Abstract P3-05-07: Improving CAR T cell function by reversing the immunosuppressive tumor environment of breast cancer

Abstract

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 breast cancer, we generated T cells expressing a CAR directed to the TAA mucin-1 (MUC1). T cells expressing this CAR (86±1.9%, n=5) specifically killed MUC1-expressing cells (MDA-MB-468 – 45.9±7.3%, MCF-7 – 36.8±3.6) but not MUC1(-) 293T cells (3.7±1.6% specific lysis, 20:1 E:T, n=3). Although these CAR T cells had potent anti-tumor activity against breast cancer cells, when exposed to the Th2-polarizing cytokine IL4 [which is upregulated in tumor samples (Oncomine, p<0.05)] we observed a dramatic reduction in their cytolytic potential [IL2 - 45.9±7.3% vs IL4 - 11.3±3.7% specific lysis, 20:1 E:T ratio, n=4]. Thus, to protect our CAR.MUC1 T cells from the negative influences of IL4, we generated an inverted cytokine receptor (ICR) in which the IL4 receptor exodomain was fused to the IL7 receptor endodomain (4/7 ICR). Transgenic expression of this molecule in CAR.MUC1 T cells (55±4.8% double positive cells, n=5), restored the cytolytic function of CAR T cells (30.9±8.1% specific lysis, 20:1 E:T, n=3). Next, to determine the long term effects of this modification we co-cultured transgenic T cells with MUC1+ tumor cells and measured tumor and T cells numbers. In the presence of IL4, only double positive (CAR.MUC1-4/7) T cells expanded and eliminated the tumors in vitro and in vivo. However, upon tumor elimination, transgenic T cells rapidly contracted, demonstrating the antigen- and cytokine-dependence of the product. In conclusion, CAR.MUC1-4/7 T cells can effectively target breast cancer cells and retain their cytotoxic function even in the IL4-rich tumor microenvironment. Citation Format: Bajgain P, Tawinwung S, Watanabe N, Sukumaran S, Anurathapan U, Heslop HE, Rooney CM, Brenner M, Leen AM, Vera JF. Improving CAR T cell function by reversing the immunosuppressive tumor environment of breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P3-05-07.