Abstract
Immunotherapies revive host immune responses against tumors by stimulating innate and adaptive immune effector cells with antitumor functions. Thus, detailed studies of immunological cell phenotypes and functions within the tumor microenvironment (TME) following immunotherapy treatments is critical to identifying the determinants of therapeutic success, optimizing treatment regimens, and driving curative outcomes. Oncolytic viruses such as Orf virus (OrfV) are multifunctional biologics that preferentially infect and kill cancer cells while simultaneously causing inflammation that drives anticancer immune responses. Here, we describe the immunological impact of OrfV on the ascites TME in a preclinical model of advanced-stage epithelial ovarian cancer. OrfV promoted the infiltration of several immune effector cells with increased expression of activation markers and effector cytokines into the ascites TME, which correlated with reduced ascites tumor burden and improved survival. The kinetics of the immune response and change in tumor burden following OrfV therapy revealed an optimal re-administration time to sustain antitumor immunity, further extending survival. The data presented highlight the importance of investigating immune response kinetics following immunotherapy and demonstrate that detailed kinetic profiling of immune responses can reveal novel insights into mechanisms of action that can guide the development of more effective therapies.