Abstract PR09: Targeting histone deacetylase 6 in T-cells to improve melanoma immunotherapy
Authors: Laino Andressa Sodre , Woods David M. , Celis Esteban , Weber Jeffrey , Sotomayor Eduardo 
Published: October 2015

Abstract
Epigenetic modifications are a major component of regulating cell biology and, thus, have raised attention for their implications in cancer immunotherapies. In this regard, histone deacetylases (HDACs) have emerged as key players in orchestrating both tumor and immune response. Particularly HDAC6 has been identified as modulating the regulatory T-cell suppressive activity through HSP90. The uniqueness of HDAC6 in containing two enzymatic pockets allows the development of isotype-specific small molecule inhibitors. Here a novel role of HDAC6 in regulating anti-melanoma response is exploited and shown to have positive implications for tumor infiltration lymphocyte (TIL) therapy. Initially HDAC6 expression was evaluated in T-cell subsets from mouse, healthy human cells and melanoma patients. HDAC6 expression was decreased after T-cell activation as well as in the central memory TILs subset when compared to its naïve counterpart. To further investigate the role(s) of HDAC6 in T-cell anti-tumor responses, an HDAC6KO mouse model was utilized. Despite having normal lymphocyte compartments, melanoma growth was significantly delayed in HDAC6KO when comparing to age-, sex-match wild-type (WT) mice. Tumor-free HDAC6KO mice also displayed an enhanced T-cell response following melanoma-peptide vaccination, characterized by a less pronounced contraction phase of antigen-specific CD8+ T-cells. When systemically treated with the HDAC6 specific inhibitor ACY-1215, tumor growth was slightly reduced in melanoma-bearing mice. To address whether this was a direct effect on T-cell response, WT T-cells treated ex vivo with ACY-1215 were adoptively transferred to tumor-bearing WT mice. It was found that HDAC6 inhibition improved in vivo anti-tumor response and led to a modest accumulation of central memory T-cells in the lymph nodes. To further expand these results with a potential clinical application, previously frozen TILs from melanoma patients were thawed and treated with ACY-1215 during expansion in vitro. Accordingly, HDAC6 inhibition increased the percent of both CD8+ and CD4+ central memory T-cell subsets, as indicated by CD45RO, CD45RA, CCR7 and CD62L surface markers. To build upon these results, the expression of transcription factors involved in T-cell differentiation and polarization were evaluated. The transcription factor T-BET was found to be up-regulated in CD4+ and CD8+ TILs after in vitro expansion and treatment with ACY-1215, while there was a mild decrease in expression of GATA3 and RORgT in CD4+ TILs. This data is suggestive of CD4+ TIL polarization towards a pro-inflammatory Th1 phenotype. Moreover, both CD4+ and CD8+ TILs expanded and treated with ACY-1215 displayed enhanced Ki67 expression compared to the control treatment group, indicating higher proliferative capacity as a result of HDAC6 inhibition. To address if ACY-1215 treatment could ultimately improve T-cell cytotoxicity against melanoma, TILs from one melanoma patient were treated with ACY-1215 at the same time of in vitro expansion and then co-cultured with HLA matched melanoma. Treatment of TILs with ACY-1215 resulted in 20% more killing of target cells than the control group. The data presented so far suggests a positive effect of HDAC6 inhibition in generating and maintaining anti-tumor and peptide vaccination responses in vivo. While further investigation of cellular and molecular mechanisms is necessary, the results herein described provide rationale for targeting HDAC6 to improve cancer immunotherapy.
This abstract is also presented as Poster B19.
Citation Format: Andressa Sodre Laino, David M. Woods, Esteban Celis, Jeffrey Weber, Eduardo Sotomayor. Targeting histone deacetylase 6 in T-cells to improve melanoma immunotherapy. [abstract]. In: Proceedings of the AACR Special Conference: Tumor Immunology and Immunotherapy: A New Chapter; December 1-4, 2014; Orlando, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2015;3(10 Suppl):Abstract nr PR09.