Abstract
HLA‐G displays immunotolerogenic properties towards the main effector cells involved in graft rejection through inhibition of NK‐ and CTL‐mediated cytolysis and CD4^+^ T cell alloproliferation. HLA‐G expression is restricted in healthy tissues to trophoblast and thymus but is extended to various tissues under pathological conditions. HLA‐G was detected in allograft biopsies and sera from transplanted patients who displayed a better graft acceptance. However, the cells involved in such de novo expression of HLA‐G remain to be characterized. By flow cytometry and confocal microscopy, we demonstrated that, following allogeneic stimulation in vitro, both CD4^+^ and CD8^+^ T cell subsets can express membrane‐bound HLA‐G1 and/or soluble HLA‐G5molecules. Such HLA‐G1/‐G5 expression is regulated at the transcriptional level. Soluble HLA‐G5 could be detected by using a novel monoclonal antibody, 5A6G7, specific for the intron 4‐retaining sequence of HLA‐G5. Finally, the biological relevance of these data was provided by analysis of transplanted patients in whom we identified both CD4^+^ and CD8^+^ T cells expressing HLA‐G. The HLA‐G‐positive T cells we describe here may constitute a cellular source of HLA‐G after allotransplantation and may be involved in the improved graft acceptance which is observed in HLA‐G‐positive transplanted patients.