Adoptive cell therapy with chimeric antigen receptor expressing T (CAR T) cells has shown promising therapeutic efficacy against leukemia and lymphoma. However, CAR T cells in solid tumors fail to be as effective as in liquid tumors since they enter into a hyporesponsive (exhausted or dysfunctional) state that is induced by chronic antigen stimulation in cancer. Here, we show that CAR T cells in solid tumors exhibit low effector function and high expression of inhibitory receptors such as PD-1, Tim-3 and Lag 3. We also show that the nuclear factor, Thymocyte selection-associated HMG box protein, TOX - a target of the transcription factor NFAT - is highly expressed in CAR T cells in solid tumors with PD-1 expression. To determine how TOX transcription factors contribute to exhaustion/ dysfunction in CAR T cells, we developed CAR T cells targeting huCD19 and lacking TOX and TOX 2. Surprisingly, treatment of huCD19 expressing melanoma or colorectal tumor-bearing mice with CAR T cells doubly deficient in TOX and TOX2 resulted in the eradication of solid tumors and prolonged survival of the tumor-bearing mice, compared to mice treated with WT CAR T cells or CAR T cells lacking TOX or TOX2 alone. Tumor-infiltrating CAR T cells (CAR TILs) doubly deficient in TOX and TOX2 did not increase their expression of inhibitory receptors such as PD-1, Lag3 and CD160 and showed higher expression of TCF1 compared to WT CAR TILs. Our data identify TOX and TOX2 -high mobility group transcription factors belonging to the TOX family - as critical transcriptional factors for inducing hyporesponsiveness in CAR T cells in solid tumors. Our data suggest that disruption of TOX expression or activity could be a promising strategy for cancer immunotherapy.

Citation Format: Hyungseok Seo, Joyce Chen, Arundhoti Das, Avinash Bhandoola, Anjana Rao. Disruption of TOX overcomes CAR T-cell dysfunction function in solid tumor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 938.