HLA-G expression: immune privilege for tumour cells?

The non-classical class I antigen HLA-G has been shown to play a role in foeto-maternal tolerance. It interacts with inhibitory receptors to down-regulate natural killer and T cell cytotoxic functions. We here report our investigations on HLA-G expression in melanoma cells and its implication in the induction of immune tolerance to tumours. We provide the first evidence that both malignant human melanoma cell lines and ex vivo biopsies can exhibit high levels of HLA-G transcription with differential HLA-G isoform transcription and protein expression patterns. We further demonstrated that melanoma cells that express HLA-G inhibit NK cytolysis. We thus propose that HLA-G expression may impede the elimination of malignant cells by anti-tumour immune effector cells, constituting a newly described mechanism by which tumour cells may evade immunosurveillance.