Immunophenotypic changes of fetal cord blood hematopoietic progenitor cells during gestation

We measured cell surface expression of CD34, HLA-DR, CD38, CD19, CD33, CD71 , and CD45 antigens in the hematopoietic progenitor cells of fetal cord blo od to investigate immunophenotypic changes at different gestational ages. T hese antigens were identified by flow cytometry in 11 fetuses (gestational age 19-24 wk, in 12 preterm (25-28 wk) and in ten newborn infants born at t erm. The frequency and number of CD34(+) cells were higher in the blood of the 11 fetuses; in addition, a statistically significant inverse correlatio n between number of CD34(+) cells and advancing gestational age was noted. The numbers of CD34(+)CD19(+), CD34(+)CD33(+), and CD34(+)CD45(+) coexpress ing cells were significantly higher in the fetuses, whereas CD34(+)CD38(+) cells were more represented in the neonates at term. Gestational age was in versely correlated with the number of CD34(+)CD19(+) and CD34(+)CD33(+) coe xpressing cells. A positive correlation between gestational age and CD34(+) D38(+) cells was noted. The number of CD34(-)CD19(+), CD34(-)CD38(+), and C D34(-)CD45(+) cells was higher in term infants; furthermore, a significant correlation between advancing gestational age and CD34(-)CD38(+) or CD34(-) CD45(+) cells was demonstrated. The proliferative capacity was also higher at lower gestational ages. These data suggest that the development and line age commitment of fetal cord blood hematopoietic progenitor cells are very active during the last two trimesters of pregnancy. The most significant ch anges of hematopoietic cells maturation seem to occur within 25 wk of gesta tion.