Abstract 4017: CAR T cell-mediated cytotoxicity and cytokine release in response to varying levels of antigen expression on target cells
Authors: Barnes Sierra , Sullivan Denise , Lazar Dan , Haupt Kim , Califano Danielle , Chvatal Stacie , Millard Daniel 
Published: March 2024

The development of immunotherapies relies on the use of in vitro potency assays, which are crucial for understanding the complex interactions between immune cells (effectors) and cancer cells (targets). Chimeric antigen receptor (CAR) T-cell therapy is an immunotherapeutic approach that exhibits promise; however, varying levels of antigen expression on the surface of tumor cells can influence the efficacy of CAR T cell-mediated killing. To fully understand the impact of target antigen density on CAR T cell activity, we utilized a matrix approach to assess both target cell death, using an impedance-based in vitro potency assay to quantify CAR T cell-mediated cytotoxicity, as well as cytokine release with homogeneous LumitTM immunoassays. SKOV3 (high HER2 expression), A549 (low HER2 expression), or MDA-MB-231 (no HER2 expression) target cells were seeded into a 96-well microplate with embedded electrodes in the substrate that detect the attachment and proliferation of target cells. HER2 CAR T cells were added after 24 hours at effector-to-target (E:T) ratios of 1:5 or 1:1 and target cell cytolysis was recorded continuously by the Maestro Z for 72 hours. Cytolysis of the target cells was calculated by comparing the treated wells to no treatment control wells and full lysis wells (1% TritonX). At 72 hours post CAR T cell addition, complete killing was observed in SKOV3 cells at the 1:1 ratio, while A549 cells exhibited only 80% cytolysis. MDA-MB-231 cells showed 20% cytolysis, likely due to nonspecific killing by non-engineered T cells, as approximately only 78% of the CAR T cell population was CAR positive. Because the cytolysis assay was label-free, cytokine analysis was able to be multiplexed with the same plates. To assess release of pro-inflammatory cytokines, TNF-α and IFN-γ, we collected supernatant post-antigen exposure at 24, 48, and 72 h. At the 1:1 E:T ratio, CAR T cells co-cultured with target cells expressing low (A549) or high (SKOV3) levels of HER2 had the highest TNF-α production at 24 hours, with CAR T cells co-cultured with SKOV3 cells releasing 30.6% more TNF-α when compared to A549 cells. The highest levels of IFN-γ were detected in both A549 and SKOV3 groups at the 1:1 E:T ratio, with the highest levels observed from CAR T cells co-cultured with SKOV3 cells at 72 hours, releasing approximately 1459.6 +/- 357.3 pg/mL of IFN-γ, compared to 1093.8 +/- 387.5 pg/mL IFN-γ released by CAR T cells co-cultured with A549 cells. As expected, CAR T cells co-cultured with MDA-MB-231 cells did not release any detectable TNF-α or IFN-γ at either E:T ratios during the duration of the experiment. Future work will continue to explore multiplexed potency assays for the evaluation of CAR T cell therapies.

Citation Format: Sierra Barnes, Denise Sullivan, Dan Lazar, Kim Haupt, Danielle Califano, Stacie Chvatal, Daniel Millard. CAR T cell-mediated cytotoxicity and cytokine release in response to varying levels of antigen expression on target cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4017.