AXL inhibition improves the anti-tumor activity of chimeric antigen receptor T cells.

The receptor tyrosine kinase AXL is a member of the TAM (Tyro3, AXL, and proto-oncogene tyrosine-protein kinase Mer) family and plays pleiotropic roles in cancer progression. AXL is expressed in immunosuppressive cells, which contributes to decreased efficacy of immunotherapy. Therefore, we hypothesized that AXL inhibition could serve as a strategy to overcome resistance to chimeric antigen receptor T (CART)-cell therapy. To test this, we determined the impact of AXL inhibition on CD19-targeted CART (CART19)-cell functions. Our results demonstrate that T cells and CART cells express high levels of AXL. Specifically, higher levels of AXL on activated Th2 CART cells and M2-polarized macrophages were observed. AXL inhibition with small molecules or via genetic disruption in T cells demonstrated selective inhibition of Th2 CART cells, Th2 cytokines, reversal of CART-cell inhibition, and promotion of CART-cell effector functions. AXL inhibition is a novel strategy to enhance CART-cell functions through two independent, but complementary, mechanisms: targeting Th2 cells and reversing myeloid-induced CART-cell inhibition through selective targeting of M2-polarized macrophages.