Biological Consequences of Major Histocompatibility Class-II Expression by Tumor Cells in Cancer

Immunotherapy has emerged as a key pillar of cancer treatment. To build upon the recent successes of immunotherapy, intense research efforts are aimed at a molecular understanding of anti-tumor immune responses, identification of biomarkers of immunotherapy response and resistance, and novel strategies to circumvent resistance. These studies are revealing new insight into the intricacies of tumor cell recognition by the immune system, in large part through Major Histocompatibility Complexes (MHCs). Though tumor cells widely express MHC-I, a subset of tumors originating from a variety of tissues also express MHC-II, an antigen presenting complex traditionally associated with professional antigen presenting cells (APCs). MHC-II is critical for antigen presentation to CD4+ T-lymphocytes, whose role in anti-tumor immunity is becoming increasingly appreciated. Accumulating evidence demonstrates that tumor-specific MHC-II associates with favorable outcomes in patients with cancer, including those treated with immunotherapies, and with tumor rejection in murine models. Herein, we will review current research regarding tumor-enriched MHC-II expression and regulation in a range of human tumors and murine models, and the possible therapeutic applications of tumor-specific MHC-II.

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