The influence of intravenously introduced allogeneic lymphocytes on fetal rats

Semi-allogeneic or allogeneic bone marrow cells, or allogeneic spleen cells, were injected in utero into PVG, DA and Fischer rat fetuses at 15-18 days of gestation via the vitelline vein. Prenatal (PVG x DA) F1 bone marrow cell inoculation produced allograft tolerance far more frequently in DA recipients than in PVG recipients. Inoculation of allogeneic or semi-allogeneic spleen cells into rat fetuses failed to induce allograft tolerance but sensitized the recipients. The observation that Fischer recipients could be rendered tolerant to skin allografts by prenatal inoculation of PVG, but not DA, bone marrow cells indicated that variation in susceptibility to tolerance induction among different donor-recipient strain combinations is unlikely to be explicable on the basis of strain differences in developmental maturity of the host immune system.