Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 88,539	$ 46,009
Marketable securities	12,108	134,016
Accounts receivable, net	0	67
Other receivables	1,028	2,394
Prepaid expenses and other current assets	2,277	4,161
Total current assets	103,952	186,647
Property and equipment, net	455	3,577
Facility and equipment under lease	2,505	2,247
Other assets	4,636	4,327
Total assets	111,548	196,798
Current liabilities:
Accounts payable and other accrued liabilities	41,258	43,771
Accrued payroll and benefits	11,971	9,375
Total current liabilities	53,229	53,146
Other long-term liabilities	10,766	9,409
Total liabilities	63,995	62,555
Commitments and contingencies (Note 7)
Stockholders’ equity:
Preferred stock, $0.001 par value; 5,000,000 shares authorized; no shares issued and outstanding	0	0
Common stock, $0.001 par value; 300,000,000 shares authorized; 164,502,013 and 146,083,110 issued and outstanding at December 31, 2021 and 2020, respectively	165	146
Additional paid-in capital	1,094,353	1,021,221
Accumulated other comprehensive loss	(3,042)	(1,829)
Accumulated deficit	(1,043,923)	(885,295)
Total stockholders’ equity	47,553	134,243
Total liabilities and stockholders’ equity	$ 111,548	$ 196,798