Abstract 5009: NKG2D receptor stimulation of effector CD8+ T cells alters the transcriptome and activation of mTOR to enhance anti-tumor immunity

To induce strong immune responses, naive CD8+ T cells require concurrent stimulation through the TCR and costimulatory receptors. Each costimulatory molecule can have a unique effect on the function of T cells due to differential activation of downstream signaling pathways and gene expression. However, the effect of stimulating costimulatory receptors on effector T cells is still unclear. One costimulation receptor that is likely to be engaged in the tumor microenvironment is NKG2D since the ligands for this receptor are expressed on over 80% of tumors. To determine how activation of costimulatory receptors in the tumor microenvironment alters CD8+ T cell functions, this study investigated the differential activation of signaling pathways by two costimulatory receptors, CD28 and NKG2D. To obtain an in-depth view of how stimulation through the NKG2D receptor alters T cell function, the transcriptome of NKG2D- and CD28- costimulated murine CD8+ T cells was analyzed using RNA-sequencing. These analyses showed that NKG2D costimulation of effector CD8+ T cells altered expression of over 5200 genes compared to CD3 stimulation alone. Some genes that were increased in NKG2D-stimulated cells include IFNγ, and granzymes A and C, suggesting the NKG2D stimulation enhances the anti-tumor functions of CD8+ T cells. When comparing NKG2D and CD28 costimulation, many genes were differentially regulated, including genes in the mTOR pathway. To determine if the differential activation of mTORc1 and mTORc2 signaling pathways altered T function, murine effector CD8+ T cells were activated through CD3 in combination with CD28 or NKG2D and treated with no, low, or high amounts of rapamycin to deactivate either mTORc1 or both mTORc1 and mTORc2. NKG2D-stimulated T cells increased expression of Eomes, a transcription factor that is involved in the differentiation of central memory T cells, while CD28 stimulated cells increased expression of TCF1. Rapamycin inhibition studies showed that stronger activation of mTORc1 in CD28 stimulated T cells inhibited Eomes expression and also increased TCF1 expression compared to NKG2D-stimulated T cells. In addition, NKG2D stimulation lead to differential expression of memory markers including CD127, CCR7, CD62L, and KLRG1, with NKG2D stimulation inducing a central memory phenotype compared to CD28 stimulation which caused an effector memory phenotype. Together, these data suggest that differential activation of mTORc1 by the NKG2D receptor alters CD8+ T cell differentiation to become central memory T cells. Thus, NKG2D stimulation likely enhances CD8+ T cell anti-tumor effector functions. Citation Format: Kelsey Trace, Sara Jacobson, Amorette E. Barber. NKG2D receptor stimulation of effector CD8+ T cells alters the transcriptome and activation of mTOR to enhance anti-tumor immunity. [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 5009. doi:10.1158/1538-7445.AM2015-5009