## 3 Undifferentiated Cells (Stem Cells)
### Adult Stem Cells
#### 3.4.3.2 Unbilical Cord Blood-Derived Mesenchymal Stem Cells (UCB-MSCs)  
General Information  
Umbilical cord blood (UCB) is currently recognized as a rich source of hemopoietic stem/progenitor cells. The first umbilical cord blood transplantation was performed in 1988, and the results demonstrated its therapeutic potential as a reliable cell-based therapy. Although the HSCs have been initially more widely used for various clinical situations, recently, the UCB-derived MSCs have also attracted attention for use in biomedical fields. Today, umbilical cord blood (UCB) as a part of UC is recognized as an interesting source of MSCs [233]. Like other parts of UC, the cell isolation of UCB takes advantage of the painless and non-invasive procedure without any damage to the mother or infant [234]. Up to now, a variety of methods have been proposed to collect UCB as the source of human UCB-MSCs [235]. The isolation procedure of MSCs of UCB is laborious and time-consuming, which usually results in a low rate of success. The most effective method for collecting UCB is the cannulation of the umbilical vein, which is followed by blood collection into a sterile bag containing citrate phosphate dextrose or acid citrate dextrose anti-coagulant (ACD-A) buffer [236; 237]. The isolation of UCB-MSCs is performed by using Ficoll density centrifugation media at the appropriate relative centrifugal force (RCF). After centrifugation, the formed interface layer is collected and washed with PBS. Lastly, the resulting solution is centrifuged and washed (with PBS) several times and is transferred into cell culture dishes. The cells were cultured using suitable culture media for several days. By washing cells, non-adherent cells were removed, and only the adherent cells with a fibrobl spindle-like shape (i.e., MSCs) may remain [238]. It has been previously proven that there is no significant difference between the collections obtained from Caesarean and vaginal delivery in terms of the net yield of nucleated cells [239]. A few practical tips have been suggested to increase the yield of isolated cells including blood collecting from long gestations and high infant and placenta weights as well as applying short intervals between deliveries of the baby and clamping of the cord [240]. Similar to UC-derived MSCs, the UCB-MSCs are immunosuppressive modulators that can be used for allo-transplantations and xeno-transplantations [241; 242]. However, the differentiated UCB-MSCs have also been used as a cell source in several studies. Under appropriate induction conditions (culturing in osteogenic medium), UCB-MSCs can differentiate into cell lineages of endoderm [243], mesoderm [244], and ectoderm [245]. This ability has also been observed in the UCB-MSCs obtained from other species such as horses [246]. The use of these cells with or without scaffolds for regeneration of skeletal system disorders has been applied in various studies [247; 248]. Previous reports have confirmed that UCB-MSCs are able to undergo osteogenic differentiation after culturing in the osteogenic medium [245; 249; 250]. The advantages of this type of cells for BTE applications are counted for their availability, less invasive method, and osteogenic capacity. In 2006, [PERSON] et al. compared UCB-MSCs with BM-MSCs and ASCs in terms of their morphology, the success rate of MSCs isolation, colony frequency, expansion potential, multiple differentiation capacities, and an immune phenotype [251]. Their results revealed that there are no significant differences among the cells regarding the morphology and immune phenotype. However, the isolation rate of MSCs was different for the cell sources, i.e., 100% for BM and AT, but only 63% for UCB. In addition, the colony frequency was highest in AT and lowest in UCB. On the other hand, the highest proliferation capacity belonged to UCB-MSCs, while the lowest one was for BM-MSCs. With respect to osteogenic potential, the authors concluded that UCB is an attractive alternative to BM in isolating MSCs.