HLA-G and neoplasm: In vitro studies have proved that HLA-G presented by target cells (cytotrophoblast cells, tumor cells, transfected cell lines) or soluble HLA-G5 present in microenvironment can inhibit the occurrence of cellular immune synapses of NK cells by binding to ILT2 on the surface of them, thus inhibiting the cytolysis of NK cells to target cells [22, 30].