79 The following tabl a e summarizes our research and development expenses for the periods indicated (in thousands): Year Ended December 31, Change 2023 2022 Dollar Tarcocimab a program expenses $ 90,513 $ 132,953 $ (42,440) KSI-501 program expenses 7,264 6,964 300 ABC Platform and other program expenses 20,997 27,409 (6,412) Payroll and personnel expenses 65,382 79,314 (13,932) Facilities and other research and development expenses 22,142 20,951 1,191 Total research and development expenses $ 206,298 $ 267,591 $ (61,293) Tarcocimab a program expenses decreased $42.4 million during the year ended December 31, 2023 as compared to 2022, primarily driven by the wind-down of the pivotal clinical studi t es in the tarcocimab a development program. The Phase 1 study t of KSI-501 began enrolling patients with DME in the beginning of the second quarter of 2023. KSI- 501 program expenses increased $0.3 million during the year ended December 31, 2023 as compared to 2022, primarily due to clinical trial progression, partially offs f et by a decrease in manufact f ur t ing activities. ABC Platform and other program expenses decreased $6.4 million during the year ended December 31, 2023 as compared to 2022, primarily due to timing of manufactur t ing runs. Payroll and personnel expenses decreased $13.9 million during the year ended December 31, 2023 as compared to 2022, primarily driven by forfeitur t es related to stock-based compensation expense. Facilities and other research and development expenses increased $1.2 million during the year ended December 31, 2023 as compared to 2022, due to a variety of activities including the expense related to the lease component of the Ursus manufac f turing facility, which commenced in 2023. General and Admi d nist i rative Expe x nses General and administrative expenses decreased $2.8 million, or 4%, during the year ended December 31, 2023 as compared to 2022, primarily driven by a decrease in profes f sional fees for consulting, legal and accounting expenses. Interest Income Interest income increased $9.7 million during the year ended December 31, 2023 as compared to 2022, which was mainly attributable to higher interest rates earned in 2023. Other Income (Exp E ense), e Net Other income (expense), net decreased $0.4 million during the year ended December 31, 2023 as compared to 2022, which was mainly attributable to gain from settlement of foreign currency forward contracts in 2022. Comparison of the Fisc i al Yearsr Ended December 31, 2022 and 2021 For a comparison of our results of operations for the fiscal years ended December 31, 2022 and 2021, see “Part II, Item 7. Management’s Discussion and Analysis of Financial Condition and Results of Operations” in our Annual Report on Form 10-K for the fiscal year ended December 31, 2022, filed with the SEC on March 28, 2023. Liquidity and Capital Resources; Plan of Operations Sources of Liquidity d We have funded our operations primarily through the sale and issuance of common stock, redeemable convertible prefer f red stock, convertible notes, warrants and the sale of royalties. As of December 31, 2023, we had cash and cash equivalents of $285.5 million. We believe that our current cash and cash equivalents will be sufficient to suppor u t our operations into 2026.