HETEROGENEITY OF MELANOMA ANTIGEN-1 (MAGE-1) GENE AND PROTEIN EXPRESSION IN MALIGNANT-MELANOMA

Objective: The authors' objective is to identify MAGE-1 tumor antigen in clinical melanoma specimens and to verify the extent of its express ion in tumors where evidence of specific gene transcripts can be obtai ned. Background data: The MAGE-1 gene encodes a tumor-associated antig en that can be recognized by specific cytotoxic T lymphocytes. Transcr iption of the MAGE-1 gene has previously been demonstrated in various malignancies, but the production of the specific gene product and its distribution in neoplastic tissues have not yet been addressed. Method s: Total cellular mRNA was extracted from six melanoma biopsies, rever se-transcribed and tested in 25-45 cycles of reverse polymerase chain reaction (rtPCR) in the presence of primers' pairs specific for the be ta-actin-positive control gene and for the MAGE-1-encoding gene. Concu rrently, portions of these specimens were lysed and probed for MAGE-1 protein by immunoblotting. Additional material from the same biopsies was analyzed following immunohistological staining with MAGE-1-specifi c monoclonal antibodies. Results: MAGE-1 gene transcription could be d emonstrated following 25 cycles of rtPCR in one out of six biopsies an d in three more following 35 cycles of rtPCR. 2/6 samples were negativ e even after 45 cycles of rtPCR. MAGE-1 protein production could be de tected by immunoblotting in the lysates from biopsies showing evidence of specific gene transcription. Cells positive for MAGE-1 protein exp ression could be identified by immunohistochemistry on snap-frozen sec tions in three of the four tumors displaying specific transcripts. Dis tribution of positivity ranged between focal cellular areas and single positive cells in the different tumors. Conclusions: The MAGE-1 tumor antigen can be detected by specific monoclonal antibodies in clinical tumor specimens. The pattern of positivity observed in samples showin g evidence of MAGE-1 gene expression suggests a relevant heterogeneity regarding MAGE-1 antigen production within individual tumor specimens .