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Fetal bone marrow as a source of stem cells for in utero or postnatal transplantation

We examined the potential of human fetal bone marrow (FBM) as a source of haematopoietic stem cells for transplantation. The median number of cells obtained between 20 and 24 weeks' gestation was 1·9 × 109 and a median 1·17 × 108 of these cells expressed CD34. Flow cytometry was also used to estimate the content of three different candidate stem cell populations in the tissues older than 20 weeks' gestation. A median 8·8 × 105 CD34++CD38− cells, 1·37 × 106 CD34++CD4+ cells and 2·20 × 106 CD34++CD90+ cells were detected. The content of colony‐forming units culture (CFU‐C) in the FBM ranged from 2·8 × 104 to 6·0 × 106 per fetus. The CFU‐C content could be expanded 50‐fold by culture for 1 week in serum‐deprived medium and the growth factors kit ligand and granulocyte–macrophage colony‐stimulating factor. Positive selection of FBM CD34+/++ cells was achieved using the Baxter Isolex 50 device. An average purity of 82% and yield of up to 19% of CD34+/++ cells was achieved. T cells were depleted by 99·84%. Analysis of candidate stem cell populations and primitive CFU‐C suggested a preferential enrichment of these cells over the total population of CD34+/++ cells. All FBM samples were found to be free of microbial contamination at the time of harvest and after selection of CD34+/++ cells. Thus, FBM is a safe source of stem cells. The large number of progenitors and candidate stem cells that can be obtained from FBM makes it suitable for in utero and possibly postnatal transplantation.