CIRCULATING HEMATOPOIETIC STEM-CELL POPULATIONS IN HUMAN FETUSES - IMPLICATIONS FOR FETAL GENE-THERAPY AND ALTERATIONS WITH IN-UTERO RED-CELL TRANSFUSION

Circulating progenitor cell populations in normal human fetuses and fe tuses with various hematological problems were evaluated, Thirty blood samples from 21 human fetuses (17-36 weeks of gestation) were assayed for erythroid, myeloid, and mixed-cell progenitor cells. The mean num ber of progenitor cells/10(4) blood mononuclear cells in the normal fe tal population was 103 +/- 47, Granulomonocytic and mixed progenitor c ells (capable of giving rise to both erythroid and myeloid progeny) we re the predominant progenitor types in these samples, with pure erythr oid progenitors barely detectable, The frequency of progenitor cells i n the samples from fetuses with hematologial disorders was within the range of normal in all but 1 fetus infected with parvovirus in whom ve ry few progenitor cells were detected. The frequency of progenitor cel ls in the blood did not change after intravascular red cell transfusio n for alloimmunization despite the large volumes transfused, indicatin g that transfusion may have triggered a release of progenitor cells in to the circulation. Progenitor cells in human fetal blood are present in distributions similar to those commonly detected in cord blood. The ir total number in the circulating blood is in the same order used for pediatric and adult bone marrow transplantation. These results can be used Stem cells to calculate the number of colony-forming cells which could be obtained from a fetus by in utero apheresis and which could be made available for autologous fetal gene therapy.