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. Bulk tumor RNA obtained from mice treated with ACT (Tmem+VSV-gp33) or ACT+MS-275 1, 3, and 5 days post-treatment