Intravenous transplantation of human fetal tissue, notably of the live
r and thymus, is used in emergency hematological states: aplastic anem
ia and acute leukemia. The strong manifestation of ''graft-versus-host
'' disease proved unexpected. Fetal donor hepatic cells stimulate hemo
poiesis in the recipient. In some cases true cellular chimerism has be
en observed, specifically when a transplant of human fetal tissue (THF
T) to a fetus with prenatal pathology was performed in utero. In gene
therapy attempts have been made in infuse hemopoietic stem cells intra
venously or to introduce the adenosine aminase gene int leukocytes of
patients with a deficiency of this enzyme. Treatment using transplanta
tion of human fetal tissue will help solve the problem of HLA-histocom
patibility and will make gene therapy more widely applicable.