Abstract 4026: Epigenetic changes in T cells in response to immune checkpoint blockade

Abstract

Abstract Immune checkpoint blockade therapy has led to clinical success and have established immunotherapy as one of the primary modality of cancer treatment. It leads to a durable response in around 20% of the patients (responders). Success of immune checkpoint blockade therapy relies on the increase of effector T cells and decrease of regulatory T cells in the tumor microenvironment. However, the underlying mechanism that govern the ratio of effector and regulatory T cells between responder and non-responder to checkpoint blockade is not understood. Understanding the process could reveal novel mechanisms to boost efficacy of immune checkpoint blockade. Differentiation of naïve T cells into effector and regulatory phenotype requires lineage-specifying transcription factors and epigenetic modifications that allow appropriate repression or activation of gene transcription. One key epigenetic modification for T cell differentiation is trimethylation of lysine 27 on histone H3 (H3K27me3). Loss of H3K27me3 results in increased Th-1 plasticity whereas presence of H3K27me3 on Foxp3 locus is required to maintain the function of T-regulatory cells. We hypothesize that immune checkpoint blockade changes the epigenetic landscape in tumor infiltrating T cells that results in an effector phenotype and epigenetic modification of H3K27me3 could promote an anti-tumor immune microenvironment in tumor bearing mice.We showed that in-vivo inhibition of H3K27me3 in combination with anti-CTLA4 results in reduction of tumor size and also reduction in regulatory T cells in a B16-F10 melanoma mice model compared to anti-CTLA4 treatment alone, suggesting H3K27me3 inhibition could increase the efficacy of checkpoint blockade therapy. Future studies will aim to elucidate epigenetic changes in H3K27me3 and define an epigenetic signature as a result of immune checkpoint therapy by ChIP-sequencing. Data generated in this project will greatly enhance our understanding of epigenetic regulation of T cell differentiation is response to immune checkpoint blockade and aid identifying key changes that could be further modified to overcome resistance to immune checkpoint blockade in non-responders. Citation Format: Sangeeta Goswami, Jianfeng Chen, Hao Zhao, Xuejun Zhang, Padmanee Sharma. Epigenetic changes in T cells in response to immune checkpoint blockade. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4026.