Objective: We have previously reported immunity to donor antigens following in utero transplantation (IUT) of cytokine-stimulated allogeneic hematopoietic stem cells (sca(+)/lin(-)) (day 9 of gestation). Transplanted mice showed accelerated rejection of donor skin grafts and high anti-donor cytotoxic response, a finding not seen in the control mice. This was accompanied by an enhancement of Th1 over Th2 cytokine production and persistent donor microchimerism. In order to assess the role of the thymus in allograft rejection, prenatal transplants were performed under similar experimental conditions at a later gestational age, when the thymus is more developed (day 13).

Materials and methods: Cytokine-stimulated stem cell factor (SCF) and granulocyte colony-stimulating factor (G-CSF)-purified sca(+)/lin(-) cells of C57BL/6 (H-2b, 1E(+)) background were injected into MHC-mismatched BALB/c (H-2d, 1E(-)) fetal mouse recipients at day 13 of gestation.