Cocultures of Umbilical Cord Blood Hematopoietic Progenitor Cells and Umbilical Cord Endothelium.

Purpose. The expansion of hematopoietic progenitor cells (HPC) from cord blood is limited so far. For HPC expansion and differentiation we evaluated a coculture model of cord blood-derived HPC and endothelial cells (EC) isolated from the umbilical cord.

Methods. CD34(+) HPC were cultured directly in contact with the endothelial monolayer or indirectly using a 0.4μm microporous transmembrane. EC were stimulated by various cytokines including TPO, interleukin (IL) 1β, IL4, and IL6. After 1 and 2 weeks, the HPC were counted and analyzed by flow cytometry. Their plating efficiencies were determined by methylcellulose assays, and their reconstitutive potential was analyzed by cobblestone assays. DNA microarrays on the expanding cells as well as on cytokine-stimulated EC were also performed.

Results. EC stimulation with thrombopoietin and IL4 had no significant effect on mononuclear cell expansion. In contrast, IL1β stimulation resulted in a 10 and 100fold increase of the cell number after one and two weeks, respectively. More than 90% of these cells were CD33(+) and had a plating efficiency equivalent to that of HPC post isolation (7.3 ±1.2 versus 8.3±0.68%). The number of 5-wk cobblestone-area forming cells among these expanded cells was diminished, whereas the number of 2-wk cobblestone areas did not change (10.6 versus 8.5). The expanded cells could further mature into functional granulocytes. Time-course DNA microarrays of IL1β-stimulated EC demonstrated an increased expression of genes encoding tumor necrosis factor-induced proteins, interleukins, and endothelial adhesion molecules. When IL1β was replaced by IL6, a 7-fold expansion of morphologically progenitor-like cells took place. 10–13% of these cells were positive for CD133, had a plating efficiency of 10.2±1.7%, and showed on average 14.5 five-week cobblestone areas.

Conclusion. Cocultures of cord blood-derived HPC with umbilical cord-derived EC offer alternative methods for the expansion and differentiation of hematopoietic cells.