IMMUNOSUPPRESSION BY CONDITIONED MEDIA DERIVED FROM A CLONED CHORIOCARCINOMA CELL-LINE IN SERUM-SUPPLEMENTED AND DEFINED MEDIA

PROBLEM: Immunosuppressive factor(s) of trophoblast origin may contrib ute to the immunological privilege afforded the fetal allograft. Chara cterization of these immunoregulators in humans has been impeded by a lack of sufficient quantities of early gestational trophoblast for exp erimentation. METHOD: In this study, a cloned choriocarcinoma cell lin e (BeWo) was evaluated as an experimental model of trophoblast-derived immunoregulation. BeWo cells were cultured in both serum-supplemented (15% fetal bovine serum; FCS-CM) and serum-free (10% bovine serum alb umin, BSA-CM; 0.01% gelatin, Gel-CM) media. Immunosuppressive activity was determined through the use of interleukin-2-dependent (CTLL-2) an d -independent (LBRM) cell lines. Human chorionic gonadotropin (hCG) l evels were determined by an immunoradiometric assay, and cellular morp hology was assessed by light microscopy. RESULTS: In the serum-supplem ented cultures, a portion of cells underwent transformation from singl e nucleated cytotrophoblast to multinucleated syncytiotrophoblast duri ng days 1 to 5 of culture and was accompanied by a rise in hCG. Serum- free cultures were characterized as islands of cytotrophoblast and did not exhibit differentiation. FCS-CM suppressed CTLL-2 and LBRM prolif eration with estimated EC(50) values of 415 and 280 mu g protein/ mL, respectively. Gel-CM suppressed CTLL-2 and LBRM proliferation with EC( 50) values of 12 and 7 mu g protein/mL, respectively. BSA-CM suppresse d CTLL-2 proliferation with an EC(50) Of 132 mu g protein/mL, but fail ed to suppress LBRM proliferation below 50% of control. CONCLUSION: Th ese results suggest that the BeWo cell line is a promising model for t he study of trophoblast-derived suppressive factors and that these fac tors can be generated in serum-free medium.