Monoclonal antibody defining a human syncytiotrophoblastic polypeptide immunologically related to mammalian...

Antigenic material previously detected in human placental trophoblastic cells by immunoperoxidase staining using a goat antiserum against the feline RD114 retrovirus structural protein p30 was isolated by immunochromatography from normal syncytiotrophoblast. The antigen was used to immunize mice, and of the monoclonal antibodies produced by murine hybridomas an IgG1 was selected which reacted in enzyme immunoassay with the syncytiotrophoblast antigen and with purified RD114. This antibody, designated HPS-1, stained normal and neoplastic syncytiotrophoblasts in a manner similar to that of the goat antibodies, detected in immunoblotting a Mr = 130 000 polypeptide in cultured human choriocarcinoma cells and reacted in spot immunoblotting tests with purified preparations of mammalian retroviruses but not with an avian retrovirus. The polypeptide antigen may represent activation of human endogenous retroviral genes in syncytiotrophoblast.