Mild hypoxia and human bone marrow mesenchymal stem cells synergistically enhance expansion and homing capacity of human cord blood CD34+ stem cells

Objective(s): Cord blood (CB) is known as a valuable source of hematopoietic stem cells (HSC). Identifying strategies that enhance expansion and maintain engraftment and homing capacity of HSCs can improve transplant efficiency. In this study, we examined different culture conditions on ex vivo expansion and homing capacity of CB-HSCs. Materials and Methods: In this study, 4-5 different units of human CB in each of 3 independent experiments were collected.CD34+ HSC was isolated, cultured in the serum-free medium(Stem line II) and supplemented with cytokines: FMS-like tyrosine kinase 3 ligand (FLt3L), Thrombopoietin (TPO), stem cell factor (SCF) with/without bone marrow mesenchymal stem cell (BM-MSC) feeder layer in normoxia (20% O2) and mild hypoxia (5% O2) for 7 days. Before and after this period, total nucleated cell count (TNC), CD34+ cells count, Colony-forming cell (CFC) assay, migration assay and CXCR4 expression were evaluated by real time PCR. Data analysis was performed with t- test and ANOVA. P-value less than 0.05 was considered as statistically significant differences. Results: At the end of 7 days of culture, the highest count of TNC, CD34+ cells, CFUs, migration percentage and CXCR4 mRNA level were observed in feeder+cytokine group at 5% O2 tension. Our findings demonstrated statistically significant (1.7-3.2 fold) increase of CXCR4 gene expression in hypoxia versus normoxia. Conclusion: Combination of BM-MSC and mild hypoxia (5% O2) not only improves HSC expansion but also enhances homing capacity of HSC and better mimickes the niche microenvironment conditions.