Immune ontogeny and engraftment receptivity in the sheep fetus.

Objective: The biologic explanation for fetal receptivity to donor engraftment and subsequent long-term tolerance following transplantation early in gestation is not known. We investigated the role fetal immune ontogeny might play in fetal transplantation tolerance in sheep.

Methods: Engraftment of allogeneic and xenogeneic HSC was determined 60 days following transplantation at different time points in sheep fetal gestation.