Persistence of intramyocardially transplanted murine induced pluripotent stem cell-derived cardiomyocytes from different developmental stages

Regeneration of Nonhuman Primate Hearts With Human Induced Pluripotent Stem Cell-Derived Cardiac Spheroids

BACKGROUND

The clinical application of human induced pluripotent stem cell-derived cardiomyocytes (CMs) for cardiac repair commenced with the epicardial delivery of engineered cardiac tissue; however, the feasibility of the direct delivery of human induced pluripotent stem cell-derived CMs into the cardiac muscle layer, which has reportedly induced electrical integration, is unclear because of concerns about poor engraftment of CMs and posttransplant arrhythmias. Thus, in this study, we prepared purified human induced pluripotent stem cell-derived cardiac spheroids (hiPSC-CSs) and investigated whether their direct injection could regenerate infarcted nonhuman primate hearts.

METHODS

We performed 2 separate experiments to explore the appropriate number of human induced pluripotent stem cell-derived CMs. In the first experiment, 10 cynomolgus monkeys were subjected to myocardial infarction 2 weeks before transplantation and were designated as recipients of hiPSC-CSs containing 2×107 CMs or the vehicle. The animals were euthanized 12 weeks after transplantation for histological analysis, and cardiac function and arrhythmia were monitored during the observational period. In the second study, we repeated the equivalent transplantation study using more CMs (6×107 CMs).

RESULTS

Recipients of hiPSC-CSs containing 2×107 CMs showed limited CM grafts and transient increases in fractional shortening compared with those of the vehicle (fractional shortening at 4 weeks after transplantation [mean ± SD]: 26.2±2.1%; 19.3±1.8%; P<0.05), with a low incidence of posttransplant arrhythmia. Transplantation of increased dose of CMs resulted in significantly greater engraftment and long-term contractile benefits (fractional shortening at 12 weeks after transplantation: 22.5±1.0%; 16.6±1.1%; P<0.01, left ventricular ejection fraction at 12 weeks after transplantation: 49.0±1.4%; 36.3±2.9%; P<0.01). The incidence of posttransplant arrhythmia slightly increased in recipients of hiPSC-CSs containing 6×107 CMs.

CONCLUSIONS

We demonstrated that direct injection of hiPSC-CSs restores the contractile functions of injured primate hearts with an acceptable risk of posttransplant arrhythmia. Although the mechanism for the functional benefits is not fully elucidated, these findings provide a strong rationale for conducting clinical trials using the equivalent CM products.

CRISPR-Cas9 immune-evasive hESCs are rejected following transplantation into immunocompetent mice

Although current stem cell therapies exhibit promising potential, the extended process of employing autologous cells and the necessity for donor-host matching to avert the rejection of transplanted cells significantly limit the widespread applicability of these treatments. It would be highly advantageous to generate a pluripotent universal donor stem cell line that is immune-evasive and, therefore, not restricted by the individual's immune system, enabling unlimited application within cell replacement therapies. Before such immune-evasive stem cells can be moved forward to clinical trials, in vivo testing via transplantation experiments in immune-competent animals would be a favorable approach preceding preclinical testing. By using human stem cells in immune competent animals, results will be more translatable to a clinical setting, as no parts of the immune system have been altered, although in a xenogeneic setting. In this way, immune evasiveness, cell survival, and unwanted proliferative effects can be assessed before clinical trials in humans. The current study presents the generation and characterization of three human embryonic stem cell lines (hESCs) for xenogeneic transplantation in immune-competent mice. The major histocompatibility complexes I- and II-encoding genes, B2M and CIITA, have been deleted from the hESCs using CRISPR-Cas9-targeted gene replacement strategies and knockout. B2M was knocked out by the insertion of murine CD47. Human-secreted embryonic alkaline phosphatase (hSEAP) was inserted in a safe harbor site to track cells in vivo. The edited hESCs maintained their pluripotency, karyotypic normality, and stable expression of murine CD47 and hSEAP in vitro. In vivo transplantation of hESCs into immune-competent BALB/c mice was successfully monitored by measuring hSEAP in blood samples. Nevertheless, transplantation of immune-evasive hESCs resulted in complete rejection within 11 days, with clear immune infiltration of T-cells on day 8. Our results reveal that knockout of B2M and CIITA together with species-specific expression of CD47 are insufficient to prevent rejection in an immune-competent and xenogeneic context.

Human PSC-derived cardiac cells and their products: therapies for cardiac repair

Despite the dramatic improvements in the management of patients with chronic heart failure which have occurred over the last decades, some of them still exhaust conventional drug-based therapies without being eligible for more aggressive options like heart transplantation or implantation of a left ventricular assist device. Cell therapy has thus emerged as a possible means of filling this niche. Multiple cell types have now been tested both in the laboratory but also in the clinics and it is fair to acknowledge that none of the clinical trials have yet conclusively proven the efficacy of cell-based approaches. These clinical studies, however, have entailed the use of cells from various sources but of non-cardiac lineage origins. Although this might not be the main reason for their failures, the discovery of pluripotent stem cells capable of generating cardiomyocytes now raises the hope that such cardiac-committed cells could be therapeutically more effective. In this review, we will first describe where we currently are with regard to the clinical trials using PSC-differentiated cells and discuss the main issues which remain to be addressed. In parallel, because the capacity of cells to stably engraft in the recipient heart has increasingly been questioned, it has been hypothesized that a major mechanism of action could be the cell-triggered release of biomolecules that foster host-associated reparative pathways. Thus, in the second part of this review, we will discuss the rationale, clinically relevant advantages and pitfalls associated with the use of these PSC "products".

Injectable Decellularized Extracellular Matrix Hydrogel Containing Stromal Cell-Derived Factor 1 Promotes Transplanted Cardiomyocyte Engraftment and Functional Regeneration after Myocardial Infarction

Transplantation of exogenous cardiomyocytes (CMs) is a hopeful method to treat myocardial infarction (MI). However, its clinical application still remains challenging due to low retention and survival rates of the transplanted cells. Herein, a stromal cell-derived factor 1 (SDF-1)-loaded injectable hydrogel based on a decellularized porcine extracellular matrix (dECM) is developed to encapsulate and deliver CMs locally to the infarct area of the heart. The soluble porcine cardiac dECM is composed of similar components such as the human cardiac ECM, which could be self-assembled into a nanofibrous hydrogel at physiological temperature to improve the retention of transplanted CMs. Furthermore, the chemokine SDF-1 could recruit endogenous cells to promote angiogenesis, mitigating the ischemic microenvironment and improving the survival of CMs. The results in vitro show that this composite hydrogel exhibits good biocompatibility, anti-apoptosis property, and chemotactic effects for mesenchymal stromal cells and endothelial cells through SDF-1-CXCR4 axis. Moreover, intramyocardial injection of this composite hydrogel to the infarcted area leads to the promotion of angiogenesis and inhibition of fibrosis, reducing the infarction size and improving the cardiac function. The combination of natural biomaterials, exogenous cells, and bioactive factors shows potential for MI treatment in the clinical application.

Living myocardial slices: Advancing arrhythmia research

Living myocardial slices (LMS) are ultrathin (150-400 µm) sections of intact myocardium that can be used as a comprehensive model for cardiac arrhythmia research. The recent introduction of biomimetic electromechanical cultivation chambers enables long-term cultivation and easy control of living myocardial slices culture conditions. The aim of this review is to present the potential of this biomimetic interface using living myocardial slices in electrophysiological studies outlining advantages, disadvantages and future perspectives of the model. Furthermore, different electrophysiological techniques and their application on living myocardial slices will be discussed. The developments of living myocardial slices in electrophysiology research will hopefully lead to future breakthroughs in the understanding of cardiac arrhythmia mechanisms and the development of novel therapeutic options.

Cardiac regeneration: Options for repairing the injured heart

Cardiac regeneration is one of the grand challenges in repairing injured human hearts. Numerous studies of signaling pathways and metabolism on cardiac development and disease pave the way for endogenous cardiomyocyte regeneration. New drug delivery approaches, high-throughput screening, as well as novel therapeutic compounds combined with gene editing will facilitate the development of potential cell-free therapeutics. In parallel, progress has been made in the field of cell-based therapies. Transplantation of human pluripotent stem cell (hPSC)-derived cardiomyocytes (hPSC-CMs) can partially rescue the myocardial defects caused by cardiomyocyte loss in large animals. In this review, we summarize current cell-based and cell-free regenerative therapies, discuss the importance of cardiomyocyte maturation in cardiac regenerative medicine, and envision new ways of regeneration for the injured heart.