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 contribute to the immunological privilege afforded the fetal allograft. Characterization of these immunoregulators in humans has been impeded by a lack of sufficient quantities of early gestational trophoblast for experimentation. METHOD: In this study, a cloned choriocarcinoma cell line (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 albumin, BSA-CM; 0.01% gelatin, Gel-CM) media. Immunosuppressive activity was determined through the use of interleukin-2-dependent (CTLL-2) and -independent (LBRM) cell lines. Human chorionic gonadotropin (hCG) levels were determined by an immunoradiometric assay, and cellular morphology was assessed by light microscopy. RESULTS: In the serum-supplemented cultures, a portion of cells underwent transformation from single nucleated cytotrophoblast to multinucleated syncytiotrophoblast during 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 proliferation 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 suppressed CTLL-2 proliferation with an EC(50) Of 132 mu g protein/mL, but failed to suppress LBRM proliferation below 50% of control. CONCLUSION: These results suggest that the BeWo cell line is a promising model for the study of trophoblast-derived suppressive factors and that these factors can be generated in serum-free medium.