HLA-G protein expression is not induced during malignant transformation

To evaluate the biological relevance of HLA-G expression during tumoral tra nsformation, we analyzed its expression in different malignant cells and im mune effector cells infiltrating solid tumors. Our analysis of 33 tumor cel l lines and 53 tumoral biopsies demonstrated that: i) six tumor cell lines display HLA-G transcription with differential alternative splicing patterns and only Jeg3 choriocarcinoma and MCF-7 breast adenocarcinoma cell lines e xpress HLA-G translated products, and ii) HLA-G antigens are not expressed in malignantly transformed cells derived from lung (n=18), liver (n=5), col on (n=5), breast (n=10), kidney (n=5), ovary (n=5),and larynx (n=5) tissues ex vivo. The healthy tissues surrounding these tumor tissues do not expres s HLA-G molecules either. On the other hand, surprisingly, HLA-G products w ere detected in activated macrophages and dendritic cells localized in tumo ral biopsies of 5 out of 18 different lung carcinomas. No HLA-G labelling m as observed in resident mononuclear phagocytes of surrounding healthy tissu es. Our observations clearly demonstrate that HLA-G is not a marker of mali gnant cells but appears as a gene expressed in tumor-associated macrophages and dendritic cells, preferentially in those recruited in lung carcinomas. Our findings suggest that specific environmental factors around lung tumor s could be involved in the induction of HLA-G protein expression.