**4. Behavioral Di**ff**erences Between iPSC and Primary ECs During In Vitro Culture**

The significant vasculogenic potential of iPSC-ECs in vitro has been highlighted in several studies. Among the most noteworthy, there is the one carried out by Clayton et al., who compared three lines of endothelial cells: iPSC, induced Endothelial Cells (iECs) and cells derived from Human Coronary Artery (HCAECs) [92]. IPSC-ECs were obtained from neonatal fibroblasts through a retroviral overexpression of Oct4, SOX2, KLF4 and c-Myc and differentiated into endothelial cells. To score cell behavior concerning tubulogenesis, the authors measured cell migration and inflammatory response. Among the three cell lines (iECs, HCAECs and iPSC-ECs), the iPSC-ECs showed the best rate of vascular network formation. This result was also confirmed by cell migration assay and inflammatory response evaluation [92]. In a different study, Adams et al. compared iPSC-ECs to HUVECs by generating a human endothelium and by measuring the functional contribution of both the cell lines [93].

The results indicated that the inflammatory response, particularly the expression of cytokines and adhesion molecules as well as the number of transmigrating leukocytes, expressed by iPSC-ECs were similar to those reported for primary cells (HUVECs).

In the same study, the authors tested the electrical resistance of the cells as an indicator of the barrier function physiologically exerted by the vascular endothelium. Interestingly, iPSC–ECs displayed a lower permeability compared to HUVECs, indicating that these cells are able to create a functional endothelial barrier. This result was also corroborated by the analysis of structural protein organization that showed a better dynamic resistance of iPSC-ECs [93] when exposed to thrombin.
