HDACi promotes inflammatory remodeling of the tumor microenvironment to enhance epitope spreading and antitumor immunity. HDACi promotes inflammatory remodeling of the tumor microenvironment to enhance epitope spreading and antitumor immunity

Adoptive cell therapy (ACT) with tumor-specific memory T cells has shown increasing efficacy in regressing solid tumors. However, tumor antigen heterogeneity represents a longitudinal challenge for durable clinical responses due to the therapeutic selective pressure for immune escape variants. Here, we demonstrate that delivery of class I histone deacetylase inhibitor, MS-275, promotes sustained tumor regression by synergizing with ACT in a coordinated manner to enhance cellular apoptosis. We find that MS-275 alters the tumor inflammatory landscape to support antitumor immunoactivation through the recruitment and maturation of cross-presenting CD103+ and CD8+ dendritic cells and depletion of regulatory T cells. Activated endogenous CD8+ T cell responses against non-target tumor antigens was critically required for the prevention of tumor recurrence. Importantly, MS-275 alters the immunodominance hierarchy by directing epitope spreading towards endogenous retroviral tumor-associated antigen, p15E. Our data suggest that MS-275 multi-mechanistically improves epitope spreading to promote long-term clearance of solid tumors. Overall design: Bulk tumor RNA obtained from mice treated with ACT (Tmem+VSV-gp33) or ACT+MS-275 1, 3, and 5 days post-treatment