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Stock-based compensation (Tables)
 12 Months Ended
Dec. 31, 2025
Share-Based Payment Arrangement [Abstract]  
Schedule of stock-based compensation expense
Stock-based compensation expense was as follows (in thousands):
Years Ended December 31,
20252024
Stock-based compensation expense:
Research and development$8,977 $12,539 
General and administrative10,122 17,123 
Total stock-based compensation expense$19,099 $29,662 
Summary of stock option activity
The following table summarizes the stock option activity under the Company’s equity awards plans for the year ended December 31, 2025:
Number of
Options		Weighted-Average
Exercise Price		Weighted-Average
Remaining
Contractual
Term (in years)		Aggregate
Intrinsic
Value
(in thousands)
Outstanding as of December 31, 202411,508,150 $12.00 7.70$2,877 
Granted2,172,150 2.92 
Exercised(50,000)2.15 
Forfeited/expired(769,813)8.99 
Outstanding as of December 31, 202512,860,487 $8.26 6.39$156 
Exercisable as of December 31, 20259,026,492 $9.66 5.69$8 
Vested and expected to vest as of December 31, 202512,860,487 $8.26 6.39$156 
Other information related to the option activity of the Company was as follows:
Years Ended December 31,
20252024
Weighted-average fair value of options granted$2.33 $5.59 
Intrinsic value of options exercised (in thousands)$62 $407 
On three separate dates in April, September, and October 2024, the Company's Board of Directors approved the grant of non-qualified stock options to purchase shares of the Company's common stock to three new employees. Options granted under these inducement grants vest over a period of four years with 25% of the award vesting on the first anniversary of the vesting start date and the balance vesting in equal quarterly installments thereafter.
Number of
Options		Weighted-Average
Exercise Price		Weighted-Average
Remaining
Contractual
Term (in years)		Aggregate
Intrinsic
Value
(in thousands)
Outstanding as of December 31, 2024990,360 $5.11 9.28$40 
Granted— — 
Exercised— — 
Forfeited/expired(146,880)6.32 
Outstanding as of December 31, 2025843,480 $4.90 8.27$— 
Exercisable as of December 31, 2025344,137 $4.52 8.07$— 
Vested and expected to vest as of December 31, 2025843,480 $4.90 8.27$— 
Other information related to the option activity of the Company was as follows:
Years Ended December 31,
20252024
Weighted-average fair value of options granted$— $4.94 
Summary of significant valuation assumptions
The following table summarizes assumptions used in the Black-Scholes option pricing model to determine the fair value of stock options granted to employees:
Years Ended December 31,
20252024
Expected option life (years)
5.50 - 6.08
5.50 - 6.11
Risk-free interest rate
3.97% - 4.43%
3.56% - 4.46%
Expected volatility
96.87% - 102.94%
102.82% - 104.41%
Expected dividend yield0.00%0.00%
The following table summarizes assumptions used in the Black-Scholes option pricing model to determine the fair value of stock options granted to employees in the year ended December 31 2024:
Expected option life (years)
6.08 - 6.11
Risk-free interest rate
3.63% - 4.64%
Expected volatility
103.11% - 103.85%
Expected dividend yield0.00%
Summary of RSU activity
The following table summarizes the activity under the Company’s equity plans with respect to PSUs for the year ended December 31, 2025:
 SharesWeighted-Average
Grant Date
Fair Value
Outstanding as of December 31, 202498,000 $18.17 
Granted— — 
Vested— — 
Forfeited(98,000)18.17 
Outstanding as of December 31, 2025— $— 
The following table summarizes the activity under the Company’s equity plans with respect to RSUs for the year ended December 31, 2025:
 SharesWeighted-Average
Grant Date
Fair Value
Outstanding as of December 31, 20241,505,289 $6.61 
Granted1,954,500 3.18 
Vested(414,192)6.48 
Forfeited(226,846)4.59 
Outstanding as of December 31, 20252,818,751 $4.41 
As of December 31, 2025, the unrecognized compensation cost related to outstanding RSUs was $9.1 million which is expected to be recognized over a weighted-average period of 2.7 years.