Mid-trimester fetal livers are a rich source of CD34(+/++) cells for transplantation

Human fetal livers (FL), between 16 and 24 weeks of gestation, were studied for their potential as a source of hematopoietic stem cells for prenatal a nd postnatal transplantation. In this report we give a quantitative evaluat ion of human FL as a source of candidate stem cells, and develop a protocol for the isolation of these cells free of microbial contaminants and almost free of mature T cells. Human FLs contained a median 1.9 x 10(9) viable ce lls and a mean of 1.3 x 10(8) CD34(+/++) cells (range 1.1 x 10(7) to 4.7 x 10(8)). Regardless of gestational age, no significant differences mere appa rent in the numbers of total progenitors or in the numbers of candidate ste m cells (CD34(++) CD38(-) and CD34(++)CD(4+)), suggesting that the expansio n in the liver of the early compartments of hematopoietic progenitors reach es a plateau after the sixteenth week of gestation. Colony-forming units cu lture (CFU-C) were found to range from 4.1 x 10(6) to 2.5 x 10(7) per FL. P ositive selection of FL CD34(++) cells was achieved using the Baxter Isolex 50 device. An average purity of 74% and yield of 29% of CD34(+/++) cells w as achieved. T cells were depleted by 99.95%, resulting in a mean of 6.5 x 10(3) T cells per processed liver. Analysis of candidate stem cell populati ons and primitive colony-forming cells (CFC) suggested a preferential enric hment of these cells over the total population of CD34(+/++) cells. Process ed CD34(+/++) cells were found to be sterile. In conclusion, purification o f FL progenitors between 16 and 24 weeks of gestation results in a large nu mber of early progenitors suitable for irt utero and possibly postnatal tra nsplantation.