Trophoblast organoids as a model for maternal-fetal interactions during human placentation

The placenta is the extraembryonic organ that supports the fetus during intrauterine life. Although placental dysfunction results in major disorders of pregnancy with immediate and lifelong consequences for both mother and child, our knowledge of the human placenta is limited due to lack of functional experimental models1. Upon implantation, the trophectoderm of the blastocyst rapidly proliferates and generates the trophoblast, the unique cell type of the placenta. In vivo, the proliferative villous cytotrophoblast cells (VCT) differentiate into two main sub-populations: syncytiotrophoblast (SCT), the multinucleated epithelium of the villi responsible for nutrient exchange and hormone production, and extravillous trophoblast (EVT) that anchor the placenta to the maternal decidua and transform the maternal spiral arteries2. Here, we describe the generation of long-term, genetically-stable organoid cultures of trophoblast cells that can differentiate to SCT and EVT. We used HLA-typing to confirm the organoids are fetally-derived, and verified their identity against four trophoblast-specific criteria3. The cultures organise into villous-like structures, and we detected secretion of placental-specific peptides and hormones, including hCG, GDF15, PSGs and PAPPA, by mass spectrometry. The organoids also differentiate to HLA-G+ EVT that vigorously invade in 3D. Analysis of the methylome reveals the organoids closely resemble normal first-trimester placentas. This organoid model will be transformative for studying human placental development and for investigating trophoblast interactions with the local and systemic maternal environment.