Tissue specific stem cells are responsible for proper and balanced development of each organ. In placenta, cytotrophoblast stem cells are proliferative cells which can differentiate into both extravillous trophoblasts and syncytiotrophoblasts. Due to considerable ethical and practical issues in studying these phenomena in human, we aimed to produce cytotrophoblast stem cell lines. To do so, human embryonic stem cells were grown as embryoid bodies and selected based on their HCG production. The cell lines were then characterized and their interaction with endometrial stroma was also analyzed. Cytotrophoblast stem cell lines were positive for both CK7 and HCG and also expressed HPL and SSEA1. While most cells were mononucleated, cell fusion and formation of syncytium was also observed by time. These cells did not express human embryonic stem cell markers including TRA-1-60, SSEA3, SSEA4, OCT4, SOX2, FGF4 and NANOG but were positive for trophoblast-related mRNAs ie CDX2, HLA-G and CD9. Furthermore, trophoblast bodies closely mimicked early invasive stages of implantation when incubated with human endometrial stroma in vitro. In conclusion, these cytotrophoblast stem cell lines represent a good model for studies related to early trophoblast invasion in human.

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