Abstract 294: In vitro efficacy studies to support engineered T cell therapies
Authors: Holt Sanne L. , Vermond Sophie , Hazenoot Monique , McLaughlin Rene , Guadagnoli Marco , Vlaming Marijn 
Published: July 2021

Abstract
Cell therapies, such as Chimeric Antigen Receptor (CAR) and T Cell Receptor (TCR) T cells, are some of the latest immune-therapeutic approaches, showing great momentum in research and now the clinic. Only recently, two anti-CD19-CAR-T products have been approved by the FDA and EMA for treatment of CD19+ lymphoid malignancies, including Acute Lymphoblastic Leukemia (B-ALL) and Diffuse Large B cell Lymphoma (DLBCL). Many more CAR-T cell products are being explored, targeting a wide variety of tumor antigens, directed towards both liquid and solid tumors as well other clinical indications such as autoimmune diseases or organ transplantations. In early stage development (pre-clinical research), the use of in vivo animal models has presented significant hurdles in translatability of cell therapies. As a result, the establishment of high-quality in vitro efficacy and safety studies to foster the development of such therapies has become critical. The purpose of this study is to show a number of in vitro efficacy experiments aimed at determining cell therapy activity, specificity and potency using an anti-HER2 CAR-T as a model system. To asses therapeutic activity, a proof of concept (PoC) study must be in place in which the therapy is tested for its ability to kill a reactive control cell line. Activity tests can be used to aid disease indications (including a panel of cell lines or primary material) and importantly, to aid lead optimization. Especially for cell therapies, activity experiments should be combined with “cellular fitness” tests, which are able to determine a therapy's ability to expand and persist following serial rounds of tumor challenges. Here we have developed an in vitro CAR-T activity and Repeated Antigen Stimulation (RAS) assay. Furthermore, specificity studies are aimed at quantifying the absence of killing of control cells that are negative for the target antigen. Here we used a three-way co-culture system in which effector cells are incubated with positive target cells and negative control cells in order to determine specificity under activating cellular conditions. Finally, to determine cell therapy potency we have used cytotoxicity co-culture experiments in which different effector-target ratios are tested at different time points to allow quantification of lower and upper limits of the cellular therapy to be tested. Our studies can generate a robust and essential efficacy data package that defines and describes a cell therapy's activity, specificity and potency, and is applicable to CAR-T cells and other engineered cell therapy approaches. One lesson learnt the hard way is that the most active and potent drug is not always the safest; for all cell therapies efficacy and safety will need to be balance and taken into considering during early development and lead optimization. Having developed a robust in vitro efficacy and safety platform, we keep strengthening our abilities to select the best therapies to further progress to clinic.
Citation Format: Sanne L. Holt, Sophie Vermond, Monique Hazenoot, Rene McLaughlin, Marco Guadagnoli, Marijn Vlaming. In vitro efficacy studies to support engineered T cell therapies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 294.