Improving Chimeric Antigen Receptor-Modified T Cell Function by Reversing the Immunosuppressive Tumor Microenvironment of Pancreatic Cancer

The adoptive transfer of T cells redirected to tumor-associated antigens via transgenic expression of chimeric antigen receptors (CARs) has produced tumor responses, even in patients with refractory diseases. To target pancreatic cancer, we generated CAR T cells directed against prostate stem cell antigen (PSCA) and demonstrated specific tumor lysis. However, pancreatic tumors employ immune evasion strategies such as the production of inhibitory cytokines, which limit CAR T cell persistence and function. Thus, to protect our cells from the immunosuppressive cytokine IL-4, we generated an inverted cytokine receptor in which the IL-4 receptor exodomain was fused to the IL-7 receptor endodomain (4/7 ICR). Transgenic expression of this molecule in CAR-PSCA T cells should invert the inhibitory effects of tumor-derived IL-4 and instead promote T cell proliferation. We now demonstrate the suppressed activity of CAR T cells in tumor-milieu conditions and the ability of CAR/ICR T cells to thrive in an IL-4-rich microenvironment, resulting in enhanced antitumor activity. Importantly, CAR/ICR T cells remained both antigen and cytokine dependent. These findings support the benefit of combining the 4/7 ICR with CAR-PSCA to treat pancreatic cancer, a PSCA-expressing tumor characterized by a dense immunosuppressive environment rich in IL-4.