Improved Exercise Capacity and Ischemia 6 and 12 Months After Transendocardial Injection of Autologous Bone Marrow Mononuclear Cells for Ischemic Cardiomyopathy
Background— We recently reported the safety and feasibility of autologous bone marrow mononuclear cell (ABMMNC) injection into areas of ischemic myocardium in patients with end-stage ischemic cardiomyopathy. The present study evaluated the safety and efficacy of this therapy at 6- and 12-month follow-up.
Methods and Results— Twenty patients with 6- and 12-month follow-up (11 treated subjects; 9 controls) were enrolled in this prospective, nonrandomized, open-label study. Complete clinical and laboratory evaluations as well as exercise stress (ramp treadmill), 2-dimensional Doppler echocardiography, single-photon emission computed tomography (SPECT) perfusion scanning, and 24-hour Holter monitoring were performed at baseline and follow-up. Transendocardial delivery of ABMMNCs was performed with the aid of electromechanical mapping to identify viable myocardium. Each patient received 15 ABMMNC injections of 0.2 mL each. At 6 and 12 months, total reversible defect, as measured by SPECT perfusion scanning, was significantly reduced in the treatment group as compared with the control group. At 12 months, exercise capacity was significantly improved in the treatment group. This improvement correlated well with monocyte, B-cell, hematopoietic progenitor cell, and early hemapoietic progenitor cell phenotypes.
Conclusions— The 6- and 12-month follow-up data in this study suggest that transendocardial injection of ABMMNCs in patients with end-stage ischemic heart disease may produce a durable therapeutic effect and improve myocardial perfusion and exercise capacity.
Coronary artery disease (CAD) remains a major cause of morbidity and mortality in the Western world.1 The irreversible loss of cardiomyocytes after myocardial infarction leads to left ventricular (LV) remodeling and in the end to ischemic heart failure.2 In many patients, the progression of CAD leads to successive rounds of revascularization therapies that commonly result in an end-stage coronary anatomy unsuited for further revascularization and associated with LV dysfunction. In recent years, stem cell transplantation has emerged as a potential modality for the treatment of cardiovascular diseases on the basis of its possible ability to induce neovascularization and tissue replacement.3–5 Many advances in understanding stem cell biology have occurred, and there is increasing evidence that cell transplantation may improve the perfusion and contractile function of the ischemic myocardium.6–12 Accordingly, stem cell transplantation could be an alternative therapy for CAD patients who have no other standard options for treatment.
We have recently reported initial safety and feasibility data for autologous bone marrow mononuclear cell (ABMMNC) injection into areas of ischemic myocardium in patients with end-stage ischemic heart failure.13 Short-term follow-up showed improvement in perfusion as assessed by single-photon emission computed tomography (SPECT) and regional contractility.
Despite the accumulating evidence pointing toward a therapeutic benefit of ABMMNC therapy, many questions remain unanswered: what is the ideal stem cell for therapy, the ideal mechanism of action (ie, secretion of growth factors and cytokines, cell-to-cell interactions), the lifespan of stem cells within the myocardium, and the duration of the therapeutic effect. Moreover, there remains concern about the potential toxicity of such therapy, eg, the possibility of creating a chronic pro-arrhythmic state, pro-inflammatory state, or both. To help answer these questions, we report here on the safety and efficacy of ABMMNC injection at 6 and 12 months of follow-up.
This is a prospective, nonrandomized, open-label study of 23 patients with severe ischemic heart failure and no other option for standard revascularization therapies. Patients were enrolled sequentially, with the first 14 patients being assigned to the treatment group and the last 9 patients assigned to the control group. In accordance with the ethics committee’s recommendations, an initial group of 4 patients was enrolled in a safety study. After 4 months of follow-up of the initially injected patients (once safety had been determined), the remaining study patients were enrolled. All patients were placed on maximally tolerated medical therapy at time of enrollment. The following inclusion criteria were required for patient enrollment: (1) chronic CAD with reversible perfusion defect detectable by SPECT; (2) LV ejection fraction (EF) <40%; (3) ineligibility for percutaneous or surgical revascularization, as assessed by coronary arteriography; and (4) signed, informed consent. Ineligibility for surgical or percutaneous revascularization procedures was determined by 2 expert committees: a surgical committee comprising 2 cardiovascular surgeons and 1 noninvasive cardiologist, and an interventional committee comprising 2 interventional cardiologists and 1 noninvasive cardiologist. Patients were not enrolled in the study if any one of the following exclusion criteria were met: (1) difficulty in obtaining vascular access for percutaneous procedures; (2) previous or current history of neoplasia or other comorbidity that could impact the patient’s short-term survival; (3) significant ventricular dysrhythmias (sustained ventricular tachycardia); (4) LV aneurysm; (5) unexplained baseline laboratory abnormalities; (6) bone tissue with abnormal radiological aspect; (7) primary hematologic disease; (8) acute myocardial infarction within 3 months of enrollment in the study; (9) presence of intraventricular thrombus as shown by 2-dimensional (2D) Doppler echocardiography; (10) hemodynamic instability at the time of the procedure; (11) atrial fibrillation; and (12) any condition that, in the judgment of the investigator, would place the patient at undue risk.
The ethics committee of Procardiaco Hospital (Rio de Janeiro) and the Brazilian National Research Ethics Council approved the study protocol.
Baseline evaluation in both groups included pertinent laboratory evaluations (complete blood count, C-reactive protein [CRP], brain natriuretic peptide [BNP], and serum creatinine levels), functional status (New York Heart Association and Canadian Cardiovascular Society Angina Score class), exercise testing (ramp treadmill protocol),14 dipyridamole SPECT perfusion scanning, and 2D echocardiography as previously described.13 Twenty-four-hour Holter monitoring and signal-averaged electrocardiography (SAECG) were also performed at baseline.
Bone Marrow Aspiration and Isolation of Mononuclear Cells
Approximately 4 hours before the cell injection procedure, bone marrow (50 mL) was aspirated under local anesthesia from the posterior iliac crest. ABMMNCs were isolated by density gradient in Ficoll-Paque Plus (Amersham Biosciences). Mononuclear cells were exhaustively washed with heparinized saline containing 5% human serum albumin and filtered through 100-μm nylon mesh to remove cell aggregates. The cells were finally resuspended in saline with 5% human serum albumin for injection.
A small fraction of the cell suspension was used for cell counting and viability testing by trypan blue exclusion. Cell viability was shown to be >90% (96.2±4.9%), assuring the quality of the cell suspension. Post-hoc characterization of leukocyte differentiation markers by flow cytometry and functional assays were performed on another fraction of cells. The clonogenic capacity of hematopoietic progenitors was evaluated by colony-forming assays (granulocyte-macrophage colony-forming unit) as previously described.15
A high correlation between granulocyte-macrophage colony-forming units and CD45loCD34+ cells was seen (Spearman r=0.77, P=0.0012). Fibroblast colony-forming unit assays were performed as previously described16 to determine the presence of putative progenitor mesenchymal lineages. Cultures of the clinically used cell preparations were grown and proved negative for bacterial and fungal contamination.
Antibodies and Staining Procedure for Fluorescence-Activated Cell Sorter Analysis
The following antibodies were either biotinylated or conjugated with FITC (Pharmingen), phycoerythrin, or PerCP: anti-CD45 as a pan-leukocyte marker (clone HI30), anti-CD34 as a hematopoietic progenitor marker (clone HPCA-II), anti-CD3 as a pan–T-cell marker (clone SK7), anti-CD4 as a T-cell subpopulation marker (clone SK3), and anti-CD8 as a T-cell subpopulation marker (clone SK1), from Becton Dickinson; anti-CD14 as a monocyte marker (clone TUK4), anti-CD19 as a pan–B-cell marker (clone SJ25-C1), and anti-CD56 as an NK-cell marker (clone NKI nbl-1), from Caltag Laboratories (Burlingame, Calif); and anti-HLA-DR (MHC-II, clone B8.12.2) from Beckman-Coulter. The biotinylated antibodies were revealed with streptavidin PECy7 (Caltag Laboratories). Three-color immunofluorescence analysis was used for the identification of leukocyte populations in total nucleated bone marrow cell suspensions. After staining, erythrocytes were lysed using the Becton Dickinson lysis buffer solution according to the manufacturer’s instructions, and CD45 antibody was used to assess the percentages of leukocytes in each sample. Data acquisition and analyses were performed on a Calibur fluorescence-activated cell sorter equipped with CellQuest 3.1 software (Becton Dickinson).
Transendocardial Delivery of Autologous Bone Marrow Mononuclear Cells
In the cell-injection treatment group, patients were taken to the cardiac catheterization laboratory ≈1 hour before the anticipated arrival of the bone marrow cells from the laboratory. Left heart catheterization with biplane left ventricular angiography was performed. Subsequently, electromechanical mapping (EMM) of the left ventricle was performed as previously described.17 The general region for treatment was selected by matching the area identified previously by SPECT perfusion imaging as ischemic. The electromechanical map was then used to target the specific treatment area by identifying viable myocardium (unipolar voltage ≥6.9 mV) within that region. Areas associated with decreased mechanical activity (local linear shortening <12%, indicating hibernating myocardium) were preferred.
The NOGA injection catheter was prepared by adjusting the needle extension at 0° and 90° flex and by placing 0.1 mL of ABMMNCs to fill the needle dead space. The injection catheter tip was placed across the aortic valve and into the target area, and each injection site was carefully evaluated before the cells were injected. Before every injection of cells into the LV wall, the following safety criteria had to be met to assure intramyocardial delivery: (1) perpendicular position of the catheter in relation to the LV wall; (2) excellent loop stability (<4 mm); (3) maximal needle extension of 6 mm; and (4) presence of a premature ventricular contraction (PVC) on extension of the needle into the myocardium.
Correlation of Bone Marrow Mononuclear Cell Subpopulation and Improvement in Reversible Perfusion Defects
For every treated patient, the size of the myocardial area injected (mm2), the absolute cell number injected, and the concentration of each specific cell phenotype (103 cells/mm2) were calculated and subsequently correlated with the reduction in total reversible defect as determined by quantitative SPECT (at baseline versus at 6 months) using exact Pearson moment correlation.
Two-Month, 6-Month, and 12-Month Follow-up Evaluations
All patients, both treated and control, underwent noninvasive follow-up evaluations at 2 and 6 months, which consisted of a repeat baseline laboratory evaluation, clinical evaluation, dipyridamole SPECT perfusion scanning, ramp treadmill protocol, 2D echocardiography, repeat 24-hour Holter monitoring, and SAECG. The same noninvasive follow-up evaluation protocol (except for Holter monitoring and SAECG) was performed at 12 months. Dipyridamole SPECT imaging studies were performed using the same stress procedure at baseline and at follow-up, as previously described.13 Studies were read by a blinded, experienced observer. The predicted Vo2max was used to tailor the patient workload. Treadmill speed was initially 0.5 mph, and inclination was 0% to 10% with a planned exercise duration of 10 minutes.18
The values of the continuous variables were presented as means and standard deviations; the values of the categorical variables were presented as percentages. Comparisons between the treated and control groups and comparisons between the 4 time points (baseline versus 2 months versus 6 months versus 12 months) were made using repeated-measures ANOVA. P≤0.05 was considered statistically significant.
One patient was lost to follow-up and did not undergo 6-month and 12-month evaluations. Patient demographics did not differ significantly between the treatment and control groups (Table 1). Neither did β-blocker, angiotensin-converting enzyme inhibitor, or nitrate use (Table 2).
The mean total procedural time for mapping and injection was 81±19 minutes. Electromechanical maps comprised an average of 89±9 points. Each injection of 2 million cells was delivered in a volume of 0.2 mL.
There were no major periprocedural complications. One patient had a transient episode of pulmonary edema that was easily reversed with loop diuretics after the procedure. No sustained arrhythmias were associated with the injection procedures, nor did any significant arrhythmias occur while the patients were hospitalized. All patients were discharged on the third hospital day as per protocol. As previously reported, 1 patient in the treatment group died at 14 weeks, presumably of sudden cardiac death. A second patient died at 11 months, presumably of a neurological cause.
White blood cell count (WBC), CRP, BNP, and serum creatinine levels at baseline, 2 months, 6 months, and 12 months are shown in Table 3. Of all baseline and follow-up laboratory values, only serum creatinine levels varied between the control and treatment groups at follow-up. Follow-up serum creatinine levels were significantly elevated in the control group as compared with the treatment group (P=0.04). The levels of CRP and WBC at baseline and follow-up were not significantly different between the 2 groups. There was a trend toward lower BNP levels in the treatment group at 12-month follow-up (P=0.08).
Two-Month, 6-Month, and 12-Month Follow-up Evaluations
At the 2-month follow-up, there was a significant improvement in symptoms (New York Heart Association and Canadian Cardiovascular Society Angina Score) in the treatment group as compared with the control group (Table 4). This improvement was maintained at 6 and 12 months in the treatment group as compared with the control group (Table 4).
Nuclear perfusion imaging studies in the treated and control groups were similar at baseline for the amount of total reversible defect and percent of rest defect with 50% activity (scar). At the 2-month follow-up, there was a significant reduction in myocardial ischemia in the treatment group as compared with the control group (Table 4). This improvement was maintained at 6 and 12 months (P=0.01), despite worsening of myocardial ischemia in the treatment group (Table 4).
Exercise capacity as assessed by metabolic equivalents and Vo2max was similar between the 2 groups at baseline. At the 2-month follow-up, there was a significant increase in exercise capacity, as measured in terms of metabolic equivalents and Vo2, in the treatment group as compared with the control group (Table 4). This significant improvement was maintained at 6 and 12 months, as exercise capacity improved slightly in the treatment group. There was no statistically significant difference between the 2 groups in terms of LVEF on the 2D echocardiogram over time (Table 4).
There were no sustained ventricular arrhythmias found by 24-hour Holter monitoring at baseline and follow-up and no significant differences in the number of PVCs at the 2- and 6-month follow-ups (Table 4). Nor were there significant differences in SAECG parameters at either follow-up (Table 4).
Correlation Between Bone Marrow Mononuclear Cell Subpopulations and Improvement in Reversible Perfusion Defects
Monocyte, B-cell, hematopoietic progenitor cell, and early hematopoietic progenitor cell subpopulations correlated with improvement in reversible perfusion defects at 6 months (Table 5). There was also a trend toward correlation between the fibroblast colony-forming unit subpopulation (progenitor mesenchymal cell phenotype) and improvement in reversible perfusion defects at 6 months (Table 5).
The results of our study suggest that injection of ABMMNCs is safe and improves perfusion and exercise capacity when viable ischemic areas of myocardium are targeted.
Preliminary evidence suggests that bone marrow progenitor cells may be involved in the process of postnatal physiological organ vascularization.19 Other evidence suggests that bone marrow-derived progenitor cells may be recruited to participate in the natural healing process that occurs after tissue injury and vascular trauma.20 Many preclinical studies have shown that the insertion of bone marrow mononuclear cells into ischemic myocardium can help re-establish tissue vascularization.3,4,6,7 Furthermore, pioneering clinical studies have preliminarily confirmed the therapeutic benefit of bone marrow mononuclear cell therapy after acute myocardial infarction or in the setting of chronic myocardial ischemia.8–13
Previous studies have shown that bone marrow cells can differentiate into cardiomyocytes and endothelial cells in vitro and in vivo.8,21 In theory, ABMMNCs could contribute to neoangiogenesis or myocardial tissue replacement (or both) and as a consequence improve myocardial perfusion or LV remodeling. Improvement in tissue vascularization may also result from the ability of bone marrow cells to secrete angiogenic factors. Additionally, bone marrow cell injections per se could elicit an inflammatory response that activates an angiogenic process. Although the mechanisms leading to a possible benefit are incompletely understood, the sustained improvement in perfusion that we have observed in the present study is intriguing.
The bone marrow mononuclear cell subset, which is quite heterogeneous, comprises mesenchymal stem cells, hematopoietic progenitor cells, endothelial progenitor cells, and more committed cell lineages such as natural killer lymphocytes, T lymphocytes, and B lymphocytes. There is much controversy regarding which stem cell subtype might be responsible for the therapeutic benefit of bone marrow mononuclear cell transplantation into ischemic myocardium.22 In the present study, several different subpopulations of ABMMNCs correlated with improvement in myocardial perfusion. The statistical correlation was excellent for monocytes (r=0.8), good for B cells (r=0.7), and moderate for both hematopoietic progenitor cells and early hematopoietic progenitor cells (r=0.6). It seems, therefore, that various bone marrow cell subpopulations may contribute to improved perfusion. More specifically, the present study results suggest that the bone marrow monocyte subpopulation might have an important role to play in the angiogenic process. This would be in agreement with preliminary evidence that endothelial progenitor cells are derived from the monocyte/macrophage subpopulation and that their angiogenic effects most likely result from growth factor secretion.23 Meanwhile, the contributions of cytokines and growth factors secreted by monocytes and hematopoietic progenitor cells, the intricacies of cell-to-cell interactions, and the fate of transplanted cells remain to be defined.
The homing of transplanted cells to the target ischemic area and their engraftment there are thought to be prerequisites for the therapeutic success of stem cell transplantation.22 The transendocardial route of delivery was chosen to maximize engraftment. EMM technology has been widely confirmed to be accurate for delineating and identifying scarred and viable myocardium and for differentiating degrees of infarct transmurality.17 EMM thus offers a theoretical benefit over surgical or intracoronary approaches because viability of the target site can be determined before each injection. Many treated sites targeted in this study were in areas of totally occluded epicardial vascular beds, making intracoronary delivery impossible. Furthermore, the potential for provoking ischemia by coronary manipulation was avoided.
The study population and the prospective assessment of exercise capacity in this study are unique. All patients had previously had myocardial infarction, had no other revascularization treatment options, and had compromised LV function (mean LVEF [treatment group], 30%). Whereas most of the studies described in the literature concern patients with preserved LVEF,9,11,12 our study concerns a high-risk subgroup within the population of patients with CAD. Thus, our findings might be of potential significance.
The transendocardial injection of ABMMNCs significantly improved exercise capacity, heart failure, and angina symptoms at the 2-month follow-up. Symptomatic improvement was significant and the increase in exercise capacity was sustained at 6 and 12 months, with the treatment group steadily improving and the control group remaining stable over time. In addition to the improved exercise capacity, the treatment group also showed a trend toward a lower mean BNP level at 12 months when compared with the control group (740 versus 507 pg/mL, respectively). BNP levels have been shown to be an important prognostic marker in heart failure patients.24 Heart failure patients with a Vo2max of <14 mL/kg per minute also have a higher long-term mortality.18,25 Thus, the increase in Vo2max (from 17.3 mL/kg per minute to 25.1 mL/kg per minute) and the trend toward improvement in BNP levels that were observed in the treated group at 12 months will be important if confirmed by larger studies.
The short-term safety of transendocardial injection of ABMMNCs13 or filtered ABMCs26 into ischemic myocardium has been demonstrated. However, the question of whether cell transplantation increases the potential for malignant arrhythmias has also been raised.5 ABMMNCs appear to offer the advantage of electrical stability because data from the present study showed no malignant arrhythmias on any 24-hour Holter monitoring studies, no change in the number of PVCs after ABMMNC injection, and no change in SAECG parameters. Neither serum CRP levels nor WBC counts were elevated at 6 and 12 months after transendocardial injection of ABMMNCs, suggesting that the injected cells did not elicit any important inflammatory response despite their potential for producing growth factors, cytokines, and other proinflammatory substances.
The major limitations of this study are the small number of patients enrolled and the study design, which limits any conclusions about efficacy. Because of ethics committee concerns, patients in the control group were not enrolled concurrently with treated patients and did not receive a placebo injection. However, treatment and control groups have had similar follow-up schedules up to 12 months. The benefits of cell therapy seen in this study could be attributable to the placebo effect seen in phase I trials. Potential biases include selection bias (eg, tertiary hospital population) and investigator bias, although SPECT, Holter monitoring, and treadmill studies were read blindly and both groups were matched in terms of demographics, baseline laboratory values, treadmill workload, and Vo2max. Similar reversible and fixed ischemic defects were present in both groups at baseline. In addition, the present study population was relatively young when compared with heart failure patients normally seen in clinical practice. This might limit the implications of the present study results because it is now known that the function of progenitor cells is age-dependent.27
In this initial prospective, nonrandomized, open-label study in patients with CAD, LV dysfunction, and no other revascularization treatment options, sustained improvement in exercise capacity and myocardial perfusion was noted 6 months and 12 months after transendocardial ABMMNC therapy, without any clinical evidence of significant harm from the procedure itself. Further investigation in larger, randomized trials is warranted.
↵*Drs Perin and Dohmann are co-principal investigators.
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