HLA AND CANCER

This review provides updated information on HLA class I and II antigens in cancer. The expression of HLA antigens in normal and tumor tissues, the physiological organization of the components of HLA antigen-processing machinery, the expression patterns of HLA antigens associated with the molecular and regulatory defects identified to date, as well as their functional and clinical significance, are described. This review summarizes clinical and experimental data on the complexity of immune escape mechanisms used by tumour cells to avoid T and natural killer cell responses. The variety of class I HLA phenotypes that can be produced by tumor cells during this process is presented. We also discuss here the potential capacity of metastatic lesions to recover MHC/HLA class I expression after immunotherapy, which depends on the reversible/ soft or irreversible/hard nature of the molecular mechanism responsible for the altered HLA class I phenotypes, and which determines the progression or regression of metastatic lesions in response to treatment. HLA сlass II genes play key roles in connecting innate and adaptive immunity in tumor rejection and when the escape route via HLA-I is already established. Antigens сlass II HLA expression in tumor cells and gives tumor cells the ability to present antigens, becoming less aggressive, and improves prognosis. Malignant tumors, as a genetic disease, are caused by structural alterations of the genome which can give rise to the expression of tumor-associated antigens in the form of either structurally altered molecules or of overexpressed normal molecules. Tumor associated antigens recognized by the immune system and induce a T-cell-mediated immune response. Outgrowing cancers use different strategies to evade destruction by the immune system. Immune evasion mechanisms affecting the expression and/or function of HLA-antigens are of special interest to tumor immunologists, since these molecules play a crucial role in the interaction of malignant cells with immune cells. This review describes the potential role of immunity control points in immunosuppression and therapeutic strategies for restoring the cytotoxicity of immune cells.