The highest concentration of primitive hematopoietic progenitor cells in cord blood is found in extremely premature infants.

We used two independent in vitro assays to measure the frequency and proliferative potential of primitive hematopoietic progenitors from the cord blood of 23-41 wk of gestation newborns and adult bone marrow. The frequency of primitive progenitors in the circulating blood cells of 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 the primitive progenitors form 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 transduction with recombinant retrovirus vectors, and a high efficiency of gene transfer was observed in both primitive and committed progenitors. These data demonstrate that there are major ontogenic shifts in primitive progenitor/stem cell populations in the circulation throughout development as well as programmatic changes in hematopoietic progenitor cell proliferation. In addition, fetal cord blood cells may prove useful targets for genetic manipulation and autologous transplantation.