Targeting Ubiquitin-like Protein, ISG15, as a Novel Tumor Associated Antigen in Colorectal Cancer

SIMPLE SUMMARY: Despite their potential and promising anti-tumor efficacy, previously developed cancer vaccines targeting different tumor-associated antigens for colorectal cancer (CRC) have not yet proven to be successful. Interferon-stimulated gene 15 (ISG15) is emerging as an important oncoprotein with a potential diagnostic signature and therapeutic target for a multitude of cancer, including CRC. In this study, we investigated the therapeutic efficacy of Listeria-based vaccines targeting ISG15 (Lm-LLO-ISG15) in CRC. We found that the Lm-LLO-ISG15 vaccination results in anti-tumor efficacy against the MC38 tumor model by recruiting cytotoxic T lymphocytes and leading to a more favorable effector to regulatory T cell ratio (T(eff)/T(reg)) in the tumor microenvironment. ABSTRACT: Colorectal cancer (CRC) is the third leading cause of cancer-related deaths in both men and women in the United States. While immune checkpoint inhibitor (ICI) therapy is demonstrating remarkable clinical responses, the resistance and immune-related toxicities associated with ICIs demonstrate the need to develop additional immunotherapy options for CRC patients. Cancer vaccines represent a safe and promising treatment approach for CRC. As previously developed tumor-associated antigen (TAA)-based cancer vaccines for CRC are not demonstrating promising results, we propose that interferon-stimulated gene 15 (ISG15) is a novel TAA and therapeutic target for CRC. Our work demonstrates the anti-tumor efficacy of a Listeria-based vaccine targeting ISG15, designated Lm-LLO-ISG15, in an immunocompetent CRC murine model. The Lm-LLO-ISG15-mediated anti-tumor response is associated with an increased influx of functional T cells, higher production of multiple intracellular cytokines response, a lower number of regulatory T cells, and a greater ratio of effector to regulatory T cells (T(eff)/T(reg)) in the tumor microenvironment.