HLA-G in melanoma: can the current controversies be solved?

The potential role of HLA-G in tumor immune escape has stimulated interest in the analysis of HLA-G antigens in malignant cells. Malignant melanoma is the tumor which has been mostly analyzed for HLA-G expression. Results obtained by seven groups of investigators about HLA-G expression in 108 melanoma cell lines have been concordant. HLA-G mRNA has been found in about 50% of the cell lines tested, whereas HLA-G protein has been found in less than 1% of the cell lines analyzed. In contrast, results obtained from six groups of investigators about HLA-G protein expression in 133 melanoma lesions have been conflicting. The possible causes of these conflicting results as well as the reasons for the discrepancy in HLA-G expression between cultured melanoma cell lines and surgically removed lesions have been discussed. Lastly, data about the potential clinical relevance of HLA-G expression in melanoma has been reviewed. The available data in the literature strongly suggest that progress in this exciting research area would greatly benefit from experiments to solve the current controversies in the field.