Trophoblast organoids with physiological polarity model placental structure and function

Human trophoblast organoids (TOs) are a three-dimensional ex vivo culture model that can be used to study various aspects of placental development, physiology, and pathology. Previously, we showed that TOs derived from full-term human placental tissue could be used as models of trophoblast innate immune signaling and teratogenic virus infections. Here, we developed a method to culture TOs under conditions that recapitulate the cellular orientation of chorionic villi in vivo, with the multi-nucleated syncytiotrophoblast (STB) localized to the outer surface of organoids and the proliferative cytotrophoblasts (CTBs) located on the inner surface. We show that standard TOs containing the STB layer inside the organoid (STB(in)) develop into organoids containing the STB on the outer surface (STB(out)) when cultured in suspension with gentle agitation. STB(out) organoids secrete higher levels of select STB-associated hormones and cytokines, including human chorionic gonadotropin (hCG) and interferon (IFN)-λ2. Using membrane capacitance measurements, we also show that the outermost surface of STB(out) organoids contain large syncytia comprised of >50 nuclei compared to STB(in) organoids that contain small syncytia (<10 nuclei) and mononuclear cells. The growth of TOs under conditions that mimic the cellular orientation of chorionic villi in vivo thus allows for the study of a variety of aspects of placental biology under physiological conditions.