Abstract 4703: Improving CAR T cell function by reversing the immunosuppressive tumor microenvironment of pancreatic cancer
Authors: Mohammed Somala , Sukumaran Sujita , Bajgain Pradip , Anurathapan Usanarat , Heslop Helen E. , Rooney Cliona M. , Brenner Malcolm K. , Leen Ann M. , Vera Juan F. 
Published: August 2015

Abstract
Adoptive transfer of T cells redirected to tumor-associated antigens (TAAs) by expression of chimeric antigen receptors (CARs) can produce tumor responses, even in patients with resistant malignancies. To target pancreatic ductal adenocarcinoma (PDAC), we generated T cells expressing a CAR directed to the TAA prostate stem cell antigen (PSCA). T cells expressing this CAR were able to kill PSCA(+) tumor cell lines CAPAN1 and K562-PSCA but not PSCA(-)293T cells (74±4%, 73±6% and 9±3% specific lysis, respectively, 10:1 E:T, n = 3). Although these CAR-T cells had potent anti-tumor activity, pancreatic tumors employ immune evasion strategies such as the production of inhibitory cytokines, which limit in vivo CAR-T cell persistence and effector function. Indeed, when we examined the serum of patients with pancreatic cancer (n = 8) we found the levels of the immunosuppressive cytokine IL4 to be elevated relative to patients with benign pancreatic disorders or normal healthy controls (14.25±19.48 pg/mL vs 7.28±9.03 vs 1.13±1.42 pg/mL). Thus, to protect our CAR-PSCA T cells from the negative influences of IL-4, we generated a chimeric cytokine receptor in which the IL4 receptor exodomain was fused to the IL7 receptor endodomain (IL4/7 ChR). Transgenic expression of this molecule in CAR-PSCA T cells should invert the inhibitory effects of tumor-derived IL4 and instead promote the proliferation of the effector CAR T cells. In preliminary experiments we successfully co-expressed both CAR-PSCA and IL4/7 ChR (47.5±12.3% double-positive cells, n = 4) on primary T cells. These T cells retained their tumor-specific activity (80±8% specific lysis against CAPAN1, 10:1 E:T, n = 3) and when cultured in conditions that mimic the tumor milieu (IL4 12.5 ng/ml), CAR-PSCA 4/7R ChR-modified T cells continued to expand (increase from 2×10e6 cells on day 0 to 5.53±8.46×10e10 cells on day 28), unlike unmodified CAR-PSCA T cells which plateaued at 3.84±5.43×10e8 cells (n = 4). Indeed, in the presence of IL4, transgenic cells had a selective advantage (comprising 44.8±11.0% of the population on day 0 and 87.6±10.0% on day 28; n = 4). However, even after prolonged cytokine exposure these T cells remained both antigen- and cytokine-dependent. In conclusion, CAR-PSCA 4/7 ChR-modified tumor-specific T cells can effectively target pancreatic cancer cells and should be equipped to expand, persist, and retain their cytotoxic function even in the presence of high levels of IL4 in the tumor microenvironment.
Citation Format: Somala Mohammed, Sujita Sukumaran, Pradip Bajgain, Usanarat Anurathapan, Helen E. Heslop, Cliona M. Rooney, Malcolm K. Brenner, Ann M. Leen, Juan F. Vera. Improving CAR T cell function by reversing the immunosuppressive tumor microenvironment of pancreatic cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4703. doi:10.1158/1538-7445.AM2015-4703