Although trophoblast stem cells can be obtained directly from blastocyst outgrowths in the mouse, this has never been described in primates. In human and non-human primates, trophoblast cells have been obtained from embryonic stem (ES) cells or embryoid bodies (EBs). The results reported here show for the first time that cells with the characteristics of trophoblast stem cells can be derived directly from rhesus monkey blastocyst outgrowths. The cells expressed trophoblast markers and were maintained for multiple passages in the absence of feeder layers or growth factors. The cells could be maintained as adherent, mononuclear cells by regular passaging, but they formed syncytial-like structures if maintained in culture for prolonged periods or if incubated in the presence of 17β-estradiol. The cells also demonstrated invasive behavior similar to extravillous trophoblasts. The availability of these lines provides a useful experimental system for studying trophoblast differentiation and for developing novel intervention strategies to treat placental dysfunction.
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