Abstract It became well known that the immune suppressive niche inside the tumor microenvironment (TME) accounts for tumor immune escape and progression, in which the regulatory T cells (Tregs) play an important role. Although some progress has been made in identifying transcriptional and epigenetic events in Treg functional regulation in TME, a fundamental gap remains in our understanding the detailed epigenetic networks mediating Treg survival, expansion and enhanced immune suppressive function induced by TME. Vacuolar protein sorting 72 homolog (VPS72), a histone chaperone that recognizes and exchanges histone H2A.Z for standard histone H2A, has been shown in in vitro studies that regulate gene transcriptions especially related in mitochondrial metabolism through chromatin remodeling, although the in vivo biological function of VPS72 remains unknown. Our preliminary studies revealed the higher expression and positive correlation between VPS72 and Foxp3 in the Tregs inside the TME. Intriguingly, our Treg-specific VPS72 KO and H2A.Z KO mouse models showed normal thymic Treg development, but dramatically interrupted peripheral Treg maintenance and function. These results led to our central hypothesis that VPS72 is a critical epigenetic factor that can be induced by TME factors and enhance Treg stability and function through H2A.Z chromatin remodeling of Treg in the TME. In the proposed studies, we are using Treg-specific constitutive and inducible gene deletion mouse models to determine the role of VPS72 and H2AZ in peripheral Treg cell maintenance, stability and function in the cancer. Using combined scRNA-seq, scATAC-seq, and CUT & RUN- seq multi-omic analysis, we will delineate the epigenetic strategies and detailed molecular mechanisms and signaling pathways VPS72 used in controlling Treg homeostasis and function. In transplant and spontaneous melanoma tumor models, we will evaluate the anti-tumor effects of VPS72 and H2AZ suppression. Furthermore, TME factors and related molecular mechanisms in upregulating VPS72 expression of Tregs in TME will be also investigated. Results from the proposed study will not only enhance our understanding of Treg biology but will also facilitate the development of more efficient Treg-based intervention strategies for cancer treatment.

Narrative It became well known that the immune suppressive niche inside the tumor microenvironment (TME) accounts for tumor immune escape and progression, in which the regulatory T cells (Tregs) play an important role. Vacuolar protein sorting 72 homolog (VPS72), a histone chaperone that recognizes and exchanges histone H2A.Z for standard histone H2A. In the proposed studies, we will use gene deletion mouse models to determine the role of VPS72 and H2AZ in Treg cell maintenance, stability, and function in the tumor. Results from the proposed study will not only enhance our understanding of Treg biology but will also facilitate the development of more efficient Treg-based intervention strategies for cancer treatment.