Background: It is widely accepted that most if not all villous cytotrophoblasts from term placentae are committed to differentiate into syncytiotrophoblast, but that early in gestation villous cytotrophoblasts are bipotential and capable of differentiating into either extravillous trophoblasts (EVTs) or syncytiotrophoblast. In contrast, our previous work has suggested that two separate populations of cytotrophoblast exist in the first trimester, one committed to EVT differentiation and the other to syncytiotrophoblast differentiation. In this work, we have isolated and characterized the population of 'EVT progenitors'.
Methods: First trimester villous explants were cultured for 10 days then subjected to sequential trypsinization. Viable cells that adhered to Matrigel following trypsinization were cultured for up to 5 days and characterized by immunohistochemistry.
Results: The isolation protocol yielded >90% cytokeratin positive trophoblasts, which expressed markers characteristic of EVT progenitors. Over 5 days of culture, these isolated putative EVT progenitors did not syncytialize, but approximately 20% differentiated into HLA-G positive EVTs.
Conclusions: It is likely that the isolated putative EVT progenitors are the population of EVT progenitors previously identified in vivo. The characteristics of these isolated putative EVT progenitors provides further evidence for separate progenitors of EVT and syncytiotrophoblast in the first trimester.