PASSAGE BIO, INC., 10-Q filed on 5/14/2024
Quarterly Report
v3.24.1.1.u2
Document and Entity Information - shares
3 Months Ended
Mar. 31, 2024
May 09, 2024
Document and Entity Information    
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Mar. 31, 2024  
Document Transition Report false  
Entity File Number 001-39231  
Entity Registrant Name Passage BIO, Inc.  
Entity Incorporation, State or Country Code DE  
Entity Tax Identification Number 82-2729751  
Entity Address, Address Line One One Commerce Square  
Entity Address, Address Line Two 2005 Market Street, 39th Floor  
Entity Address, City or Town Philadelphia  
Entity Address, State or Province PA  
Entity Address, Postal Zip Code 19103  
City Area Code 267  
Local Phone Number 866-0311  
Title of 12(b) Security Common Stock  
Trading Symbol PASG  
Security Exchange Name NASDAQ  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Non-accelerated Filer  
Entity Small Business true  
Entity Emerging Growth Company true  
Entity Ex Transition Period false  
Entity Shell Company false  
Entity Common Stock, Shares Outstanding   61,640,596
Entity Central Index Key 0001787297  
Current Fiscal Year End Date --12-31  
Document Fiscal Year Focus 2024  
Document Fiscal Period Focus Q1  
Amendment Flag false  
v3.24.1.1.u2
Balance Sheets - USD ($)
$ in Thousands
Mar. 31, 2024
Dec. 31, 2023
Current assets:    
Cash and cash equivalents $ 36,773 $ 21,709
Marketable securities 67,752 92,585
Prepaid expenses and other current assets 1,784 923
Prepaid research and development 1,984 2,742
Total current assets 108,293 117,959
Property and equipment, net 14,489 15,295
Right of use assets - operating leases 17,087 16,858
Other assets 662 433
Total assets 140,531 150,545
Current liabilities:    
Accounts payable 1,687 1,298
Accrued expenses and other current liabilities 7,483 11,670
Operating lease liabilities 3,671 3,373
Total current liabilities 12,841 16,341
Operating lease liabilities - noncurrent 22,807 22,921
Total liabilities 35,648 39,262
Commitments and contingencies (note 9)
Stockholders' equity:    
Preferred stock, $0.0001 par value: 10,000,000 shares authorized; no shares issued and outstanding at both March 31, 2024 and December 31, 2023
Common stock, $0.0001 par value: 300,000,000 shares authorized; 61,611,796 shares issued and outstanding at March 31, 2024 and 54,944,130 shares issued and outstanding at December 31, 2023 6 5
Additional paidin capital 716,125 705,789
Accumulated other comprehensive income (loss) (69) (43)
Accumulated deficit (611,179) (594,468)
Total stockholders' equity 104,883 111,283
Total liabilities and stockholders' equity $ 140,531 $ 150,545
v3.24.1.1.u2
Balance Sheets (Parenthetical) - $ / shares
Mar. 31, 2024
Dec. 31, 2023
Balance Sheets    
Preferred stock, par value (in dollars per share) $ 0.0001 $ 0.0001
Preferred stock, shares authorized 10,000,000 10,000,000
Preferred stock, shares issued 0 0
Preferred stock, shares outstanding 0 0
Common stock, par value (in dollars per share) $ 0.0001 $ 0.0001
Common stock, shares authorized 300,000,000 300,000,000
Common stock, shares issued 61,611,796 54,944,130
Common stock, shares outstanding 61,611,796 54,944,130
v3.24.1.1.u2
Statements of Operations and Comprehensive Loss - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2024
Mar. 31, 2023
Operating expenses:    
Research and development $ 11,535 $ 16,836
General and administrative 6,515 19,047
Loss from operations (18,050) (35,883)
Other income (expense), net 1,339 1,545
Net loss $ (16,711) $ (34,338)
Per share information:    
Net loss per share of common stock, basic $ (0.30) $ (0.63)
Net loss per share of common stock, diluted $ (0.30) $ (0.63)
Weighted average common shares outstanding, basic 56,295,540 54,618,799
Weighted average common shares outstanding, diluted 56,295,540 54,618,799
Comprehensive loss:    
Net loss $ (16,711) $ (34,338)
Unrealized gain (loss) on marketable securities (26) 539
Comprehensive loss $ (16,737) $ (33,799)
v3.24.1.1.u2
Statements of Stockholders' Equity - USD ($)
$ in Thousands
Common stock
Additional paid-in capital
Accumulated other comprehensive income (loss)
Accumulated deficit
Total
Balance at Beginning of period at Dec. 31, 2022 $ 5 $ 694,733 $ (966) $ (492,406) $ 201,366
Balance at Beginning of period (in shares) at Dec. 31, 2022 54,614,690        
Stockholders' equity          
Exercise of stock options and vesting of restricted stock units (in shares) 12,000        
Unrealized gain (loss) on marketable securities     539   539
Share-based compensation expense   2,784     2,784
Net loss       (34,338) (34,338)
Balance at end of period at Mar. 31, 2023 $ 5 697,517 (427) (526,744) 170,351
Balance at end of period (in shares) at Mar. 31, 2023 54,626,690        
Balance at Beginning of period at Dec. 31, 2023 $ 5 705,789 (43) (594,468) 111,283
Balance at Beginning of period (in shares) at Dec. 31, 2023 54,944,130        
Stockholders' equity          
Issuance of common stock under the ATM Facility, net of offering costs $ 1 8,741     8,742
Issuance of common stock under the ATM Facility, net of offering costs (in share) 6,000,000        
Exercise of stock options and vesting of restricted stock units (in shares) 667,666        
Unrealized gain (loss) on marketable securities     (26)   (26)
Share-based compensation expense   1,595     1,595
Net loss       (16,711) (16,711)
Balance at end of period at Mar. 31, 2024 $ 6 $ 716,125 $ (69) $ (611,179) $ 104,883
Balance at end of period (in shares) at Mar. 31, 2024 61,611,796        
v3.24.1.1.u2
Statements of Cash Flows - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2024
Mar. 31, 2023
Cash flows used in operating activities:    
Net loss $ (16,711) $ (34,338)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:    
Depreciation and amortization 806 978
Sharebased compensation 1,595 2,784
Amortization of premium and discount on marketable securities, net (444) (98)
Changes in operating assets and liabilities:    
Prepaid expenses and other current assets, and other assets (1,090) 3,075
Prepaid research and development 758 4,346
Right of use assets and operating lease liabilities (45) (21)
Accounts payable 389 (1,039)
Accrued expenses and other current and noncurrent liabilities (4,187) 1,867
Net cash provided by (used in) operating activities (18,929) (22,446)
Cash flows provided by (used in) investing activities:    
Purchases of marketable securities (13,809) (51,396)
Sales or maturities of marketable securities 39,060 72,639
Purchases of property and equipment   (26)
Net cash provided by (used in) investing activities 25,251 21,217
Cash flows provided by (used in) financing activities:    
Proceeds from issuance of common stock under the ATM Facility, net of offering costs 8,742  
Net cash provided by (used in) financing activities 8,742  
Net increase (decrease) in cash and cash equivalents 15,064 (1,229)
Cash and cash equivalents at beginning of period 21,709 34,601
Cash and cash equivalents at end of period 36,773 33,372
Supplemental disclosure of noncash investing and financing activities:    
Unrealized gain (loss) on marketable securities (26) 539
Property and equipment in accounts payable and accrued expenses and other current liabilities   $ 36
Right of use assets recognized upon the execution of sublease (422)  
Operating lease liabilities recognized upon the execution of sublease $ 422  
v3.24.1.1.u2
Nature of Operations
3 Months Ended
Mar. 31, 2024
Nature of Operations  
Nature of Operations

1. Nature of Operations

Passage Bio, Inc., or the Company, a Delaware corporation incorporated in July 2017, is a clinical stage genetic medicines company on a mission to improve the lives of patients with neurodegenerative diseases. The Company’s primary focus is the development and advancement of cutting-edge, one-time therapies designed to target critical underlying pathology in these conditions. The Company has a strategic research collaboration with the Trustees of the University of Pennsylvania’s, or Penn, Gene Therapy Program, or GTP.

Through this collaboration, the Company has developed its lead clinical product candidate, PBFT02, for the treatment of frontotemporal dementia, or FTD, caused by progranulin deficiency, or FTD-GRN, which seeks to elevate progranulin levels to restore lysosomal function and slow disease progression.

v3.24.1.1.u2
Risks and Liquidity
3 Months Ended
Mar. 31, 2024
Risks and Liquidity  
Risks and Liquidity

2. Risks and Liquidity

The Company has incurred recurring losses and negative cash flows from operations since inception and had an accumulated deficit of $611.2 million as of March 31, 2024. The Company anticipates incurring additional losses until such time, if ever, that it can generate significant sales of its product candidates currently in development. Substantial additional capital will be needed by the Company to fund its operations and to develop its product candidates.

The Company’s operations have consisted primarily of conducting preclinical studies, developing licensed technology, conducting clinical trials, and manufacturing clinical supply to support clinical trials. The Company faces risks associated with early-stage biotechnology companies whose product candidates are in development. Product candidates currently under development will require significant additional research and development efforts and establishing manufacturing capacity and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital for the Company to complete its research and development, achieve its research and development objectives, defend its intellectual property rights, and recruit and retain skilled personnel, and key members of management. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will realize revenue from product sales.

On March 5, 2021, the Company entered into a Sales Agreement, or the Sales Agreement, with Cowen and Company, LLC, or Cowen, relating to the applicable terms of at-the-market equity offerings, or the ATM Facility, pursuant to which the Company may, but is not obligated to, offer and sell, from time to time, shares of its common stock with an aggregate offering price up to $125.0 million through Cowen, as sales agent in the ATM Facility. During the three months ended March 31, 2024, the Company issued 6,000,000 shares of common stock under the ATM Facility, resulting in net proceeds of $8.7 million after deducting offering costs of $0.3 million.

The Company plans to seek additional funding through public or private equity offerings, debt financings, other collaborations, strategic alliances and 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 strategic alliances or other arrangements on favorable terms, or at all. The terms of any financing may adversely affect the holdings or the rights of the Company’s stockholders. If the Company is unable to obtain funding or prospects of funding are unfavorable, the Company could be required to further delay, reduce or eliminate research and development programs, product portfolio expansion or future commercialization efforts, which could adversely affect its business prospects.

In accordance with Accounting Standards Update, or ASU, No. 2014-15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern, the Company has evaluated whether there are certain conditions and events, considered in the aggregate, that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date that the financial statements are issued. As of the issuance date of these financial statements, the Company expects that its cash, cash equivalents and marketable debt securities will be sufficient to fund its forecasted operating expenses and capital expenditure requirements for at least the next twelve months from the issuance date of these financial statements.

v3.24.1.1.u2
Summary of Significant Accounting Policies
3 Months Ended
Mar. 31, 2024
Summary of Significant Accounting Policies  
Summary of Significant Accounting Policies

3. Summary of Significant Accounting Policies

The Company’s complete summary of significant accounting policies can be found in “Note 3. Summary of Significant Accounting Policies” in the audited financial statements included in the Company’s Annual Report filed on Form 10-K for the year ended December 31, 2023.

Basis of Presentation

The accompanying unaudited financial statements have been prepared in accordance with generally accepted accounting principles in the United States, or GAAP. Any reference in these notes to applicable guidance is meant to refer to GAAP as found in the Accounting Standards Codification, or ASC, and Accounting Standards Updates promulgated by the Financial Accounting Standards Board, or FASB.

Interim Financial Statements

The accompanying unaudited interim financial statements have been prepared from the books and records of the Company in accordance with GAAP for interim financial information and Rule 10-01 of Regulation S-X promulgated by the United States Securities and Exchange Commission, or SEC, which permits reduced disclosures for interim periods. All adjustments, consisting only of normal recurring adjustments, necessary for a fair presentation of the accompanying balance sheets, statements of operations and comprehensive loss, stockholders’ equity, and cash flows have been made. Although these interim financial statements do not include all of the information and footnotes required for complete annual financial statements, management believes the disclosures are adequate to make the information presented not misleading. Unaudited interim results of operations and cash flows are not necessarily indicative of the results that may be expected for the full year. Unaudited interim financial statements and footnotes should be read in conjunction with the audited financial statements and footnotes included in the Company’s 2023 Annual Report filed on Form 10-K.

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 and disclosure of contingent assets and contingent liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. Actual results could differ from those estimates.

Estimates and assumptions are periodically reviewed and the effects of the revisions are reflected in the accompanying financial statements in the period they are determined to be necessary.

Fair Value of Financial Instruments

Management believes that the carrying amounts of the Company’s financial instruments, including cash equivalents, prepaid expenses, and accounts payable, approximate fair value due to the short-term nature of those instruments.

Concentration of Credit Risk

Financial instruments that potentially subject the Company to significant concentrations of credit risk consist primarily of cash, cash equivalents, and marketable securities. The Company maintains a deposit account in a federally insured financial institution in excess of federally insured limits. The Company also maintains a money market account in a federally insured financial institution in excess of federally insured limits. The Company has not experienced any losses in such accounts and believes it is not exposed to significant risk on its cash and cash equivalents beyond the normal credit risk associated with commercial banking relationships.

The Company maintains a portfolio of marketable debt securities, which is diversified to limit exposure related to counterparty risk, industry risk, and security type risk. The Company maintains an investment policy which dictates the allocation of funds within its portfolio of marketable debt securities. The Company has not experienced any material losses in such portfolio.

Segment Information

Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. The Company views its operations and manages its business in one segment.

Cash and Cash Equivalents

The Company considers all highly-liquid investments that have maturities of three months or less when acquired to be cash equivalents. Cash equivalents as of March 31, 2024 consisted of various securities as described in Note 4. Cash consists of cash deposits at banking institutions.

Marketable Securities

The Company classifies its marketable securities as available-for-sale, which include commercial paper, certificates of deposit, corporate debt securities, United States, or U.S., government debt securities and U.S. government agency securities with original maturities of greater than three months. These securities are carried at fair market value, with unrealized gains and losses reported in comprehensive loss and accumulated other comprehensive income (loss) within stockholders’ equity. Any premium or discount arising at purchase of debt securities is amortized and/or accreted over the term of the security to other income (expense), net. Gains or losses on marketable securities sold are recognized as a component of other income (expense), net in the statement of operations and comprehensive loss on the specific identification method. All marketable securities are available for use, as needed, to fund operations and therefore, the Company classifies all marketable securities as current assets within the balance sheet.

Property and Equipment, Net

Property and equipment, net consists of laboratory equipment, office equipment, computer hardware and software, furniture and fixtures, and leasehold improvements and are recorded at cost. Maintenance and repairs that do not improve or extend the lives of the respective assets are expensed as incurred. Property and equipment are depreciated on a straight-line basis over their estimated useful lives. The Company estimates useful life on an asset-by-asset basis, which generally consists of three years for computer hardware and software, five years for office equipment, five years for laboratory equipment, and seven years for furniture and fixtures. Leasehold improvements are amortized over the shorter of the lease term or the estimated useful life of the asset.

When property and equipment are retired or otherwise disposed of, the costs and accumulated depreciation are removed from the respective accounts, with any resulting gain or loss recognized concurrently. The Company did not recognize any losses on disposals of property and equipment for the three months ended March 31, 2024 and 2023.

The Company reviews long-lived assets, such as property and equipment, for impairment when events or changes in circumstances indicate the carrying amount of the assets may not be recoverable. The Company did not recognize any impairment expenses for property and equipment for the three months ended March 31, 2024 and 2023.

Leasing

The Company evaluates leases at their inception to determine if they are an operating lease or a finance lease. As of March 31, 2024, the Company has classified all leases with terms greater than one year, as operating leases.

The Company recognizes assets and liabilities for operating leases at their inception, based on the present value of all payments due under the lease agreement. The Company uses its incremental borrowing rate to determine the present value of operating leases, which is determined by referencing collateralized borrowing rates for debt instruments with terms similar to the respective lease. The Company utilizes the accounting policy election to not separate lease and non-lease components and the accounting policy election to not apply the recognition requirement to leases with a term of twelve months or less.

The Company reviews long-lived assets, such as right of use assets, or ROU assets, for impairment when events or changes indicate the carrying amount of the ROU assets may not be recoverable. The Company did not recognize any impairment expenses for ROU assets for the three months ended March 31, 2024 and 2023.

Share-Based Compensation

The Company measures share-based awards at grant-date fair value and records compensation expense on a straight-line basis over the vesting period of the awards. The Company’s share-based compensation consists of restricted stock units, or RSUs, and options to purchase common stock, or stock option awards.

The Company uses the Black-Scholes option pricing model to value its stock option awards.

Estimating the fair value of stock option awards requires the input of assumptions, including, the expected term of stock options, and stock price volatility. The assumptions used in estimating the fair value of share-based awards represent management's estimate and involve inherent uncertainties and the application of management's judgment. As a result, if factors change and management uses different assumptions, share-based compensation expense could be materially different for future awards.

The expected term of the stock options is estimated using the “simplified method,” as the Company has limited historical information from which to develop reasonable expectations about future exercise patterns and post-vesting employment termination behavior for its stock option grants. The simplified method is the midpoint between the vesting period and the contractual term of the option. For stock price volatility, the Company uses a composite of comparable public company data as a basis for its expected volatility to calculate the fair value of option grants. The selection of comparable public company data requires the application of management’s judgement.

The Company accounts for forfeitures of RSUs and stock option awards as they occur.

Research and Development

Research and development costs are expensed as incurred and consist primarily of expenses incurred with GTP, contract research organizations, contract manufacturing organizations, internal analytical and testing activities, and employee-related expenses, including salaries, benefits, and share-based compensation. Management makes estimates of the Company’s external accrued research and development expenses, which primarily relates to contract research organizations and contract manufacturing organizations, as of each balance sheet date in the Company’s financial statements based on an estimate of progress to completion of specific tasks using facts and circumstances known to the Company at that time. The Company determines the estimates by reviewing contracts, vendor agreements, change orders, and through discussions with the Company’s internal clinical personnel and external service providers as to the progress to completion of services and the agreed-upon fee to be paid for such services. If the actual timing of the performance of services or the level of effort varies from the estimate, the Company will adjust the accrual and related expenses accordingly.

Other Income (Expense), Net

Other income (expense), net consists of interest earned on the Company’s cash equivalents and marketable securities, amortization of premium and discount on our marketable securities, and the sale of certain tax credits.

The Company recorded $1.3 million to other income (expense), net for the three months ended March 31, 2024, which is attributable to $1.3 million of interest income and the amortization of premium and discount on the Company’s marketable securities.

The Company recorded $1.5 million to other income (expense), net for three months ended March 31, 2023, which consisted of $1.1 million attributable to interest income and the amortization of premium and discount on the Company’s marketable securities, and $0.4 million related to the sale of certain tax credits.

Net Loss Per Share

Basic net loss per share of common stock is computed by dividing net loss by the weighted average number of shares of common stock outstanding during each period. Diluted loss per share of common stock includes the effect, if any, from the potential exercise or conversion of securities, such as stock options, which would result in the issuance of incremental shares of common stock. For diluted net loss per share, the weighted-average number of shares of common stock is the same for basic net loss per share due to the fact that when a net loss exists, dilutive securities are not included in the calculation as the impact is anti-dilutive.

The following potentially dilutive securities have been excluded from the computation of diluted weighted-average shares of common stock outstanding, as they would be anti-dilutive:

Three Months Ended March 31, 

2024

    

2023

Stock options

12,392,973

 

13,609,572

Unvested restricted stock units

400,167

1,193,666

Employee stock purchase plan

91,663

131,436

12,884,803

 

14,934,674

Recently Adopted Accounting Pronouncements

In November 2023, the FASB issued ASU No. 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures, or ASU 2023-07, which expands segment disclosures by requiring disclosure of significant segment expenses that are regularly provided to the chief operating decision maker and included within each reported measure of segment profit or loss, an amount and description of its composition for other segment items, and interim disclosures of a reportable segment’s profit or loss and assets. The disclosures required under ASU 2023-07 are also required for public entities with a single reportable segment. ASU 2023-07 is effective for the Company’s first fiscal year beginning after December 15, 2023 and for interim periods within the Company’s first fiscal year beginning after December 15, 2024, with early adoption permitted. The Company does not expect the adoption of ASU 2023-07 to have a material impact on its financial statements or disclosures.

In December 2023, the FASB issued ASU No. 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures, or ASU 2023-09, which requires that an entity, on an annual basis, disclose additional income tax information, primarily related to the rate reconciliation and income taxes paid. The amendments in ASU 2023-09 are intended to enhance the transparency and decision usefulness of income tax disclosures. The amendments in this ASU are effective for annual periods beginning after December 15, 2024 with early adoption permitted. The Company is currently evaluating the impact of this guidance on disclosures.

v3.24.1.1.u2
Cash, Cash Equivalents and Marketable Securities
3 Months Ended
Mar. 31, 2024
Cash, Cash Equivalents and Marketable Securities  
Cash, Cash Equivalents and Marketable Securities

4. Cash, Cash Equivalents and Marketable Securities

The following table provides details regarding the Company’s portfolio of cash and cash equivalents:

Cost or

(in thousands)

    

Amortized cost

    

Unrealized gains

    

Unrealized losses

    

Fair value

March 31, 2024:

 

  

 

  

 

  

 

  

Cash accounts in banking institutions

$

6,041

$

-

$

-

$

6,041

Money market funds

23,895

-

-

23,895

Commercial paper

991

-

-

991

Certificates of deposit

1,336

-

-

1,336

Corporate debt securities

4,510

-

-

4,510

Total

$

36,773

$

-

$

-

$

36,773

December 31, 2023:

 

  

 

  

 

  

 

  

Cash accounts in banking institutions

$

3,596

$

-

$

-

$

3,596

Money market funds

13,763

-

-

13,763

Commercial paper

2,670

-

-

2,670

Corporate debt securities

1,680

-

-

1,680

Total

$

21,709

$

-

$

-

$

21,709

The following table provides details regarding the Company’s portfolio of marketable securities:

(in thousands)

    

Amortized cost

    

Unrealized gains

    

Unrealized losses

    

Fair value

March 31, 2024:

 

  

 

  

 

  

 

  

Certificates of deposit

$

9,818

$

2

$

(1)

$

9,819

Commercial paper

30,800

-

(17)

30,783

Corporate debt securities

16,667

5

(1)

16,671

U.S. government securities

10,536

-

(57)

10,479

Total

$

67,821

$

7

$

(76)

$

67,752

December 31, 2023:

 

  

 

  

 

  

 

  

Certificates of deposit

$

10,950

$

6

$

-

$

10,956

Commercial paper

34,601

9

(4)

34,606

Corporate debt securities

22,940

8

(8)

22,940

U.S. government securities

16,049

0

(44)

16,005

U.S. government agency securities

8,088

-

(10)

8,078

Total

$

92,628

$

23

$

(66)

$

92,585

The contractual maturities of the Company’s marketable securities as of March 31, 2024, are as follows:

(in thousands)

Amortized Cost

Fair Value

Due within one year

$

67,821

$

67,752

Due after one year through five years

-

-

Total

$

67,821

$

67,752

v3.24.1.1.u2
Fair Value of Financial Instruments
3 Months Ended
Mar. 31, 2024
Fair Value of Financial Instruments  
Fair Value of Financial Instruments

5. Fair Value of Financial Instruments

Fair value is the price that could be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. Fair value determination in accordance with applicable accounting guidance requires that a number of significant judgments be made. Additionally, fair value is used on a nonrecurring basis to evaluate assets for impairment or as required for disclosure purposes by applicable accounting guidance on disclosures about fair value of financial instruments. Depending on the nature of the assets and liabilities, various valuation techniques and assumptions are used when estimating fair value. The carrying amounts of certain of the Company’s financial instruments, including prepaid expense and accounts payable are shown at cost, which approximates fair value due to the short-term nature of these instruments. The Company follows the provisions of ASC Topic 820, Fair Value Measurement, for financial assets and liabilities measured on a recurring basis. The guidance requires fair value measurements be classified and disclosed in one of the following three categories:

Level 1: Unadjusted quoted prices in active markets that are accessible at the measurement date for identical, unrestricted assets or liabilities.
Level 2: Quoted prices in markets that are not active, or inputs which are observable, either directly or indirectly, for substantially the full term of the asset or liabilities.
Level 3: Prices or valuation techniques that require inputs that are both significant to the fair value measurement and unobservable (i.e., supported by little or no market activity).

The following fair value hierarchy table presents information about the Company’s assets measured at fair value on a recurring basis. Included within cash and cash equivalents on the balance sheet, but excluded from the fair value hierarchy table, are cash deposits held at financial institutions:

Fair value measurement at

reporting date using

Quoted prices

 

in active

 

Significant

 

 

markets for

 

other

 

Significant

 

identical

 

observable

 

unobservable

 

assets

 

inputs

inputs

(in thousands)

    

(Level 1)

    

(Level 2)

    

(Level 3)

March 31, 2024:

 

  

 

  

 

  

Assets

 

  

 

  

 

  

Cash equivalents:

Money market funds

$

23,895

$

-

$

-

Commercial paper

-

991

-

Certificates of deposit

-

1,336

-

Corporate debt securities

-

4,510

-

Total cash equivalents

23,895

6,837

-

Marketable securities:

Certificates of deposit

-

9,819

-

Commercial paper

-

30,783

-

Corporate debt securities

-

16,671

-

U.S. government securities

-

10,479

-

Total marketable securities

-

67,752

-

Total financial assets

$

23,895

$

74,589

$

-

December 31, 2023:

Assets

 

  

 

  

 

  

Cash equivalents:

Money market funds

$

13,763

$

-

$

-

Commercial paper

-

2,670

-

Corporate debt securities

-

1,680

-

Total cash equivalents

13,763

4,350

-

Marketable securities:

Certificates of deposit

-

10,956

-

Commercial paper

-

34,606

-

Corporate debt securities

-

22,940

-

U.S. government securities

-

16,005

-

U.S. government agency securities

-

8,078

-

Total marketable securities

-

92,585

-

Total financial assets

$

13,763

$

96,935

$

-

v3.24.1.1.u2
Property and Equipment, net
3 Months Ended
Mar. 31, 2024
Property and Equipment, net  
Property and Equipment, net

6. Property and Equipment, Net

Property and equipment, net, consists of the following:

(in thousands)

March 31, 2024

December 31, 2023

Laboratory equipment

$

10,065

$

10,065

Office equipment

119

119

Computer hardware and software

1,077

1,077

Furniture and fixtures

419

419

Leasehold improvements

10,213

10,213

Construction in progress

638

638

Total property and equipment

22,531

22,531

Accumulated depreciation and amortization

(8,042)

(7,236)

$

14,489

$

15,295

Depreciation expense was $0.8 million and $1.0 million for the three months ended March 31, 2024 and 2023, respectively.

v3.24.1.1.u2
Accrued Expenses and Other Current Liabilities
3 Months Ended
Mar. 31, 2024
Accrued Expenses and Other Current Liabilities  
Accrued Expenses and Other Current Liabilities

7. Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following:

(in thousands)

    

March 31, 2024

    

December 31, 2023

Professional fees

$

857

$

1,176

Compensation and related benefits

 

2,134

 

6,636

Research and development

 

2,492

 

1,858

Amount due to Catalent in connection with Amended Catalent Agreements

 

2,000

 

2,000

$

7,483

$

11,670

v3.24.1.1.u2
Leases
3 Months Ended
Mar. 31, 2024
Leases  
Leases

8. Leases

2005 Market Street Lease Agreement

The Company is party to a lease agreement for office space, or the 2005 Market Street Lease Agreement, in Philadelphia, Pennsylvania. Under the 2005 Market Street Lease Agreement, the Company leased approximately 37,000 square feet. The 2005 Market Street Lease Agreement commenced in February 2021 and is expected to expire in December 2031. The Company has an option to extend the term of the 2005 Market Street Lease Agreement by two additional terms of five years each. The Company has an option to early terminate the 2005 Market Street Lease Agreement as of April 2029, given notice is provided to the landlord no less than fifteen months prior to April 2029. The optional extension and termination terms were not recognized as part of the Company’s measurement of the ROU asset and operating lease liability as of March 31, 2024. During 2023 the Company subleased all of the space at 2005 Market Street as further described in Sublease Agreement A and Sublease Agreement B below.

Sublease Agreement A

On August 7, 2023, the Company entered into a sublease agreement with a counterparty, or Sublessee A, to sublease approximately 8,000 square feet of the 2005 Market Street Lease Agreement, or Sublease Agreement A. This sublease term began on November 1, 2023, and continues through March 31, 2029. In the event the Company does not elect its early termination option under the 2005 Market Street Lease Agreement, Sublessee A has an option to extend the

sublease agreement through November 30, 2031. The base sublease rent is $0.1 million per year and increases by 2.75% annually through the expiration of the agreement. Additionally, Sublessee A is required to pay the portion of the common area maintenance expenses, operating expenses and use and occupancy taxes which the Company is required to pay under the 2005 Market Street Lease Agreement.

Pursuant to ASC 842, the Company concluded the sublease is a separate lease, as the Company was not relieved of the primary obligation under the 2005 Market Street Lease Agreement. The Company continues to account for the 2005 Market Street Lease Agreement as a lessee and in the same manner as prior to the execution of Sublease Agreement A. The Company accounted for Sublease Agreement A as the lessor, and concluded the lease qualified as an operating lease, as it did not meet the criteria of a sales-type or direct financing lease.

As a result of Sublease Agreement A, in 2023 the Company determined an impairment indicator was present. The Company compared the estimated undiscounted cash flows to the carrying value of the asset group, which includes ROU assets, leasehold improvements, and other property and equipment allocable to Sublease Agreement A. The Company concluded the carrying value of the asset group was not recoverable as it exceeded the estimated undiscounted cash flows. The Company calculated the amount of impairment using a discounted cash flow model to calculate the fair value of the asset group which incorporated the net identifiable cash flows for the term of Sublease Agreement A, including an estimate for cash flows in the residual period, and an estimated borrowing rate of a market participant subtenant. The impairment charge was recorded as of the lease execution date.

Sublease Agreement B

On September 29, 2023, the Company entered into a sublease agreement with a counterparty, or Sublessee B, to sublease approximately 29,000 square feet of the 2005 Market Street Lease Agreement, or Sublease Agreement B. This sublease term began on March 1, 2024, and continues through August 2026. Sublessee B has an option to extend the term of the sublease agreement through March 31, 2029. The base sublease rent is $0.9 million per year for the entire term of the sublease. Additionally, Sublessee B is required to pay applicable use and occupancy taxes but is not obligated to make payments for operating expenses and common area maintenance expenses which the Company is required to pay under the 2005 Market Street Lease Agreement.

Pursuant to ASC 842, the Company concluded the sublease is a separate lease, as the Company was not relieved of the primary obligation under the 2005 Market Street Lease Agreement. The Company continues to account for the 2005 Market Street Lease Agreement as a lessee and in the same manner as prior to the execution of the Sublease Agreement B. The Company accounted for Sublease Agreement B as the lessor, and concluded the lease qualified as an operating lease, as it did not meet the criteria of a sales-type or direct financing lease.

As a result of Sublease Agreement B, in 2023 the Company determined an impairment indicator was present. The Company compared the estimated undiscounted cash flows to the carrying value of the asset group, which includes ROU assets, leasehold improvements, and other property and equipment allocable to Sublease Agreement B. The Company concluded the carrying value of the asset group was not recoverable as it exceeded the estimated undiscounted cash flows. The Company calculated the amount of impairment using a discounted cash flow model to calculate the fair value of the asset group which incorporated the net identifiable cash flows for the term of Sublease Agreement B, including an estimate for cash flows in the residual period, and an estimated borrowing rate of a market participant subtenant. The impairment charge was recorded as of the lease execution date.

1835 Market Street Sublease Agreement

On February 20, 2024, the Company entered into a sublease agreement with a counterparty, or the 1835 Market Street Sublease Agreement. Under the 1835 Market Street Sublease Agreement, the Company subleased approximately 16,000 square feet of office space in Philadelphia, Pennsylvania. The sublease term began on March 26, 2024 and expires on September 30, 2025. The Company has the option to extend the term of the sublease agreement through February 28,

2029. The base sublease rent is $0.3 million per year for the original 18-month term of the sublease. Additionally, the Company is required to pay utility costs associated with the subleased premises. The optional extension was not recognized as part of the Company’s measurement of the ROU asset and operating lease liability as of March 31, 2024.

Laboratory Lease Agreement

The Company is also party to a lease agreement for laboratory space, or the Laboratory Lease Agreement, in Hopewell, New Jersey. The laboratory is focused on state-of-the-art analytical capabilities, assay development and validation, and clinical product testing to support both viral vector manufacturing and clinical development. The Laboratory Lease Agreement commenced in March 2021 and is expected to expire in March 2036. The Company has an option to extend the term of the Laboratory Lease Agreement by up to two five-year terms. This option to extend was not recognized as part of the Company's measurement of the ROU asset and operating lease liability as of March 31, 2024.

The following table summarizes future minimum lease payments for the Company’s lessee operating leases, which comprises the 2005 Market Street Lease Agreement, 1835 Market Street Sublease Agreement, and the Laboratory Lease Agreement. The below table does not include expected cash inflows related to Sublease Agreement A and Sublease Agreement B, as the Company was not relieved of its primarily obligation under the 2005 Market Street Lease Agreement:

(in thousands)

    

    

2024

$

2,906

2025

 

3,883

2026

 

3,757

2027

 

3,863

2028

 

3,973

Thereafter

 

25,706

Total undiscounted lease payments

44,088

Less: imputed interest

(17,610)

Total lease liabilities

$

26,478

The following table summarizes lease expense by lease type that was recognized during the three months ended March 31, 2024 and 2023:

Three Months Ended

Three Months Ended

($ in thousands)

March 31, 2024

March 31, 2023

Operating lease cost

$

831

$

831

Variable lease cost

720

478

$

1,551

$

1,309

The following table shows the weighted average discount rate and weighted average remaining lease term of the operating leases:

Three Months Ended

Three Months Ended

($ in thousands)

March 31, 2024

March 31, 2023

Weighted-average discount rate

9.7%

9.7%

Weighted-average remaining lease term (years)

10.9

12.0

The cash paid for amounts included in the measurement of our operating lease liabilities for the three months ended March 31, 2024 and 2023 was $0.9 million recorded in operating cash flows.

v3.24.1.1.u2
Commitments and Contingencies
3 Months Ended
Mar. 31, 2024
Commitments and Contingencies.  
Commitments and Contingencies

Amended and Restated Research, Collaboration and License Arrangement with Penn

The Company has a research, collaboration and licensing agreement with Penn, as amended, or the Penn Agreement, for research and development collaborations and exclusive license rights to patents for certain products and technologies. Under the Penn Agreement, the Company has the option to obtain exclusive licenses to, and to fund, certain research relating to the preclinical development of selected products in research programs in rare monogenic central nervous system, or CNS indications. The Company has eight remaining options available to commence additional licensed programs for CNS indications until August 3, 2026.

The Penn Agreement includes an exploratory research program to identify targets and early product candidates in certain agreed upon non-monogenic, non-rare, or large, CNS indications. The initial term of the exploratory research program is three years, or until August 2024, which term can be extended by mutual agreement. During such term, the Company will have an exclusive right of first negotiation to include additional targets to the exploratory research program in the agreed upon large CNS indications. Under the exploratory research program, the Company will have the right to further develop and commercialize any gene therapy product candidates specific for those selected targets that arise from the exploratory research programs by exercising one of its remaining eight options. The Company currently does not have any active exploratory research programs.

If the Company were to exercise any of the remaining options, it would owe Penn a non-refundable aggregate fee of $1.0 million per product indication, with $0.5 million due upfront and another $0.5 million fee owed upon a further developmental milestone.

The Company also funds discovery research conducted by Penn through August 3, 2026 and will receive exclusive rights, subject to certain limitations, to platform technologies resulting from the discovery research for the Company’s products developed with GTP, such as novel capsids, toxicity reduction technologies and delivery and formulation improvements. This funding commitment for the discovery research is $5.0 million annually, paid in quarterly increments of $1.3 million through June 2026.

The Penn Agreement requires that the Company make payments of up to (i) $16.5 million per product candidate for rare, monogenic disorders in the aggregate and (ii) $39.0 million per product candidate in the aggregate arising from the exploratory program for large CNS indications. Each payment will be due upon the achievement of specific development milestone events by such licensed product for a first indication, reduced development milestone payments for the second and third indications and no development milestone payments for subsequent indications. In addition, on a product-by-product basis, the Company is obligated to make up to $55.0 million in sales milestone payments on each licensed product based on annual sales of the licensed product in excess of defined thresholds.

Upon successful commercialization of a product using the licensed technology, the Company is obligated to pay to Penn, on a licensed product-by-licensed product and country-by-country basis, tiered royalties (subject to customary reductions) in the mid-single digits on annual worldwide net sales of such licensed product. In addition, the Company is obligated to pay to Penn a percentage of sublicensing income, ranging from the mid-single digits to low double digits, for sublicenses under the Penn Agreement. The agreement will expire on a licensed product-by-licensed product and country-by-country basis upon the later of (i) the expiration of the last valid claim of the licensed patent rights that covers the exploitation of such licensed product in such country, and (ii) the expiration of the royalty period. In addition, the Company will pay a tiered transaction fee of 1-2% of the net proceeds upon certain change of control events.

Catalent Agreements

In June 2019, the Company entered into a collaboration agreement, or the Collaboration Agreement, with Catalent Maryland, a unit of Catalent, Inc., or Catalent. As part of the Collaboration Agreement, the Company was required to

pay an annual fee for five years ending in 2025 for the exclusive use of a dedicated clean room suite, or the Clean Room Suite.

In April 2020, the Company entered into a development services and clinical supply agreement, or the Manufacturing and Supply Agreement, with Catalent to secure clinical scale manufacturing capacity for batches of active pharmaceutical ingredients for the Company’s gene therapy product candidates. Under the terms of the Manufacturing and Supply Agreement, Catalent agreed to manufacture batches of drug product for the Company’s gene therapy product candidates at the Clean Room Suite at a Catalent facility provided for in the Collaboration Agreement. The Manufacturing and Supply Agreement provided for a term of five years. The Manufacturing and Supply Agreement also included minimum annual purchase commitments.

Under both the Collaboration Agreement and the Manufacturing and Supply Agreement, the Company had an annual minimum commitment of $10.6 million per year owed to Catalent for five years from November 2020 subject to certain inflationary adjustments.

On March 31, 2023, the Company entered into certain letter agreements, the Letter Agreements, amending each of (i) the Collaboration Agreement and (ii) the Manufacturing and Supply Agreement, together with the Collaboration Agreement, the Original Catalent Agreements. On November 9, 2023, to supersede and implement the terms of the Letter Agreements, the Company entered into an amended and restated collaboration agreement and an amended and restated manufacturing and supply agreement, together the Amended Catalent Agreements.

The Amended Catalent Agreements eliminate the minimum annual purchase obligation and the obligation to pay an annual fee for use of the Clean Room Suite, thereby eliminating the annual minimum commitment of $10.6 million per year owed to Catalent through November 2025 under the Original Catalent Agreements. In consideration of this, the Company had an obligation to make aggregate payments to Catalent of $6.0 million between June 30, 2023 and May 1, 2024.

The Amended Catalent Agreements extend the term of the Original Catalent Agreements until November 6, 2030, and establish a limited exclusive relationship between the Company and Catalent for the manufacture of bulk drug substance and drug product for the Company’s adeno-associated virus delivery therapeutic product candidates for the treatment of FTD and GM1. The limited exclusive relationship under the Amended Catalent Agreements converts to a non-exclusive relationship (i) in the event Catalent fails to meet certain performance standards and (ii) following certain conditional events related to the divestiture by the Company of either FTD or GM1, in which case, if such events occur, the Company would pay Catalent certain fees. In addition, in the event of certain transactions, the Company may terminate the Amended Catalent Agreements for convenience with respect to such products, in which case, the Company would pay to Catalent a certain termination fee.

Immediately prior to the execution of the Letter Agreements, the Company had a $5.3 million prepaid asset related to upfront payments made to secure the Clean Room Suite. In connection with the Letter Agreements, the Company no longer has exclusive access to the Clean Room Suite at Catalent and, as a result, the Company recognized an expense of $5.3 million related to the elimination of the prepaid asset during the three months ended March 31, 2023.

The Company classified the $11.3 million of expenses, which comprises of $6.0 million in aggregate payments due to Catalent and the $5.3 million elimination of the prepaid asset, as general and administrative expense within the statement of operations for the three months ended March 31, 2023, as both amounts did not directly relate to the future advancement of the Company’s research and development programs.

As of March 31, 2024, the Company has made payments of $4.0 million under the Amended Catalent Agreements. The remaining $2.0 million of aggregate payments due to Catalent under the Amended Catalent Agreements are included in accrued expenses and other current liabilities as of March 31, 2024, and were paid in May 2024.

Litigation

In the normal course of business, the Company from time to time is named as a party to legal claims and actions. The Company records a loss contingency reserve for a legal proceeding when the potential loss is considered probable and can be reasonably estimated. The Company has not recorded any amounts for loss contingencies as of March 31, 2024.

The Company is currently a defendant in litigation with a former employee in the Court of Common Pleas of Philadelphia County (Commerce Division), or the Court, relating to a claim of breach of contract and violation of the Pennsylvania Wage Payment and Collection Law. The plaintiff claims that, pursuant to an alleged settlement agreement reached on February 3, 2020, the Company agreed to issue plaintiff 150,000 shares of its common stock and that such shares would not be subject to the reverse stock split implemented by the Company in connection with its initial public offering on February 14, 2020. The plaintiff’s claim is for an amount in the mid-single digit millions of dollars. The Company disagrees with the allegations that there was ever a binding settlement agreement or that any shares would not be subject to the reverse stock split, and the Company believes the plaintiff’s claim is without merit. In October 2023, the Court denied both the Company’s and the plaintiff’s motions for summary judgement and therefore the Company anticipates that this matter will go to trial in 2024. The Company intends to vigorously defend against these claims, and believes it has strong arguments to prevail in the litigation. There can be no assurance that the Company will prevail on its claims.

Employment Agreements

The Company has entered into employment agreements with certain key personnel providing for up to 18 months of salary continuation, up to 150% of target annual bonus amounts, and acceleration of vesting in stock-based compensation awards in certain circumstances.

v3.24.1.1.u2
Share-Based Compensation
3 Months Ended
Mar. 31, 2024
Share-Based Compensation  
Share-Based Compensation

10. Share-Based Compensation

Equity Incentive Plan

The Company has three equity incentive plans: the 2018 Equity Incentive Plan, as amended, or the 2018 Plan, the 2020 Equity Incentive Plan, or the Incentive Plan, and the 2021 Equity Inducement Plan, or the Inducement Plan. New awards can only be granted under the Incentive Plan and the Inducement Plan.

The total number of shares authorized under the Incentive Plan as of March 31, 2024 was 15,848,867. Additionally, 3,635,337 shares previously issued under the 2018 Plan which were forfeited are available for issuance under the Incentive Plan. As of March 31, 2024, 8,077,109 shares were available for future grants under the Incentive Plan. The number of shares of the Company’s common stock that may be issued pursuant to rights granted under the Incentive Plan shall automatically increase on January 1st of each year, commencing on January 1, 2021 and continuing for ten years, in an amount equal to five percent of the total number of shares of the Company’s common stock outstanding on December 31st of the preceding calendar year, subject to the discretion of the board of directors to determine a lesser number of shares shall be added for such year. As a result, the number of shares reserved for issuance under the Incentive Plan increased by 2,747,206 and 2,730,735 shares in January 2024 and 2023, respectively.

The Incentive Plan provides for the granting of common stock, incentive stock options, nonqualified stock options, restricted stock awards, and/or stock appreciation rights to employees, directors, and other persons, as determined by the Company’s board of directors. The Company’s stock options awarded to date under the Incentive Plan vest based on a requisite service period, generally over four-year periods, and have a term of ten years.

The Inducement Plan was approved by the Company’s board of directors in July 2021. The total number of shares authorized under the Inducement Plan as of March 31, 2024 was 2,500,000. Of this amount, 1,203,425 shares were available for future grants as of March 31, 2024. The Inducement Plan provides for the granting of nonqualified stock

options and restricted stock awards to employees hired by the Company, as determined by the Company’s board of directors. The Company’s stock options awarded to date under the Inducement Plan vest based on requisite service period and have a term of ten years. The Company’s restricted stock units awarded to date under the Inducement Plan vest based on requisite service period and have a term based on each award agreement.

The Company measures share-based awards at their grant-date fair value and records compensation expense on a straight-line basis over the vesting period of the awards. The Company recorded share-based compensation expense in the following expense categories in its accompanying statements of operations for the period presented:

Three Months Ended March 31, 

(in thousands)

2024

    

2023

Research and development

$

818

$

1,628

General and administrative

 

777

 

1,156

$

1,595

$

2,784

The following table summarizes stock option activity for the three months ended March 31, 2024:

    

    

    

Weighted

Weighted

average

average

remaining

Number of

exercise price

contractual

shares

per share

term (years)

Outstanding at January 1, 2024

 

9,290,308

 

$

5.63

 

8.0

Granted

 

3,639,950

1.48

 

  

Exercised

 

 

  

Forfeited

 

(537,285)

8.02

 

  

Expired

Outstanding at March 31, 2024

 

12,392,973

$

4.31

 

8.4

Vested and exercisable at March 31, 2024

 

5,273,496

$

7.44

 

7.2

Vested or expected to vest at March 31, 2024

 

12,392,973

$

4.31

 

8.4

The weighted average grant date fair value of options granted was $1.12 and $0.83 for the three months ended March 31, 2024 and 2023, respectively. As of March 31, 2024, the total unrecognized compensation expense related to unvested stock option awards was $10.4 million, which the Company expects to recognize over a weighted average period of 2.5 years.

The fair value of each option was estimated on the date of grant using the weighted average assumptions in the table below:

Three Months Ended March 31, 

2024

2023

Expected volatility

88.4

%  

92.4

%

Risk‑free interest rate

4.3

%

3.5

%

Expected term

6.0

years

6.0

years

Expected dividend yield

Restricted Stock Units

The Company issues RSUs to employees that vest over periods as determined by the board of directors. Any unvested shares are forfeited upon termination of services. The fair value price of the RSUs is equal to the fair market value of the Company’s common stock on the date of grant. Compensation expense is recognized on a straight-line basis over the vesting period of the RSUs.

The following table summarizes activity related to RSU awards during the three months ended March 31, 2024:

    

    

Weighted average

 

Number of shares

 

grant date fair value

Unvested balance at January 1, 2024

 

927,000

 

$

2.37

Granted

 

147,500

 

1.29

Vested

(667,666)

1.90

Forfeited

 

(6,667)

 

7.70

Unvested balance at March 31, 2024

 

400,167

 

$

2.67

As of March 31, 2024, the total unrecognized expense related to all RSUs was $0.8 million, which the Company expects to recognize over a weighted-average period of 0.7 years.

Employee Stock Purchase Plan

The Company’s 2020 Employee Stock Purchase Plan, or the ESPP, became effective on February 28, 2020. The ESPP authorizes the issuance of up to 1,981,766 shares of the Company’s common stock. Of this amount, 1,478,155 were available for future grants as of March 31, 2024. The number of shares of the Company’s common stock that may be issued pursuant to rights granted under the ESPP shall automatically increase on January 1st of each year and continuing for ten years, in an amount equal to one percent of the total number of shares of the Company’s common stock outstanding on December 31st of the preceding calendar year, subject to the discretion of the board of directors to determine a lesser number of shares shall be added for such year. The board of directors determined the shares authorized for issuance under the ESPP would not be increased in 2024.

Under the ESPP, eligible employees can purchase the Company’s common stock through accumulated payroll deductions at such times as are established by the Compensation Committee. Eligible employees may purchase the Company’s common stock at 85% of the lower of the fair market value of the Company’s common stock on the first day of the offering period or on the last day of the offering period. The offering periods under the ESPP have a duration of six months, with periods ending in May and November of each calendar year. Eligible employees may contribute up to 15% of their eligible compensation. Under the ESPP, a participant may not accrue rights to purchase more than $25,000 worth of the Company’s common stock for each calendar year in which such right is outstanding or purchase more than 4,000 shares of the Company’s common stock in any single offering period.

In accordance with the guidance in ASC 718-50, Compensation – Stock Compensation, the ability to purchase shares of the Company’s common stock at 85% of the lower of the price on the first day of the offering period or the last day of the offering period (i.e. the purchase date) represents an option and, therefore, the ESPP is a compensatory plan under this guidance. Accordingly, share-based compensation expense is determined based on the option’s grant-date fair value as estimated by applying the Black-Scholes option-pricing model and is recognized over the withholding period.

v3.24.1.1.u2
Subsequent Events
3 Months Ended
Mar. 31, 2024
Subsequent Events.  
Subsequent Events

11. Subsequent Events

None.

v3.24.1.1.u2
Summary of Significant Accounting Policies (Policies)
3 Months Ended
Mar. 31, 2024
Summary of Significant Accounting Policies  
Basis of Presentation

Basis of Presentation

The accompanying unaudited financial statements have been prepared in accordance with generally accepted accounting principles in the United States, or GAAP. Any reference in these notes to applicable guidance is meant to refer to GAAP as found in the Accounting Standards Codification, or ASC, and Accounting Standards Updates promulgated by the Financial Accounting Standards Board, or FASB.

Interim Financial Statements

Interim Financial Statements

The accompanying unaudited interim financial statements have been prepared from the books and records of the Company in accordance with GAAP for interim financial information and Rule 10-01 of Regulation S-X promulgated by the United States Securities and Exchange Commission, or SEC, which permits reduced disclosures for interim periods. All adjustments, consisting only of normal recurring adjustments, necessary for a fair presentation of the accompanying balance sheets, statements of operations and comprehensive loss, stockholders’ equity, and cash flows have been made. Although these interim financial statements do not include all of the information and footnotes required for complete annual financial statements, management believes the disclosures are adequate to make the information presented not misleading. Unaudited interim results of operations and cash flows are not necessarily indicative of the results that may be expected for the full year. Unaudited interim financial statements and footnotes should be read in conjunction with the audited financial statements and footnotes included in the Company’s 2023 Annual Report filed on Form 10-K.

Use of Estimates

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 and disclosure of contingent assets and contingent liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. Actual results could differ from those estimates.

Estimates and assumptions are periodically reviewed and the effects of the revisions are reflected in the accompanying financial statements in the period they are determined to be necessary.

Fair Value of Financial Instruments

Fair Value of Financial Instruments

Management believes that the carrying amounts of the Company’s financial instruments, including cash equivalents, prepaid expenses, and accounts payable, approximate fair value due to the short-term nature of those instruments.

Concentration of Credit Risk

Concentration of Credit Risk

Financial instruments that potentially subject the Company to significant concentrations of credit risk consist primarily of cash, cash equivalents, and marketable securities. The Company maintains a deposit account in a federally insured financial institution in excess of federally insured limits. The Company also maintains a money market account in a federally insured financial institution in excess of federally insured limits. The Company has not experienced any losses in such accounts and believes it is not exposed to significant risk on its cash and cash equivalents beyond the normal credit risk associated with commercial banking relationships.

The Company maintains a portfolio of marketable debt securities, which is diversified to limit exposure related to counterparty risk, industry risk, and security type risk. The Company maintains an investment policy which dictates the allocation of funds within its portfolio of marketable debt securities. The Company has not experienced any material losses in such portfolio.

Segment Information

Segment Information

Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. The Company views its operations and manages its business in one segment.

Cash and Cash Equivalents

Cash and Cash Equivalents

The Company considers all highly-liquid investments that have maturities of three months or less when acquired to be cash equivalents. Cash equivalents as of March 31, 2024 consisted of various securities as described in Note 4. Cash consists of cash deposits at banking institutions.

Marketable Securities

Marketable Securities

The Company classifies its marketable securities as available-for-sale, which include commercial paper, certificates of deposit, corporate debt securities, United States, or U.S., government debt securities and U.S. government agency securities with original maturities of greater than three months. These securities are carried at fair market value, with unrealized gains and losses reported in comprehensive loss and accumulated other comprehensive income (loss) within stockholders’ equity. Any premium or discount arising at purchase of debt securities is amortized and/or accreted over the term of the security to other income (expense), net. Gains or losses on marketable securities sold are recognized as a component of other income (expense), net in the statement of operations and comprehensive loss on the specific identification method. All marketable securities are available for use, as needed, to fund operations and therefore, the Company classifies all marketable securities as current assets within the balance sheet.

Property and Equipment, Net

Property and Equipment, Net

Property and equipment, net consists of laboratory equipment, office equipment, computer hardware and software, furniture and fixtures, and leasehold improvements and are recorded at cost. Maintenance and repairs that do not improve or extend the lives of the respective assets are expensed as incurred. Property and equipment are depreciated on a straight-line basis over their estimated useful lives. The Company estimates useful life on an asset-by-asset basis, which generally consists of three years for computer hardware and software, five years for office equipment, five years for laboratory equipment, and seven years for furniture and fixtures. Leasehold improvements are amortized over the shorter of the lease term or the estimated useful life of the asset.

When property and equipment are retired or otherwise disposed of, the costs and accumulated depreciation are removed from the respective accounts, with any resulting gain or loss recognized concurrently. The Company did not recognize any losses on disposals of property and equipment for the three months ended March 31, 2024 and 2023.

The Company reviews long-lived assets, such as property and equipment, for impairment when events or changes in circumstances indicate the carrying amount of the assets may not be recoverable. The Company did not recognize any impairment expenses for property and equipment for the three months ended March 31, 2024 and 2023.

Leasing

Leasing

The Company evaluates leases at their inception to determine if they are an operating lease or a finance lease. As of March 31, 2024, the Company has classified all leases with terms greater than one year, as operating leases.

The Company recognizes assets and liabilities for operating leases at their inception, based on the present value of all payments due under the lease agreement. The Company uses its incremental borrowing rate to determine the present value of operating leases, which is determined by referencing collateralized borrowing rates for debt instruments with terms similar to the respective lease. The Company utilizes the accounting policy election to not separate lease and non-lease components and the accounting policy election to not apply the recognition requirement to leases with a term of twelve months or less.

The Company reviews long-lived assets, such as right of use assets, or ROU assets, for impairment when events or changes indicate the carrying amount of the ROU assets may not be recoverable. The Company did not recognize any impairment expenses for ROU assets for the three months ended March 31, 2024 and 2023.

Share-Based Compensation

Share-Based Compensation

The Company measures share-based awards at grant-date fair value and records compensation expense on a straight-line basis over the vesting period of the awards. The Company’s share-based compensation consists of restricted stock units, or RSUs, and options to purchase common stock, or stock option awards.

The Company uses the Black-Scholes option pricing model to value its stock option awards.

Estimating the fair value of stock option awards requires the input of assumptions, including, the expected term of stock options, and stock price volatility. The assumptions used in estimating the fair value of share-based awards represent management's estimate and involve inherent uncertainties and the application of management's judgment. As a result, if factors change and management uses different assumptions, share-based compensation expense could be materially different for future awards.

The expected term of the stock options is estimated using the “simplified method,” as the Company has limited historical information from which to develop reasonable expectations about future exercise patterns and post-vesting employment termination behavior for its stock option grants. The simplified method is the midpoint between the vesting period and the contractual term of the option. For stock price volatility, the Company uses a composite of comparable public company data as a basis for its expected volatility to calculate the fair value of option grants. The selection of comparable public company data requires the application of management’s judgement.

The Company accounts for forfeitures of RSUs and stock option awards as they occur.

Research and Development

Research and Development

Research and development costs are expensed as incurred and consist primarily of expenses incurred with GTP, contract research organizations, contract manufacturing organizations, internal analytical and testing activities, and employee-related expenses, including salaries, benefits, and share-based compensation. Management makes estimates of the Company’s external accrued research and development expenses, which primarily relates to contract research organizations and contract manufacturing organizations, as of each balance sheet date in the Company’s financial statements based on an estimate of progress to completion of specific tasks using facts and circumstances known to the Company at that time. The Company determines the estimates by reviewing contracts, vendor agreements, change orders, and through discussions with the Company’s internal clinical personnel and external service providers as to the progress to completion of services and the agreed-upon fee to be paid for such services. If the actual timing of the performance of services or the level of effort varies from the estimate, the Company will adjust the accrual and related expenses accordingly.

Other Income (Expense), Net

Other Income (Expense), Net

Other income (expense), net consists of interest earned on the Company’s cash equivalents and marketable securities, amortization of premium and discount on our marketable securities, and the sale of certain tax credits.

The Company recorded $1.3 million to other income (expense), net for the three months ended March 31, 2024, which is attributable to $1.3 million of interest income and the amortization of premium and discount on the Company’s marketable securities.

The Company recorded $1.5 million to other income (expense), net for three months ended March 31, 2023, which consisted of $1.1 million attributable to interest income and the amortization of premium and discount on the Company’s marketable securities, and $0.4 million related to the sale of certain tax credits.

Net Loss Per Share

Net Loss Per Share

Basic net loss per share of common stock is computed by dividing net loss by the weighted average number of shares of common stock outstanding during each period. Diluted loss per share of common stock includes the effect, if any, from the potential exercise or conversion of securities, such as stock options, which would result in the issuance of incremental shares of common stock. For diluted net loss per share, the weighted-average number of shares of common stock is the same for basic net loss per share due to the fact that when a net loss exists, dilutive securities are not included in the calculation as the impact is anti-dilutive.

The following potentially dilutive securities have been excluded from the computation of diluted weighted-average shares of common stock outstanding, as they would be anti-dilutive:

Three Months Ended March 31, 

2024

    

2023

Stock options

12,392,973

 

13,609,572

Unvested restricted stock units

400,167

1,193,666

Employee stock purchase plan

91,663

131,436

12,884,803

 

14,934,674

Recently Adopted Accounting Pronouncements

Recently Adopted Accounting Pronouncements

In November 2023, the FASB issued ASU No. 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures, or ASU 2023-07, which expands segment disclosures by requiring disclosure of significant segment expenses that are regularly provided to the chief operating decision maker and included within each reported measure of segment profit or loss, an amount and description of its composition for other segment items, and interim disclosures of a reportable segment’s profit or loss and assets. The disclosures required under ASU 2023-07 are also required for public entities with a single reportable segment. ASU 2023-07 is effective for the Company’s first fiscal year beginning after December 15, 2023 and for interim periods within the Company’s first fiscal year beginning after December 15, 2024, with early adoption permitted. The Company does not expect the adoption of ASU 2023-07 to have a material impact on its financial statements or disclosures.

In December 2023, the FASB issued ASU No. 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures, or ASU 2023-09, which requires that an entity, on an annual basis, disclose additional income tax information, primarily related to the rate reconciliation and income taxes paid. The amendments in ASU 2023-09 are intended to enhance the transparency and decision usefulness of income tax disclosures. The amendments in this ASU are effective for annual periods beginning after December 15, 2024 with early adoption permitted. The Company is currently evaluating the impact of this guidance on disclosures.

v3.24.1.1.u2
Summary of Significant Accounting Policies (Tables)
3 Months Ended
Mar. 31, 2024
Summary of Significant Accounting Policies  
Schedule of antidilutive securities excluded from computation of earnings per share

Three Months Ended March 31, 

2024

    

2023

Stock options

12,392,973

 

13,609,572

Unvested restricted stock units

400,167

1,193,666

Employee stock purchase plan

91,663

131,436

12,884,803

 

14,934,674

v3.24.1.1.u2
Cash, Cash Equivalents and Marketable Securities (Tables)
3 Months Ended
Mar. 31, 2024
Cash, Cash Equivalents and Marketable Securities  
Schedule of details regarding the Company's portfolio of cash and cash equivalents

Cost or

(in thousands)

    

Amortized cost

    

Unrealized gains

    

Unrealized losses

    

Fair value

March 31, 2024:

 

  

 

  

 

  

 

  

Cash accounts in banking institutions

$

6,041

$

-

$

-

$

6,041

Money market funds

23,895

-

-

23,895

Commercial paper

991

-

-

991

Certificates of deposit

1,336

-

-

1,336

Corporate debt securities

4,510

-

-

4,510

Total

$

36,773

$

-

$

-

$

36,773

December 31, 2023:

 

  

 

  

 

  

 

  

Cash accounts in banking institutions

$

3,596

$

-

$

-

$

3,596

Money market funds

13,763

-

-

13,763

Commercial paper

2,670

-

-

2,670

Corporate debt securities

1,680

-

-

1,680

Total

$

21,709

$

-

$

-

$

21,709

Schedule of details regarding the Company's portfolio of marketable securities

(in thousands)

    

Amortized cost

    

Unrealized gains

    

Unrealized losses

    

Fair value

March 31, 2024:

 

  

 

  

 

  

 

  

Certificates of deposit

$

9,818

$

2

$

(1)

$

9,819

Commercial paper

30,800

-

(17)

30,783

Corporate debt securities

16,667

5

(1)

16,671

U.S. government securities

10,536

-

(57)

10,479

Total

$

67,821

$

7

$

(76)

$

67,752

December 31, 2023:

 

  

 

  

 

  

 

  

Certificates of deposit

$

10,950

$

6

$

-

$

10,956

Commercial paper

34,601

9

(4)

34,606

Corporate debt securities

22,940

8

(8)

22,940

U.S. government securities

16,049

0

(44)

16,005

U.S. government agency securities

8,088

-

(10)

8,078

Total

$

92,628

$

23

$

(66)

$

92,585

Schedule of contractual maturities of our marketable securities

(in thousands)

Amortized Cost

Fair Value

Due within one year

$

67,821

$

67,752

Due after one year through five years

-

-

Total

$

67,821

$

67,752

v3.24.1.1.u2
Fair Value of Financial Instruments (Tables)
3 Months Ended
Mar. 31, 2024
Fair Value of Financial Instruments  
Summary of assets measured at fair value on a recurring basis

Fair value measurement at

reporting date using

Quoted prices

 

in active

 

Significant

 

 

markets for

 

other

 

Significant

 

identical

 

observable

 

unobservable

 

assets

 

inputs

inputs

(in thousands)

    

(Level 1)

    

(Level 2)

    

(Level 3)

March 31, 2024:

 

  

 

  

 

  

Assets

 

  

 

  

 

  

Cash equivalents:

Money market funds

$

23,895

$

-

$

-

Commercial paper

-

991

-

Certificates of deposit

-

1,336

-

Corporate debt securities

-

4,510

-

Total cash equivalents

23,895

6,837

-

Marketable securities:

Certificates of deposit

-

9,819

-

Commercial paper

-

30,783

-

Corporate debt securities

-

16,671

-

U.S. government securities

-

10,479

-

Total marketable securities

-

67,752

-

Total financial assets

$

23,895

$

74,589

$

-

December 31, 2023:

Assets

 

  

 

  

 

  

Cash equivalents:

Money market funds

$

13,763

$

-

$

-

Commercial paper

-

2,670

-

Corporate debt securities

-

1,680

-

Total cash equivalents

13,763

4,350

-

Marketable securities:

Certificates of deposit

-

10,956

-

Commercial paper

-

34,606

-

Corporate debt securities

-

22,940

-

U.S. government securities

-

16,005

-

U.S. government agency securities

-

8,078

-

Total marketable securities

-

92,585

-

Total financial assets

$

13,763

$

96,935

$

-

v3.24.1.1.u2
Property and Equipment, net (Tables)
3 Months Ended
Mar. 31, 2024
Property and Equipment, net  
Schedule of Property, Plant and Equipment, Useful Life [Table Text Block]

(in thousands)

March 31, 2024

December 31, 2023

Laboratory equipment

$

10,065

$

10,065

Office equipment

119

119

Computer hardware and software

1,077

1,077

Furniture and fixtures

419

419

Leasehold improvements

10,213

10,213

Construction in progress

638

638

Total property and equipment

22,531

22,531

Accumulated depreciation and amortization

(8,042)

(7,236)

$

14,489

$

15,295

v3.24.1.1.u2
Accrued Expenses and Other Current Liabilities (Tables)
3 Months Ended
Mar. 31, 2024
Accrued Expenses and Other Current Liabilities  
Schedule of accrued liabilities and other current liabilities

(in thousands)

    

March 31, 2024

    

December 31, 2023

Professional fees

$

857

$

1,176

Compensation and related benefits

 

2,134

 

6,636

Research and development

 

2,492

 

1,858

Amount due to Catalent in connection with Amended Catalent Agreements

 

2,000

 

2,000

$

7,483

$

11,670

v3.24.1.1.u2
Leases (Tables)
3 Months Ended
Mar. 31, 2024
Leases  
Schedule of future minimum rental payments for operating leases

(in thousands)

    

    

2024

$

2,906

2025

 

3,883

2026

 

3,757

2027

 

3,863

2028

 

3,973

Thereafter

 

25,706

Total undiscounted lease payments

44,088

Less: imputed interest

(17,610)

Total lease liabilities

$

26,478

Summary of operating leases

Three Months Ended

Three Months Ended

($ in thousands)

March 31, 2024

March 31, 2023

Operating lease cost

$

831

$

831

Variable lease cost

720

478

$

1,551

$

1,309

Three Months Ended

Three Months Ended

($ in thousands)

March 31, 2024

March 31, 2023

Weighted-average discount rate

9.7%

9.7%

Weighted-average remaining lease term (years)

10.9

12.0

v3.24.1.1.u2
Share-Based Compensation (Tables)
3 Months Ended
Mar. 31, 2024
Share-Based Compensation  
Schedule of share-based compensation expense category

Three Months Ended March 31, 

(in thousands)

2024

    

2023

Research and development

$

818

$

1,628

General and administrative

 

777

 

1,156

$

1,595

$

2,784

Summary of stock option activity plan

    

    

    

Weighted

Weighted

average

average

remaining

Number of

exercise price

contractual

shares

per share

term (years)

Outstanding at January 1, 2024

 

9,290,308

 

$

5.63

 

8.0

Granted

 

3,639,950

1.48

 

  

Exercised

 

 

  

Forfeited

 

(537,285)

8.02

 

  

Expired

Outstanding at March 31, 2024

 

12,392,973

$

4.31

 

8.4

Vested and exercisable at March 31, 2024

 

5,273,496

$

7.44

 

7.2

Vested or expected to vest at March 31, 2024

 

12,392,973

$

4.31

 

8.4

Schedule of weighted average assumptions applied to options

Three Months Ended March 31, 

2024

2023

Expected volatility

88.4

%  

92.4

%

Risk‑free interest rate

4.3

%

3.5

%

Expected term

6.0

years

6.0

years

Expected dividend yield

Summary of activity related to restricted stock unit

    

    

Weighted average

 

Number of shares

 

grant date fair value

Unvested balance at January 1, 2024

 

927,000

 

$

2.37

Granted

 

147,500

 

1.29

Vested

(667,666)

1.90

Forfeited

 

(6,667)

 

7.70

Unvested balance at March 31, 2024

 

400,167

 

$

2.67

v3.24.1.1.u2
Risks and Liquidity (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 05, 2021
Mar. 31, 2024
Dec. 31, 2023
Risks And Liquidity [Line Items]      
Accumulated deficit   $ (611,179) $ (594,468)
Sale of common stock, net of issuance costs   $ 8,742  
ATM Facility      
Risks And Liquidity [Line Items]      
Shares issued   6,000,000  
Proceeds from issuance of common stock, net of offering costs   $ 8,700  
Issuance cost   $ 300  
ATM Facility | Maximum      
Risks And Liquidity [Line Items]      
Sale of common stock, net of issuance costs $ 125,000    
v3.24.1.1.u2
Summary of Significant Accounting Policies (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2024
Mar. 31, 2023
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Other income (expense), net $ 1,339 $ 1,545
Amortization of premium and discount $ 1,300 1,100
Gain (loss) on sale of tax credits   $ 400
Amount of antidilutive securities excluded from computation of earnings per share 12,884,803 14,934,674
Stock options (including shares subject to repurchase)    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Amount of antidilutive securities excluded from computation of earnings per share 12,392,973 13,609,572
Unvested restricted stock units    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Amount of antidilutive securities excluded from computation of earnings per share 400,167 1,193,666
Employee stock purchase plan    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Amount of antidilutive securities excluded from computation of earnings per share 91,663 131,436
Computer hardware and software    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Useful life 3 years  
Office equipment    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Useful life 5 years  
Laboratory equipment    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Useful life 5 years  
Furniture and fixtures    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Useful life 7 years  
v3.24.1.1.u2
Cash, Cash Equivalents and Marketable Securities - Portfolio of Cash and Cash Equivalents (Details) - USD ($)
$ in Thousands
Mar. 31, 2024
Dec. 31, 2023
Cash and cash equivalents    
Cost or Amortized cost $ 36,773 $ 21,709
Fair value 36,773 21,709
Cash accounts in banking institutions    
Cash and cash equivalents    
Cost or Amortized cost 6,041 3,596
Fair value 6,041 3,596
Money market funds    
Cash and cash equivalents    
Cost or Amortized cost 23,895 13,763
Fair value 23,895 13,763
Commercial paper    
Cash and cash equivalents    
Cost or Amortized cost 991 2,670
Fair value 991 2,670
Certificates of deposit    
Cash and cash equivalents    
Cost or Amortized cost 1,336  
Fair value 1,336  
Corporate debt securities    
Cash and cash equivalents    
Cost or Amortized cost 4,510 1,680
Fair value $ 4,510 $ 1,680
v3.24.1.1.u2
Cash, Cash Equivalents and Marketable Securities - Portfolio of Marketable Securities (Details) - USD ($)
$ in Thousands
Mar. 31, 2024
Dec. 31, 2023
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]    
Amortized cost $ 67,821 $ 92,628
Unrealized gains 7 23
Unrealized losses (76) (66)
Fair value 67,752 92,585
Certificates of deposit    
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]    
Amortized cost 9,818 10,950
Unrealized gains 2 6
Unrealized losses (1)  
Fair value 9,819 10,956
Commercial paper    
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]    
Amortized cost 30,800 34,601
Unrealized gains   9
Unrealized losses (17) (4)
Fair value 30,783 34,606
Corporate debt securities    
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]    
Amortized cost 16,667 22,940
Unrealized gains 5 8
Unrealized losses (1) (8)
Fair value 16,671 22,940
U.S. government securities    
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]    
Amortized cost 10,536 16,049
Unrealized gains   0
Unrealized losses (57) (44)
Fair value $ 10,479 16,005
U.S. government agency securities    
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]    
Amortized cost   8,088
Unrealized losses   (10)
Fair value   $ 8,078
v3.24.1.1.u2
Cash, Cash Equivalents and Marketable Securities - (Contractual Final Maturities of Marketable Securities) (Details)
$ in Thousands
Mar. 31, 2024
USD ($)
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]  
Due within one year, Amortized Cost $ 67,821
Total, Amortized Cost 67,821
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Fair Value [Abstract]  
Due within one year, Fair Value 67,752
Total, Fair Value $ 67,752
v3.24.1.1.u2
Fair Value of Financial Instruments (Recurring basis) (Details) - USD ($)
$ in Thousands
Mar. 31, 2024
Dec. 31, 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash equivalents $ 36,773 $ 21,709
Marketable securities 67,752 92,585
Certificates of deposit    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities 9,819 10,956
Commercial paper    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities 30,783 34,606
Corporate debt securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities 16,671 22,940
U.S. government securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities 10,479 16,005
U.S. government agency securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities   8,078
Money market funds    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash equivalents 23,895 13,763
Commercial paper    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash equivalents 991 2,670
Certificates of deposit    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash equivalents 1,336  
Corporate debt securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash equivalents 4,510 1,680
Level 1 | Recurring    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash equivalents 23,895 13,763
Total financial assets 23,895 13,763
Level 1 | Recurring | Money market funds    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash equivalents 23,895 13,763
Level 2 | Recurring    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash equivalents 6,837 4,350
Marketable securities 67,752 92,585
Total financial assets 74,589 96,935
Level 2 | Recurring | Certificates of deposit    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities 9,819 10,956
Level 2 | Recurring | Commercial paper    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash equivalents   2,670
Marketable securities 30,783 34,606
Level 2 | Recurring | Corporate debt securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash equivalents   1,680
Marketable securities 16,671 22,940
Level 2 | Recurring | U.S. government securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities 10,479 16,005
Level 2 | Recurring | U.S. government agency securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities   $ 8,078
Level 2 | Recurring | Commercial paper    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash equivalents 991  
Level 2 | Recurring | Certificates of deposit    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash equivalents 1,336  
Level 2 | Recurring | Corporate debt securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash equivalents $ 4,510  
v3.24.1.1.u2
Property and Equipment, net (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2024
Mar. 31, 2023
Dec. 31, 2023
Property, Plant and Equipment [Line Items]      
Total property and equipment $ 22,531   $ 22,531
Accumulated depreciation and amortization (8,042)   (7,236)
Total, property plant and equipment net 14,489   15,295
Depreciation expense 806 $ 978  
Laboratory equipment      
Property, Plant and Equipment [Line Items]      
Total property and equipment 10,065   10,065
Office equipment      
Property, Plant and Equipment [Line Items]      
Total property and equipment 119   119
Computer hardware and software.      
Property, Plant and Equipment [Line Items]      
Total property and equipment 1,077   1,077
Furniture and fixtures      
Property, Plant and Equipment [Line Items]      
Total property and equipment 419   419
Leasehold improvements      
Property, Plant and Equipment [Line Items]      
Total property and equipment 10,213   10,213
Construction in progress      
Property, Plant and Equipment [Line Items]      
Total property and equipment $ 638   $ 638
v3.24.1.1.u2
Accrued Expenses and Other Current Liabilities (Details) - USD ($)
$ in Thousands
Mar. 31, 2024
Dec. 31, 2023
Accrued Expenses and Other Current Liabilities    
Professional fees $ 857 $ 1,176
Compensation and related benefits 2,134 6,636
Research and development 2,492 1,858
Amount due to Catalent in connection with Amended Catalent Agreements 2,000 2,000
Accrued expenses and other current liabilities $ 7,483 $ 11,670
v3.24.1.1.u2
Leases (Details)
$ in Thousands
3 Months Ended
Feb. 20, 2024
USD ($)
ft²
Sep. 29, 2023
USD ($)
ft²
Aug. 07, 2023
USD ($)
ft²
Feb. 03, 2020
shares
Mar. 31, 2024
USD ($)
ft²
item
Lessee, Lease, Description [Line Items]          
Common stock | shares       150,000  
Target annual bonus         150.00%
Future minimum lease payments          
2024         $ 2,906
2025         3,883
2026         3,757
2027         3,863
2028         3,973
Thereafter         25,706
Total undiscounted lease payments         44,088
Less: imputed interest         (17,610)
Total Lease Liabilities         $ 26,478
Operating Leases For Office Space          
Lessee, Lease, Description [Line Items]          
Area leased | ft²         37,000
Option to extend lease         true
Number of extension terms | item         2
Renewal term of lease         5 years
Option to terminate lease         true
Notice Period for termination lease         15 months
Sublease Agreement A          
Lessee, Lease, Description [Line Items]          
Area leased | ft²     8,000    
Option to extend lease     true    
sublease     $ 100    
Annual increase in sublease rent (as a percent)     2.75%    
Sublease Agreement B          
Lessee, Lease, Description [Line Items]          
Area leased | ft²   29,000      
Option to extend lease   true      
sublease   $ 900      
1835 Market Street Sublease Agreement          
Lessee, Lease, Description [Line Items]          
Area leased | ft² 16,000        
Term of the lease 18 months        
Option to extend lease true        
sublease $ 300        
Maximum | Operating Leases For Laboratory Space          
Lessee, Lease, Description [Line Items]          
Number of extension terms | item         2
Extended term of new lease agreement         5 years
v3.24.1.1.u2
Leases - Operating lease cost (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2024
Mar. 31, 2023
Leases    
Operating lease cost $ 831 $ 831
Variable lease cost 720 478
Lease cost $ 1,551 $ 1,309
Weighted-average discount rate 9.70% 9.70%
Weighted-average remaining lease term (years) 10 years 10 months 24 days 12 years
Operating lease payments $ 900 $ 900
v3.24.1.1.u2
Commitments and Contingencies - Collaboration Agreements (Details) - USD ($)
$ in Millions
1 Months Ended 3 Months Ended 11 Months Ended
Aug. 03, 2020
Feb. 03, 2020
Apr. 30, 2020
Jun. 30, 2019
Mar. 31, 2024
Mar. 31, 2023
May 01, 2024
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]              
Common stock   150,000          
Target annual bonus         150.00%    
Catalent Maryland, Inc. (Catalent)              
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]              
Annual fee payable, term       5 years      
Period for which annual fee is payable     5 years        
Term of manufacturing and supply agreement     5 years        
Minimum amount agreed to purchase in batches of drug product     $ 10.6        
Aggregate payments on collaboration             $ 6.0
Accrued payments on collaboration         $ 2.0    
Prepaid assets related to upfront payments         5.3    
Payments made         4.0    
Catalent Maryland, Inc. (Catalent) | General and administrative              
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]              
Expenses on elimination of prepaid asset         5.3 $ 5.3  
Expense on write off         11.3    
Expense on write off of aggregate payments         6.0    
Amended and restated agreement with Penn              
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]              
Annual fee payable $ 5.0            
Quarterly fee payable 1.3            
Upfront payments 1.0            
Upfront fee payable upon clinical candidate designation 0.5            
Upfront fee due $ 0.5            
Amount payable per product candidate for rare, monogenic disorders         16.5    
Amount payable per product candidate arising from the exploratory program for large CNS indications         39.0    
Sales milestone payments         $ 55.0    
Amended and restated agreement with Penn | Minimum              
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]              
Collaboration agreement, tiered transaction fee percent         1.00%    
Amended and restated agreement with Penn | Maximum              
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]              
Collaboration agreement, tiered transaction fee percent         2.00%    
v3.24.1.1.u2
Share-Based Compensation - Equity Incentive Plan & ESPP (Details)
1 Months Ended 3 Months Ended
Feb. 28, 2020
USD ($)
shares
Jan. 31, 2024
shares
Jan. 31, 2023
shares
Mar. 31, 2024
plan
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of equity incentive plans | plan       3
Number of shares purchased 4,000      
Equity Incentive Plan        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Shares authorized       15,848,867
Shares available for future grant       3,635,337
Shares available for future grant       8,077,109
Period till which there is automatic increase in rights granted under the Plan       10 years
Percent of the total number of shares of the Company's common stock outstanding       5.00%
Term of award       10 years
Vesting period       4 years
Additional number of common shares reserved for future issuance   2,747,206 2,730,735  
Equity Inducement Plan 2021        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Shares authorized       2,500,000
Shares available for future grant       1,203,425
Term of award       10 years
Employee Stock Purchase Plan        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Shares authorized 1,981,766      
Shares available for future grant       1,478,155
Period till which there is automatic increase in rights granted under ESPP 10 years      
Percentage of common stock outstanding 1.00%      
Percentage of stock purchase price 85.00%      
Percentage of maximum employee contribution 15.00%      
Maximum amount of common stock that can be purchased | $ $ 25,000      
v3.24.1.1.u2
Share-Based Compensation - Share-based compensation expense (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2024
Mar. 31, 2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Share-based compensation expense $ 1,595 $ 2,784
Research and development    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Share-based compensation expense 818 1,628
General and administrative    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Share-based compensation expense $ 777 $ 1,156
v3.24.1.1.u2
Share-Based Compensation - Stock Option Activity (Details) - USD ($)
$ / shares in Units, $ in Millions
3 Months Ended 12 Months Ended
Mar. 31, 2024
Mar. 31, 2023
Dec. 31, 2023
Number of shares      
Outstanding, Beginning of period 9,290,308    
Granted 3,639,950    
Forfeited (537,285)    
Outstanding, Ending of period 12,392,973   9,290,308
Vested and exercisable at March 31, 2024 5,273,496    
Vested or expected to vest at March 31, 2024 12,392,973    
Weighted average exercise price per share      
Outstanding, Beginning of period $ 5.63    
Granted 1.48    
Forfeited 8.02    
Outstanding, Ending of period 4.31   $ 5.63
Vested and exercisable at March 31, 2024 7.44    
Vested or expected to vest at March 31, 2024 $ 4.31    
Weighted average remaining contractual term (years)      
Outstanding 8 years 4 months 24 days   8 years
Vested and exercisable at March 31, 2024 7 years 2 months 12 days    
Vested or expected to vest at March 31, 2024 8 years 4 months 24 days    
Weighted average grant date fair value of options granted $ 1.12 $ 0.83  
Unrecognized compensation expense related to unvested stock option awards $ 10.4    
Weighted average period for recognition 2 years 6 months    
v3.24.1.1.u2
Share-Based Compensation - Assumptions Used in Determining Fair Value & Early exercise of Stock Options (Details) - Employee Stock Option
3 Months Ended
Mar. 31, 2024
Mar. 31, 2023
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]    
Expected volatility 88.40% 92.40%
Risk-free interest rate 4.30% 3.50%
Expected term 6 years 6 years
v3.24.1.1.u2
Share-Based Compensation - Restricted Stock Units (Details) - USD ($)
$ / shares in Units, $ in Millions
3 Months Ended
Mar. 31, 2024
Dec. 31, 2023
Weighted average grant date fair value    
Weighted average period for recognition 2 years 6 months  
Unvested restricted stock units    
Number of shares    
Unvested balance, Beginning 927,000  
Granted 147,500  
Vested (667,666)  
Forfeited (6,667)  
Unvested balance, Ending 400,167  
Weighted average grant date fair value    
Unvested balance, Weighted average grant date fair value, Beginning $ 2.67 $ 2.37
Granted, Weighted average grant date fair value 1.29  
Vested, Weighted average grant date fair value 1.90  
Forfeited, Weighted average grant date fair value 7.70  
Unvested balance, Weighted average grant date fair value, Ending $ 2.67  
Total unrecognized expense $ 0.8  
Weighted average period for recognition 8 months 12 days  
v3.24.1.1.u2
Pay vs Performance Disclosure - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2024
Mar. 31, 2023
Pay vs Performance Disclosure    
Net Income (Loss) $ (16,711) $ (34,338)
v3.24.1.1.u2
Insider Trading Arrangements
3 Months Ended
Mar. 31, 2024
Trading Arrangements, by Individual  
Rule 10b5-1 Arrangement Adopted false
Non-Rule 10b5-1 Arrangement Adopted false
Rule 10b5-1 Arrangement Terminated false
Non-Rule 10b5-1 Arrangement Terminated false