A Novel Role for Histone Deacetylase 10 (HDAC10) in the Regulation of PD-L1 Expression and Immune Tolerance Mediated By Antigen Presenting Cells (APCs)

Antigen-presenting cells (APCs) play a central role in determining T-cell activation versus T-cell anergy in the context of tumor growth. The inflammatory status of APCs at the time of tumor antigen presentation has been proposed as explanation for the induction of such divergent T-cell outcomes. This overall inflammatory status of APCs can be regulated epigenetically.

HDAC10 is a member of the class IIb family of HDACs that represses gene transcription independent of its deacetylase activity when tethered to a promoter. It is normally expressed in liver, kidney, pancreas and spleen and its overexpression has been shown to accelerate cancer development. While we previously demonstrated a role for HDAC6, the other member of the class IIb family, in control of APC inflammatory vs tolerogenic status (Cheng F et al, J Immunol 2014), little is known about the role (if any) of HDAC10 in regulating APC's function.

Here we show for the first time that knockdown of HDAC10 in APCs, using shRNA specific for murine HDAC10 or non-target control (NT), resulted in the induction of inflammatory APCs displaying an 20-30% increased expression of MHC class II molecules and abrogation of PD-L1 gene transcription (4 fold decreased) and expression as compared to controls. To further confirm these results in vivo, HDAC10 knock out (KO) mice were used. These HDAC10 KO mice, as compared to wild type (WT) mice, reveal no gross macroscopic abnormalities in any lymphoid organs. Macrophages isolated from HDAC10 KO mice demonstrated increased expression of MHC II molecules and decreased expression of PD-L1, analogous to the shRNA data. Furthermore, in vitro co-culture of these macrophages with antigen-specific CD4⁺ T cells lead to effective priming of naïve CD4⁺ T-cells and restoration of the responsiveness of tolerant T-cells, as determined by their 3 fold increased production of IL-2 and IFN-g in response to cognate antigen. This demonstrates that APCs lacking HDAC10 are more immunogenic than control cells. Finally, to assess the role of HDAC10 in tumor immunity, we challenged HDAC10KO mice as well as WT control with murine mantle cell lymphoma (MCL) cells (FC-muMCL1 cells) given s.c. and measured tumor growth. A significant delay in MCL growth was observed in HDAC10KO mice as compared to WT controls (p<0.05). Studies are ongoing to assess the phenotype and function of APCs and T-cells isolated from these MCL-bearing mice.

In summary, our studies have unveiled previously unknown immunoregulatory properties of HDAC10. In particular, its regulatory effects upon the expression of the tolerogenic molecule PD-L1, opens new frontiers for the understanding of PD-L1 regulation and points to disruption of the HDAC10/PD-L1 axis as a novel epigenetic target for cancer immunotherapy.