Original Contribution
Intracoronary Transplantation of Autologous Bone Marrow Mesenchymal Stem Cells for Ischemic Cardiomyopathy Due to Isolated Chron
November 2006
Myocardial infarction is the leading cause of congestive heart failure (CHF) and death in developed western countries and in China as well. The current pharmacotherapy for CHF includes neurohormonal inhibition with beta-blockers and angiotensin-converting enzyme inhibitors, both of which can improve clinical outcomes by limiting left ventricular remodeling.1 Other treatments such as percutaneous coronary intervention (PCI) and coronary artery bypass graft surgery (CABG) are limited in preventing ventricular remodeling because they cannot repair or replace damaged myocardium.2 Heart transplantation, however, is associated with high morbidity and mortality, followed by immunosuppressive drug usage and lower survival rates,3 and is not considered a conventional clinical therapeutic method. Cellular cardiomyoblast, the replacement or regeneration of cardiomyocytes through cell transplantation, may decrease remodeling of the left ventricle after ischemia or infarction and can improve clinical prognosis.4 Experimental and clinical studies have shown that several different seed cells (donor cells) may replace necrotic myocardium and improve left ventricular function in both the acute and chronic phases of myocardial infarction.5–7
The ideal seed cell is a subject of intense scientific, ethical and political debate. Human adult mesenchymal stem cells are accessible from the bone marrow and peripheral blood, allowing autologous transplantation. These stem cells are pluripotent cells and can differentiate into special tissues, such as cardiomyocytes, endothelial cells, and smooth-muscle cells.8–10 Mesenchymal stem cell transplantation eliminates the need for immunosuppression, even when allogenic stem cells are used. Previous studies have shown that implantation of autologous or allogenic swine mesenchymal stem cells after myocardial infarction can sustain engraftment in the host myocardium, differentiate into cardiomyocytes, maintain wall thickness, reduce ventricular remodeling and improve cardiac function.11,12 Chen et al13 reported improvement in cardiac function of infarcted myocardium with intracoronary transplantation of human mesenchymal stem cells identified by noninvasive and cardiac electromechanical mapping. Mesenchymal stem cells seem to be superior to other seed cells because there is no ethical limitation. However, the culture and expansion of mesenchymal stem cells requires an extended period of time.
Several clinical studies confirm the improvement of cardiac function after the transplantation of bone marrow mononuclear cells in patients with chronic ischemic cardiomyopathy. There is still controversy in angiogenesis after transplantation of bone marrow-derived stem cells.14–16 Many important fundamental issues regarding stem cell transplantation still remains unanswered. One of these is the usefulness of bone marrow-derived mesenchymal stem cell transplantation and another is the feasibility for chronic ischemic cardiomyopathy. This prospective study attempts to answer these questions.
Methods
Patient population. This is a prospective, randomized study conducted from October 2003 to January 2005 and involved 48 patients with severe ischemic heart failure due to an isolated chronic occluded left anterior descending artery (LAD). Patients were randomly divided into two groups. After the study protocol was approved by the ethics committee of Nanjing First hospital and Nanjing Medical University, 24 patients were placed in a group that used stem cell implantation, and another 24 patients were used as a control group without cell therapy. Initially, 2 patients were enrolled for a safety study and after 3 months of follow up, the remaining study patients began to enroll. All patients were placed on maximum medical therapy at the time of their enrollment. The inclusion criteria were: (1) isolated, chronic, total or subtotal occluded LAD due to previous anterior wall infarction untreated by either thrombolysis or primary PCI; (2) reversible perfusion defect detectable by single-photon emission computed tomography (SPECT); (3) left ventricular ejection fraction (LVEF) Percutaneous coronary intervention. PCI was carried out in all hemodynamically stable patients after they were placed under maximum medication. Heparin 10,000 IU was injected through the side arm of the arterial sheath after successful puncture. A special guiding catheter was engaged in the ostial left coronary artery. A stepwise choice of guidewires was made, beginning with the Cross-It® 100 (Guidant Corp., Indianapolis, Indiana) or the PT Graphix (Boston Scientific Corp., Natick, Massachusetts), to the Cross-It® 200, the Crosswire-NT and the Conquest guidewire (Terumo Medical, Japan) in attempts to cross the occluded lesions. If PCI failed, patients were sent to surgery and were excluded from this study. Stents were deployed in all patients after balloon inflation if residual stenosis was > 20%. The stent-to-artery ratio was 1.1:1. Postdilatation with a high-pressure, noncompliant balloon was performed for all drug-eluting stents. After the procedure, patients were monitored in the coronary care unit for 7 days.
Culture and transplantation of bone marrow mesenchymal stem cells. Sixty milliliters of autologous bone marrow were aspirated under local anesthesia from the ilium of all patients during the morning of the eighth day after the PCI procedure, and were then cultured for 7 days. Culture and transplantation of bone marrow mesenchymal stem cells were carried out using our previously described methods.13 Bone marrow mesenchymal stem cells were harvested and washed three to four times with heparinized saline. Two hours before transplantation, the stem cell suspension was mixed with heparin, filtered and prepared for implantation. Each milliliter of the final stem cell suspension had over 5 x 106 cells. A small fraction of the cell suspension was used for cell counting and viability testing by trypan blue exclusion. Cell viability was > 92%, assuring the quality of the cell suspension.
The LAD was occluded at the proximal edge of the previously placed stent as described by Chen et al.13 The bone marrow mesenchymal stem cell suspension, containing 5 x 106 cells, was directly injected through an inflated over-the-wire balloon catheter at high pressure (1 MPa) into the target coronary artery. The balloon was continuously inflated for at least two minutes to occlude the anterior blood flow (Figure 1).
Clinical evaluation. All patients went through a noninvasive evaluation at baseline, 7 days, 1, 3, 6, 9 and 12 months, which consisted of a complete clinical investigation, laboratory evaluation, chest X-ray, exercise stress test with ramp treadmill protocol, 2-D Doppler echocardiogram, SPECT perfusion scan and metabolic images, and 24-hour Holter monitoring. Treadmill speed was initially 0.5 mph, and the inclination was increased from 0% to 10%.
Statistical analysis. The values of the continuous variables were expressed as mean and standard deviations; the values of the categorical variables were presented as percentages. Comparisons between the cell therapy and control groups and between the 6 time points (at baseline, 1, 3, 6, 9 and 12 months) were made using repeated measures ANOVA. A p-value p p 5–7,17–19 However, until now, no research has critically demonstrated that one kind of seed cell is better than the other. These reports on stem cell research cover all types of stem cells including fetal cardiomyocytes, skeletal myoblasts, endothelial progenitor cells, embryonic stem cells and adult mesenchymal cells. Given ethical and arrhythmogenic problems, fetal cardiomyocytes and skeletal myoblasts have gradually disappeared from clinical practice. Human embryonic stem cells are pluripotent cells and can differentiate into all cell types of the body, including cardiomyocytes, but with a much lower efficiency of conversion into cardiomyocytes compared with those of mice.20–22 As a result, the future application of human embryonic stem cells in clinical trials is limited because of their lack of availability and intense unresolved ethical and political issues. There are only two kinds of clinically used donor cells (endothelial progenitor cells and mesenchymal stem cells). These seed cells have stronger capacities to differentiate into myocardium in a damaged or infarcted region. After accumulating more experiences in the transplantation of mesenchymal stem cells or endothelial progenitor cells (EPC) for treatment of acute myocardial infarction, several researchers have prospectively studied the role of both EPC and fresh bone marrow-derived mononuclear cells in reducing left ventricular remodeling in patients with chronic ischemic hearts. Strauer et al14 reported that functional and metabolic regeneration of infarcted and chronically avital tissue was successfully achieved in humans through bone marrow mononuclear cell transplantations in 18 consecutive patients with chronic myocardial infarction. After 3 months, the infarct size of the cell therapy group was reduced by 30%, and global LVEF and infarcted wall movement velocity increased significantly, whereas no significant changes were observed in the control group. Similar results were obtained by Erbs et al15 who enrolled 26 patients with a chronic, totally occluded coronary artery. After recanalization of the artery, patients were randomly assigned to the blood-derived circulating progenitor cells (CPCs) group or control group. At 3 months, intracoronary transplantation of CPCs was conducted after successful PCI and resulted in an improvement of macro and microvascular function, contributing to the recruitment of hibernating myocardium. The uniform advantage of these studies was the reduced preparation time for stem cells in comparison with transplantation of bone marrow mesenchymal stem cells, which required more than 2 weeks to culture and expand.13 The extended preparation of mesenchymal stem cells is not a problem for patients with chronic myocardial infarction. Heeschen et al23 reported that bone marrow mononuclear cells, derived from patients with ischemic cardiomyopathy, have a significantly reduced migratory and colony-forming activity in vitro and a reduced neovascularization capacity in vivo, despite similar content of hematopoietic stem cells. This functional impairment of bone marrow mononuclear cells from patients with ischemic cardiomyopathy may limit their therapeutic potential for clinical cell therapy. Treatment of adult mesenchymal stem cells from abdominal subcutaneous fatty tissue with 5-azacytidine induced direct differentiation into cardiomyocytes in a rabbit model.24 Similarly, Tomita et al25 reported that bone marrow cells cultured with 5-azacytidine can differentiate into cardiac-like cells in vivo before injection. However, the role in the treatment of chronic ischemic cardiomyopathy is not entirely clear.
Our previous clinical study13 demonstrated that human bone marrow mesenchymal stem cells can improve the cardiac function in patients with acute myocardial infarction after successful PCI. The present study was designed to examine the effect of intracoronary injection of autologous bone marrow mesenchymal stem cells on cardiac function in patients with chronic ischemic cardiomyopathy. It demonstrated that mesenchymal stem cell transplantation improved cardiac function as assessed by ramp exercise, SPECT and echocardiography. Most importantly, some of these improvements were maintained throughout the entire period of follow up. Although the mortality in the stem cell group was lower when compared to the control group, there is not enough power in this study to definitively determine the mortality difference.
Study limitations. The present study has a small number of patients enrolled. About 70% of patients received drug-eluting stents. Since this study was performed in China, a country dominated by social medicine, ICD and follow-up angiography are not standard forms of practice because of the financial situation of individual patients. The impact of mortality and the true restenosis rate are unknown. It may affect the result of LV function and perfusion. The long-term effects that occur after mesenchymal stem cell injection will require further study.
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