Two antigens recognized by autologous cytolytic T lymphocytes on a melanoma result from a single point mutation in an essential housekeeping gene.
We have pursued our analysis of antigens recognized by autologous cytolytic T lymphocytes (CTLs) on the melanoma cells of patient LB33. This patient enjoys an unusually favorable evolution, which is associated with a strong and sustained antitumor CTL response. We reported previously the analysis of two melanoma cell lines, MEL.A and MEL.B, which were derived from metastases removed from the patient at 5 years' distance. Autologous CTL clones derived from blood lymphocytes recognized several antigens presented by different HLA class I molecules on MEL.A. The MEL.B cells resisted lysis by these CTLs because they have lost expression of most HLA molecules, suggesting that they were selected in vivo by the anti-MEL.A CTL response. One of the MEL.A antigens was shown to result from a point mutation in the tumor. Here we report the cloning of a gene that encodes two other MEL.A antigens. This new gene, MUM-2, is expressed ubiquitously. In the melanoma cells of patient LB33, it contains a point mutation that changes one amino acid in the translated protein. Two different antigenic peptides, one presented to CTL by HLA-B44 molecules and another by HLA-C6 molecules, overlap and contain the mutated residue. Gene MUM-2 is homologous to an essential yeast gene, bet5, that was recently shown to be implicated in the vesicular transport of proteins from the endoplasmic reticulum to the Golgi. In a mutant yeast with a disrupted bet5 gene, both the wild-type and the mutated MUM-2 genes could complement for bet5 function. These results indicate that the antigenic mutation does not destroy the function of the protein, a function that is conserved in eukaryotic cells. The identification of these antigens suggests that point mutations could be the major cause of the strong immunogenicity of MEL.A cells.
Chiari
R
R
Cellular Genetics Unit, Université Catholique de Louvain, Brussels, Belgium.
Foury
F
F
De Plaen
E
E
Baurain
J F
JF
Thonnard
J
J
Coulie
P G
PG
D000595:Amino Acid Sequence; D000951:Antigens, Neoplasm / Q000235:genetics* / Q000276:immunology; D001483:Base Sequence; D018076:DNA, Complementary / Q000235:genetics; D005816:Genetic Complementation Test; D015235:HLA-B Antigens / Q000276:immunology; D059948:HLA-B44 Antigen; D006801:Humans; D008545:Melanoma / Q000235:genetics / Q000276:immunology*; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D017354:Point Mutation / Q000235:genetics*; D016133:Polymerase Chain Reaction / Q000379:methods; D012333:RNA, Messenger / Q000235:genetics; D012878:Skin Neoplasms / Q000235:genetics / Q000276:immunology*; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology*; D014407:Tumor Cells, Cultured; D033921:Vesicular Transport Proteins; D015003:Yeasts / Q000235:genetics
D000951:Antigens, Neoplasm; D018076:DNA, Complementary; D015235:HLA-B Antigens; D059948:HLA-B44 Antigen; D026901:Membrane Transport Proteins; D012333:RNA, Messenger; C401314:TRAPPC1 protein, human; D033921:Vesicular Transport Proteins