Improving Cancer Immunotherapy with CRISPR/Cas9-Mediated Gene Knockout of A2AR, PD-1, and CTLA-4 in T Cells

Cancer is the second leading cause of death in the United States overall and the leading cause among individuals younger than 85 years. T lymphocytes (T cells) are important for regulating and directing immune responses in the adaptive immune system to keep the body healthy and functional. However, T cells show limited efficacy when killing solid cancer cells. T cells become dysfunctional due to immunosuppression in the tumor microenvironment (TME), which results in reduced T cell persistence, reduced cytokine production, and reduced cytotoxicity. CRISPR/Cas9, a precise gene editing tool, may be used to knock out genes associated with immunosuppression and boost antitumor immunity in T cells. In this review, we examine single-gene knockouts of three major contributors to immunosuppression in T cells within the TME: A2AR, PD-1, and CTLA-4. To determine the effects of the immunosuppressive gene knockouts, we analyze studies that use in vitro experiments and in vivo xenografts of immunodeficient mice. Our review suggests that CRISPR-mediated gene knockout of A2AR, PD-1, and CTLA-4 results in enhanced T cell proliferation, improved persistence, elevated cytotoxicity, and increased cytokine production, ultimately boosting T cell antitumor immunity and combating solid tumors. However, clinical trials are needed to demonstrate the long-term safety, immunity, and persistence of the recently proposed therapy.