A MAGE-A3 peptide presented by HLA-DP4 is recognized on tumor cells by CD4(+) cytolytic T lymphocytes

Antigens encoded by MAGE-A3 and recognized by T cells are interesting targe ts for tumor immunotherapy because they are strictly tumor specific and sha red by many tumors of various histological types, A number of MAGE-A3 antig enic peptides presented by HLA class I molecules have been used in clinical trials, and regressions of melanoma metastasis have been observed, We repo rt here the identification of a MAGE-A3 epitope, TQHFVQENYLEY, presented to CD4(+) T lymphocytes by HLA-DP4 molecules, which are expressed in similar to 76% of Caucasians, This new epitope may be useful both for therapeutic v accination and for the evaluation of the immune response in cancer patients . Interestingly, the CD4(+) T cells Lysed HLA-DP4 tumor cells expressing MA GE-A3, indicating that this epitope, in contrast to other class-II MAGE-A3 epitopes, Is presented at the surface of tumor cells, The study of this dis parity in the presentation of two epitopes from the same protein may lead t o a better understanding of the endogenous class II presentation pathway.