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Logo of nihpaAbout Author manuscriptsSubmit a manuscriptNIH Public Access; Author Manuscript; Accepted for publication in peer reviewed journal;
 
Circ Res. Author manuscript; available in PMC Sep 30, 2012.
Published in final edited form as:
PMCID: PMC3206967
NIHMSID: NIHMS328387
Imaging: Guiding the Clinical Translation of Cardiac Stem Cell Therapy
Patricia K. Nguyen,abc Feng Lan,abc Yongming Wang,abc and Joseph C. Wuabc
aDepartment of Medicine, Division of Cardiology, Stanford University School of Medicine, Stanford, California 94305, USA
bDepartment of Radiology, Molecular Imaging Program at Stanford (MIPS), Stanford University School of Medicine, Stanford, California 94305, USA
cInstitute for Stem Cell Biology and Regenerative Medicine, Stanford University School of Medicine, Stanford, California 94305, USA
Correspondence should be addressed to: Joseph C. Wu, MD, PhD, 265 Campus Drive, Rm G1120B, Stanford, CA 94305, joewu/at/stanford.edu
Stem cells have been touted as the holy grail of medical therapy with promises to regenerate cardiac tissue, but it appears the jury is still out on this novel therapy. Using advanced imaging technology, scientists have discovered that these cells do not survive nor engraft long-term. In addition, only marginal benefit has been observed in large animal studies and human trials. However, all is not lost. Further application of advanced imaging technology will help scientists unravel the mysteries of stem cell therapy and address the clinical hurdles facing its routine implementation. In this review, we will discuss how advanced imaging technology will help investigators better define the optimal delivery method, improve survival and engraftment, and evaluate efficacy and safety. Insights gained from this review may direct the development of future preclinical investigations and clinical trials.
Keywords: stem cell therapy, imaging, cardiovascular medicine
Heart failure remains the leading cause of death worldwide, accounting for 1 in 9 deaths in the United States in 2007.1 Unfortunately, most current therapies do not address the issue of cardiomyocyte loss and serve only to delay progression or alleviate symptoms until potential orthotopic heart transplantation. Stem cell regenerative therapy has emerged as a promising alternative to improve heart function and prevent the development of end stage heart failure. New advances in stem cell technology have led to an explosion of preclinical and clinical studies using various delivery protocols and cell types, each touting their clinical advantages. Although results from early animal studies and pilot human trials were encouraging, findings from larger randomized studies have been underwhelming. Two recent meta-analyses of 18 and 10 trials showed only marginal benefit,2, 3 and two large-scale randomized Phase II trials using bone marrow-derived cells (BMCs) demonstrated conflicting results.4, 5 The reasons for these puzzling findings remain unclear, but may be further explored by applying imaging technology to guide stem cell therapy. In this review, we discuss how recent advances in imaging technology can help address the many challenges facing the clinical translation of stem cell therapy (Figure 1).
Figure 1
Figure 1
Application of advanced imaging to meet the challenges of stem cell therapy for cardiac disease
Advanced imaging technology can provide anatomical and functional assessment (e.g., conventional anatomical and functional imaging) as well as visualization of biological processes at the cellular and molecular level (e.g., molecular imaging). Both disciplines utilize various imaging modalities such as radionuclide, optical, magnetic resonance, computed tomographic, and ultrasound technology. Selecting the most effective imaging strategy requires a determination of whether the imaging system can meet the necessary requirements for spatial and temporal resolution, sensitivity, and penetration depth for visualization of the imaging target. Table 1 details the advantages and limitations of different imaging modalities and can serve as a guide for selecting the most appropriate strategy for the chosen indication.
TABLE 1
TABLE 1
Comparison of modalities for conventional and molecular imaging
While conventional anatomical and functional imaging can provide an overall road map for cell delivery as well as an assessment of the effects of stem cell therapy, molecular imaging can be used to track stem cells in vivo and to study their potential mechanistic benefits. In molecular imaging, imaging probes are used to target the biological process of interest. These imaging probes consist of a carrier (i.e., a cell, nanoparticle, and microbubble), which structurally binds a ligand designed to recognize the molecular target and a signal element to generate a detectable signal (Figure 2). The ideal imaging probe should have the following important properties: 1) high imaging specificity for tracking the desired biological process, 2) high imaging sensitivity for detection by available imaging modalities, 3) minimal cellular toxicity, and 4) minimal systemic toxicity.
Figure 2
Figure 2
Fundamental concepts in molecular imaging of stem cell therapy
In general, there are two main labeling approaches, each with its unique advantages and disadvantages: 1) direct labeling with radionuclides or iron nanoparticles and 2) reporter gene/probe labeling. Using the direct labeling approach, contrast agents (e.g., signal elements) either bind to cell surface proteins or are transported into the target cell by diffusion, endocytosis, or active transport (e.g., radiolabeled indium oxine and superparamagnetic iron oxide particles) (Figure 3A). In contrast, reporter gene/probe labeling requires cell transfection or transduction with a reporter gene that produces specific proteins (i.e., membrane transport, surface receptor, and intracellular storage proteins as well as intracellular enzymes) that can take up exogenously administered contrast agents. By far the most widely used reporter genes are firefly luciferase (Luc) and herpes simplex virus thymidine kinase (HSV-tk) and their mutants. After delivery of their respective substrates, these enzymes catalyze a chemical reaction that produces a detectable signal (Figure 3B).
Figure 3
Figure 3
Direct and reporter gene labeling for molecular imaging
The major advantage of reporter gene/probe labeling, especially for in vivo cell tracking, is that cells must be viable with intact protein synthesis machinery in order to produce a detectable signal. In contrast, the signal produced by direct labeling with radioisotopes can be diluted by cell division or dissipate after radioactive decay and/or may persist despite cell death due to the engulfment of dead cells by macrophages.6 Iron labeling by MRI, for example, can remain in the injected site long after cell death, providing erroneous information on the long-term fate of cells despite its superiority in cellular localization.6 Reporter gene/probe imaging is thus better suited for in vivo monitoring of cell viability. In one of the first clinical applications of reporter imaging, the positron emission tomography (PET) reporter probe HSV-tk was used to track and monitor “suicide gene” therapy for gliomas and hepatocellular carcinomas.7, 8 More recently, Yaghoubi et al demonstrated that reporter gene imaging could track the fate of exogenously administered, genetically modified, and therapeutic cytolytic T cells in patients with glioblastoma.9 However, widespread application has been slowed by safety concerns, such as the potential risk of immunogenicity and tumorgenicity caused by random reporter gene integration, as well as limited sensitivity due to reporter gene/probe slicing.10
Both conventional and molecular imaging may help determine the best strategy for stem cell delivery. A lack of an optimized and standardized protocol for safe and effective stem cell delivery is a potential reason for the inconsistent results from previous trials. In preclinical and clinical studies, cells have been delivered via intravenous, intracoronary, or intramyocardial routes.11 Cells have also been administered as early as minutes and as late as a few months post infarction in acute and chronic ischemic models, respectively. Unfortunately, these significant protocol variations have impeded the accurate interpretation of preclinical and clinical trial results, as it is unclear whether the limitation lies with the regenerative capacity of stem cell therapy or with the techniques of delivery.
Determining the Most Optimal Delivery Method
Stem cells have been delivered via intravenous, intracoronary, and direct intramyocardial routes. Small animal preclinical studies have been restricted to intravenous or intramyocardial delivery due to the small size of the murine and rat coronary arteries. Conversely, the intracoronary approach appears to be preferred in large animal and human trials, despite the lack of evidence for its superiority. Only a few studies have directly compared the cellular retention and engraftment of various delivery routes using in vivo imaging. One such study compared the delivery efficiency of intracoronary compared to peripheral intravenous injection of fluorescence and 99mTc labeled autologous BMCs in a swine model of myocardial infarction.12 For intravenous injection, radioactivity was mainly detected in the lungs with cardiac activity at only minimal levels one-hour after injection. For intracoronary injection, 34.8±9.9% of cells were detected in the heart one-hour post injection, but the number of cells declined precipitously to 6.0±1.7% at 24 hours. Cell detection, however, may be limited by the tracer’s short half-life.
Although intravenous or intracoronary injection is relatively easier and safer, direct intramyocardial injection bypasses the need for cell homing to the injured myocardium, which can be challenging. For example, in a previous clinical trial, only 1.3-2.6% of fluorine-18 fluorodeoxyglucose (18F-FDG) labeled cells were detected in the infarcted myocardium 50 to 75 minutes after intracoronary injection.13 On the other hand, a higher number of cells have been found in the myocardium after direct myocardial injection, but the potential success of this technique may be less predictable.14 To address these limitations, a recent study has found that seeding cells within a fibrin porous biomatrix improved myocardial cell retention in an immunodeficient mouse model of left ventricular (LV) remodeling.15 Taken together, these findings suggest that intramyocardial injection with adjuvant agents to improve cell retention is the preferred delivery method. Greater enthusiasm for this approach may be generated with imaging guidance to accurately delineate the peri-infarct area and to safely deliver cells into the myocardium.
Defining the Peri-infarct Area During Direct Intramyocardial Injection
One approach to ensure the safety and consistency of intramyocardial delivery is to use image guided delivery. To derive the most benefit from direct intramyocardial injection, cells need to be physically placed near the target area of injury, and ideally in the border zone between viable and non-viable tissue, but not directly into the infarct. In this location, cells can provide the most benefit and have sufficient access to nutrients from the blood supply. Because the ischemic microenvironment may be less hostile in the peri-infarct area than in the infarct zone, cells may also have a relatively higher chance of survival and engraftment in the peri-infarct area.
Recent advances in imaging technology have enabled image-based navigation of stem cell injection. The best established technique for three-dimensional (3D) intra cardiac navigation is intraventricular electromechanical mapping, which offers superior spatial orientation compared to x-ray fluoroscopy alone. Electromechanical mapping records point-by-point measures of electrophysiologic and motion data, enabling the formation of an electroanatomical map to define the peri-infarct area.16 Although it has been successfully applied in a number of Phase I clinical studies including an ongoing multi-center trial of intramyocardial delivery of bone marrow mononuclear cells,17 the accuracy of electromechanical mapping has been questioned due to overlap of electrical and mechanical data between normal and abnormal myocardium as well as positional artifacts such as heart motion, subject movement, and catheter induced bundle branch block.16 Other disadvantages include a limited access to remote areas, radiation exposure, and lengthy procedure time that can take up to 40 minutes or longer for higher resolution imaging, as more points need to be mapped.16
More recent advances in imaging technology have facilitated the development of two alternative techniques that may be used for defining the peri-infarct area at the time of cell delivery. The first is the emergence of the C-arm computed tomography (CT), which enables multiple serial ECG-triggered rotational acquisitions during slow intravenous contrast injection to achieve a 3D data cube with multi-planar reconstruction of the heart (Figure 1).18 Although this technique has been used to localize areas of injured myocardium induced by radiofrequency ablation,19 further study is needed to determine if the C-arm CT can provide delayed enhancement images of the infarcted myocardium similar to standard CT to enable imaging-based guidance of cell delivery.
The second alternative is the development of software that facilitates co-registration of CT or magnetic resonance imaging (MRI) delayed enhancement images with x-ray fluoroscopy.20, 21 The latter has the advantage of less radiation exposure, greater spatial resolution, and more validated protocols for viability imaging. Tomkowiak et al recently built customized software that has been shown to accurately register and overlay images acquired by MRI with those acquired from x-ray fluoroscopy by aligning discrete anatomical landmarks in a swine myocardial infarction model (Figure 1).21 Further study is required to demonstrate whether this technique can be applied to intramyocardial stem cell injections into the peri-infarct area.
A potential reason for the marginal and inconsistent benefit in cardiac function noted in clinical trials is the variability in cell survival, engraftment, and differentiation. It is likely that functional improvement will require the presence of an adequate number of cells to differentiate into cardiac myocytes, recruit endogenous stem cells, and release paracrine factors to enhance the function of surviving cardiomycytes. Molecular imaging has enabled in vivo monitoring of stem cell fate and may help investigators identify important strategies to improve cell survival, proliferation, engraftment, and differentiation.
Determining Survival, Proliferation, and Engraftment
Unlike MRI, which can provide only qualitative information on cell location and engraftment, reporter gene-based bioluminescence imaging (BLI) and nuclear imaging can quantify cell survival, proliferation, and engraftment. BLI, however, is limited to small animals due to poor optical transmission. An attractive alternative is PET imaging of 18F-FDG labeled cells, which allows quantification of engraftment in vivo in small animal and large animal models as well as humans.13, 22 However, the half-life of 18F is only 110 minutes and, therefore, only acute evaluation of biodistribution immediately after transplantation is feasible. For serial monitoring, single positron emission computed tomography (SPECT) imaging of 111In-labeled cells, which has a half-life of 2.8 days, can be used to follow subjects two weeks post cell delivery.23 Perhaps the best long-term monitoring strategy for large animals and humans is PET reporter gene imaging with HSV-tk. Because the reporter gene is incorporated into the cell genome, enabling continuous transcription of the reporter enzyme if the cell remains viable, serial imaging can be performed after initial and repeated administrations of the radiolabeled substrate. An attractive alternative to the more commonly used HSV-tk is the sodium-iodide symporter (NIS), which promotes in vivo cellular uptake of 99mTc or 124I for cell tracking using SPECT or PET, respectively. The advantage of NIS is that it is an endogenous mammalian gene that is potentially less immunogenic than HSV-tk. However, the feasibility of this technique has only been demonstrated in small animals.24
Using these various in vivo imaging techniques, studies have revealed that only a limited number of cells engraft and most cells die shortly after transplantation. Specifically, cell tracking studies have found that myocardial engraftment is less than 10% within 48 hours irrespective of cell type, the number of cells implanted, and delivery route.25, 26 The majority of cells are not found in the myocardium, but are either trapped in the pulmonary or microvasculature27, 28 or localize to remote organs.14, 29 Cell homing and retention in the infarcted myocardium, however, does occur. In a mouse model, Sheikh et al demonstrated that bone marrow mononuclear cells from a male donor injected intravenously preferentially home in on and are retained in the myocardium in female mice with ischemia-reperfusion injury compared to sham mice.30 The authors used in vivo cell tracking by BLI and ex vivo quantitative real time polymerase chain reaction analysis for the male Sry gene four weeks post injection. Interestingly, in a dog model of myocardial infarction, Kraitchman et al showed that intravenous injection of mesenchymal stem cells (MSCs) redistribute from the lung to infarcted myocardium,31 one-day post injection, further supporting that stem cells home to the injured tissue. Nevertheless, at present, the degree of cell homing and retention appears inadequate.
Even more disappointing is the fact that most cells die shortly after transplantation.6, 32-36 After delivery of human embryonic stem cell (ESC)-derived cardiomyocytes in an immunodeficient mouse model of myocardial infarction, in vivo BLI demonstrated that 90% of cells died within 3 weeks of delivery.34 Other investigators have also demonstrated failure of long-term survival (>8 weeks post delivery) for additional cell types, including MSCs,33, 36 skeletal myobalsts,33 cardiac resident stem cells,35 bone marrow mononuclear cells,30 adipose stromal cells,36 and ESC-derived endothelial cells32 in small animal models (Figure 4). Similarly, in a porcine model of myocardial infarction, Gyöngyösi et al could only detect faint focal activity in the myocardium 7 days post injection of porcine MSCs transfected with a PET reporter gene (Figure 5).37 Failure of cell detection beyond 7 days in large animal models is likely due to limited resolution and sensitivity of PET for long-term monitoring. As the cell number declines over time, PET may be unable to detect the generated signal, especially given that only a fraction of cells are labeled by reporter genes due to variable viral transduction efficiency as well as reporter gene/probe silencing.26 Taken together, these findings emphasize the need to understand the reasons behind poor cell retention and survival in order to identify methods for their improvement.
Figure 4
Figure 4
Figure 4
Figure 4
Poor long-term survival of transplanted cells in small animal models regardless of cell type and timing of delivery
Figure 5
Figure 5
Poor long-term survival of transplanted cells in a large animal model after transplantation
Imaging Cell Differentiation
In addition to poor survival and engraftment, directed differentiation of pluripotent stem cells into functional cardiomyocytes remains challenging. Cardiac differentiation appears to be enhanced by prior in vitro induction, which was confirmed by a study using BLI and stem cells expressing fluorescent and Luc genes under control of the cardiac sodium-calcium exchanger-1 (Nxc-1) promoter.38 Cells that showed markedly enhanced Luc expression upon induction of differentiation in vitro continued to express Luc for 2-4 weeks post transplantation in vivo. This finding has been supported by the emergence of several differentiation protocols for cardiomyocyte generation from pluripotent stem cells, using various growth factors, chemical, and physical stimuli.39 Despite these efforts, cardiomyocyte differentiation in vitro is largely uncontrolled and inefficient, with a success rate of <25%, under most protocols,40 highlighting the need for better understanding of the mechanisms regulating differentiation. Interestingly, one study has elucidated the role of STAT3 activity in ESC differentiation using BLI and a custom-designed STAT3 reporter construct driving a fluorescent protein and Luc.41 Subject to further investigation, in vivo imaging of cardiac differentiation has the potential to provide valuable insight into the control of stem cell differentiation.
Identifying Methods to Improve Cell Engraftment and Differentiation
By providing greater understanding of the mechanism behind poor engraftment and inefficient differentiation, in vivo imaging can guide the development of techniques to address these limitations. In vivo imaging has evaluated the optimal timing for stem cell delivery (acute vs. sub acute infarction),42 determined the spatiotemporal kinetics of BMC homing,30 compared delivery of various stem cell types,33 and assessed the potential role of pro-angiogenic or pro-survival agents to meet these limitations.43, 44 For example, Swijnenburg et al used in vivo cell tracking to determine whether timing of cell delivery would affect cell viability, but found no significant difference in cell survival or cardiac function when cells were delivered immediately (acute) versus 7 days (sub acute) after myocardial infarction (Figure 4C).42 In another study, acute donor cell death was seen in all cell types when comparing engraftment rate of bone marrow mononuclear cells, MSCs, skeletal myoblasts, and fibroblasts (Figure 4B).33 More recently, Hu et al showed that the addition of a microRNA prosurvival cocktail (miR-21, miR-24, and miR-221) was associated with enhanced survival of cardiac progenitor cells by BLI and improved cardiac function by echocardiography.44
Using BLI, investigators have also determined the kinetics of donor cell rejection across different immunological barriers.45-47 Swijnenburg et al demonstrated that survival of transplanted human ESCs was significantly limited in immunocompetent as opposed to immunodeficient mice, but could be mitigated by administration of immunosuppressive agents.45 Because these traditional regimens have shown only marginal improvement in survival, a recent study demonstrated that brief treatment with three co-stimulatory receptor blocking agents (i.e., cytotoxic T-lymphocyte-associated antigen 4 (CTL4)-Ig, anti-CD40 ligand, and anti-lymphocyte function-associated antigen 1) induced long-term engraftment of mouse ESCs, human ESCs, mouse iPSCs, human iPSCs, and more differentiated ESC- and iPSC-derivatives.47 As an alternative to adjuvant immunosuppressive therapy, multiple investigators are exploring whether the administration of autologous iPSCs, which are reprogrammed from somatic cells, may be more immunoprivileged. The feasibility of transplantation of autologous iPSCs in large animal models was recently reported using combined PET and MRI (Figure 6).48 Whether iPSCs are immune tolerated, however, has been recently challenged by a study that demonstrated that iPSCs could also induce a T-cell dependent immune response in syngeneic recipients, despite their autologous origins.46 Overall, these studies underscore the importance of in vivo imaging in developing strategies to enable the clinical translation of stem cell therapy.
Figure 6
Figure 6
Feasibility of in vivo imaging of transplantation of autologous canine induced pluripotent stem cells
It was previously believed that the principal mechanism underlying the benefit of stem cell therapy was the regeneration of functional endothelial cells (ECs), vascular smooth muscle cells (VSMCs), and cardiomyoctyes. Early studies in murine models of myocardial infarction have shown that cardiac stem cells appeared to integrate into the surrounding native myocardium and regenerate damaged tissue.49 With the advent of in vivo imaging, it has become evident that <10% of cells are retained in the myocardium 24 hours post injection and most injected cells do not survive, engraft, or proliferate beyond 8 weeks.25, 26 Because of the number of newly regenerated cells is too low to explain the significant functional improvement observed in most preclinical and clinical studies, it has been suggested that the functional benefit of therapy is related to secretion of soluble factors that protect the heart, induce neovascularization, and attenuate pathological remodeling (i.e., paracrine effect).49 Although the exact mechanism associated with improvement in LV function remains unclear, molecular imaging may help elucidate some of these unknowns.
Protecting the Myocardium
A potential application of in vivo imaging is to provide confirmation that stem cells release cytoprotective molecules that increase cardiomyocyte survival (i.e., factors that reduce apoptosis and necrosis). Data in animal models suggest that even very low levels of apoptosis (23 myocytes per 105 cardiac nuclei) could result in progressive lethal dilated cardiomyopathy that may be prevented by the administration of stem cell therapy.50 The feasibility of in vivo imaging of cell death has been demonstrated using 99mTc labeled annexin albeit with difficulty differentiating necrosis from apoptosis.51 These limitations may be addressed using a combined annexin-labeled magnetofluorescent nanoparticle (AnxCLIO-cy5.5) with gadolinium-DTPA-NBD, to detect apoptosis and necrosis, respectively.52 Incorporating methods to image stem cell death may help develop future therapies to improve stem cell survival.
Inducing Neovascularization
Another important application of in vivo imaging is to verify that stem cells promote angiogenesis and arteriogenesis via release of paracrine factors, given that only a small number of vessels contain donor cells.49 In animal models of hindlimb ischemia and myocardial infarction, stem cell administration was associated with increased expression of pro-angiogenic factors,53, 54 resulting in an increase in capillary density and collateral development, that can occur prior to any significant improvement in blood flow.55 In support of these findings, in vitro imaging using time elapse microscopy has shown that co-culture of ESCs with ECs results in EC migration, proliferation, lumen formation, and anastamosis to existing vasculature.56 The feasibility of in vivo imaging of angiogenesis in large animals and humans has already been demonstrated using radionuclide probes targeting αvβ3 integrin (i.e., 18F-Galacto-RGD and 123I-Gluco-RGD),57, 58 which are receptors that mediate endothelial cell migration, proliferation, and survival. Although it has yet to be applied directly to stem cell imaging, this technique has been used to demonstrate neovascularization after treatment with vascular endothelial growth factor in a porcine model of myocardial infarction, paving the way for its application to assess the benefits of stem cell therapy (Figure 7).58 It will be important to apply these imaging techniques in future studies to correlate the degree of angiogenesis with improvement in LV function.
Figure 7
Figure 7
Monitoring of therapeutic angiogenesis using 123I-Gluco-RGD labeling of αvβ3 integrin for SPECT imaging
Attenuating Pathological Remodeling
In vivo imaging may also help us better understand how stem cell therapy attenuates pathological remodeling. Stem cell administration has been found to decrease fibrosis, resulting in improvement in LV dilatation and systolic and diastolic function.59 These positive effects on post-infarct remodeling may be mediated by release of molecules that limit local inflammation (e.g., monocyte chemoattractant protein) and factors that modulate proliferation of fibroblasts and synthesis of collagen and extracellular matrix (i.e., metalloproteinases, tissue inhibitor of metalloproteinase, transforming growth factor, serine proteases, and serine protease inhibitors).60 Imaging of leukocyte trafficking, protease activation, collagen deposition, and myocardial fibrosis in animal models of myocardial infarction has already been achieved using various imaging techniques, including fluorescence molecular tomography, MRI, and radionuclide imaging.60 Future studies evaluating these processes before and after stem cell therapy will improve our understanding of how stem cell therapy minimizes scar formation and prevents heart failure progression.
In addition to reducing scar formation, stem cell administration has been shown to reverse abnormal myocardial energetics that has been associated with heart failure. Progressive LV dilatation results in increased LV wall stress, myocyte overstretching, and a shift toward expression of fetal contractile proteins, resulting in imbalance in ATP delivery and demand.61 Administration of BMCs has resulted in improvement of metabolism in both small and large animal models, as measured by nuclear magnetic resonance spectroscopy.62, 63 The development of an ultrafast magnetization saturation transfer method may facilitate examination ATP kinetics in humans in future clinical trials.64
Evaluating the Efficacy of Stem Cell Therapy
Over the last decade, significant resources have been invested in the development of stem cell therapy for cardiac regeneration, yet results from large animal and human studies based on analysis of global left ventricular ejection fraction (LVEF) have been underwhelming. In a recent meta-analyses of 52 published large animal preclinical studies (n=888 animals, median follow-up=4 weeks with range 2-17 weeks) using various types of cardiac stem cells, treated animals showed improvement in LVEF by 7.5%, resulting from a significant decrease in end systolic volume.65 Important predictors of improvement in LVEF include the use of MSCs, left anterior descending artery infarction, chronic occlusion models, higher number of cells (≥107), and cell injection at least 1 week after myocardial infarction. Animal type and route of delivery were not predictive. Similarly, two meta-analyses of clinical studies (n=10 studies with 698 patients and n=18 studies with 999 patients) using BMCs showed an increase in LVEF of 3-4% and a reduction in end systolic volume of 4-6 ml with median follow-up of 6 months (3 to 18 months), measured predominantly by echocardiography and MRI.2, 3 As shown in Table 2, the primary endpoint of most clinical studies has been the evaluation of LV size and global LVEF. Perhaps incorporating additional functional and anatomical measures, such as regional systolic function, diastolic function, perfusion, infarct size and viability, will further elucidate the benefits of stem cell therapy.
TABLE 2
TABLE 2
Effects of cell therapy on EF, perfusion, infarct size, and viability
Cardiac Function
The majority of preclinical and clinical studies have measured changes in LV size and function pre- and post-treatment to evaluate the effectiveness of cardiac regenerative therapy. The accurate and precise measurement of these parameters is critical given the relatively small changes observed after stem cell therapy. Unfortunately, M-mode (i.e., fractional shortening) and two-dimensional echocardiography (i.e., Simpson’s rule) make geometrical assumptions about the left ventricle that can lead to inaccurate measurements, especially in the presence of regional wall motion abnormalities. Poor inter- and intra-observer variability also limit the use of these techniques for serial imaging. These limitations can be addressed by the use of 3D echocardiography and cardiac MRI, which provide improved accuracy and reproducibility.
An alternative approach, and perhaps a more sensitive marker, is to assess regional contractile function by measuring strain and strain rate by echocardiography or MRI. The strain and strain rate reflect the absolute deformation and the speed of deformation (shortening and thickening) of the myocardium from an applied force in a specific myocardial segment and layer (i.e., endocardial and epicardial walls), respectively. This technique subtracts motion due to the effects of neighboring segments (e.g., tethering) that can mask pathological deformation and impart abnormal motion to normal segments. Abnormal strain and strain rate imaging, for example, have been found in patients with diabetes, amyloidosis, and doxorubicin-induced cardiac injury, who have normal LVEF.66 Similarly, a recent report in 67 ST-elevation myocardial infarction patients randomized to intracoronary infusion with bone marrow progenitor cells or placebo showed significantly greater improvement in regional strain rate in the treatment group with no significant differences in LVEF (Figure 8).67 Further application of this technique in preclinical and clinical studies may reveal a more impressive contribution of stem cell therapy for improving contractile function.
Figure 8
Figure 8
Improvement in regional systolic function after treatment with bone marrow progenitor cells in a patient who suffered an acute myocardial infarction
Diastolic Function
In addition to systolic dysfunction, an abnormal LV filling pattern is common in patients with ischemic heart disease and is a marker of poor prognosis. Moreover, patients who have improvement in LV filling after treatment have fewer symptoms and better survival.68 Despite this evidence, the evaluation of diastolic function has been performed in only a handful of clinical studies, unlike in animal studies where invasive PV loop measurements of LV relaxation are mainstay. In an initial study, Schaefer et al reported improvement in mitral valve filling (E/A ratio) for up to 18 months in patients after acute myocardial infarction, who were randomized to treatment with intracoronary infusion of bone marrow cell therapy, but the effect lasted less than 5 years.69 Other diastolic function parameters showed no difference. Dieterichsen et al also showed improvement in diastolic function (i.e., E/e’ ratio left atrial volume, and plasma NT-pro-BNP) in patients with chronic ischemic heart disease after repeat intracoronary administration of BMCs at 12-month follow-up.70 Although echocardiographic measures of diastolic function are noninvasive and, therefore, preferred for serial evaluation in patients, they correlate only modestly with invasive pressure volume loop analysis, the gold standard for evaluating LV relaxation. Perhaps further development and validation of strain imaging by echocardiography or MRI, which has the potential to be a more accurate and precise measure of LV relaxation properties, will generate greater interest for the incorporation of noninvasive diastolic function measures in clinical stem cell trials.71, 72
Myocardial Perfusion
The potential for stem cell induced vasculogenesis has prompted several studies to measure myocardial perfusion. Although the majority of studies appear to show improvement, more in-depth analysis reveals that the data are both limited and conflicting (Table 2). For example, only six studies evaluate both stress and rest phases,73-81 and only two studies incorporate PET data,82, 83 which provide a more quantitative assessment of myocardial perfusion. Results have also been inconsistent. Although SPECT perfusion data at rest have shown a decrease in the number of segments with perfusion defects after treatment, studies incorporating both stress and rest phases only show a decrease in overall ischemia extent, but not in the number of rest perfusion defects. Even more discouraging is that only one of the two studies incorporating PET perfusion showed improvement in overall myocardial blood flow in the treatment compared to the control group. Interestingly, all studies evaluating regional myocardial blood flow by intracoronary Doppler wire showed improvement in coronary flow reserve in the infarct related vessel after treatment.84-90 Performing serial evaluation with intracoronary Doppler wire, however, is not without risk. Taken together, these findings suggest that further evaluation of regional as well as global myocardial perfusion reserve by PET should be performed to confirm that stem cell therapy contributes to detectable levels of vasculogenesis in the myocardium.
Infarct Size and Viability
Although a variety of methods can be used to assess the effects of stem cell therapy on infarct size and the amount of viable tissue, direct visualization by contrast enhanced MRI, radionuclide imaging (i.e., PET or SPECT), and electromechanical mapping are preferred over indirect approaches that evaluate the extent and severity of LV dysfunction, such as LV angiography, 2D echocardiography, or cine MRI. Because of its precise delineation of scar tissue and the ability to distinguish between subendocardial and transmural infarction, contrast enhanced MRI is considered the most accurate for assessing infarct size. Interestingly, the majority of stem cell studies using contrast enhanced MRI have failed to show a significant change in infarct size,4, 82, 84, 86, 91-93 whereas, other techniques have demonstrated a significant decrease (Table 2).
The reasons for this discrepancy remain unclear because previous studies have provided only limited details on how contrast enhancement images were acquired and analyzed, two critical factors for determining changes in infarct size. One reason may be prior studies failed to control for the time interval between contrast injection and image acquisition, which is known to affect infarct size, especially in acute settings where gadolinium can enhance the area at risk as well as the infarct core.94 Additionally, previous studies have used traditional methods of image analysis, which have poor reproducibility.95 Finally, these studies did not evaluate changes specific to the peri-infarct area, which has been shown to have independent prognostic value beyond LV infarct size, volume, or ejection fraction.96, 97 Perhaps a more standardized and comprehensive approach to image acquisition and analysis will provide clearer evidence that stem cell therapy reduces the size of both the peri-infarct and infarct zones.
To determine viability, 18F-FDG PET, which measures glucose metabolism, is considered the gold standard for its superior sensitivity and specificity compared to other functional measures of viability, including stress echocardiography and SPECT.98 All clinical studies using 18F-FDG PET have consistently shown improvement in the myocardial viability (Table 2).83, 88, 99-101 In contrast to glucose metabolism, improvement in contractile reserve measured by dobutamine echocardiography has not been shown in all studies.75, 102, 103 This is not surprising, because myocardium that is severely dysfunctional due to extensive cellular damage usually does not have intact contractile reserve but may have preserved glucose metabolism.104 Additional studies incorporating both these measures will be important to further delineate the benefits of stem cell therapy in improving myocardial viability.
In addition to establishing the efficacy of stem cell therapies, routine clinical implementation of novel cell based treatment will depend on the successful resolution of important safety concerns such as cell migration, tumorgenicity, and arrhythmogenicity. Particularly challenging is the monitoring of cell biodistribution because administered cells may be essentially indistinguishable from host cells. As discussed previously, short-term in vivo cell monitoring has already been achieved in clinical trials using radionuclide based imaging techniques. Safety concerns, however, continue to impede regulatory approval of iron oxide and reporter genes labeling techniques for longer term monitoring. Also problematic is the detection of the low number of cells that may migrate to non-target organs. This need may be potentially met by a recently approved class of fluorocarbon-based reagents designed to safely and efficiently label cells ex vivo without the use of transfection agents.105
The ability to track stem cells in vivo is also vital for detecting the formation of inappropriate ectopic tissues and for guiding their elimination. This is especially critical for human ESCs and iPSCs, which have the potential to form teratomas (tumors composed of a haphazard array of somatic cell types) and teratocarcinomas (a malignant tumor composed of a teratoma mixed with embryonal carcinoma and/or choriocarcinoma).106 Although multi-modality approaches have been applied to image teratoma formation in vivo using MRI and reporter gene-based optical imaging, the former is limited by sensitivity, and the latter by poor tissue penetration. An alternative approach is to use the PET reporter probe 64Cu-radiolabeled cyclic arginine-glycine-aspartic acid (RGD) peptides to image αvβ3 integrin expression, whose up-regulation is known to play a key role in angiogenesis and metastasis (Figure 1).107 Cao et al recently demonstrated the superiority of this technique for monitoring tumorgenicity after ESC transplantation compared to more commonly used PET tracers (18F-FDG and 18F-FLT), which are less sensitive in detecting teratoma formation.108 Finally, molecular imaging can also monitor suicide gene ablation of teratomas using HSV-tk as both a PET reporter gene and suicide gene, respectively.109
Quantification and localization of cell engraftment will be important to limit arrhythmogenic risk. Although higher levels of cell engraftment may be associated with improved efficacy, focal grafts can create inhomogeneities within the myocardium that predispose the heart to re-entrant arrhythmias. In support of this theory, in vitro studies using skeletal myoblasts, neonatal cardiomyocytes, and MSCs have found that the risk of re-entrant arrhythmias appears to be dose dependent.110 Results from subsequent in vivo Phase I clinical trials, however, have been conflicting with an increase in arrhythmogenic risk associated with skeletal myoblasts,111 whereas, minimal risk has been found with transplantation of MSCs and BMCs.110 However, with so few cells surviving long-term in vivo, to conclude that the arrhythmogenic risk of stem cells other than skeletal myoblasts is low would be premature. Overall, these studies in cell migration, tumorgenicity, and arrhythmogenicity demonstrate that in vivo imaging can help investigators monitor recipients after transplantation.
With parallel developments in conventional and molecular imaging technology, investigators are well positioned to apply and extend current capabilities to facilitate the clinical translation of stem cell therapy. These invaluable tools have already helped researchers study issues related to poor engraftment, identify possible mechanisms of benefit, and characterize potential safety concerns. With this knowledge in hand, investigators can now focus on finding solutions to the challenges facing the clinical implementation of regenerative therapy.
In the next several years, we anticipate that investigators will gravitate toward cell delivery under direct visual guidance using advanced imaging modalities, including MRI and CT. In vivo tracking of cells during and shortly after delivery will enable identification of techniques to improve initial engraftment such as administration of agents that optimize cell adhesion, control hemodynamics, and prevent migration to non-target areas. Longer-term tracking of cells remains a challenge, especially in humans, given the limitations of the direct cell labeling and the risks of insertional mutagenesis or immunogenicity associated with reporter gene labeling. Greater focus on the development of a safe, robust technique to label and follow cell viability, differentiation, and migration is needed prior to routine implementation. In the meantime, currently available techniques will be used to identify the optimal cell type, timing of delivery, and immunosuppressive regimens in animal models to improve cell engraftment and survival. Future studies will also likely apply advanced imaging technology to provide mechanistic insight to determine whether regulation of these processes may augment the benefits of stem cell therapy. Finally, we encourage investigators to provide a more comprehensive evaluation of benefits of stem cell therapy beyond an evaluation of global systolic function. We firmly believe that application of the advanced imaging techniques reviewed here will be instrumental to the successful clinical implementation of this novel therapy.
Acknowledgments
We thank Amy Morris for preparing the illustrations. Due to space limitations, we are unable to include all of the important papers relevant to induced pluripotent stem cell derivation and application; we apologize to those investigators whom we omitted here.
FUNDING SOURCES This work was supported by the ACC/GE Career Development Award (PKN); NIH HL099117 and NIH EB009689 (JCW).
ABBREVIATIONS
AMIacute myocardial infarction
BLIbioluminescence imaging
BMCsbone marrow-derived cells
CEcontrast enhanced
CMcardiomyocytes
CTcomputed tomography
Cucopper
CPchest pain
DEdelayed enhancement
ECGelectrocardiogram
ECsendothelial cells
EGFPenhance green fluorescent protein
EMelectromechanical mapping
ESCsembryonic stem cells
Ffluorine
FDGfluorodeoxyglucose
FHBG9-(4-fluoro-3-hydroxymethylbutyl)guanine
FIfluorescence imaging
FLTfluorothymidine
FLucfirefly luciferase
FRIfluorescence reflectance imaging
FMTfluorescence molecular tomography
GCSFgranulocyte colony stimulating factor
HSV-tkherpes simplex virus thymidine kinase
Iiodine
iPSCsinduced pluripotent stem cells
Inindium
Lucluciferase
LVleft ventricular
LVAleft ventricular angiography
LVEFleft ventricular ejection fraction
MBFmyocardial blood flow
MSCmesenchymal stem cells
MRImagnetic resonance imaging
NH3ammonia
NISsodium-iodide symporter
Obsobservational
Oxoxine
RNVradionuclide ventriculography
Rndrandomized
RGDarginine-glycine-aspartic acid
PETpositron emission tomography
SPECTsingle positron emission computed tomography
Tctechnetium
3Dthree-dimensional
2Dtwo-dimensional
VSMCsvascular smooth muscle cells

Footnotes
The authors have declared that no conflict of interest exists.
Disclosures None
1. Roger VL, Go AS, Lloyd-Jones DM, Adams RJ, Berry JD, Brown TM, Carnethon MR, Dai S, de Simone G, Ford ES, Fox CS, Fullerton HJ, Gillespie C, Greenlund KJ, Hailpern SM, Heit JA, Ho PM, Howard VJ, Kissela BM, Kittner SJ, Lackland DT, Lichtman JH, Lisabeth LD, Makuc DM, Marcus GM, Marelli A, Matchar DB, McDermott MM, Meigs JB, Moy CS, Mozaffarian D, Mussolino ME, Nichol G, Paynter NP, Rosamond WD, Sorlie PD, Stafford RS, Turan TN, Turner MB, Wong ND, Wylie-Rosett J. Heart disease and stroke statistics--2011 update: a report from the American Heart Association. Circulation. 2011;123:e18–e209. [PubMed]
2. Lipinski MJ, Biondi-Zoccai GGL, Abbate A, Khianey R, Sheiban I, Bartunek J, Vanderheyden M, Kim H-S, Kang H-J, Strauer BE, Vetrovec GW. Impact of intracoronary cell therapy on left ventricular function in the setting of acute myocardial infarction: a collaborative systematic review and meta-analysis of controlled clinical trials. J Am Coll Cardiol. 2007;50:1761–1767. [PubMed]
3. Abdel-Latif A, Bolli R, Tleyjeh IM, Montori VM, Perin EC, Hornung CA, Zuba-Surma EK, Al-Mallah M, Dawn B. Adult bone marrow-derived cells for cardiac repair: a systematic review and meta-analysis. Arch Intern Med. 2007;167:989–997. [PubMed]
4. Meyer GP, Wollert KC, Lotz J, Steffens J, Lippolt P, Fichtner S, Hecker H, Schaefer A, Arseniev L, Hertenstein B, Ganser A, Drexler H. Intracoronary bone marrow cell transfer after myocardial infarction: eighteen months’ follow-up data from the randomized, controlled BOOST (BOne marrOw transfer to enhance ST-elevation infarct regeneration) trial. Circulation. 2006;113:1287–1294. [PubMed]
5. Traverse JH, McKenna DH, Harvey K, Jorgenso BC, Olson RE, Bostrom N, Kadidlo D, Lesser JR, Jagadeesan V, Garberich R, Henry TD. Results of a phase 1, randomized, double-blind, placebo-controlled trial of bone marrow mononuclear stem cell administration in patients following ST-elevation myocardial infarction. Am Heart J. 2010;160:428–434. [PMC free article] [PubMed]
6. Li Z, Suzuki Y, Huang M, Cao F, Xie X, Connolly AJ, Yang PC, Wu JC. Comparison of reporter gene and iron particle labeling for tracking fate of human embryonic stem cells and differentiated endothelial cells in living subjects. Stem Cells. 2008;26:864–873. [PMC free article] [PubMed]
7. Jacobs A, Voges J, Reszka R, Lercher M, Gossmann A, Kracht L, Kaestle C, Wagner R, Wienhard K, Heiss WD. Positron-emission tomography of vector-mediated gene expression in gene therapy for gliomas. Lancet. 2001;358:727–729. [PubMed]
8. Penuelas I, Haberkorn U, Yaghoubi S, Gambhir SS. Gene therapy imaging in patients for oncological applications. European Journal of Nuclear Medicine and Molecular Imaging. 2005;32(Suppl 2):S384–403. [PubMed]
9. Yaghoubi SS, Jensen MC, Satyamurthy N, Budhiraja S, Paik D, Czernin J, Gambhir SS. Noninvasive detection of therapeutic cytolytic T cells with 18F-FHBG PET in a patient with glioma. Nat Clin Pract Oncol. 2009;6:53–58. [PMC free article] [PubMed]
10. Krishnan M, Park JM, Cao F, Wang D, Paulmurugan R, Tseng JR, Gonzalgo ML, Gambhir SS, Wu JC. Effects of epigenetic modulation on reporter gene expression: implications for stem cell imaging. Faseb J. 2006;20:106–108. [PMC free article] [PubMed]
11. Segers VFM, Lee RT. Stem-cell therapy for cardiac disease. Nature. 2008;451:937–942. [PubMed]
12. Forest VF, Tirouvanziam AM, Perigaud C, Fernandes S, Fusellier MS, Desfontis JC, Toquet CS, Heymann MF, Crochet DP, Lemarchand PF. Cell distribution after intracoronary bone marrow stem cell delivery in damaged and undamaged myocardium: implications for clinical trials. Stem Cell Res Ther. 2010;1:4. [PMC free article] [PubMed]
13. Hofmann M, Wollert KC, Meyer GP, Menke A, Arseniev L, Hertenstein B, Ganser A, Knapp WH, Drexler H. Monitoring of bone marrow cell homing into the infarcted human myocardium. Circulation. 2005;111:2198–2202. [PubMed]
14. Hou D, Youssef EA, Brinton TJ, Zhang P, Rogers P, Price ET, Yeung AC, Johnstone BH, Yock PG, March KL. Radiolabeled cell distribution after intramyocardial, intracoronary, and interstitial retrograde coronary venous delivery: implications for current clinical trials. Circulation. 2005;112:I150–156. [PubMed]
15. Xiong Q, Hill KL, Li Q, Suntharalingam P, Mansoor A, Wang X, Jameel MN, Zhang P, Swingen C, Kaufman DS, Zhang J. A fibrin patch-based enhanced delivery of human embryonic stem cell-derived vascular cell transplantation in a porcine model of postinfarction left ventricular remodeling. Stem Cells. 2011;29:367–375. [PMC free article] [PubMed]
16. Gyöngyösi M, Dib N. Diagnostic and prognostic value of 3D NOGA mapping in ischemic heart disease. Nat Rev Cardiol. 2011;8:393–404. [PubMed]
17. Willerson JT, Perin EC, Ellis SG, Pepine CJ, Henry TD, Zhao DX, Lai D, Penn MS, Byrne BJ, Silva G, Gee A, Traverse JH, Hatzopoulos AK, Forder JR, Martin D, Kronenberg M, Taylor DA, Cogle CR, Baraniuk S, Westbrook L, Sayre SL, Vojvodic RW, Gordon DJ, Skarlatos SI, Moye LA, Simari RD. Intramyocardial injection of autologous bone marrow mononuclear cells for patients with chronic ischemic heart disease and left ventricular dysfunction (First mononuclear cells injected in the US [FOCUS]): Rationale and design. American Heart Journal. 2010;160:215–223. [PMC free article] [PubMed]
18. Lauritsch G, Boese J, Wigstrom L, Kemeth H, Fahrig R. Towards cardiac C-arm computed tomography. IEEE Trans Med Imaging. 2006;25:922–934. [PubMed]
19. Girard EE, Al-Ahmad A, Rosenberg J, Luong R, Moore T, Lauritsch G, Boese J, Fahrig R. Contrast-enhanced C-arm CT evaluation of radiofrequency ablation lesions in the left ventricle. JACC Cardiovasc Imaging. 2011;4:259–268. [PMC free article] [PubMed]
20. Knecht S, Skali H, O’Neill MD, Wright M, Matsuo S, Chaudhry GM, Haffajee CI, Nault I, Gijsbers GH, Sacher F, Laurent F, Montaudon M, Corneloup O, Hocini M, Haissaguerre M, Orlov MV, Jais P. Computed tomography-fluoroscopy overlay evaluation during catheter ablation of left atrial arrhythmia. Europace. 2008;10:931–938. [PubMed]
21. Tomkowiak MT, Klein AJ, Vigen KK, Hacker TA, Speidel MA, Vanlysel MS, Raval AN. Targeted transendocardial therapeutic delivery guided by MRI-X-ray image fusion. Catheter Cardiovasc Interv. 2011 Advance publication. [PubMed]
22. Terrovitis J, Lautamaki R, Bonios M, Fox J, Engles JM, Yu J, Leppo MK, Pomper MG, Wahl RL, Seidel J, Tsui BM, Bengel FM, Abraham MR, Marban E. Noninvasive quantification and optimization of acute cell retention by in vivo positron emission tomography after intramyocardial cardiac-derived stem cell delivery. J Am Coll Cardiol. 2009;54:1619–1626. [PMC free article] [PubMed]
23. Bindslev L, Haack-Sorensen M, Bisgaard K, Kragh L, Mortensen S, Hesse B, Kjaer A, Kastrup J. Labelling of human mesenchymal stem cells with indium-111 for SPECT imaging: effect on cell proliferation and differentiation. Eur J Nucl Med Mol Imaging. 2006;33:1171–1177. [PubMed]
24. Terrovitis J, Kwok KF, Lautamaki R, Engles JM, Barth AS, Kizana E, Miake J, Leppo MK, Fox J, Seidel J, Pomper M, Wahl RL, Tsui B, Bengel F, Marban E, Abraham MR. Ectopic expression of the sodium-iodide symporter enables imaging of transplanted cardiac stem cells in vivo by single-photon emission computed tomography or positron emission tomography. J Am Coll Cardiol. 2008;52:1652–1660. [PubMed]
25. Wu JC, Abraham MR, Kraitchman DL. Current perspectives on imaging cardiac stem cell therapy. J Nucl Med. 2010;51(Suppl 1):128S–136S. [PMC free article] [PubMed]
26. Chen IY, Wu JC. Cardiovascular Molecular Imaging: Focus on Clinical Translation. Circulation. 2011;123:425–443. [PMC free article] [PubMed]
27. Toma C, Wagner WR, Bowry S, Schwartz A, Villanueva F. Fate of culture-expanded mesenchymal stem cells in the microvasculature: in vivo observations of cell kinetics. Circ Res. 2009;104:398–402. [PMC free article] [PubMed]
28. Gyöngyösi M, Hemetsberger R, Wolbank S, Pichler V, Kaun C, Posa A, Petrasi Z, Petnehazy Ö, Hofer-Warbinek R, de Martin R, Gruber F, Benedek I, Benedek T, Kovacs I, Benedek I, Jr, Plass CA, Charwat S, Maurer G. Delayed recovery of myocardial blood flow after intracoronary stem cell administration. Stem Cell Rev. 2011;7:616–623. [PubMed]
29. Gyöngyösi M, Hemetsberger R, Wolbank S, Kaun C, Posa A, Marian T, Balkay L, Emri M, Galuska L, Mikecz P, Petrasi Z, Charwat S, Hemetsberger H, Blanco J, Maurer G. Imaging the migration of therapeutically delivered cardiac stem cells. JACC Cardiovasc Imaging. 2010;3:772–775. [PubMed]
30. Sheikh AY, Lin S-A, Cao F, Cao Y, van der Bogt KEA, Chu P, Chang C-P, Contag CH, Robbins RC, Wu JC. Molecular imaging of bone marrow mononuclear cell homing and engraftment in ischemic myocardium. Stem Cells. 2007;25:2677–2684. [PMC free article] [PubMed]
31. Kraitchman DL, Tatsumi M, Gilson WD, Ishimori T, Kedziorek D, Walczak P, Segars WP, Chen HH, Fritzges D, Izbudak I, Young RG, Marcelino M, Pittenger MF, Solaiyappan M, Boston RC, Tsui BM, Wahl RL, Bulte JW. Dynamic imaging of allogeneic mesenchymal stem cells trafficking to myocardial infarction. Circulation. 2005;112:1451–1461. [PMC free article] [PubMed]
32. Li Z, Wu JC, Sheikh AY, Kraft D, Cao F, Xie X, Patel M, Gambhir SS, Robbins RC, Cooke JP, Wu JC. Differentiation, survival, and function of embryonic stem cell derived endothelial cells for ischemic heart disease. Circulation. 2007;116:I-46–54. [PMC free article] [PubMed]
33. van der Bogt KE, Sheikh AY, Schrepfer S, Hoyt G, Cao F, Ransohoff KJ, Swijnenburg RJ, Pearl J, Lee A, Fischbein M, Contag CH, Robbins RC, Wu JC. Comparison of different adult stem cell types for treatment of myocardial ischemia. Circulation. 2008;118:S121–129. [PMC free article] [PubMed]
34. Cao F, Wagner RA, Wilson KD, Xie X, Fu JD, Drukker M, Lee A, Li RA, Gambhir SS, Weissman IL, Robbins RC, Wu JC. Transcriptional and functional profiling of human embryonic stem cell-derived cardiomyocytes. PloS one. 2008;3:e3474. [PMC free article] [PubMed]
35. Li Z, Lee A, Huang M, Chun H, Chung J, Chu P, Hoyt G, Yang P, Rosenberg J, Robbins RC, Wu JC. Imaging survival and function of transplanted cardiac resident stem cells. J Am Coll Cardiol. 2009;53:1229–1240. [PMC free article] [PubMed]
36. van der Bogt KE, Schrepfer S, Yu J, Sheikh AY, Hoyt G, Govaert JA, Velotta JB, Contag CH, Robbins RC, Wu JC. Comparison of transplantation of adipose tissue- and bone marrow-derived mesenchymal stem cells in the infarcted heart. Transplantation. 2009;87:642–652. [PMC free article] [PubMed]
37. Gyöngyösi M, Blanco J, Marian T, Tron L, Petnehazy O, Petrasi Z, Hemetsberger R, Rodriguez J, Font G, Pavo IJ, Kertesz I, Balkay L, Pavo N, Posa A, Emri M, Galuska L, Kraitchman DL, Wojta J, Huber K, Glogar D. Serial noninvasive in vivo positron emission tomographic tracking of percutaneously intramyocardially injected autologous porcine mesenchymal stem cells modified for transgene reporter gene expression. Circulation: Cardiovascular Imaging. 2008;1:94–103. [PMC free article] [PubMed]
38. Kammili RK, Taylor DG, Xia J, Osuala K, Thompson K, Menick DR, Ebert SN. Generation of novel reporter stem cells and their application for molecular imaging of cardiac-differentiated stem cells in vivo. Stem Cells Dev. 2010;19:1437–1448. [PMC free article] [PubMed]
39. Irion S, Nostro MC, Kattman SJ, Keller GM. Directed differentiation of pluripotent stem cells: from developmental biology to therapeutic applications. Cold Spring Harb Symp Quant Biol. 2008;73:101–110. [PubMed]
40. Burridge PW, Thompson S, Millrod MA, Weinberg S, Yuan X, Peters A, Mahairaki V, Koliatsos VE, Tung L, Zambidis ET. A universal system for highly efficient cardiac differentiation of human induced pluripotent stem cells that eliminates interline variability. PLoS One. 2011;6:e18293. [PMC free article] [PubMed]
41. Xie X, Chan KS, Cao F, Huang M, Li Z, Lee A, Weissman IL, Wu JC. Imaging of STAT3 signaling pathway during mouse embryonic stem cell differentiation. Stem Cells Dev. 2009;18:205–214. [PMC free article] [PubMed]
42. Swijnenburg R-J, Govaert JA, van der Bogt KEA, Pearl JI, Huang M, Stein W, Hoyt G, Vogel H, Contag CH, Robbins RC, Wu JC. Timing of bone marrow cell delivery has minimal effects on cell viability and cardiac recovery after myocardial Infarction. Circulation: Cardiovascular Imaging. 2010;3:77–85. [PMC free article] [PubMed]
43. Huang M, Nguyen P, Jia F, Hu S, Gong Y, de Almeida P, Wang L, Nag D, Kay M, Giaccia A, Robbins R, Wu JC. Inhibition of hypoxia inducible factor degradation enhances stem cell mobilization andangiogenesis after myocardial infarction. Circulation. 2011;124(suppl 1) in press. [PMC free article] [PubMed]
44. Hu S, Huang M, Nguyen P, Gong Y, Li Z, Jia F, Liu J, Nag D, Robbins R, Wu J. MicroRNA prosurvival cocktail for improving engraftment and function of cardiac progenitor cell transplantation. Circulation. 2011;124(suppl 1) in press. [PMC free article] [PubMed]
45. Swijnenburg R-J, Schrepfer S, Govaert JA, Cao F, Ransohoff K, Sheikh AY, Haddad M, Connolly AJ, Davis MM, Robbins RC, Wu JC. Immunosuppressive therapy mitigates immunological rejection of human embryonic stem cell xenografts. Proceedings of the National Academy of Sciences. 2008;105:12991–12996. [PubMed]
46. Zhao T, Zhang ZN, Rong Z, Xu Y. Immunogenicity of induced pluripotent stem cells. Nature. 2011;474:212–215. [PubMed]
47. Pearl JI, Lee AS, Leveson-Gower DB, Sun N, Ghosh Z, Lan F, Ransohoff J, Negrin RS, Davis MM, Wu JC. Short-term immunosuppression promotes engraftment of embryonic and induced pluripotent stem cells. Cell Stem Cell. 2011;8:309–317. [PMC free article] [PubMed]
48. Lee AS, Xu D, Nguyen PK, Nag D, Lyons JK, Han L, Hu S, Lan F, Huang M, Liu J, Narsinh KN, Long CT, de Almeida P, Levi B, Kooreman N, Bangs C, Pacharinsak C, Yeung AC, Gambhir SS, Longaker MT, Wu JC. Preclinical derivation and imaging of autologously transplanted canine induced pluripotent stem cells. Journal of Biological Chemistry. 2011 [PubMed]
49. Gnecchi M, Zhang Z, Ni A, Dzau VJ. Paracrine Mechanisms in Adult Stem Cell Signaling and Therapy. Circ Res. 2008;103:1204–1219. [PMC free article] [PubMed]
50. Wencker D, Chandra M, Nguyen K, Miao W, Garantziotis S, Factor SM, Shirani J, Armstrong RC, Kitsis RN. A mechanistic role for cardiac myocyte apoptosis in heart failure. J Clin Invest. 2003;111:1497–1504. [PMC free article] [PubMed]
51. Hofstra L, Liem IH, Dumont EA, Boersma HH, van Heerde WL, Doevendans PA, De Muinck E, Wellens HJ, Kemerink GJ, Reutelingsperger CP, Heidendal GA. Visualisation of cell death in vivo in patients with acute myocardial infarction. Lancet. 2000;356:209–212. [PubMed]
52. Sosnovik DE, Garanger E, Aikawa E, Nahrendorf M, Figuiredo JL, Dai G, Reynolds F, Rosenzweig A, Weissleder R, Josephson L. Molecular MRI of cardiomyocyte apoptosis with simultaneous delayed-enhancement MRI distinguishes apoptotic and necrotic myocytes in vivo: potential for midmyocardial salvage in acute ischemia. Circ Cardiovasc Imaging. 2009;2:460–467. [PMC free article] [PubMed]
53. Cho SW, Moon SH, Lee SH, Kang SW, Kim J, Lim JM, Kim HS, Kim BS, Chung HM. Improvement of postnatal neovascularization by human embryonic stem cell derived endothelial-like cell transplantation in a mouse model of hindlimb ischemia. Circulation. 2007;116:2409–2419. [PubMed]
54. Das H, George JC, Joseph M, Das M, Abdulhameed N, Blitz A, Khan M, Sakthivel R, Mao HQ, Hoit BD, Kuppusamy P, Pompili VJ. Stem cell therapy with overexpressed VEGF and PDGF genes improves cardiac function in a rat infarct model. PLoS One. 2009;4:e7325. [PMC free article] [PubMed]
55. Leong-Poi H, Christiansen J, Heppner P, Lewis CW, Klibanov AL, Kaul S, Lindner JR. Assessment of endogenous and therapeutic arteriogenesis by contrast ultrasound molecular imaging of integrin expression. Circulation. 2005;111:3248–3254. [PubMed]
56. Li J, Stuhlmann H. In vitro imaging of angiogenesis using embryonic stem cell-derived endothelial cells. Stem Cells Dev. 2011 Advance publication. [PMC free article] [PubMed]
57. Higuchi T, Bengel FM, Seidl S, Watzlowik P, Kessler H, Hegenloh R, Reder S, Nekolla SG, Wester HJ, Schwaiger M. Assessment of alphavbeta3 integrin expression after myocardial infarction by positron emission tomography. Cardiovasc Res. 2008;78:395–403. [PubMed]
58. Johnson LL, Schofield L, Donahay T, Bouchard M, Poppas A, Haubner R. Radiolabeled arginine-glycine-aspartic acid peptides to image angiogenesis in swine model of hibernating myocardium. JACC Cardiovasc Imaging. 2008;1:500–510. [PMC free article] [PubMed]
59. Berry MF, Engler AJ, Woo YJ, Pirolli TJ, Bish LT, Jayasankar V, Morine KJ, Gardner TJ, Discher DE, Sweeney HL. Mesenchymal stem cell injection after myocardial infarction improves myocardial compliance. Am J Physiol Heart Circ Physiol. 2006;290:H2196–2203. [PubMed]
60. Jaffer FA, Sosnovik DE, Nahrendorf M, Weissleder R. Molecular imaging of myocardial infarction. J Mol Cell Cardiol. 2006;41:921–933. [PubMed]
61. Jameel MN, Zhang J. Myocardial energetics in left ventricular hypertrophy. Curr Cardiol Rev. 2009;5:243–250. [PMC free article] [PubMed]
62. Gnecchi M, He H, Melo LG, Noiseaux N, Morello F, de Boer RA, Zhang L, Pratt RE, Dzau VJ, Ingwall JS. Early beneficial effects of bone marrow-derived mesenchymal stem cells overexpressing Akt on cardiac metabolism after myocardial infarction. Stem Cells. 2009;27:971–979. [PMC free article] [PubMed]
63. Zeng L, Hu Q, Wang X, Mansoor A, Lee J, Feygin J, Zhang G, Suntharalingam P, Boozer S, Mhashilkar A, Panetta CJ, Swingen C, Deans R, From AH, Bache RJ, Verfaillie CM, Zhang J. Bioenergetic and functional consequences of bone marrow-derived multipotent progenitor cell transplantation in hearts with postinfarction left ventricular remodeling. Circulation. 2007;115:1866–1875. [PubMed]
64. Xiong Q, Du F, Zhu X, Zhang P, Suntharalingam P, Ippolito J, Kamdar FD, Chen W, Zhang J. ATP production rate via creatine kinase or ATP synthase in vivo: a novel superfast magnetization saturation transfer method. Circulation Research. 2011;108:653–663. [PMC free article] [PubMed]
65. van der Spoel TIG, Jansen of Lorkeers SJ, Agostoni P, van Belle E, Gyöngyösi M, Sluijter JPG, Cramer MJ, Doevendans PA, Chamuleau SAJ. Human relevance of preclinical studies in stem cell therapy: systematic review and meta-analysis of large animal models of ischaemic heart disease. Cardiovascular Research. 2011 Advance publication. [PubMed]
66. Dandel M, Lehmkuhl H, Knosalla C, Suramelashvili N, Hetzer R. Strain and strain rate imaging by echocardiography - basic concepts and clinical applicability. Curr Cardiol Rev. 2009;5:133–148. [PMC free article] [PubMed]
67. Herbots L, D’Hooge J, Eroglu E, Thijs D, Ganame J, Claus P, Dubois C, Theunissen K, Bogaert J, Dens J, Kalantzi M, Dymarkowski S, Bijnens B, Belmans A, Boogaerts M, Sutherland G, Van de Werf F, Rademakers F, Janssens S. Improved regional function after autologous bone marrow-derived stem cell transfer in patients with acute myocardial infarction: a randomized, double-blind strain rate imaging study. Eur Heart J. 2009;30:662–670. [PubMed]
68. Carluccio E, Biagioli P, Alunni G, Murrone A, Leonelli V, Pantano P, Vincenti G, Giombolini C, Ragni T, Reboldi G, Gentile F, Ambrosio G. Effect of revascularizing viable myocardium on left ventricular diastolic function in patients with ischaemic cardiomyopathy. Eur Heart J. 2009;30:1501–1509. [PubMed]
69. Schaefer A, Zwadlo C, Fuchs M, Meyer GP, Lippolt P, Wollert KC, Drexler H. Long-term effects of intracoronary bone marrow cell transfer on diastolic function in patients after acute myocardial infarction: 5-year results from the randomized-controlled BOOST trial--an echocardiographic study. Eur J Echocardiogr. 2010;11:165–171. [PubMed]
70. Diederichsen ACP, Moller JE, Thayssen P, Videbaek L, Saekmose SG, Barington T, Kassem M. Changes in left ventricular filling patterns after repeated injection of autologous bone marrow cells in heart failure patients. Scandinavian Cardiovascular Journal. 2010;44:139–145. [PubMed]
71. Wakami K, Ohte N, Sakata S, Kimura G. Myocardial radial strain in early diastole is useful for assessing left ventricular early diastolic function: comparison with invasive parameters. Journal of the American Society of Echocardiography. 2008;21:446–451. [PubMed]
72. Azevedo CF, Amado LC, Kraitchman DL, Gerber BL, Osman NF, Rochitte CE, Edvardsen T, Lima JA. Persistent diastolic dysfunction despite complete systolic functional recovery after reperfused acute myocardial infarction demonstrated by tagged magnetic resonance imaging. Eur Heart J. 2004;25:1419–1427. [PubMed]
73. Perin E. Transendocardial injection of autologous mononuclear bone marrow cells in end-stage ischemic heart failure patients: one-year follow-up. Int J Cardiol. 2004;95(Suppl 1):S45–46. [PubMed]
74. Perin EC, Dohmann HF, Borojevic R, Silva SA, Sousa AL, Mesquita CT, Rossi MI, Carvalho AC, Dutra HS, Dohmann HJ, Silva GV, Belem L, Vivacqua R, Rangel FO, Esporcatte R, Geng YJ, Vaughn WK, Assad JA, Mesquita ET, Willerson JT. Transendocardial, autologous bone marrow cell transplantation for severe, chronic ischemic heart failure. Circulation. 2003;107:2294–2302. [PubMed]
75. Katritsis DG, Sotiropoulou PA, Karvouni E, Karabinos I, Korovesis S, Perez SA, Voridis EM, Papamichail M. Transcoronary transplantation of autologous mesenchymal stem cells and endothelial progenitors into infarcted human myocardium. Catheter Cardiovasc Interv. 2005;65:321–329. [PubMed]
76. Fuchs S, Kornowski R, Weisz G, Satler LF, Smits PC, Okubagzi P, Baffour R, Aggarwal A, Weissman NJ, Cerqueira M, Waksman R, Serrruys P, Battler A, Moses JW, Leon MB, Epstein SE. Safety and feasibility of transendocardial autologous bone marrow cell transplantation in patients with advanced heart disease. Am J Cardiol. 2006;97:823–829. [PubMed]
77. Fuchs S, Satler LF, Kornowski R, Okubagzi P, Weisz G, Baffour R, Waksman R, Weissman NJ, Cerqueira M, Leon MB, Epstein SE. Catheter-based autologous bone marrow myocardial injection in no-option patients with advanced coronary artery disease: a feasibility study. Journal of the American College of Cardiology. 2003;41:1721–1724. [PubMed]
78. Beeres SL, Bax JJ, Dibbets P, Stokkel MP, Zeppenfeld K, Fibbe WE, van der Wall EE, Schalij MJ, Atsma DE. Effect of intramyocardial injection of autologous bone marrow-derived mononuclear cells on perfusion, function, and viability in patients with drug-refractory chronic ischemia. J Nucl Med. 2006;47:574–580. [PubMed]
79. Beeres SL, Bax JJ, Dibbets-Schneider P, Stokkel MP, Fibbe WE, van der Wall EE, Schalij MJ, Atsma DE. Sustained effect of autologous bone marrow mononuclear cell injection in patients with refractory angina pectoris and chronic myocardial ischemia: twelve-month follow-up results. Am Heart J. 2006;152:684 e611–686. [PubMed]
80. Gyöngyösi M, Lang I, Dettke M, Beran G, Graf S, Sochor H, Nyolczas N, Charwat S, Hemetsberger R, Christ G, Edes I, Balogh L, Krause KT, Jaquet K, Kuck KH, Benedek I, Hintea T, Kiss R, Preda I, Kotevski V, Pejkov H, Zamini S, Khorsand A, Sodeck G, Kaider A, Maurer G, Glogar D. Combined delivery approach of bone marrow mononuclear stem cells early and late after myocardial infarction: the MYSTAR prospective, randomized study. Nat Clin Pract Cardiovasc Med. 2009;6:70–81. [PubMed]
81. Grajek S, Popiel M, Gil L, Breborowicz P, Lesiak M, Czepczynski R, Sawinski K, Straburzynska-Migaj E, Araszkiewicz A, Czyz A, Kozlowska-Skrzypczak M, Komarnicki M. Influence of bone marrow stem cells on left ventricle perfusion and ejection fraction in patients with acute myocardial infarction of anterior wall: randomized clinical trial: Impact of bone marrow stem cell intracoronary infusion on improvement of microcirculation. Eur Heart J. 2010;31:691–702. [PubMed]
82. Janssens S, Dubois C, Bogaert J, Theunissen K, Deroose C, Desmet W, Kalantzi M, Herbots L, Sinnaeve P, Dens J, Maertens J, Rademakers F, Dymarkowski S, Gheysens O, Van Cleemput J, Bormans G, Nuyts J, Belmans A, Mortelmans L, Boogaerts M, Van de Werf F. Autologous bone marrow-derived stem-cell transfer in patients with ST-segment elevation myocardial infarction: double-blind, randomised controlled trial. Lancet. 2006;367:113–121. [PubMed]
83. Castellani M, Colombo A, Giordano R, Pusineri E, Canzi C, Longari V, Piccaluga E, Palatresi S, Dellavedova L, Soligo D, Rebulla P, Gerundini P. The role of PET with 13N-ammonia and 18F-FDG in the assessment of myocardial perfusion and metabolism in patients with recent AMI and intracoronary stem cell injection. J Nucl Med. 2010;51:1908–1916. [PubMed]
84. Erbs S, Linke A, Adams V, Lenk K, Thiele H, Diederich KW, Emmrich F, Kluge R, Kendziorra K, Sabri O, Schuler G, Hambrecht R. Transplantation of blood-derived progenitor cells after recanalization of chronic coronary artery occlusion: first randomized and placebo-controlled study. Circ Res. 2005;97:756–762. [PubMed]
85. Assmus B, Schächinger V, Teupe C, Britten M, Lehmann R, Dobert N, Grunwald F, Aicher A, Urbich C, Martin H, Hoelzer D, Dimmeler S, Zeiher AM. Transplantation of progenitor cells and regeneration enhancement in acute myocardial infarction (TOPCARE-AMI) Circulation. 2002;106:3009–3017. [PubMed]
86. Britten MB, Abolmaali ND, Assmus B, Lehmann R, Honold J, Schmitt J, Vogl TJ, Martin H, Schächinger V, Dimmeler S, Zeiher AM. Infarct remodeling after intracoronary progenitor cell treatment in patients with acute myocardial infarction (TOPCARE-AMI): mechanistic insights from serial contrast-enhanced magnetic resonance imaging. Circulation. 2003;108:2212–2218. [PubMed]
87. Schächinger V, Assmus B, Britten MB, Honold J, Lehmann R, Teupe C, Abolmaali ND, Vogl TJ, Hofmann W-K, Martin H, Dimmeler S, Zeiher AM. Transplantation of progenitor cells and regeneration enhancement in acute myocardial infarction: Final one-year results of the TOPCARE-AMI Trial. J Am Coll Cardiol. 2004;44:1690–1699. [PubMed]
88. Dobert N, Britten M, Assmus B, Berner U, Menzel C, Lehmann R, Hamscho N, Schächinger V, Dimmeler S, Zeiher AM, Grunwald F. Transplantation of progenitor cells after reperfused acute myocardial infarction: evaluation of perfusion and myocardial viability with FDG-PET and thallium SPECT. Eur J Nucl Med Mol Imaging. 2004;31:1146–1151. [PubMed]
89. Schächinger V, Erbs S, Elsasser A, Haberbosch W, Hambrecht R, Holschermann H, Yu J, Corti R, Mathey DG, Hamm CW, Suselbeck T, Assmus B, Tonn T, Dimmeler S, Zeiher AM. Intracoronary bone marrow-derived progenitor cells in acute myocardial infarction. N Engl J Med. 2006;355:1210–1221. [PubMed]
90. Kang HJ, Kim HS, Zhang SY, Park KW, Cho HJ, Koo BK, Kim YJ, Soo Lee D, Sohn DW, Han KS, Oh BH, Lee MM, Park YB. Effects of intracoronary infusion of peripheral blood stem-cells mobilised with granulocyte-colony stimulating factor on left ventricular systolic function and restenosis after coronary stenting in myocardial infarction: the MAGIC cell randomised clinical trial. Lancet. 2004;363:751–756. [PubMed]
91. Lunde K, Solheim S, Aakhus S, Arnesen H, Abdelnoor M, Egeland T, Endresen K, Ilebekk A, Mangschau A, Fjeld JG, Smith HJ, Taraldsrud E, Grogaard HK, Bjornerheim R, Brekke M, Muller C, Hopp E, Ragnarsson A, Brinchmann JE, Forfang K. Intracoronary injection of mononuclear bone marrow cells in acute myocardial infarction. N Engl J Med. 2006;355:1199–1209. [PubMed]
92. Assmus B, Honold J, Schächinger V, Britten MB, Fischer-Rasokat U, Lehmann R, Teupe C, Pistorius K, Martin H, Abolmaali ND, Tonn T, Dimmeler S, Zeiher AM. Transcoronary transplantation of progenitor cells after myocardial infarction. N Engl J Med. 2006;355:1222–1232. [PubMed]
93. Assmus B, Walter DH, Lehmann R, Honold J, Martin H, Dimmeler S, Zeiher AM, Schächinger V. Intracoronary infusion of progenitor cells is not associated with aggravated restenosis development or atherosclerotic disease progression in patients with acute myocardial infarction. Eur Heart J. 2006;27:2989–2995. [PubMed]
94. Oshinski JN, Yang Z, Jones JR, Mata JF, French BA. Imaging time after Gd-DTPA injection is critical in using delayed enhancement to determine infarct size accurately with magnetic resonance imaging. Circulation. 2001;104:2838–2842. [PubMed]
95. Flett AS, Hasleton J, Cook C, Hausenloy D, Quarta G, Ariti C, Muthurangu V, Moon JC. Evaluation of techniques for the quantification of myocardial scar of differing etiology using cardiac magnetic resonance. JACC Cardiovasc Imaging. 2011;4:150–156. [PubMed]
96. Yan AT, Shayne AJ, Brown KA, Gupta SN, Chan CW, Luu TM, Di Carli MF, Reynolds HG, Stevenson WG, Kwong RY. Characterization of the peri-infarct zone by contrast-enhanced cardiac magnetic resonance imaging Is a powerful predictor of post-myocardial infarction mortality. Circulation. 2006;114:32–39. [PubMed]
97. Heidary S, Patel H, Chung J, Yokota H, Gupta SN, Bennett MV, Katikireddy C, Nguyen P, Pauly JM, Terashima M, McConnell MV, Yang PC. Quantitative tissue characterization of infarct core and border zone in patients with ischemic cardiomyopathy by magnetic resonance is associated with future cardiovascular events. J Am Coll Cardiol. 2010;55:2762–2768. [PubMed]
98. Bax JJ, Wijns W, Cornel JH, Visser FC, Boersma E, Fioretti PM. Accuracy of currently available techniques for prediction of functional recovery after revascularization in patients with left ventricular dysfunction due to chronic coronary artery disease: comparison of pooled data. J Am Coll Cardiol. 1997;30:1451–1460. [PubMed]
99. Bartunek J, Vanderheyden M, Vandekerckhove B, Mansour S, De Bruyne B, De Bondt P, Van Haute I, Lootens N, Heyndrickx G, Wijns W. Intracoronary injection of CD133-positive enriched bone marrow progenitor cells promotes cardiac recovery after recent myocardial infarction: feasibility and safety. Circulation. 2005;112:I178–183. [PubMed]
100. Chen SL, Fang WW, Ye F, Liu YH, Qian J, Shan SJ, Zhang JJ, Chunhua RZ, Liao LM, Lin S, Sun JP. Effect on left ventricular function of intracoronary transplantation of autologous bone marrow mesenchymal stem cell in patients with acute myocardial infarction. Am J Cardiol. 2004;94:92–95. [PubMed]
101. Strauer BE, Brehm M, Zeus T, Bartsch T, Schannwell C, Antke C, Sorg RV, Kogler G, Wernet P, Muller HW, Kostering M. Regeneration of human infarcted heart muscle by intracoronary autologous bone marrow cell transplantation in chronic coronary artery disease: the IACT Study. J Am Coll Cardiol. 2005;46:1651–1658. [PubMed]
102. Strauer BE, Brehm M, Zeus T, Kostering M, Hernandez A, Sorg RV, Kogler G, Wernet P. Repair of infarcted myocardium by autologous intracoronary mononuclear bone marrow cell transplantation in humans. Circulation. 2002;106:1913–1918. [PubMed]
103. Fernandez-Aviles F, San Roman JA, Garcia-Frade J, Fernandez ME, Penarrubia MJ, de la Fuente L, Gomez-Bueno M, Cantalapiedra A, Fernandez J, Gutierrez O, Sanchez PL, Hernandez C, Sanz R, Garcia-Sancho J, Sanchez A. Experimental and clinical regenerative capability of human bone marrow cells after myocardial infarction. Circ Res. 2004;95:742–748. [PubMed]
104. Sloof GW, Knapp FF, Jr, van Lingen A, Eersels J, Poldermans D, Bax JJ. Nuclear imaging is more sensitive for the detection of viable myocardium than dobutamine echocardiography. Nucl Med Commun. 2003;24:375–381. [PubMed]
105. Partlow KC, Chen J, Brant JA, Neubauer AM, Meyerrose TE, Creer MH, Nolta JA, Caruthers SD, Lanza GM, Wickline SA. 19F magnetic resonance imaging for stem/progenitor cell tracking with multiple unique perfluorocarbon nanobeacons. FASEB Jo. 2007;21:1647–1654. [PubMed]
106. Solter D. From teratocarcinomas to embryonic stem cells and beyond: a history of embryonic stem cell research. Nat Rev Genet. 2006;7:319–327. [PubMed]
107. Li ZB, Cai W, Cao Q, Chen K, Wu Z, He L, Chen X. (64)Cu-labeled tetrameric and octameric RGD peptides for small-animal PET of tumor alpha(v)beta(3) integrin expression. J Nucl Med. 2007;48:1162–1171. [PubMed]
108. Cao F, Li Z, Lee A, Liu Z, Chen K, Wang H, Cai W, Chen X, Wu JC. Noninvasive de novo imaging of human embryonic stem cell-derived teratoma formation. Cancer Research. 2009;69:2709–2713. [PMC free article] [PubMed]
109. Cao F, Drukker M, Lin S, Sheikh A, Xie X, Li Z, Connolly A, Weissman I, Wu J. Molecular imaging of embryonic stem cell misbehavior and suicide gene ablation. Cloning Stem Cells. 2007;9:107–117. [PubMed]
110. Menasche P. Stem cell therapy for heart failure: are arrhythmias a real safety concern? Circulation. 2009;119:2735–2740. [PubMed]
111. Menasche P, Alfieri O, Janssens S, McKenna W, Reichenspurner H, Trinquart L, Vilquin JT, Marolleau JP, Seymour B, Larghero J, Lake S, Chatellier G, Solomon S, Desnos M, Hagege AA. The Myoblast Autologous Grafting in Ischemic Cardiomyopathy (MAGIC) trial: first randomized placebo-controlled study of myoblast transplantation. Circulation. 2008;117:1189–1200. [PubMed]
112. Cao F, Lin S, Xie X, Ray P, Patel M, Zhang X, Drukker M, Dylla S, Connolly A, Chen X, Weissman I, Gambhir S, Wu J. In vivo visualization of embryonic stem cell survival, proliferation, and migration after cardiac delivery. Circulation. 2006;113:1005–1014. [PubMed]
113. van den Borne SWM, Isobe S, Verjans JW, Petrov A, Lovhaug D, Li P, Zandbergen HR, Ni Y, Frederik P, Zhou J, Arbo B, Rogstad A, Cuthbertson A, Chettibi S, Reutelingsperger C, Blankesteijn WM, Smits JFM, Daemen MJAP, Zannad F, Vannan MA, Narula N, Pitt B, Hofstra L, Narula J. Molecular imaging of interstitial alterations in remodeling myocardium after myocardial infarction. J Am Coll Cardiol. 2008;52:2017–2028. [PubMed]
114. Gyöngyösi M, Hemetsberger R, Wolbank S, Kaun C, Posa A, Marian T, Balkay L, Emri M, Galuska L, Mikecz P, Petrasi Z, Charwat S, Hemetsberger H, Blanco J, Maurer G. Imaging the migration of therapeutically delivered cardiac stem cells. J Am Coll Cardiol Img. 2010;3:772–775. [PubMed]
115. Swijnenburg R-J, Govaert JA, van der Bogt KEA, Pearl JI, Huang M, Stein W, Hoyt G, Vogel H, Contag CH, Robbins RC, Wu JC. Timing of bone marrow cell delivery has minimal effects on cell viability and cardiac recovery after myocardial infarction. Circulation: Cardiovascular Imaging. 2010;3:77–85. [PMC free article] [PubMed]
116. Gyöngyösi M, Blanco J, Marian T, Trón L, Petneházy Ö, Petrasi Z, Hemetsberger R, Rodriguez J, Font G, Pavo IJ, Kertész I, Balkay L, Pavo N, Posa A, Emri M, Galuska L, Kraitchman DL, Wojta J, Huber K, Glogar D. Serial noninvasive in vivo positron emission tomographic tracking of percutaneously intramyocardially injected autologous porcine mesenchymal stem cells modified for transgene reporter gene expression. Circulation: Cardiovascular Imaging. 2008;1:94–103. [PMC free article] [PubMed]
117. Johnson LL, Schofield L, Donahay T, Bouchard M, Poppas A, Haubner R. Radiolabeled arginine-glycine-aspartic acid peptides to image angiogenesis in swine model of hibernating myocardium. JACC: Cardiovascular Imaging. 2008;1:500–510. [PMC free article] [PubMed]
118. Herbots L, D’Hooge J, Eroglu E, Thijs D, Ganame J, Claus P, Dubois C, Theunissen K, Bogaert J, Dens J, Kalantzi M, Dymarkowski S, Bijnens B, Belmans A, Boogaerts M, Sutherland G, Van de Werf F, Rademakers F, Janssens S. Improved regional function after autologous bone marrow-derived stem cell transfer in patients with acute myocardial infarction: a randomized, double-blind strain rate imaging study. European Heart Journal. 2009;30:662–670. [PubMed]
119. Perin EC, Dohmann HF, Borojevic R, Silva SA, Sousa AL, Silva GV, Mesquita CT, Belem L, Vaughn WK, Rangel FO, Assad JA, Carvalho AC, Branco RV, Rossi MI, Dohmann HJ, Willerson JT. Improved exercise capacity and ischemia 6 and 12 months after transendocardial injection of autologous bone marrow mononuclear cells for ischemic cardiomyopathy. Circulation. 2004;110:II213–218. [PubMed]
120. Wollert KC, Meyer GP, Lotz J, Ringes-Lichtenberg S, Lippolt P, Breidenbach C, Fichtner S, Korte T, Hornig B, Messinger D, Arseniev L, Hertenstein B, Ganser A, Drexler H. Intracoronary autologous bone-marrow cell transfer after myocardial infarction: the BOOST randomised controlled clinical trial. Lancet. 2004;364:141–148. [PubMed]
121. Li ZQ, Zhang M, Jing YZ, Zhang WW, Liu Y, Cui LJ, Yuan L, Liu XZ, Yu X, Hu TS. The clinical study of autologous peripheral blood stem cell transplantation by intracoronary infusion in patients with acute myocardial infarction. Int J Cardiol. 2007;115:52–56. [PubMed]
122. Chang SA, Kim HK, Lee HY, Choi SY, Koo BK, Kim YJ, Sohn DW, Oh BH, Park YB, Choi YS, Kang HJ, Kim HS. Restoration of left ventricular synchronous contraction after acute myocardial infarction by stem cell therapy: new insights into the therapeutic implication of stem cell therapy for acute myocardial infarction. Heart. 2008;94:995–1001. [PubMed]
123. Hare JM, Traverse JH, Henry TD, Dib N, Strumpf RK, Schulman SP, Gerstenblith G, DeMaria AN, Denktas AE, Gammon RS, Hermiller JB, Jr, Reisman MA, Schaer GL, Sherman W. A randomized, double-blind, placebo-controlled, dose-escalation study of intravenous adult human mesenchymal stem cells after acute myocardial infarction. J Am Coll Cardiol. 2009;54:2277–2286. [PMC free article] [PubMed]
124. Plewka M, Krzeminska-Pakula M, Lipiec P, Peruga JZ, Jezewski T, Kidawa M, Wierzbowska-Drabik K, Korycka A, Robak T, Kasprzak JD. Effect of intracoronary injection of mononuclear bone marrow stem cells on left ventricular function in patients with acute myocardial infarction. Am J Cardiol. 2009;104:1336–1342. [PubMed]
125. Tendera M, Wojakowski W, Ruzyllo W, Chojnowska L, Kepka C, Tracz W, Musialek P, Piwowarska W, Nessler J, Buszman P, Grajek S, Breborowicz P, Majka M, Ratajczak MZ. Intracoronary infusion of bone marrow-derived selected CD34+CXCR4+ cells and non-selected mononuclear cells in patients with acute STEMI and reduced left ventricular ejection fraction: results of randomized, multicentre myocardial regeneration by intracoronary infusion of selected population of stem cells in acute myocardial infarction (REGENT) trial. Eur Heart J. 2009;30:1313–1321. [PubMed]
126. Miettinen JA, Ylitalo K, Hedberg P, Jokelainen J, Kervinen K, Niemela M, Saily M, Koistinen P, Savolainen ER, Ukkonen H, Pietila M, Airaksinen KE, Knuuti J, Vuolteenaho O, Makikallio TH, Huikuri HV. Determinants of functional recovery after myocardial infarction of patients treated with bone marrow-derived stem cells after thrombolytic therapy. Heart. 2010;96:362–367. [PubMed]