en Original Research: Basic Science in Medicine Original Research: Basic Science in Medicine 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. Ex vivo expansion; Stem cells; Umbilical cord blood; Mesenchymal stem cells. 257 263 http://mjiri.iums.ac.ir/browse.php?a_code=A-10-298-60&slc_lang=en&sid=1 M SOLElMANI 20031947532846003448 20031947532846003448 No From the Hematology Dept .. School of'Medical Sciences. Tarbiat Modares University, Tehran H MOZDARANI mozdaranh@modares.ac.ir 20031947532846003449 20031947532846003449 Yes Medical Genetics Dept. School of Medical Sciences, Tarbiat Modares University, Tehran AA POURFATHOLLAH 20031947532846003450 20031947532846003450 No From the Hematology Dept .. School of'Medical Sciences. Tarbiat Modares University, Tehran Y MORTAZAVI 20031947532846003451 20031947532846003451 No From the Hematology Dept .. School of'Medical Sciences. Tarbiat Modares University, Tehran K ALIMOGHADDAM 20031947532846003452 20031947532846003452 No Bone Marrow Transplantation Center. Shariati Hospital, Tehran, A HAJIFATHALI 20031947532846003453 20031947532846003453 No the Iranian Blood Trans(ilsion Organization,Tehran Z ZONOBI 20031947532846003454 20031947532846003454 No Shahid Beheshti Medical Sciences University. Tehran. Iran