Ex vivo Expansion of Umbilical Cord Blood Stem Cells Using Different Combinations of Cytokines and Stromal Cells

Abstract

Umbilical cord blood is a promising source of hematopoietic stem cells (HSC) for allogeneic transplantation. However, graft rejection and delayed engraftment remain major limitations, both of which are related to a limited number of stem cells in the cord blood graft. Ex vivo expansion of HSC has been suggested as one of the ways of overcoming the challenges caused by a limited hematopoietic cell number from cord blood stem cell transplantation. In this study, we quantified and characterized an ex vivo expansion capacity of cord blood-derived HSC in a liquid culture system under different conditions. These conditions included: the combinations and concentrations of hematopoietic growth factors [stem cell factor (SCF), granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin (IL)-3, IL-6 and erythropoietin (EPO)], placental conditioning medium (PCM), and stromal cell support. During culture, the mean nucleated cell count, the mean CD34+ cell count, fold expansion, viability, clonogenic assays and immunophenotypic characterization were performed on day 0, day 7, day 12 and day 14 on the expanded cellular product. The maximum expansion was achieved using GF2 (SCF + IL-3 + GM-CSF) with stromal cell support. The mean CD34+ cell expansion on days 7 and 12 was 16.25- and 21.4-fold (5.2–32), respectively, and the mean nucleated cell expansion was 15.1- and 21-fold (18.1–23.2). The mean nucleated cell viability on day 12 was 87.9% (85.6–92.5). After 12 days, granulocyte-macrophage colony-forming units CFU-GEMM showed a 20.4-fold increase. A 21.4-fold increase in the CD34+ cells and a 20-fold increase in the CFU-GEMM should provide enough cells from a single cord blood unit to reduce the period of cytopenia after single unit cord blood transplantation. Even if there was some doubt about the long-term repopulating capacity of the expanded cells part of the collected umbilical cord cells (25%) could be expanded till day 12 after transplanting the major part (75%) of the collection.