0001193125-21-000941 | S-1 | XBRL Viewer

Nature of the Business and Basis of Presentation

1. Nature of the Business and Basis of Presentation

The Company was incorporated on

October 21, 2016

as Torus Therapeutics, Inc. and subsequently changed its name to Generation Bio Co. (the “Company” or “Generation Bio”). The Company is an innovative genetic medicines company creating a new class of gene therapy utilizing its proprietary

non-viral

gene therapy platform to provide durable, redosable treatments for millions of patients living with rare and prevalent diseases. The Company’s

non-viral

gene therapy platform incorporates its high-capacity DNA construct called closed-ended DNA (“ceDNA”), its cell-targeted lipid nanoparticle delivery system (“ctLNP”) and its established, scalable capsid-free manufacturing process. Using its approach, the Company is developing novel gene therapies to provide targeted delivery of genetic payloads that include large and multiple genes to a range of tissues across a broad array of diseases. The Company is also engineering its gene therapies to be redosable, which may enable individualized patient titration to reach the desired therapeutic expression and to maintain efficacy throughout a patient’s life. The Company is headquartered in Cambridge, Massachusetts.

COVID-19

pandemic and the ability to secure additional capital to fund operations. Programs currently under development will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval prior to commercialization of a product. These efforts require significant amounts of additional capital, adequate personnel and infrastructure and extensive compliance-reporting capabilities. Even if the Company’s development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales.

On June 16, 2020, the Company completed its initial public offering (“IPO”) pursuant to which it issued and sold 12,105,263 shares of its common stock, including 1,578,947 shares pursuant to the full exercise of the underwriters’ option to purchase additional shares, at a public offering price of $19.00 per share, resulting in net proceeds of $210.7 million, after deducting underwriting discounts and commissions and other offering expenses. Upon the closing of the IPO, all of the Company’s outstanding convertible preferred stock automatically converted into shares of common stock.

The accompanying consolidated financial statements have been prepared on the basis of continuity of operations, realization of assets and the satisfaction of liabilities and commitments in the ordinary course of business. Since inception, the Company has funded its operations with proceeds from the sales of instruments convertible into convertible preferred stock (which converted into convertible preferred stock in 2017), the sale of convertible preferred stock, and most recently, with proceeds from the sale of common stock in the IPO completed in June 2020. The Company has incurred recurring losses, including net losses of $61.3 million for the year ended December 31, 2019 and $56.3 million for the nine months ended September 30, 2020. As of September 30, 2020, the Company had an accumulated deficit of $164.7 million. The Company expects to continue to generate operating losses in the foreseeable future. As of November 10, 2020, the issuance date of these interim condensed consolidated financial statements, the Company expects that its cash, cash equivalents and marketable securities will be sufficient to fund its operating expenses and capital expenditure requirements for at least 12 months.

The Company will need to obtain additional funding through public or private equity offerings, debt financings, collaborations, strategic alliances and/or licensing arrangements. The Company may not be able to obtain financing on acceptable terms, or at all, and the Company may not be able to enter into collaborations or strategic alliances or licensing arrangements. The terms of any financing may adversely affect the holdings or the rights of the Company’s stockholders. Arrangements with collaborators or others may require the Company to relinquish rights to certain of its technologies or programs. If the Company is unable to obtain funding, the Company could be forced to delay, reduce or eliminate some or all of its research and development programs, pipeline expansion or commercialization efforts, which could adversely affect its business prospects. Although management will continue to pursue these plans, there is no assurance that the Company will be successful in obtaining sufficient funding on terms acceptable to the Company to fund continuing operations when needed or at all.

The accompanying consolidated financial statements reflect the operations of the Company and the Company’s wholly owned subsidiary, Generation Bio Securities Corporation. Intercompany balances and transactions have been eliminated in consolidation. The accompanying consolidated financial statements have been prepared in conformity with generally accepted accounting principles (“GAAP”) in the United States of America. Any reference in these notes to applicable guidance is meant to refer to the authoritative GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”).

1. Nature of the business and basis of presentation

The Company was incorporated on October 21, 2016 as Torus Therapeutics, Inc. and subsequently changed its name to Generation Bio Co. (the “Company” or “Generation Bio”). The Company is an innovative genetic medicines company creating a new class of gene therapy utilizing its proprietary

non-viral

gene therapy platform to provide durable, redosable treatments for millions of patients living with rare and prevalent diseases. The Company’s

non-viral

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, the ability to establish clinical- and commercial-scale manufacturing processes and the ability to secure additional capital to fund operations. Programs currently under development will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval prior to commercialization of a product. These efforts require significant amounts of additional capital, adequate personnel and infrastructure and extensive compliance-reporting capabilities. Even if the Company’s development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales.

The accompanying consolidated financial statements have been prepared on the basis of continuity of operations, realization of assets and the satisfaction of liabilities and commitments in the ordinary course of business. Through December 31, 2019, the Company has funded its operations with the proceeds from instruments convertible into convertible preferred stock (which converted into convertible preferred stock in 2017) and the sale of convertible preferred stock. Since inception, the Company has incurred recurring losses, including net losses of $61.3 million for the year ended December 31, 2019. As of December 31, 2019, the Company had an accumulated deficit of $108.5 million. The Company expects to continue to generate operating losses in the foreseeable future. As of April 9, 2020, the issuance date of the annual consolidated financial statements for the year ended December 31, 2019, the Company expected that its cash and cash equivalents, including gross proceeds of $111.5 million it received in January 2020 from the sale of Series C convertible preferred stock (see Note 13), would be sufficient to fund its operating expenses and capital expenditure requirements for at least 12 months from the issuance date of the annual consolidated financial statements.

The Company is seeking to complete an initial public offering (“IPO”) of its common stock. Upon the completion of a qualified public offering on specified terms, the Company’s outstanding convertible preferred stock will automatically convert into shares of common stock (see Note 6).

The Company will need to obtain additional funding through public or private equity offerings, debt financings, collaborations, strategic alliances and/or licensing arrangements. The Company may not be able to obtain financing on acceptable terms, or at all, and the Company may not be able to enter into collaborative or strategic alliances or licensing arrangements. The terms of any financing may adversely affect the holdings or the rights of the Company’s stockholders. Arrangements with collaborators or others may require the Company to relinquish rights to certain of its technologies or programs. If the Company is unable to obtain funding, the Company could be forced to delay, reduce or eliminate some or all of its research and development programs, pipeline expansion or commercialization efforts, which could adversely affect its business prospects.

Although management will continue to pursue these plans, there is no assurance that the Company will be successful in obtaining sufficient funding on terms acceptable to the Company to fund continuing operations when needed or at all.

Summary of Significant Accounting Policies

9 Months Ended

12 Months Ended

Sep. 30, 2020

Dec. 31, 2019

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Use of estimates

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expenses during the reporting periods. Significant estimates and assumptions reflected in these condensed consolidated financial statements include, but are not limited to, the accrual of research and development expenses and stock-based compensation expense. The Company bases its estimates on historical experience, known trends and other market-specific or other relevant factors that it believes to be reasonable under the circumstances. On an ongoing basis, management evaluates its estimates, as there are changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results may differ from those estimates or assumptions.

Unaudited interim financial information

The balance sheet at December 31, 2019 was derived from audited financial statements but does not include all disclosures required by GAAP. The accompanying unaudited financial statements as of September 30, 2020 and for the three and nine months ended September 30, 2019 and 2020 have been prepared by the Company pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”) for interim financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. These financial statements should be read in conjunction with the Company’s audited financial statements included elsewhere in this prospectus. In the opinion of management, all adjustments, consisting only of normal recurring adjustments necessary for a fair presentation of the Company’s financial position as of September 30, 2020, the results of operations for the three and nine months ended September 30, 2019 and 2020, and cash flows for the nine months ended September 30, 2019 and 2020 have been made. The results of operations for the three and nine months ended September 30, 2020 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2020 or any other period.

Concentrations of credit risk and of significant suppliers

Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents, and marketable securities. The Company believes it is not exposed to significant credit risk due to the financial strength of the depository institutions in which the cash and cash equivalents are held. The Company maintains its cash equivalents in money market funds that invest in U.S. treasury securities. The Company’s marketable securities as of September 30, 2020 consisted of U.S government treasury securities, U.S. government agency bonds, commercial paper and corporate debt securities. The Company has adopted an investment policy that limits the amounts the Company may invest in the securities of single issuer with the exclusion of the U.S. government. The Company has not experienced any credit losses and does not believe that it is subject to significant credit risk.

The Company is dependent on a small number of third-party suppliers for its drug substance and drug product. In particular, the Company relies, and expects to continue to rely, on third-party suppliers for certain materials and components required for the production of any product candidates it may develop for its programs. These programs could be adversely affected by a significant interruption in the supply process.

Fair value measurements

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

•

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

•

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

•

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

The Company’s cash equivalents and marketable securities are carried at fair value, determined according to the fair value hierarchy described above (see Note 3). The carrying values of the Company’s accounts payable and accrued expenses approximate their fair values due to the short-term nature of these liabilities.

Recently adopted accounting pronouncements

In August 2018, the FASB issued ASU

2018-13,

Fair Value Measurement (Topic 820): Disclosure Requirements for Fair Value Measurement. The new standard added, modified or removed disclosure requirements under Topic 820 for clarity and consistency. ASU

2018-13

is effective for all entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. The Company adopted ASU

2018-03

on January 1, 2020 and the adoption did not have a material impact on its consolidated financial statements.

Recently issued accounting pronouncements

From time to time, new accounting pronouncements are issued by the FASB or other standard setting bodies that the Company adopts as of the specified effective date. The Company qualifies as an “emerging growth company” as defined in the Jumpstart Our Business Startups Act of 2012 and has elected not to “opt out” of the extended transition related to complying with new or revised accounting standards, which means that when a standard is issued or revised and it has different application dates for public and nonpublic companies, the Company can adopt the new or revised standard at the time nonpublic companies adopt the new or revised standard and can do so until such time that the Company either (i) irrevocably elects to “opt out” of such extended transition period or (ii) no longer qualifies as an emerging growth company.

In February 2016, the FASB issued ASU

2016-02,

Leases (Topic 842). The new standard requires that all lessees recognize the assets and liabilities that arise from leases on the balance sheet and disclose qualitative and quantitative information about its leasing arrangements. In July 2018, the FASB issued ASU

2018-11,

which provides entities with an additional transition method to adopt Topic 842. Under the new transition method, an entity initially applies the new lease requirements at the adoption date, not the earliest period presented, and recognizes a cumulative effect adjustment to the opening balance of retained earnings in the period of adoption. For public entities, the guidance was effective for annual reporting periods beginning after December 15, 2018 and for interim periods within those fiscal years. For nonpublic entities, the guidance was effective for annual reporting periods beginning after December 15, 2019. Early adoption is permitted for all entities. In November 2019, the FASB issued ASU

2019-10,

which deferred the effective date for nonpublic entities to annual reporting periods beginning after December 15, 2020, and interim periods within fiscal years beginning after December 15, 2021. In June 2020, the FASB issued ASU

2020-05,

which grants a

one-year

effective-date delay for nonpublic entities to annual reporting periods beginning after December 15, 2021 and to interim periods within fiscal years beginning after December 15, 2022. Early adoption continues to be allowed. The Company plans to adopt ASU

2016-02

on January 1, 2021 using the modified retrospective approach transition method as of the date of adoption such that prior periods will not be restated. The Company will also elect a package of practical expedients, under which an entity need not reassess whether any expired or existing contracts are or contain leases, the lease classification for any expired or existing leases, or initial direct costs for any existing leases. The adoption of the new standard is expected to result in the recognition of material liabilities and

right-of-use

assets, however, the Company has not completed its assessment.

In June 2016, the FASB issued ASU

2016-13,

Financial Instruments – Credit Losses (Topic 326). The new standard adjusts the accounting for assets held at amortized costs basis, including marketable securities accounted for as

available-for-sale.

The standard eliminates the probable initial recognition threshold and requires an entity to reflect its current estimate of all expected credit losses. The allowance for credit losses is a valuation account that is deducted from the amortized cost basis of the financial assets to present the net amount expected to be collected. For public entities, the guidance is effective for annual reporting periods beginning after December 15, 2019 and for interim periods within those fiscal years. For nonpublic entities, the guidance was effective for annual reporting periods beginning after December 15, 2020. Early adoption is permitted for all entities. In November 2019, the FASB issued ASU

2019-10,

which deferred the effective date for nonpublic entities to annual reporting periods beginning after December 15, 2022, including interim periods within those fiscal years. The Company is currently evaluating when to adopt the guidance and the impact the guidance will have on its consolidated financial statements.

2. Summary of significant accounting policies

Use of estimates

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expenses during the reporting periods. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, the accrual of research and development expenses and stock-based compensation expense. The Company bases its estimates on historical experience, known trends and other market-specific or other relevant factors that it believes to be reasonable under the circumstances. On an ongoing basis, management evaluates its estimates, as there are changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results may differ from those estimates or assumptions.

Concentrations of credit risk and of significant suppliers

Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash and cash equivalents. The Company has not experienced any other-than-temporary losses with respect to its cash and cash equivalents and does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships.

Deferred offering costs

The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated

with in-process equity

financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded as a reduction of the carrying value of the preferred stock or, for issuances of common stock, in stockholder’s equity (deficit) as a reduction of additional

paid-in

capital generated as a result of the offering. Should the planned equity financing be abandoned, the deferred offering costs will be expensed immediately as a charge to operating expenses in the consolidated statement of operations and comprehensive loss. As of December 31, 2019, the Company recorded $0.1 million of deferred offering costs related to its Series C convertible preferred stock financing (see Note 13). Upon the issuance of the Series C convertible preferred stock in January 2020 (unaudited), the deferred offering costs were reclassified as a reduction to the carrying value of the preferred stock.

Cash equivalents

The Company considers all highly liquid investments with a remaining maturity when purchased of three months or less to be cash equivalents.

Restricted cash

Amounts included in restricted cash represent amounts pledged as collateral for letters of credit required for security deposits on the Company’s leased facilities. These amounts are classified as restricted cash (current and noncurrent) on the Company’s consolidated balance sheets.

Marketable securities

The Company’s marketable securities, which consisted of debt securities as of December 31, 2018, are classified

as available-for-sale and

are reported at fair value. Unrealized gains and losses

on available-for-sale debt

securities are reported as a component of accumulated other comprehensive income (loss) in stockholders’ equity (deficit). Realized gains and losses and declines in value determined to be other than temporary are based on the specific identification method and are included as a component of other income (expense), net in the consolidated statements of operations and comprehensive loss.

The Company evaluates its marketable securities with unrealized losses for other-than-temporary impairment. When assessing marketable securities for other-than-temporary declines in value, the Company considers such factors as, among other things, how significant the decline in value is as a percentage of the original cost, how long the market value of the investment has been less than its original cost, the Company’s ability and intent to retain the investment for a period of time sufficient to allow for any anticipated recovery in fair value and market conditions in general. If any adjustment to fair value reflects a decline in the value of the investment that the Company considers to be “other than temporary,” the Company reduces the investment to fair value through a charge to the statement of operations and comprehensive loss. No such adjustments were necessary during the periods presented.

Fair value measurements

•

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

•

The Company’s cash equivalents and marketable securities are carried at fair value, determined according to the fair value hierarchy described above (see Note 3). The carrying values of the Company’s tenant receivable, accounts payable and accrued expenses approximate their fair values due to the short-term nature of these assets and liabilities.

Deferred rent

Payment escalations, rent holidays and other lease incentives that may be included in lease agreements are accrued or deferred as appropriate such that rent expense for each lease is recognized on a straight-line basis over the respective lease term. Adjustments for such items are recorded as deferred rent and amortized over the respective lease terms.

Property and equipment

Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation and amortization expense is recognized using the straight-line method over the estimated useful life of each asset as follows:



		Estimated useful life
Laboratory equipment		5 years
Computer equipment and software		3 years
Furniture and fixtures		5 years
Leasehold improvements		Shorter of remaining life of lease or useful life

Costs for capital assets not yet placed into service are capitalized as

construction-in-progress

and depreciated once placed into service. Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation and amortization are removed from the accounts and any resulting gain or loss is included in loss from operations. Expenditures for repairs and maintenance which do not improve or extend the life of the respective assets are charged to expense as incurred.

Impairment of long-lived assets

Long-lived assets consist of property and equipment. The Company evaluates the recoverability of its long-lived assets when circumstances indicate that an event of impairment may have occurred. The Company recognizes an impairment loss only if the carrying amount of a long-lived asset is not recoverable based on its undiscounted future cash flows. Impairment is measured based on the difference between the carrying value of the related assets and the fair value of such assets. The Company did not record any impairment losses on long-lived assets during the years ended December 31, 2018 or 2019.

Classification and accretion of convertible preferred stock

The Company’s convertible preferred stock is classified outside of stockholders’ equity (deficit) on the consolidated balance sheets because the holders of such shares have redemption rights in the event of a deemed liquidation that, in certain situations, is not solely within the control of the Company and would require the redemption of the then-outstanding convertible preferred stock. A deemed liquidation includes Liquidation Events as that term is defined in Note 6. The Company’s Series A and Series B convertible preferred stock are not redeemable, except in the event of a deemed liquidation (see Note 6). Because the occurrence of a deemed liquidation event is not currently probable, the carrying values of the convertible preferred stock are not being accreted to their redemption values. If a deemed liquidation event became probable, the carrying values of the convertible preferred stock would be accreted to redemption values.

Segment information

The Company has determined that its chief executive officer is the chief operating decision maker (“CODM”). The CODM reviews financial information presented on a consolidated basis. Resource allocation decisions are made by the CODM based on consolidated results. There are no segment managers who are held accountable by the CODM for operations, operating results, and planning for levels or components below the consolidated unit level. As such, the Company has concluded that it operates as one segment. All long-lived assets are located in the United States.

Revenue recognition

To date, the Company has derived its revenue by providing services to pharmaceutical and life sciences companies. On January 1, 2019, the Company adopted ASU

2014-09,

discussed below under the heading “Recently Adopted Accounting Pronouncements”, which amended revenue recognition principles and provides a single, comprehensive set of criteria for revenue recognition across all industries. The new revenue standard provides a five-step framework whereby revenue is recognized when control of promised goods or services is transferred to a customer at an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. To determine revenue recognition for arrangements that the Company determines are within the scope of the new revenue standard, the Company performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the Company satisfies a performance obligation.

The Company only applies the five-step model to contracts when collectability of the consideration to which the Company is entitled in exchange for the goods or services it transfers to the customer is determined to be probable. Amounts are recorded as accounts receivable when the Company’s right to consideration is unconditional. The Company does not assess whether a contract has a significant financing component if the expectation at contract inception is that the period between payment by the customer and the transfer of the promised goods or services to the customer will be one year or less. The Company recognizes revenue when it satisfies its performance obligations by delivering the services to its customers in an amount that reflects the consideration to which it expects to be entitled in exchange for those services.

Amounts received prior to satisfying the revenue recognition criteria are recorded as deferred revenue on the accompanying balance sheets. Amounts expected to be recognized as revenue within 12 months of the balance sheet date are classified as current deferred revenue. The Company had no deferred revenue as of December 31, 2019. The Company expenses incremental costs of obtaining a contract as and when incurred if the expected amortization period of the asset that would have been recognized is one year or less or the amount is immaterial. As of December 31, 2019, the Company had not capitalized any costs to obtain contracts.

Research and development costs

Research and development costs are expensed as incurred. Research and development expenses consist of costs incurred in performing research and development activities, including salaries and bonuses, stock-based compensation, employee benefits, facilities costs, laboratory supplies, depreciation and amortization, manufacturing expenses and external costs of vendors engaged to conduct preclinical development activities as well as the cost of licensing technology.

Upfront payments and milestone payments made for the licensing of technology are expensed as research and development expenses in the period in which they are incurred. Advance payments for goods or services to be received in the future for use in research and development activities are recorded as prepaid expenses. The prepaid amounts are expensed as the related goods are delivered or the services are performed.

Research and manufacturing contract costs and accruals

The Company has entered into various research and development and manufacturing contracts. These agreements are generally cancelable, and related payments are recorded as the corresponding expenses are incurred. The Company records accruals for estimated ongoing costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the research studies and manufacturing activities, including the phase or completion of events, invoices received and contracted costs. Significant judgments and

estimates are made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual costs.

Patent costs

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

Stock-based compensation

The Company measures stock options with service-based vesting or performance-based vesting granted to employees,

non-employees

and directors based on the fair value on the date of grant using the Black-Scholes option-pricing model. The Company measures restricted common stock awards using the difference between the purchase price per share of the award, if any, and the fair value of the Company’s common stock at the date of grant. The Company’s board of directors values the Company’s common stock, taking into consideration its most recently available valuation of common stock performed by third parties as well as additional factors which may have changed since the date of the most recent contemporaneous valuation through the date of grant.

Compensation expense for awards with service-based vesting is generally recognized over the vesting period of the award using the straight-line method to record the expense. The Company uses the graded-vesting method to record the expense of awards with both service-based and performance-based vesting conditions, commencing once achievement of the performance condition becomes probable. The Company accounts for forfeitures of share-based awards as they occur. The Company classifies stock-based compensation expense in its consolidated statements of operations and comprehensive loss in the same manner in which the award recipient’s payroll costs are classified or in which the award recipient’s service payments are classified.

Prior to the adoption of ASU

2018-07

on January 1, 2019 discussed below, the Company measured the fair value of stock-based awards granted to

non-employees

on the date that the related service was complete, which was generally the vesting date of the award. Prior to the service completion date, compensation expense was recognized over the period during which services were rendered by such

non-employees.

At the end of each financial reporting period prior to the service completion date, the fair value of the unvested awards was remeasured using the then-current fair value of the Company’s common stock and updated assumption inputs in the Black-Scholes option-pricing model for options or the then-current fair value of the Company’s common stock for restricted common stock awards.

Comprehensive loss

Comprehensive loss includes net loss as well as other changes in stockholders’ equity (deficit) that result from transactions and economic events other than those with stockholders. For the years ended December 31, 2018 and 2019, the Company’s only element of other comprehensive loss was unrealized gains (losses) on marketable securities.

Income taxes

The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the consolidated financial statements or in the Company’s tax returns. Deferred tax assets and liabilities are determined on the basis of the differences between the financial statements and tax basis of assets and

liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies.

The Company accounts for uncertainty in income taxes recognized in the consolidated financial statements by applying

a two-step process

to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is

deemed more-likely-than-not to

be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the consolidated financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties. The Company’s policy is to recognize interest and/or penalties related to income tax matters in income tax expense. The Company had accrued no amounts for interest and penalties on its consolidated balance sheets at December 31, 2018 and 2019.

Net loss per share

The Company follows the

two-class

method when computing net income (loss) per share as the Company has issued shares that meet the definition of participating securities. The

two-class

method determines net income (loss) per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The

two-class

method requires income (loss) available to common stockholders for the period to be allocated between common stock and participating securities based upon their respective rights to share in the earnings as if all income (loss) for the period had been distributed.

Basic net income (loss) per share attributable to common stockholders is computed by dividing net income (loss) attributable to common stockholders by the weighted average number of common shares outstanding for the period. Diluted net income (loss) per share attributable to common stockholders is computed by adjusting net income (loss) attributable to common stockholders to reallocate undistributed earnings based on the potential impact of dilutive securities. Diluted net income (loss) per share attributable to common stockholders is computed by dividing the diluted net income (loss) attributable to common stockholders by the weighted average number of common shares outstanding for the period, including potential dilutive common shares.

The Company’s participating securities contractually entitle the holders of such shares to participate in dividends but do not contractually require the holders of such shares to participate in losses of the Company. Accordingly, in periods in which the Company reports a net loss, such losses are not allocated to such participating securities. In periods in which the Company reports a net loss attributable to common stockholders, diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive. The Company reported a net loss attributable to common stockholders for the years ended December 31, 2018 and 2019.

Recently adopted accounting pronouncements

In May 2014, the FASB issued ASU

2014-09,

Revenue from Contracts with Customers (Topic 606), which supersedes all existing revenue recognition requirements, including most industry-specific guidance. The new standard requires a company to recognize revenue when it transfers goods or services to customers in an amount that reflects the consideration that the Company expects to receive for those goods or services. The FASB has subsequently issued several amendments to ASU

2014-09

that have the same effective date and transition date. For public entities, the guidance was effective for annual reporting periods beginning after December 15, 2017 and for interim periods within that reporting period. For nonpublic entities, the guidance is effective for annual reporting periods beginning after December 15, 2018. The Company adopted ASU

2014-09

on January 1, 2019 using the modified retrospective transition method. The adoption did not have an impact on its consolidated financial statements.

In June 2018, the FASB issued ASU

2018-07,

Compensation-Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting. The new standard largely aligns the accounting for share-based payment awards issued to employees and nonemployees by expanding the scope of ASC 718 to apply to nonemployee share-based transactions, as long as the transaction is not effectively a form of financing. For public entities,

ASU 2018-07 was

required to be adopted for annual periods beginning after December 15, 2018, including interim periods within those fiscal years.

For non-public entities,

ASU 2018-07 is

effective for annual periods beginning after December 15, 2019. Early adoption is permitted for all entities but no earlier than the Company’s adoption of

ASU 2014-09. The

Company early

adopted ASU 2018-07 on

January 1, 2019 and the adoption did not have a material impact on the Company’s consolidated financial statements.

In August 2018, the FASB issued ASU

2018-13,

2018-13

is effective for all entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. The Company adopted ASU

2018-03

on January 1, 2020 and the adoption did not have a material impact on its consolidated financial statements.

Recently issued accounting pronouncements

In February 2016, the FASB issued ASU

2016-02,

2018-11,

2019-10,

which deferred the effective date for nonpublic

entities to annual reporting periods beginning after December 15, 2020, and interim periods within fiscal years beginning after December 15, 2021. Early adoption continues to be allowed. The Company will adopt ASU

2016-02

right-of-use

assets, however, the Company has not completed its assessment.

In June 2016, the FASB issued ASU

2016-13,

Financial Instruments – Credit Losses (Topic 326). The new standard adjusts the accounting for assets held at amortized costs basis, including marketable securities accounted for as

available-for-sale.

2019-10,

Fair Value of Financial Assets

9 Months Ended

12 Months Ended

Sep. 30, 2020

Dec. 31, 2019

Fair Value Disclosures [Abstract]

Fair Value of Financial Assets

3. Fair Value of Financial Assets

The Company did not have marketable securities at December 31, 2019. As of September 30, 2020, marketable securities by security type consisted of the following:


	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
	(in thousands)
U.S. treasury securities	$	132,184	$	16	$	—	$	132,200
U.S. government agency bonds		11,995		2		—		11,997
Commercial paper		59,891		—		—		59,891
Corporate debt securities		17,665		8		—		17,673

Totals	$	221,735	$	26	$	—	$	221,761

As of September 30, 2020, marketable securities consisted of investments that mature within one year.

The following tables present the Company’s assets that are measured at fair value on a recurring basis and indicate the level within the fair value hierarchy of the valuation techniques the Company utilized to determine such fair value, which is described further within Note 2, Summary of Significant Accounting Policies:



	Fair Value Measurements at December 31, 2019 Using:
	Level 1		Level 2		Level 3		Total
	(in thousands)
Cash equivalents:
Money market funds	$	15,076	$	—	$	—	$	15,076

Totals	$	15,076	$	—	$	—	$	15,076



	Fair Value Measurements at September 30, 2020 Using:
	Level 1		Level 2		Level 3		Total
	(in thousands)
Cash equivalents:
Money market funds	$	57,394	$	—	$	—	$	57,394
Marketable securities:
U.S. treasury securities		—		132,200		—		132,200
U.S. government agency bonds		—		11,997		—		11,997
Commercial paper		—		59,891		—		59,891
Corporate debt securities		—		17,673		—		17,673

Totals	$	57,394	$	221,761	$	—	$	279,155

Money market funds were valued based on quoted market prices, which represent a Level 1 measurement within the fair value hierarchy. The Company’s marketable securities, which consisted of U.S. treasury securities, U.S. government agency bonds, commercial paper and corporate debt securities were valued using quoted prices in active markets for similar securities, which represent a Level 2 measurement within the fair value hierarchy.

3. Marketable securities and fair value measurements

Marketable securities by security type consisted of the following:



	December 31, 2018
(in thousands)	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair value
U.S. treasury bills and notes	$	67,574	$	—	$	(9	)	$	67,565

	$	67,574	$	—	$	(9	)	$	67,565

The Company did not have marketable securities as of December 31, 2019.

Summary of Significant Accounting Policies:



	Fair value measurements at December 31, 2018 using:
(in thousands)	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	7,244	$	—	$	—	$	7,244
Marketable securities
U.S. treasury bills and notes		—		67,565		—		67,565

Totals	$	7,244	$	67,565	$	—	$	74,809



	Fair value measurements at December 31, 2019 using:
(in thousands)	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	15,076	$	—	$	—	$	15,076

Totals	$	15,076	$	—	$	—	$	15,076

U.S. government money market funds were valued by the Company based on quoted market prices, which represent a Level 1 measurement within the fair value hierarchy. U.S. treasury bills and notes were valued by the Company using quoted prices in active markets for similar securities, which represent a Level 2 measurement within the fair value hierarchy. During the years ended December 31, 2018 and 2019, there were no transfers between Level 1, Level 2 and Level 3.

- 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

Property and equipment, net

12 Months Ended

Dec. 31, 2019

Property, Plant and Equipment [Abstract]

Property and equipment, net

4. Property and equipment, net

Property and equipment, net consisted of the following:



	December 31,
(in thousands)	2018			2019
Laboratory equipment	$	3,053		$	5,029
Computer equipment and software		261			740
Furniture and fixtures		—			826
Leasehold improvements		1,561			12,993
Construction in progress		—			4,487

		4,875			24,075
Less: Accumulated depreciation and amortization		(389	)		(2,230	)

	$	4,486		$	21,845

Depreciation and amortization expense for the years ended December 31, 2018 and 2019 was $0.3 million and $1.9 million, respectively. At December 31, 2019, construction in progress was related to the

build-out

of leasehold improvements in the Company’s new facility.

Accrued Expenses and Other Current Liabilities

9 Months Ended

12 Months Ended

Sep. 30, 2020

Dec. 31, 2019

Payables and Accruals [Abstract]

Accrued Expenses and Other Current Liabilities

4. Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following:



	December 31, 2019		September 30, 2020
	(in thousands)
Accrued employee compensation and benefits	$	3,255	$	3,798
Accrued external research and development expenses		1,344		2,037
Accrued professional fees		619		890
Deferred rent		1,370		1,380
Other		319		640

	$	6,907	$	8,745

5. Accrued expenses

Accrued expenses consisted of the following:



	December 31,
(in thousands)	2018		2019
Accrued employee compensation and benefits	$	2,572	$	3,255
Accrued external research and development expenses		1,284		1,344
Accrued professional fees		102		619
Deferred rent		4		1,370
Other		912		319

	$	4,874	$	6,907

Convertible Preferred Stock

9 Months Ended

12 Months Ended

Sep. 30, 2020

Dec. 31, 2019

Temporary Equity Disclosure [Abstract]

Convertible Preferred Stock

5. Convertible Preferred Stock

The Company had issued Series A convertible preferred stock (the “Series A”), Series B convertible preferred stock (the “Series B”) and Series C convertible preferred stock (the “Series C”). Collectively the Series A, Series B and Series C are referred to as the Preferred Stock.

On January 9, 2020, the Company issued and sold 19,936,296 shares of Series C at a price of $5.5914 per share for gross proceeds of $111.5 million. The Company incurred issuance costs in connection with this transaction of $2.6 million.

Upon the closing of the IPO in June 2020, the Company’s Preferred Stock automatically converted into 27,094,085 shares of common stock.

6. Convertible preferred stock

The Company has issued Series A convertible preferred stock (the “Series A”), Series B convertible preferred stock (the “Series B”) and Series C convertible preferred stock (the “Series C”). Collectively the Series A, Series B and Series C are referred to as the Preferred Stock. On February 22, 2018, the Company issued and sold 10,974,644 shares of Series B at a price of $9.1457 per share for gross proceeds of $100.4 million. The Company incurred issuance costs in connection with this transaction of $0.2 million.

On January 9, 2020 (unaudited), the Company issued and sold 19,936,296 shares of Series C at a price of $5.5914 per share for gross proceeds of $111.5 million. The Company incurred issuance costs in connection with this transaction of $2.6 million.

Upon issuance of each class of Preferred Stock, the Company assessed the embedded conversion and liquidation features of the shares and determined that such features did not require the Company to separately account for these features. The Company also concluded that no beneficial conversion feature existed on the issuance date of each class of Preferred Stock.

Preferred Stock consisted of the following at December 31, 2018 and 2019:



(in thousands except share amounts)	Preferred stock authorized		Preferred stock issued and outstanding		Carrying value		Liquidation preference		Common stock issuable upon conversion
Series A Preferred Stock		15,451,020		15,451,020	$	15,404	$	15,451		8,747,675
Series B Preferred Stock		10,974,644		10,974,644		100,189		100,371		6,213,352	(1)

		26,425,664		26,425,664	$	115,593	$	115,822		14,961,027	(1)

(1)

Upon issuance and sale of the Series C in January 2020 (see Note 13), the 10,974,644 outstanding shares of Series B became convertible into 7,059,406 shares of common stock and the 26,425,664 outstanding shares of Preferred Stock became convertible into 15,807,081 shares of common stock.

The holders of Preferred Stock have the following rights and preferences:

Voting

The holders of Preferred Stock are entitled to vote, together with the holders of common stock, on matters submitted to stockholders for a vote. The holders of Preferred Stock are entitled to the number of votes equal to the number of shares of common stock into which each such share of Preferred Stock could convert. In addition, the holders of Series A, voting exclusively and as a separate class, are entitled to elect two directors of the Company. The holders of Series B, voting exclusively and as a separate class, are entitled to elect one director of the Company.

Conversion

Each share of Preferred Stock is convertible at the option of the holder at any time after the date of issuance. Each share of Preferred Stock will be automatically converted into shares of common stock at the applicable conversion ratio then in effect upon the closing of a firm commitment public offering of common stock with a price of at least $8.0496 per share and at least $40.0 million of gross proceeds to the Company. Shares of Series A will be automatically converted into shares of common stock at the applicable conversion ratio then in effect upon written consent of the holders of at least a majority of the then-outstanding shares of Series A. Shares of Series B will be automatically converted into shares of common stock at the applicable conversion ratio then in effect upon written consent of the holders of at least 57% of the then-outstanding shares of Series B. Shares of Series C will be automatically converted into shares of common stock at the applicable conversion ratio then in effect upon written consent of the holders of at least a majority of the then-outstanding shares of Series C.

The conversion ratio of each series of Preferred Stock is determined by dividing the Original Issue Price of each series by the Conversion Price of each series. The Original Issue Price is $1.00 per share for Series A and $9.1457 per share for Series B. The Conversion Price at issuance was $1.7663 per share for Series A and $16.1540 per share (when rounded to the nearest

ten-thousandth)

for Series B, subject to appropriate adjustment in the event of any stock split, stock dividend, combination or other similar recapitalization and other adjustments as set forth in the Company’s certificate of incorporation, as amended and restated. As a result, as of December 31, 2018 and 2019, each outstanding share of Series A and Series B was convertible into common stock on a

1.7663-for-one

basis. The Original Issue Price is $5.5914 per share for Series C and the Conversion Price of the Series C is $9.8761 per share (when rounded to the nearest

ten-thousandth),

subject to appropriate adjustment in the event of any stock split, stock dividend, combination or other similar recapitalization and other adjustments as set forth in the Company’s certificate of incorporation, as amended and restated. As a result, each outstanding share of Series C is convertible into common stock on a

1.7663-for-one

basis.

Upon the issuance and sale of Series C in January 2020 at the Original Issue Price of $5.5914 per share, the Conversion Price of the Series B was adjusted to $14.2180 per share (when rounded to the nearest

ten-thousandth)

(see Note 13).

Dividends

The holders of Preferred Stock are entitled to receive noncumulative dividends if and when declared by the Company’s board of directors at a rate of 6.0% of the Original Issuance Price per share of each series of Preferred Stock (subject to appropriate adjustment in the event of any stock split, stock dividend, combination or other similar recapitalization with respect to such shares) per annum. The Company may not declare, pay or set aside any dividends on shares of any other series of capital stock of the Company, other than dividends on common stock payable in common stock, unless the holders of the Preferred Stock first receive, or simultaneously receive, a dividend on each outstanding share of Preferred Stock in an amount equal to the greater of (i) 6.0% of the Original Issuance Price of each series of Preferred Stock (subject to appropriate adjustment in the event of any stock split, stock dividend, combination or other similar recapitalization with respect to such shares) per annum from the date of issuance of such shares, and (ii) (A) in the case of a dividend on common stock or any class or series of stock that is convertible into common stock, that dividend per share of Preferred Stock as would equal the product of (1) the dividend payable on each share of such class or series determined, if applicable, as if all shares of such class or series had been converted into common stock and (2) the number of shares of common stock issuable upon conversion of each share of Preferred Stock, or (B) in the case of a dividend on any class or series that is not convertible into common stock, at a rate per share of Preferred Stock determined by (1) dividing the amount of the dividend payable on each share of such class or series of capital stock by the Original Issue Price of such class or series of capital stock (subject to appropriate adjustment in the event of any stock dividend, stock split, combination of or other similar recapitalization affecting such shares) and (2) multiplying such fraction by an amount equal to the Original Issue Price of each series of Preferred Stock. If the Company declares, pays or sets aside, on the same date, a dividend on shares of more than one class or series of capital stock of the Company, the dividend payable to the holders of the Preferred Stock shall be calculated based upon the dividend on the class or series of capital stock that would result in the highest Preferred Stock dividend. No dividends were declared or paid during the years ended December 31, 2018 or 2019.

Liquidation

In the event of any voluntary or involuntary liquidation, dissolution

or winding-up of

the Company or Liquidating Event (as described below), the holders of shares of Preferred Stock will receive, in preference to the common stockholders, an amount equal to the greater of (i) the Original Issue Price per share of the respective share of Preferred Stock, plus all dividends declared but unpaid on such shares, or (ii) the amount the holders would receive if the Preferred Stock were converted into common stock prior to such liquidation event. In the event that the assets available for distribution to the Company’s stockholders are not sufficient to permit payment to the holders of Preferred Stock in the full amount to which they are entitled, the assets available for distribution will be distributed on a pro rata basis among the holders of the Preferred Stock. After the payment of all preferential amounts to the holders of the Preferred Stock then, to the extent available, the remaining assets available for distribution shall be distributed among the holders of the common stock ratably based on the number of shares of common stock held by each holder.

Unless the holders of (i) at least a majority of the then-outstanding shares of Preferred Stock, voting together as a single class on

an as-converted basis,

(ii) at least 57% of the then-outstanding shares of Series B, voting together as a separate series on an

as-converted

basis, and (iii) at least a majority of the then-outstanding shares of Series C, voting together as a separate series on an

as-converted

basis, elect otherwise, a Liquidating Event shall include a merger or consolidation (other than one in which stockholders of the Company own a majority by voting power of the outstanding shares of the surviving or acquiring corporation) or a sale, lease, transfer, exclusive license or other disposition of all or substantially all of the assets of the Company.

Common stock

12 Months Ended

Dec. 31, 2019

Common stock [Abstract]

Common stock

7. Common stock

The voting, dividend and liquidation rights of the holders of the Company’s common stock are subject to and qualified by the rights, powers and preferences of the holders of the Preferred Stock set forth above. Each share of common stock entitles the holder to one vote, together with the holders of the Preferred Stock, on all matters submitted to the stockholders for a vote.

Equity

9 Months Ended

Sep. 30, 2020

Equity [Abstract]

Equity

6. Equity

As of September 30, 2020, the Company’s amended and restated certificate of incorporation authorizes the Company to issue 150,000,000 shares of common stock, par value $0.0001 per share, and 5,000,000 shares of preferred stock, par value $0.0001 per share, all of which preferred stock is undesignated.

Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders. Common stockholders are not entitled to receive dividends, unless declared by the board of directors.

Stock-based compensation

12 Months Ended

Dec. 31, 2019

License Agreements Disclosure [Abstract]

Stock-based compensation

8. Stock-based compensation

2017 Stock Incentive Plan

The Company’s 2017 Stock Incentive Plan (the “2017 Plan”) provides for the Company to grant incentive stock options or nonstatutory stock options, restricted stock, restricted stock units and other equity awards to employees, directors and consultants of the Company. The 2017 Plan is administered by the board of directors or, at the discretion of the board of directors, by a committee of the board of directors. The exercise prices, vesting and other restrictions on any award under the 2017 Plan are determined at the discretion of the board of directors, or its committee if so delegated.

Stock options granted under the 2017 Plan with service-based vesting conditions generally vest over four years and expire after ten years. The exercise price for stock options granted is not less than the fair value of common stock as determined by the board of directors as of the date of grant.

The total number of shares of common stock that may be issued under the 2017 Plan was 8,407,405 shares as of December 31, 2019, of which 773,652 shares remained available for future issuance. Shares that are expired, terminated, surrendered or canceled without having been fully exercised will be available for future awards under the 2017 Plan.

Stock option valuation

The fair value of stock option grants is estimated using the Black-Scholes option-pricing model. The Company historically has been a private company and lacks company-specific historical and implied volatility information. Therefore, it estimates its expected stock volatility based on the historical volatility of a publicly traded set of peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded stock price. For options with service-based vesting conditions, the expected term of the Company’s stock options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future.

The following table presents, on a weighted average basis, the assumptions used in the Black-Scholes option-pricing model to determine the fair value of stock options granted:

Stock options



	Year ended December 31,
	2018		2019

Risk-free interest rate		2.70%		2.00%
Expected volatility		76.0%		75.7%
Expected dividend yield		—		—
Expected term (in years)		6.1		6.0

The following table summarizes the Company’s stock option activity since December 31, 2018:



	Number of shares			Weighted average exercise price		Weighted average contractual term (in years)		Aggregate intrinsic value (in thousands)
Outstanding as of December 31, 2018		2,784,581		$	4.05		9.4	$	1,403
Granted		1,200,954			5.92
Exercised		(34,740	)		2.88
Forfeited		(576,911	)		3.89

Outstanding as of December 31, 2019		3,373,884		$	4.76		8.79	$	8,492

Vested and expected to vest as of December 31, 2019		3,373,884		$	4.76		8.79	$	8,492
Options exercisable as of December 31, 2019		852,647		$	4.05		8.38	$	2,735

The aggregate intrinsic value of stock 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 strike prices lower than the fair value of the Company’s common stock.

The weighted average grant-date fair value of awards granted during the years ended December 31, 2018 and 2019 was $3.59 per share and $4.46 per share, respectively.

There were no stock options exercised during the year ended December 31, 2018. The total intrinsic value of stock options exercised during the year ended December 31, 2019 was $0.1 million.

Restricted common stock

The Company issued 394,213 shares of service-based restricted common stock awards during the year ended December 31, 2018. The Company did not issue any restricted common stock awards during the year ended December 31, 2019.

The following table summarizes the Company’s restricted common stock activity since December 31, 2018:



	Shares			Weighted average grant date fair value
Unvested restricted common stock as of December 31, 2018		2,819,949		$	1.24
Issued		—			—
Vested		(1,055,997	)		1.30
Forfeited		(58,764	)		0.73

Unvested restricted common stock as of December 31, 2019		1,705,188		$	1.22

The total fair value of restricted common stock vested during the years ended December 31, 2018 and 2019 was approximately $1.2 million and $7.0 million, respectively.

Stock-Based Compensation

The Company records compensation cost for all share-based payment arrangements, including employee, director and consultant stock options and restricted common stock. The Company recorded stock-based compensation expense in the following expense categories of its consolidated statements of operations and comprehensive loss:



	Year ended December 31,
(in thousands)	2018		2019

Research and development expenses	$	2,093	$	2,753
General and administrative expenses		1,395		1,454

	$	3,488	$	4,207

As of December 31, 2019, total unrecognized compensation cost related to unvested stock-based awards was $10.9 million, which is expected to be recognized over a weighted average period of 2.4 years.

Income taxes

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Income taxes

9. Income taxes

For the years ended December 31, 2018 and 2019, the Company recorded no income tax benefits for the net operating losses incurred or for the research and development tax credits generated in each year, due to its uncertainty of realizing a benefit from those items. All of the Company’s operating losses since inception have been generated in the United States.

A reconciliation of the U.S. federal statutory income tax rate to the Company’s effective income tax rate is as follows:



	Year ended December 31,
	2018		2019
Federal statutory income tax rate		(21.0)%		(21.0)%
State income taxes, net of federal benefit		(5.6)		(5.9)
Federal and state research and development tax credits		(6.5)		(5.1)
Stock-based compensation expense		1.6		1.0
Other		—		0.2
Change in deferred tax asset valuation allowance		31.5		30.8

Effective income tax rate		0.0%		0.0%

Net deferred tax assets as of December 31, 2018 and 2019 consisted of the following:



	December 31,
(in thousands)	2018			2019
Deferred tax assets:
Net operating loss carryforwards	$	10,183		$	25,023
Research and development tax credit carryforwards		2,878			5,998
Deferred rent		—			4,740
Other		1,701			1,469

Total deferred tax assets		14,762			37,230
Deferred tax liabilities:
Property and equipment		(516	)		(4,117	)

Total deferred tax liabilities		(516	)		(4,117	)

Valuation allowance		(14,246	)		(33,113	)

Net deferred tax assets	$	—		$	—

As of December 31, 2019, the Company had federal net operating loss carryforwards of $91.9 million, which may be available to offset future taxable income, of which $8.2 million of the total net operating loss carryforwards expire at various dates beginning in 2036, while the remaining $83.7 million do not expire but may be limited in their usage to an annual deduction equal to 80% of annual taxable income. As of December 31, 2019, the Company had state net operating loss carryforwards of $90.6 million, which may be available to offset future taxable income and expire at various dates beginning in 2036. In addition, as of December 31, 2019, the Company also had federal and state research and development tax credit carryforwards of $4.0 million and $2.5 million, respectively, which may be available to reduce future tax liabilities and expire at various dates beginning in 2036 and 2032, respectively.

Utilization of the U.S. federal and state net operating loss carryforwards and research and development tax credit carryforwards may be subject to a substantial annual limitation under Section 382 and Section 383 of the

Internal Revenue Code of 1986, and corresponding provisions of state law, due to ownership changes that have occurred previously or that could occur in the future. These ownership changes may limit the amount of carryforwards that can be utilized annually to offset future taxable income and tax liabilities. In general, an ownership change, as defined by Section 382, results from transactions increasing the ownership of certain stockholders or public groups in the stock of a corporation by more than 50% over a three-year period. The Company has not conducted a study to assess whether a change of control has occurred or whether there have been multiple changes of control since inception due to the significant complexity and cost associated with such a study. If the Company has experienced a change of control, as defined by Section 382, at any time since inception, utilization of the net operating loss carryforwards or research and development tax credit carryforwards may be subject to an annual limitation, which is determined by first multiplying the value of the Company’s stock at the time of the ownership change by the applicable

long-term tax-exempt rate,

and then could be subject to additional adjustments. Any limitation may result in expiration of a portion of the net operating loss carryforwards or research and development tax credit carryforwards before their utilization. Further, until a study is completed by the Company and any limitation is known, no amounts are being presented as an uncertain tax position.

The Company has evaluated the positive and negative evidence bearing upon its ability to realize the deferred tax assets, which consist primarily of net operating loss carryforwards and research and development tax credit carryforwards. Management has considered the Company’s history of cumulative net losses incurred since inception, estimated future taxable income and prudent and feasible tax planning strategies and has concluded that it is more likely than not that the Company will not realize the benefits of federal and state net deferred tax assets. Accordingly, a full valuation allowance has been established against the net deferred tax assets as of December 31, 2018 and 2019. The Company reevaluates the positive and negative evidence at each reporting period.

The changes in the valuation allowance for deferred tax assets during the year ended December 31, 2018 and 2019 related primarily to the increases in net operating loss carryforwards and research and development tax credit carryforwards. The changes in the valuation allowance for 2018 and 2019 were as follows:



	Year ended December 31,
(in thousands)	2018		2019
Valuation allowance as of beginning of year	$	2,976	$	14,246
Increases recorded to income tax provision		11,270		18,867

Valuation allowance as of end of year	$	14,246	$	33,113

The Company assesses the uncertainty in its income tax positions to determine whether a tax position of the Company is more likely than not to be sustained upon examination, including resolution of any related appeals of litigation processes, based on the technical merits of the position. For tax positions meeting

the more-likely-than-not threshold,

the tax amount recognized in the financial statements is reduced by the largest benefit that has a greater than 50% likelihood of being realized upon the ultimate settlement with the relevant taxing authority. No reserve for uncertain tax positions or related interest and penalties has been recorded at December 31, 2018 and 2019.

The Company files income tax returns as prescribed by the tax laws of the jurisdictions in which it operates. In the normal course of business, the Company is subject to examination by federal and state jurisdictions, where applicable. There are currently no pending tax examinations. The Company is open to future tax examination under statute from 2016 to the present.

- 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

License Agreements

12 Months Ended

Dec. 31, 2019

License Agreements

10. License agreements

NIH

The Company has an agreement with the U.S. Department of Health and Human Services, as represented by The National Heart, Lung, and Blood Institute, an Institute of the National Institutes of Health (“NIH”), entered into in 2017, pursuant to which NIH granted the Company a

non-exclusive

license, with the right to grant sublicenses, under certain NIH intellectual property related to the Company’s ceDNA construct. In July 2019, the agreement was amended to include Association Institut de Myologie, Universite Pierre et Marie Curie, Centre National de la Recherche Scientifique, and Inserm Transfert SA, collectively referred to as the French Institutions, as a licensor.

The Company is obligated to make future milestone payments of up to $0.4 million per licensed product upon the achievement of specified milestones as well as royalties on a licensed

product-by-licensed

product and

country-by-country basis

of a low single digit percentage of annual net sales of licensed products. The Company is obligated to pay a high single-digit royalty percentage of all sublicensing income. The royalties on net sales may be reduced by up to 25% in certain circumstances as defined in the agreement. The Company’s royalty obligation expires on a

licensed product-by-licensed product

and

country-by-country basis

upon the expiration of the

last-to-expire

licensed intellectual property rights in such country. Additionally, the Company is required to reimburse the French Institutions for a portion of certain past and ongoing patent related expenses related to the licensed technology. The agreement requires the Company to use reasonable commercial efforts to meet certain performance milestones and execute a commercial development plan within specified timeframes.

Unless terminated earlier, the agreement remains in effect until the last to expire of the licensed patent rights on a licensed

product-by-licensed

product and

country-by-country basis.

NIH and the French Institutions may terminate the agreement if the Company fails to perform its material obligations, including but not limited to its failure to meet the applicable performance milestones despite using commercially reasonable efforts, and has not remediated such deficiency within a specified time period. NIH and the French Institutions can terminate the agreement in the event the Company becomes insolvent, files a petition in bankruptcy, has such a petition filed against it, or determines to file a petition in bankruptcy. In addition, NIH and the French Institutions may terminate the agreement in the event of a material breach by the Company and failure to cure such breach within a certain period of time. The company is currently in compliance with the terms of the agreement. The Company can voluntarily terminate the agreement with prior notice to NIH and the French Institutions.

During each of the years ended December 31, 2018 and 2019, the Company recorded research and development expense of less than $0.1 million under this agreement.

UMass

The Company has an agreement with the University of Massachusetts as represented by and solely on behalf of its Medical School (“UMass”), entered into in 2017, pursuant to which UMass granted the Company an exclusive license, with the right to grant sublicenses, under the UMass intellectual property related to the Company’s ceDNA construct.

The Company is obligated to make future milestone payments of up to $0.8 million per licensed product upon the achievement of specified milestones as well as royalties on a licensed

product-by-licensed

product and

country-by-country basis

of a low single digit percentage of annual net sales of licensed products, subject to annual minimum royalties as defined in the agreement. Additionally, the Company has agreed to pay a

low-to-mid

single-digit royalty percentage of all sublicensing income, which will vary depending on when the sublicense agreement to a third party was executed. The milestone payments are

non-refundable

and

non-creditable

against any other payments due to UMass under the agreement. The Company’s royalty obligation expires on a

licensed product-by-licensed product

and

country-by-country basis

upon the expiration of the

last-to-expire

licensed intellectual property rights in such country. The agreement requires the Company to use diligent efforts to meet certain performance milestones within specified timeframes.

As part of the arrangement, the Company agreed to issue 125,677 shares of its common stock to UMass. The Company recorded $0.1 million as research and development expense and

additional-paid-in

capital at the time of the agreement in 2017, representing the fair value of the common stock at that time. The shares were issued in August 2019.

Unless terminated earlier, the agreement will continue until the

last-to-expire

valid claim of the licensed patents. UMass may terminate the agreement if the Company fails to perform its material obligations, including but not limited to its failure to meet the applicable performance milestones despite using commercially reasonable efforts, and has not remediated such deficiency within a specified time period or negotiated a revised performance timeline. UMass can terminate the agreement if the Company fails to make any payments within a specified period after receiving written notice of such failure, or in the event of a material breach by the Company and failure to cure such breach within a certain period of time. The Company is currently in compliance with the terms of the agreement. The Company can voluntarily terminate the agreement with prior notice to UMass.

During each of the years ended December 31, 2018 and 2019, the Company recorded research and development expense of less than $0.1 million under this agreement.

Other license agreements

The Company has other license agreements under which it may become subject to future additional fees and milestone payments.

Stock-Based Awards

9 Months Ended

Sep. 30, 2020

Commitments and Contingencies Disclosure [Abstract]

Stock-Based Awards

7. Stock-Based Awards

Stock incentive plans

The Company’s 2017 Stock Incentive Plan (the “2017 Plan”) provided for the Company to grant incentive stock options or nonstatutory stock options, restricted stock, restricted stock units and other equity awards to employees, directors and consultants of the Company. In January 2020, the number of shares of common stock authorized for issuance under the 2017 Plan was increased from 8,407,405 shares to 10,275,717 shares.

In May 2020 the Company’s board of directors adopted, and in June 2020 the Company’s stockholders approved, the 2020 Stock Incentive Plan (the “2020 Plan” and, together with the 2017 Plan the “Plans”), which became effective on June 11, 2020. The 2020 Plan provides for the grant of incentive stock options, nonstatutory stock options, stock appreciation rights, restricted stock awards, restricted stock units and other stock-based awards. Upon effectiveness of the 2020 Plan, the number of shares of common stock reserved for issuance under the 2020 Plan was the sum of (1) 2,547,698 shares; plus (2) the number of shares (up to a maximum of 7,173,014 shares) as was equal to the sum of (x) the number of shares of common stock reserved for issuance under the 2017 Plan that remained available for grant under the 2017 Plan on June 11, 2020 and (y) the number of shares of common stock subject to outstanding awards granted under the 2017 Plan that expire, terminate or are otherwise surrendered, cancelled, forfeited or repurchased by the Company at their original issuance price pursuant to a contractual repurchase right; plus (3) an annual increase, to be added on the first day of each fiscal year, beginning with the fiscal year ending December 31, 2021 and continuing until, and including, the fiscal year ending December 31, 2030, equal to the lesser of (i) 4% of the number of shares of common stock outstanding on such date, and (ii) an amount determined by the board of directors. Upon the effectiveness of the 2020 Plan, the Company ceased granting additional awards under the 2017 Plan.

The Plans are administered by the board of directors or, at the discretion of the board of directors, by a committee of the board of directors. The exercise prices, vesting and other restrictions on any award under the Plans are determined at the discretion of the board of directors, or its committee if so delegated. Stock options granted under the Plans with service-based vesting conditions generally vest over four years and expire after ten years. The exercise price for stock options granted is not less than the fair value of common stock as of the date of grant. Prior to the Company’s IPO, fair value of common stock was determined by the board of directors. Subsequent to the IPO, fair value of common stock will be based on quoted market prices.

As of September 30, 2020, 2,640,244 shares remained available for future issuance under the 2020 Plan. Shares subject to outstanding awards granted under the Plans that expire, terminate or are otherwise surrendered, cancelled, forfeited or repurchased by the Company at their original issuance price pursuant to a contractual repurchase right will be available for future awards under the 2020 Plan.

Grant of stock options

During the nine months ended September 30, 2020, the Company granted service-based options to certain employees, directors and consultants for the purchase of 2,114,361 shares of common stock with a weighted average grant date fair value of $8.71 per share that vest over approximately four years.

During the nine months ended September 30, 2020, the Company granted performance-based options to certain employees, directors and consultants for the purchase of 717,154 shares of common stock with a weighted average grant date fair value of $3.26 per share that vest upon the achievement of specified milestones.

Employee stock purchase plan

In May 2020 the Company’s board of directors adopted, and in June 2020 the Company’s stockholders approved, the 2020 Employee Stock Purchase Plan (the “2020 ESPP”), which became effective June 11, 2020. The 2020 ESPP will be administered by the Company’s board of directors or by a committee appointed by the board of directors. The 2020 ESPP initially provides participating employees with the opportunity to purchase up to an aggregate of 481,231 shares of common stock. The number of shares of common stock reserved for issuance under the 2020 ESPP will automatically increase on the first day of each fiscal year, beginning with the fiscal year commencing on January 1, 2021 and continuing for each fiscal year until, and including the fiscal year commencing on, January 1, 2030, in an amount equal to the lowest of (1) 1,302,157 shares of common stock, (2) 1% of the number of shares of common stock outstanding on such date, and (3) an amount determined by the board of directors. No offering periods have commenced under the 2020 ESPP and 481,231 shares remain available for issuance.

Stock-based compensation

Stock-based compensation expense was classified in the statements of operations and comprehensive loss as follows:



	Three Months Ended September 30,				Nine Months Ended September 30,
	2019		2020		2019		2020
	(in thousands)
Research and development expenses	$	688	$	1,204	$	2,039	$	2,967
General and administrative expenses		392		957		1,083		2,066

	$	1,080	$	2,161	$	3,122	$	5,033

As of September 30, 2020, total unrecognized compensation cost related to unvested stock-based awards was $23.6 million, which is expected to be recognized over a weighted average period of 3.2 years. Additionally, as of September 30, 2020, the Company has unrecognized compensation cost related to unvested stock-based awards with performance-based vesting conditions for which performance has not been deemed probable of $2.3 million.

Commitments and Contingencies

9 Months Ended

12 Months Ended

Sep. 30, 2020

Dec. 31, 2019

Commitments and Contingencies

9. Commitments and Contingencies

The Company leases its office and laboratory space under a noncancelable operating lease that was entered into in August 2018, as amended in June 2020, and expires in 2029. The Company has an option to extend for one additional term of

five years

at the greater of the then-current base rent, or the then-current fair market value. The lease agreement includes provisions for a free-rent period and annual rent increases, which are accrued or deferred as appropriate such that rent expense for the lease is recognized on a straight-line basis over the lease term. The Company is responsible for real estate taxes, maintenance, and other operating expenses applicable to the leased premises. The lease provides for a tenant improvement allowance, at the cost of the lessor, not to exceed $14.7 million. Costs incurred by the Company for tenant improvements but not yet reimbursed by the landlord are presented on the accompanying consolidated balance sheets as tenant receivable. The Company posted a customary letter of credit in the amount of approximately $2.1 million as a security deposit. The letter of credit is subject to increase if the Company were to sublease any portion of the leased premises.

Rent expense for the three months ended September 30, 2019 and 2020 was $2.5 million and $1.8 million, respectively. Rent expense for the nine months ended September 30, 2019 and 2020 was $6.0 million and $5.5 million, respectively.

Future minimum lease payments as of September 30, 2020 are as follows:



Year Ending December 31,	(in thousands)
2020 (remaining 3 months)	$	1,745
2021		7,053
2022		7,251
2023		7,441
2024		7,679
Thereafter		35,451

	$	66,620

401(k) Plan

The Company has a defined-contribution plan under Section 401(k) of the Internal Revenue Code of 1986 (the “401(k) Plan”). The 401(k) Plan covers all employees who meet defined minimum age and service requirements and allows participants to defer a portion of their annual compensation on

a pre-tax basis.

In September 2020, the Company adopted a match program for employee contributions to the 401(k) Plan up to a maximum of four percent of the employee’s salary for the year ended December 31, 2021.

Indemnification agreements

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

Legal proceedings

The Company, from time to time, may be party to litigation arising in the ordinary course of business. The Company was not subject to any material legal proceedings during the three and nine months ended September 30, 2020.

11. Commitments and contingencies

The Company leases its office and laboratory space under a noncancelable operating lease that was entered into in August 2018, as amended in July 2019, and expires in 2029. The Company has an option to extend for one additional term of five years at the greater of the then-current base rent, or the then-current fair market value. The lease agreement includes provisions for a free-rent period and annual rent increases, which are accrued or deferred as appropriate such that rent expense for the lease is recognized on a straight-line basis over the lease term (see Note 2). The Company is responsible for real estate taxes, maintenance, and other operating expenses applicable to the leased premises. The lease provides for a tenant improvement allowance, at the cost of the lessor, not to exceed $14.7 million. Costs incurred by the Company for tenant improvements but not yet reimbursed by the landlord are presented on the accompanying consolidated balance sheets as tenant receivable. As of December 31, 2018 and 2019, the Company had a tenant receivable of $1.3 million and $0.4 million, respectively. The Company posted a customary letter of credit in the amount of approximately $2.1 million as a security deposit. The letter of credit is subject to increase if the Company were to sublease any portion of the leased premises.

Previously, the Company leased its office and laboratory space under noncancelable operating leases that expired during 2019.

Rent expense for the years ended December 31, 2018 and 2019 was $3.5 million and $7.9 million, respectively.

Future minimum lease payments as of December 31, 2019 are as follows:



Year ending December 31,	(in thousands)
2020	$	6,867
2021		7,053
2022		7,251
2023		7,441
2024		7,679
Thereafter		35,451

	$	71,742

401(k) Plan

a pre-tax basis.

As currently established, the Company is not required to make, and to date has not made, any contributions to the 401(k) Plan.

Indemnification agreements

Legal proceedings

The Company, from time to time, may be party to litigation arising in the ordinary course of business. The Company was not subject to any material legal proceedings during the years ended December 31, 2018 and 2019.

Net Loss per Share

9 Months Ended

12 Months Ended

Sep. 30, 2020

Dec. 31, 2019

Earnings Per Share [Abstract]

Net Loss per Share

8. Net Loss per Share

The following potential dilutive securities, presented based on amounts outstanding at each period end, have been excluded from the calculation of diluted net loss per share because including them would have had an anti-dilutive impact:



	September 30,
	2019		2020
Convertible preferred stock (as converted to common stock)		14,961,027		—
Unvested restricted common stock		1,970,209		956,718
Stock options to purchase common stock		3,171,498		5,581,717

		20,102,734		6,538,435

12. Net loss per share

Net loss per share

The Company has generated a net loss in all periods presented, therefore the basic and diluted net loss per share attributable to common stockholders are the same as the inclusion of the potentially dilutive securities would be anti-dilutive. The Company excluded the following potential common shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share attributable to common stockholders for the periods indicated:



	Year ended December 31,
	2018		2019

Convertible preferred stock (as converted to common stock)		14,961,027		14,961,027
Unvested restricted common stock		2,819,949		1,705,188
Stock options to purchase common stock		2,784,581		3,373,884

		20,565,557		20,040,099

Subsequent events

12 Months Ended

Dec. 31, 2019

Subsequent Events [Abstract]

Subsequent events

13. Subsequent events

The Company reviewed for subsequent events through April 9, 2020, the date the consolidated financial statements were issued and June 8, 2020, the date the revised consolidated financial statements were issued, to ensure that these consolidated financial statements include appropriate disclosure of events both recognized in the consolidated financial statements as of December 31, 2019 and events which occurred subsequently but were not recognized in the consolidated financial statements. The Company has concluded that no subsequent events have occurred that require disclosure, except as described below.

(a)

Issuance and sale of Series C

In January 2020, the Company issued and sold 19,936,296 shares of Series C at a price of $5.5914 per share, for gross proceeds of $111.5 million. The terms of the Series C are substantially the same as the terms of the Series A and Series B except for the liquidation preference per share, which is equal to the per share price paid. In connection with the issuance, the Company increased the number of authorized shares of Preferred Stock from 26,425,664 shares to 46,361,960 shares. Because the price per share of the Series C in this transaction was lower than the Conversion Price of the Company’s Series B, in accordance with the Company’s certificate of incorporation, as amended and restated, the Conversion Price of Series B was adjusted from $16.1540 to $14.2180 per share (when rounded to the nearest

ten-thousandth).

As a result, the 10,974,644 outstanding shares of Series B as of December 31, 2019 became convertible into 7,059,406 shares of common stock.

(b)

Increase in shares available for issuance under the 2017 Plan

In January 2020, the number of shares of common stock authorized for issuance under the 2017 Plan was increased from 8,407,405 shares to 10,275,717 shares.

(c)

Grant of stock options under the 2017 Plan

On March 5, 2020, the Company granted options with service-based vesting criteria for the purchase of an aggregate of 947,411 shares of common stock, at an exercise price of $5.16 per share. The aggregate grant-date fair value of these options was $3.4 million, which is expected to be recognized over approximately four years.

On March 5, 2020, the Company granted options with performance-based vesting criteria for the purchase of an aggregate of 717,198 shares of common stock, at an exercise price of $5.16 per share. The aggregate grant-date fair value of these options was $2.3 million, which will be recognized once it becomes probable that the milestone will be achieved and the shares will vest.

On March 31, 2020, the Company granted options with service-based vesting criteria for the purchase of an aggregate of 63,834 shares of common stock, at an exercise price of $5.25 per share. The aggregate grant-date fair value of these options was $0.2 million, which is expected to be recognized over approximately four years.

(d)

Reverse stock split

The Company’s Board of Directors and stockholders approved a

one-for-1.7663

reverse stock split of the Company’s common stock that became effective on June 5, 2020. All share and per share amounts in the consolidated financial statements and notes thereto have been retroactively adjusted for all periods presented to give effect to this reverse split and adjustment of the Preferred Stock conversion ratios.

Summary of Significant Accounting Policies (Policies)

9 Months Ended

12 Months Ended

Sep. 30, 2020

Dec. 31, 2019

Unaudited interim financial information

Use of estimates

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expenses during the reporting periods. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, the accrual of research and development expenses and stock-based compensation expense. The Company bases its estimates on historical experience, known trends and other market-specific or other relevant factors that it believes to be reasonable under the circumstances. On an ongoing basis, management evaluates its estimates, as there are changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results may differ from those estimates or assumptions.

Concentrations of credit risk and of significant suppliers

Deferred offering costs

The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated

with in-process equity

paid-in

Cash equivalents

The Company considers all highly liquid investments with a remaining maturity when purchased of three months or less to be cash equivalents.

Restricted cash

Marketable securities

The Company’s marketable securities, which consisted of debt securities as of December 31, 2018, are classified

as available-for-sale and

are reported at fair value. Unrealized gains and losses

on available-for-sale debt

Fair value measurements

•

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

•

Fair value measurements

•

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

•

The Company’s cash equivalents and marketable securities are carried at fair value, determined according to the fair value hierarchy described above (see Note 3). The carrying values of the Company’s tenant receivable, accounts payable and accrued expenses approximate their fair values due to the short-term nature of these assets and liabilities.

Deferred rent

Property and equipment



		Estimated useful life
Laboratory equipment		5 years
Computer equipment and software		3 years
Furniture and fixtures		5 years
Leasehold improvements		Shorter of remaining life of lease or useful life

Costs for capital assets not yet placed into service are capitalized as

construction-in-progress

Impairment of long-lived assets

Classification and accretion of convertible preferred stock

Segment information

Revenue recognition

To date, the Company has derived its revenue by providing services to pharmaceutical and life sciences companies. On January 1, 2019, the Company adopted ASU

2014-09,

Research and development costs

Research and manufacturing contract costs and accruals

Patent costs

Stock-based compensation

The Company measures stock options with service-based vesting or performance-based vesting granted to employees,

non-employees

Prior to the adoption of ASU

2018-07

on January 1, 2019 discussed below, the Company measured the fair value of stock-based awards granted to

non-employees

non-employees.

Comprehensive loss

Income taxes

The Company accounts for uncertainty in income taxes recognized in the consolidated financial statements by applying

a two-step process

deemed more-likely-than-not to

Net loss per share

The Company follows the

two-class

method when computing net income (loss) per share as the Company has issued shares that meet the definition of participating securities. The

two-class

Recently issued accounting pronouncements

Recently adopted accounting pronouncements

In August 2018, the FASB issued ASU

2018-13,

2018-13

is effective for all entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. The Company adopted ASU

2018-03

on January 1, 2020 and the adoption did not have a material impact on its consolidated financial statements.

Recently issued accounting pronouncements

In February 2016, the FASB issued ASU

2016-02,

2018-11,

2019-10,

2020-05,

which grants a

one-year

2016-02

right-of-use

assets, however, the Company has not completed its assessment.

In June 2016, the FASB issued ASU

2016-13,

Financial Instruments – Credit Losses (Topic 326). The new standard adjusts the accounting for assets held at amortized costs basis, including marketable securities accounted for as

available-for-sale.

2019-10,

Recently adopted accounting pronouncements

In May 2014, the FASB issued ASU

2014-09,

2014-09

on January 1, 2019 using the modified retrospective transition method. The adoption did not have an impact on its consolidated financial statements.

In June 2018, the FASB issued ASU

2018-07,

ASU 2018-07 was

required to be adopted for annual periods beginning after December 15, 2018, including interim periods within those fiscal years.

For non-public entities,

ASU 2018-07 is

effective for annual periods beginning after December 15, 2019. Early adoption is permitted for all entities but no earlier than the Company’s adoption of

ASU 2014-09. The

Company early

adopted ASU 2018-07 on

January 1, 2019 and the adoption did not have a material impact on the Company’s consolidated financial statements.

In August 2018, the FASB issued ASU

2018-13,

2018-13

is effective for all entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. The Company adopted ASU

2018-03

on January 1, 2020 and the adoption did not have a material impact on its consolidated financial statements.

Recently issued accounting pronouncements

In February 2016, the FASB issued ASU

2016-02,

2018-11,

2019-10,

which deferred the effective date for nonpublic

2016-02

right-of-use

assets, however, the Company has not completed its assessment.

In June 2016, the FASB issued ASU

2016-13,

Financial Instruments – Credit Losses (Topic 326). The new standard adjusts the accounting for assets held at amortized costs basis, including marketable securities accounted for as

available-for-sale.

2019-10,

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2019

Summary of Property and equipment

Depreciation and amortization expense is recognized using the straight-line method over the estimated useful life of each asset as follows:



		Estimated useful life
Laboratory equipment		5 years
Computer equipment and software		3 years
Furniture and fixtures		5 years
Leasehold improvements		Shorter of remaining life of lease or useful life

Fair Value of Financial Assets (Tables)

9 Months Ended

12 Months Ended

Sep. 30, 2020

Dec. 31, 2019

Fair Value Disclosures [Abstract]

Summary of marketable securities

The Company did not have marketable securities at December 31, 2019. As of September 30, 2020, marketable securities by security type consisted of the following:


	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
	(in thousands)
U.S. treasury securities	$	132,184	$	16	$	—	$	132,200
U.S. government agency bonds		11,995		2		—		11,997
Commercial paper		59,891		—		—		59,891
Corporate debt securities		17,665		8		—		17,673

Totals	$	221,735	$	26	$	—	$	221,761

Marketable securities by security type consisted of the following:



	December 31, 2018
(in thousands)	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair value
U.S. treasury bills and notes	$	67,574	$	—	$	(9	)	$	67,565

	$	67,574	$	—	$	(9	)	$	67,565

Summary of assets measured at fair value on a recurring basis



	Fair Value Measurements at December 31, 2019 Using:
	Level 1		Level 2		Level 3		Total
	(in thousands)
Cash equivalents:
Money market funds	$	15,076	$	—	$	—	$	15,076

Totals	$	15,076	$	—	$	—	$	15,076



	Fair Value Measurements at September 30, 2020 Using:
	Level 1		Level 2		Level 3		Total
	(in thousands)
Cash equivalents:
Money market funds	$	57,394	$	—	$	—	$	57,394
Marketable securities:
U.S. treasury securities		—		132,200		—		132,200
U.S. government agency bonds		—		11,997		—		11,997
Commercial paper		—		59,891		—		59,891
Corporate debt securities		—		17,673		—		17,673

Totals	$	57,394	$	221,761	$	—	$	279,155

Summary of Significant Accounting Policies:



	Fair value measurements at December 31, 2018 using:
(in thousands)	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	7,244	$	—	$	—	$	7,244
Marketable securities
U.S. treasury bills and notes		—		67,565		—		67,565

Totals	$	7,244	$	67,565	$	—	$	74,809



	Fair value measurements at December 31, 2019 using:
(in thousands)	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	15,076	$	—	$	—	$	15,076

Totals	$	15,076	$	—	$	—	$	15,076

Property and equipment, net (Tables)

12 Months Ended

Dec. 31, 2019

Property, Plant and Equipment [Abstract]

Summary of Property and equipment, net

Property and equipment, net consisted of the following:



	December 31,
(in thousands)	2018			2019
Laboratory equipment	$	3,053		$	5,029
Computer equipment and software		261			740
Furniture and fixtures		—			826
Leasehold improvements		1,561			12,993
Construction in progress		—			4,487

		4,875			24,075
Less: Accumulated depreciation and amortization		(389	)		(2,230	)

	$	4,486		$	21,845

Accrued Expenses and Other Current Liabilities (Tables)

9 Months Ended

12 Months Ended

Sep. 30, 2020

Dec. 31, 2019

Payables and Accruals [Abstract]

Summary of Accrued expenses and other current liabilities

Accrued expenses and other current liabilities consisted of the following:



	December 31, 2019		September 30, 2020
	(in thousands)
Accrued employee compensation and benefits	$	3,255	$	3,798
Accrued external research and development expenses		1,344		2,037
Accrued professional fees		619		890
Deferred rent		1,370		1,380
Other		319		640

	$	6,907	$	8,745

Accrued expenses consisted of the following:



	December 31,
(in thousands)	2018		2019
Accrued employee compensation and benefits	$	2,572	$	3,255
Accrued external research and development expenses		1,284		1,344
Accrued professional fees		102		619
Deferred rent		4		1,370
Other		912		319

	$	4,874	$	6,907

Convertible Preferred Stock (Tables)

12 Months Ended

Dec. 31, 2019

Temporary Equity Disclosure [Abstract]

Summary of Preferred Stock

Preferred Stock consisted of the following at December 31, 2018 and 2019:



(in thousands except share amounts)	Preferred stock authorized		Preferred stock issued and outstanding		Carrying value		Liquidation preference		Common stock issuable upon conversion
Series A Preferred Stock		15,451,020		15,451,020	$	15,404	$	15,451		8,747,675
Series B Preferred Stock		10,974,644		10,974,644		100,189		100,371		6,213,352	(1)

		26,425,664		26,425,664	$	115,593	$	115,822		14,961,027	(1)

(1)

Stock-based compensation (Tables)

12 Months Ended

Dec. 31, 2019

Summary of Inputs Used in Black-Scholes Option Pricing Model

The following table presents, on a weighted average basis, the assumptions used in the Black-Scholes option-pricing model to determine the fair value of stock options granted:

Stock options



	Year ended December 31,
	2018		2019

Risk-free interest rate		2.70%		2.00%
Expected volatility		76.0%		75.7%
Expected dividend yield		—		—
Expected term (in years)		6.1		6.0

Summarizes the Company's stock option activity

The following table summarizes the Company’s stock option activity since December 31, 2018:



	Number of shares			Weighted average exercise price		Weighted average contractual term (in years)		Aggregate intrinsic value (in thousands)
Outstanding as of December 31, 2018		2,784,581		$	4.05		9.4	$	1,403
Granted		1,200,954			5.92
Exercised		(34,740	)		2.88
Forfeited		(576,911	)		3.89

Outstanding as of December 31, 2019		3,373,884		$	4.76		8.79	$	8,492

Vested and expected to vest as of December 31, 2019		3,373,884		$	4.76		8.79	$	8,492
Options exercisable as of December 31, 2019		852,647		$	4.05		8.38	$	2,735

summarizes the Company's restricted common stock activity

The following table summarizes the Company’s restricted common stock activity since December 31, 2018:



	Shares			Weighted average grant date fair value
Unvested restricted common stock as of December 31, 2018		2,819,949		$	1.24
Issued		—			—
Vested		(1,055,997	)		1.30
Forfeited		(58,764	)		0.73

Unvested restricted common stock as of December 31, 2019		1,705,188		$	1.22

Summary of stock-based compensation expense was classified in the statements of operations and comprehensive loss

The Company recorded stock-based compensation expense in the following expense categories of its consolidated statements of operations and comprehensive loss:



	Year ended December 31,
(in thousands)	2018		2019

Research and development expenses	$	2,093	$	2,753
General and administrative expenses		1,395		1,454

	$	3,488	$	4,207

Income taxes (Tables)

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

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

A reconciliation of the U.S. federal statutory income tax rate to the Company’s effective income tax rate is as follows:



	Year ended December 31,
	2018		2019
Federal statutory income tax rate		(21.0)%		(21.0)%
State income taxes, net of federal benefit		(5.6)		(5.9)
Federal and state research and development tax credits		(6.5)		(5.1)
Stock-based compensation expense		1.6		1.0
Other		—		0.2
Change in deferred tax asset valuation allowance		31.5		30.8

Effective income tax rate		0.0%		0.0%

Summary of Net deferred tax assets

Net deferred tax assets as of December 31, 2018 and 2019 consisted of the following:



	December 31,
(in thousands)	2018			2019
Deferred tax assets:
Net operating loss carryforwards	$	10,183		$	25,023
Research and development tax credit carryforwards		2,878			5,998
Deferred rent		—			4,740
Other		1,701			1,469

Total deferred tax assets		14,762			37,230
Deferred tax liabilities:
Property and equipment		(516	)		(4,117	)

Total deferred tax liabilities		(516	)		(4,117	)

Valuation allowance		(14,246	)		(33,113	)

Net deferred tax assets	$	—		$	—

Summary of changes in the valuation allowance for deferred tax assets



	Year ended December 31,
(in thousands)	2018		2019
Valuation allowance as of beginning of year	$	2,976	$	14,246
Increases recorded to income tax provision		11,270		18,867

Valuation allowance as of end of year	$	14,246	$	33,113

Stock-Based Awards (Tables)

9 Months Ended

Sep. 30, 2020

Summary of stock-based compensation expense was classified in the statements of operations and comprehensive loss

Stock-based compensation expense was classified in the statements of operations and comprehensive loss as follows:



	Three Months Ended September 30,				Nine Months Ended September 30,
	2019		2020		2019		2020
	(in thousands)
Research and development expenses	$	688	$	1,204	$	2,039	$	2,967
General and administrative expenses		392		957		1,083		2,066

	$	1,080	$	2,161	$	3,122	$	5,033

Net Loss per Share (Tables)

9 Months Ended

12 Months Ended

Sep. 30, 2020

Dec. 31, 2019

Earnings Per Share [Abstract]

Summary of potential dilutive securities, presented based on amounts outstanding



	September 30,
	2019		2020
Convertible preferred stock (as converted to common stock)		14,961,027		—
Unvested restricted common stock		1,970,209		956,718
Stock options to purchase common stock		3,171,498		5,581,717

		20,102,734		6,538,435

The Company excluded the following potential common shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share attributable to common stockholders for the periods indicated:



	Year ended December 31,
	2018		2019

Convertible preferred stock (as converted to common stock)		14,961,027		14,961,027
Unvested restricted common stock		2,819,949		1,705,188
Stock options to purchase common stock		2,784,581		3,373,884

		20,565,557		20,040,099

Commitments and Contingencies (Tables)

9 Months Ended

12 Months Ended

Sep. 30, 2020

Dec. 31, 2019

Commitments and Contingencies Disclosure [Abstract]

Summary of future minimum lease payments

Future minimum lease payments as of September 30, 2020 are as follows:



Year Ending December 31,	(in thousands)
2020 (remaining 3 months)	$	1,745
2021		7,053
2022		7,251
2023		7,441
2024		7,679
Thereafter		35,451

	$	66,620

Future minimum lease payments as of December 31, 2019 are as follows:



Year ending December 31,	(in thousands)
2020	$	6,867
2021		7,053
2022		7,251
2023		7,441
2024		7,679
Thereafter		35,451

	$	71,742

Nature of the Business and Basis of Presentation - Additional information (Detail) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended		9 Months Ended		12 Months Ended
	Jun. 16, 2020	Jan. 31, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Jan. 09, 2020
Date of incorporation					Oct. 21, 2016
Net loss			$ (20,849)	$ (16,128)	$ (56,297)	$ (45,254)	$ (61,317)	$ (35,803)
Used in BS			$ (164,749)		(164,749)		$ (108,452)	$ (47,135)
Proceeds from issuance of convertible preferred stock					$ 108,854
Series C Convertible Preferred Stock [Member]
Shares issued price		$ 5.5914							$ 5.5914
Proceeds from issuance of convertible preferred stock		$ 111,500
Common Stock [Member]
Shares issued during the period					12,105,263
Common Stock [Member] \| IPO [Member]
Shares issued during the period	12,105,263
Shares issued price	$ 19.00
Sale of Stock, Consideration Received on Transaction	$ 210,700
Common Stock [Member] \| Over-Allotment Option [Member]
Shares issued during the period	1,578,947

Summary of Significant Accounting Policies - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Accounting Policies [Line Items]
Income Tax rate settlement	50.00%
Series C Convertible Preferred Stock [Member]
Accounting Policies [Line Items]
Deferred offering costs	$ 0.1

Summary of Significant Accounting Policies - Summary Of Property And Equipment (Detail)	12 Months Ended
	Dec. 31, 2019
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment	5 years
Computer Equipment and Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment	3 years
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment	5 years
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, Useful life	Shorter of remaining life of lease or useful life

Fair Value of Financial Assets - Summary of marketable securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2018
Marketable Securities [Line Items]
Gross unrealized losses	$ 0	$ (9)
Fair Value, Recurring [Member]
Marketable Securities [Line Items]
Amortized cost	221,735	67,574
Gross unrealized gain	26	0
Estimated fair value	221,761	67,565
Fair Value, Recurring [Member] \| U.S. treasury securities
Marketable Securities [Line Items]
Amortized cost	132,184	67,574
Gross unrealized gain	16	0
Gross unrealized losses	0	(9)
Estimated fair value	132,200	$ 67,565
Fair Value, Recurring [Member] \| U.S. government agency bonds
Marketable Securities [Line Items]
Amortized cost	11,995
Gross unrealized gain	2
Estimated fair value	11,997
Fair Value, Recurring [Member] \| Commercial paper
Marketable Securities [Line Items]
Amortized cost	59,891
Estimated fair value	59,891
Fair Value, Recurring [Member] \| Corporate debt securities
Marketable Securities [Line Items]
Amortized cost	17,665
Gross unrealized gain	8
Estimated fair value	$ 17,673

Fair Value of Financial Assets - Summary of assets measured at fair value on a recurring basis (Detail) - Fair Value, Recurring [Member] - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash equivalents:
Totals	$ 279,155	$ 15,076	$ 74,809
Marketable securities:
Marketable securities	221,761		67,565
Level 1
Cash equivalents:
Totals	57,394	15,076	7,244
Level 2
Cash equivalents:
Totals	221,761		67,565
Money Market Funds
Cash equivalents:
Cash equivalents	57,394	15,076	7,244
Money Market Funds \| Level 1
Cash equivalents:
Cash equivalents	57,394	$ 15,076	7,244
U.S. treasury securities
Marketable securities:
Marketable securities	132,200		67,565
U.S. treasury securities \| Level 2
Marketable securities:
Marketable securities	132,200		$ 67,565
U.S. government agency bonds
Marketable securities:
Marketable securities	11,997
U.S. government agency bonds \| Level 2
Marketable securities:
Marketable securities	11,997
Commercial paper
Marketable securities:
Marketable securities	59,891
Commercial paper \| Level 2
Marketable securities:
Marketable securities	59,891
Corporate debt securities
Marketable securities:
Marketable securities	17,673
Corporate debt securities \| Level 2
Marketable securities:
Marketable securities	$ 17,673

Property and equipment, net - Schedule of Property and Equipment (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross		$ 24,075	$ 4,875
Less: Accumulated depreciation and amortization		(2,230)	(389)
Property, Plant and Equipment, Net	$ 22,888	21,845	4,486
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross		5,029	3,053
Computer Equipment and Software [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross		740	261
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross		826
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross		12,993	$ 1,561
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross		$ 4,487

Property and equipment, net - Additional Information (Detail) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment, Net, by Type [Abstract]
Depreciation and amortization expense	$ 2,441	$ 1,185	$ 1,864	$ 347

Accrued Expenses and Other Current Liabilities - Summary of Accrued expenses and other current liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Accrued Expenses And Other Liabilities Current [Line Items]
Accrued employee compensation and benefits	$ 3,798	$ 3,255	$ 2,572
Accrued external research and development expenses	2,037	1,344	1,284
Accrued professional fees	890	619	102
Deferred rent	1,380	1,370	4
Other	640	319	912
Total	$ 8,745	$ 6,907	$ 4,874

Income taxes - Additional Information (Detail) $ in Millions		12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)
Income Tax [Line Items]
Net operating loss carry forwards	$ 8.2	$ 8.2
Operating Loss Carry forward Remaining Amount	$ 83.7	83.7
Percentage on annual taxable income	80.00%
Tax Credit Carryforward, Amount	$ 2.5	$ 2.5
Percentage of change in ownership	50.00%
Unrecognized Tax Benefits of income tax rate	50.00%
Tax Credit Carry forward, Expiration Year		2036
Operating Loss Carry forwards, Expiration Year		2036
Federal income tax Authority [Member]
Income Tax [Line Items]
Net operating loss carry forwards	$ 91.9	$ 91.9
State and Local Jurisdiction [Member]
Income Tax [Line Items]
Net operating loss carry forwards	90.6	90.6
Federal and state research and development tax credit carry forwards [Member]
Income Tax [Line Items]
Tax Credit Carryforward, Amount	$ 4.0	$ 4.0

Income taxes - Summary of Reconciliation of the U.S. Federal Statutory Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Federal statutory income tax rate	(21.00%)	(21.00%)
State income taxes, net of federal benefit	(5.90%)	(5.60%)
Federal and state research and development tax credits	(5.10%)	(6.50%)
Stock-based compensation expense	1.00%	1.60%
Other	0.20%	0.00%
Change in deferred tax asset valuation allowance	30.80%	31.50%
Effective income tax rate	0.00%	0.00%

Income taxes - Summary of Net Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Net operating loss carryforwards	$ 25,023	$ 10,183
Research and development tax credit carryforwards	5,998	2,878
Deferred rent	4,740	0
Other	1,469	1,701
Total deferred tax assets	37,230	14,762
Deferred tax liabilities:
Property and equipment	(4,117)	(516)
Total deferred tax liabilities	(4,117)	(516)
Valuation allowance	(33,113)	(14,246)
Net deferred tax assets	$ 0	$ 0

Income taxes - Summary of Changes in the Valuation Allowance for Deferred Tax Assets (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Valuation Allowance [Abstract]
Valuation allowance as of beginning of year	$ 14,246	$ 2,976
Increases recorded to income tax provision	18,867	11,270
Valuation allowance as of end of year	$ 33,113	$ 14,246

License Agreements - Additional Information (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended		12 Months Ended
	Dec. 31, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
License Agreements Disclosure [Line Items]
Research and Development Expense		$ 15,308	$ 13,447	$ 42,158	$ 37,403	$ 50,134	$ 28,152
NIH [Member]
License Agreements Disclosure [Line Items]
Research and Development Expense						100	100
NIH [Member] \| License Agreement Terms [Member]
License Agreements Disclosure [Line Items]
Future milestone obligation	$ 400					400
Percentage of increase decrease in net sales	25.00%
UMass [Member] \| License Agreement Terms [Member]
License Agreements Disclosure [Line Items]
Future milestone obligation	$ 800					$ 800
Shares Issued For Services						125,677
Research and Development Expense						$ 100	$ 100
Adjustments to Additional Paid in Capital, Other						$ 100

Equity - Additional Information (Detail) - $ / shares	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Equity [Abstract]
Common stock, shares authorized	150,000,000	46,750,000	46,750,000
Common stock, par value per share	$ 0.0001	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	5,000,000	0
Preferred stock, par value per share	$ 0.0001	$ 0.0001

Stock-Based Awards - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions		9 Months Ended	12 Months Ended
	Jun. 11, 2020	Sep. 30, 2020	Dec. 31, 2019	Jan. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compenation by share based payment arrangement number of options granted			1,200,954
Share based compenation by share based payment arrangement number of options granted weighted average exercise price per share			$ 5.92
Period of vesting of employee stock options		4 years
Unrecognised stock compensation on account of unvested options		$ 23.6	$ 10.9
Unrecognised stock compensation on account of unvested options remaining period over which the compensation is to be recognised		3 years 2 months 12 days	2 years 4 months 24 days
Unvested Stock Awards for Which Performance is not Probable
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognised stock compensation on account of unvested options		$ 2.3
Service Based Options [Member] \| Certain Employees Directors and Consultants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation vesting period service based		4 years
Share based compenation by share based payment arrangement number of options granted		2,114,361
Share based compenation by share based payment arrangement number of options granted weighted average exercise price per share		$ 8.71
Performance Based Options [Member] \| Certain Employees Directors and Consultants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compenation by share based payment arrangement number of options granted		717,154
Share based compenation by share based payment arrangement number of options granted weighted average exercise price per share		$ 3.26
2020 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock reserved for future issuance	2,547,698
Stock based compensation period of expiry		10 years
Common stock shares available for future issuance		2,640,244
2020 Stock Incentive Plan \| Maximum \| Additional From 2017 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock reserved for future issuance	7,173,014
2020 Stock Incentive Plan \| Maximum \| Annual Increase 2021 To 2030
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of common stock shares additionally reserved for issuance	4.00%
Employee Stock Purchase Plan 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation by share based payment arrangement number of shares authorized for issuance	481,231
Common stock shares available for future issuance		481,231
Employee Stock Purchase Plan 2020 \| Maximum \| Annual Increase 2021 To 2030
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of common stock shares additionally reserved for issuance	1.00%
Number of share instruments newly issued under a share-based compensation plan	1,302,157
Common Stock [Member] \| 2017 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation by share based payment arrangement number of shares authorized for issuance		10,275,717	8,407,405	10,275,717

Stock-Based Awards - Summary of Stock-Based Compensation Expense was Classified in the Statements of Operations and Comprehensive Loss (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 2,161	$ 1,080	$ 5,033	$ 3,122
Research and development expense [Member]
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	1,204	688	2,967	2,039
General and administrative expenses
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 957	$ 392	$ 2,066	$ 1,083

Stock-based compensation - Summary of Inputs Used in Black-Scholes Option Pricing Model (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	2.00%	2.70%
Expected volatility	75.70%	76.00%
Expected term (in years)	6 years	6 years 1 month 6 days

Stock-based compensation - Summarizes the Company's Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares Outstanding , Beginning	2,784,581
Number of shares \| Granted	1,200,954
Number of shares \| Exercised	(34,740)
Number of shares \| Forfeited	(576,911)
Number of shares Outstanding , Ending	3,373,884	2,784,581
Number of shares \| Vested and expected to vest	3,373,884
Number of shares \| Options exercisable	852,647
Weighted average exercise price Outstanding , Beginning	$ 4.05
Weighted average exercise price \| Granted	5.92
Weighted average exercise price \| Exercised	2.88
Weighted average exercise price \| Forfeited	3.89
Weighted average exercise price Outstanding , Ending	4.76	$ 4.05
Weighted average exercise price \| Vested and expected to vest	4.76
Weighted average exercise price \| Options exercisable	$ 4.05
Weighted average contractual term (in years) Outstanding , Beginning	8 years 9 months 14 days	9 years 4 months 24 days
Weighted average contractual term (in years) Outstanding , Ending	8 years 9 months 14 days	9 years 4 months 24 days
Weighted average contractual term (in years) \| Vested and expected to vest	8 years 9 months 14 days
Weighted average contractual term (in years) \| Options exercisable	8 years 4 months 17 days
Aggregate intrinsic value (in thousands) Outstanding	$ 8,492	$ 1,403
Aggregate intrinsic value (in thousands) \| Vested and expected to vest	8,492
Aggregate intrinsic value (in thousands) \| Options exercisable	$ 2,735

Stock-based compensation - Summarizes the Company's Restricted Common Stock Activity (Detail)	12 Months Ended
	Dec. 31, 2019 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested restricted common stock, Beginning \| Shares \| shares	2,819,949
Vested \| Shares \| shares	(1,055,997)
Forfeited \| Shares \| shares	(58,764)
Unvested restricted common stock, Ending \| Shares \| shares	1,705,188
Weighted average grant date fair value of Unvested restricted common stock, Beginning \| $ / shares	$ 1.24
Weighted average grant date fair value of Unvested restricted common stock, Vested \| $ / shares	1.30
Weighted average grant date fair value of Unvested restricted common stock, Forfeited \| $ / shares	0.73
Weighted average grant date fair value of Unvested restricted common stock, Ending \| $ / shares	$ 1.22

Stock-based compensation - Summary of Stock-Based Compensation Expense was Classified in the Statements of Operations and Comprehensive Loss (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 4,207	$ 3,488
Research and development expense [Member]
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	2,753	2,093
General and administrative expenses
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 1,454	$ 1,395

Stock-based compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognised stock compensation on account of unvested options	$ 23.6	$ 10.9
Unrecognised stock compensation on account of unvested options remaining period over which the compensation is to be recognised	3 years 2 months 12 days	2 years 4 months 24 days
weighted average grant-date fair value		$ 1.30
Share based compenation by share based payment arrangement number of options granted		1,200,954
Common Stock [Member] \| 2017 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation by share based payment arrangement number of shares authorised for issuance		8,407,405
Stock reserved for future issuance		773,652
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
fair value of restricted common stock		$ 7.0	$ 1.2
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
weighted average grant-date fair value		$ 4.46	$ 3.59
No of stock option exercised		$ 0.1	$ 0.0
No of Instrinic stock option exercised		$ 0.1	$ 0.0
Service Based Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compenation by share based payment arrangement number of options granted		0	394,213

Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Disclosure of Commitement and Contingencies [Line Items]
Lessee operating lease year of expiry			2029		2029
Operating lease agreement option to renewal term	5 years		5 years		5 years
Tenant improvement allowance maximum	$ 14.7		$ 14.7		$ 14.7
Letter of Credit for Security Deposit	2.1		2.1		2.1
Rent expense operating lease	$ 1.8	$ 2.5	$ 5.5	$ 6.0	7.9	$ 3.5
Tenant receivable					$ 0.4	$ 1.3

Commitments and Contingencies - Summary of Future Minimum Lease Payments (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
2020 (remaining 3 months)	$ 1,745	$ 6,867
2021	7,053	7,053
2022	7,251	7,251
2023	7,441	7,441
2024	7,679	7,679
Thereafter	35,451	35,451
Future Monimum Lease Payments	$ 66,620	$ 71,742

Convertible Preferred Stock - Additional Information (Detail) - USD ($)
$ / shares in Units, $ in Thousands

9 Months Ended

12 Months Ended

Jan. 31, 2020

Jan. 09, 2020

Dec. 31, 2019

Dec. 31, 2018

Feb. 22, 2018

Sep. 30, 2020

Dec. 31, 2018

Jun. 16, 2020

Proceeds from issuance of convertible preferred stock

$ 108,854

Value per share of common stock

^[1]

14,961,027

$ 0.0001

Original issue price [Member]

Preferred Stock, Dividend Rate, Percentage

$ 5.5914

6.00%

Conversion issue price [Member]

$ 14.2180

Common Stock [Member]

Series B Convertible Preferred Stock [Member]

27,094,085

10,974,644

$ 9.1457

Gross proceeds

$ 100,400

Stock issuance of costs

$ 200

$ 181

Series B Convertible Preferred Stock [Member] | Common Stock [Member]

26,425,664

Series C Convertible Preferred Stock [Member]

15,807,081

19,936,296

Proceeds from issuance of convertible preferred stock

$ 5.5914

$ 111,500

Gross proceeds

$ 111,500

Stock issuance of costs

$ 2,600

$ 2,640

Series C Convertible Preferred Stock [Member] | Common Stock [Member]

10,974,644

Convertible Preferred Stock [Member]

7,059,406

Proceeds from issuance of convertible preferred stock

$ 40,000

Value per share of common stock

$ 8.0496

Series A Preferred Stock [Member]

Preferred stock conversion basis

8,747,675

1.7663-for-one basis

Series A Preferred Stock [Member] | Original issue price [Member]

Series A Preferred Stock [Member] | Conversion issue price [Member]

$ 1.00

Series B Preferred Stock [Member]

1.7663%

^[1]

6,213,352

Preferred stock conversion basis

57.00%

1.7663-for-one basis

Series B Preferred Stock [Member] | Original issue price [Member]

Series B Preferred Stock [Member] | Conversion issue price [Member]

$ 9.1457

Series C Preferred Stock [Member]

16.154%

Preferred stock conversion basis

57.00%

1.7663-for-one basis

Series C Preferred Stock [Member] | Original issue price [Member]

Series C Preferred Stock [Member] | Conversion issue price [Member]

$ 5.5914

$ 9.8761

[1]	Upon issuance and sale of the Series C in January 2020 (see Note 13), the 10,974,644 outstanding shares of Series B became convertible into 7,059,406 shares of common stock and the 26,425,664 outstanding shares of Preferred Stock became convertible into 15,807,081 shares of common stock.

Convertible Preferred Stock - Summary of Preferred Stock (Detail) - USD ($)
$ in Thousands

Sep. 30, 2020

Dec. 31, 2019

Dec. 31, 2018

Preferred stock, shares authorized

26,425,664

Preferred stock issued and outstanding

26,425,664

Carrying value

$ 115,593

Liquidation preference

$ 115,822

Common stock issuable upon conversion

^[1]

14,961,027

Series A Preferred Stock [Member]

Preferred stock, shares authorized

15,451,020

Preferred stock issued and outstanding

15,451,020

Carrying value

$ 15,404

Liquidation preference

$ 15,451

Common stock issuable upon conversion

8,747,675

Series B Preferred Stock [Member]

Preferred stock, shares authorized

10,974,644

Preferred stock issued and outstanding

10,974,644

Carrying value

$ 100,189

Liquidation preference

$ 100,371

Common stock issuable upon conversion

^[1]

6,213,352

[1]	Upon issuance and sale of the Series C in January 2020 (see Note 13), the 10,974,644 outstanding shares of Series B became convertible into 7,059,406 shares of common stock and the 26,425,664 outstanding shares of Preferred Stock became convertible into 15,807,081 shares of common stock.

Convertible Preferred Stock - Summary of Preferred Stock (Parenthetical) (Detail) - shares

Jun. 16, 2020

Jan. 31, 2020

Dec. 31, 2019

Dec. 31, 2018

^[1]

14,961,027

Common Stock [Member]

Series C Convertible Preferred Stock [Member]

27,094,085

Series C Convertible Preferred Stock [Member] | Common Stock [Member]

10,974,644

Series B Convertible Preferred Stock [Member]

7,059,406

Series B Convertible Preferred Stock [Member] | Common Stock [Member]

26,425,664

15,807,081

[1]	Upon issuance and sale of the Series C in January 2020 (see Note 13), the 10,974,644 outstanding shares of Series B became convertible into 7,059,406 shares of common stock and the 26,425,664 outstanding shares of Preferred Stock became convertible into 15,807,081 shares of common stock.

Net Loss per Share - Summary of Potential Dilutive Securities, Presented Based on Amounts Outstanding (Detail) - shares	9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive net loss per share	6,538,435	20,102,734	20,040,099	20,565,557
Convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive net loss per share		14,961,027	14,961,027	14,961,027
Unvested restricted common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive net loss per share	956,718	1,970,209	1,705,188	2,819,949
Stock option to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive net loss per share	5,581,717	3,171,498	3,373,884	2,784,581

Subsequent events - Additional Information (Detail)
$ / shares in Units, $ in Millions

9 Months Ended

12 Months Ended

Jun. 05, 2020

Mar. 31, 2020

$ / shares

Mar. 05, 2020

$ / shares

Jan. 31, 2020

USD ($)

$ / shares

Jan. 09, 2020

USD ($)

$ / shares

Feb. 22, 2018

USD ($)

$ / shares

Sep. 30, 2020

Dec. 31, 2019

$ / shares

Dec. 31, 2018

Jun. 16, 2020

Convertible preferred stock, shares authorized

26,425,664

Convertible Preferred Stock Conversion Price | $ / shares

$ 16.1540

Temporary Equity, Shares Outstanding

26,425,664

Share based compenation by share based payment arrangement number of options granted

^[1]

14,961,027

1,200,954

Share based compenation by share based payment arrangement number of options granted weighted average exercise price per share | $ / shares

$ 5.92

Common Stock [Member]

Common Stock [Member] | 2017 Stock Incentive Plan

27,094,085

Share based compensation by share based payment arrangement number of shares authorized for issuance

10,275,717

8,407,405

Subsequent Event [Member]

Convertible preferred stock, shares authorized

46,361,960

26,425,664

Convertible Preferred Stock Conversion Price | $ / shares

$ 14.2180

Reverse Stock Split description

one-for-1.7663 reverse stock split

Stock Split Conversion Ratio

1.7663

Subsequent Event [Member] | 2017 Stock Incentive Plan | Service Based Options [Member]

Share based compenation by share based payment arrangement number of options granted

63,834

947,411

Share based compenation by share based payment arrangement number of options granted weighted average exercise price per share | $ / shares

$ 5.25

$ 5.16

Weighted average grant date fair value of Unvested restricted common stock, Issued | $ / shares

$ 0.2

$ 3.4

Stock based compensation vesting period service based

4 years

Subsequent Event [Member] | 2017 Stock Incentive Plan | Performance Based Options [Member]

Share based compenation by share based payment arrangement number of options granted

717,198

Share based compenation by share based payment arrangement number of options granted weighted average exercise price per share | $ / shares

$ 5.16

Weighted average grant date fair value of Unvested restricted common stock, Issued | $ / shares

$ 2.3

Subsequent Event [Member] | Common Stock [Member]

Series B Convertible Preferred Stock [Member]

7,059,406

Shares issued price | $ / shares

10,974,644

$ 9.1457

Gross proceeds | $

$ 100.4

Temporary Equity, Shares Outstanding

10,974,644

Series B Convertible Preferred Stock [Member] | Common Stock [Member]

26,425,664

Series C Convertible Preferred Stock [Member]

15,807,081

Shares issued price | $ / shares

19,936,296

$ 5.5914

Gross proceeds | $

$ 111.5

Series C Convertible Preferred Stock [Member] | Common Stock [Member]

10,974,644