Comparison of CAR-T Cell-Mediated Cytotoxicity Assays with Suspension Tumor Cells Using High-Throughput Plate-Based Image Cytometry Method

Abstract In the recent decade, chimeric antigen receptor (CAR)-T cell therapy has revolutionized strategies for cancer treatments due to its highly effective clinical efficacy and response for B cell malignancies. Currently, there are six CAR-T cell products available in the market including Kymriah, Yescarta, Tecartus, Breyanzi, Abecma, and Carvykt. The success of CAR-T cell therapy has stimulated the increase in the research and development of various CAR constructs to target different tumor types. Therefore, a robust and efficient in vitro potency assay is needed to quickly identify potential CAR gene design from a library of construct candidates. Traditionally, in vitro CAR-T cell-mediated cytotoxicity is assessed using release assays such as 51Cr (radioactivity), calcein (fluorescence), and LDH (enzymatic). However, release assays indirectly measure cell death via molecules released in supernatant and typically limited to only endpoint assays. In addition, handling and disposing of 51Cr hazardous materials is less preferred. Luciferase reporter assay, although highly sensitive, has similar drawbacks as the release assays. Finally, flow cytometry method can directly measure cell death and viability, but can be time-consuming and requires a large number of CAR-T cells when the effector-to-target (E:T) ratio is high. Furthermore, additional steps are required for adherent cells that require trypsinization. Image cytometry methodologies have been utilized for various CAR-T cell-mediated cytotoxicity assay using different fluorescent labeling methods, mainly due to their ease-of-use, ability to capture cell images for verification, and higher throughput performance. In this work, we employed the Celigo high-throughput plate-based Image Cytometer to evaluate and compare two CAR-T cell-mediated cytotoxicity assays using GFP-expressing or fluorescent dye-labeled myeloma and plasmacytoma cells. Performing time- and E:T ratio-dependent CAR-T cell-mediated cytotoxicity assays, the GFP-based method demonstrated higher sensitivity in detecting the level of cytotoxicity when compared to the CMFDA/DAPI viability method. We have established the criteria and considerations for the selection of cytotoxicity assays that are fit-for-purpose to ensure the results produced are meaningful for the specific testing conditions. Citation Format: Leo Li-Ying Chan, Yu-Jun Sun, Yi-Chun Chen, Wei-Kai Hua, Sariena Chiung-Yuan Wu. Comparison of CAR-T cell-mediated cytotoxicity assays with suspension tumor cells using high-throughput plate-based image cytometry method. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5326.