Chimeric Trop2 virus-like particles: a potential immunotherapeutic approach against pancreatic cancer.

Trop2 is a recently discovered cell surface glycoprotein overexpressed in pancreatic cancer which could potentially be used as an immunotherapeutic target. Enveloped virus-like particles (VLPs) are highly immunogenic and versatile immune stimulatory agents which can be modified to incorporate exogenous proteins on their membrane envelope to use as cancer vaccines. In this study, we investigated the effects of murine Trop2 (mTrop2) VLP immunization in a pancreatic cancer syngeneic murine model. VLPs incorporating mTrop2 were used to immunize C57BL/6 tumor-bearing mice. Immunization with mTrop2 VLPs led to a significant reduction in tumor growth accompanied by a broad activation and tumor infiltration of CD4(+) and CD8(+) T cells as well as natural killer and natural killer T cells. VLP immunization generated mTrop2-specific cytotoxic T lymphocytes and antibodies with no measurable induction of autoimmunity. Importantly, VLP immunization decreased the population of regulatory T cells and myeloid-derived suppressor cells inside the tumor tissue resulting in decreased levels of immunosuppressive cytokines like interleukin-10 and transforming growth factor-β while promoting the activation of immature macrophages and dendritic cells. Furthermore, combination of VLP immunization with gemcitabine treatment showed an improved effect significantly increasing the survival of tumor bearing mice. Our results demonstrate that mTrop2 VLP immunization can activate broad antitumor immune responses and affect key players in the tumor microenvironment overcoming a major barrier, which has limited the efficacy of cancer vaccines. This study presents a novel immunotherapeutic approach which could potentially be used as an alternative treatment option in combination therapies to treat pancreatic cancer patients.