Human placental cells transformed with temperature-sensitive simian virus 40 are immortalized and mimic the phenotype of invasive cytotrophoblasts at both permissive and nonpermissive temperatures.

Establishment of the human placenta is essential for subsequent development of the embryo. Previous studies from our laboratories have demonstrated that chorionic villus cytotrophoblast stem cells undergo a stepwise differentiation process in vivo that results in their ability to invade the uterine wall. This process can be mimicked by isolated primary first-trimester cytotrophoblasts in vitro. Efforts to study the regulation of this differentiation pathway have been hampered by the inability of the isolated cytotrophoblast to replicate in culture. We therefore performed experiments to determine the suitability of the temperature-sensitive simian virus 40-transformed cell line SPA 255-26 (SPA-26), derived from early-gestation cytotrophoblasts, for studying the cytotrophoblast differentiation pathway that results in uterine invasion. Our results show that this cell line exhibits many properties of differentiated early-gestation cytotrophoblasts at both permissive and nonpermissive temperature. These cells were invasive in vitro and expressed the repertoire of hormones, adhesion molecules, and proteinases characteristic of an advanced stage of cytotrophoblast differentiation in vivo. Thus, these cells should be useful in studying the regulation of the adhesive and invasive behavior of human cytotrophoblasts.