A flow cytometry-based method to screen for modulators of tumor-specific T cell cytotoxicity

Cancer immunotherapy relies on the ability of immune cells to kill malignant cells. The cytotoxic T lymphocyte (CTL) response is perhaps the functional measure that best reflects cell-mediated immunity against cancer. Straightforward methods that facilitate quantitative evaluation of the potency of compounds that can modulate T cell-mediated, tumor antigen-specific immune responses are central in the screening cascade when searching for new immunotherapeutic agents for cancer. Here we describe a simple, sensitive method, based on flow cytometry analyses, to quantitatively measure cytotoxicity in vitro. We provide examples that validate its feasibility and specificity using CD8⁺ T lymphocytes specific for a surrogate tumor antigen, and a blocking antibody for the inhibitory PD-1/PD-L1 axis. This method can nonetheless be applied to the screening of virtually any cytotoxicity modulatory compound, including antibodies and small molecules or T cell-based therapies, and can be scaled up for high-throughput workflow and automation.