Mechanisms of bone marrow-derived cell therapy in ischemic cardiomyopathy with left ventricular assist device bridge to transplant

Abstract

Background: Clinical trials report improvements in function and perfusion with direct injection of bone marrow cells into the hearts of patients with ischemic cardiomyopathy. Preclinical data suggest these cells improve vascular density, which would be expected to decrease fibrosis and inflammation.

Objectives: The goal of this study was to test the hypothesis that bone marrow stem cells (CD34+) will improve histological measurements of vascularity, fibrosis, and inflammation in human subjects undergoing left ventricular assist device (LVAD) placement as a bridge to cardiac transplantation.

Methods: Subjects with ischemic cardiomyopathy who were scheduled for placement of an LVAD as a bridge to transplantation underwent bone marrow aspiration the day before surgery; the bone marrow was processed into cell fractions (bone marrow mononuclear cells, CD34+, and CD34-). At LVAD implantation, all fractions and a saline control were injected epicardially into predetermined areas and each injection site marked. At the time of transplantation, injected areas were collected. Data were analyzed by paired Student t test comparing the effect of cell fractions injected within each subject.

Results: Six subjects completed the study. There were no statistically significant differences in complications with the procedure versus control subjects. Histological analysis indicated that myocardium injected with CD34+ cells had decreased density of endothelial cells compared to saline-injected myocardium. There were no significant differences in fibrosis or inflammation between groups; however, density of activated fibroblasts was decreased in both CD34+ and CD34- injected areas.

Conclusions: Tissue analysis does not support the hypothesis that bone marrow-derived CD34+ cells promote increased vascular tissue in humans with ischemic cardiomyopathy via direct injection.

Keywords: angiogenesis; cell therapy; heart failure; ischemia.

CENTRAL ILLUSTRATION Cell Therapy in the Human Heart

Injection of bone marrow fractions into the heart does not increase vascularity but may decrease activated fibroblasts and induce proliferation of resident cardiac cells in human subjects with end-stage heart disease and left ventricular assist device support.

FIGURE 1. Study Enrollment

Of the 18 originally excluded patients, 13 consented to safety data collection, serving as controls. BTT = bridge to transplantation LVAD; DT = destination therapy LVAD; IABP = intra-aortic balloon pump; IsCM = ischemic cardiomyopathy; LVAD = left ventricular assist device; OR = operating room.

FIGURE 2. Injection of CD34+ Cells: No Increased Endothelial Density

(A) Endothelial density quantified as percent positive area stained for CD31 (mean ± SE); *p = 0.02 versus saline (B–E) Representative sections of CD31 immunohistochemistry from a single subject. BMMC = bone marrow mononuclear cells.

FIGURE 3. Injection of Bone Marrow-derived Cells: No Decreased Fibrosis

(A) Cardiac fibrosis quantified as percent positive picrosirius red area (mean ± SE). (B) Changes in fibrosis in individual subjects A1-A6 by treatment group. Subject A5 is the only female subject. (C–F) Representative sections showing fibrosis for subjects A3 and A5 in saline and CD34+ injected tissue. Abbreviations as in Figure 2.

FIGURE 4. Effects of Bone Marrow-derived Cell Injection on Beneficial Remodeling

Plots represent the difference from saline-injected sample (mean ± SE) for (A) macrophages (CD68 positive); (B) activated fibroblasts (alpha-smooth muscle actin [αSMA] positive, exclusive of blood vessels; *p = 0.04 for CD34+ versus saline and p = 0.01 for CD34-depleted versus saline); and (C) proliferating cells (Ki-67 positive; *p = 0.08 versus saline). (D) Representative micrograph of Ki-67 immunohistochemistry in CD34+ cell injected tissue.

FIGURE 5. Effects of Bone Marrow-derived Cells and Cell Phenotype

The effects of bone marrow-derived cells may be independent of the injected cell phenotype as evidenced by (A and B) iron-positive cells in injected tissue, and (C–E) Pearson correlation coefficient between tissue injected with CD34+ versus CD34-depleted cell populations. Abbreviations as in Figure 4.