IFNG and melanoma: However, the analysis of the HLA class I antigen alterations in melanoma cell lines from ESTDAB showed that the most frequently observed phenotype is the down-regulation of HLA-B locus that is reversible after treatment with IFN-γ whereas the total lack of expression as a consequence of gene mutations or deletions leading to HLA heavy chain or β2m deficiency is only found in a minor group of samples (33).