Establishment and characterization of first trimester human trophoblast cells with extended lifespan

We established trophoblast cell cultures with extended lifespans by introducing into first trimester human trophoblasts the gene encoding simian virus 40 large T antigen. The transfected trophoblasts were characterized according to their expression of various morphological and functional markers. Both parental (HTR-8) and transfected (HTR-8/SVneo) lines were morphologically similar and positive for cytokeratin, confirming their epithelial (trophoblastic) identity. Whereas the parental cells senesced after 12-14 passages, the transfectants have been in culture for over 32 passages. Human chorionic gonadotrophin was detected only in the HTR-8/SVneo cells and not in the parental cells. Both lines required at least 5% serum in order to sustain growth in vitro and responded to transforming growth factor-beta (TGF-beta) with reduced [3H]-thymidine incorporation in a dose-dependent manner. Treatment with TGF-beta also resulted in decreased secretion of plasminogen activators (PAs) and reduced PA activity by both lines. Both cell lines secreted mostly 72-kDa type IV collagenase as determined by substrate gel zymography, but the level of secretion of this enzyme was not significantly affected by TGF-beta in either line. Even though both lines exhibited similar in vitro invasive abilities, only the invasiveness of the parental cells was reduced by TGF-beta. Neither parental or transfected cells were capable of growth in soft agar and no sign of tumor formation was evident more than 5 months after subcutaneous inoculation of the transfected cells into nude mice. These results indicate that apart from their ability to sustain prolonged growth in culture, the transfected HTR-8/SVneo cells share a number of phenotypic properties with the parental trophoblast cells. For this reason, these transfected trophoblasts may prove to be an important tool for the study of placental function and/or tumor progression.