Tumor Microenvironment Remodeling by Intratumoral Oncolytic Vaccinia Virus Enhances the Efficacy of Immune-Checkpoint Blockade

Purpose: Cancer immunotherapy is a potent treatment modality, but its clinical benefit depends on the tumor's immune profile. Here, we used mJX-594 (JX), a targeted and GM-CSF-armed oncolytic vaccinia virus, as a strategy to remodel the tumor microenvironment (TME) and subsequently increase sensitivity to alpha PD-1 and/or alpha CTLA-4 immunotherapy. Experimental Design: The remodeling of the TME was determined using histologic, flow-cytometric, and Nano-String immune profiling analyses. JX was intratumorally injected into implanted Renca kidney tumors or MMTV-PyMT transgenic mouse breast cancers with or without alpha PD-1 and/or alpha CTLA-4. Various combination regimens were used to evaluate immunotherapeutic anticancer responses. Results: Intratumoral injection of JX remodeled the TME through dynamic changes in the immune system, as shown by increased tumor-infiltrating T cells and upregulation of immune-related gene signatures. This remodeling induced conversion of a noninflamed tumor into an inflamed tumor. JX virotherapy led to enhanced abscopal effects in distant tumors, with increased intratumoral infiltration of CD8 thorn T cells. A depletion study revealed that GM-CSF is an indispensable regulator of anticancer efficacy of JX. Dual-combination therapy with intratumoral JX and systemic alpha PD-1 or alpha CTLA-4 further enhanced the anticancer immune response, regardless of various treatment schedules. Of note, triple combination immunotherapy with JX, alpha PD-1, and alpha CTLA-4 elicited the most potent anticancer immunity and induced complete tumor regression and long-term overall survival. Conclusions: Our results show that intratumoral JX treatment induces dramatic remodeling of the TME and more potently suppresses cancer progression with immune-checkpoint blockades by overcoming resistance to immunotherapy.