2 years
Estimated lease expiring month and year			2023-01
ROU asset			$ 3,100
Lease liability			2,500
Utilization fee			$ 3,200
Lessee operating lease, lease term including renewal option			2 years
Prepaid utilization fee			$ 600
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. As of September 30, 2021, the Company has no reasonable certainty that this option to extend will be exercised.
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				6,000		$ 6,000
Lease liability	6,000				6,000		6,000
Sublease with AMAG Pharmaceuticals
Leases [Line Items]
ROU asset	17,300				17,300		17,300
Lease liability	$ 17,300				$ 17,300		$ 17,300

Leases - Summary of Operating Lease Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Leases [Abstract]
2021 (remaining 3 months)	$ 2,260
2022	7,167
2023	5,273
2024	3,177
2025	3,255
Thereafter	16,582
Total lease payments	37,714
Less: interest (3.40% - 5.75%)	(6,364)
Total lease liability	31,350
Operating lease liability, current	6,297	$ 3,229
Operating lease liability, long term	$ 25,053	$ 5,463

Leases - Summary of Operating Lease Liabilities (Details) (Parenthetical)	Sep. 30, 2021
Lessor Lease Description [Line Items]
Operating lease interest percentage	4.95%
Minimum
Lessor Lease Description [Line Items]
Operating lease interest percentage	3.40%
Maximum
Lessor Lease Description [Line Items]
Operating lease interest percentage	5.75%

Accrued Expenses - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Payables And Accruals [Abstract]
Employee compensation and benefits	$ 4,198	$ 3,314
Professional fees	755	696
Research and development	10,436	3,347
Other	409	173
Total accrued expenses	$ 15,798	$ 7,530

Sponsored Research, Collaboration and License Agreements - Additional Information (Details)	1 Months Ended					3 Months Ended		9 Months Ended
	Nov. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jun. 30, 2019 USD ($) Installment	Aug. 31, 2017 USD ($)	Jun. 30, 2017 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) Milestone	Sep. 30, 2020 USD ($)
Sponsored Research, Collaboration and License Agreements [Line Items]
Research and development expense						$ 33,062,000	$ 17,182,000	$ 79,132,000	$ 32,906,000
CPRIT \| Non-commercial License Agreement
Sponsored Research, Collaboration and License Agreements [Line Items]
Maximum paid percentage of grant award proceeds until which revenue share is payable				400.00%
Royalty payments								0	0
CPRIT \| Grant
Sponsored Research, Collaboration and License Agreements [Line Items]
Revenue from grant				$ 9,000,000.0
Period of grant				3 years
Percentage of obligation of grant funds used				50.00%
Cost incurred to obtain or fulfill the contract				$ 0
Grant funds received returned amount		$ 2,600,000
Interest relating to grant funds returned		100,000
Deferred revenue balance		$ 0
A&R License Agreement \| BCM
Sponsored Research, Collaboration and License Agreements [Line Items]
Non-refundable license fee payments					$ 250,000
Milestone payments								$ 40,000,000.0
Minimum percentage of eligible to receive tiered royalties						1.00%		1.00%
Second License Agreement \| BCM
Sponsored Research, Collaboration and License Agreements [Line Items]
Non-refundable license fee payments	$ 125,000
Milestone payments								$ 30,000,000.0
Minimum percentage of eligible to receive tiered royalties						1.00%		1.00%
Non-refundable license fee payments, first year through fourth anniversary of effective date								$ 20,000
Non-refundable license fee payments fifth anniversary of effective date and continuing thereafter								40,000
SRA-2 \| BCM
Sponsored Research, Collaboration and License Agreements [Line Items]
Agreement for research activities, term			1 year
Agreement for research activities, additional term with written consent			1 year
Research activities performing fees			$ 1,000,000.0
Number of installment for research activities payments \| Installment			4
Research Agreement \| BCM
Sponsored Research, Collaboration and License Agreements [Line Items]
Agreement for research activities, term	3 years
Research activities performing fees	$ 2,000,000.0
Total research activities performing fees, over the term	$ 6,000,000.0
Collective Agreements \| BCM
Sponsored Research, Collaboration and License Agreements [Line Items]
Research and development expense						$ 700,000	$ 100,000	2,800,000	$ 900,000
Collective Agreements \| BCM \| Accrued Expenses
Sponsored Research, Collaboration and License Agreements [Line Items]
Accrued milestone expenses						$ 200,000		$ 200,000
Number of milestone events \| Milestone								3

Funding Arrangements - Additional Information (Details) - Grant - USD ($) $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended
	Jun. 30, 2017	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Research And Development Arrangement Contract To Perform For Others [Line Items]
Research grant, description and terms				In June 2017, the Company was awarded a Small Business Innovation Research (“SBIR”) grant by the National Institute of Health (“NIH”) in the amount of $3.0 million. This grant was effective from September 15, 2017 to June 30, 2020 and in April 2020, the Company received an extension through June 30, 2021.
Research revenue grant awarded	$ 3.0
Grant revenue received		$ 0.0	$ 0.4	$ 0.0	$ 0.7
Research related income recognized		$ 0.0	$ 0.2	$ 0.0	$ 0.6

Stockholders Equity - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	Aug. 03, 2020	Sep. 30, 2021	Dec. 31, 2020
Class Of Stock [Line Items]
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, shares authorized		150,000,000	150,000,000
Common stock, par value		$ 0.0001	$ 0.0001
IPO
Class Of Stock [Line Items]
Preferred stock, par or stated value per share	$ 0.0001
Preferred stock, shares authorized	10,000,000
Common stock issued and sold	18,687,500
Public offering price per share	$ 17.00
Proceeds from issuance of common stock	$ 292.0
Stock issued upon conversion of preferred stock	39,859,139
Over-Allotment Option
Class Of Stock [Line Items]
Common stock issued and sold	2,437,500

Stockholders Equity - Schedule of Reserved Shares of Common Stock for Issuance (Details) - shares	Sep. 30, 2021	Dec. 31, 2020
Class Of Stock [Line Items]
Reserved shares of common stock for issuance	13,223,638	11,279,849
Unvested Restricted Stock
Class Of Stock [Line Items]
Reserved shares of common stock for issuance	3,126,635	3,410,979
Option To Purchase Common Stock
Class Of Stock [Line Items]
Reserved shares of common stock for issuance	6,028,476	3,972,909
Stock Available For Grant \| 2020 Stock Option and Grant Plan
Class Of Stock [Line Items]
Reserved shares of common stock for issuance	4,068,527	3,895,961

Stock-Based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions			1 Months Ended	3 Months Ended	9 Months Ended
	Jan. 01, 2021	Jul. 02, 2020	Jul. 31, 2020	Sep. 30, 2021	Sep. 30, 2021	Dec. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Reserved shares of common stock for issuance				13,223,638	13,223,638	11,279,849
Weighted average grant-date fair value of stock options granted					$ 25.30
Common stock, par value				$ 0.0001	$ 0.0001	$ 0.0001
Restricted Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Awards forfeited or cancelled					94,709
Number of shares granted					1,047,613
Unrecognized stock-based compensation cost				$ 36.1	$ 36.1
Weighted average period of cost expected to be recognized					3 years 1 month 24 days
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted average period of cost expected to be recognized					3 years 25 days
Unrecognized stock-based compensation expenses				$ 81.7	$ 81.7
2018 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Awards vesting period					4 years
Awards contractual term					10 years
Common stock shares granted				6,715,415	6,715,415
Number of shares of common stock issuable upon exercise of outstanding options				64,042	64,042
Awards forfeited or cancelled				20,128	30,280
Reserved shares of common stock for issuance				0	0
2020 Stock Option and Grant Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Awards vesting period		4 years
Awards contractual term		10 years
Common stock authorized for issuance		8,008,734
Cumulative increase in number shares reserved for issuance, percentage		5.00%
Shares added to number of available shares under plan	3,255,343
Common stock issuable upon exercise of outstanding options					5,964,434
2020 Stock Option and Grant Plan \| Restricted Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares granted					1,298,620
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				4,068,527	4,068,527	3,895,961
2020 ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Reserved shares of common stock for issuance			611,354
Cumulative increase in number shares reserved for issuance, percentage			1.00%
Common stock, par value			$ 0.0001
Annual increase in number of shares reserved for issuance			1,222,707

Stock-Based Compensation - Summary of Restricted Common Stock Activity (Details) - Restricted Common Stock	9 Months Ended
	Sep. 30, 2021 $ / shares shares
Number of Shares
Number of Shares, Unvested as of January 1, 2021 \| shares	3,410,979
Number of Shares, Granted \| shares	1,047,613
Number of Shares, Forfeited \| shares	(94,709)
Number of Shares, Vested \| shares	(1,237,248)
Number of Shares, Unvested as of September 30, 2021 \| shares	3,126,635
Weighted Average Grant Date Fair Value
Weighted Average Grant Date Fair Value, Unvested as of January 1, 2021 \| $ / shares	$ 3.55
Weighted Average Grant Date Fair Value, Granted \| $ / shares	34.76
Weighted Average Grant Date Fair Value, Forfeited \| $ / shares	25.44
Weighted Average Grant Date Fair Value, Vested \| $ / shares	2.44
Weighted Average Grant Date Fair Value, Unvested as of September 30, 2021 \| $ / shares	$ 13.79

Stock-Based Compensation - Summary of Stock Option Activity (Details) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021 USD ($) $ / shares shares	Dec. 31, 2020 USD ($) $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Options Outstanding, Beginning Balance \| shares	3,972,909
Number of Options, Granted \| shares	2,264,138
Number of Options, Exercised \| shares	(9,425)
Number of Options, Forfeited \| shares	(199,146)
Number of Options Outstanding, Ending Balance \| shares	6,028,476	3,972,909
Options vested and exercisable at September 30, 2021 \| shares	1,063,653
Weighted Average Exercise Price, Options outstanding as of January 1, 2021 \| $ / shares	$ 17.84
Weighted Average Exercise Price, Granted \| $ / shares	33.09
Weighted Average Exercise Price, Exercised \| $ / shares	17.00
Weighted Average Exercise Price, Forfeited \| $ / shares	25.29
Weighted Average Exercise Price, Options outstanding as of September 30, 2021 \| $ / shares	23.33	$ 17.84
Weighted Average Exercise Price, Options vested and exercisable at September 30, 2021 \| $ / shares	$ 17.09
Weighted Average Contractual Life, Options outstanding	9 years 25 days	9 years 6 months 29 days
Weighted Average Contractual Life, Options vested and exercisable at September 30, 2021	8 years 9 months 21 days
Aggregate Intrinsic Value, Options outstanding at January 1, 2021 \| $	$ 81,822
Aggregate Intrinsic Value, Exercised \| $	71
Aggregate Intrinsic Value, Forfeited \| $	948
Aggregate Intrinsic Value, Options outstanding at September 30, 2021 \| $	31,564	$ 81,822
Aggregate Intrinsic Value, Options vested and exercisable at September 30, 2021 \| $	$ 8,800

Stock-Based Compensation - Schedule of Estimated Fair Value Assumptions Using Black Scholes Option-Pricing Model (Details) - $ / shares	3 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Expected term (in years)	6 years 1 month 2 days	6 years 21 days
Expected volatility	93.76%	95.00%
Risk-free interest rate	0.97%	0.84%
Fair value of common stock	$ 20.05	$ 33.09

Stock-Based Compensation - Schedule of Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 10,286	$ 3,860	$ 28,115	$ 4,998
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	4,010	3,092	11,274	3,400
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 6,276	$ 768	$ 16,841	$ 1,598

Income Taxes - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Current income tax expense (benefit)	$ 0	$ 0	$ 0	$ 0
Deferred income tax expense (benefit)	$ 0	$ 0	$ 0	$ 0

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		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Numerator:
Net loss – basic and diluted	$ (45,510)	$ (23,614)	$ (114,021)	$ (44,585)
Denominator:
Weighted-average common shares outstanding — basic and diluted	62,962,434	40,465,705	62,588,898	15,195,000
Net loss per share – basic and diluted	$ (0.72)	$ (0.58)	$ (1.82)	$ (2.93)

Net Loss per Share - Potential Dilutive Securities Excluded From Computation Of Diluted Net Loss Per Share Attributable To Common Stockholders (Details) - shares	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
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	6,028,476	3,661,905
Unvested Restricted Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	3,126,635	3,554,488

Related Party Transactions - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Related Party Transaction [Line Items]
Amount due to related party	$ 1,945		$ 1,945		$ 572
Consulting fees to members of management	100	$ 100	300	$ 500
ElevateBio and Affiliates
Related Party Transaction [Line Items]
Expenses related to services with related party	$ 600	$ 2,300	$ 4,100	$ 4,800