HLA molecules are classified into two main types: Class I and Class II. HLA Class I molecules (HLA-A, HLA-B, HLA-C) are expressed on almost all nucleated cells and present endogenous antigens to CD8+ T cells. HLA Class II molecules (HLA-DP, HLA-DQ, HLA-DR) are primarily expressed on antigen-presenting cells and present exogenous antigens to CD4+ T cells. Both classes play critical roles in the immune response against cancer.
