Engineering Replication Defective Herpes Simplex Virus 1 Vectors for the Treatment of Cancer

Abstract

Although immunotherapies, including virotherapy, have had clinical success in treating cancer over the past few years, certain patients do not respond to these treatments and others ultimately relapse or experience dose-limiting toxicities that prevent further treatment. We first tested if a non-replicating herpes simplex virus 1 (HSV-1) vaccine vector, termed d106S, could serve as a safe and effective immunotherapy for treating cancer. We engineered this virus to express the pleiotropic Th1 cytokine interleukin-12 (IL-12) and used the B16 mouse model of melanoma to study its effects. Although d106S-IL12 induced an interferon (IFN) response and resulted in production of antigen-specific CD8+ T cells, none of the mice fully cleared their tumors, instead, tumors entered a state of immune equilibrium, whereby they remained as stable masses for the duration of treatment. Many immunotherapies induce a form of immune equilibrium in patients, and we therefore used d106S-IL12 as a tool to understand the contributions of various immune mediators in promoting tumor rejection or outgrowth. We profiled the immune response, identifying blockade of innate inflammatory cytokines as possible synergistic interventions. Indeed, depletions of tumor necrosis factor-α (TNF-α), IL-1β, or IL-6 enhanced survival in mice treated with d106S-IL12 and helped to overcome equilibrium in some tumors. Single-cell RNA-sequencing demonstrated that IL-12 virotherapy induced a shift towards Th1 responses and reduction in regulatory T cells. Blockade of inflammatory cytokines resulted in downregulation of inflammatory pathways in macrophages, shifting immune equilibrium towards tumor clearance. Further profiling revealed a dependence on IFNγ for maintaining equilibrium, and that CD4+ and CD8+ T cells play redundant roles in controlling tumor outgrowth. Despite the importance of IFNγ, tumor sensing of this cytokine was not required. We also engineered a d106S vector expressing an IL-2 mimetic that enhanced d106S-IL12 efficacy and created a d106S-CXCL13 vector that aimed to generate a model to study tertiary lymph node formation in cancer. Finally, we tested the role of CD47, a “don’t eat me” signal, in a cancer vaccine. This work helps us better understand the response to immunotherapies and raises the possibility of synergistic enhancement of existing cancer immunotherapies.