Bone Marrow-Derived B Cells Preserve Ventricular Function After Acute Myocardial Infarction

ObjectivesIn view of evidence that mature cells play a role in modulating the stem cell niche and thereby stem cell potential and proliferation, we hypothesized that a mature bone marrow (BM) mononuclear cell (MNC) infusion subfraction may have particular potency in promoting hematopoietic or resident stem cell-induced cardiac repair post-infarction.BackgroundTreatment of acute myocardial infarction (MI) with BM MNC infusion has shown promise for improving patient outcomes. However, clinical data are conflicting, and demonstrate modest improvements. BM MNCs consist of different subpopulations including stem cells, progenitors, and differentiated leukocytes.MethodsStem cells (c-kit+) and subsets of mature cells including myeloid lineage, B and T-cells were isolated from bone marrow harvested from isogeneic donor rats. Recipient rats had baseline echocardiography then coronary artery ligation; 1 × 106 cells (enriched subpopulations or combinations of subpopulations of BM MNC) or saline was injected into ischemic and ischemic border zones. Cell subpopulations were either injected fresh or after overnight culture. After 2 weeks, animals underwent follow-up echocardiography. Cardiac tissue was assayed for cardiomyocyte proliferation and apoptosis.ResultsFractional ventricular diameter shortening was significantly improved compared with saline (38 ± 3.2%) when B cells alone were injected fresh (44 ± 3.0%, p = 0.035), or after overnight culture (51 ± 2.9%, p < 0.001), or after culture with c-kit+ cells (44 ± 2.4%, p = 0.062). B cells reduced apoptosis at 48 h after injection compared with control cells (5.7 ± 1.2% vs. 12.6 ± 2.0%, p = 0.005).ConclusionsIntramyocardial injection of B cells into early post-ischemic myocardium preserved cardiac function by cardiomyocyte salvage. Other BM MNC subtypes were either ineffective or suppressed cardioprotection conferred by an enriched B cell population.