EXPANSION OF HUMAN CORD BLOOD PRIMITIVE PROGENITORS IN SERUM-FREE MEDIA USING HUMAN BONE MARROW MESENCHYMAL STEM CELLS

Ex vivo expansion of human umbilical cord blood cells (HUCBC) is explored by several investigators to enhance the repopulating potential of HUCBC. The proliferation and expansion of human hematopoietic stem cells (HSC) in ex vivo culture was examined with the goal of generating a suitable clinical protocol for expanding HSC for patient transplantation. Using primary human mesenchymal stem cells, we established a serum-free culture system to expand human primitive progenitors and transplantable stem cells. Non-enriched cord blood CD34+ cells were cultured on a monolayer of human mesenchymal stem cells in the presence of tlu-ombopoietin (TPO), flt31flk2 ligand (FL), and/or stem cell factor (SCF), interleukin 6 (IL-6), interleukin 3 (IL-3) under serum-free conditions. After I or 2 weeks of culture, cells were examined for clonogenic progenitors and percentage of CD34+ CD38- cells. In the presence of TPO, FL, and SCF, fetal MSC cells supported more than a 35- and 20-fold expansion of CD34+ cells and colonyforming units in culture after 1 and 2 weeks of incubation, respectively. In addition, LTC-IC assay were expanded more than 7- and 16-fold after 1 and 2 weeks of culture, respectively. UCB-HSC can be expanded in culture to numbers theoretically adequate for safe, rapid engraftment of adult patients. Additional studies are needed to establish the functional activity of expanded UCB-HSC. This ex vivo expansion system should prove valuable in clinical settings in which stromal cells are available from recipients or stem cell donors.