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 h aematopoietic stem cells for transplantation. The median number of cells ob tained between 20 and 24 weeks' gestation was 1.9 x 10(9) and a median 1.17 x 10(8) of these cells expressed CD34. Flow cytometry was also used to est imate the content of three different candidate stem cell populations in the tissues older than 20 weeks' gestation. A median 8.8 x 10(5) CD34(++)CD38( -) cells, 1.37 x 10(6) CD34(++)CD4(+) cells and 2.20 x 10(6) CD34(++)CD90() cells were detected. The content of colony-forming units culture (CFU-C) in the FBM ranged from 2.8 x 10(4) to 6.0 x 10(6) per fetus. The CFU-C cont ent could be expanded 50-fold by culture for 1 week in serum-deprived mediu m and the growth factors kit ligand and granulocyte-macrophage colony-stimu lating factor. Positive selection of FBM CD34(+/++) cells was achieved usin g 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%. Anal ysis of candidate stem cell populations and primitive CFU-C suggested a pre ferential 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.