CHARACTERISTICS OF TROPHOBLAST CELLS MIGRATING FROM FIRST TRIMESTER CHORIONIC VILLUS EXPLANTS AND PROPAGATED IN CULTURE

We developed a method of propagating pure first trimester human tropho blast cells growing out of primary explants of mechanically derived ch orionic villus fragments (Yagel et al, 1989; Graham et al, 1992). We h ave now extensively characterized these cells during their initial out growth and in long-term culture, employing a variety of markers and te chniques as outlined below. By double label immunofluorescence using e pithelial (cytokeratin) and mesenchymal (vimentin) cell markers, we id entified the chorionic villus migrant cell populations as pure trophob last (39 per cent of outgrowths) or a mixture of trophoblast and fibro blast (61 per cent). Further phenotyping of the pure trophoblast outgr owths by double label immunostaining using anti-cytokeratin antibody a nd a panel of other primary antisera revealed that these cells exhibit a variety of markers characteristic of extravillous invasive trophobl ast cells in situ: insulin-like growth factor (IGF)-II, NDOG-5, prolif erating cell nuclear antigen (PCNA), human leucocyte antigen framework antigen (W6/32) and a distinct set of integrins including alpha 1, al pha 3, alpha 5, alpha v and beta(1) subunits and alpha(v) beta(3)/beta (5) vitonectin receptor. They were negative for alpha(6) and beta(4) i ntegrin subunits. Immunogold electron microscopy of explants grown on type IV collagen gel revealed the production of conventional and oncof etal types of fibronectin by mononucleate tropholast cells and human p lacental lactogen by multinucleate cells. immunolabelling, flow cytome try and immunoprecipitation revealed that this phenotypic profile was retained with complete fidelity in the long-term culture; thus, tropho blasts migrating out of first trimester chorionic villus explants and their propagated progeny belong to the invasive extravillous trophobla st of the placenta.