Abstract
Pregnancy is a critical point of vulnerability to infection and other insults that could compromise proper fetal development. The placenta acts as a protective and nutrient-permeable barrier to most infectious agents, but a few are capable of bypassing its defenses. Remarkably little is known about how exposure to these select pathogens might impact ongoing placental development. Here we demonstrate that Toxoplasma gondii entirely misdirects the developmental program of trophoblast stem cells. Infection of progenitor cytotrophoblasts prevents fusion and differentiation to infection-resistant syncytiotrophoblast. Rather, T. gondii elicits a unique transcriptional identity that polarizes cytotrophoblasts to the infection-permissive extravillous trophoblast fate. Strong evidence of developmental disruption is found in multiple orthogonal models, including trophoblast stem cells, trophoblast organoids, and chorionic villi. Manipulation of cell fate by the parasite is most dramatic in trophoblast organoids, where we see robust outgrowth of HLA-G(+) extravillous trophoblasts. Collectively, these data show that Toxoplasma antagonizes differentiation of an infection-resistant cell type by inducing formation of an infection-permissive cell type, therefore potentiating its own transmission to the fetus.