Comparison of T Cell Activities Mediated by Human TCRs and CARs That Use the Same Recognition Domains

Abstract

<p class="first" id="P1">Adoptive T cell therapies have achieved significant clinical responses, especially in hematopoietic cancers. Two types of receptor systems have been used to redirect the activity of T cells, normal heterodimeric T-cell receptors (TCRs) or synthetic chimeric antigen receptors (CARs). TCRs recognize peptide-HLA complexes whereas CARs typically use an antibody-derived scFv (single-chain fragments variable) that recognizes cancer-associated cell-surface antigens. While both receptors mediate diverse effector functions, a quantitative comparison of the sensitivity and signaling capacity of TCRs and CARs has been limited due to their differences in affinities and ligands. Here we describe their direct comparison by using TCRs that could be formatted either as conventional αβ heterodimers, or as scFv constructs linked to CD3ζ and CD28 signaling domains or to CD3ζ only. Two high-affinity TCRs (K _D values of approximately 50 and 250 nM) against MART1/HLA-A2 or WT1/HLA-A2 were used, allowing MART1 or WT1 peptide titrations to easily assess the impact of antigen density. Although CARs were expressed at higher surface levels than TCRs, they were 10 to 100-fold less sensitive, even in the absence of the CD8 co-receptor. Mathematical modeling demonstrated that lower CAR sensitivity could be attributed to less efficient signaling kinetics. Furthermore, reduced cytokine secretion observed at high antigen density for both TCRs and CARs suggested a role for negative regulators in both systems. Interestingly, at high antigen density, CARs also mediated greater maximal release of some cytokines, such as IL-2 and IL-6. These results have implications for next-generation design of receptors used in adoptive T cell therapies. </p>