Abstract PR03: Molecular characterization of in vitro exhausted T cells

In previous work we observed that restimulating human PBMCs with anti-CD3/28 beads 4 days after a primary stimulation resulted in an exhausted phenotype, as characterized by loss of T cells9 ability to secrete IL-2, TNFa, and IFNg. To further characterize the molecular phenotype of these cells, we isolated CD4+ and CD8+ T cells from our exhausted and non-exhausted samples and performed Nanostring gene expression analysis. Both exhausted CD4+ and CD8+ T cells exhibited upregulation of a 25-gene exhaustion gene signature, as compared to non-exhausted control cells. In addition, a number of immunologically important molecules are modulated in the exhausted cells. For example, MIF (macrophage migration inhibitory factor) mRNA is induced in the exhausted T cells. Closer examination of MIF expression in TCGA suggests that MIF level is inversely correlated to survival in indications such as HCC and H/N cancer. Furthermore, pathway analysis of differential gene expression revealed the JAK/STAT signaling pathway as significantly upregulated in the exhausted cells. Treatment of exhausted cells with a JAK inhibitor resulted in a partial reversal of the exhausted phenotype, as shown by restored cytokine secretion. Thus we show for the first time the involvement of JAK signaling in human T cell exhaustion, which may provide rationale for combining JAK inhibitors with other immune therapies for cancer. In summary, the in vitro T cell exhaustion model system has yielded intriguing activity nodes during T cell function. Future exploration in such immunological states may identify novel therapeutic targets and combination opportunities for immuno-oncology. This abstract is also being presented as Poster B17. Citation Format: William Hastings, Kenzie MacIsaac, Wei Guan, Pamela Shaw, Glenn Dranoff, Z Alexander Cao. Molecular characterization of in vitro exhausted T cells. [abstract]. In: Proceedings of the AACR Precision Medicine Series: Targeting the Vulnerabilities of Cancer; May 16-19, 2016; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2017;23(1_Suppl):Abstract nr PR03.