REOVIRUS-DRIVEN MYELOID CELLS IN ONCOLYTIC VIRUS THERAPY AND INFECTION
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Cancer-associated immunosuppression represents a major contributor to tumor progression and impairment of spontaneous or therapeutically-induced anti-tumor immunity. Myeloid cells are a key mediator of such immunosuppression. These tumor-associated myeloid cells promote angiogenesis, metastasis, and prevent immune-mediated attack and elimination of cancer cells. Thus, it is not surprising that current cancer immunotherapeutic approaches, which exploit immune cell functions to target cancer, aim to overcome immunosuppression within the tumor microenvironment (TME). Oncolytic viruses (OVs) represent a novel class of anti-cancer therapeutic agents. OVs, including reovirus, preferentially target and kill cancer cells. Additionally, numerous OVs readily overturn the otherwise suppressed immune system and facilitate the activation of beneficial anti-tumor T cell responses. Contrary to this paradigm, our previous findings illustrated that reovirus transiently augments a myeloid cell population, commonly associated with an immunosuppressive phenotype, following reovirus administration. Thus, this thesis focuses on elucidating the biological and therapeutic impact that these cells have on reovirus-based OV therapy. As such, the broad objectives of this thesis are to 1) phenotypically and functionally characterize reovirus-driven myeloid cells in the context of OV therapy, 2) implement complementary immunological interventions to modulate these cells during therapy, and 3) develop a mass spectrometry-based proteomics platform to understand how these cells respond throughout virus infection in vivo. The following work illustrates that reovirus drives the accumulation of suppressive monocytic myeloid cells (MMCs) within the TME and enhances tumor-associated immunosuppression. Depletion of these MMCs in the TME (using gemcitabine) accelerated the development of anti-tumor T cell immunity and improved therapeutic efficacy. Although the use of gemcitabine hampered MMC accumulation, it also hindered reovirus replication. Hence, an alternative approach to manipulate these MMCs could benefit OV therapy effectiveness. Lastly, the implementation of our quantitative temporal in vivo proteomics platform unveiled that reovirus-driven MMCs, in the context of infection and absence of a TME, naturally possess anti-viral/pro-inflammatory properties and are precursors for antigen-presenting cells. With such environmentally-dependent and contrasting cellular properties, our data suggest that, as an alternative to MMC depletion strategies, future work could harness the pro-inflammatory phenotype of these MMCs to further potentiate the generation of anti-tumor immunity during OV therapy.