Accrued Expenses
 12 Months Ended
Dec. 31, 2021
Payables and Accruals [Abstract]  
Accrued Expenses Accrued Expenses
Accrued expenses consist of the following (in thousands):
 December 31,
 20212020
Payroll and employee related expenses$3,179 $3,049 
Collaboration and licensing— 1,350 
Accrued patent fees309 534 
Accrued external research and development costs4,339 2,029 
Accrued professional and consulting services815 798 
Accrued interest170 170 
Other1,721 216 
Accrued expenses$10,533 $8,146 
Other accrued expenses as of December 31, 2021 include a $0.9 million estimated liability for plaintiff’s litigation relating to the two lawsuits described further within Note 17.