Comparison of different methods for separation and ex vivo expansion of cord blood progenitor cells.

Umbilical cord blood is capable of hematopoietic stem cell reconstitution in children. However, the major limitation of cord blood is a relatively low content of pluripotent progenitor cells. Thus, safe engraftment for adolescents and for adults is still not predictable and a technology for ex vivo expansion of umbilical cord blood cells is desirable. In a first step, four different methods of red cell depletion followed by magnetic cell sorting of CD34+ cells were evaluated in this study in order to assess the efficacy and safety of optimal stem cell recovery. A modified two-step Ficoll gradient separation and a hydroxyethyl starch separation tended to produce a better WBC/MNC recovery (median 94.2+/-2.44% vs. 90.2+/-5. 8%) as compared with standard Ficoll gradient separation and a gelatin-based procedure (median 78.35+/-7.1% vs. 67.2+/-5.5%). However, the recovery of CD34+ cells after magnetic cell sorting did not reach a statistically significant difference after the four different methods of red cell depletion, indicating that the recovery of WBC/MNC is not predictably correlated with the recovery of stem cells within these fractions. In a second step, we established three different cytokine combinations by adding the megakaryocyte growth and development factor +/- erythropoietin and granulocyte colony-stimulating factor to a fetal calf serum containing medium with Flt 3, stem cell factor, and interleukin-3. Net expansion of total colony-forming cells 20- to 50-fold and expansion of colony-forming cells after 5 weeks of culture 1.5- to 3-fold were obtained over a period of 7-14 days. These results demonstrate that cord blood stem cells can be expanded substantially in this short-term culture system.