Measuring Chimeric Antigen T Cell Activation One Molecule at a Time

T cells exquisitely discriminate between antigenic and self-peptide ligands presented on major histocompatibility complexes (pMHCs) despite subtle differences in affinities. This aspect of adaptive immunity is required for robust, specific, and highly selective T cell activation and to avoid autoimmunity in the background of more abundant self pMHCs. We recently introduced a reconstitution-based molecular impulse-response assay that demonstrated how T cell receptors (TCR) execute this single molecule precision in antigenic pMHC detection. Interestingly, T cells effect a spatiotemporally-correlated antigen detection mechanism that translates a series of input ligand:TCR binding events into activation responses. Cell-based immunotherapies reprogram T cells to eliminate cancer cells through the engineering of tumor-associated antigen-specific (TAA) chimeric antigen receptors (CARs). Many TAAs are epitopes of highly overexpressed cell surface proteins but are rarely tumor-exclusive. CARs have been highly effective in eliminating cancers of blood cells but continue to be minimally effective against solid tumors. The hyperactivation of CAR T cells, as well as off-target toxicity, have plagued the translation of mobilizing T cells as a therapeutic. We propose that a mechanistic, single molecule understanding of the CAR T cell input:response function is needed to optimally harness anti-tumor responses and minimize side effects. I will discuss our efforts to measure molecular activation thresholds in primary, anti-tumor CAR T cells.

Learning Objectives:

1. Define single molecule triggering of T cells

2. Explain an impulse-response function

3. Identify at least 2 parameters that may control CAR T cell triggering and activation.