Subpopulations of CD34‐positive haemopoietic progenitors in fetal blood

Flow cytometry was used to determine the percentage and number of circulating CD34+ cells in fetal blood from 100 pregnancies at 13-38 weeks gestation. When expressed as a percentage of the total number of lymphocytes, the proportion of CD34+ cells decreased exponentially from a mean of 11.1% (9.2 x 10(7)/l) at 13 weeks to 1.0% (3.0 x 10(7)/l) at 38 weeks (r = 0.751, P < 0.0001). The use of primitive fetal blood CD34+ progenitor cells for prenatal somatic gene therapy may have distinct advantages over postnatal somatic gene therapy.