Stem cell therapy for end-stage heart failure: indispensable role for the cell?

Bone marrow-derived mesenchymal stromal cell treatment in patients with ischaemic heart failure: final 4-year follow-up of the MSC-HF trial

AIMS

The study assessed 4-year outcomes of intramyocardial injections of autologous bone marrow-derived mesenchymal stromal cells (MSCs) in patients with ischaemic heart failure.

METHODS AND RESULTS

The MSC-HF trial was a randomized, double-blind, placebo-controlled trial. Patients were randomized 2:1 to intramyocardial injections of MSCs or placebo. The primary endpoint was change in left ventricular end-systolic volume (LVESV), measured by magnetic resonance imaging or computed tomography. Sixty patients aged 30-80 years with ischaemic heart failure, New York Heart Association class II-III, left ventricular ejection fraction (LVEF) <45% and no further treatment options were randomized. Patients were followed clinically for 12 months and in addition 4-year data of hospitalizations and survival were retrieved. After 12 months, LVESV was significantly reduced in the MSC group and not in the placebo group, with difference between groups of 17.0 ± 16.2 mL (95% confidence interval 8.3-25.7, P = 0.0002). There were also significant improvements in LVEF of 6.2% (P < 0.0001), stroke volume of 16.1 mL (P < 0.0001) and myocardial mass (P = 0.009) between groups. A significant dose-response effect was also observed. Moreover, a significant reduction in the amount of scar tissue and quality of life score in the MSC group but not in the placebo group was observed. After 4 years, there were significantly fewer hospitalizations for angina in the MSC group and otherwise no differences in hospitalizations or survival. No side effects were identified.

CONCLUSIONS

Intramyocardial injections of autologous bone marrow-derived MSCs improved myocardial function and myocardial mass in patients with ischaemic heart failure.

Exosomes from Cardiomyocyte Progenitor Cells and Mesenchymal Stem Cells Stimulate Angiogenesis Via EMMPRIN

To date, cellular transplantation therapy has not yet fulfilled its high expectations for cardiac repair. A major limiting factor is lack of long-term engraftment of the transplanted cells. Interestingly, transplanted cells can positively affect their environment via secreted paracrine factors, among which are extracellular vesicles, including exosomes: small bi-lipid-layered vesicles containing proteins, mRNAs, and miRNAs. An exosome-based therapy will therefore relay a plethora of effects, without some of the limiting factors of cell therapy. Since cardiomyocyte progenitor cells (CMPC) and mesenchymal stem cells (MSC) induce vessel formation and are frequently investigated for cardiac-related therapies, the pro-angiogenic properties of CMPC and MSC-derived exosome-like vesicles are investigated. Both cell types secrete exosome-like vesicles, which are efficiently taken up by endothelial cells. Endothelial cell migration and vessel formation are stimulated by these exosomes in in vitro models, mediated via ERK/Akt-signaling. Additionally, these exosomes stimulated blood vessel formation into matrigel plugs. Analysis of pro-angiogenic factors revealed high levels of extracellular matrix metalloproteinase inducer (EMMPRIN). Knockdown of EMMPRIN on CMPCs leads to a diminished pro-angiogenic effect, both in vitro and in vivo. Therefore, CMPC and MSC exosomes have powerful pro-angiogenic effects, and this effect is largely mediated via the presence of EMMPRIN on exosomes.

Bone marrow-derived mesenchymal stromal cell treatment in patients with severe ischaemic heart failure: a randomized placebo-controlled trial (MSC-HF trial)

AIMS

Regenerative treatment with mesenchymal stromal cells (MSCs) has been promising in patients with ischaemic heart failure but needs confirmation in larger randomized trials. We aimed to study effects of intra-myocardial autologous bone marrow-derived MSC treatment in patients with severe ischaemic heart failure.

METHODS AND RESULTS

The MSC-HF trial is a randomized, double-blind, placebo-controlled trial. Patients were randomized 2 : 1 to intra-myocardial injections of MSC or placebo, respectively. The primary endpoint was change in left ventricular end-systolic volume (LVESV), measured by magnetic resonance imaging or computed tomography at 6 months follow-up. Sixty patients aged 30-80 years with severe ischaemic heart failure, New York Heart Association (NYHA) classes II-III, left ventricular ejection fraction (LVEF) <45% and no further treatment options were randomized. Fifty-five patients completed the 6-month follow-up (37 MSCs vs. 18 placebo). At 6 months, LVESV was reduced in the MSC group: -7.6 (95% CI -11.8 to -3.4) mL (P = 0.001), and increased in the placebo group: 5.4 (95% CI -0.4 to 11.2) mL (P = 0.07). The difference between groups was 13.0 (95% CI 5.9-20.1) mL (P = 0.001). Compared with placebo, there were also significant improvements in LVEF of 6.2% (P<0.0001), stroke volume of 18.4 mL (P < 0.0001), and myocardial mass of 5.7 g (P = 0.001). No differences were found in NYHA class, 6-min walking test and Kansas City cardiomyopathy questionnaire. No side effects were identified.

CONCLUSION

Intra-myocardial injections of autologous culture expanded MSCs were safe and improved myocardial function in patients with severe ischaemic heart failure.

STUDY REGISTRATION NUMBER

NCT00644410 (ClinicalTrials.gov).

Cardiac Repair and Regeneration: The Value of Cell Therapies

Ischaemic heart disease is the predominant contributor to cardiovascular morbidity and mortality; one million myocardial Infarctions occur per year in the USA, while more than five million patients suffer from chronic heart failure. Recently, heart failure has been singled out as an epidemic and is a staggering clinical and public health problem associated with significant mortality, morbidity and healthcare expenditures, particularly among those aged ≥65 years. Death rates have improved dramatically over the last four decades, but new approaches are nevertheless urgently needed for those patients who go on to develop ventricular dysfunction and chronic heart failure. Over the past decade, stem cell transplantation has emerged as a promising therapeutic strategy for acute or chronic ischaemic cardiomyopathy. Multiple candidate cell types have been used in preclinical animal models and in humans to repair or regenerate the injured heart, either directly or indirectly (through paracrine effects), including: embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs), neonatal cardiomyocytes, skeletal myoblasts (SKMs), endothelial progenitor cells, bone marrow mononuclear cells (BMMNCs), mesenchymal stem cells (MSCs) and, most recently, cardiac stem cells (CSCs). Although no consensus has emerged yet, the ideal cell type for the treatment of heart disease should: (a) improve heart function; (b) create healthy and functional cardiac muscle and vasculature, integrated into the host tissue; (c) be amenable to delivery by minimally invasive clinical methods; (d) be available 'off the shelf' as a standardised reagent; (e) be tolerated by the immune system; (f) be safe oncologically, i.e. not create tumours; and (g) circumvent societal ethical concerns. At present, it is not clear whether such a 'perfect' stem cell exists; what is apparent, however, is that some cell types are more promising than others. In this brief review, we provide ongoing data on agreement and controversy arising from clinical trials and touch upon the future directions of cell therapy for heart disease.

Nanotubular crosstalk with distressed cardiomyocytes stimulates the paracrine repair function of mesenchymal stem cells

Mesenchymal stem cells (MSC) are known to repair broken heart tissues primarily through a paracrine fashion while emerging evidence indicate that MSC can communicate with cardiomyocytes (CM) through tunneling nanotubes (TNT). Nevertheless, no link has been so far established between these two processes. Here, we addressed whether cell-to-cell communication processes between MSC and suffering cardiomyocytes and more particularly those involving TNT control the MSC paracrine regenerative function. In the attempt to mimic in vitro an injured heart microenvironment, we developed a species mismatch coculture system consisting of terminally differentiated CM from mouse in a distressed state and human multipotent adipose derived stem cells (hMADS). In this setting, we found that crosstalk between hMADS and CM through TNT altered the secretion by hMADS of cardioprotective soluble factors such as VEGF, HGF, SDF-1α, and MCP-3 and thereby maximized the capacity of stem cells to promote angiogenesis and chemotaxis of bone marrow multipotent cells. Additionally, engraftment experiments into mouse infarcted hearts revealed that in vitro preconditioning of hMADS with cardiomyocytes increased the cell therapy efficacy of naïve stem cells. In particular, in comparison with hearts treated with stem cells alone, those treated with cocultured ones exhibited greater cardiac function recovery associated with higher angiogenesis and homing of bone marrow progenitor cells at the infarction site. In conclusion, our findings established the first relationship between the paracrine regenerative action of MSC and the nanotubular crosstalk with CM and emphasize that ex vivo manipulation of these communication processes might be of interest for optimizing current cardiac cell therapies.

Cigarette smoke adversely affects functions and cell membrane integrity in c-kit+ cardiac stem cells

Cigarette smoking is a major risk factor for numerous diseases including cardiovascular diseases. Exposure to cigarette smoke (CS) leads to increased cardiovascular risk, myocardial injury, and mortality. Stem cell therapy is one of the promising therapeutic options available to treat myocardial injuries. Understanding the impact of cigarette smoke extract (CSE) on stem cell function would be valuable in determining the risk passed on during transplant. In this study, the impact of CSE on cardiac stem cell (CSC) functions was investigated using c-kit+ rat cardiac stem cells as the experimental model. Here, we hypothesized that CSE attenuates CSC membrane integrity, causes cytotoxicity, and affects many CSC functions via multiple mechanisms including modulation of extracellular stress-regulated kinase (ERK) (44/42) signaling and oxidative stress. The effects of CSE on CSCs were examined in vitro. Based on a published method, CSE was prepared. CSE-induced ERK signaling was detected by western blotting. CSE-induced modulation of catalase activity was also measured. Functional modulations due to CSE were examined via several methods including Apostain, BrdU, and LDH assays. In agreement with the CSE-induced activation of ERK, CSE-induced reduction in viability, migration, and increase in both cytotoxicity and para-cellular permeability were observed in CSCs. These results suggest that CSE impaired CSC responses that contribute to decreased ability of CSC to respond to stress or injury leading to exacerbation of the damage. Our findings will contribute to the understanding of the discipline and might contribute to the development of stem cell therapy approaches in the future.

Mesenchymal stem cell therapy for cardiac inflammation: immunomodulatory properties and the influence of toll-like receptors

BACKGROUND

After myocardial infarction (MI), the inflammatory response is indispensable for initiating reparatory processes. However, the intensity and duration of the inflammation cause additional damage to the already injured myocardium. Treatment with mesenchymal stem cells (MSC) upon MI positively affects cardiac function. This happens likely via a paracrine mechanism. As MSC are potent modulators of the immune system, this could influence this postinfarct immune response. Since MSC express toll-like receptors (TLR), danger signal (DAMP) produced after MI could influence their immunomodulatory properties.

SCOPE OF REVIEW

Not much is known about the direct immunomodulatory efficiency of MSC when injected in a strong inflammatory environment. This review focuses first on the interactions between MSC and the immune system. Subsequently, an overview is provided of the effects of DAMP-associated TLR activation on MSC and their immunomodulative properties after myocardial infarction.

MAJOR CONCLUSIONS

MSC can strongly influence most cell types of the immune system. TLR signaling can increase and decrease this immunomodulatory potential, depending on the available ligands. Although reports are inconsistent, TLR3 activation may boost immunomodulation by MSC, while TLR4 activation suppresses it.

GENERAL SIGNIFICANCE

Elucidating the effects of TLR activation on MSC could identify new preconditioning strategies which might improve their immunomodulative properties.

MicroRNAs in Cardiovascular Regenerative Medicine: Directing Tissue Repair and Cellular Differentiation

MicroRNAs (miRNAs) are a class of short noncoding RNA molecules, approximately 22 nucleotides in length, which regulate gene expression through inhibition of the translation of target genes. It is now generally accepted that miRNAs guide processes and cellular functions through precise titration of gene dosage, not only for a single gene but also controlling the levels of a large cohort of gene products. miRNA expression is altered in cardiovascular disease and may thereby limit and impair cardiovascular repair responses. Increasing evidence of the essential role of miRNAs in the self-renewal and differentiation of stem cells suggests the opportunity of using the modulation of miRNA levels or their function in directing cell transplantation, cell behavior, and thereby organ healing. In this paper, an overview of miRNA biogenesis and their way of action and different roles that miRNAs play during the myocardial responses to injury and upon cell transplantation will be provided. We focused on cardiomyocyte survival, angiogenesis, extracellular matrix production, and how miRNAs can direct cell plasticity of injected cells and thus drive differentiation for cardiovascular phenotypes, including vascular differentiation and cardiomyocyte differentiation.

Ultrastructural evidence of exosome secretion by progenitor cells in adult mouse myocardium and adult human cardiospheres

The demonstration of beneficial effects of cell therapy despite the persistence of only few transplanted cells in vivo suggests secreted factors may be the active component of this treatment. This so-called paracrine hypothesis is supported by observations that culture media conditioned by progenitor cells contain growth factors that mediate proangiogenic and cytoprotective effects. Cardiac progenitor cells in semi-suspension culture form spherical clusters (cardiospheres) that deliver paracrine signals to neighboring cells. A key component of paracrine secretion is exosomes, membrane vesicles that are stored intracellularly in endosomal compartments and are secreted when these structures fuse with the cell plasma membrane. Exosomes have been identified as the active component of proangiogenic effects of bone marrow CD34⁺ stem cells in mice and the regenerative effects of embryonic mesenchymal stem cells in infarcted hearts in pigs and mice. Here, we provide electron microscopic evidence of exosome secretion by progenitor cells in mouse myocardium and human cardiospheres. Exosomes are emerging as an attractive vector of paracrine signals delivered by progenitor cells. They can be stored as an “off-the-shelf” product. As such, exosomes have the potential for circumventing many of the limitations of viable cells for therapeutic applications in regenerative medicine.

Heterogeneity in SDF-1 expression defines the vasculogenic potential of adult cardiac progenitor cells

Rationale

The adult myocardium has been reported to harbor several classes of multipotent progenitor cells (CPCs) with tri-lineage differentiation potential. It is not clear whether c-kit+CPCs represent a uniform precursor population or a more complex mixture of cell types.

Objective

To characterize and understand vasculogenic heterogeneity within c-kit+presumptive cardiac progenitor cell populations.

Methods and Results

c-kit+, sca-1+ CPCs obtained from adult mouse left ventricle expressed stem cell-associated genes, including Oct-4 and Myc, and were self-renewing, pluripotent and clonogenic. Detailed single cell clonal analysis of 17 clones revealed that most (14/17) exhibited trilineage differentiation potential. However, striking morphological differences were observed among clones that were heritable and stable in long-term culture. 3 major groups were identified: round (7/17), flat or spindle-shaped (5/17) and stellate (5/17). Stellate morphology was predictive of vasculogenic differentiation in Matrigel. Genome-wide expression studies and bioinformatic analysis revealed clonally stable, heritable differences in stromal cell-derived factor-1 (SDF-1) expression that correlated strongly with stellate morphology and vasculogenic capacity. Endogenous SDF-1 production contributed directly to vasculogenic differentiation: both shRNA-mediated knockdown of SDF-1 and AMD3100, an antagonist of the SDF-1 receptor CXC chemokine Receptor-4 (CXCR4), reduced tube-forming capacity, while exogenous SDF-1 induced tube formation by 2 non-vasculogenic clones. CPCs producing SDF-1 were able to vascularize Matrigel dermal implants in vivo, while CPCs with low SDF-1 production were not.

Conclusions

Clonogenic c-kit+, sca-1+ CPCs are heterogeneous in morphology, gene expression patterns and differentiation potential. Clone-specific levels of SDF-1 expression both predict and promote development of a vasculogenic phenotype via a previously unreported autocrine mechanism.

Stem cell therapy for chronic heart failure: lessons from a 15-year experience

Although cell therapy has entered the clinical arena since 2000, its benefits are still controversial. This is partly due to a shift of the whole paradigm from the mere provision of new cells intended to replenish the pool of dead cardiomyocytes to the exploitation of the cell's paracrine effects to activate host-associated cytoprotective signalling pathways, particularly those involved in angiogenesis, prevention of apoptosis and possibly recruitment of endogenous cells capable to mature into functional cardiomyocytes. This review will discuss how these two basic mechanisms (direct donor cell-derived myocardial regeneration versus paracrine signalling) underlie the rational selection of cells in light of the target clinical indication, with a particular focus on chronic heart failure, and will emphasize the importance of optimizing cell delivery and survival to fully exploit the potential benefits of this novel approach to acute and chronic heart diseases.

Cardiomyocyte progenitor cell-derived exosomes stimulate migration of endothelial cells

Patients suffering from heart failure as a result of myocardial infarction are in need of heart transplantation. Unfortunately the number of donor hearts is very low and therefore new therapies are subject of investigation. Cell transplantation therapy upon myocardial infarction is a very promising strategy to replace the dead myocardium with viable cardiomyocytes, smooth muscle cells and endothelial cells, thereby reducing scarring and improving cardiac performance. Despite promising results, resulting in reduced infarct size and improved cardiac function on short term, only a few cells survive the ischemic milieu and are retained in the heart, thereby minimizing long-term effects. Although new capillaries and cardiomyocytes are formed around the infarcted area, only a small percentage of the transplanted cells can be detected months after myocardial infarction. This suggests the stimulation of an endogenous regenerative capacity of the heart upon cell transplantation, resulting from release of growth factor, cytokine and other paracrine molecules by the progenitor cells--the so-called paracrine hypothesis. Here, we focus on a relative new component of paracrine signalling, i.e. exosomes. We are interested in the release and function of exosomes derived from cardiac progenitor cells and studied their effects on the migratory capacity of endothelial cells.

Biology and applications of mesenchymal stem cells

Undifferentiated adult stem cells are responsible for cell replacement in adult organisms. Initially isolated from the bone marrow, they are now known to be distributed throughout the organism as a whole, with a perivascular location. They are defined by properties which include proliferation as adherent cells, a defined immunophenotype, and the capacity to differentiate in vitro into osteoblasts, adipocytes and chondroblasts. Mesenchymal stem cells (MSCs) are considered as one of the most promising cell types for therapeutic applications. Mechanisms responsible for this therapeutic role are not well understood, and may involve diferentiation or, as most evidences point out, paracrine activity. The ability to modulate the immune system opens a wide range of applications, mainly for autoimmune diseases and graft-versus-host disease. Preclinical and clinical studies show promising results, but controversial results are still reported, indicating the need for further basic and preclinical investigation on their therapeutic potential. This review will focus on recent advances in understanding MSC biology and applications in cell therapy.