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 expression in tumors where evidence of specific gene transcripts can be obtained.

BACKGROUND DATA

The MAGE-1 gene encodes a tumor-associated antigen that can be recognized by specific cytotoxic T lymphocytes. Transcription 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.

METHODS

Total cellular mRNA was extracted from six melanoma biopsies, reverse-transcribed and tested in 25-45 cycles of reverse polymerase chain reaction (rtPCR) in the presence of primers' pairs specific for the beta-actin-positive control gene and for the MAGE-1-encoding gene. Concurrently, 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-specific monoclonal antibodies.

RESULTS

MAGE-1 gene transcription could be demonstrated following 25 cycles of rtPCR in one out of six biopsies and in three more following 35 cycles of rtPCR. 2/6 samples were negative even after 45 cycles of rtPCR. MAGE-1 protein production could be detected by immunoblotting in the lysates from biopsies showing evidence of specific gene transcription. Cells positive for MAGE-1 protein expression could be identified by immunohistochemistry on snap-frozen sections in three of the four tumors displaying specific transcripts. Distribution 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 showing evidence of MAGE-1 gene expression suggests a relevant heterogeneity regarding MAGE-1 antigen production within individual tumor specimens.