Expansion of umbilical cord blood HSPCs by regulation of microencapsulated osteoblasts under hypoxic condition

Osteoblasts play an essential role in the construction of hematopoietic stem/progenitor cell (HSPCs) niches, and hypoxic condition is another characteristic in these areas. This study was aimed to create a novel culture system, which simulates the hematopoietic microenvironment by applying osteoblasts-gelatin-alginate-chitosan microcapsules and hypoxia incubator in order to investigate their supporting effects on ex vivo expansion of HSPCs. The osteoblasts were encapsulated by the polyelectrolyte-complexation method and then co-cultured with isolated cord blood mononuclear cells (CB-MNCs) in hypoxia and normoxia incubators, respectively, and the culture of CB-MNCs in single-culture system was conducted, which was regarded as control. The expansion of HSPCs was evaluated by counting the CB-MNCs number, colony-forming assay and CD34+ flow cytometric analysis. Meanwhile the pH value, glucose and lactic acid concentrations were detected every day. After culture of 7 days, the expansion of CB-MNCs co-cultured with encapsulated osteoblasts under hypoxia condition is 18.68±1.60 folds (p<0.01). At the same time, the percentage of CD34+ cells increase from 2.0% to 2.5%, the cell number expands 23.36±2.01 folds (p<0.01), and the number of CFU-Cs increases 11.6±0.9 folds (p<0.01). ANOVA results indicate that the osteoblasts have significant effect on HSPCs expansion; however, the hypoxia condition demonstrated its influence largely only under the existence of osteoblasts. The investigation provides an experimental basis for further research on the mechanisms of regulation of HSPCs by osteoblasts and the new method for large-scale expansion of HSPCs in vitro.