The Important Role of FLT3-L in Ex Vivo Expansion of Hematopoietic Stem Cells following Co-Culture with Mesenchymal Stem Cells

Objective

Hematopoietic stem cells (HSCs) transplantation using umbilical cord blood (UCB) has improved during the last decade. Because of cell limitations, several studies focused on the ex vivo expansion of HSCs. Numerous investigations were performed to introduce the best cytokine cocktails for HSC expansion The majority used the Fms-related tyrosine kinase 3 ligand (FLT3-L) as a critical component. According to FLT3-L biology, in this study we have investigated the hypothesis that FLT3-L only effectively induces HSCs expansion in the presence of a mesenchymal stem cell (MSC) feeder.

Materials and Methods

In this experimental study, HSCs and MSCs were isolated from UCB and placenta, respectively. HSCs were cultured in different culture conditions in the presence and absence of MSC feeder and cytokines. After ten days of culture, total nucleated cell count (TNC), cluster of differentiation 34+(CD34⁺) cell count, colony forming unit assay (CFU), long-term culture initiating cell (LTC-IC), homeobox protein B4 (HoxB4) mRNA and surface CD49d expression were evaluated. The fold increase for some culture conditions was compared by the t test.

Results

HSCs expanded in the presence of cytokines and MSCs feeder. The rate of expansion in the co-culture condition was two-fold more than culture with cytokines (P<0.05). FLT3-L could expand HSCs in the co-culture condition at a level of 20-fold equal to the presence of stem cell factor (SCF), thrombopoietin (TPO) and FLT3-L without feeder cells. The number of extracted colonies from LTC-IC and CD49d expression compared with a cytokine cocktail condition meaningfully increased (P<0.05).

Conclusion

FLT3-L co-culture with MSCs can induce high yield expansion of HSCs and be a substitute for the universal cocktail of SCF, TPO and FLT3-L in feeder-free culture.

Megakaryocytic differentiation of CD133+ hematopoietic stem cells by down-regulation of microRNA-10a

MicroRNAs (miRNA), as a class of non-coding RNAs, play a crucial role in normal hematopoiesis. Recent studies on miRNA profiling during hematopoiesis showed miR-10a down-regulation in megakaryocytic differentiation. Here we investigated whether decrease in miR-10a can differentiate umbilical cord blood CD133+ cells to megakaryocytic series. We ectopically induced miR-10a down-regulation by locked nucleic acid anti-miR-10a transfection of CD133+ cells. The megakaryocytic differentiation was evaluated by CD42/CD61 and CD41 surface expression and colonogenic capacity in Megacult media. In addition, real-time polymerase chain reaction was done for detection of miR-10a and its target HoxA1 mRNA. HOXA1 protein expression was detected by flow cytometry as mean fluorescent intensity that shows the antibody reaction proteins. Our findings showed megakaryocytic differentiation of about 28% of umbilical cord blood CD133+ stem cells with bright expression of CD42/CD61 and CD41 in parallel with increase in HoxA1 mRNA and protein level. Colony forming of CD61+ cells in Megacult demonstrated the colonogenic capacity of differentiated progenitor cells. In conclusion, MiR-10a has a role in megakaryocyte differentiation of stem cells via HOXA1 transcription factor targeting.

The High Yield Expansion and Megakaryocytic Differentiation of Human Umbilical Cord Blood CD133(+) Cells

OBJECTIVE

Despite of many benefits, umbilical cord blood (UCB) hematopoietic stem cell (HSC) transplantation is associated with low number of stem cells and slow engraftment; in particular of platelets. So, expanded HSCs and co-transfusion of megakaryocyte (MK) progenitor cells can shorten this period. In this study, we evaluated the cytokine conditions for maximum expansion and MK differentiation of CD133(+) HSCs.

MATERIALS AND METHODS

In this experimental study, The CD133(+) cells were separated from three cord blood samples by magnetic activated cell sorting (MACS) method, expanded in different cytokine combinations for a week and differentiated in thrombopoietin (TPO) for the second week. Differentiation was followed by the flow cytometry detection of CD41 and CD61 surface markers. Colony forming unit (CFU) assay and DNA analysis were done for colonogenic capacity and ploidy assay.

RESULTS

CD133(+) cells showed maximum expansion in the stem span medium with stem cell factor (SCF) + FMS-like tyrosine kinase 3-ligand (Flt3-L) + TPO but the maximum differentiation was seen when CD133(+) cells were expanded in stem span medium with SCF + Interleukin 3 (IL-3) + TPO for the first and in TPO for the second week. Colony Forming Unit-MK (CFU-MK) was formed in three sizes of colonies in the mega-cult medium. In the DNA analysis; 25.2 ± 6.7% of the cells had more than 2n DNA mass.

CONCLUSION

Distinct differences in the MK progenitor cell count were observed when the cells were cultured in stem span medium with TPO, SCF, IL-3 and then the TPO in the second week. Such strategy could be applied for optimization of CD133(+) cells expansion followed by MK differentiation.