Consolidated Balance Sheets - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 65,126,000	$ 85,820,000
Investments	29,690,000	0
Prepaid expenses and other current assets	3,588,000	6,845,000
Accounts receivable	1,785,000
Total current assets	100,189,000	92,665,000
Property and equipment, net	19,495,000	26,294,000
Operating lease assets	11,356,000
Restricted investments	1,400,000	1,400,000
Restricted cash		113,000
Total assets	132,440,000	120,472,000
Current liabilities:
Accounts payable	4,859,000	6,415,000
Accrued expenses and other current liabilities	10,884,000	15,207,000
Operating lease liabilities	4,456,000
Deferred revenue - related party	20,960,000	20,419,000
Deferred revenue	4,834,000
Total current liabilities	45,993,000	42,041,000
Note payable, net of discount	24,648,000
Operating lease liabilities, net of current portion	15,676,000
Lease incentive obligation, net of current portion		6,776,000
Deferred rent		2,216,000
Deferred revenue, net of current portion - related party	89,111,000	116,840,000
Deferred revenue, net of current portion	4,834,000
Other long-term liabilities	502,000	644,000
Total liabilities	180,764,000	168,517,000
Commitments and contingencies (Note 14)
Stockholders’ (deficit):
Preferred stock, $0.001 par value; 10,000,000 shares authorized at December 31, 2019 and 2018; no shares issued and outstanding at December 31, 2019 and 2018
Common stock, $0.001 par value; 200,000,000 shares authorized at December 31, 2019 and 2018; 70,143,252 and 40,936,735 shares issued and outstanding at December 31, 2019 and 2018	70,000	41,000
Additional paid-in capital	411,255,000	341,284,000
Accumulated deficit	(459,649,000)	(389,370,000)
Total stockholders’ deficit	(48,324,000)	(48,045,000)
Total liabilities and stockholders’ deficit	$ 132,440,000	$ 120,472,000