Human Tumor Antigens and Cancer Immunotherapy

Figure 2

Processing of tumor antigens recognized by CD8⁺ T cells. CTL recognize peptides that are produced by the degradation of cellular proteins by the proteasome. Four types of proteasome exist, two of which are represented here (standard proteasome and immunoproteasome). Peptides resulting from proteasome degradation are then transported in the lumen of the ER by the TAP transporter. Peptides bearing an extended N-terminus can be further trimmed by additional proteases such as ERAP1 before being loaded on HLA class I molecules with the help of the peptide loading complex, which is composed of TAP, tapasin (Tpn), the oxidoreductase ERp57, and the chaperone calreticulin (CRT). Peptide/HLA complexes are then transferred to the cell surface through the secretory pathway.