Heterogeneity in antigen expression on cancer cells limits clinical benefit of engineered T-cell therapies and underpins treatment resistance through antigen escape. Here, we present a strategy to improve recognition and lysis of tumors with suboptimal antigen expression through a separate engineered receptor that selectively boosts cytotoxic signaling and immune synapse formation. This synapse-stabilizing receptor (SSR) harbors a modified linker for activation of T cells (LAT) endodomain that amplifies CD3ζ signaling upon binding to a secondary tumor antigen resulting in an augmented Ca2+ flux, activation of MAPK and NF-kB signaling, maturation of immune synapse, and enhanced T-cell degranulation. Removing C-terminal amino acids 178-233 in the LAT endodomain (LAT177) was necessary to minimize SSR-mediated cytotoxicity. In models of acute myeloid leukemia, we show that a CD38-targeting SSR boosts cytolysis of antigen-low cancer cells via a C-type lectin-like molecule-1 (CLL1)-specific chimeric antigen receptor (CAR) and a survivin-specific T cell receptor (TCR). Unlike another CAR, SSR does not produce significant cytotoxicity against normal CD38+ tissues. Our study thus shows that SSR arming enhances targeting of antigenically heterogeneous cancers without compromising safety and selectivity of therapeutic T cells.
Tsai et al. (Wed,) studied this question.