title: Endosomal proteases influence the repertoire of MAGE-A3 epitopes recognized in vivo by CD4+ T cells.
abstract: Little is known about the repertoire of MAGE-A3 CD4(+) T-cell epitopes recognized in vivo by neoplastic patients and how antigen processing influences epitope formation. Here, we first show that MAGE-A3-specific CD4(+) T cells are present in the blood of advanced melanoma patients. MAGE-A3(111-125), MAGE-A3(191-205), and MAGE-A3(281-300) were recognized by 7, 6, and 5 of the 11 patients tested, respectively. MAGE-A3(146-160) and MAGE-A3(171-185) were also recognized in two and one cases, whereas no recognition of MAGE-A3(161-175) and MAGE-A3(243-258) was observed. Cytokines produced were mainly interleukin 5 and/or granulocyte macrophage colony-stimulating factor, suggesting impairment of productive polarized Th1 responses. Secondly, proteases inhibitors were used to modulate in vitro the recognition by CD4(+) T-cells clones of dendritic cells loaded with MAGE-A3-expressing cell lysates. We found that formation of MAGE-A3(111-125) depended on both leupeptin-sensitive and pepstatin-sensitive proteases. In contrast, we found that MAGE-A3(161-175), which was never recognized ex vivo, was formed by leupeptin but destroyed by pepstatin-sensitive proteases. Collectively, our results show that (a) anti-MAGE-A3 CD4(+) T-cell immunity develops in vivo in neoplastic patients and is focused toward immunodominant epitopes, (b) the response in advanced disease is skewed toward a Th2 type, and (c) endosomal/lysosomal proteases in dendritic cells influence the repertoire of the epitopes recognized.
authors.affiliation: Department of Oncology, Scientific Institute H. San Raffaele, Milan, Italy.
authors.forename: Jill
authors.initials: J
authors.lastname: Marturano
authors.forename: Renato
authors.initials: R
authors.lastname: Longhi
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Russo
authors.forename: Maria Pia
authors.initials: MP
authors.lastname: Protti
mesh_terms: D017951:Antigen Presentation; D000951:Antigens, Neoplasm / Q000737:chemistry*; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology / Q000378:metabolism*; D003713:Dendritic Cells / Q000378:metabolism; D011992:Endosomes / Q000378:metabolism*; D000939:Epitopes / Q000737:chemistry; D006801:Humans; D016130:Immunophenotyping; D007963:Leukocytes, Mononuclear / Q000378:metabolism; D007976:Leupeptins / Q000737:chemistry; D008954:Models, Biological; D009363:Neoplasm Proteins / Q000737:chemistry*; D010436:Pepstatins / Q000494:pharmacology; D010447:Peptide Hydrolases / Q000378:metabolism*; D010455:Peptides / Q000737:chemistry; D018418:Th2 Cells / Q000737:chemistry
chemical_list: D000951:Antigens, Neoplasm; D000939:Epitopes; D007976:Leupeptins; C072013:MAGEA3 protein, human; D009363:Neoplasm Proteins; D010436:Pepstatins; D010455:Peptides; D010447:Peptide Hydrolases; C032854:leupeptin; C031375:pepstatin