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Stock-based compensation (Tables)
 3 Months Ended
Mar. 31, 2022
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, 20228,342,429 $11.25 
Granted1,917,634 6.05 
Exercised(26,951)3.58 
Cancelled(204,371)12.74 
Outstanding at March 31, 202210,028,741 $10.25 
Vested and expected to vest at March 31, 202210,028,741 $10.25 
Exercisable at March 31, 20224,307,274 $8.14 
Schedule of Restricted Stock Activity A summary of the RSU activity is as follows:
Number of Shares
Unvested at January 1, 2022817,609 
Granted870,524 
Vested(167,174)
Forfeited(64,519)
Unvested at March 31, 20221,456,440 
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 statement of operations and comprehensive loss:
Three Months Ended
March 31,
(in thousands)20222021
Stock options$4,118 $3,114 
Restricted stock units1,209 806 
Employee stock purchase plan158 119 
Stock-based compensation expense included in total operating expenses$5,485 $4,039 
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
March 31,
(in thousands)20222021
Research and development$2,933 $2,301 
General and administrative2,552 1,738 
Stock-based compensation expense included in total operating expenses$5,485 $4,039 
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
March 31,
20222021
Risk-free interest rate1.6 %0.6 %
Expected dividend yield— %— %
Expected term (years)6.046.06
Expected stock price volatility87 %83 %