Cardiospheres recapitulate a niche-like microenvironment rich in stemness and cell-matrix interactions, rationalizing their enhanced functional potency for myocardial repair

ROCK inhibitor Y-27632 increases the cloning efficiency of limbal stem/progenitor cells by improving their adherence and ROS-scavenging capacity

Rho-associated coiled-coil kinase (ROCK) inhibitor Y-27632 has been shown to increase proliferative capacity and even immortalize primary keratinocytes. Here, we demonstrate that rabbit primary limbal epithelial cells (LECs) treated with Y-27632 also exhibited improved colony-forming efficiency by enhancing the expansion of the stem/progenitor cells. Moreover, Y-27632 treatment improved the rapid adherence of limbal stem/progenitor cells in the initial inoculation of primary cells. In addition, Y-27632 treatment elevated the intracellular glutathione level and decreased cellular reactive oxygen species (ROS) accumulation during the expansion of LECs. Therefore, ROCK inhibitor Y-27632 increased the cloning efficiency of rabbit limbal stem/progenitor cells by improving their adherence and ROS scavenging capacity.

High density sphere culture of adult cardiac cells increases the levels of cardiac and progenitor markers and shows signs of vasculogenesis

3D environment and high cell density play an important role in restoring and supporting the phenotypes of cells represented in cardiac tissues. The aim of this study was therefore to investigate the suitability of high density sphere (HDS) cultures for studies of cardiomyocyte-, endothelial-, and stem-cell biology. Primary adult cardiac cells from nine human biopsies were cultured using different media for up to 9 weeks. The possibilities to favor a certain cell phenotype and induce production of extra cellular matrix (ECM) were studied by histology, immunohistochemistry, and quantitative real-time PCR. Defined media gave significant increase in both cardiac- and progenitor-specific markers and also an intraluminal position of endothelial cells over time. Cardiac media showed indication of differentiation and maturity of HDS considering the ECM production and activities within NOTCH regulation but no additional cardiac differentiation. Endothelial media gave no positive effects on endothelial phenotype but increased proliferation without fibroblast overgrowth. In addition, indications for early vasculogenesis were found. It was also possible to affect the Wnt signaling in HDS by addition of a glycogen synthase kinase 3 (GSK3) inhibitor. In conclusion, these findings show the suitability of HDS as in vitro model for studies of cardiomyocyte-, endothelial-, and stem-cell biology.

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.

Amine-enriched surface modification facilitates expansion, attachment, and maintenance of human cardiac-derived c-kit positive progenitor cells

BACKGROUND

Stem cells have a low expansion rate and are difficult to maintain in vitro. To overcome the problems of cardiovascular regeneration, we developed a novel method of stem cell cultivation in culture vessels with amine and carboxyl coatings.

METHODS AND RESULTS

We isolated cardiac stem/progenitor cells from infant-derived heart tissue by using c-kit antibody (human cardiac-derived c-kit positive progenitor cells; hCPC(c-kit+)); the cells differentiated into endothelial cells, smooth muscle cells, and cardiomyocytes. To characterize the effect of surface modification on hCPC(c-kit+) expansion, cellular attachment, c-kit expression maintenance, and cardiomyocyte differentiation, we tested hCPC(c-kit+) cultured on non-coated (control), amine-coated (amine), and carboxyl-coated (carboxyl) vessels. Ex vivo proliferation, c-kit maintenance, and cellular attachment were significantly enhanced in the amine group. The amine coating also increased procollagen type I (pro-COL1) expression and increased phosphorylation signals, such as focal adhesion kinase (FAK) and cytosolic Src, as well as enhanced ERK/CDK2 signaling. In addition, there was significant downregulation of the stress signal transducer, JNK, in the amine group. However, cardiomyogenesis remained unchanged in the control, amine, and carboxyl groups.

CONCLUSIONS

Although surface modifications had no effect on early induction cardiomyogenesis, amine-enriched surface modification may increase hCPC(c-kit+) expansion. The amine-enriched surface improved cellular proliferation and attachment during ex vivo hCPC(c-kit+) expansion, possibly by modulating intracellular signal transducers.

Isolation and expansion of adult cardiac stem/progenitor cells in the form of cardiospheres from human cardiac biopsies and murine hearts

The successful isolation and ex vivo expansion of resident cardiac stem/progenitor cells from human heart biopsies has allowed us to study their biological characteristics and their applications in therapeutic approaches for the repair of ischemic/infarcted heart, the preparation of tissue-engineered cardiac grafts and, possibly, the design of cellular kits for drug screening applications. From the first publication of the original method in 2004, several adjustments and slight changes have been introduced to optimize and adjust the procedure to the evolving experimental and translational needs. Moreover, due to the wide applicability of such a method (which is based on the exploitation of intrinsic functional properties of cells with regenerative properties that are present in most tissues), the key steps of this procedure have been used to derive several kinds of tissue-specific adult stem cells for preclinical or clinical purposes.In order to define the original procedure, complete with the up-to-date modifications introduced through the years, an exhaustive description of the current protocol is performed in this chapter, with particular attention in highlighting critical steps and troubleshoots. The procedure described here consists of modular steps, that could be employed to derive cells from any kind of tissue biopsy, and needs to be considered the gold standard of all the so-called "explant methods" or "cardiosphere methods," and it represents a milestone in the clinical translation of autologous cell therapy.

Regeneration in heart disease-Is ECM the key?

The heart possesses a regeneration potential derived from endogenous and exogenous stem and progenitor cell populations, though baseline regeneration appears to be sub-therapeutic. This limitation was initially attributed to a lack of cells with cardiomyogenic potential following an insult to the myocardium. Rather, recent studies demonstrate increased numbers of cardiomyocyte progenitor cells in diseased hearts. Given that the limiting factor does not appear to be cell quantity but rather repletion of functional cardiomyocytes, it is crucial to understand potential mechanisms inhibiting progenitor cell differentiation. One of the extensively studied areas in heart disease is extracellular matrix (ECM) remodeling, with both the composition and mechanical properties of the ECM undergoing changes in diseased hearts. This review explores the influence of ECM properties on cardiomyogenesis and adult cardiac progenitor cells.

Biochemistry and biology: heart-to-heart to investigate cardiac progenitor cells

BACKGROUND

Cardiac regenerative medicine is a rapidly evolving field, with promising future developments for effective personalized treatments. Several stem/progenitor cells are candidates for cardiac cell therapy, and emerging evidence suggests how multiple metabolic and biochemical pathways strictly regulate their fate and renewal.

SCOPE OF REVIEW

In this review, we will explore a selection of areas of common interest for biology and biochemistry concerning stem/progenitor cells, and in particular cardiac progenitor cells. Numerous regulatory mechanisms have been identified that link stem cell signaling and functions to the modulation of metabolic pathways, and vice versa. Pharmacological treatments and culture requirements may be exploited to modulate stem cell pluripotency and self-renewal, possibly boosting their regenerative potential for cell therapy.

MAJOR CONCLUSIONS

Mitochondria and their many related metabolites and messengers, such as oxygen, ROS, calcium and glucose, have a crucial role in regulating stem cell fate and the balance of their functions, together with many metabolic enzymes. Furthermore, protein biochemistry and proteomics can provide precious clues on the definition of different progenitor cell populations, their physiology and their autocrine/paracrine regulatory/signaling networks.

GENERAL SIGNIFICANCE

Interdisciplinary approaches between biology and biochemistry can provide productive insights on stem/progenitor cells, allowing the development of novel strategies and protocols for effective cardiac cell therapy clinical translation. This article is part of a Special Issue entitled Biochemistry of Stem Cells.

TGFβ-dependent epithelial-to-mesenchymal transition is required to generate cardiospheres from human adult heart biopsies

Autologous cardiac progenitor cells (CPCs) isolated as cardiospheres (CSps) represent a promising candidate for cardiac regenerative therapy. A better understanding of the origin and mechanisms underlying human CSps formation and maturation is undoubtedly required to enhance their cardiomyogenic potential. Epithelial-to-mesenchymal transition (EMT) is a key morphogenetic process that is implicated in the acquisition of stem cell-like properties in different adult tissues, and it is activated in the epicardium after ischemic injury to the heart. We investigated whether EMT is involved in the formation and differentiation of human CSps, revealing that an up-regulation of the expression of EMT-related genes accompanies CSps formation that is relative to primary explant-derived cells and CSp-derived cells grown in a monolayer. EMT and CSps formation is enhanced in the presence of transforming growth factor β1 (TGFβ1) and drastically blocked by the type I TGFβ-receptor inhibitor SB431452, indicating that TGFβ-dependent EMT is essential for the formation of these niche-like 3D-multicellular clusters. Since TGFβ is activated in the myocardium in response to injury, our data suggest that CSps formation mimics an adaptive mechanism that could potentially be enhanced to increase in vivo or ex vivo regenerative potential of adult CPCs.

Human cardiosphere-derived cells from patients with chronic ischaemic heart disease can be routinely expanded from atrial but not epicardial ventricular biopsies

To investigate the effects of age and disease on endogenous cardiac progenitor cells, we obtained right atrial and left ventricular epicardial biopsies from patients (n = 22) with chronic ischaemic heart disease and measured doubling time and surface marker expression in explant- and cardiosphere-derived cells (EDCs, CDCs). EDCs could be expanded from all atrial biopsy samples, but sufficient cells for cardiosphere culture were obtained from only 8 of 22 ventricular biopsies. EDCs from both atrium and ventricle contained a higher proportion of c-kit+ cells than CDCs, which contained few such cells. There was wide variation in expression of CD90 (atrial CDCs 5–92 % CD90+; ventricular CDCs 11–89 % CD90+), with atrial CDCs cultured from diabetic patients (n = 4) containing 1.6-fold more CD90+ cells than those from non-diabetic patients (n = 18). No effect of age or other co-morbidities was detected. Thus, CDCs from atrial biopsies may vary in their therapeutic potential.

Prometheus's heart: what lies beneath

A heart attack kills off many cells in the heart. Parts of the heart become thin and fail to contract properly following the replacement of lost cells by scar tissue. However, the notion that the same adult cardiomyocytes beat throughout the lifespan of the organ and organism, without the need for a minimum turnover, gives way to a fascinating investigations. Since the late 1800s, scientists and cardiologists wanted to demonstrate that the cardiomyocytes cannot be generated after the perinatal period in human beings. This curiosity has been passed down in subsequent years and has motivated more and more accurate studies in an attempt to exclude the presence of renewed cardiomyocytes in the tissue bordering the ischaemic area, and then to confirm the dogma of the heart as terminally differentiated organ. Conversely, peri-lesional mitosis of cardiomyocytes were discovered initially by light microscopy and subsequently confirmed by more sophisticated technologies. Controversial evidence of mechanisms underlying myocardial regeneration has shown that adult cardiomyocytes are renewed through a slow turnover, even in the absence of damage. This turnover is ensured by the activation of rare clusters of progenitor cells interspersed among the cardiac cells functionally mature. Cardiac progenitor cells continuously interact with each other, with the cells circulating in the vessels of the coronary microcirculation and myocardial cells in auto-/paracrine manner. Much remains to be understood; however, the limited functional recovery in human beings after myocardial injury clearly demonstrates weak regenerative potential of cardiomyocytes and encourages the development of new approaches to stimulate this process.

Secondary sphere formation enhances the functionality of cardiac progenitor cells

Loss of cardiomyocytes impairs cardiac function after myocardial infarction (MI). Recent studies suggest that cardiac stem/progenitor cells could repair the damaged heart. However, cardiac progenitor cells are difficult to maintain in terms of purity and multipotency when propagated in two-dimensional culture systems. Here, we investigated a new strategy that enhances potency and enriches progenitor cells. We applied the repeated sphere formation strategy (cardiac explant → primary cardiosphere (CS) formation → sphere-derived cells (SDCs) in adherent culture condition → secondary CS formation by three-dimensional culture). Cells in secondary CS showed higher differentiation potentials than SDCs. When transplanted into the infarcted myocardium, secondary CSs engrafted robustly, improved left ventricular (LV) dysfunction, and reduced infarct sizes more than SDCs did. In addition to the cardiovascular differentiation of transplanted secondary CSs, robust vascular endothelial growth factor (VEGF) synthesis and secretion enhanced neovascularization in the infarcted myocardium. Microarray pathway analysis and blocking experiments using E-selectin knock-out hearts, specific chemicals, and small interfering RNAs (siRNAs) for each pathway revealed that E-selectin was indispensable to sphere initiation and ERK/Sp1/VEGF autoparacrine loop was responsible for sphere maturation. These results provide a simple strategy for enhancing cellular potency for cardiac repair. Furthermore, this strategy may be implemented to other types of stem/progenitor cell-based therapy.

Cell-based therapy for prevention and reversal of myocardial remodeling

Although pharmacological and interventional advances have reduced the morbidity and mortality of ischemic heart disease, there is an ongoing need for novel therapeutic strategies that prevent or reverse progressive ventricular remodeling following myocardial infarction, the process that forms the substrate for ventricular failure. The development of cell-based therapy as a strategy to repair or regenerate injured tissue offers extraordinary promise for a powerful anti-remodeling therapy. In this regard, the field of cell therapy has made major advancements in the past decade. Accumulating data from preclinical studies have provided novel insights into stem cell engraftment, differentiation, and interactions with host cellular elements, as well as the effectiveness of various methods of cell delivery and accuracy of diverse imaging modalities to assess therapeutic efficacy. These findings have in turn guided rationally designed translational clinical investigations. Collectively, there is a growing understanding of the parameters that underlie successful cell-based approaches for improving heart structure and function in ischemic and other cardiomyopathies.

Functional performance of human cardiosphere-derived cells delivered in an in situ polymerizable hyaluronan-gelatin hydrogel

The vast majority of cells delivered into the heart by conventional means are lost within the first 24 h. Methods are needed to enhance cell retention, so as to minimize loss of precious material and maximize effectiveness of the therapy. We tested a cell-hydrogel delivery strategy. Cardiosphere-derived cells (CDCs) were grown from adult human cardiac biopsy specimens. In situ polymerizable hydrogels made of hyaluronan and porcine gelatin (Hystem(®)-C™) were formulated as a liquid at room temperature so as to gel within 20 min at 37 °C. CDC viability and migration were not compromised in Hystem-C™. Myocardial infarction was created in SCID mice and CDCs were injected intramyocardially in the infarct border zone. Real-time PCR revealed engraftment of CDCs delivered in Hystem-C™ was increased by nearly an order of magnitude. LVEF (left ventricular ejection fraction) deteriorated in the control (PBS only) group over the 3-week time course. Hystem-C™ alone or CDCs alone preserved LVEF relative to baseline, while CDCs delivered in Hystem-C™ resulted in a sizable boost in LVEF. Heart morphometry revealed the greatest attenuation of LV remodeling in the CDC + Hystem-C™ group. Histological analysis suggested cardiovascular differentiation of the CDCs in Hystem-C™. However, the majority of functional benefit is likely from paracrine mechanisms such as tissue preservation and neovascularization. A CDC/hydrogel formulation suitable for catheter-based intramyocardial injection exhibits superior engraftment and functional benefits relative to naked CDCs.

Direct comparison of different stem cell types and subpopulations reveals superior paracrine potency and myocardial repair efficacy with cardiosphere-derived cells

OBJECTIVES

The goal of this study was to conduct a direct head-to-head comparison of different stem cell types in vitro for various assays of potency and in vivo for functional myocardial repair in the same mouse model of myocardial infarction.

BACKGROUND

Adult stem cells of diverse origins (e.g., bone marrow, fat, heart) and antigenic identity have been studied for repair of the damaged heart, but the relative utility of the various cell types remains unclear.

METHODS

Human cardiosphere-derived cells (CDCs), bone marrow-derived mesenchymal stem cells, adipose tissue-derived mesenchymal stem cells, and bone marrow mononuclear cells were compared.

RESULTS

CDCs revealed a distinctive phenotype with uniform expression of CD105, partial expression of c-kit and CD90, and negligible expression of hematopoietic markers. In vitro, CDCs showed the greatest myogenic differentiation potency, highest angiogenic potential, and relatively high production of various angiogenic and antiapoptotic-secreted factors. In vivo, injection of CDCs into the infarcted mouse hearts resulted in superior improvement of cardiac function, the highest cell engraftment and myogenic differentiation rates, and the least-abnormal heart morphology 3 weeks after treatment. CDC-treated hearts also exhibited the lowest number of apoptotic cells. The c-kit(+) subpopulation purified from CDCs produced lower levels of paracrine factors and inferior functional benefit when compared with unsorted CDCs. To validate the comparison of cells from various human donors, selected results were confirmed in cells of different types derived from individual rats.

CONCLUSIONS

CDCs exhibited a balanced profile of paracrine factor production and, among various comparator cell types/subpopulations, provided the greatest functional benefit in experimental myocardial infarction.

Functional impairment of human resident cardiac stem cells by the cardiotoxic antineoplastic agent trastuzumab

Trastuzumab (TZM), a monoclonal antibody against the ERBB2 protein, increases survival in ERBB2-positive breast cancer patients. Its clinical use, however, is limited by cardiotoxicity. We sought to evaluate whether TZM cardiotoxicity involves inhibition of human adult cardiac-derived stem cells, in addition to previously reported direct adverse effects on cardiomyocytes. To test this idea, we exposed human cardiosphere-derived cells (hCDCs), a natural mixture of cardiac stem cells and supporting cells that has been shown to exert potent regenerative effects, to TZM and tested the effects in vitro and in vivo. We found that ERBB2 mRNA and protein are expressed in hCDCs at levels comparable to those in human myocardium. Although clinically relevant concentrations of TZM had no effect on proliferation, apoptosis, or size of the c-kit-positive hCDC subpopulation, in vitro assays demonstrated diminished potential for cardiogenic differentiation and impaired ability to form microvascular networks in TZM-treated cells. The functional benefit of hCDCs injected into the border zone of acutely infarcted mouse hearts was abrogated by TZM: infarcted animals treated with TZM + hCDCs had a lower ejection fraction, thinner infarct scar, and reduced capillary density in the infarct border zone compared with animals that received hCDCs alone (n = 12 per group). Collectively, these results indicate that TZM inhibits the cardiomyogenic and angiogenic capacities of hCDCs in vitro and abrogates the morphological and functional benefits of hCDC transplantation in vivo. Thus, TZM impairs the function of human resident cardiac stem cells, potentially contributing to TZM cardiotoxicity.

Experimental acute myocardial infarction: telocytes involvement in neo-angiogenesis

We used rat experimental myocardial infarction to study the ultrastructural recovery, especially neo-angiogenesis in the infarction border zone. We were interested in the possible role(s) of telocytes (TCs), a novel type of interstitial cell very recently discovered in myocardim (see http://www.telocytes.com). Electron microscopy, immunocytochemistry and analysis of several proangiogenic microRNAs provided evidence for TC involvement in neo-angiogenesis after myocardial infarction. Electron microscopy showed the close spatial association of TCs with neoangiogenetic elements. Higher resolution images provided the following information: (a) the intercellular space between the abluminal face of endothelium and its surrounding TCs is frequently less than 50 nm; (b) TCs establish multiple direct nanocontacts with endothelial cells, where the extracellular space seems obliterated; such nanocontacts have a length of 0.4–1.5 μm; (c) the absence of basal membrane on the abluminal face of endothelial cell. Besides the physical contacts (either nanoscopic or microscopic) TCs presumably contribute to neo-angiognesis via paracrine secretion (as shown by immunocytochemistry for VEGF or NOS2). Last but not least, TCs contain measurable quantities of angiogenic microRNAs (e.g. let-7e, 10a, 21, 27b, 100, 126-3p, 130a, 143, 155, 503). Taken together, the direct (physical) contact of TCs with endothelial tubes, as well as the indirect (chemical) positive influence within the ‘angiogenic zones’, suggests an important participation of TCs in neo-angiogenesis during the late stage of myocardial infarction.

Magnetic enhancement of cell retention, engraftment, and functional benefit after intracoronary delivery of cardiac-derived stem cells in a rat model of ischemia/reperfusion

The efficiency of stem cell transplantation is limited by low cell retention. Intracoronary (IC) delivery is convenient and widely used but exhibits particularly low cell retention rates. We sought to improve IC cell retention by magnetic targeting. Rat cardiosphere-derived cells labeled with iron microspheres were injected into the left ventricular cavity of syngeneic rats during brief aortic clamping. Placement of a 1.3 Tesla magnet ~1 cm above the heart during and after cell injection enhanced cell retention at 24 h by 5.2-6.4-fold when 1, 3, or 5 × 10(5) cells were infused, without elevation of serum troponin I (sTnI) levels. Higher cell doses (1 or 2 × 10(6) cells) did raise sTnI levels, due to microvascular obstruction; in this range, magnetic enhancement did not improve cell retention. To assess efficacy, 5 × 10(5) iron-labeled, GFP-expressing cells were infused into rat hearts after 45 min ischemia/20 min reperfusion of the left anterior coronary artery, with and without a superimposed magnet. By quantitative PCR and optical imaging, magnetic targeting increased cardiac retention of transplanted cells at 24 h, and decreased migration into the lungs. The enhanced cell engraftment persisted for at least 3 weeks, at which time left ventricular remodeling was attenuated, and therapeutic benefit (ejection fraction) was higher, in the magnetic targeting group. Histology revealed more GFP(+) cardiomyocytes, Ki67(+) cardiomyocytes and GFP(-)/ckit(+) cells, and fewer TUNEL(+) cells, in hearts from the magnetic targeting group. In a rat model of ischemia/reperfusion injury, magnetically enhanced intracoronary cell delivery is safe and improves cell therapy outcomes.

Cardiac telocytes - their junctions and functional implications

Telocytes (TCs) form a cardiac network of interstitial cells. Our previous studies have shown that TCs are involved in heterocellular contacts with cardiomyocytes and cardiac stem/progenitor cells. In addition, TCs frequently establish ‘stromal synapses’ with several types of immunoreactive cells in various organs (www.telocytes.com). Using electron microscopy (EM) and electron microscope tomography (ET), we further investigated the interstitial cell network of TCs and found that TCs form ‘atypical’ junctions with virtually all types of cells in the human heart. EM and ET showed different junction types connecting TCs in a network (puncta adhaerentia minima, processus adhaerentes and manubria adhaerentia). The connections between TCs and cardiomyocytes are ‘dot’ junctions with nanocontacts or asymmetric junctions. Junctions between stem cells and TCs are either ‘stromal synapses’ or adhaerens junctions. An unexpected finding was that TCs have direct cell–cell (nano)contacts with Schwann cells, endothelial cells and pericytes. Therefore, ultrastructural analysis proved that the cardiac TC network could integrate the overall ‘information’ from vascular system (endothelial cells and pericytes), nervous system (Schwann cells), immune system (macrophages, mast cells), interstitium (fibroblasts, extracellular matrix), stem cells/progenitors and working cardiomyocytes. Generally, heterocellular contacts occur by means of minute junctions (point contacts, nanocontacts and planar contacts) and the mean intermembrane distance is within the macromolecular interaction range (10–30 nm). In conclusion, TCs make a network in the myocardial interstitium, which is involved in the long-distance intercellular signaling coordination. This integrated interstitial system appears to be composed of large homotropic zones (TC–TC junctions) and limited (distinct) heterotropic zones (heterocellular junctions of TCs).

Recurrent genomic instability of chromosome 1q in neural derivatives of human embryonic stem cells

Human pluripotent stem cells offer a limitless source of cells for regenerative medicine. Neural derivatives of human embryonic stem cells (hESCs) are currently being used for cell therapy in 3 clinical trials. However, hESCs are prone to genomic instability, which could limit their clinical utility. Here, we report that neural differentiation of hESCs systematically produced a neural stem cell population that could be propagated for more than 50 passages without entering senescence; this was true for all 6 hESC lines tested. The apparent spontaneous loss of evolution toward normal senescence of somatic cells was associated with a jumping translocation of chromosome 1q. This chromosomal defect has previously been associated with hematologic malignancies and pediatric brain tumors with poor clinical outcome. Neural stem cells carrying the 1q defect implanted into the brains of rats failed to integrate and expand, whereas normal cells engrafted. Our results call for additional quality controls to be implemented to ensure genomic integrity not only of undifferentiated pluripotent stem cells, but also of hESC derivatives that form cell therapy end products, particularly neural lines.

Transplantation of platelet gel spiked with cardiosphere-derived cells boosts structural and functional benefits relative to gel transplantation alone in rats with myocardial infarction

The emerging field of stem cell therapy and biomaterials has begun to provide promising strategies for the treatment of ischemic cardiomyopathy. Platelet gel and cardiosphere-derived cells (CDCs) are known to be beneficial when transplanted separately post-myocardial infarction (MI). We hypothesize that pre-seeding platelet gel with CDCs can enhance therapeutic efficacy. Platelet gel and CDCs were derived from venous blood and heart biopsies of syngeneic rats, respectively. In vitro, the viability, growth, and morphology of CDCs cultured in platelet gel were characterized. When delivered into infarcted rat hearts, platelet gel pre-seeded with CDCs was more efficiently populated with endogenous cardiomyocytes and endothelial cells than platelet gel alone. Recruitment of endogenous c-kit positive cells was enhanced in the hearts treated with gel with CDC. At 3 weeks, the hearts treated with CDC-seeded platelet gel exhibited the greatest attenuation of adverse left ventricular (LV) remodeling and the highest cardiac function (i.e., LV ejection fraction) as compared to hearts transplanted with Gel only or vehicle controls. Histological analysis revealed that, though some transplanted CDCs differentiated into cardiomyocytes and endothelial cells in the recipients' hearts, most of the incremental benefit arose from CDC-mediated endogenous repair. Pre-seeding platelet gel with CDCs enhanced the functional benefit of biomaterial therapy for treating myocardial infarction.

From ontogenesis to regeneration: learning how to instruct adult cardiac progenitor cells

Since the first observations over two centuries ago by Lazzaro Spallanzani on the extraordinary regenerative capacity of urodeles, many attempts have been made to understand the reasons why such ability has been largely lost in metazoa and whether or how it can be restored, even partially. In this context, important clues can be derived from the systematic analysis of the relevant distinctions among species and of the pathways involved in embryonic development, which might be induced and/or recapitulated in adult tissues. This chapter provides an overview on regeneration and its mechanisms, starting with the lesson learned from lower vertebrates, and will then focus on recent advancements and novel insights concerning regeneration in the adult mammalian heart, including the discovery of resident cardiac progenitor cells (CPCs). Subsequently, it explores all the important pathways involved in regulating differentiation during development and embryogenesis, and that might potentially provide important clues on how to activate and/or modulate regenerative processes in the adult myocardium, including the potential activation of endogenous CPCs. Furthermore the importance of the stem cell niche is discussed, and how it is possible to create in vitro a microenvironment and culture system to provide adult CPCs with the ideal conditions promoting their regenerative ability. Finally, the state of clinical translation of cardiac cell therapy is presented. Overall, this chapter provides a new perspective on how to approach cardiac regeneration, taking advantage of important lessons from development and optimizing biotechnological tools to obtain the ideal conditions for cell-based cardiac regenerative therapy.

Mechanisms of cardiogenesis in cardiovascular progenitor cells

Self-renewing cells of the vertebrate heart have become a major subject of interest in the past decade. However, many researchers had a hard time to argue against the orthodox textbook view that defines the heart as a postmitotic organ. Once the scientific community agreed on the existence of self-renewing cells in the vertebrate heart, their origin was again put on trial when transdifferentiation, dedifferentiation, and reprogramming could no longer be excluded as potential sources of self-renewal in the adult organ. Additionally, the presence of self-renewing pluripotent cells in the peripheral blood challenges the concept of tissue-specific stem and progenitor cells. Leaving these unsolved problems aside, it seems very desirable to learn about the basic biology of this unique cell type. Thus, we shall here paint a picture of cardiovascular progenitor cells including the current knowledge about their origin, basic nature, and the molecular mechanisms guiding proliferation and differentiation into somatic cells of the heart.

The effects of mechanical stress on the growth, differentiation, and paracrine factor production of cardiac stem cells

Stem cell therapies have been clinically employed to repair the injured heart, and cardiac stem cells are thought to be one of the most potent stem cell candidates. The beating heart is characterized by dynamic mechanical stresses, which may have a significant impact on stem cell therapy. The purpose of this study is to investigate how mechanical stress affects the growth and differentiation of cardiac stem cells and their release of paracrine factors. In this study, human cardiac stem cells were seeded in a silicon chamber and mechanical stress was then induced by cyclic stretch stimulation (60 cycles/min with 120% elongation). Cells grown in non-stretched silicon chambers were used as controls. Our result revealed that mechanical stretching significantly reduced the total number of surviving cells, decreased Ki-67-positive cells, and increased TUNEL-positive cells in the stretched group 24 hrs after stretching, as compared to the control group. Interestingly, mechanical stretching significantly increased the release of the inflammatory cytokines IL-6 and IL-1β as well as the angiogenic growth factors VEGF and bFGF from the cells in 12 hrs. Furthermore, mechanical stretching significantly reduced the percentage of c-kit-positive stem cells, but increased the expressions of cardiac troponin-I and smooth muscle actin in cells 3 days after stretching. Using a traditional stretching model, we demonstrated that mechanical stress suppressed the growth and proliferation of cardiac stem cells, enhanced their release of inflammatory cytokines and angiogenic factors, and improved their myogenic differentiation. The development of this in vitro approach may help elucidate the complex mechanisms of stem cell therapy for heart failure.

Recent concepts for the roles of progenitor/stem cell niche in heart repair

Progenitor/stem cell (PSC) has shown great promise for generation in failing heart. Advances in PSC biology have greatly enhanced our understanding of how PSC self-renewal, migration, maintenance of stemness, and cell-fate commitment depend on the balance of complex signals in their microenvironment. Endogenous PSC exists within structural and functional units known as PSC niches, which play important roles in directing PSC behavior. Recent years have witnessed great progress in our understanding of the PSC niche in cardiovascular biology. PSC based therapy could lead to successful cardiac regeneration or repair. Realizing the potential of therapeutic strategies is based on 1) differentiation of the PSC into all of the cellular constituents of the heart; 2) release of paracrine/ autocrine factors from the PSC; 3) fusion of the PSC with the existing constituents of the heart; and 4) stimulation of endogenous repair (regeneration of PSC niches). Importantly, cardiac PSC niches contain supporting cells and these cell-cell interactions have crucial regulatory roles in PSC based therapy. These findings have important implications for heart development, bioengineering, and furthermore elucidate a broader dimension of PSC control within the niche toward cardiomyocyte phenotype.

Culture of human mesenchymal stem cells at low oxygen tension improves growth and genetic stability by activating glycolysis

Expansion of human stem cells before cell therapy is typically performed at 20% O(2). Growth in these pro-oxidative conditions can lead to oxidative stress and genetic instability. Here, we demonstrate that culture of human mesenchymal stem cells at lower, physiological O(2) concentrations significantly increases lifespan, limiting oxidative stress, DNA damage, telomere shortening and chromosomal aberrations. Our gene expression and bioenergetic data strongly suggest that growth at reduced oxygen tensions favors a natural metabolic state of increased glycolysis and reduced oxidative phosphorylation. We propose that this balance is disturbed at 20% O(2), resulting in abnormally increased levels of oxidative stress. These observations indicate that bioenergetic pathways are intertwined with the control of lifespan and decisively influence the genetic stability of human primary stem cells. We conclude that stem cells for human therapy should be grown under low oxygen conditions to increase biosafety.

Human cardiac stem cells isolated from atrial appendages stably express c-kit

The in vivo studies of myocardial infarct using c-kit⁺/Lin⁻ cardiac stem cells (CSCs) are still in the early stage with margin or no beneficial effects for cardiac function. One of the potential reasons may be related to the absence of fully understanding the properties of these cells both in vitro and in vivo. In the present study, we aimed to systematically examine how CSCs adapted to in vitro cell processes and whether there is any cell contamination after long-term culture. Human CSCs were enzymatically isolated from the atrial appendages of patients. The fixed tissue sections, freshly isolated or cultured CSCs were then used for identification of c-kit⁺/Lin⁻ cells, detection of cell contamination, or differentiation of cardiac lineages. By specific antibody staining, we demonstrated that tissue sections from atrial appendages contained less than 0.036% c-kit⁺/Lin⁻ cells. For the first time, we noted that without magnetic activated cell sorting (MACS), the percentages of c-kit⁺/Lin⁻ cells gradually increased up to ∼40% during continuously culture between passage 2 to 8, but could not exceed >80% unless c-kit MACS was carried out. The resulting c-kit⁺/Lin⁻ cells were negative for CD34, CD45, CD133, and Lin markers, but positive for KDR and CD31 in few patients after c-kit MACS. Lin depletion seemed unnecessary for enrichment of c-kit⁺/Lin⁻ cell population. Following induced differentiation, c-kit⁺/Lin⁻ CSCs demonstrated strong differentiation towards cardiomyocytes but less towards smooth and endothelial cells. We concluded that by using an enzymatic dissociation method, a large number, or higher percentage, of relative pure human CSCs with stable expression of c-kit⁺ could be obtained from atrial appendage specimens within ∼4 weeks following c-kit MACS without Lin depletion. This simple but cost-effective approach can be used to obtain enough numbers of stably-expressed c-kit⁺/Lin⁻ cells for clinical trials in repairing myocardial infarction.

Safety and efficacy of allogeneic cell therapy in infarcted rats transplanted with mismatched cardiosphere-derived cells

BACKGROUND

Cardiosphere-derived cells (CDCs) are an attractive cell type for tissue regeneration, and autologous CDCs are being tested clinically. However, autologous therapy necessitates patient-specific tissue harvesting and cell processing, with delays to therapy and possible variations in cell potency. The use of allogeneic CDCs, if safe and effective, would obviate such limitations. We compared syngeneic and allogeneic CDC transplantation in rats from immunologically-mismatched inbred strains.

METHODS AND RESULTS

In vitro, CDCs expressed major histocompatibility complex class I but not class II antigens or B7 costimulatory molecules. In mixed-lymphocyte cocultures, allogeneic CDCs elicited negligible lymphocyte proliferation and inflammatory cytokine secretion. In vivo, syngeneic and allogeneic CDCs survived at similar levels in the infarcted rat heart 1 week after delivery, but few syngeneic (and even fewer allogeneic) CDCs remained at 3 weeks. Allogeneic CDCs induced a transient, mild, local immune reaction in the heart, without histologically evident rejection or systemic immunogenicity. Improvements in cardiac structure and function, sustained for 6 months, were comparable with syngeneic and allogeneic CDCs. Allogeneic CDCs stimulated endogenous regenerative mechanisms (cardiomyocyte cycling, recruitment of c-kit(+) cells, angiogenesis) and increased myocardial vascular endothelial growth factor, insulin-like growth factor-1, and hepatocyte growth factor equally with syngeneic CDCs.

CONCLUSIONS

Allogeneic CDC transplantation without immunosuppression is safe, promotes cardiac regeneration, and improves heart function in a rat myocardial infarction model, mainly through stimulation of endogenous repair mechanisms. The indirect mechanism of action rationalizes the persistence of benefit despite the evanescence of transplanted cell survival. This work motivates the testing of allogeneic human CDCs as a potential off-the-shelf product for cellular cardiomyoplasty.

Self-renewal and scalability of human embryonic stem cells for human therapy

Human embryonic stem cells (hESCs) can undergo unlimited self-renewal and retain the pluripotency to differentiate into all cell types in the body. Therefore, as a renewable source of various cell types, hESCs hold great promise for human cell replacement therapy. While significant progress has been made in establishing the culture conditions for the long-term self-renewal of hESCs, several challenges remain to be overcome for the clinical application of hESCs. One such challenge is to develop strategies to scale-up the production of clinic-grade hESCs in xeno-free and chemically defined medium without inducing genomic instability. To achieve this goal, it is critical to elucidate the molecular pathways required to maintain the self-renewal, survival and genomic stability of hESCs. This article describes recent progress in addressing this challenge and discusses the strategies to improve the scalability of the production of hESCs by inhibiting their apoptosis.

Cardiosphere-derived cells improve function in the infarcted rat heart for at least 16 weeks--an MRI study

Aims

Endogenous cardiac progenitor cells, expanded from explants via cardiosphere formation, present a promising cell source to prevent heart failure following myocardial infarction. Here we used cine-magnetic resonance imaging (MRI) to track administered cardiosphere-derived cells (CDCs) and to measure changes in cardiac function over four months in the infarcted rat heart.

Methods and Results

CDCs, cultured from neonatal rat heart, comprised a heterogeneous population including cells expressing the mesenchymal markers CD90 and CD105, the stem cell marker c-kit and the pluripotency markers Sox2, Oct3/4 and Klf-4. CDCs (2×10⁶) expressing green fluorescent protein (GFP+) were labelled with fluorescent micron-sized particles of iron oxide (MPIO). Labelled cells were administered to the infarcted rat hearts (n = 7) by intramyocardial injection immediately following reperfusion, then by systemic infusion (4×10⁶) 2 days later. A control group (n = 7) was administered cell medium. MR hypointensities caused by the MPIOs were detected at all times and GFP+ cells containing MPIO particles were identified in tissue slices at 16 weeks. At two days after infarction, cardiac function was similar between groups. By 6 weeks, ejection fractions in control hearts had significantly decreased (47±2%), but this was not evident in CDC-treated hearts (56±3%). The significantly higher ejection fractions in the CDC-treated group were maintained for a further 10 weeks. In addition, CDC-treated rat hearts had significantly increased capillary density in the peri-infarct region and lower infarct sizes. MPIO-labelled cells also expressed cardiac troponin I, von Willebrand factor and smooth muscle actin, suggesting their differentiation along the cardiomyocyte lineage and the formation of new blood vessels.

Conclusions

CDCs were retained in the infarcted rat heart for 16 weeks and improved cardiac function.

Biomaterials to Enhance Stem Cell Function in the Heart

Transplantation of stem cells into the heart can improve cardiac function after myocardial infarction and in chronic heart failure, but the extent of benefit and of reproducibility of this approach are insufficient. Survival of transplanted cells into myocardium is poor, and new strategies are needed to enhance stem cell differentiation and survival in vivo. In this review, we describe how biomaterials can enhance stem cell function in the heart. Biomaterials can mimic or include naturally occurring extracellular matrix and also instruct stem cell function in different ways. Biomaterials can promote angiogenesis, enhance engraftment and differentiation of stem cells, and accelerate electromechanical integration of transplanted stem cells. Biomaterials can also be used to deliver proteins, genes, or small RNAs together with stem cells. Furthermore, recent evidence indicates that the biophysical environment of stem cells is crucial for their proliferation and differentiation, as well as their electromechanical integration. Many approaches in regenerative medicine will likely ultimately require integration of molecularly designed biomaterials and stem cell biology to develop stable tissue regeneration.

Genomic instability in cultured stem cells: associated risks and underlying mechanisms

Embryonic stem cells, mesenchymal stem cells and induced pluripotent stem cells expanded in vitro exhibit genomic instability. Commonly reported abnormalities include aneuploidy, deletions and duplications (including regions also amplified in cancer). Genomic instability confers an increased risk of malignant transformation that may impact the safety of cultured stem cell transplantation. Possible mechanisms responsible for this genomic instability include DNA repair mechanism abnormalities, telomere crisis, mitotic spindle abnormalities and inappropriate induction of meiotic pathways. Prior to widespread use of these cells in regenerative medicine, it will be critical to gain an understanding of the mechanisms responsible for genomic instability to develop strategies to prevent the accrual of chromosomal defects during expansion in vitro.

Three-dimensional biomaterials for the study of human pluripotent stem cells

The self-renewal and differentiation of human pluripotent stem cells (hPSCs) have typically been studied in flat, two-dimensional (2D) environments. In this Perspective, we argue that 3D model systems may be needed in addition, as they mimic the natural 3D tissue organization more closely. We survey methods that have used 3D biomaterials for expansion of undifferentiated hPSCs, directed differentiation of hPSCs and transplantation of differentiated hPSCs in vivo.

Telocytes and putative stem cells in the lungs: electron microscopy, electron tomography and laser scanning microscopy

This study describes a novel type of interstitial (stromal) cell — telocytes (TCs) — in the human and mouse respiratory tree (terminal and respiratory bronchioles, as well as alveolar ducts). TCs have recently been described in pleura, epicardium, myocardium, endocardium, intestine, uterus, pancreas, mammary gland, etc. (see www.telocytes.com). TCs are cells with specific prolongations called telopodes (Tp), frequently two to three per cell. Tp are very long prolongations (tens up to hundreds of μm) built of alternating thin segments known as podomers (≤ 200 nm, below the resolving power of light microscope) and dilated segments called podoms, which accommodate mitochondria, rough endoplasmic reticulum and caveolae. Tp ramify dichotomously, making a 3-dimensional network with complex homo- and heterocellular junctions. Confocal microscopy reveals that TCs are c-kit- and CD34-positive. Tp release shed vesicles or exosomes, sending macromolecular signals to neighboring cells and eventually modifying their transcriptional activity. At bronchoalveolar junctions, TCs have been observed in close association with putative stem cells (SCs) in the subepithelial stroma. SCs are recognized by their ultrastructure and Sca-1 positivity. Tp surround SCs, forming complex TC-SC niches (TC-SCNs). Electron tomography allows the identification of bridging nanostructures, which connect Tp with SCs. In conclusion, this study shows the presence of TCs in lungs and identifies a TC-SC tandem in subepithelial niches of the bronchiolar tree. In TC-SCNs, the synergy of TCs and SCs may be based on nanocontacts and shed vesicles.

Three-dimensional spheroid culture of human gingiva-derived mesenchymal stem cells enhances mitigation of chemotherapy-induced oral mucositis

Mesenchymal stem cells (MSCs) are capable of regenerative and immunomodulatory functions in cell-based therapies in a variety of human diseases and injuries; however, their therapeutic efficacy and potential side effects remain major obstacles in clinical applications. We report here a 3D spheroid culture approach to optimize stem cell properties and therapeutic effects of human gingiva-derived mesenchymal stem cells (GMSCs) in mitigation of experimental oral mucositis. Under growth condition of ultra-low attachment, GMSCs spontaneously aggregated into 3D spheroids and exhibited distinct early stem cell phenotype characterized by elevated expression Stro-1 and CXC chemokine receptor 4 (CXCR-4) as well as OCT-4 and Nanog, 2 important transcriptional factors relevant to stem cell properties, and decreased expression of MSC-associated markers, including CD29, CD90, and CD105. Functionally, spheroid GMSCs are capable of enhanced multipotency and augmented secretion of several chemokines and cytokines relevant to cell migration, survival, and angiogenesis. More importantly, spheroid GMSCs expressed increased levels of reactive oxygen species, hypoxia-inducible factor (HIF)-1 and -2α, and manganese superoxide dismutase, which correlated with improved resistance to oxidative stress-induced apoptosis. Using an in vivo murine model of chemotherapy-induced oral mucositis, we demonstrated that spheroid-derived GMSCs possessed better therapeutic efficacy than their adherent cells in reversing body weight loss and promoting the regeneration of disrupted epithelial lining of the mucositic tongues. These findings suggest that 3D spheroid culture allows early stemness preservation and potentially precondition GMSCs for enhanced mitigation of oral mucositis.

Efficient derivation of NPCs, spinal motor neurons and midbrain dopaminergic neurons from hESCs at 3% oxygen

This protocol has been designed to generate neural precursor cells (NPCs) from human embryonic stem cells (hESCs) using a physiological oxygen (O(2)) level of 3% (previously termed hypoxia) and chemically defined conditions. The first stage involves suspension culture of hESC colonies at 3% O(2), where they acquire a neuroepithelial identity over a period of 2 weeks. This timescale is comparable to that observed at 20% O(2), but survival is enhanced. Sequential application of retinoic acid and purmorphamine (PM), from day 14 to day 28, directs differentiation toward spinal motor neurons. Alternatively, addition of fibroblast growth factor-8 and PM generates midbrain dopaminergic neurons. OLIG2 (encoding oligodendrocyte lineage transcription factor 2) induction in motor neuron precursors is twofold greater than that at 20% O(2), whereas EN1 (encoding engrailed homeobox 1) expression is enhanced fivefold. NPCs (at 3% O(2)) can be differentiated into all three neural lineages, and such cultures can be maintained long term in the absence of neurotrophins. The ability to generate defined cell types at 3% O(2) should represent a significant advancement for in vitro disease modeling and potentially for cell-based therapies.

Kidney spheroids recapitulate tubular organoids leading to enhanced tubulogenic potency of human kidney-derived cells

Cell-based approaches utilizing autologous human renal cells require their isolation, expansion in vitro, and reintroduction back into the host for renal tissue regeneration. Nevertheless, human kidney epithelial cells (hKEpCs) lose their phenotype, dedifferentiate, and assume the appearance of fibroblasts after relatively few passages in culture. We hypothesized that growth conditions may influence hKEpC phenotype and function. hKEpCs retrieved from human nephrectomy tissue samples showed the ability to reproducibly form kidney spheres when grown in suspension culture developed in nonadherent conditions. Genetic labeling and time-lapse microscopy indicated, at least in part, the aggregation of hKEpCs into 3D spheroids rather than formation of pure clonally expanded spheres. Characterization of hKEpC spheroids by real-time polymerase chain reaction and FACS analysis showed upregulation of some renal developmental and "stemness" markers compared with monolayer and mostly an EpCAM(+)CD24(+)CD133(+)CD44(+) spheroid cell phenotype. Oligonucleotide microarrays, which were used to identify global transcriptional changes accompanying spheroid formation, showed predominantly upregulation of cell matrix/cell contact molecules and cellular biogenesis processes and downregulation of cell cycle, growth, and locomotion. Accordingly, hKEpC spheroids slowly proliferated as indicated by low Ki-67 staining, but when grafted in low cell numbers onto the chorioallantoic membrane (CAM) of the chick embryo, they exclusively reconstituted various renal tubular epithelia. Moreover, efficient generation of kidney spheroids was observed after long-term monolayer culture resulting in reestablishment of tubulogenic capacity upon CAM grafting. Thus, generation of a tubular organoid in hKEpC spheroids may provide a functional benefit for kidney-derived cells in vivo.

Substrates for cardiovascular tissue engineering

Cardiovascular tissue engineering aims to find solutions for the suboptimal regeneration of heart valves, arteries and myocardium by creating 'living' tissue replacements outside (in vitro) or inside (in situ) the human body. A combination of cells, biomaterials and environmental cues of tissue development is employed to obtain tissues with targeted structure and functional properties that can survive and develop within the harsh hemodynamic environment of the cardiovascular system. This paper reviews the up-to-date status of cardiovascular tissue engineering with special emphasis on the development and use of biomaterial substrates. Key requirements and properties of these substrates, as well as methods and readout parameters to test their efficacy in the human body, are described in detail and discussed in the light of current trends toward designing biologically inspired microenviroments for in situ tissue engineering purposes.

Intramyocardial injection of autologous cardiospheres or cardiosphere-derived cells preserves function and minimizes adverse ventricular remodeling in pigs with heart failure post-myocardial infarction

OBJECTIVES

The purpose of this study was to test the safety and efficacy of direct injection of cardiosphere-derived cells (CDCs) and their 3-dimensional precursors, cardiospheres, for cellular cardiomyoplasty in a mini-pig model of heart failure after myocardial infarction.

BACKGROUND

Intracoronary administration of CDCs has been demonstrated to reduce infarct size and improve hemodynamic indexes in the mini-pig model, but intramyocardial injection of CDCs or cardiospheres has not been assessed in large animals.

METHODS

Autologous cardiospheres or CDCs grown from endomyocardial biopsies were injected through thoracotomy 4 weeks after anteroseptal myocardial infarction. Engraftment optimization with luciferase-labeled CDCs guided the choice of cell dose (0.5 million cells/site) and target tissue (20 peri-infarct sites). Pigs were randomly allocated to placebo (n = 11), cardiospheres (n = 8), or CDCs (n = 10). Functional data were acquired before injection and again 8 weeks later, after which organs were harvested for histopathology.

RESULTS

Beyond the immediate perioperative period, all animals survived to protocol completion. Ejection fraction was equivalent at baseline, but at 8 weeks was higher than placebo in both of the cell-treated groups (placebo vs. CDC, p = 0.01; placebo vs. cardiospheres, p = 0.01). Echocardiographic and hemodynamic indexes of efficacy improved disproportionately with cardiospheres; likewise, adverse remodeling was more attenuated with cardiospheres than with CDCs. Provocative electrophysiologic testing showed no differences among groups, and no tumors were found.

CONCLUSIONS

Dosage-optimized direct injection of cardiospheres or CDCs is safe and effective in preserving ventricular function in porcine ischemic cardiomyopathy. Although CDCs and cardiospheres have equivalent effects on left ventricular ejection fraction, cardiospheres are superior in improving hemodynamics and regional function, and in attenuating ventricular remodeling.

Derivation of neural precursor cells from human ES cells at 3% O(2) is efficient, enhances survival and presents no barrier to regional specification and functional differentiation

In vitro stem cell systems traditionally employ oxygen levels that are far removed from the in vivo situation. This study investigates whether an ambient environment containing a physiological oxygen level of 3% (normoxia) enables the generation of neural precursor cells (NPCs) from human embryonic stem cells (hESCs) and whether the resultant NPCs can undergo regional specification and functional maturation. We report robust and efficient neural conversion at 3% O(2), demonstration of tri-lineage potential of resultant NPCs and the subsequent electrophysiological maturation of neurons. We also show that NPCs derived under 3% O(2) can be differentiated long term in the absence of neurotrophins and can be readily specified into both spinal motor neurons and midbrain dopaminergic neurons. Finally, modelling the oxygen stress that occurs during transplantation, we demonstrate that in vitro transfer of NPCs from a 20 to 3% O(2) environment results in significant cell death, while maintenance in 3% O(2) is protective. Together these findings support 3% O(2) as a physiologically relevant system to study stem cell-derived neuronal differentiation and function as well as to model neuronal injury.

Cardiac cell therapy: where we've been, where we are, and where we should be headed

INTRODUCTION

Stem cell therapy has emerged as a promising strategy for the treatment of ischemic cardiomyopathy.

SOURCES OF DATA

Multiple candidate cell types have been used in preclinical animal models and in clinical trials to repair or regenerate the injured heart either directly (through formation of new transplanted tissue) or indirectly (through paracrine effects activating endogenous regeneration).

AREAS OF AGREEMENT

(i) Clinical trials examining the safety and efficacy of bone marrow derived cells in patients with heart disease are promising, but results leave much room for improvement. (ii) The safety profile has been quite favorable. (iii) Efficacy has been inconsistent and, overall, modest. (iv) Tissue retention of cells after delivery into the heart is disappointingly low. (v) The beneficial effects of adult stem cell therapy are predominantly mediated by indirect paracrine mechanisms.

AREAS OF CONTROVERSY

The cardiogenic potential of bone marrow-derived cells, the mechanism whereby small numbers of poorly-retained cells translate to measurable clinical benefit, and the overall impact on clinical outcomes are hotly debated. GROWING POINTS/AREAS TIMELY FOR DEVELOPING RESEARCH: This overview of the field leaves us with cautious optimism, while motivating a search for more effective delivery methods, better strategies to boost cell engraftment, more apt patient populations, safe and effective 'off the shelf' cell products and more potent cell types.