## 3 Undifferentiated Cells (Stem Cells)
### Adult Stem Cells
#### 3.4.3 Unbilical Cord Perivascular Cells (HUCPVCs)  
General Information  
The perivascular region of the human umbilical cord has been recently identified as a rich source of adult MSCs. Human umbilical cord perivascular cells (HUCPVCs) are different from those isolated from the bulk of Wharton's Jelly. As stated by the International Society for Cell Therapy, these cells contain a subpopulation that shows the minimum criteria of mesenchymal stromal cells such as multi-lineage differentiation capacity [264]. Like ADSCs, the proliferation rate of HUCPVCs is higher than BM-MSCs with a significantly greater colony forming unit-fibroblast (CFU-F) frequency at harvest equaling 1:300 [265]. Similar to other UC-derived MSCs, HUCPVCs may suppress immunoreactions in hosts due to the lack of expression of class I and II major histocompatibility (MHC) antigens [265; 266]. A simple method has been proposed by [PERSON] et al. for the isolation of HUCPVCs from the UC. First, three vessels with their surrounding tissue are isolated from the WJ matrix. Then, both sides of the isolated vessels are tied by a silk suture and then placed into a 50 mL centrifuge tube containing a digestion solution (1 mg/mL collagenase in PBS) for 24 hours. Lastly, the vessels are removed from the digestion medium, and the resulting suspension was centrifuged. The resulting medium contains HUCPVCs, which adhere to TC dishes [267]. Currently, there is a relative paucity of reports on the potential of these cells to differentiate into different lineages. However, the multi-lineage differentiation of HUCPVCs has been claimed  
Figure 8: The systemic transplantation of human CD34+ cells/EPCs results in their recruitment to the fracture site. This causes a favorable environment for fracture healing by enhancing vasculogenesis/angiogenesis and osteogenesis, which leads to functional recovery from the fracture. With permission from Reference [262]. by [PERSON] et al. [264]. Furthermore, the therapeutic potential of HUCPVCs has been previously reported for wound healing [268] and myocardial infarction [269]. In addition, there are some reports of their application in bone regeneration strategies [270; 271]. Applications in BTE  
In 2013, [PERSON] et al. presented HUCPVCs as a reliable cell source for skeletal regeneration [272]. They isolated CD146+ HUCPVCs from the UC and then purified and enriched them using CD146 Magnetic MicroBeads. The multi-lineage differentiation capacity of this population was identified under normoxic and hypoxic conditions in vitro. Moreover, the authors demonstrated in vivo osteogenesis of HUCPVCs-Gelfoam-alginate 3D complexes via the implantation of them into a critical-sized bone defect model in SCID mice. The in vitro results showed that the hypoxic conditions can suppress the osteogenic differentiation but may increase cell proliferation and colony-forming efficiency of the cells in comparison with that under normoxic conditions. The in vivo results confirmed the active role of CD146+ HUCPVCs in the new bone formation and produced cartilaginous callus and bony callus. According to these data, the authors stated that CD146+ HUCPVCs could be considered a highly promising cell type for use in bone tissue regeneration. [PERSON] in 2016 proved the osteogenic capacity of HUCPVCs [273]. They cultured these cells in an osteogenic medium (DMEM-LG containing \(10^{-7}\) M dexamethasone, 0.2 mM ascorbic acid, and 10 mM glycerol 2-phosphate) for 21 days. Regarding flow cytometry and immunofluorescence staining results, HUCPVCs expressed \(\alpha\)-SMA, MAP1B, and Tenascin-C, which confirmed that these cells are the ancestors of MSCs in the vascular area. In addition, alizarin red staining revealed that the cells could give rise to osteogenic lineages. [PERSON] et al. analyzed and employed HUCPVCs as a proper alternative of MSCs for BTE strategies [271]. They investigated the in vitro differentiation of HUCPVCs cultured with bone marrow conditioned medium (BM-CM) and evaluated their bone formation potency in vivo.