Figure 6.

Tumor antigens recognized by immune cells. Tumor antigens are categorized based on the pattern of gene expression. The production of antigenic peptides by cancer cells is illustrated herein. (A) Viral antigens are only expressed in virus-infected cells; (B) Differentiation antigens are encoded by genes with tissue-specific expression; (C) Cancer-germline genes are expressed in tumors or germ cells because of whole-genome demethylation; (D) Some genes are overexpressed in tumors owing to increased transcription or gene amplification. The resulting peptides are upregulated on these tumors, but also show a low level of expression in some noncancerous tissues; (E) However, mutated genes may yield a mutant peptide (neoantigen), which is recognized as nonself by immune cells. CEA, carcinoembryonic Ag; EGFR, epidermal growth factor receptor; EBV, Epstein-Barr virus; HPV, human papillomavirus; hTERT, human telomerase reverse transcriptase; MAGE-A3, melanoma-associated antigen 3; MART-1, melanoma antigen recognized by T cells-1; MCC, Merkel cell carcinoma. This figure is adapted from our previous article [63].