Abstract 1389: In vitro killing assays for evaluation of immuno-oncology drug candidates
Authors: Arnold Johan , Janss Thibaut J. , Lefevre Simon , Vlaming Martijn , Boelen Ellen , Pattijn Sofie 
Published: June 2022

Abstract
The need to better understand the tumor microenvironment (TME) dictates the characterization of the cell types involved, the roles they play and how they respond to treatment. To develop novel cancer immunotherapies, in vitro primary immune cell bioassays offer an early assessment of their effects on the various players of the TME. Cytotoxic cells are key players in the anti-tumor immune response. CD8+ T cells, also known as cytotoxic T lymphocytes, recognize and kill cells presenting antigens bound to MHC class I molecules, such as neoantigens present on the tumor cell surface. Activation of CD8+ T cells requires at least two signals from antigen presenting cells: binding of their T cell receptor (TCR) to the appropriate peptide presented on MHC I and co-stimulation by B7 binding to CD28. However, the TME possesses several mechanisms to reduce immune cell activity, such as the expression of checkpoint inhibitors dampening the immune system. Natural killer (NK) cells represent another type of cytotoxic cells, with their innate immune activity dictating an important role in anti-tumor immunity. NK cells induce apoptosis via the release of perforin and granzymes from granules, eliminating cells lacking expression MHC I, including cancer cells that have lost expression of MHC I. However, also the activity of NK cells can be hampered in the TME, notably by the PD1/PDL1 interaction.Increasing the activity of CD8+ T and NK cells as a therapeutic anti-tumor strategy has become an important point of attention. Such strategies can have several shapes, with Antibody-dependent cell-mediated cytotoxicity (ADCC) activity of IgG1 isotypes being one of the mechanisms that can be exploited by immunoglobulin-based therapeutics. Another way to increase the killing of tumor cells is to re-direct T cells to tumor cells by employing bi-specific antibodies targeting specific tumor associated antigens. Using this strategy, T cell activation can be concentrated in the TME, thereby also avoiding off-tumor activity. Real-time in vitro assessment of the potential enhanced killing capacity of CD8+ T and NK cells elicited by test molecules could further provide pivotal information on the functional dynamics of test molecules. Using high quality primary human immune cells, in vitro bioassays were developed with improved robustness and reproducibility to screen for the potential to enhance tumor cell killing by novel therapeutics. The ability to evaluate the compounds capacity to increase or induce a cytotoxic activity profile and thereby facilitate the anti-tumor immune response is essential in the early drug development process.
Citation Format: Johan Arnold, Thibaut J. Janss, Simon Lefevre, Martijn Vlaming, Ellen Boelen, Sofie Pattijn. In vitro killing assays for evaluation of immuno-oncology drug candidates [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1389.