Mesenchymal Stem Cells as a Feeder Layer Can Prevent Apoptosis of Expanded Hematopoietic Stem Cells Derived from Cord Blood

Umbilical cord blood (UCB) has been used for transplantation in the treatment of hematologic disorders as a source of hematopoietic stem cells (HSCs). Because of insufficient number of cord blood CD34+ cells, the
expansion of these cells seems to be important for clinical application. Mesenchymal stromal cells (MSCs),
playing an important role in HSCs maintenance, were used as feeder layer. Apoptosis and cell cycle distribution
of expanded cells were analyzed in MSCs co-culture and cytokine conditions and results were compared.
Three culture conditions of cord blood HSCs were prepared ex-vivo for 14 days: cytokines (SCF, TPO and
Flt3L) with MSCs feeder layer, cytokines without MSCs feeder layer and co-culture with MSCs without cytokines. Expansion was followed by measuring the total nucleated cells (TNCs), CD34+ cells and colony-
forming unit (CFU) output. Flow cytometry analysis of stained cells by annexin V and propidium iodide was
performed for detection of apoptosis rate and cell cycle distribution in expanded cells. Maximum cord blood CD34+ cells expansion was observed in day 10. The mean fold change of TNCs and CD34+ cells at day 10 in the
co-culture system with cytokines was significantly higher than the cytokine culture without MSCs feeder layer
and co-culture system without cytokines (n=6, p=0.023). The highest apoptosis rate and the least number of cells
in Go/G1 phase were observed in cytokine culture without feeder layer (p=0.041). The expansion of cord blood
HSCs on MSCs as a feeder layer resulted in higher proliferation and reduction in apoptosis rate.