BACKGROUND: Ex vivo expansion of HPCs is an attractive approach to overcoming the current limitations of human cord blood transplantation. It is important not only to define the optimal culture conditions but also to know the number of progenitor cells that can be obtained. CD34+ cells have a great variability in their cloning capacity and in their ability to expand HPCs. This study was carried out to assess whether this variability could be due to intrinsic or extrinsic factors. STUDY DESIGN AND METHODS: CD34+ cells were analyzed for the expression of CD38, CD133, and CD117 and cultured in serum-free culture medium with four cytokine combinations: SCF plus thrombopoietin plus flt3 ligand (STF), STF plus IL-3, STF plus IL-6, and STF plus IL-6 plus IL-3. After a 1-week culture, the numbers of CD34+ cells and CFUs were determined. RESULTS: The variability observed both in the cloning ability of CD34+ isolated cells and in their expansion capacity was inversely related to the frequency of the more immature CD34+CD38- cells. When more mature CD34+CD38+ cells were present within CD34+-isolated cells, a higher cloning ability, measured as CFUs, and a higher expansion capacity were observed. CONCLUSION: Enumeration of CD34+CD38- cells is correlated with the number of committed progenitors and the capacity of generating CD34+ cells, an important parameter if expansion protocols must be used in clinical transplantation.
BACKGROUND: Ex vivo expansion of HPCs is an attractive approach to overcoming the current limitations of human cord blood transplantation. It is important not only to define the optimal culture conditions but also to know the number of progenitor cells that can be obtained. CD34+ cells have a great variability in their cloning capacity and in their ability to expand HPCs. This study was carried out to assess whether this variability could be due to intrinsic or extrinsic factors. STUDY DESIGN AND METHODS: CD34+ cells were analyzed for the expression of CD38, CD133, and CD117 and cultured in serum-free culture medium with four cytokine combinations: SCF plus thrombopoietin plus flt3 ligand (STF), STF plus IL-3, STF plus IL-6, and STF plus IL-6 plus IL-3. After a 1-week culture, the numbers of CD34+ cells and CFUs were determined. RESULTS: The variability observed both in the cloning ability of CD34+ isolated cells and in their expansion capacity was inversely related to the frequency of the more immature CD34+CD38- cells. When more mature CD34+CD38+ cells were present within CD34+-isolated cells, a higher cloning ability, measured as CFUs, and a higher expansion capacity were observed. CONCLUSION: Enumeration of CD34+CD38- cells is correlated with the number of committed progenitors and the capacity of generating CD34+ cells, an important parameter if expansion protocols must be used in clinical transplantation.