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

Abstract

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 and postnatal transplantation. In this report we give a quantitative evaluation 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 × 10⁹ viable cells and a mean of 1.3 × 10⁸ CD34^+/++ cells (range 1.1 × 10⁷ to 4.7 × 10⁸). Regardless of gestational age, no significant differences were apparent in the numbers of total progenitors or in the numbers of candidate stem cells (CD34⁺⁺ CD38⁻ and CD34⁺⁺CD4⁺), suggesting that the expansion in the liver of the early compartments of hematopoietic progenitors reaches a plateau after the sixteenth week of gestation. Colony-forming units culture (CFU-C) were found to range from 4.1 × 10⁶ to 2.5 × 10⁷ per FL. Positive 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 was achieved. T cells were depleted by 99.95%, resulting in a mean of 6.5 × 10³ T cells per processed liver. Analysis of candidate stem cell populations and primitive colony-forming cells (CFC) suggested a preferential enrichment of these cells over the total population of CD34^+/++ cells. Processed CD34^+/++cells were found to be sterile. In conclusion, purification of FL progenitors between 16 and 24 weeks of gestation results in a large number of early progenitors suitable for in utero and possibly post-natal transplantation.