Abstract 2123: Reprogramming of myeloid and lymphoid cells in vitro by the HDAC6 selective inhibitor ITF3756

Abstract Anti tumor immune response is driven by the concerted action of myeloid and lymphoid cells. Tumor cells have evolved to shape an immune suppressive tumor microenvironment (TME) where the antitumor immune response is dampened in several ways. For instance, local release of cytokines such as TNF-α, leads to the up-regulation of PD-L1 expression in tumor, myeloid and T cells, thereby triggering local immune suppression through the PD-1/PD-L1 axis. Strategies aimed at downregulating the suppressor activity of myeloid cells and at reinvigorating T cell effector functions are a promising approach to drive an effective innate and adaptive anti-tumor immune response. HDAC6 is a member of the Zn-dependent histone deacetylase family of enzymes with peculiar structure and functions, that orchestrates key processes in both innate and adaptive immune cells. Inhibition of HDAC6 enzymatic activity inhibits cytokine-dependent expression of PD-L1 and upregulates the expression of surface molecules involved in T cell activation. Thus, HDAC6 inhibition represents a new approach to enhance antitumor immune response. Here we report the in vitro activity of one of our potent and selective HDAC6 inhibitors, ITF3756, on human monocytes, dendritic cells and T cells. Through the upregulation of co-stimulatory and the downregulation of inhibitory molecules, ITF3756 increased allogenic T cell proliferation induced by monocytes stimulated with TNF-α in a way comparable to an anti PD-L1 antibody. Dendritic cells differentiated from peripheral blood monocytes in the presence of ITF3756 were also more efficient in stimulating allogeneic T cell proliferation. ITF3756 decreased the expression of PD-L1 both in TNF-α activated monocytes and in immature DCs. The effect of ITF3756 on PD-L1 expression was dose dependent and required the continuous presence of ITF3756 for at least 12 hours to achieve the best effect, as determined by washout experiments. CD8 T cell differentiation and exhaustion phenotypes were also modulated by ITF3756. In an in vitro model mimicking the exhaustion process, ITF3756 drove the differentiation of CD8 T cells towards a central memory phenotype and reduced the expression of effector memory markers and the exhaustion markers PD-1 and LAG3. These results were corroborated by qPCR and RNAseq analyses. ITF3756-exposed CD8 T cells had also a higher expression of IFN-γ and Granzyme b. Taken together, these results indicate that ITF3756 can modulate the activity of both myeloid and lymphoid cells and stimulate immune recognition and function. Citation Format: Chiara Ripamonti, Andrea Stevenazzi, Barbara Vergani, Giovanni Sandrone, Mattia Marchini, Christian Steinkuhler, Gianluca Fossati. Reprogramming of myeloid and lymphoid cells in vitro by the HDAC6 selective inhibitor ITF3756 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2123.