Tumorantigen

Tumor antigen refers to a molecule, usually a protein or peptide, that is produced by tumor cells or modified in them and can be recognized by the immune system. Tumor antigens may arise from mutated genes (neoantigens), from overexpressed or aberrantly expressed normal proteins (tumor-associated antigens), differentiation antigens, cancer-testis antigens, or viral antigens in virally induced cancers.

Neoantigens originate from tumor-specific mutations and are typically not present in normal tissues, making them potentially highly immunogenic. TAAs are often shared across tumors and patients but may be subject to tolerance, which can limit T cell responses. The immunogenicity of a given antigen influences its suitability as a target for therapy or a biomarker.

Antigen presentation is central to recognition. Peptides derived from tumor antigens are presented on MHC class I molecules to CD8+ T cells and on MHC class II molecules to CD4+ T cells. Antibody responses can recognize surface or secreted antigens, and natural killer cells may engage when antibody-dependent mechanisms are involved.

Clinical relevance is most evident in cancer immunotherapy. Tumor antigens are used in cancer vaccines, in adoptive cell therapies with TCR- or CAR-engineered T cells, and as targets for monoclonal antibodies. Checkpoint inhibitors can enhance responses against existing tumor antigens by removing inhibitory signaling on T cells.

Challenges include tumor heterogeneity and antigen loss variants, the immunosuppressive tumor microenvironment, and the need for accurate identification and validation of immunogenic antigens, particularly patient-specific neoantigens.