Short-term immunosuppression promotes engraftment of embryonic and induced pluripotent stem cells

Enhanced engraftment, proliferation, and therapeutic potential in heart using optimized human iPSC-derived cardiomyocytes

Human pluripotent stem cell-derived cardiomyocytes (CMs) are a promising tool for cardiac cell therapy. Although transplantation of induced pluripotent stem cell (iPSC)-derived CMs have been reported in several animal models, the treatment effect was limited, probably due to poor optimization of the injected cells. To optimize graft cells for cardiac reconstruction, we compared the engraftment efficiency of intramyocardially-injected undifferentiated-iPSCs, day 4 mesodermal cells, and day 8, day 20, and day 30 purified iPSC-CMs after initial differentiation by tracing the engraftment ratio (ER) using in vivo bioluminescence imaging. This analysis revealed the ER of day 20 CMs was significantly higher compared to other cells. Transplantation of day 20 CMs into the infarcted hearts of immunodeficient mice showed good engraftment, and echocardiography showed significant functional improvement by cell therapy. Moreover, the imaging signal and ratio of Ki67-positive CMs at 3 months post injection indicated engrafted CMs proliferated in the host heart. Although this graft growth reached a plateau at 3 months, histological analysis confirmed progressive maturation from 3 to 6 months. These results suggested that day 20 CMs had very high engraftment, proliferation, and therapeutic potential in host mouse hearts. They also demonstrate this model can be used to track the fate of transplanted cells over a long time.

Concise Review: Pluripotent Stem Cell-Derived Cardiac Cells, A Promising Cell Source for Therapy of Heart Failure: Where Do We Stand?

Heart failure is still a major cause of hospitalization and mortality in developed countries. Many clinical trials have tested the use of multipotent stem cells as a cardiac regenerative medicine. The benefit for the patients of this therapeutic intervention has remained limited. Herein, we review the pluripotent stem cells as a cell source for cardiac regeneration. We more specifically address the various challenges of this cell therapy approach. We question the cell delivery systems, the immune tolerance of allogenic cells, the potential proarrhythmic effects, various drug mediated interventions to facilitate cell grafting and, finally, we describe the pathological conditions that may benefit from such an innovative approach. As members of a transatlantic consortium of excellence of basic science researchers and clinicians, we propose some guidelines to be applied to cell types and modes of delivery in order to translate pluripotent stem cell cardiac derivatives into safe and effective clinical trials.

Understanding Stem Cell Immunogenicity in Therapeutic Applications

Stem cells and their differentiated progeny offer great hope for treating disease by providing an unlimited source of cells for repairing or replacing damaged tissue. Initial studies suggested that, unlike 'normal' transplants, specific characteristics of stem cells enabled them to avoid immune attack. However, recent findings have revealed that the immunogenicity of stem cells may have been underestimated. Here, we review the current understanding of the mechanisms of immune recognition associated with stem cell immunogenicity, and discuss the relevance of reprogramming and differentiation strategies used to generate cells or tissue from stem cells for implantation in eliciting an immune response. We examine the effectiveness of current strategies for minimising immune attack in light of our experience in the transplantation field and, in this context, outline important challenges moving forward.

Banking on iPSC--is it doable and is it worthwhile

The discovery of induced pluripotent stem cells (iPSCs) and concurrent development of protocols for their cell-type specific differentiation have revolutionized studies of diseases and raised the possibility that personalized medicine may be achievable. Realizing the full potential of iPSC will require addressing the challenges inherent in obtaining appropriate cells for millions of individuals while meeting the regulatory requirements of delivering therapy and keeping costs affordable. Critical to making PSC based cell therapy widely accessible is determining which mode of cell collection, storage and distribution, will work. In this manuscript we suggest that moderate sized bank where a diverse set of lines carrying different combinations of commonly present HLA alleles are banked and differentiated cells are made available to matched recipients as need dictates may be a solution. We discuss the issues related to developing such a bank and how it could be constructed and propose a bank of selected HLA phenotypes from carefully screened healthy individuals as a solution to delivering personalized medicine.

Engraftment of embryonic stem cells and differentiated progeny by host conditioning with total lymphoid irradiation and regulatory T cells

Embryonic stem cells (ESCs) hold promise for the treatment of many medical conditions; however, their utility is limited by immune rejection. The objective of our study is to establish tolerance or promote engraftment of transplanted ESCs as well as mature cell populations derived from ESCs. Luciferase (luc(+))-expressing ESCs were utilized to monitor the survival of the ESCs and differentiated progeny in living recipients. Allogeneic recipients conditioned with fractioned total lymphoid irradiation (TLI) and anti-thymocyte serum (ATS) or TLI plus regulatory T cells (T(reg)) promoted engraftment of ESC allografts after transplantation. Following these treatments, the engraftment of transplanted terminally differentiated endothelial cells derived from ESCs was also significantly enhanced. Our findings provide clinically translatable strategies of inducing tolerance to adoptively transferred ESCs for cell replacement therapy of medical disorders.

The immune response of stem cells in subretinal transplantation

Stem cell transplantation is a potential curative treatment for degenerative diseases of the retina. Among cell injection sites, the subretinal space (SRS) is particularly advantageous as it is maintained as an immune privileged site by the retinal pigment epithelium (RPE) layer. Thus, the success of subretinal transplantation depends on maintenance of RPE integrity. Moreover, both embryonic stem cells (ESCs) and mesenchymal stem cells (MSCs) have negligible immunogenicity and in fact are immunosuppressive. Indeed, many studies have demonstrated that immunosuppressive drugs are not necessary for subretinal transplantation of stem cells if the blood-retinal barrier is not breached during surgery. The immunogenicity of induced pluripotent stem cells (iPSCs) appears more complex, and requires careful study before clinical application. Despite low rates of graft rejection in animal models, survival rates for ESCs, MSCs, and iPSCs in retina are generally poor, possibly due to resident microglia activated by cell transplantation. To improve graft survival in SRS transplantation, damage to the blood-retinal barrier must be minimized using appropriate surgical techniques. In addition, agents that inhibit microglial activation may be required. Finally, immunosuppressants may be required, at least temporarily, until the blood-retinal barrier heals. We review surgical methods and drug regimens to enhance the likelihood of graft survival after SRS transplantation.

Xenotransplantation of Bone Marrow-Derived Human Mesenchymal Stem Cell Sheets Attenuates Left Ventricular Remodeling in a Porcine Ischemic Cardiomyopathy Model

INTRODUCTION

Bone marrow-derived autologous human mesenchymal stem cells (MSCs) are one of the most promising cell sources for cell therapy to treat heart failure. The cell sheet technique has allowed transplantation of a large number of cells and enhanced the efficacy of cell therapy. We hypothesized that the transplantation of MSC sheets may be a feasible, safe, and effective treatment for ischemic cardiomyopathy (ICM).

METHODS AND RESULTS

Human MSCs acquired from bone marrow were positive for CD73, CD90, and CD105 and negative for CD11b and CD45 by flow cytometry. Ten MSC sheets were created from a total cell number of 1×10(8) MSCs using temperature-responsive culture dishes. These were successfully transplanted over the infarct myocardium of porcine ICM models induced by placing an ameroid constrictor on the left anterior descending coronary artery without any procedural-related complications (MSC group=6: sheet transplantation; sham group=6, oral intake of tacrolimus in both groups). Premature ventricular contractions were rarely detected by Holter electrocardiogram (ECG) in the MSC group in the first week after transplantation. On echocardiography, the cardiac performance of the MSC group was significantly better than that of the sham group at 8 weeks after transplantation. On histological examination 8 weeks after transplantation, left ventricular (LV) remodeling was significantly attenuated compared with the sham group (cardiomyocyte size and interstitial fibrosis were measured). Immunohistochemistry of the von Willebrand factor showed that the vascular density in the infarct border area was significantly greater in the MSC group than the sham group. Expression of angiogenesis-related factors in the infarct border area of the MSC group was significantly greater than that of the sham group, as measured by real-time polymerase chain reaction.

CONCLUSIONS

Bone marrow-derived MSC sheets improved cardiac function and attenuated LV remodeling in ICM without major complications, indicating that this strategy would be applicable in clinical settings.

Pluripotent stem cells and tolerance induction in organ transplantation

PURPOSE OF REVIEW

Ongoing research is constantly looking for means to modulate the immune system for long-lasting engraftment of pluripotent stem cells (PSC) during stem cell-based therapies. This study reviews data on in-vitro and in-vivo immunogenicity of embryonic and induced-PSC and describes how their immunological properties can be harnessed for tolerance induction in organ transplantation.

RECENT FINDINGS

Although PSC display immunomodulatory properties in vitro, they are capable of eliciting an immune response that leads to cell rejection when transplanted into immune-competent recipients. Nevertheless, long-term acceptance of PSC-derived cells/tissues in an allogeneic environment can be achieved using minimal host conditioning. Protocols for differentiating PSC towards haematopoietic stem cells, thymic epithelial precursors, dendritic cells, regulatory T cells and myeloid-derived suppressor cells are being developed, suggesting the possibility to use PSC-derived immunomodulatory cells to induce tolerance to a solid organ transplant.

SUMMARY

PSC and/or their derivatives possess unique immunological properties that allow for acceptance of PSC-derived tissue with minimal host conditioning. Investigators involved either in regenerative or in transplant medicine must join their efforts with the ultimate aim of using PSC as a source of donor-specific cells that would create a protolerogenic environment to achieve tolerance in solid organ transplantation.

Activating receptor NKG2D targets RAE-1-expressing allogeneic neural precursor cells in a viral model of multiple sclerosis

Transplantation of major histocompatibility complex-mismatched mouse neural precursor cells (NPCs) into mice persistently infected with the neurotropic JHM strain of mouse hepatitis virus (JHMV) results in rapid rejection that is mediated, in part, by T cells. However, the contribution of the innate immune response to allograft rejection in a model of viral-induced neurological disease has not been well defined. Herein, we demonstrate that the natural killer (NK) cell-expressing-activating receptor NKG2D participates in transplanted allogeneic NPC rejection in mice persistently infected with JHMV. Cultured NPCs derived from C57BL/6 (H-2(b) ) mice express the NKG2D ligand retinoic acid early precursor transcript (RAE)-1 but expression was dramatically reduced upon differentiation into either glia or neurons. RAE-1(+) NPCs were susceptible to NK cell-mediated killing whereas RAE-1(-) cells were resistant to lysis. Transplantation of C57BL/6-derived NPCs into JHMV-infected BALB/c (H-2(d) ) mice resulted in infiltration of NKG2D(+) CD49b(+) NK cells and treatment with blocking antibody specific for NKG2D increased survival of allogeneic NPCs. Furthermore, transplantation of differentiated RAE-1(-) allogeneic NPCs into JHMV-infected BALB/c mice resulted in enhanced survival, highlighting a role for the NKG2D/RAE-1 signaling axis in allograft rejection. We also demonstrate that transplantation of allogeneic NPCs into JHMV-infected mice resulted in infection of the transplanted cells suggesting that these cells may be targets for infection. Viral infection of cultured cells increased RAE-1 expression, resulting in enhanced NK cell-mediated killing through NKG2D recognition. Collectively, these results show that in a viral-induced demyelination model, NK cells contribute to rejection of allogeneic NPCs through an NKG2D signaling pathway.

Human Induced Pluripotent Stem Cells Are Targets for Allogeneic and Autologous Natural Killer (NK) Cells and Killing Is Partly Mediated by the Activating NK Receptor DNAM-1

Human induced pluripotent stem cells (hiPSCs) could be used to generate autologous cells for therapeutic purposes, which are expected to be tolerated by the recipient. However, iPSC-derived grafts are at risk of giving rise to teratomas in the host, if residuals of tumorigenic cells are not rejected by the recipient. We have analyzed the susceptibility of hiPSC lines to allogeneic and autologous natural killer (NK) cells. IL-2-activated, in contrast to resting NK cells killed hiPSC lines efficiently (P = 1.69 x 10(-39)). Notably, the specific lysis of the individual hiPSC lines by IL-2-activated NK cells was significantly different (P = 1.72 x 10(-6)) and ranged between 46 % and 64 % in 51Cr-release assays when compared to K562 cells. The hiPSC lines were killed by both allogeneic and autologous NK cells although autologous NK cells were less efficient (P=8.63 x 10(-6)). Killing was partly dependent on the activating NK receptor DNAM-1 (P = 8.22 x 10(-7)). The DNAM-1 ligands CD112 and CD155 as well as the NKG2D ligands MICA and MICB were expressed on the hiPSC lines. Low amounts of human leukocyte antigen (HLA) class I proteins, which serve as ligands for inhibitory and activating NK receptors were also detected. Thus, the susceptibility to NK cell killing appears to constitute a common feature of hiPSCs. Therefore, NK cells might reduce the risk of teratoma formation even after autologous transplantations of pluripotent stem cell-derived grafts that contain traces of pluripotent cells.

Avoiding immunological rejection in regenerative medicine

One of the major goals of regenerative medicine is repair or replacement of diseased and damaged tissues by transfer of differentiated stem cells or stem cell-derived tissues. The possibility that these tissues will be destroyed by immunological rejection remains a challenge that can only be overcome through a better understanding of the nature and expression of potentially immunogenic molecules associated with cell replacement therapy and the mechanisms and pathways resulting in their immunologic rejection. This review draws on clinical experience of organ and tissue transplantation, and on transplantation immunology research to consider practical approaches for avoiding and overcoming the possibility of rejection of stem cell-derived tissues.

Neonatal desensitization for the study of regenerative medicine

Cell replacement is a therapeutic option for numerous diseases of the CNS. Current research has identified a number of potential human donor cell types, for which preclinical testing through xenotransplantation in animal models is imperative. Immune modulation is necessary to promote donor cell survival for sufficient time to assess safety and efficacy. Neonatal desensitization can promote survival of human donor cells in adult rat hosts with little impact on the health of the host and for substantially longer than conventional methods, and has subsequently been applied in a range of studies with variable outcomes. Reviewing these findings may provide insight into the method and its potential for use in preclinical studies in regenerative medicine.

Stem cells and differentiation--a synoptic review of patents granted since 2009

INTRODUCTION

Innovations in human pluripotent stem cell research and their application in therapeutics have seen a giant leap in the past decade. Patent applications related to human pluripotent stem cell generation, culture and differentiation show an ever-increasing trend worldwide with hundreds of patents being applied for every year. With the turn of the second decade in stem cell patenting, a review of the latest patents issued will be significant.

AREAS COVERED

The growing need in healthcare sector has revolutionized stem cell application in clinical therapeutics by extending in unprecedented dimensions. With the potential of being able to differentiate into any desired adult cell lineage, human pluripotent stem cells find a wide range of applicability in clinical as well as cosmetic therapy. Moreover, the recent innovation of isolating a disease-specific pluripotent stem cell has opened new horizons to stem cell application in cell therapy. This review gives an overview of significant international patents granted on innovations in human pluripotent stem cell differentiation methodologies between 2009 and 2014.

EXPERT OPINION

The discovery of human pluripotent stem cells and their immense potential in clinical therapeutics has increasingly channeled scientific research in their orientation. Although being widely used to fathom human physiology, the trend in stem cell application is slowly shifting toward disease-modeling, drug safety evaluation and toxicity-testing. And in order to probe those unexplored realms of stem cell applications, a unified approach from the scientific community is imperative.

Magnetic resonance imaging of stem cell apoptosis in arthritic joints with a caspase activatable contrast agent

About 43 million individuals in the U.S. encounter cartilage injuries due to trauma or osteoarthritis, leading to joint pain and functional disability. Matrix-associated stem cell implants (MASI) represent a promising approach for repair of cartilage defects. However, limited survival of MASI creates a significant bottleneck for successful cartilage regeneration outcomes and functional reconstitution. We report an approach for noninvasive detection of stem cell apoptosis with magnetic resonance imaging (MRI), based on a caspase-3-sensitive nanoaggregation MRI probe (C-SNAM). C-SNAM self-assembles into nanoparticles after hydrolysis by caspase-3, leading to 90% amplification of (1)H MR signal and prolonged in vivo retention. Following intra-articular injection, C-SNAM causes significant MR signal enhancement in apoptotic MASI compared to viable MASI. Our results indicate that C-SNAM functions as an imaging probe for stem cell apoptosis in MASI. This concept could be applied to a broad range of cell transplants and target sites.

Human neural stem cells improve cognition and promote synaptic growth in two complementary transgenic models of Alzheimer's disease and neuronal loss

Alzheimer's disease (AD) is the most prevalent age‐related neurodegenerative disorder, affecting over 35 million people worldwide. Pathologically, AD is characterized by the progressive accumulation of β‐amyloid (Aβ) plaques and neurofibrillary tangles within the brain. Together, these pathologies lead to marked neuronal and synaptic loss and corresponding impairments in cognition. Current treatments, and recent clinical trials, have failed to modify the clinical course of AD; thus, the development of novel and innovative therapies is urgently needed. Over the last decade, the potential use of stem cells to treat cognitive impairment has received growing attention. Specifically, neural stem cell transplantation as a treatment for AD offers a novel approach with tremendous therapeutic potential. We previously reported that intrahippocampal transplantation of murine neural stem cells (mNSCs) can enhance synaptogenesis and improve cognition in 3xTg‐AD mice and the CaM/Tet‐DT_A model of hippocampal neuronal loss. These promising findings prompted us to examine a human neural stem cell population, HuCNS‐SC, which has already been clinically tested for other neurodegenerative disorders. In this study, we provide the first evidence that transplantation of research grade HuCNS‐SCs can improve cognition in two complementary models of neurodegeneration. We also demonstrate that HuCNS‐SC cells can migrate and differentiate into immature neurons and glia and significantly increase synaptic and growth‐associated markers in both 3xTg‐AD and CaM/Tet‐DT_A mice. Interestingly, improvements in aged 3xTg‐AD mice were not associated with altered Aβ or tau pathology. Rather, our findings suggest that human NSC transplantation improves cognition by enhancing endogenous synaptogenesis. Taken together, our data provide the first preclinical evidence that human NSC transplantation could be a safe and effective therapeutic approach for treating AD. © 2014 The Authors. Hippocampus Published by Wiley Periodicals, Inc.

Gene delivery in tissue engineering and regenerative medicine

As a promising strategy to aid or replace tissue/organ transplantation, gene delivery has been used for regenerative medicine applications to create or restore normal function at the cell and tissue levels. Gene delivery has been successfully performed ex vivo and in vivo in these applications. Excellent proliferation capabilities and differentiation potentials render certain cells as excellent candidates for ex vivo gene delivery for regenerative medicine applications, which is why multipotent and pluripotent cells have been intensely studied in this vein. In this review, gene delivery is discussed in detail, along with its applications to tissue engineering and regenerative medicine. A definition of a stem cell is compared to a definition of a stem property, and both provide the foundation for an in-depth look at gene delivery investigations from a germ lineage angle.

Stem cell imaging: from bench to bedside

Although cellular therapies hold great promise for the treatment of human disease, results from several initial clinical trials have not shown a level of efficacy required for their use as a first line therapy. Here we discuss how in vivo molecular imaging has helped identify barriers to clinical translation and potential strategies that may contribute to successful transplantation and improved outcomes, with a focus on cardiovascular and neurological diseases. We conclude with a perspective on the future role of molecular imaging in defining safety and efficacy for clinical implementation of stem cell therapies.

Negligible immunogenicity of induced pluripotent stem cells derived from human skin fibroblasts

Human induced pluripotent stem cells (hiPSCs) have potential applications in cell replacement therapy and regenerative medicine. However, limited information is available regarding the immunologic features of iPSCs. In this study, expression of MHC and T cell co-stimulatory molecules in hiPSCs, and the effects on activation, proliferation and cytokine production in allogeneic human peripheral blood mononuclear cells were examined. We found that no-integrate hiPSCs had no MHC-II and T cell co-stimulatory molecules expressions but had moderate level of MHC-I and HLA-G expressions. In contrast to human skin fibroblasts (HSFs) which significantly induced allogeneic T cell activation and proliferation, hiPSCs failed to induce allogeneic CD45⁺ lymphocyte and CD8⁺ T cell activation and proliferation but could induce a low level of allogeneic CD4⁺ T cell proliferation. Unlike HSFs which induced allogeneic lymphocytes to produce high levels of IFN-γ, TNF-α and IL-17, hiPSCs only induced allogeneic lymphocytes to produce IL-2 and IL-10, and promote IL-10-secreting regulatory T cell (Treg) generation. Our study suggests that the integration-free hiPSCs had low or negligible immunogenicity, which may result from their induction of IL-10-secreting Treg.

Tolerance induction to human stem cell transplants with extension to their differentiated progeny

There is increasing interest in transplantation of human stem cells for therapeutic purposes. It would benefit future application if one could achieve their long-term acceptance and functional differentiation in allogeneic hosts using minimal immunosuppression. Allogeneic stem cell transplants differ from conventional tissue transplants insofar as not all alloantigens are revealed during tolerance induction. This risks that the immune system tolerized to antigens expressed by progenitors may still remain responsive to antigens expressed later during differentiation. Here we show that brief induction with monoclonal antibody-mediated coreceptor and costimulation blockade enables long-term engraftment and tolerance towards murine ESCs, hESCs, human induced pluripotent stem cells (iPSCs) and hESC-derived progenitors in outbred murine recipients. Tolerance induced to PSC-derived progenitors extends to their differentiated progenies, and sometimes even to different tissues derived from the same donor. Global gene expression profiling identifies clear features in T cells from tolerized grafts that are distinct from those involved in rejection.

Nanotechnology in the Regeneration of Complex Tissues

Modern medicine faces a growing crisis as demand for organ transplantations continues to far outstrip supply. By stimulating the body’s own repair mechanisms, regenerative medicine aims to reduce demand for organs, while the closely related field of tissue engineering promises to deliver “off-the-self” organs grown from patients’ own stem cells to improve supply. To deliver on these promises, we must have reliable means of generating complex tissues. Thus far, the majority of successful tissue engineering approaches have relied on macroporous scaffolds to provide cells with both mechanical support and differentiative cues. In order to engineer complex tissues, greater attention must be paid to nanoscale cues present in a cell’s microenvironment. As the extracellular matrix is capable of driving complexity during development, it must be understood and reproduced in order to recapitulate complexity in engineered tissues. This review will summarize current progress in engineering complex tissue through the integration of nanocomposites and biomimetic scaffolds.

Differentiation of human umbilical cord matrix mesenchymal stem cells into neural-like progenitor cells and maturation into an oligodendroglial-like lineage

Mesenchymal stem cells (MSCs) are viewed as safe, readily available and promising adult stem cells, which are currently used in several clinical trials. Additionally, their soluble-factor secretion and multi-lineage differentiation capacities place MSCs in the forefront of stem cell types with expected near-future clinical applications. In the present work MSCs were isolated from the umbilical cord matrix (Wharton's jelly) of human umbilical cord samples. The cells were thoroughly characterized and confirmed as bona-fide MSCs, presenting in vitro low generation time, high proliferative and colony-forming unit-fibroblast (CFU-F) capacity, typical MSC immunophenotype and osteogenic, chondrogenic and adipogenic differentiation capacity. The cells were additionally subjected to an oligodendroglial-oriented step-wise differentiation protocol in order to test their neural- and oligodendroglial-like differentiation capacity. The results confirmed the neural-like plasticity of MSCs, and suggested that the cells presented an oligodendroglial-like phenotype throughout the differentiation protocol, in several aspects sharing characteristics common to those of bona-fide oligodendrocyte precursor cells and differentiated oligodendrocytes.

Strategies and processes to decellularize and recellularize hearts to generate functional organs and reduce the risk of thrombosis

Heart failure is one of the leading causes of death in the United States. Current therapies, such as heart transplants and bioartificial hearts, are helpful, but not optimal. Decellularization of porcine whole hearts followed by recellularization with patient-specific human cells may provide the ultimate solution for patients with heart failure. Great progress has been made in the development of efficient processes for decellularization, and the design of automated bioreactors. Challenges remain in selecting and culturing cells, growing the cells on the decellularized scaffolds without contamination, characterizing the regenerated organs, and preventing thrombosis. Various strategies have been proposed to prevent thrombosis of blood-contacting devices, including reendothelization and the creation of nonfouling surfaces using surface modification technologies. This review discusses the progress and remaining challenges involved with recellularizing whole hearts, focusing on the prevention of thrombosis.

Beyond GWAS in COPD: probing the landscape between gene-set associations, genome-wide associations and protein-protein interaction networks

OBJECTIVES

To use a systems biology approach to integrate genotype and protein-protein interaction (PPI) data to identify disease network modules associated with chronic obstructive pulmonary disease (COPD) and to perform traditional pathway analysis.

METHODS

We utilized a standard gene-set association approach (FORGE) using gene-based association analysis and gene-set definitions from the molecular signatures database (MSigDB). As a discovery step, we analyzed GWAS results from 2 well-characterized COPD cohorts: COPDGene and GenKOLS. We used a third well-characterized COPD case-control cohort for replication: ECLIPSE. Next, we used dmGWAS, a method that integrates GWAS results with PPI, to identify COPD disease modules.

RESULTS

No gene-sets reached experiment-wide significance in either discovery population. We identified a consensus network of 10 genes identified in modules by integrating GWAS results with PPI that replicated in COPDGene, GenKOLS, and ECLIPSE. Members of 4 gene-sets were enriched among these 10 genes: (i) lung adenocarcinoma tumor-sequencing genes, (ii) IL-7 pathway genes, (iii) kidney cell response to arsenic, and (iv) CD4 T-cell responses. Further, several genes have also been associated with pathophysiology relevant to COPD including KCNK3, NEDD4L, and RIN3. In particular, KCNK3 has been associated with pulmonary arterial hypertension, a common complication in advanced COPD.

CONCLUSION

We report a set of new genes that may influence the etiology of COPD that would not have been identified using traditional GWAS and pathway analyses alone.

Stem cell therapy for cardiac dysfunction

Following significant injury, the heart undergoes induced compensation and gradually deteriorates towards impending heart failure. Current therapy slows but does not halt the resultant adverse remodeling. Stem cell therapy, however, has the potential to regenerate or repair infarcted heart tissue and therefore is a promising therapeutic strategy undergoing intensive investigation. Due to the wide range of stem cells investigated, it is difficult to navigate this field. This review aims to summarize the main types of stem cells (both of cardiac and extra-cardiac origin) that possess promising therapeutic potential. Particular focus is placed on clinical trials supporting this therapeutic strategy.

Natural killer cell subsets differentially reject embryonic stem cells based on licensing

BACKGROUND

Embryonic stem cells (ESC) and induced pluripotent stem cells provide great promise to the future of medicine. Because immune rejection represents a major obstacle to the success of all stem cell-based therapies, many recent studies have sought to determine the key immune mediators involved in ESC rejection. The role of natural killer (NK) cells and specifically the role of NK cell licensing is not well understood in ESC rejection.

METHODS

Mouse or human ESCs were subjected to cytotoxicity assays involving their respective species-matched activated NK cells. Mouse ESCs were then transplanted to allogeneic recipients after depletion of NK cell subsets in the host. ESC engraftment was analyzed by bioluminescent imaging.

RESULTS

Depletion of all NK cells in vivo resulted in the greatest amount of ESC engraftment, confirming a role for NK cells in ESC rejection. Importantly, depletion of the Ly49C/I or Ly49G2 NK cell subsets resulted in differential ESC engraftment and rejection. This indicates that NK cell rejection of allogeneic ESC is highly differential based on the presence of licensed NK cells. Blocking NKG2D in vitro resulted in less killing of mESC by allogeneic NK cells, indicating NKG2D is a likely mechanism for NK-mediated killing of mESC.

CONCLUSIONS

In this study, we show that expression of inhibitory Ly49s correlates with the ability of NK cells to kill murine ESC in an NKG2D-dependent manner. This further suggests that the rejection of similar stem cell transplants in humans will be dependent upon the presence of licensed NK cells.

Pluripotent stem cell derived cardiomyocytes for cardiac repair

OPINION STATEMENT

The adult mammalian heart has limited capacity for regeneration, and any major injury such as a myocardial infarction results in the permanent loss of up to 1 billion cardiomyocytes. The field of cardiac cell therapy aims to replace these lost contractile units with de novo cardiomyocytes to restore lost systolic function and prevent progression to heart failure. Arguably, the ideal cell for this application is the human cardiomyocyte itself, which can electromechanically couple with host myocardium and contribute active systolic force. Pluripotent stem cells from human embryonic or induced pluripotent lineages are attractive sources for cardiomyocytes, and preclinical investigation of these cells is in progress. Recent work has focused on the efficient generation and purification of cardiomyocytes, tissue engineering efforts, and examining the consequences of cell transplantation from mechanical, vascular, and electrical standpoints. Here we discuss historical and contemporary aspects of pluripotent stem cell-based cardiac cell therapy, with an emphasis on recent preclinical studies with translational goals.

Natural killer cell-activating receptor NKG2D mediates innate immune targeting of allogeneic neural progenitor cell grafts

Cell replacement therapy holds promise for a number of untreatable neurological or psychiatric diseases but the immunogenicity of cellular grafts remains controversial. Emerging stem cell and reprogramming technologies can be used to generate autologous grafts that minimize immunological concerns but autologous grafts may carry an underlying genetic vulnerability that reduces graft efficacy or survival. Healthy allogeneic grafts are an attractive and commercially scalable alternative if immunological variables can be controlled. Stem cells and immature neural progenitor cells (NPC) do not express major histocompatibility complex (MHC) antigens and can evade adaptive immune surveillance. Nevertheless, in an experimental murine model, allogeneic NPCs do not survive and differentiate as well as syngeneic grafts, even when traditional immunosuppressive treatments are used. In this study, we show that natural killer (NK) cells recognize the lack of self-MHC antigens on NPCs and pose a barrier to NPC transplantation. NK cells readily target both syngeneic and allogeneic NPC, and killing is modulated primarily by NK-inhibiting "self" class I MHC and NK-activating NKG2D-ligand expression. The absence of NKG2D signaling in NK cells significantly improves NPC-derived neuron survival and differentiation. These data illustrate the importance of innate immune mechanisms in graft outcome and the potential value of identifying and targeting NK cell-activating ligands that may be expressed by stem cell derived grafts.

Induced pluripotent stem cells have similar immunogenic and more potent immunomodulatory properties compared with bone marrow-derived stromal cells in vitro

AIM

To evaluate the in vitro immunogenic and immunomodulatory properties of induced pluripotent stem cells (iPSCs) compared with bone marrow-derived mesenchymal stromal cells (MSCs).

MATERIALS & METHODS

Mouse embryonic fibroblasts (MEFs) were isolated from C3HeB/FeJ and C57BL/6J mice, and reprogrammed to generate iPSCs. Mixed leukocyte reactions were performed using MHC-matched and -mismatched responder leukocytes and stimulator leukocytes, iPSCs or MSCs. To assess immunogenic potential, iPSCs and MSCs were used as stimulator cells for responder leukocytes. To assess immunomodulatory properties, iPSCs and MSCs were cultured in the presence of stimulator and responder leukocytes. MEFs were used as a control.

RESULTS

iPSCs had similar immunogenic properties but more potent immunomodulatory effects than MSCs. Co-culture of MHC-mismatched leukocytes with MHC-matched iPSCs resulted in significantly less responder T-cell proliferation than observed for MHC-mismatched leukocytes alone and at more responder leukocyte concentrations than with MSCs. In addition, MHC-mismatched iPSCs significantly reduced responder T-cell proliferation when co-cultured with MHC-mismatched leukocytes, while MHC-mismatched MSCs did not.

CONCLUSION

These results provide important information when considering the use of iPSCs in place of MSCs in both regenerative and transplantation medicine.

A simple, cost-effective but highly efficient system for deriving ventricular cardiomyocytes from human pluripotent stem cells

Self-renewable human pluripotent stem cells (hPSCs) serve as a potential unlimited ex vivo source of human cardiomyocytes (CMs) for cell-based disease modeling and therapies. Although recent advances in directed differentiation protocols have enabled more efficient derivation of hPSC-derived CMs with an efficiency of ∼50%-80% CMs and a final yield of ∼1-20 CMs per starting undifferentiated hPSC, these protocols are often not readily transferrable across lines without first optimizing multiple parameters. Further, the resultant populations are undefined for chamber specificity or heterogeneous containing mixtures of atrial, ventricular (V), and pacemaker derivatives. Here we report a highly cost-effective and reproducibly efficient system for deriving hPSC-ventricular cardiomyocytes (VCMs) from all five human embryonic stem cell (HES2, H7, and H9) and human induced PSC (hiPSC) (reprogrammed from human adult peripheral blood CD34(+) cells using nonintegrating episomal vectors) lines tested. Cardiogenic embryoid bodies could be formed by the sequential addition of BMP4, Rho kinase inhibitor, activin-A, and IWR-1. Spontaneously contracting clusters appeared as early as day 8. At day 16, up to 95% of cells were cTnT(+). Of which, 93%, 94%, 100%, 92%, and 92% of cardiac derivatives from HES2, H7, H9, and two iPSC lines, respectively, were VCMs as gauged by signature ventricular action potential and ionic currents (INa(+)/ICa,L(+)/IKr(+)/IKATP(+)); Ca(2+) transients showed positive chronotropic responses to β-adrenergic stimulation. Our simple, cost-effective protocol required the least amounts of reagents and time compared with others. While the purity and percentage of PSC-VCMs were comparable to a recently published protocol, the present yield and efficiency with a final output of up to 70 hPSC-VCMs per hPSC was up to 5-fold higher and without the need of performing line-specific optimization. These differences were discussed. The results may lead to mass production of hPSC-VCMs in bioreactors.

Cardiac stem cell biology: glimpse of the past, present, and future

Cardiac regeneration strategies and de novo generation of cardiomyocytes have long been significant areas of research interest in cardiovascular medicine. In this review, we outline a variety of common cell sources and methods used to regenerate cardiomyocytes and highlight the important role that key Circulation Research articles have played in this flourishing field.

Indirect immune recognition of mouse embryonic stem cell-derived hematopoietic progenitors in vitro

The clinical use of embryonic stem cell (ESC)-derived hematopoietic progenitors (ESHPs) requires the generation of ESHPs that produce mature hematopoietic cells and do not induce immune rejection after transplantation. We compared the developmental maturity and immunogenicity of ESHPs generated using two methods: embryoid body (EB) formation and culture of ESCs with the OP9 bone marrow stromal cell line (ESC-OP9). ESHPs derived from EBs displayed an immature hematopoietic phenotype and were devoid of immunogenicity marker expression. In contrast, ESHPs derived via ESC-OP9 displayed a mature phenotype and expressed high levels of some immunostimulatory molecules. ESHPs alone could not stimulate CD4(+) T lymphocyte proliferation directly. However, preferential phagocytosis of ESHPs and T cell proliferation were observed in the presence of antigen-presenting cells, consistent with a model of indirect immune recognition of ESHPs. These results suggest that depletion of host CD4(+) T lymphocytes or antigen-presenting cells may be necessary for successful ESHP transplantation.

Costimulation blockade induces foxp3(+) regulatory T cells to human embryonic stem cells

Transplantation of human embryonic stem cells (hESCs), like other allogeneic cellular transplants, require immunomodulation or immunosuppression in order to be maintained in the recipient. Costimulation blockade applied at the time of transplantation inhibits costimulatory signals in the immunological synapse leading to a state of anergy in the donor reactive T-cell population and a state of immunological tolerance in the host. In models of solid organ transplantation, tolerance is maintained by the infiltration of Foxp3⁺ regulatory T cells into the graft. In order to study if regulatory T cells could be generated to hESC transplants, costimulation blockade (CTLA4Ig, anti-CD40L, anti-LFA-1) was administered for the first week after transplantation of two different hESC lines implanted under the kidney capsule of wild-type mice. hESC transplants were maintained indefinitely, and when harvested at long-term follow-up, Foxp3⁺ T-cells were found surrounding the graft, implying the maintenance of tolerance through the induction of regulatory T cells. These results imply that costimulation blockade could be a useful treatment strategy for the induction of tolerance to hESC transplants and may down-modulate immune responses locally around the graft.

The potential for immunogenicity of autologous induced pluripotent stem cell-derived therapies

Induced pluripotent stem cell (iPSC) technology offers the promise of immune-matched cell therapies for a wide range of diseases and injuries. It is generally assumed that cells derived from autologous iPSCs will be immune-privileged. However, there are reasons to question this assumption, including recent studies that have tested iPSC immunogenicity in various ways with conflicting results. Understanding the risk of an immune response and developing strategies to minimize it will be important steps before clinical testing. Here, we review the evidence for autologous iPSC immunogenicity, its potential causes, and approaches for assessment and mitigation.

The immunogenicity of cells derived from induced pluripotent stem cells

With their ability to undergo unlimited self-renewal in culture and to differentiate into all cell types in the body, human embryonic stem cells (hESCs) hold great potential for the treatment of currently incurable diseases. Two hESC-based cell therapies for spinal cord injury and macular degeneration have been advanced into human clinical trials. Despite this rapid progress, one key challenge of hESC-based cell therapy is the allogeneic immune rejection of hESC-derived cells by recipients. This problem could be mitigated by a recent breakthrough in the technology of induced pluripotent stem cells (iPSCs) by nuclear reprogramming of patient-specific somatic cells with defined factors, which could become a renewable source of autologous cells for cell therapy. However, recent studies revealing the abnormal epigenetics, genomic stability and immunogenicity of iPSCs have raised safety concerns over iPSC-based therapy. Recent findings related to the immunogenicity of iPSC derivatives will be summarized in this review.

Enhanced survival of transplanted human induced pluripotent stem cell-derived cardiomyocytes by the combination of cell sheets with the pedicled omental flap technique in a porcine heart

BACKGROUND

Transplantation of cardiomyocytes that are derived from human induced pluripotent stem cell-derived cardiomyocytes (hiPS-CMs) shows promise in generating new functional myocardium in situ, whereas the survival and functionality of the transplanted cells are critical in considering this therapeutic impact. Cell-sheet method has been used to transplant many functional cells; however, potential ischemia might limit cell survival. The omentum, which is known to have rich vasculature, is expected to be a source of blood supply. We hypothesized that transplantation of hiPS-CM cell sheets combined with an omentum flap may deliver a large number of functional hiPS-CMs with enhanced blood supply.

METHODS AND RESULTS

Retrovirally established human iPS cells were treated with Wnt signaling molecules to induce cardiomyogenic differentiation, followed by superparamagnetic iron oxide labeling. Cell sheets were created from the magnetically labeled hiPS-CMs using temperature-responsive dishes and transplanted to porcine hearts with or without the omentum flap (n=8 each). Two months after transplantation, the survival of superparamagnetic iron oxide-labeled hiPS-CMs, assessed by MRI, was significantly greater in mini-pigs with the omentum than in those without it; histologically, vascular density in the transplanted area was significantly greater in mini-pigs with the omentum than in those without it. The transplanted tissues contained abundant cardiac troponin T-positive cells surrounded by vascular-rich structures.

CONCLUSIONS

The omentum flap enhanced the survival of hiPS-CMs after transplantation via increased angiogenesis, suggesting that this strategy is useful in clinical settings. The combination of hiPS-CMs and the omentum flap may be a promising technique for the development of tissue-engineered vascular-rich new myocardium in vivo.

Four decades of leading-edge research in the reproductive and developmental sciences: the Infant Primate Research Laboratory at the University of Washington National Primate Research Center

The Infant Primate Research Laboratory (IPRL) was established in 1970 at the University of Washington as a visionary project of Dr. Gene (Jim) P. Sackett. Supported by a collaboration between the Washington National Primate Research Center and the Center on Human Development and Disability, the IPRL operates under the principle that learning more about the causes of abnormal development in macaque monkeys will provide important insights into the origins and treatment of childhood neurodevelopmental disabilities. Over the past 40 years, a broad range of research projects have been conducted at the IPRL. Some have described the expression of normative behaviors in nursery-reared macaques while others have focused on important biomedical themes in child health and development. This article details the unique scientific history of the IPRL and the contributions produced by research conducted in the laboratory. Past and present investigations have explored the topics of early rearing effects, low-birth-weight, prematurity, birth injury, epilepsy, prenatal neurotoxicant exposure, viral infection (pediatric HIV), diarrheal disease, vaccine safety, and assisted reproductive technologies. Data from these studies have helped advance our understanding of both risk and resiliency in primate development. New directions of research at the IPRL include the production of transgenic primate models using our embryonic stem cell-based technology to better understand and treat heritable forms of human intellectual disabilities such as fragile X.

Costimulation-adhesion blockade is superior to cyclosporine A and prednisone immunosuppressive therapy for preventing rejection of differentiated human embryonic stem cells following transplantation

RATIONALE

Human embryonic stem cell (hESC) derivatives are attractive candidates for therapeutic use. The engraftment and survival of hESC derivatives as xenografts or allografts require effective immunosuppression to prevent immune cell infiltration and graft destruction.

OBJECTIVE

To test the hypothesis that a short-course, dual-agent regimen of two costimulation-adhesion blockade agents can induce better engraftment of hESC derivatives compared to current immunosuppressive agents.

METHODS AND RESULTS

We transduced hESCs with a double fusion reporter gene construct expressing firefly luciferase (Fluc) and enhanced green fluorescent protein, and differentiated these cells to endothelial cells (hESC-ECs). Reporter gene expression enabled longitudinal assessment of cell engraftment by bioluminescence imaging. Costimulation-adhesion therapy resulted in superior hESC-EC and mouse EC engraftment compared to cyclosporine therapy in a hind limb model. Costimulation-adhesion therapy also promoted robust hESC-EC and hESC-derived cardiomyocyte survival in an ischemic myocardial injury model. Improved hESC-EC engraftment had a cardioprotective effect after myocardial injury, as assessed by magnetic resonance imaging. Mechanistically, costimulation-adhesion therapy is associated with systemic and intragraft upregulation of T-cell immunoglobulin and mucin domain 3 (TIM3) and a reduced proinflammatory cytokine profile.

CONCLUSIONS

Costimulation-adhesion therapy is a superior alternative to current clinical immunosuppressive strategies for preventing the post-transplant rejection of hESC derivatives. By extending the window for cellular engraftment, costimulation-adhesion therapy enhances functional preservation following ischemic injury. This regimen may function through a TIM3-dependent mechanism.

A surgical technique for homogenous renal distribution of substances in rats

Intra-arterial injection of mesenchymal stem cells has been proven to result in a superior nephroprotection compared to intravenous injection. This avoids initial passage through filter organs such as the lung, liver and spleen. The aim of the present study was to investigate whether suprarenal aortic delivery results in a homogenous distribution to both kidneys. Chinese ink was used to evaluate the renal distribution pattern for the comparison of two retrograde intra-aortic injection methods. In the first, the aorta caudal to the renal branches was temporarily clamped and Chinese ink was injected at the level of the renal arteries. In the second, a distal aortic clamp was combined with alternated clamping of the contralateral arteries. Immediately after injection, kidneys were harvested for histological analysis. Amniotic fluid stem cells labeled with LacZ were injected in the aorta by alternated clamping of the renal arteries in order to track the cells in a rat ischemia/reperfusion model. Without renal artery clamping, intra-aortic administration resulted in a delivery of the ink into the right kidney, whereas administration with alternated clamping of the contralateral renal artery, together with distal aortic artery clamping, resulted in a more homogenous distribution of the ink in both kidneys. Moreover, LacZ-positive cells were found in both kidneys after 6 h of injection. In conclusion, the retrograde administration of Chinese ink in two steps is a fast and reproducible technique, which results in a more homogenous distribution of the stain in both kidneys than a single administration combined by only clamping the aorta.

Development of a xeno-free autologous culture system for endothelial progenitor cells derived from human umbilical cord blood

Despite promising preclinical outcomes in animal models, a number of challenges remain for human clinical use. In particular, expanding a large number of endothelial progenitor cells (EPCs) in vitro in the absence of animal-derived products is the most critical hurdle remaining to be overcome to ensure the safety and efficiency of human therapy. To develop in vitro culture conditions for EPCs derived from human cord blood (hCB-EPCs), we isolated extracts (UCE) and collagen (UC-collagen) from umbilical cord tissue to replace their animal-derived counterparts. UC-collagen and UCE efficiently supported the attachment and proliferation of hCB-EPCs in a manner comparable to that of animal-derived collagen in the conventional culture system. Our developed autologous culture system maintained the typical characteristics of hCB-EPCs, as represented by the expression of EPC-associated surface markers. In addition, the therapeutic potential of hCB-EPCs was confirmed when the transplantation of hCB-EPCs cultured in this autologous culture system promoted limb salvage in a mouse model of hindlimb ischemia and was shown to contribute to attenuating muscle degeneration and fibrosis. We suggest that the umbilical cord represents a source for autologous biomaterials for the in vitro culture of hCB-EPCs. The main characteristics and therapeutic potential of hCB-EPCs were not compromised in developed autologous culture system. The absence of animal-derived products in our newly developed in vitro culture removes concerns associated with secondary contamination. Thus, we hope that this culture system accelerates the realization of therapeutic applications of autologous hCB-EPCs for human vascular diseases.

Tumorigenicity as a clinical hurdle for pluripotent stem cell therapies

Human pluripotent stem cells (PSCs) are a leading candidate for cell-based therapies because of their capacity for unlimited self renewal and pluripotent differentiation. These advances have recently culminated in the first-in-human PSC clinical trials by Geron, Advanced Cell Technology and the Kobe Center for Developmental Biology for the treatment of spinal cord injury and macular degeneration. Despite their therapeutic promise, a crucial hurdle for the clinical implementation of human PSCs is their potential to form tumors in vivo. In this Perspective, we present an overview of the mechanisms underlying the tumorigenic risk of human PSC-based therapies and discuss current advances in addressing these challenges.

Mechanistic molecular imaging of cardiac cell therapy for ischemic heart disease

Cell-based myocardial regeneration has emerged as a promising therapeutic option for ischemic heart disease, though not yet at the level of routine clinical utility. Despite the encouraging results from initial preclinical studies that have demonstrated improved function and reduced infarct size of the ischemic myocardium following several candidate cell transplantation, the beneficial effects and molecular mechanisms of cardiac cell therapy are still unclear in clinical applications to date, and much remains to be optimized. To improve engraftment, accurate methods are required for tracking cell fate and quantifying functional outcome. In the present review, we summarized the current status and challenges of cardiac cell therapy for ischemic heart disease and discussed the strengths and limitations of currently available in vivo imaging techniques with special focus on the newly developed multimodality approaches for assessing the efficacy of engrafted donor cells. We also addressed the hurdles these imaging modalities are facing, including issues regarding immunogenicity and tumorigenicity of transplanted stem cells, and provided some the future perspectives on stem cell imaging.

Human endometrial stem cells confer enhanced myocardial salvage and regeneration by paracrine mechanisms

Human endometrial stem cells (EnSCs) have the potential to be 'off the shelf' clinical reagents for the treatment of heart failure. Here, using an immunocompetent rat model of myocardial infarction (MI), we provide evidence that the functional benefits of EnSC transplantation are principally and possibly exclusively through a paracrine effect. Human EnSCs were delivered by intramyocardial injection into rats 30 min. after coronary ligation. EnSC therapy significantly preserved viable myocardium in the infarct zone and improved cardiac function at 28 days. Despite increased viable myocardium and vascular density, there was scant evidence of differentiation of EnSCs into any cardiovascular cell type. Cultured human EnSCs expressed a distinctive profile of cytokines that enhanced the survival, proliferation and function of endothelial cells in vitro. When injected into the peri-infarct zone, human EnSCs activated AKT, ERK1/2 and STAT3 and inhibited the p38 signalling pathway. EnSC therapy decreased apoptosis and promoted cell proliferation and c-kit+ cell recruitment in vivo. Myocardial protection and enhanced post-infarction regeneration by EnSCs is mediated primarily by paracrine effects conferred by secreted cytokines that activate survival pathways and recruit endogenous progenitor stem cells. Menstrual blood provides a potentially limitless source of biologically competent 'off the shelf' EnSCs for allogeneic myocardial regenerative medicine.

Molecular imaging: the key to advancing cardiac stem cell therapy

Cardiac stem cell therapy continues to hold promise for the treatment of ischemic heart disease despite the fact that early promising pre-clinical findings have yet to be translated into consistent clinical success. The latest human studies have collectively identified a pressing need to better understand stem cell behavior in humans and called for more incorporation of noninvasive imaging techniques into the design and evaluation of human stem cell therapy trials. This review discusses the various molecular imaging techniques validated to date for studying stem cells in living subjects, with a particular emphasis on their utilities in assessing the acute retention and the long-term survival of transplanted stem cells. These imaging techniques will be essential for advancing cardiac stem cell therapy by providing the means to both guide ongoing optimization and predict treatment response in humans.