DIFFERENTIATION OF HUMAN GERM CELL TUMOR CELLS IN VIVO AND IN VITRO

Three in vitro human germ cell tumor cell lines with different cell lineage and variable capability of differentiation were established from testicular germ cell tumors. NCR-G1 corresponding to yolk sac tumor were induced α-fetoprotein (AFP) production with retinoic acid (RA) treatment. NCR-G2 and -G3 were human embryonal carcinoma (EC) cell lines. They have cytological and immuno-phenotypic characteristics common to human EC cells as has been described in other EC cells. NCR-G2 grew as floating cell aggregates in the culture medium, whereas NCR-G3 grew as floating cell aggregate and flattered cells attached to the surface of culture dish. These flattened cells of NCR-G3 immunohistochemically expressed a variety of differentiation antigens including myogenic markers, extraembryonic trophoblastic cell marker (human chorionic gonadotropin (hCG)), and extracellular proteins. Differentiation capabilities of NCR-G3 cells became more evident when they were treated with RA. By flowcytometric analysis, human EC cell surface markers 2D7, 2H2 and 5D4 which were mouse monoclonal antibodies we obtained from immunization by NCR-G2 cells, disappeared from cell surface of RA-treated NCR-G3 cells. Consistent with these findings, the flattened cells of NCR-G3 that attached to the culture dish were negative for these antibodies. Moreover, longer exposure to RA enhanced hCG production in exposure time dependent fashion. These observations clearly indicate that NCR-G3 possess multipotent differentiation capabilities and they differentiated into the trophoblastic cell lineage other than somatic cells. In contrast to NCR-G3, NCR-G2 did not show any differentiation capabilities with RA treatment. All three germ cell tumor lines produced tumors in athymic mice with 100% efficiency. High AFP content was observed in the sera of NCR-G1 tumor-bearing mice. High hCG and AFP contents were detected in the sera of the NCR-G3 tumor-bearing mice. Thus, our newly established human germ cell tumor cell lines add new insights of molecular mechanism of human embryogenesis and differentiation of EC cells.