Human Leukocyte Antigen (HLA) molecules play a critical role in immune recognition, antigen presentation, and the regulation of immune responses.
• HLA class I molecules (e.g., HLA-A, -B, -C) are expressed on nearly all nucleated cells and present endogenous antigens to CD8⁺ cytotoxic T lymphocytes.
• Downregulation or loss of HLA class I expression is a common immune evasion strategy employed by tumors.
• Reduced HLA class I levels have been associated with poorer prognosis in several cancers, such as melanoma, colorectal, and lung cancers, because low expression hampers recognition and killing of tumor cells by cytotoxic T cells.
• HLA class II molecules (e.g., HLA-DR, -DP, -DQ) are typically expressed on professional antigen-presenting cells but can also be expressed on certain tumor cells.
HLA expression significantly influences tumor-immune interactions and, by extension, patient prognosis. While reduced HLA class I expression generally correlates with immune escape and poorer outcomes, the prognostic impact of HLA class II is more context-dependent and may vary by tumor type.
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