Evaluation of checkpoint inhibitor therapies using a mixed lymphocyte reaction (MLR) assay

Abstract

Abstract Checkpoint inhibitors block the ‘off’ signals that are engaged when T cells interact with antigen-presenting cells, such as dendritic cells (DCs). This increases T cell activation and enhances the anti-tumor response. Here we demonstrate the use of advanced flow cytometry to evaluate these immunotherapies in vitro by co-culturing immune cells from two donors in an MLR assay. Assays were set up as either one-way or two-way MLR co-cultures. One-way assays combined isolated DCs from one donor with CD4+ T cells from another. Two-way assays mixed PBMCs from two donors. Cells and checkpoint inhibitors were plated in 96 or 384-well formats for 3–6 days. Samples taken during the time course were analyzed for cell subsets and cytokine concentrations using the iQue® Advanced Flow Cytometry Platform. Expression of activation marker CD25 on T cells was 3-fold greater after 6 days in co-culture with DCs (62 ± 2 %) compared to T cells in monoculture (22 ± 9 %). The addition of an anti-PD1 checkpoint inhibitor induced a further, concentration dependent increase in CD25 expression. This was accompanied by increased production of cytokines indicative of activation and inflammation, such as TNFα and CCL2. Throughout the study, there were large differences in sensitivity to drug response between donor pairs. For example, IFNγ release increased 13.5-fold upon addition of anti-CTLA4 (17 ng/mL) with one donor pair, compared to only 1.3-fold with another. This highlights the need to characterize drug activity using multiple immune cell donor pairs. These data exemplify the use of advanced flow cytometry to generate pharmacological data for checkpoint inhibitor activity on T cells in MLR, with the potential to profile libraries of novel therapeutics in minimal time.