c-Kit signaling potentiates CAR T cell efficacy in solid tumors by CD28- and IL-2–independent costimulation

The limited efficacy of chimeric antigen receptor (CAR) T-cell therapy for solid tumors necessitates engineering strategies to promote functional persistence in an immunosuppressive environment. Herein, we exploit c-KIT signaling - a physiological pathway associated with stemness in hematopoietic progenitor cells with loss of expression during T-cell differentiation. CAR T cells with intracellular but no cell-surface receptor expression of c-Kit D816V mutation, KITv, show upregulated STAT phosphorylation, antigen-activation dependent proliferation, and susceptibility to tyrosine kinase inhibitors. KITv signaling provides CD28, IL-2-independent, and IFN-γ-mediated costimulation augmenting cytotoxicity of antigen-activated first-generation CAR T cells that translates to enhanced survival, including in TGF-β-rich and low antigen-expressing solid tumor models. KITv CAR T cells demonstrate equivalent or higher in vivo efficacy compared to second-generation CAR T cells, and further enhance efficacy as signal 3 when combined with CD28 costimulation, providing a potent approach to treat solid tumors by adoptive cell therapy. Human CD8+ T cells derived from three different healthy donors were retrovirally transduced with individual anti-MSLN CAR genes (M28z and M28z-KITv), with or without stimulated by the MSLN+ 3T3 tumor cells. RNA was collected 0 hours and 24 hours after stimulation and gene expression profiles were analyzed by Affymetrix Human Gene 2.0 ST Array (gene-level analysis).