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The cell surface receptor alpha4 integrin plays a critical role in the homing, engraftment, and maintenance of hematopoietic progenitor cells (HPCs) in the bone marrow (BM). Down-regulation or functional blockade of alpha4 integrin or its ligand vascular cell adhesion molecule-1 mobilizes long-term HPCs. We investigated the role of alpha4 integrin in the mobilization and homing of BM endothelial progenitor cells (EPCs). EPCs with endothelial colony-forming activity in the BM are exclusively alpha4 integrin-expressing cells. In vivo, a single dose of anti-alpha4 integrin antibody resulted in increased circulating EPC counts for 3 d. In hindlimb ischemia and myocardial infarction, systemically administered anti-alpha4 integrin antibody increased recruitment and incorporation of BM EPCs in newly formed vasculature and improved functional blood flow recovery and tissue preservation. Interestingly, BM EPCs that had been preblocked with anti-alpha4 integrin ex vivo or collected from alpha4 integrin-deficient mice incorporated as well as control cells into the neovasculature in ischemic sites, suggesting that alpha4 integrin may be dispensable or play a redundant role in EPC homing to ischemic tissue. These data indicate that functional disruption of alpha4 integrin may represent a potential angiogenic therapy for ischemic disease by increasing the available circulating supply of EPCs.

Information on the safety of mobilization and collection of peripheral blood progenitor cells (PBPC) in patients with advanced coronary heart disease (CHD) is limited. We report herein our early experience with patients participating in a Phase I trial of injection of autologous CD 34(+) cells into threatened, ischemic myocardium for neovascularization and symptom relief in patients with chronic refractory myocardial ischemia. All patients had advanced inoperable CHD despite the best medical therapy. Granulocyte colony stimulating factor (G-CSF, 5 microg/kg/day) was administered subcutaneously for 5 days for mobilization of CD34(+) cells into the peripheral blood. PBPCs were collected in the outpatient apheresis suite on day 5. Nine patients from our institution were evaluable. Adverse effects of mobilization included: increase in frequency and/or intensity of angina in 8 patients (88.8%); bone pain in 7 patients (77.7%); headaches in 4 patients (44.4%); 2 patients (22%) were hospitalized. Collection phase toxicities included: tingling in 5 patients (55.5%) and angina in 3 patients (33%). All procedures were completed without new myocardial infarction, congestive heart failure, or death. The median peripheral blood CD34(+) cell count on day 5 of G-CSF was 21 cells/microl (range 10-40 cells/microl). A median of 1.65 x 10(6) CD34(+) cells/kg (range: 0.13-3.0 x 10(6)/kg) were harvested. We conclude that mobilization and collection of PBPC in patients with advanced CHD can be safely performed as an outpatient procedure. Apheresis professionals should be aware of the intensity and frequency of angina in this patient population.

We have identified a subpopulation of stem cells within adult human BM, isolated at the single-cell level, that self-renew without loss of multipotency for more than 140 population doublings and exhibit the capacity for differentiation into cells of all 3 germ layers. Based on surface marker expression, these clonally expanded human BM-derived multipotent stem cells (hBMSCs) do not appear to belong to any previously described BM-derived stem cell population. Intramyocardial transplantation of hBMSCs after myocardial infarction resulted in robust engraftment of transplanted cells, which exhibited colocalization with markers of cardiomyocyte (CMC), EC, and smooth muscle cell (SMC) identity, consistent with differentiation of hBMSCs into multiple lineages in vivo. Furthermore, upregulation of paracrine factors including angiogenic cytokines and antiapoptotic factors, and proliferation of host ECs and CMCs, were observed in the hBMSC-transplanted hearts. Coculture of hBMSCs with CMCs, ECs, or SMCs revealed that phenotypic changes of hBMSCs result from both differentiation and fusion. Collectively, the favorable effect of hBMSC transplantation after myocardial infarction appears to be due to augmentation of proliferation and preservation of host myocardial tissues as well as differentiation of hBMSCs for tissue regeneration and repair. To our knowledge, this is the first demonstration that a specific population of multipotent human BM-derived stem cells can induce both therapeutic neovascularization and endogenous and exogenous cardiomyogenesis.

Background— A growing population of patients with coronary artery disease experiences angina that is not amenable to revascularization and is refractory to medical therapy. Preclinical studies have indicated that human CD34 + stem cells induce neovascularization in ischemic myocardium, which enhances perfusion and function. Methods and Results— Twenty-four patients (19 men and 5 women aged 48 to 84 years) with Canadian Cardiovascular Society class 3 or 4 angina who were undergoing optimal medical treatment and who were not candidates for mechanical revascularization were enrolled in a double-blind, randomized (3:1), placebo-controlled dose-escalating study. Patients received granulocyte colony-stimulating factor 5 μg · kg −1 · d −1 for 5 days with leukapheresis on the fifth day. Selection of CD34 + cells was performed with a Food and Drug Administration–approved device. Electromechanical mapping was performed to identify ischemic but viable regions of myocardium for injection of cells (versus saline). The total dose of cells was distributed in 10 intramyocardial, transendocardial injections. Patients were required to have an implantable cardioverter-defibrillator or to temporarily wear a LifeVest wearable defibrillator. No incidence was observed of myocardial infarction induced by mobilization or intramyocardial injection. The intramyocardial injection of cells or saline did not result in cardiac enzyme elevation, perforation, or pericardial effusion. No incidence of ventricular tachycardia or ventricular fibrillation occurred during the administration of granulocyte colony-stimulating factor or intramyocardial injections. One patient with a history of sudden cardiac death/ventricular tachycardia/ventricular fibrillation had catheter-induced ventricular tachycardia during mapping that required cardioversion. Serious adverse events were evenly distributed. Efficacy parameters including angina frequency, nitroglycerine usage, exercise time, and Canadian Cardiovascular Society class showed trends that favored CD34 + cell–treated patients versus control subjects given placebo. Conclusions— A randomized trial of intramyocardial injection of autologous CD34 + cells in patients with intractable angina was completed that provides evidence for feasibility, safety, and bioactivity. A larger phase IIb study is currently under way to further evaluate this therapy.