We recently demonstrated that marrow stromal cells (MSCs) augment collateral remodeling through release of several cytokines such as VEGF and bFGF rather than via cell incorporation into new or remodeling vessels. The present study was designed to characterize the full spectrum of cytokine genes expressed by MSCs and to further examine the role of paracrine mechanisms that underpin their therapeutic potential. Normal human MSCs were cultured under normoxic or hypoxic conditions for 72 hours. The gene expression profile of the cells was determined using Affymetrix GeneChips representing 12 000 genes. A wide array of arteriogenic cytokine genes were expressed at baseline, and several were induced >1.5-fold by hypoxic stress. The gene array data were confirmed using ELISA assays and immunoblotting of the MSC conditioned media (MSC ^CM ). MSC ^CM promoted in vitro proliferation and migration of endothelial cells in a dose-dependent manner; anti-VEGF and anti-FGF antibodies only partially attenuated these effects. Similarly, MSC ^CM promoted smooth muscle cell proliferation and migration in a dose-dependent manner. Using a murine hindlimb ischemia model, murine MSC ^CM enhanced collateral flow recovery and remodeling, improved limb function, reduced the incidence of autoamputation, and attenuated muscle atrophy compared with control media. These data indicate that paracrine signaling is an important mediator of bone marrow cell therapy in tissue ischemia, and that cell incorporation into vessels is not a prerequisite for their effects.

Background—Valve thrombosis has yet to be fully evaluated after transcatheter aortic valve implantation. This study aimed to report the prevalence, timing, and treatment of transcatheter heart valve (THV) thrombosis. Methods and Results—THV thrombosis was defined as follows (1) THV dysfunction secondary to thrombosis diagnosed based on response to anticoagulation therapy, imaging modality or histopathology findings, or (2) mobile mass detected on THV suspicious of thrombus, irrespective of dysfunction and in absence of infection. Between January 2008 and September 2013, 26 (0.61%) THV thromboses were reported out of 4266 patients undergoing transcatheter aortic valve implantation in 12 centers. Of the 26 cases detected, 20 were detected in the Edwards Sapien/Sapien XT cohort and 6 in the Medtronic CoreValve cohort. In patients diagnosed with THV thrombosis, the median time to THV thrombosis post–transcatheter aortic valve implantation was 181 days (interquartile range, 45–313). The most common clinical presentation was exertional dyspnea (n=17; 65%), whereas 8 (31%) patients had no worsening symptoms. Echocardiographic findings included a markedly elevated mean aortic valve pressure gradient (40.5±14.0 mm Hg), presence of thickened leaflets or thrombotic apposition of leaflets in 20 (77%) and a thrombotic mass on the leaflets in the remaining 6 (23%) patients. In 23 (88%) patients, anticoagulation resulted in a significant decrease of the aortic valve pressure gradient within 2 months. Conclusions—THV thrombosis is a rare phenomenon that was detected within the first 2 years after transcatheter aortic valve implantation and usually presented with dyspnea and increased gradients. Anticoagulation seems to have been effective and should be considered even in patients without visible thrombus on echocardiography.

Background— T lymphocytes, components of the immune and inflammatory systems, are involved in such normal processes as wound healing and host defense against infection and in such pathological processes as tumor growth and atherosclerotic plaque development. Angiogenesis is a mechanism common to each. Because CD4+ T lymphocytes are active in regulating humoral and cellular responses of the immune system, we determined whether CD4+ cells contribute to collateral vessel development by using the mouse ischemic hindlimb model. Methods and Results— One week after ischemia, CD4 ^−/− mice showed reduced collateral flow induction, macrophage number, and vascular endothelial growth factor levels in the ischemic muscle compared with wild-type mice. There was also delayed recovery of hindlimb function and increased muscle atrophy/fibrosis. Spleen-derived purified CD4+ T cells infused into CD4 ^−/− mice selectively localized to the ischemic limb and significantly increased collateral flow as well as macrophage number and vascular endothelial growth factor levels in the ischemic muscle. Muscle function and damage also improved. Conclusions— These results indicate an important role of CD4+ cells in collateral development, as demonstrated by a 25% decrease in blood flow recovery after femoral artery ligation. Our data also suggest that CD4+ T cells control the arteriogenic response to acute hindlimb ischemia, at least in part, by recruiting macrophages to the site of active collateral artery formation, which in turn triggers the development of collaterals through the synthesis of arteriogenic cytokines.

Initial animal studies of single angiogenic agents, such as vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF), generated enthusiasm for the concept that these agents might enhance collateral development and thereby provide alternative therapies for patients with vascular disease not amenable to traditional revascularization. The enthusiasm, apparently justified by the subsequent results of small nonrandomized phase-I clinical trials, was then tempered by the subsequent disappointing results of randomized clinical trials. In light of these disappointing results, investigators have pursued alternative strategies in an attempt to improve tissue perfusion. One such strategy is the utilization of bone marrow-derived cell therapy. This review discusses mechanistic pathways mediating the effects of such cell therapy, summarizes the animal and early clinical experience, and speculates on the potential of genetic manipulation of bone marrow-derived cells in an attempt to further enhance their potency.