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Stock-based compensation (Tables)
 6 Months Ended
Jun. 30, 2024
Share-Based Payment Arrangement [Abstract]  
Schedule of Stock Option Activity Under Plan
A summary of stock option activity is as follows:
Number
of Shares		Weighted-
Average
Exercise Price
Outstanding at January 1, 202410,902,845 $7.42 
Granted2,678,525 $2.91 
Exercised(14,223)$3.25 
Cancelled/forfeited(924,795)$7.23 
Outstanding at June 30, 202412,642,352 $6.48 
Exercisable at June 30, 20247,121,556 $8.16 
Schedule of Restricted Stock Activity
A summary of the RSU activity is as follows:
Number of Shares
Unvested at January 1, 20243,834,108 
Granted2,360,949 
Vested(754,153)
Forfeited(a)
(500,054)
Unvested at June 30, 20244,940,850 
(a) Includes 14,467 rescinded RSUs.
Schedule of Stock-Based Compensation Expense by Award Type
The following table presents stock-based compensation expense by award type included within the Company’s condensed consolidated statements of operations and comprehensive loss:
Three Months Ended June 30,Six Months Ended June 30,
(in thousands)2024202320242023
Stock options$2,498 $4,288 $5,095 $8,507 
Restricted stock units and other stock awards
1,813 2,060 3,762 3,953 
Employee stock purchase plan114 295 228 590 
Stock-based compensation expense included in total operating expenses$4,425 $6,643 $9,085 $13,050 
Schedule of Stock-Based Compensation Expense as Reflected in the Company's Condensed Consolidated Statements of Operations and Comprehensive Loss
The following table presents stock-based compensation expense as reflected in the Company’s condensed consolidated statements of operations and comprehensive loss:
Three Months Ended June 30,Six Months Ended June 30,
(in thousands)2024202320242023
Research and development$2,362 $3,396 $4,890 $6,728 
General and administrative2,063 3,247 4,195 6,322 
Stock-based compensation expense included in total operating expenses$4,425 $6,643 $9,085 $13,050 
Schedule of Weighted Average Assumptions for Estimating Fair Value of Option Awards
The fair value of each option award is estimated on the date of grant using the Black-Scholes option pricing model with the following weighted average assumptions:
Three Months Ended
June 30,		Six Months Ended June 30,
2024202320242023
Risk-free interest rate4.4 %3.7 %4.0 %3.6 %
Expected dividend yield— %— %— %— %
Expected term (years)5.495.845.986.04
Expected stock price volatility118 %100 %116 %99 %