Protocol for In Utero Fetal-to-Fetal Kidney Transplantation in Rats.

Congenital renal disorders, such as the Potter sequence, result from renal dysgenesis. To explore a prenatal therapeutic approach for fetuses with kidney insufficiency, we established an in utero transplantation protocol using donor fetal kidneys. Although numerous rodent studies have reported cellular injections into fetal recipients, no protocol to date has described whole-organ transplantation during gestation. Here, we present a step-by-step method for grafting donor fetal kidneys (embryonic day 14.0-16.5) into allogeneic rat fetuses at embryonic day 18.0-18.5, resulting in term neonates that retain the grafts postnatally. A 15-16 G needle preloaded with the donor kidney is inserted transuterinely, depositing the organ into the subcutaneous space of the fetus. Four days later, the term pups are delivered naturally and evaluated for graft development. This protocol enables organ-level transplantation and longitudinal assessment of graft maturation within the unique fetal environment, which differs markedly from adult settings in terms of growth factor availability and immune reactivity. To our knowledge, this is the first protocol to successfully achieve whole-organ transplantation directly into fetuses in utero. Therefore, the model provides a valuable platform for studying developmental organogenesis, fetal immunology, and regenerative strategies that leverage embryonic cues. Key features • Subcutaneous transplantation of fetal kidneys into recipient fetuses minimizes surgical invasiveness and significantly improves fetal survival. • Natural delivery enables pups to nurse from the dam, allowing extended postnatal observation. • Use of green fluorescent protein (GFP)-expressing donor tissue permits real-time visualization of graft location and growth. • The protocol is readily adaptable for xenotransplantation and studies of immunological tolerance during fetal development.