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 that promote functional persistence in an immunosuppressive environment. Herein, we exploit c-Kit signaling, a physiological pathway associated with stemness in hematopoietic progenitor cells (T cells lose expression of c-Kit during differentiation). CAR T cells with intracellular expression—but no cell-surface receptor expression—of the c-Kit D816V mutation (KITv) have upregulated STAT phosphorylation, antigen-activation-dependent proliferation, CD28- and IL-2–independent and IFN-?–mediated costimulation, augmenting the cytotoxicity of first-generation CAR T cells. This translates to enhanced survival, including in TGF-ß–rich and low-antigen-expressing solid tumor models. KITv CAR T cells have equivalent or better in vivo efficacy than second-generation CAR T cells and are susceptible to tyrosine kinase inhibitors (safety switch). When combined with CD28 costimulation, KITv costimulation functions as a third signal, enhancing efficacy and providing a potent approach to treat solid tumors. Overall design: Mesothelin-specific CAR T cells either Unstimulated or Stimulated with Mesothelin-expressing target cells were flow stained and CD8+ cells were sorted for RNA extraction and gene expression analysis.