Transplantation of endothelial progenitor cells transferred by vascular endothelial growth factor gene for vascular regeneration of ischemic flaps

HOXD9 regulated mitophagy to promote endothelial progenitor cells angiogenesis and deep vein thrombosis recanalization and resolution

BACKGROUND

Deep vein thrombosis (DVT) is a common vascular surgical disease caused by the coagulation of blood in the deep veins, and predominantly occur in the lower limbs. Endothelial progenitor cells (EPCs) are multi-functional stem cells, which are precursors of vascular endothelial cells. EPCs have gradually evolved into a promising treatment strategy for promoting deep vein thrombus dissolution and recanalization through the stimulation of various physical and chemical factors.

METHODS

In this study, we utilized a mouse DVT model and performed several experiments including qRT-PCR, Western blot, tube formation, wound healing, Transwell assay, immunofluorescence, flow cytometry analysis, and immunoprecipitation to investigate the role of HOXD9 in the function of EPCs cells. The therapeutic effect of EPCs overexpressing HOXD9 on the DVT model and its mechanism were also explored.

RESULTS

Overexpression of HOXD9 significantly enhanced the angiogenesis and migration abilities of EPCs, while inhibiting cell apoptosis. Additionally, results indicated that HOXD9 specifically targeted the HRD1 promoter region and regulated the downstream PINK1-mediated mitophagy. Interestingly, intravenous injection of EPCs overexpressing HOXD9 into mice promoted thrombus dissolution and recanalization, significantly decreasing venous thrombosis.

CONCLUSIONS

The findings of this study reveal that HOXD9 plays a pivotal role in stimulating vascular formation in endothelial progenitor cells, indicating its potential as a therapeutic target for DVT management.

VEGF and Other Gene Therapies Improve Flap Survival-A Systematic Review and Meta-Analysis of Preclinical Studies

Surgical flaps are basic tools in reconstructive surgery. Their use may be limited by ischemia and necrosis. Few therapies address or prevent them. Genetic therapy could improve flap outcomes, but primary studies in this field present conflicting results. This systematic review and meta-analysis aimed to appraise the efficacy of external gene delivery to the flap for its survival in preclinical models. This review was registered with PROSPERO (CRD42022359982). PubMed, Embase, Web of Science, and Scopus were searched to identify studies using animal models reporting flap survival outcomes following any genetic modifications. Random-effects meta-analysis was used to calculate mean differences in flap survival with accompanying 95% CI. The risk of bias was assessed using the SYRCLE tool. Subgroup and sensitivity analyses were performed to ascertain the robustness of primary analyses, and the evidence was assessed using the GRADE approach. The initial search yielded 690 articles; 51 were eventually included, 36 of which with 1576 rats were meta-analyzed. VEGF gene delivery to different flap types significantly improved flap survival area by 15.66% (95% CI 11.80-19.52). Other interventions had smaller or less precise effects: PDGF-13.44% (95% CI 3.53-23.35); VEGF + FGF-8.64% (95% CI 6.94-10.34); HGF-5.61% (95% CI 0.43-10.78); FGF 3.84% (95% CI 1.13-6.55). Despite considerable heterogeneity, moderate risk of bias, and low quality of evidence, the efficacy of VEGF gene therapy remained significant in all sensitivity analyses. Preclinical data indicate that gene therapy is effective for increasing flap survival, but further animal studies are required for successful clinical translation.

A Chemotactic Functional Scaffold with VEGF-Releasing Peptide Amphiphiles Facilitates Bone Regeneration by BMP-2 in a Large-Scale Rodent Cranial Defect Model

BACKGROUND

Current common techniques for repairing calvarial defects by autologous bone grafting and alloplastic implants have significant limitations. In this study, the authors investigated a novel alternative approach to bone repair based on peptide amphiphile nanofiber gels that are engineered to control the release of vascular endothelial growth factor (VEGF) to recruit circulating stem cells to a site of bone regeneration and facilitate bone healing by bone morphogenetic protein-2 (BMP-2).

METHODS

VEGF release kinetics from peptide amphiphile gels were evaluated. Chemotactic functional scaffolds were fabricated by combining collagen sponges with peptide amphiphile gels containing VEGF. The in vitro and in vivo chemotactic activities of the scaffolds were evaluated by measuring mesenchymal stem cell migration, and angiogenic capability of the scaffolds was also evaluated. Large-scale rodent cranial bone defects were created to evaluate bone regeneration after implanting the scaffolds and other control materials.

RESULTS

VEGF was released from peptide amphiphile in a controlled-release manner. In vitro migration of mesenchymal stem cells was significantly greater when exposed to chemotactic functional scaffolds compared to control scaffolds. In vivo chemotaxis was evidenced by migration of tracer-labeled mesenchymal stem cells to the chemotactic functional scaffolds. Chemotactic functional scaffolds showed significantly increased angiogenesis in vivo. Successful bone regeneration was noted in the defects treated with chemotactic functional scaffolds and BMP-2.

CONCLUSIONS

The authors' observations suggest that this bioengineered construct successfully acts as a chemoattractant for circulating mesenchymal stem cells because of controlled release of VEGF from the peptide amphiphile gels. The chemotactic functional scaffolds may play a role in the future design of clinically relevant bone graft substitutes for large-scale bone defects.

Intra-arterial injection of human adipose-derived stem cells improves viability of the random component of axial skin flaps in nude mice

BACKGROUND

Skin flap necrosis is a common postoperative complication in reconstructive surgery. Recent evidence suggests that subcutaneously injected adipose-derived stem cells (ASCs) increase the viability of random skin flaps. Here, we examined whether intra-arterial human ASC administration could improve random component survival of axial skin flaps in nude mice.

METHODS

Human ASCs isolated from a healthy volunteer by liposuction were injected into nude mice through the right femoral artery at a low (1 × 10³ cells), medium (1 × 10⁴ cells), or high (1 × 10⁵ cells) dose. After ASC infusion, right superficial inferior epigastric vessels were ligated to create unipedicled superficial inferior epigastric artery (SIEA) flap with random extension.

RESULTS

Flap survival was higher in mice from all three ASC-treated groups, and particularly the medium-dose group was 30% better, than in the control group. Histological examination demonstrated a significantly higher vascular density in the axial skin flap in nude mice treated with the medium ASC dose than in control mice. PKH26-labeled ASCs were identified in skin flaps of ASC-treated mice; some endothelial cells exhibited positive staining for human HLA-A. Compared to the control group, mice in ASC-treated groups had higher vascular endothelial growth factor levels and lower tumor necrosis factor α, interferon γ, and interleukin-6 levels.

CONCLUSIONS

Intra-arterial human ASC administration increased the survival of axial skin flaps by attenuating inflammatory reactions and enhancing neovascularization. Intra-arterial ASC administration might yield a higher rate of these cells and of engraftment in the skin flaps. This approach may have a therapeutic role in increasing flap survival.

Microvascular Fragment Transplantation Improves Rat Dorsal Skin Flap Survival

BACKGROUND

The development of flap necrosis distally remains a concern during microsurgical flap transfers because, at least in part, of decreased perfusion. Microvascular fragments (MVFs) are microvessels isolated from adipose tissue that are capable of improving tissue perfusion in a variety of tissue defects. The aim of this study was to determine whether the transplantation of MVFs in a dorsal rat skin flap model can improve flap survival.

METHODS

A 10 × 3 cm flap was raised in a cranial to caudal fashion on the dorsal side of 16 Lewis rats, with the caudal side remaining intact. The rats were equally divided into a treatment group (MVFs) and a control group (sterile saline). At the time of surgery, sterile saline with or without MVFs was injected directly into the flap. Microvessel density was determined after harvesting flap tissue by counting vessels that positively stained for Griffonia simplicifolia lectin I-isolectin B4. Laser Doppler was used to measure blood flow before and after surgery and 7 and 14 days later. Flap survival was evaluated 7 and 14 days after surgery by evaluating the percentage of viable tissue of the flap with photodigital planimetry.

RESULTS

Despite the lack of a significant difference in microvessel density and tissue perfusion, flap survival increased 6.4% (P < 0.05) in MVF-treated animals compared with controls.

CONCLUSIONS

The use of MVFs may be a means to improve flap survival. Future studies are required to delineate mechanisms whereby this occurs and to further optimize their application.

Development of chemotactic smart scaffold for use in tissue regeneration

BACKGROUND

Regenerative medicine aims to obviate the need for autologous grafting through the use of bioengineered constructs that combine stem cells, growth factors, and biocompatible vehicles. Human mesenchymal stem cells and vascular endothelial growth factor (VEGF) have both shown promise for use in this context, the former because of their pluripotent capacity and the latter because of its chemotactic activity. The authors harnessed the regenerative potential of human mesenchymal stem cells and VEGF to develop a chemotactic scaffold for use in tissue engineering.

METHODS

Human mesenchymal stem cells were transduced with human VEGF via lentivirus particles to secrete VEGF. The chemotactic activity of the VEGF-transduced stem cells was evaluated via a trans-well assay. Migration through semipermeable membranes was significantly greater in chambers filled with medium conditioned by VEGF-transduced cells. VEGF-transduced cells were then seeded on apatite-coated poly(lactic-co-glycolic acid) scaffolds, thereby creating the Smart Scaffold. To determine in vivo angiogenesis, the Smart Scaffolds were implanted into subcutaneous pockets in the backs of nude mice.

RESULTS

Significantly larger numbers of capillaries were observed in the Smart Scaffold compared with control implants on immunohistologic studies. For the chemotactic in vivo study, human mesenchymal stem cells tagged with a fluorescent dye (1,1-dioctadecyl-3,3,3,3-tetramethylindotricarbocyanine iodide) were injected intravenously via tail vein after the subcutaneous implantation of the Smart Scaffolds. In vivo fluorescent imaging revealed that fluorescent dye-tagged human mesenchymal stem cells successfully accumulated within the Smart Scaffolds.

CONCLUSION

These observations suggest that VEGF may play a vital role in the design of clinically relevant tissue regeneration graft substitutes through its angiogenic effects and ability to chemoattract mesenchymal stem cells.

Ischemic preconditioning increases endothelial progenitor cell number to attenuate partial nephrectomy-induced ischemia/reperfusion injury

OBJECTIVES

The objective of this study was to investigate the role of endothelial progenitor cells (EPCs) in the modulation of ischemia-reperfusion injury (IRI) in a partial nephrectomy (PN) rat model using early-phase ischemic preconditioning (IPC).

MATERIALS AND METHODS

Ninety male Sprague-Dawley rats were randomly divided into three groups following right-side nephrectomy: Sham-operated rats (surgery without vascular clamping); PN rats (renal blood vessels were clamped for 40 min and PN was performed); and IPC rats (pretreated with 15 min ischemia and 10 min reperfusion). At 1, 3, 6, 12, 24 h, and 3 days after reperfusion, the pool of circulating EPCs and kidneys were harvested. The extent of renal injury was assessed, along with EPC number, cell proliferation, angiogenesis, and vascular growth factor expression.

RESULTS

Pretreated rats exhibited significant improvements in renal function and morphology. EPC numbers in the kidneys were increased at 12 h following reperfusion in the IPC group as compared to the PN or Sham groups. Cell proliferation (including endothelial and tubular epithelial cells) and angiogenesis in peritubular capillaries were markedly increased in kidneys treated with IPC. In addition, vascular endothelial growth factor-A (VEGF-A) and stromal cell-derived factor-1α (SDF-1α) expression in the kidneys of pretreated rats was increased compared to rats subjected to PN.

CONCLUSIONS

OUR INVESTIGATION SUGGESTED THAT: (1) the early phase of IPC may attenuate renal IRI induced by PN; (2) EPCs play an important role in renal protection, involving promotion of cell proliferation and angiogenesis through release of several angiogenic factors.

The increase of VEGF secretion from endothelial progenitor cells post ultrasonic VEGF gene delivery enhances the proliferation and migration of endothelial cells

We investigated the feasibility of exogenous gene expression in endothelial progenitor cells (EPCs) through the use of ultrasonic microbubble transfection (UMT). EPCs originating from porcine peripheral blood were cultured in a medium containing constructed vascular endothelial growth factor (VEGF) pDNA followed by UMT. Simultaneously, comprehensive functional evaluations were conducted to investigate the effects of UMT of the VEGF gene on the EPCs. The results showed that UMT yielded significant VEGF protein expression. VEGF-containing supernatant originating from EPCs post UMT led to significantly enhanced activities of proliferation by more than 20% and migration by approximately 30% in human aortic endothelial cells. The duration of additional secretion of VEGF protein attributable to the exogenous VEGF gene in the EPCs post UMT lasted more than 96 hours. In conclusion, UMT successfully delivers the VEGF gene into porcine EPCs, and VEGF-containing supernatant derived from EPCs post UMT enhances the proliferation and migration of human aortic endothelial cells.

Enhanced repair of segmental bone defects of rats with hVEGF-165 gene-modified endothelial progenitor cells seeded in nanohydroxyapatite/collagen/poly(l-lactic acid) scaffolds

A new type of tissue-engineered bone was constructed by seeding hVEGF165 gene-modified endothelial progenitor cells into the nanohydroxyapatite/collagen/poly(L-lactic acid) scaffolds. These were implanted into the segmental femoral defects of rats to explore the promotion of angiogenesis and osteogenesis. The bone marrow of Sprague Dawley rats was cultured and proliferated, and the endothelial progenitor cells were transfected with Ad5–hVEGF165–EGFP. The gene-modified endothelial progenitor cells were seeded into the nanohydroxyapatite/collagen/poly(L-lactic acid) scaffolds; the growth was observed by scanning electron microscope, and the proliferation was evaluated by methyl thiazolyl tetrazolium assay. In vivo, 80 Sprague Dawley rats were divided randomly into four groups; segmental femoral defects (5 mm) were made and allografted: group A with hVEGF165/endothelial progenitor cells–nanohydroxyapatite/collagen/poly(L-lactic acid), group B with mock endothelial progenitor cells–nanohydroxyapatite/collagen/poly(L-lactic acid), group C with endothelial progenitor cells–nanohydroxyapatite/collagen/poly(L-lactic acid), and group D with scaffolds only. Radiographic, histological, and microvessel density tests were performed to evaluate the angiogenic and osteogenic ability. Reverse transcription polymerase chain reaction and western blot results showed that the target gene was expressed by endothelial progenitor cells. The scanning electron microscope findings and methyl thiazolyl tetrazolium assay revealed that endothelial progenitor cells were attached and proliferated within the nanohydroxyapatite/collagen/poly(L-lactic acid) scaffolds. The average radiographic score and capillary density were the highest in group A, and those in groups B and C were higher than that of group D. The histology showed osteogenesis and scaffold degradation in group A, with less in groups B and C and little in group D. The hVEGF165 gene-modified endothelial progenitor cells, which promoted angiogenesis and osteogenesis in bone-defected areas and the hVEGF165/endothelial progenitor cells–nanohydroxyapatite/collagen/poly(L-lactic acid) composites, may have potential application in repair of segmental bone defects.

Identification of the Fra-1 transcription factor in healing skin flaps transplants: a potential role as a negative regulator of VEGF release from keratinocytes

The molecular mechanisms underlying successful myocutaneous skin flap integration, as well as the ischemic loss of transplanted tissue on surgery, remain largely unknown. In this study we used a mouse model of caudally based skin flaps to determine molecular patterns of acute transplant re-integration. Gene chip-based transcriptional analysis revealed an up-regulation of the transcription factor Fra-1 in murine skin flap tissue. Epidermal keratinocytes at the wound margins represented a dominant cellular source of Fra-1 in mice. Moreover, Fra-1 protein showed a clear nuclear localization. In addition, Fra-1 protein was also present in nuclei of wound margin keratinocytes located near the suture line in human skin flaps. In vitro studies using the human keratinocyte cell line HaCaT showed that epidermal growth factor (EGF) was a potent inducer of Fra-1 expression in keratinocytes. Ablation of Fral-1 protein using a specific Fra-1 small interfering (si)RNA markedly increased the EGF-induced vascular endothelial growth factor (VEGF) expression from keratinocytes. These data suggest the involvement of an injury-induced Fra-1 transcription factor as a regulator of keratinocyte gene expression, which might act as an antagonistic player to restrict epithelial-driven angiogenic responses during normal skin flap integration.

Endothelial progenitor cells: novel biomarker and promising cell therapy for cardiovascular disease

Bone-marrow-derived EPCs (endothelial progenitor cells) play an integral role in the regulation and protection of the endothelium, as well as new vessel formation. Peripheral circulating EPC number and function are robust biomarkers of vascular risk for a multitude of diseases, particularly CVD (cardiovascular disease). Importantly, using EPCs as a biomarker is independent of both traditional and non-traditional risk factors (e.g. hypertension, hypercholesterolaemia and C-reactive protein), with infused ex vivo-expanded EPCs showing potential for improved endothelial function and either reducing the risk of events or enhancing recovery from ischaemia. However, as the number of existing cardiovascular risk factors is variable between patients, simple EPC counts do not adequately describe vascular disease risk in all clinical conditions and, as such, the risk of CVD remains. It is likely that this limitation is attributable to variation in the definition of EPCs, as well as a difference in the interaction between EPCs and other cells involved in vascular control such as pericytes, smooth muscle cells and macrophages. For EPCs to be used regularly in clinical practice, agreement on definitions of EPC subtypes is needed, and recognition that function of EPCs (rather than number) may be a better marker of vascular risk in certain CVD risk states. The present review focuses on the identification of measures to improve individual risk stratification and, further, to potentially individualize patient care to address specific EPC functional abnormalities. Herein, we describe that future therapeutic use of EPCs will probably rely on a combination of strategies, including optimization of the function of adjunct cell types to prime tissues for the effect of EPCs.

Cord blood-derived early outgrowth endothelial progenitor cells

The presence of circulating endothelial repopulating cells in the adult human peripheral blood has been proposed since long time ago. In the late 1990s, the putative endothelial progenitor cells (EPCs) were first identified and reported by Asahara and co-workers. Since then, a number of studies have demonstrated that these cells are derived from bone marrow and induce microvascular vasculogenesis and re-endothelialization of injured vessels. Meantime, human umbilical cord blood also gained much attention for the reason of possible additional source to obtain EPCs since cord blood has been shown to contain more number of active hematopoietic stem cells as compared to adult peripheral blood. This review summarizes the aspect of human cord blood-derived EPCs with special focuses into their identity and future clinical application.

Neovascularization in diabetes

Diabetes and its complications are a major public health burden in the developed world. The major cause of diabetic complications is abnormal growth of new blood vessels. This dysfunctional neovascularization results in significant morbidity and mortality in patients with diabetes and, as such, is a major focus of basic and clinical investigation. It has become clear that hyperglycemia disrupts tissue-level signaling in response to hypoxia and ischemia, impairs the vasculogenic potential of circulating stem cells and fundamentally alters the structure and function of key neovascularization proteins, including hypoxia-inducible factor-1. These mechanistic and pathophysiologic studies have revealed new therapeutic targets to restore normal neovascularization and to ameliorate and prevent diabetic vascular complications.

Angiogenesis and plastic surgery

SUMMARY

Angiogenesis, the formation of new blood vessels from an existing vascular bed, is a normal physiological process which also underpins many--apparently unrelated--pathological states. It is an integral factor in determining the success or failure of many procedures in plastic and reconstructive surgery. As a result, the ability to control the process would be of great therapeutic benefit. To appreciate the potential benefits and limitations of recent advances in our understanding of angiogenesis, it is important to comprehend the basic physiology of blood vessel formation. This review aims to summarise current knowledge of the way in which angiogenesis is controlled and to look at how disordered vessel development results in pathology relevant to plastic surgery. Through this we hope to provide a comprehensive overview of the recent advances in angiogenesis as they relate to plastic surgery, particularly the promotion of flap survival, tendon healing, nerve regeneration, fracture healing and ulcer treatments.

Mesenchymal stem cells transduced by vascular endothelial growth factor gene for ischemic random skin flaps

BACKGROUND

Vascular endothelial growth factor (VEGF) plays an important role in inducing angiogenesis. Mesenchymal stem cells may have the potential for differentiation into several types of cells, including vascular endothelial cells. In this study, the authors explored the feasibility of applying mesenchymal stem cells transduced by the VEGF gene to the treatment of ischemic random skin flaps.

METHODS

Mesenchymal stem cells were isolated from Sprague-Dawley rat bone marrow and cultured in vitro. Plasmid pcDNA3.1(-)/VEGF165 containing the VEGF gene was transduced into the mesenchymal stem cells by liposome. The mesenchymal stem cells were stained with chloromethyl-1-1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanineperchlorate before the transplantation. Thirty rats were randomized into three groups. Groups A, B, and C were injected with mesenchymal stem cells transduced with pcDNA3.1(-)/VEGF165 plasmid, mesenchymal stem cells, and medium only, respectively. On the fourth day after injection, random dorsal skin flaps measuring 9 x 2 cm were elevated. The survival, neovascularization, and blood flow recovery of the flaps were detected.

RESULTS

VEGF-transduced mesenchymal stem cells expressed VEGF highly in vitro and in vivo. Transplanted mesenchymal stem cells survived and incorporated into the capillary networks in the ischemic rat flaps. The viability measurements showed an increased percentage flap survival in group A (83.1 +/- 2.6 percent) as compared with either group B (66.4 +/- 6.1 percent) or group C (51.5 +/- 7.5 percent) (p < 0.01). The capillary density and the blood perfusion of the flaps in the experimental group were significantly higher than those in the other two groups (p < 0.01).

CONCLUSION

VEGF-transduced mesenchymal stem cells can increase ischemic flap neovascularization and augment the surviving areas.

Tissue engineering of urethra using human vascular endothelial growth factor gene-modified bladder urothelial cells

Acquired or congenital abnormalities may lead to urethral damage or loss, often requiring surgical reconstruction. Urethrocutaneous fistula and strictures are common complications, due to inadequate blood supply. Thus, adequate blood supply is a key factor for successful urethral tissue reconstruction. In this study, urethral grafts were prepared by seeding rabbit bladder urothelial cells (UCs) modified with human vascular endothelial growth factor (VEGF(165)) gene in the decellularized artery matrix. A retroviral pMSCV-VEGF(165)-GFP vector was cloned by insertion of VEGF open reading frame into the vector pMSCV-GFP (murine stem cell virus [MSCV]; green fluorescent protein [GFP]). Retrovirus was generated using package cell line 293T. Rabbit UCs were expanded ex vivo and modified with either MSCV-VEGF(165)-GFP or control MSCV-GFP retrovirus. Transduction efficiency was analyzed by fluorescence-activated cell sorting. The expression of VEGF(165) was examined by immunofluorescence, reverse transcript-polymerase chain reaction, Western blot, and enzyme-linked immunosorbent assay (ELISA). Decellularized rabbit artery matrix was seeded with genetically modified UCs and was subsequently cultured for 1 week prior to subcutaneous implantation into nude mice. Four weeks after implantation, the implants were harvested and analyzed by fluorescence microscopy, and by histologic and immunohistochemical staining. Ex vivo transduction efficiency of UCs was greater than 50% when concentrated retrovirus was used. The modified cells expressed both VEGF and GFP protein. Furthermore, the VEGF-modified UCs secreted VEGF in a time-dependent manner. Scanning electron microscopy and histochemical analysis of cross sections of the cultured urethral grafts showed that the seeded cells were attached and proliferated on the luminal surface of the decellularized artery matrix. In the subcutaneously implanted vessels, VEGF-modified cells significantly enhanced neovascularization and the formation of a urethral layer compared to GFP-modified cells. These results indicate that VEGF gene therapy may be a suitable approach to increase the blood supply in tissue engineering for treatment of urethral damage or loss.

Umbilical cord blood stem cells: Implications for cardiovascular regenerative medicine

The treatment of cardiovascular disease has benefited from advances in pharmacologic and intravascular intervention reducing the morbidity and mortality associated with this disease. To address the need in managing clinically complex vascular disease with limited therapeutic options studies have focused on cellular therapy as a means to augment compensatory mechanisms and to potentially prevent escalation and advancement of disease. Umbilical cord blood (UCB) is a rich source of hematopoietic stem cells (HSC) and thus may be a potential source of cells for this type of therapy. UCB can be collected at no risk to the donor, is immediately available, has a wider availability of HLA phenotypes with a possible lower immune reactivity and does not provoke ethically charged debates. Moreover, stem cells isolated from patients with chronic disease have impairment of their reparative abilities thus limiting their therapeutic impact. The potential of UCB HSC in augmenting this process has been studied extensively both in vitro and in vivo and has shown a benefit in acute and chronic vascular ischemia. Although studies suggest efficacy with no obvious safety concerns the mechanism for this therapeutic effect is unknown.

UC blood hematopoietic stem cells and therapeutic angiogenesis

Studies suggest that mobilized hematopoietic stem cells (HSC) are recruited to ischemic tissue and stimulate angiogenesis. Critical observations in pre-clinical studies have identified an augmentation of endogenous microvascular collateralization that is beyond that directly attributable to anatomic incorporation and differentiation of infused human cells into the vascular endothelium. Evidence links age-associated reductions in the levels of circulating marrow-derived HSC characterized by expression of early HSC markers CD133 and CD34, with the occurrence of cardiovascular events and associated death. Utilizing the patient's own HSC to augment angiogenesis has several disadvantages, including reduced function of these cells and logistical issues related to cell collection from individual patients. Thus an available source of allogeneic HSC such as UC blood for cellular therapy may be optimal.