Cell therapy for the repair of the mammalian heart

There are immense interests in utilising cell therapy for myocardial repair. Although bone marrow cells are the most extensively studied cell type to-date, evidences of the benefits of using these cells are conflicting. In this thesis, I explore the methodologies used for in-vitro and in-vivo studies of cell therapy, and define the potential of bone marrow cells for myocardial repair. I have identified a potential drawback with the use of green fluorescent protein for the cell therapy studies. The use of cardiac explants was also not suitable for my in-vitro studies of cell therapy. I further demonstrated that there were limitations in the current microscopic techniques used for identifying myocyte nucleus, and this can be a potential source of error in in-vivo studies in which myocyte nuclear events, such as proliferation, and transdifferentiation are evaluated. With this in mind, lineage tracing was used to show that bone marrow cells did not differentiate into myocytes when transplanted immediately after acute myocardial infarction. In addition, no functional improvement was also observed on echocardiography. To compliment my pre-clinical work, two randomised trials were conducted. The first trial showed that intramuscular or intracoronary injections of bone marrow cells into scarred myocardium did not contribute to any meaningful regeneration. The second trial investigated the potential cardioprotective paracrine effects of bone marrow cells, and showed that they did not provide additional cardioprotection when used as an adjunct during cardiopulmonary bypass. While these studies contributed to our understanding and planning of future work in this field, many key questions remain unanswered – whether bone marrow cells can truly benefit the heart, and if so, what are the mechanisms? When and to whom it should be given? Hopefully, my final study on novel biomarkers will eventually aid the identification of patients who will benefit from cell therapy

Lineage tracing of cardiac explant derived cells.

Aims Cultured cardiac explants produce a heterogeneous population of cells including a distinctive population of refractile cells described here as small round cardiac explant derived cells (EDCs). The aim of this study was to explore the source, morphology and cardiogenic potential of EDCs. Methods Transgenic MLC2v-Cre/ZEG, and actin-eGFP mice were used for lineage-tracing of EDCs in vitro and in vivo. C57B16 mice were used as cell transplant recipients of EDCs from transgenic hearts, as well as for the general characterisation of EDCs. The activation of cardiac-specific markers were analysed by: immunohistochemistry with bright field and immunofluorescent microscopy, electron microscopy, PCR and RT-PCR. Functional engraftment of transplanted cells was further investigated with calcium transient studies. Results Production of EDCs was highly dependent on the retention of blood-derived cells or factors in the cultured explants. These cells shared some characteristics of cardiac myocytes in vitro and survived engraftment in the adult heart in vivo. However, EDCs failed to differentiate into functional cardiac myocytes in vivo as demonstrated by the absence of stimulation-evoked intracellular calcium transients following transplantation into the peri-infarct zone. Conclusions This study highlights that positive identification based upon one parameter alone such as morphology or immunofluorescene is not adequate to identify the source, fate and function of adult cardiac explant derived cells

Randomized Controlled Trial of Intramuscular or Intracoronary Injection of Autologous Bone Marrow Cells into Scarred Myocardium

Introduction Previous studies on the transplantation of autologous bone marrow cells (BMC) in patients with chronic ischemic heart disease have focused on their effects on viable, peri-infarct tissue. We conducted a blinded, randomized controlled study to investigate whether intramuscular (IM) or intracoronary (IC) administration of BMC into non-viable scarred myocardium during coronary artery bypass grafting (CABG) improves contractile function of scar segments compared with CABG alone. Methods 63 elective CABG patients, with established myocardial scars diagnosed by dobutamine stress echocardiography (DSE) and confirmed at surgery, were randomized into control, IM or IC treatment groups. The BMC obtained at the time of surgery were injected into the middepth of the scar in the IM group or via the graft conduit supplying the scar in the IC group. Contractile function of the scar segments was assessed by DSE before and 6 months after treatment. Cardiac magnetic resonance imaging was also performed in the last 33 patients at the same time points. Results 12.5-29.4% of patients showed improved wall motion in at least one scar segment after BMC treatment but this effect was similar to that in the control group. Quantitatively, %systolic fractional thickening in scar segments did not improve with BMC administration. Scar transmurality, %infarct volume, left ventricular volumes and ejection fractions were also not improved by BMC. Discussion Autologous BMC, injected directly into the scar or the artery supplying the scar, do not improve contractility of non-viable scarred myocardium. Furthermore, BMC do not reduce scar size nor improve left ventricular function