THE HIGHEST CONCENTRATION OF PRIMITIVE HEMATOPOIETIC PROGENITOR CELLSIN CORD-BLOOD IS FOUND IN EXTREMELY PREMATURE-INFANTS

We used two independent in vitro assays to measure the frequency and p roliferative potential of primitive hematopoietic progenitors from the cord blood of 23-41 wk of gestation newborns and adult bone marrow. T he frequency of primitive progenitors in the circulating blood cells o f infants at 23-31 wk of gestation was significantly greater than the frequency in adult bone marrow or cord blood of more mature newborns. In addition, on a cell to cell basis, the proliferative potential of t he primitive progenitors from immature infants (23-31 wk) was greater than in adult bone marrow or cord blood of term newborns. Circulating cord blood cells from immature infants were used as targets for transd uction with recombinant retrovirus vectors, and a high efficiency of g ene transfer was observed in both primitive and committed progenitors. These data demonstrate that there are major ontogenic shifts in primi tive progenitor/stem cell populations in the circulation throughout de velopment as well as programmatic changes in hematopoietic progenitor cell proliferation. In addition, fetal cord blood cells may prove usef ul targets for genetic manipulation and autologous transplantation.