Intravesical VAX014 Synergizes with PD-L1 Blockade to Enhance Local and Systemic Control of Bladder Cancer

Abstract

Emerging clinical evidence indicates that the combination of local administration of immunotherapy with systemic immune-checkpoint blockade targeting the PD-1/PD-L1 pathway improves response rates in select solid tumor indications; however, limited clinical experience with this approach exists in advanced bladder cancer patients. VAX014 is a novel bacterial minicell-based, integrin-targeted oncolytic agent undergoing clinical investigation for intravesical (IVE) treatment of nonmuscle-invasive bladder cancer. Here, we demonstrated that the antitumor activity of VAX014 following IVE administration was dependent upon CD4+ and CD8+ T cells in two syngeneic orthotopic bladder tumor models (MB49 and MBT-2). PD-L1 upregulation was found to be an acquired immune-resistance mechanism in the MB49 model, and the combination of VAX014 with systemic PD-L1 blockade resulted in a significant improvement in bladder tumor clearance rates and development of protective antitumor immunologic memory. Combination treatment also led to enhanced systemic antitumor immune responses capable of clearing distal intradermal tumors and controlling pulmonary metastasis. Distal tumors actively responding to combination therapy demonstrated a phenotypic shift from regulatory T cell to Th1 in intratumoral CD4+ T cells, which was accompanied by a higher percentage of activated CD8+ T cells and higher IFNγ. Finally, VAX014's target integrins α3β1 and α5β1 were overexpressed in tumor biopsies from advanced-stage bladder cancer patients, as well as in both the MB49 and MBT-2 orthotopic mouse models of bladder cancer. These collective findings provide a rationale for the clinical investigation of VAX014 and systemic PD-1/PD-L1 blockade in advanced-stage bladder cancer.