Abstract 4992: In vitro exhausted T cell assay for immuno-oncology candidates

The need to better understand the tumour microenvironment (TME) dictates the characterization of the cell types involved, the roles they play and how they respond to treatment. To develop better cancer immunotherapies, in vitro primary immune cell bioassays offer an early assessment of their effects on the various players of the TME. Here we describe the development of an exhausted T cell assay and demonstrate its potential in identifying candidates that can reverse exhaustion. Exhausted T cells were first discovered in LCMV virus infections where chronic stimulation due to remaining virus antigens leads to T cells that stop responding to stimulation and lose their functionality (cytokine secretion and cytotoxic activity). The same phenotype was afterwards found in the tumor microenvironment where a lot of T cells were found to be “anergic”. Reversing their loss of functionality as a therapeutic strategy has made the characterization of these exhausted T cells a priority. Their phenotype is currently defined by an increase in the expression of a specific set of cell surface markers such as PD-1, TIM-3 and LAG-3. As exhaustion builds, the expression of these marker increases while T cell functionality decreases. The loss of functionality is defined by a reduction in cytokine secretion, proliferation and cytotoxic activity in the presence of an antigen. To evaluate this phenotype in more depth, transcription factors can also be monitored. For example, BLIMP-1 and BATF, which play a role in PD-1 expression, are shown to increase following exhaustion. Using primary immune cells, in vitro bioassays were developed to better screen the potential effect of new therapeutics on exhausted T cells. Their ability to reverse the exhausted phenotype and facilitate the anti-tumour immune response can as a result be assessed early in the drug development process. These experiments help advance our understanding of the tumour microenvironment and optimize the therapeutic effects of new drugs, design better clinical trials and ultimately discover relevant biomarkers. Citation Format: Amin Osmani, Juliette Lamy, Thibaut Janss, Severine Giltaire, Sofie Pattijn, Jana Schockaert. In vitro exhausted T cell assay for immuno-oncology candidates [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4992.