Personnel expenses primarily include salary, benefits, stock-based compensation and payroll taxes. The $7.4 million increase in personnel expenses for the year ended December 31, 2023, as compared to the year ended December 31, 2022, was primarily due to higher stock-based compensation expense and an increase in employee headcount.
Laboratory supplies expenses include laboratory materials and supplies, services and other related expenses incurred in the development of our technology. The $1.0 million decrease in laboratory supply expenses for the year ended December 31, 2023, as compared to the year ended December 31, 2022, was primarily due to lower laboratory services, materials and supplies purchases.
Facility expenses include depreciation, amortization, utilities, rent, maintenance and other related expenses incurred at our facilities. The $0.2 million increase in facility expenses for the year ended December 31, 2023, as compared to the year ended December 31, 2022, was primarily due to higher repairs and depreciation expense.
Product development expenses include clinical investigator site fees, external trial monitoring costs, data accumulation costs, contracted research and outside clinical drug product manufacturing. The $27.2 million increase in product development expenses for the year ended December 31, 2023, as compared to the year ended December 31, 2022, was primarily due to an increase in barzolvolimab clinical trial and contract manufacturing expenses.
General and Administrative Expense
The $3.7 million increase in general and administrative expenses for the year ended December 31, 2023, as compared to the year ended December 31, 2022, was primarily due to higher stock-based compensation, recruiting and barzolvolimab commercial planning expenses, partially offset by a decrease in legal expenses.
Gain on Fair Value Remeasurement of Contingent Consideration
The $6.9 million gain on fair value remeasurement of contingent consideration for the year ended December 31, 2022 was primarily due to our decision to deprioritize the CDX-1140 program.
Litigation Settlement Related Loss
We recorded a loss of $15.0 million in the second quarter of 2022 related to the Initial Payment due under the Settlement Agreement with SRS. During the fourth quarter of 2023, we announced positive topline results from our Phase 2 clinical trial of barzolvolimab in patients with moderate to severe CSU, which satisfied the requirement of “successful completion” of a Phase 2 Clinical Trial of barzolvolimab such that we were obligated to make the applicable milestone payment under the Settlement Agreement in the amount of $12.5 million. During the fourth quarter of 2023, we paid the $12.5 million milestone in cash and recorded a litigation settlement related loss of $12.5 million.
Investment and Other Income, Net
The $10.2 million increase in investment and other income, net for the year ended December 31, 2023, as compared to the year ended December 31, 2022, was primarily due to higher interest rates on fixed income investments and higher other income related to our sale of New Jersey tax benefits.
LIQUIDITY AND CAPITAL RESOURCES
Our cash equivalents are highly liquid investments with a maturity of three months or less at the date of purchase and consist primarily of investments in money market mutual funds with commercial banks and financial institutions. We maintain cash balances with financial institutions in excess of insured limits. We do not anticipate any losses with respect to such cash balances. We invest our excess cash balances in marketable securities, including municipal bond securities, U.S. government agency securities and high- grade corporate bonds that meet high credit quality standards, as specified in our investment policy. Our investment policy seeks to manage these assets to achieve our goals of preserving principal and maintaining adequate liquidity.
The use of our cash flows for operations has primarily consisted of salaries and wages for our employees; facility and facility-related costs for our offices, laboratories and manufacturing facility; fees paid in connection with preclinical studies, clinical studies, contract manufacturing, laboratory supplies and services; and consulting, legal and other professional fees. We anticipate that our cash