The advancement of human pluripotent stem cell-derived therapies into the clinic

Function Follows Form - A Review of Cardiac Cell Therapy

The investment of nearly 2 decades of clinical investigation into cardiac cell therapy has yet to change cardiovascular practice. Recent insights into the mechanism of cardiac regeneration help explain these results and provide important context in which we can develop next-generation therapies. Non-contractile cells such as bone marrow or adult heart derivatives neither engraft long-term nor induce new muscle formation. Correspondingly, these cells offer little functional benefit to infarct patients. In contrast, preclinical data indicate that transplantation of bona fide cardiomyocytes derived from pluripotent stem cells induces direct remuscularization. This new myocardium beats synchronously with the host heart and induces substantial contractile benefits in macaque monkeys, suggesting that regeneration of contractile myocardium is required to fully recover function. Through a review of the preclinical and clinical trials of cardiac cell therapy, distinguishing the primary mechanism of benefit as either contractile or non-contractile helps appreciate the barriers to cardiac repair and establishes a rational path to optimizing therapeutic benefit.

Using transcription factors for direct reprogramming of neurons in vitro

Cell therapy offers great promises in replacing the neurons lost due to neurodegenerative diseases or injuries. However, a key challenge is the cellular source for transplantation which is often limited by donor availability. Direct reprogramming provides an exciting avenue to generate specialized neuron subtypes in vitro, which have the potential to be used for autologous transplantation, as well as generation of patient-specific disease models in the lab for drug discovery and testing gene therapy. Here we present a detailed review on transcription factors that promote direct reprogramming of specific neuronal subtypes with particular focus on glutamatergic, GABAergic, dopaminergic, sensory and retinal neurons. We will discuss the developmental role of master transcriptional regulators and specification factors for neuronal subtypes, and summarize their use in promoting direct reprogramming into different neuronal subtypes. Furthermore, we will discuss up-and-coming technologies that advance the cell reprogramming field, including the use of computational prediction of reprogramming factors, opportunity of cellular reprogramming using small chemicals and microRNA, as well as the exciting potential for applying direct reprogramming in vivo as a novel approach to promote neuro-regeneration within the body. Finally, we will highlight the clinical potential of direct reprogramming and discuss the hurdles that need to be overcome for clinical translation.

Cardiac fibrosis - A short review of causes and therapeutic strategies

Fibrotic diseases cause annually more than 800,000 deaths worldwide, whereof the majority accounts for lung and cardiac fibrosis. A pathological remodeling of the extracellular matrix either due to ageing or as a result of an injury or disease leads to fibrotic scars. In the heart, these scars cause several cardiac dysfunctions either by reducing the ejection fraction due to a stiffened myocardial matrix, or by impairing electric conductance, or they can even lead to death. Today it is known that there are several different types of cardiac scars depending on the underlying cause of fibrosis. In this review, we present an overview of what is known about cardiac fibrosis including the role of cardiac cells and extracellular matrix in this disease. We will further summarize current diagnostic tools and highlight pre-clinical or clinical therapeutic strategies to address cardiac fibrosis.

[Stem cell-based cardiac regeneration after myocardial infarction]

Myocardial infarction leads to an irreversible loss of vital myocardial cells. The transplantation of new cardiomyocytes into the heart was first described over 20 years ago and represents a straightforward approach to remuscularize a damaged heart. Due to the lack of human cells a clinical application seemed ambitious; however, dramatic progress in stem cell biology over the last two decades has paved the way towards a clinical application. This is especially important as the prognosis for patients with terminal heart failure is still poor. The transplantation of either cardiomyocytes or engineered heart tissue derived from pluripotent stem cells (either embryonic stem cells or induced pluripotent stem cells) might represent a new regenerative approach. Transplantation of either cells or tissue constructs has now been evaluated in several preclinical models, which have demonstrated that an injured heart can be (partially) remuscularized; however, major hurdles towards a clinical application are the transplantation-related occurrence of arrhythmia, the potential tumorigenicity of pluripotent cells and the required immunosuppression. Several groups are working hard to solve these problems and we are optimistic that the first clinical studies will take place within the next few years.

Cardiac progenitor cells application in cardiovascular disease

Stem cells (SCs) have special potency to differentiate into different types of cells, especially cardiomyocytes. In order to demonstrate the therapeutic applications of these cells, various investigations are recently being developed. Cardiac progenitor cells are endogenous cardiac SCs that found to express tyrosine kinase receptors, c-Kit and other stemness features in adult heart, contributing to the regeneration of cardiac tissue after injury. This lineage is able to efficiently trans-differentiate into different cell types such as cardiomyocytes, endothelial cells, and smooth muscle cells. Noticeably, several cardiac progenitor cells have been identified until yet. The therapeutic applications of cardiac SCs have been studied previously, which could introduce a novel therapeutic approach in the treatment of cardiac disorders. The current review enlightens the potency of cardiac progenitor cells features and differentiation capacity, with current applications in cardiovascular field.

Engineering Cardiac Muscle Tissue: A Maturating Field of Research

Twenty years after the initial description of a tissue engineered construct, 3-dimensional human cardiac tissues of different kinds are now generated routinely in many laboratories. Advances in stem cell biology and engineering allow for the generation of constructs that come close to recapitulating the complex structure of heart muscle and might, therefore, be amenable to industrial (eg, drug screening) and clinical (eg, cardiac repair) applications. Whether the more physiological structure of 3-dimensional constructs provides a relevant advantage over standard 2-dimensional cell culture has yet to be shown in head-to-head-comparisons. The present article gives an overview on current strategies of cardiac tissue engineering with a focus on different hydrogel methods and discusses perspectives and challenges for necessary steps toward the real-life application of cardiac tissue engineering for disease modeling, drug development, and cardiac repair.

Immunological Properties of Murine Parthenogenetic Stem Cells and Their Differentiation Products

The perspective to transplant grafts derived from pluripotent stem cells has gained much attention in recent years. Parthenogenetic stem cells (PSCs) are an alternative pluripotent stem cell type that is attractive as source of grafts for allogeneic transplantations because most PSCs are haploidentical for the major histocompatibility complex (MHC). This reduced immunogenetic complexity of PSCs could tremendously simplify the search for MHC-matched allogeneic stem cells. In this study, we have characterized immunological properties of the MHC haploidentical PSC line A3 (H2^d/d) and the heterologous PSC line A6 (H2^b/d). Both PSC lines largely lack MHC class I molecules, which present peptides to cytotoxic T lymphocytes (CTLs) and serve as ligands for inhibitory natural killer (NK) receptors. They express ligands for activating NK receptors, including the NKG2D ligand RAE-1, and the DNAM-1 ligands CD112 and CD155. Consequently, both PSC lines are highly susceptible to killing by IL-2-activated NK cells. In vitro-differentiated cells acquire resistance and downregulate ligands for activating NK receptors but fail to upregulate MHC class I molecules. The PSC line A6 and differentiated A6 cells are largely resistant to CTLs derived from T cell receptor transgenic OT-I mice after pulsing of the targets with the appropriate peptide. The high susceptibility to killing by activated NK cells may constitute a general feature of pluripotent stem cells as it has been also found with other pluripotent stem cell types. This activity potentially increases the safety of transplantations, if grafts contain traces of undifferentiated cells that could be tumorigenic in the recipient.

A data analysis framework for biomedical big data: Application on mesoderm differentiation of human pluripotent stem cells

The development of high-throughput biomolecular technologies has resulted in generation of vast omics data at an unprecedented rate. This is transforming biomedical research into a big data discipline, where the main challenges relate to the analysis and interpretation of data into new biological knowledge. The aim of this study was to develop a framework for biomedical big data analytics, and apply it for analyzing transcriptomics time series data from early differentiation of human pluripotent stem cells towards the mesoderm and cardiac lineages. To this end, transcriptome profiling by microarray was performed on differentiating human pluripotent stem cells sampled at eleven consecutive days. The gene expression data was analyzed using the five-stage analysis framework proposed in this study, including data preparation, exploratory data analysis, confirmatory analysis, biological knowledge discovery, and visualization of the results. Clustering analysis revealed several distinct expression profiles during differentiation. Genes with an early transient response were strongly related to embryonic- and mesendoderm development, for example CER1 and NODAL. Pluripotency genes, such as NANOG and SOX2, exhibited substantial downregulation shortly after onset of differentiation. Rapid induction of genes related to metal ion response, cardiac tissue development, and muscle contraction were observed around day five and six. Several transcription factors were identified as potential regulators of these processes, e.g. POU1F1, TCF4 and TBP for muscle contraction genes. Pathway analysis revealed temporal activity of several signaling pathways, for example the inhibition of WNT signaling on day 2 and its reactivation on day 4. This study provides a comprehensive characterization of biological events and key regulators of the early differentiation of human pluripotent stem cells towards the mesoderm and cardiac lineages. The proposed analysis framework can be used to structure data analysis in future research, both in stem cell differentiation, and more generally, in biomedical big data analytics.

The Tumorigenicity of Multipotent Adult Germline Stem Cells Transplanted into the Heart Is Affected by Natural Killer Cells and by Cyclosporine A Independent of Its Immunosuppressive Effects

Transplantation of stem cells represents an upcoming therapy for many degenerative diseases. For clinical use, transplantation of pluripotent stem cell-derived cells should lead to integration of functional grafts without immune rejection or teratoma formation. Our previous studies showed that the risk of teratoma formation is highly influenced by the immune system of the recipients. In this study, we have observed a higher teratoma formation rate when undifferentiated so-called multipotent adult germline stem cells (maGSCs) were transplanted into the heart of T, B, and natural killer (NK) cell-deficient RAG2^−/−γc^−/− mice than in RAG2^−/− mice, which still have NK cells. Notably, in both strains, the teratoma formation rate was significantly reduced by the immunosuppressive drug cyclosporine A (CsA). Thus, CsA had a profound effect on teratoma formation independent of its immunosuppressive effects. The transplantation into RAG2^−/− mice led to an activation of NK cells, which reached the maximum 14 days after transplantation and was not affected by CsA. The in vivo-activated NK cells efficiently killed YAC-1 and also maGSC target cells. This NK cell activation was confirmed in C57BL/6 wild-type mice whether treated with CsA or not. Sham operations in wild-type mice indicated that the inflammatory response to open heart surgery rather than the transplantation of maGSCs activated the NK cell system. An activation of NK cells during the transplantation of stem cell-derived in vitro differentiated grafts might be clinically beneficial by reducing the risk of teratoma formation by residual pluripotent cells.

New Developments in Cardiac Regeneration

Numerous pharmacological and device therapies have improved adverse cardiac remodelling and mortality in heart failure. However, none are able to regenerate damaged cardiac tissue. Stem cell based therapies using multipotent (adult) stem cells and pluripotent stem cells are new approaches that could potentially achieve the elusive goal of true cardiac regeneration. Over the past two decades, various stem cell based approaches have been shown to improve left ventricular function in pre-clinical animal models. Promising results rapidly led to clinical trials, initially using bone marrow-derived mononuclear cells, then mesenchymal stromal cell populations and, more recently, progenitor cells from the adult heart itself. These have been shown to be safe and have advanced our understanding of potential suitable recipients, cell delivery routes, and possible mechanisms of action. However, efficacy in these trials has been inconsistent. Human pluripotent stem cells (hPSCs) are another potential source of stem cells for cardiac regeneration. They could theoretically provide an unlimited source of cardiomyocytes or cardiac progenitors. Pre-clinical studies in both small and large animal models have shown robust engraftment and improvements in cardiac function. The first clinical trial using hPSC-derived cardiac derivatives has now commenced and others are imminent. In this brief review article, we summarise recent developments in stem cell therapies aimed at cardiac regeneration, including discussion of types of cell and non-cell-based strategies being explored.

Human development: a Special Issue

Summary: With this Special Issue, Development signals its strong interest in the field of human development – a new research frontier opened up by recent technological advances.