During 2020, operating activities used $46.6 million of cash, primarily resulting from our net loss of $53.3 million, adjusted for non-cash items and the effect of changes in operating assets and liabilities. Non-cash adjustments primarily include depreciation and amortization expense including gain on disposal of $1.8 million, stock-based compensation of $0.7 million and non-cash interest expense of $0.6 million. Net cash provided by changes in our operating assets and liabilities for 2020 consisted primarily of a $5.1 million increase in accounts payable, accrued expenses, deferred revenue, and deferred rent, partially offset by a $1.5 million increase in prepaid expenses and other current assets. The increase in accounts payable and accrued expenses related to our increased level of operating activities and timing of vendor invoicing and payments. The increase in deferred revenue resulted from a grant payment we received from the Bill & Melinda Gates Foundation in 2020. The increase in prepaid expenses and other assets was due to our increased level of research collaborations and manufacturing development activities related to our product candidates.
Investing Activities
During 2021, investing activities used $15.0 million of cash consisting of purchases of property and equipment, of which a substantial majority related to purchases of laboratory equipment and facilities improvements for our manufacturing plant in Rochester, New York, construction of cleanrooms and preclinical manufacturing capacity in our facility in Burlington, Massachusetts, and laboratory construction in our facility in Woburn, Massachusetts.
During 2020, investing activities used $10.0 million of cash, consisting of purchases of property and equipment, of which a substantial majority related to laboratory and facilities improvements in Research Triangle Park, North Carolina and purchases of laboratory equipment and facilities improvements for our manufacturing facility in Rochester, New York.
Financing Activities
During 2021, financing activities provided $43.5 million of cash, consisting primarily of $24.9 million of net proceeds from secured term loans, $13.5 million of net proceeds from convertible debt issuances, and net proceeds of $10.4 million from a new secured debt agreement, partially offset by $2.9 million of deferred offering costs, $1.8 million of repayments on our secured debt, and $0.6 million of payments related to our capital lease obligations.
During 2020, financing activities provided $125.8 million of cash, consisting primarily of $108.9 million of net proceeds from the issuance of Series D Preferred Stock, $16.6 million of net proceeds from the issuance of convertible notes and $1.2 million provided by tenant improvement loans, which were partially offset by $0.9 million of repayments on our note payable, capital lease obligations and tenant improvement loans.
Contractual Obligations and Commitments
Operating Lease Obligations
We have non-cancelable operating lease obligations, consisting primarily of lease payment obligations for our facilities, including our headquarters in Medford, Massachusetts; clean rooms in Burlington, Massachusetts; office, laboratory and greenhouse space in Research Triangle Park, North Carolina; laboratory and office space in Woburn, Massachusetts; and our manufacturing facilities in Rochester, New York. The leases for these facilities expire on various dates through 2026, unless extended.
In October 2021, we entered into a lease for new laboratory, office and greenhouse space in Research Triangle Park, North Carolina, with a commencement date of January 2022. The lease term expires in July 2033, unless extended. The base rent for this lease is $2.3 million per year, subject to a 3% increase each year.
See Note 18, Commitments and Contingencies — Operating Leases, of the notes to our 2021 Consolidated Financial Statements for further information on our future operating lease obligations
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