High homogeneity of mage, bage, gage, tyrosinase and Melan-A/Mart-1 gene expression in clusters of multiple simultaneous metastases of human melanoma: Implications for protocol design of therapeutic antigen-specific vaccination strategies

Human melanoma cells express several antigens which are recognized by autologous and specific CTL clones in association with HLA-class-1 molecules. Many of these antigens represent suitable targets for tumor immunotherapy, since their expression in human melanoma cells is common and highly specific. In order to achieve real clinical success with therapeutic vaccination strategies, one important requirement is the expression of the target antigen by all the tumor lesions of a patient. We have studied this issue by assessing, through an RT-PCR approach, the expression of MAGE-1, MAGE-2, MAGE-3, BAGE, GAGE-112, Tyrosinase and Melan-A/MART-1 genes in 17 clusters of simultaneous in-transit or regional lymph node metastases collected form 15 stage-III and I stage-IV (AJCC/UICC pTNM system) melanoma patients. In 14 out of 17 clusters of simultaneous metastatic lesions (82%), the homogeneity in the pattern of gene expression within the cluster was complete. Heterogeneity within the same cluster was observed in only 3 out of 17 clusters (18%) and represented only minor features. Our data reveal that, in AJCC-stage-III melanoma patients, different but simultaneous metastatic lesions express the same pattern of antigen-coding genes. These observations have 2 main clinical implications: (i) the antigenic characterization of one single and easily accessible lesion allows identification of optimal targets for an active antigen-specific immunotherapy treatment; (ii) almost all the metastatic lesions are expected to be hit by the immune response eventually induced against the tumor antigen. Moreover, these data suggest that active specific immunotherapy directed against MAGE-1, MAGE-3, BAGE, GAGE-1/2, Melan-A/MART- 1 and Tyrosinase antigens could be exploited as an adjuvant treatment to surgery in high-risk.