HLA-G promotes immune tolerance.

HLA-G is a non-classical major histocompatibility complex class I molecule that differs from the classical HLA-A, -B and -C molecules by (i) alternative splicing of mRNAs encoding for at least four membrane-bound and two soluble HLA-G isoforms, (ii) a limited polymorphism, and (iii) a tissue-restricted distribution. Studies over the past few years have elucidated the function of HLA-G demonstrating inhibition of both NK cell- and T cell-mediated cytolysis. Furthermore, aside from its expression during pregnancy, we have shown that HLA-G is also expressed in solid tumor cells (i.e. human melanoma cell lines and ex vivo melanoma biopsies). Here we present a review of the current state of knowledge of the immunotolerant functions of HLA-G and their implications in materno-fetal tolerance and tumor immunosurveillance.