Bone marrow cells for cardiac repair

Abstract

Although mortality from myocardial infarction is decreasing in developed countries, the overall burden from cardiovascular disease remains enormous, and morbidity is likely to increase as aging patients survive longer [1Mathur A. Martin J.F. Stem cells and repair of the heart.Lancet. 2004; 364: 183-192Abstract Full Text Full Text PDF PubMed Scopus (216) Google Scholar]. Therapies that can offer even partial restoration of organ function are likely to be pursued with alacrity. There is widespread belief that bone marrow-derived cells may provide an attractive and relatively inexpensive alternative or adjunct to the pharmaceutical or surgical management of heart disease. Interest in the cell therapy of heart disease was initially stimulated by evidence that autologous skeletal myoblasts could differentiate into striated muscle in damaged myocardium and improve cardiac function in animal models [2Murry C.E. Wiseman R.W. Schwartz S.M. Hauschka S.D. Skeletal myoblast transplantation for repair of myocardial necrosis.J Clin Invest. 1996; 98: 2512-2523Crossref PubMed Scopus (546) Google Scholar, 3Atkins B.Z. Hueman M.T. Meuchel J.M. Cottman M.J. Hutcheson K.A. Taylor D.A. Myogenic cell transplantation improves in vivo regional performance in infarcted rabbit myocardium.J Heart Lung Transplant. 1999; 18: 1173-1180Abstract Full Text Full Text PDF PubMed Scopus (106) Google Scholar] and patients [4Menasche P. Hagege A.A. Vilquin J.T. et al.Autologous skeletal myoblast transplantation for severe postinfarction left ventricular dysfunction.J Am Coll Cardiol. 2003; 41: 1078-1083Abstract Full Text Full Text PDF PubMed Scopus (1009) Google Scholar]. These studies have led to an ongoing prospective randomized trial of autologous human skeletal myoblasts. Interest increased to enthusiasm when Orlic et al. [5Orlic D. Kajstura J. Chimenti S. Bodine D.M. Leri A. Anversa P. Bone marrow stem cells regenerate infarcted myocardium.Pediatr Transplant. 2003; 3: 86-88Crossref Scopus (236) Google Scholar], using a murine myocardial infarct model, showed that the direct intramyocardial injection of lineage-depleted c-kit+ bone marrow cells led to improved hemodynamic function and the presence of green fluorescent protein-marked cardiomyocytes and vascular structures in the damaged myocardium. Since then, numerous animal models have been investigated, and several clinical studies, including a prospective randomized trial, have been reported. Although it is perhaps too early to provide definitive outcomes, these laboratory and clinical studies have raised additional, and sometimes perplexing, questions. In most cases, investigators have used transgenic mouse models with marked hematopoietic cells to assess the effect on and fate of the cell population of interest. Differences in outcome may, in part, be explained by wide variations in technique. For example, 2 different murine models of myocardial infarction have been used: the fixed occlusion of a coronary artery and an ischemia/reperfusion approach that better mimics human pathophysiology. The timing and routes of the administration of the cells (Table 1) also vary from study to study and may be critical determinants of outcome. Moreover, a variety of cell types have been administered and prepared under different culture conditions (Table 2).Table 1Routes of Administration in Laboratory and Clinical StudiesIntramyocardial (into border zone of infarct or into scar), direct during CABG or percutaneouslyTransendocardial (requires electromechanical mapping technique) (NOGA)IntracoronaryIntravenousStem cell mobilization by cytokines (G-CSF)CABG indicates coronary artery bypass grafting; G-CSF, granulocyte colony-stimulating factor. Open table in a new tab Table 2Cell Types AdministeredUnmanipulated bone marrow cellsCultured mononuclear bone marrow-derived cellsAdherent bone marrow-derived cellsBone marrow stromal cellsPeripheral blood-derived mononuclear cellsG-CSF-mobilized peripheral blood cellsCD133-enriched G-CSF-mobilized peripheral blood cellsCD34+ bone marrow cellsLin− c-kit+ Sca 1+ cellsLin− c-kit+ cellsG-CSF indicates granulocyte colony-stimulating factor. Open table in a new tab CABG indicates coronary artery bypass grafting; G-CSF, granulocyte colony-stimulating factor. G-CSF indicates granulocyte colony-stimulating factor. The observation of engraftment of hematopoietic cells at sites of ischemic myocardium remains controversial. Whereas some investigators have observed significant levels of engraftment [5Orlic D. Kajstura J. Chimenti S. Bodine D.M. Leri A. Anversa P. Bone marrow stem cells regenerate infarcted myocardium.Pediatr Transplant. 2003; 3: 86-88Crossref Scopus (236) Google Scholar, 6Orlic D. Kajstura J. Chimenti S. et al.Mobilized bone marrow cells repair the infarcted heart, improving function and survival.Proc Natl Acad Sci U S A. 2001; 18: 10344-10349Crossref Scopus (1924) Google Scholar, 7Jackson K.A. Majka S.M. Wang H. et al.Regeneration of ischemic cardiac muscle and vascular endothelium by adult stem cells.J Clin Invest. 2001; 107: 1395-1402Crossref PubMed Scopus (1760) Google Scholar], although what distinguishes directed homing and physiologic engraftment from passive adhesion and trapping is not clearly addressed in the literature, others have not detected significant levels of hematopoietic cells in the injured myocardium [8Agbulut O. Vandervelde S. Al Attar N. et al.Comparison of human skeletal myoblasts and bone marrow-derived CD133+ progenitors for the repair of infarcted myocardium.J Am Coll Cardiol. 2004; 44: 458-463Abstract Full Text Full Text PDF PubMed Scopus (127) Google Scholar, 9Murry C.E. Soonpaa M.H. Reinecke H. et al.Haematopoietic stem cells do not transdifferentiate into cardiac myocytes in myocardial infarcts.Nature. 2004; 428: 664-668Crossref PubMed Scopus (1886) Google Scholar, 10Balsam L.B. Wagers A.J. Christensen J.L. Kofidis T. Welssman I.L. Robbins R.C. Haematopoietic stem cells adopt mature haematopoietic fates in ischaemic myocardium.Nature. 2004; 428: 668-673Crossref PubMed Scopus (1524) Google Scholar]. Perhaps even more controversial is the issue of the differentiation of hematopoietic cells into cardiomyocytes. Several investigators have documented the acquisition of cardiomyocyte characteristics in hematopoietic cells that have lodged at sites of myocardial ischemia [5Orlic D. Kajstura J. Chimenti S. Bodine D.M. Leri A. Anversa P. Bone marrow stem cells regenerate infarcted myocardium.Pediatr Transplant. 2003; 3: 86-88Crossref Scopus (236) Google Scholar, 6Orlic D. Kajstura J. Chimenti S. et al.Mobilized bone marrow cells repair the infarcted heart, improving function and survival.Proc Natl Acad Sci U S A. 2001; 18: 10344-10349Crossref Scopus (1924) Google Scholar, 7Jackson K.A. Majka S.M. Wang H. et al.Regeneration of ischemic cardiac muscle and vascular endothelium by adult stem cells.J Clin Invest. 2001; 107: 1395-1402Crossref PubMed Scopus (1760) Google Scholar]. This is consistent with the observation that up to 16% of cardiomyocytes in male cardiac transplant recipients of female hearts are derived from recipient male cells, by using the Y-chromosome as a marker [11Quaini F. Urbanek K. Beltrami A.P. et al.Chimerism of the transplanted heart.N Engl J Med. 2002; 346: 5-15Crossref PubMed Scopus (1110) Google Scholar]. Also, cardiomyocytes of male origin have been documented in females undergoing allotransplantation with male donor marrow, albeit at lower levels (0.23%) [12Deb A. Wang S. Skelding K.A. Miller D. Simper D. Caplice N.M. Bone marrow-derived cardiomyocytes are present in adult human heart a study of gender-mismatched bone marrow transplantation patients.Circulation. 2003; 107: 1247-1249Crossref PubMed Scopus (345) Google Scholar]. Nevertheless, a recent and particularly careful study with a murine transgenic experimental myocardial infarct model failed to find any evidence of transdifferentiation of hematopoietic stem cells into cardiomyocytes [9Murry C.E. Soonpaa M.H. Reinecke H. et al.Haematopoietic stem cells do not transdifferentiate into cardiac myocytes in myocardial infarcts.Nature. 2004; 428: 664-668Crossref PubMed Scopus (1886) Google Scholar]. In that study, the marker was the nuclear localized β-galactosidase reporter driven by the cardiac-specific α-myosin heavy-chain gene promoter. Consequently, detection of transdifferentiated hematopoietic cells did not rely on an immunofluorescence readout and hence was not subject to the potentially confounding feature of autofluorescence that could lead to a false-positive result. Another study found low levels of marker-positive (green fluorescent protein-positive) cells that did not express cardiac specific markers but retained the CD45 antigen [10Balsam L.B. Wagers A.J. Christensen J.L. Kofidis T. Welssman I.L. Robbins R.C. Haematopoietic stem cells adopt mature haematopoietic fates in ischaemic myocardium.Nature. 2004; 428: 668-673Crossref PubMed Scopus (1524) Google Scholar]. A possible explanation for the presence of cardiomyocytes derived from hematopoietic cells is cell fusion. Although the sex-mismatched allotransplant study failed to find any evidence of cell fusion between host cardiomyocytes and donor hematopoietic cells at a frequency of less than 1 in 368, another study demonstrated in vitro cell fusion between mouse bone marrow cells and male embryonic stem cells [13Terada N. Hamazaki T. Oka M. et al.Bone marrow cells adopt the phenotype of other cells by spontaneous cell fusion.Nature. 2002; 416: 542-545Crossref PubMed Scopus (1756) Google Scholar]. In an elegant study using the Cre/lox recombination technique, Alvarez-Dolado et al. [14Alvarez-Dolado M. Pardal R. Garcia-Verdugo J.M. et al.Fusion of bone-marrow-derived cells with Purkinje neurons, cardiomyocytes and hepatocytes.Nature. 2003; 425: 968-973Crossref PubMed Scopus (1411) Google Scholar] showed that bone marrow-derived cells can fuse spontaneously with cardiomyocytes in vivo at levels of up to 0.9%. Controversies regarding the frequency and origin of the cells lodging in ischemic myocardium notwithstanding, many studies confirm improvement in hemodynamic parameters—especially left ventricular function—after treatment with a variety of hematopoietic and other cells (including bone marrow stromal cells) in experimental myocardial infarct models [5Orlic D. Kajstura J. Chimenti S. Bodine D.M. Leri A. Anversa P. Bone marrow stem cells regenerate infarcted myocardium.Pediatr Transplant. 2003; 3: 86-88Crossref Scopus (236) Google Scholar, 8Agbulut O. Vandervelde S. Al Attar N. et al.Comparison of human skeletal myoblasts and bone marrow-derived CD133+ progenitors for the repair of infarcted myocardium.J Am Coll Cardiol. 2004; 44: 458-463Abstract Full Text Full Text PDF PubMed Scopus (127) Google Scholar, 14Alvarez-Dolado M. Pardal R. Garcia-Verdugo J.M. et al.Fusion of bone-marrow-derived cells with Purkinje neurons, cardiomyocytes and hepatocytes.Nature. 2003; 425: 968-973Crossref PubMed Scopus (1411) Google Scholar, 15Thompson R.B. Emani S.M. Davis B.H. et al.Comparison of intracardiac cell transplantation autologous skeletal myoblasts versus bone marrow cells.Circulation. 2003; 108: II264-II271Crossref PubMed Google Scholar]. There seems to be a consensus that improvement in cardiac function is unlikely to be the result of the relatively low frequency of lodged or engrafted cells. A number of possible explanations have been offered, although without compelling evidence, for the beneficial effect, and these are listed in Table 3.Table 3Possible Explanations for Improved Cardiac Function after Administration of Bone Marrow-Derived CellsNeovascularizationParacrine effect: cytokine/chemokine releaseExtracellular matrix remodelingRecruitment of endogenous stem cellsEngraftment/differentiation/cell fusion of administered cells Open table in a new tab At least 9 small clinical trials investigating more than 100 patients receiving bone marrow-derived cells have been reported and are summarized in Table 4. Several conclusions emerge from an appraisal of these studies. First, acute complication rates seem very low, although the number of subjects in any given study is small and long-term follow-up has yet to be reported for any trial. Second, uncertainty remains regarding the importance of a host of variables regarding outcome. These variables include the route of cell delivery and the optimum timing after myocardial infarction for the cells to be delivered. Which cell type and cell dose give the best results remains unknown. In the pilot and phase I studies that have been reported to date, the measurement of outcome has appropriately focused on acute toxicity and changes in global left ventricular function. It remains unknown whether the beneficial effects observed in some of the trials are sustained or predict clinically important outcomes, such as a reduction in mortality after acute myocardial infarction or a lower incidence of severe congestive cardiomyopathy. These outcomes must await the results of phase II/III trials and, especially, prospective, randomized, and (preferably) blinded studies, with which the cardiology community is very familiar. Finally, the time is approaching for groups to develop multicenter studies that can address some of these critical issues that will better and more rapidly determine the appropriate role of therapy with bone marrow-derived cells in cardiac regeneration.Table 4Clinical Trial SummaryStudySample SizeRoute of DeliveryCell TypeOutcomeComplicationsCommentHamano 2001 [16Hamano K. Nishida M. Hirata K. et al.Local implantation of autologous bone marrow cells for therapeutic angiogenesis in patients with ischemic heart disease clinical trial and preliminary results.Jpn Circ J. 2001; 65: 845-847Crossref PubMed Scopus (324) Google Scholar]5Intramyocardial injection during CABGBM mononuclear cellsImproved coronary perfusion in 3 of 5 at 1 yNoneCABG confounding factor; results compared with 30 historical controlsStrauer 2002 [17Strauer B.E. Brehm M. Zeus T. et al.Repair of infarcted myocardium by autologous intracoronary mononuclear bone marrow cell transplantation in humans.Circulation. 2002; 106: 1913-1918Crossref PubMed Scopus (1930) Google Scholar]10Intracoronary via balloon catheter 7–8 days after MICultured BM mononuclear cellsReduced infarct size, improved wall motion, and LVE systolic volume compared with 10 historical controls at 3 moNoneComparison with historical controlsAssmus 2002 [18Assmus B. Schachinger V. Teupe C. et al.Transplantation of progenitor cells and regeneration enhancement in acute myocardial infarction (TOPCARE-AMI).Circulation. 2002; 106: 3009-3017Crossref PubMed Scopus (2000) Google Scholar]20Angioplasty and stenting followed by intracoronary infusion 3–4 d after MIBM mononuclear cells (n = 9) versus peripheral blood mononuclear cells cultured for 3 d (n = 11)Improved global LVEF and regional wall motion and reduced end-systolic LV volume. No difference between BM and PB cellsNoneCompared with 11 patients matched for EF, infarct size, and localizationStamm 2003 [19Stamm C. Westphal B. Kleine H.D. et al.Autologous bone marrow stem cell transplantation for myocardial regeneration.Lancet. 2003; 361: 45-46Abstract Full Text Full Text PDF PubMed Scopus (1226) Google Scholar]6CABG and intramyocardial injection >10 d to <3 months after MIBM mononuclear cells positively selected for AC133+ fraction containing some CD34− cellsGlobal LV function improved in 4 and infarct tissue perfusion improved in 5, 3–9 mo later2-wk supraventricular arrythmiasCABG a confounding factor; specific role of AC133+ cells unknownTse 2003 [20Tse H.F. Kwong Y.L. Chan J.K.F. Lo G. Ho C.L. Lau C.P. Angiogenesis in ischaemic myocardium by intramyocardial autologous bone marrow mononuclear cell implantation.Lancet. 2003; 361: 47-49Abstract Full Text Full Text PDF PubMed Scopus (785) Google Scholar]8Electromechanical mapping guided by percutaneous catheter-mediated transendocardial injection in patients with refractory stable anginaBM mononuclear cellsImproved regional wall thickening and wall motion and percentage of area of hypoperfused myocardium at 90 dNoneSmall pilot (no control group)Perin 2003 [21Perin E.C. Dohmann H.F. Borojevic R. et al.Transendocardial, autologous bone marrow cell transplantation for severe, chronic ischemic heart failure.Circulation. 2003; 107: 2294-2302Crossref PubMed Scopus (1150) Google Scholar]14Transendocardial delivery by catheter and NOGA mapping in patients with end-stage ischemic heart diseaseBM mononuclear cellsImproved global LV function at 2 mo and improved EF (20%–29%) and reduced end-systolic volume at 4 moOne patient died suddenly at 14 wkResults compared with 7 control patientsFuchs 2003 [22Fuchs S. Satler L.F. Kornowski R. et al.Catheter based autologous bone marrow myocardial injection in no-option patients with advanced coronary artery disease.J Am Coll Cardiol. 2003; 41: 1721-1724Abstract Full Text Full Text PDF PubMed Scopus (368) Google Scholar]10Transendocardial injection with electromechanical guidance in patients with refractory severe symptomatic chronic myocardial ischemiaFiltered unfractionated BM cells.Improvement in CCS angina score and stress induced ischemia but not treadmill exercise duration at 3 moNone (2 patients readmitted for pain)Pilot study (no control group)Kang 2004 [23Kang H.J. Kim H.S. Zhang S.Y. et al.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: 751-756Abstract Full Text Full Text PDF PubMed Scopus (851) Google Scholar]27 randomized to cell infusion (n = 10), G-CSF (n = 10), control (n = 7); only 11 evaluable (7, 3, 1, respectively)Intracoronary infusion in post-MI patients undergoing percutaneous coronary intervention and stentingRandomized to G-CSF alone versus G-CSF-mobilized mononuclear PB cellsImproved myocardial perfusion and LVEF at 6 mo7 of 11 patients exhibited re-stenosisInterpretation problematic because of small numbersWollert (BOOST Trial) 2004 [24Wollert K.C. Meyer G.P. Lotz J. et al.Intracoronary autologous bone marrow cell transfer after myocardial infarction the BOOST randomised controlled clinical trial.Lancet. 2004; 364: 141-148Abstract Full Text Full Text PDF PubMed Scopus (1974) Google Scholar]Randomized trial of BM cells (n = 30) versus optimum postinfarction treatment (n = 30)Intracoronary infusion of unfractionated BM cells 4–8 d after successful percutaneous coronary intervention and stentingUnfractionated BM cellsLVEF improved (6.7 versus 0.7%)NoneRandomized trial Open table in a new tab There are well-established precedents that the investigation of potentially effective therapy need not be delayed until definitive mechanisms of action are elucidated. For example, embarking on a large study to address the role of unfractionated BM cells would seem reasonable, despite our lack of knowledge of how the cells improve cardiac function. Nevertheless, given the lack of preclinical data correlating levels of donor cell engraftment at sites of ischemic myocardium with myocardial function and the recent report of a lack, not only of hematopoietically derived cardiomyocytes, but of the engraftment of hematopoietic donor cells themselves [9Murry C.E. Soonpaa M.H. Reinecke H. et al.Haematopoietic stem cells do not transdifferentiate into cardiac myocytes in myocardial infarcts.Nature. 2004; 428: 664-668Crossref PubMed Scopus (1886) Google Scholar], a re-evaluation is in order. Preclinical studies that correlate cardiac function end points with cell types and frequencies would be valuable. Control experiments that evaluate potential paracrine effects of the cells are also needed. Transgenic and xenogeneic animal models are available to address these issues, and the results will allow us to design more pertinent clinical trials.