The fetus as an optimal donor and recipient of hemopoietic stem cells.

In the present work we used allogeneic in utero transplantation of fetal stem cells in sheep and monkeys. Thus, both the donor and recipient cells had preimmune status. We showed engraftment of allogeneic stem cells in the tolerant environment of the host. The engrafted cells showed trilineage (lymphoid, erythroid and myeloid) expression of differentiation. Long term maintenance of these engrafted cells was observed. We also demonstrated that ex vivo incubation of donor cells with growth factor can enhance the engraftment. Moreover, we have shown that the engrafted cells respond to phlebotomy in the same manner as endogenous cells. We, therefore, conclude that (a) Preimmune fetuses are highly suitable for stem cell transplantation both as donors and recipients. (b) Engraftment can be modulated by brief maneuvers such as ex vivo manipulation. (c) Functionally, the engrafted cells can respond to hemopoietic stimuli in a similar manner as the endogenous cells. Implications of this transplantation system in clinical medicine is discussed. Everyone who is involved in organ transplantation must, sooner or later, come to grips with immunological barriers which establishes the individuality of each organism by recognizing "self" from "non-self". Transplanters must overcome this barrier, if allogeneic organ transplantation is to be successful. In the case of hemopoietic stem cells (HSC), where immunocompetent cells are transplanted, graft-vs-host disease (GVHD) may also be expected. Tolerance can be expected when the recipient is genetically immunodeficient, thus being unable to mount an immunological barrier.(ABSTRACT TRUNCATED AT 250 WORDS)