Adoptive cell transfer of T cells genetically modified to express a T cell receptor reactive to a tumor antigen (TCR-Td T cells) has emerged as one of the most promising approaches for the treatment of malignancies. However, recent clinical studies report objective clinical response rates lower than 30%. Providing a plausible explanation for these responses, studies have shown that, in tumor-bearing hosts, transferred T cells encounter an inhospitable environment characterized by immune suppression. Hence, rendering TCR-Td CD8+ T cells resistant to these negative environmental cues could significantly improve clinical responses in cancer patients. Given the stimulatory role of the NKG2D receptor, we investigated its ability to control CD8+ T cell suppression. Our data show for the first time that NKG2D stimulation in human TCR-Td CD8+ T cells (similar to those used in clinical trials) and mouse CD8+ T cells results in complete resistance to suppression by TGF-? and augmented therapeutic anti-tumor responses against melanoma. Our data also show that NKG2D-activated TCR-Td CD8+ T cell resistance to suppression by TGF-? is accompanied by the upregulation of two negative regulators of TGF-? signaling, RGS3 and PDPK1. While these findings depict novel functions for NKG2D in CD8+ T cells, how these pathways are interconnected in NKG2D signaling and resistance to suppression remains to be determined. We hypothesize that NKG2D-induced resistance of TCR-Td CD8+ T cells to suppression is mediated by the PI3K, Grb2, and JNK pathways and the combined effects of RGS3 and PDPK1. Thus, the objective of this proposal is to dissect the proximal and distal signaling pathways utilized by NKG2D to confer resistance to TGF-? and enhanced anti-tumor immunity. To do this, we will use human and mouse CD8+ T cells transduced to express a TCR against a tyrosinase peptide/HLA-A2 and h3T transgenic mice, which express the same receptor. Our study posits a new paradigm; human CD8+ T cells can be transcriptionally manipulated by NKG2D signaling to achieve resistance to TGF-?. We believe that human TCR-Td CD8+ T cells could be easily conditioned prior to ACT by an NKG2D agonist to enhance their survival and therapeutic anti-tumor capacity.
Currently, suppression is a factor that limits the effectiveness of adoptive cell transfer of CD8+ T cells genetically modified to express a tumor-reactive T cell receptor (TCR-Td T cells). Our objective is to dissect the signaling utilized by NKG2D to avert TCR-Td T cell suppression.
