Human blastoids model blastocyst development and implantation

Abstract A model of human bastocyst formed from stem cells (blastoid) would support scientific and medical advances. However, its predictive power will depend on the ability to faithfully, efficiently, and timely recapitulate the sequences of blastocyst specification, morphogenesis, and patterning, and form cells reflecting the blastocyst stage. Here we show that naïve human pluripotent stem cells cultured in PXGL conditions and then triply inhibited for the Hippo, transforming growth factor- β (TGF-β), and extracellular signal-regulated kinase (ERK) pathways efficiently form blastoids (>70%). Within 4 days, blastoids sequentially produce analogs of the blastocyst-stage trophoblast and epiblast, followed by the formation of analogs of the primitive endoderm and the polar trophoblasts. This results in the formation of transcriptional analogs of the blastocyst (>96%) and a minority of postimplantation analogs (e.g., amnion, mesoderm). Blastoids efficiently form the embryonic-abembryonic axis marked by the maturation of the polar region (NR2F2+), which acquires the specific potential to directionally attach to hormonally stimulated endometrial cells, as in utero. Such a human blastoid is a scalable, versatile, and ethical model to study human development and implantation in vitro.