Tumorigenicity assay essential for facilitating safety studies of hiPSC-derived cardiomyocytes for clinical application

Detection of Residual iPSCs Following Differentiation of iPSC-Derived Retinal Pigment Epithelial Cells

Purpose: The goal of this study was to develop a lot release assay for iPSC residuals following directed differentiation of iPSCs to retinal pigment epithelial (RPE) cells. Methods: RNA Sequencing (RNA Seq) of iPSCs and RPE derived from them was used to identify pluripotency markers downregulated in RPE cells. Quantitative real time PCR (qPCR) was then applied to assess iPSC residuals in iPSC-derived RPE. The limit of detection (LOD) of the assay was determined by performing spike-in assays with known quantities of iPSCs serially diluted into an RPE suspension. Results: ZSCAN10 and LIN28A were among 8 pluripotency markers identified by RNA Seq as downregulated in RPE. Based on copy number and expression of pseudogenes and lncRNAs ZSCAN10 and LIN28A were chosen for use in qPCR assays for residual iPSCs. Reverse transcription PCR indicated generally uniform expression of ZSCAN10 and LIN28A in 21 clones derived from 8 iPSC donors with no expression of either in RPE cells derived from 5 donor lines. Based on qPCR, ZSCAN10, and LIN28A expression in iPSCs was generally uniform. The LOD for ZSCAN10 and LIN28A in qPCR assays was determined using spike in assays of RPE derived from 2 iPSC lines. Analysis of ΔΔCt found the limit of detection to be <0.01% of cells, equivalent to <1 iPSC/10,000 RPE cells in both iPSC lines. Conclusions: qPCR for ZSCAN10 and LIN28A detects <1 in 10,000 residual iPSCs in a population of iPSC-derived RPE providing an adequate LOD of iPSC residuals for lot release testing.

The Role of Stem Cells in the Treatment of Cardiovascular Diseases

Cardiovascular diseases (CVDs) are the leading cause of death and include several vascular and cardiac disorders, such as atherosclerosis, coronary artery disease, cardiomyopathies, and heart failure. Multiple treatment strategies exist for CVDs, but there is a need for regenerative treatment of damaged heart. Stem cells are a broad variety of cells with a great differentiation potential that have regenerative and immunomodulatory properties. Multiple studies have evaluated the efficacy of stem cells in CVDs, such as mesenchymal stem cells and induced pluripotent stem cell-derived cardiomyocytes. These studies have demonstrated that stem cells can improve the left ventricle ejection fraction, reduce fibrosis, and decrease infarct size. Other studies have investigated potential methods to improve the survival, engraftment, and functionality of stem cells in the treatment of CVDs. The aim of the present review is to summarize the current evidence on the role of stem cells in the treatment of CVDs, and how to improve their efficacy.

Pre-clinical evaluation of the efficacy and safety of human induced pluripotent stem cell-derived cardiomyocyte patch

BACKGROUND

Cell- or tissue-based regenerative therapy is an attractive approach to treat heart failure. A tissue patch that can safely and effectively repair damaged heart muscle would greatly improve outcomes for patients with heart failure. In this study, we conducted a preclinical proof-of-concept analysis of the efficacy and safety of clinical-grade human induced pluripotent stem cell-derived cardiomyocyte (hiPSC-CM) patches.

METHODS

A clinical-grade hiPSC line was established using peripheral blood mononuclear cells from a healthy volunteer that was homozygous for human leukocyte antigens. The hiPSCs were differentiated into cardiomyocytes. The obtained hiPSC-CMs were cultured on temperature-responsive culture dishes for patch fabrication. The cellular characteristics, safety, and efficacy of hiPSCs, hiPSC-CMs, and hiPSC-CM patches were analyzed.

RESULTS

The hiPSC-CMs expressed cardiomyocyte-specific genes and proteins, and electrophysiological analyses revealed that hiPSC-CMs exhibit similar properties to human primary myocardial cells. In vitro and in vivo safety studies indicated that tumorigenic cells were absent. Moreover, whole-genome and exome sequencing revealed no genomic mutations. General toxicity tests also showed no adverse events posttransplantation. A porcine model of myocardial infarction demonstrated significantly improved cardiac function and angiogenesis in response to cytokine secretion from hiPSC-CM patches. No lethal arrhythmias were observed.

CONCLUSIONS

hiPSC-CM patches are promising for future translational research and may have clinical application potential for the treatment of heart failure.

Cancer Spheroids Embedded in Tissue-Engineered Skin Substitutes: A New Method to Study Tumorigenicity In Vivo

Tumorigenic assays are used during a clinical translation to detect the transformation potential of cell-based therapies. One of these in vivo assays is based on the separate injection of each cell type to be used in the clinical trial. However, the injection method requires many animals and several months to obtain useful results. In previous studies, we showed the potential of tissue-engineered skin substitutes (TESs) as a model for normal skin in which cancer cells can be included in vitro. Herein, we showed a new method to study tumorigenicity, using cancer spheroids that were embedded in TESs (cTES) and grafted onto athymic mice, and compared it with the commonly used cell injection assay. Tumors developed in both models, cancer cell injection and cTES grafting, but metastases were not detected at the time of sacrifice. Interestingly, the rate of tumor development was faster in cTESs than with the injection method. In conclusion, grafting TESs is a sensitive method to detect tumor cell growth with and could be developed as an alternative test for tumorigenicity.

Exploring the promising potential of induced pluripotent stem cells in cancer research and therapy

The advent of iPSCs has brought about a significant transformation in stem cell research, opening up promising avenues for advancing cancer treatment. The formation of cancer is a multifaceted process influenced by genetic, epigenetic, and environmental factors. iPSCs offer a distinctive platform for investigating the origin of cancer, paving the way for novel approaches to cancer treatment, drug testing, and tailored medical interventions. This review article will provide an overview of the science behind iPSCs, the current limitations and challenges in iPSC-based cancer therapy, the ethical and social implications, and the comparative analysis with other stem cell types for cancer treatment. The article will also discuss the applications of iPSCs in tumorigenesis, the future of iPSCs in tumorigenesis research, and highlight successful case studies utilizing iPSCs in tumorigenesis research. The conclusion will summarize the advancements made in iPSC-based tumorigenesis research and the importance of continued investment in iPSC research to unlock the full potential of these cells.

Establishment of a protocol to administer immunosuppressive drugs for iPS cell-derived cardiomyocyte patch transplantation in a rat myocardial infarction model

Transplantation of human allogeneic induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) is a new, promising treatment for severe heart failure. However, immunorejection is a significant concern in allogeneic hiPSC-CM transplantation, requiring the administration of several immunosuppressive agents. An appropriate protocol for the administration of immunosuppressants may substantially affect the efficacy of hiPSC-CM transplantation in case of heart failure owing to allogeneic transplantation. In this study, we investigated the effect of immunosuppressant administration duration on the efficacy and safety of allogenic hiPSC-CM patch transplantation. We used a rat model of myocardial infarction to evaluate cardiac function using echocardiography six months after the transplantation of hiPSC-CM patches with immunosuppressant administration for either two or four months and compared them to control rats (sham operation, no immunosuppressant administration). Histological analysis performed at 6 months after hiPSC-CM patch transplantation revealed significant improvement in cardiac function in immunosuppressant-treated rats compared with those in the control group. Moreover, fibrosis and cardiomyocyte size was significantly reduced and the number of structurally mature blood vessels was significantly increased in the immunosuppressant-treated rats compared to control rats. However, there were no significant differences between the two immunosuppressant-treated groups. Our results show that prolonged administration of immunosuppressive agents did not enhance the effectiveness of hiPSC-CM patch transplantation, and therefore, highlight the importance of an appropriate immunological regimen for the clinical application of such transplantation.

The evaluation of tumorigenicity and characterization of colonies in a soft agar colony formation assay using polymerase chain reaction

In regenerative medicine, the tumorigenic potency of cells in cellular therapy products (CTPs) is a major concern for their application to patients. This study presents a method-the soft agar colony formation assay using polymerase chain reaction (PCR)-to evaluate tumorigenicity. MRC-5 cells, contaminated with HeLa cells, were cultured for up to 4 weeks in soft agar medium. Cell-proliferation-related mRNAs, Ki-67 and cyclin B, could be detected in 0.01% of HeLa cells after 5 days of culture, whereas cyclin-dependent kinase 1 (CDK1) could be detected after 2 weeks. On the other hand, CDK2, proliferating cell nuclear antigen (PCNA), and minichromosome maintenance protein 7 (MCM7) were not useful to detect HeLa cells even after 4 weeks of culture. The cancer stem cell (CSC) markers, aldehyde dehydrogenase 1 (ALDH1) and CD133 in 0.01% of HeLa cells, could be detected 2 and 4 weeks after culture, respectively. However, another CSC marker CD44 was not useful because its expression was also detected in MRC-5 cells alone. This study suggests that the application of the PCR method to the soft agar colony formation assay could evaluate not only the tumorigenic potency in the short-term but also characterize the colonies, eventually improving the safety of CTPs.

A clinical-grade HLA haplobank of human induced pluripotent stem cells matching approximately 40% of the Japanese population

BACKGROUND

Human induced pluripotent stem cells (iPSCs) are expected to be useful for regenerative medicine for many diseases. Many researchers have focused on and enabled the generation of differentiated cells or tissue-like structures, including organoids, which help to ameliorate target diseases. To promote such cell therapies, we established a clinically applicable iPSC haplobank matching as many people as possible in Japan.

METHODS

Through cooperation with several organizations, we recruited donors whose human leukocyte antigens (HLAs) involved in immunorejection were homozygous. The peripheral or umbilical cord blood collected from the donors was used for iPSC production by electroporation of episomal vectors. These iPSC lines were then subjected to testing, including genome analyses and sterility, to maximize safety.

FINDINGS

We constructed a clinical-grade haplobank of 27 iPSC lines from 7 donors according to good manufacturing practice regulations. However, reasons to avoid using iPSC lines include the presence of residual episomal vectors or genetic mutations in cancer-related genes.

CONCLUSIONS

This haplobank provides HLA-matched iPSC lines for approximately 40% of the Japanese population. Since the haplobank's release in 2015, these iPSC lines have been used in more than 10 clinical trials. The establishment of this haplobank is an important step toward the clinical application of iPSCs in cell therapies.

FUNDING

This study was supported by a research center network for the realization of regenerative medicine of the Japan Agency for Medical Research and Development (AMED) under grant number JP20bm0104001h0108.

Advances in Cellular Reprogramming-Based Approaches for Heart Regenerative Repair

Continuous loss of cardiomyocytes (CMs) is one of the fundamental characteristics of many heart diseases, which eventually can lead to heart failure. Due to the limited proliferation ability of human adult CMs, treatment efficacy has been limited in terms of fully repairing damaged hearts. It has been shown that cell lineage conversion can be achieved by using cell reprogramming approaches, including human induced pluripotent stem cells (hiPSCs), providing a promising therapeutic for regenerative heart medicine. Recent studies using advanced cellular reprogramming-based techniques have also contributed some new strategies for regenerative heart repair. In this review, hiPSC-derived cell therapeutic methods are introduced, and the clinical setting challenges (maturation, engraftment, immune response, scalability, and tumorigenicity), with potential solutions, are discussed. Inspired by the iPSC reprogramming, the approaches of direct cell lineage conversion are merging, such as induced cardiomyocyte-like cells (iCMs) and induced cardiac progenitor cells (iCPCs) derived from fibroblasts, without induction of pluripotency. The studies of cellular and molecular pathways also reveal that epigenetic resetting is the essential mechanism of reprogramming and lineage conversion. Therefore, CRISPR techniques that can be repurposed for genomic or epigenetic editing become attractive approaches for cellular reprogramming. In addition, viral and non-viral delivery strategies that are utilized to achieve CM reprogramming will be introduced, and the therapeutic effects of iCMs or iCPCs on myocardial infarction will be compared. After the improvement of reprogramming efficiency by developing new techniques, reprogrammed iCPCs or iCMs will provide an alternative to hiPSC-based approaches for regenerative heart therapies, heart disease modeling, and new drug screening.

The consequences of recurrent genetic and epigenetic variants in human pluripotent stem cells

It is well established that human pluripotent stem cells (hPSCs) can acquire genetic and epigenetic changes during culture in vitro. Given the increasing use of hPSCs in research and therapy and the vast expansion in the number of hPSC lines available for researchers, the International Society for Stem Cell Research has recognized the need to reassess quality control standards for ensuring the genetic integrity of hPSCs. Here, we summarize current knowledge of the nature of recurrent genetic and epigenetic variants in hPSC culture, the methods for their detection, and what is known concerning their effects on cell behavior in vitro or in vivo. We argue that the potential consequences of low-level contamination of cell therapy products with cells bearing oncogenic variants are essentially unknown at present. We highlight the key challenges facing the field with particular reference to safety assessment of hPSC-derived cellular therapeutics.

Navigating regulatory pathways for translation of biologic cartilage repair products

Long-term clinical repair of articular cartilage remains elusive despite advances in cartilage tissue engineering. Only one cartilage repair therapy classified as a "cellular and gene therapy product" has obtained Food and Drug Administration (FDA) approval within the past decade although more than 200 large animal cartilage repair studies were published. Here, we identify the challenges impeding translation of strategies and technologies for cell-based cartilage repair, such as the disconnect between university funding and regulatory requirements. Understanding the barriers to translation and developing solutions to address them will be critical for advancing cell therapy products for cartilage repair to clinical use.

Case report: Transplantation of human induced pluripotent stem cell-derived cardiomyocyte patches for ischemic cardiomyopathy

Despite major therapeutic advances, heart failure, as a non-communicable disease, remains a life-threatening disorder, with 26 million patients worldwide, causing more deaths than cancer. Therefore, novel strategies for the treatment of heart failure continue to be an important clinical need. Based on preclinical studies, allogenic human induced pluripotent stem cell-derived cardiomyocyte (hiPSC-CM) patches have been proposed as a potential therapeutic candidate for heart failure. We report the implantation of allogeneic hiPSC-CM patches in a patient with ischemic cardiomyopathy (ClinicalTrials.gov, #jRCT2053190081). The patches were produced under clinical-grade conditions and displayed cardiogenic phenotypes and safety in vivo (severe immunodeficient mice) without any genetic mutations in cancer-related genes. The patches were then implanted via thoracotomy into the left ventricle epicardium of the patient under immunosuppressive agents. Positron emission tomography and computed tomography confirmed the potential efficacy and did not detect tumorigenesis in either the heart or other organs. The clinical symptoms improved 6 months after surgery, without any major adverse events, suggesting that the patches were well-tolerated. Furthermore, changes in the wall motion in the transplanted site were recovered, suggesting a favorable prognosis and the potential tolerance to exercise. This study is the first report of a successful transplant of hiPSC-CMs for severe ischemic cardiomyopathy.

Manipulating Cardiomyocyte Plasticity for Heart Regeneration

Pathological heart injuries such as myocardial infarction induce adverse ventricular remodeling and progression to heart failure owing to widespread cardiomyocyte death. The adult mammalian heart is terminally differentiated unlike those of lower vertebrates. Therefore, the proliferative capacity of adult cardiomyocytes is limited and insufficient to restore an injured heart. Although current therapeutic approaches can delay progressive remodeling and heart failure, difficulties with the direct replenishment of lost cardiomyocytes results in a poor long-term prognosis for patients with heart failure. However, it has been revealed that cardiac function can be improved by regulating the cell cycle or changing the cell state of cardiomyocytes by delivering specific genes or small molecules. Therefore, manipulation of cardiomyocyte plasticity can be an effective treatment for heart disease. This review summarizes the recent studies that control heart regeneration by manipulating cardiomyocyte plasticity with various approaches including differentiating pluripotent stem cells into cardiomyocytes, reprogramming cardiac fibroblasts into cardiomyocytes, and reactivating the proliferation of cardiomyocytes.

Highly sensitive and non-disruptive detection of residual undifferentiated cells by measuring miRNAs in culture supernatant

The clinical usage of induced pluripotent stem cell (iPSC)-derived regenerative medicine products is limited by the possibility of residual undifferentiated cells forming tumours after transplantation. Most of the existing quality control tests involve crushing of cells. As a result, the cells to be transplanted cannot be directly tested, thereby increasing the cost of transplantation. Therefore, we tested a highly sensitive and non-disruptive quality-testing method that involves measuring microRNAs (miRNAs) in culture supernatants released by cells. By measuring miR-302b in the culture supernatant, residual iPSCs were detected with higher sensitivity than by measuring LIN28 (Lin-28 Homolog A) in the cells. To use this method, we also monitored the progression of differentiation. Our novel highly sensitive and non-disruptive method for detecting residual undifferentiated cells will contribute to reducing the manufacturing cost of iPSC-derived products and improving the safety of transplantation.

Scalable manufacturing of clinical-grade differentiated cardiomyocytes derived from human-induced pluripotent stem cells for regenerative therapy

Basic research on human pluripotent stem cell (hPSC)‐derived cardiomyocytes (CMs) for cardiac regenerative therapy is one of the most active and complex fields to achieve this alternative to heart transplantation and requires the integration of medicine, science, and engineering. Mortality in patients with heart failure remains high worldwide. Although heart transplantation is the sole strategy for treating severe heart failure, the number of donors is limited. Therefore, hPSC‐derived CM (hPSC‐CM) transplantation is expected to replace heart transplantation. To achieve this goal, for basic research, various issues should be considered, including how to induce hPSC proliferation efficiently for cardiac differentiation, induce hPSC‐CMs, eliminate residual undifferentiated hPSCs and non‐CMs, and assess for the presence of residual undifferentiated hPSCs in vitro and in vivo. In this review, we discuss the current stage of resolving these issues and future directions for realizing hPSC‐based cardiac regenerative therapy.

Manufacturing clinical-grade human induced pluripotent stem cell-derived beta cells for diabetes treatment

The unlimited proliferative capacity of human pluripotent stem cells (hPSCs) fortifies it as one of the most attractive sources for cell therapy application in diabetes. In the past two decades, vast research efforts have been invested in developing strategies to differentiate hPSCs into clinically suitable insulin‐producing endocrine cells or functional beta cells (β cells). With the end goal being clinical translation, it is critical for hPSCs and insulin‐producing β cells to be derived, handled, stored, maintained and expanded with clinical compliance. This review focuses on the key processes and guidelines for clinical translation of human induced pluripotent stem cell (hiPSC)‐derived β cells for diabetes cell therapy. Here, we discuss the (1) key considerations of manufacturing clinical‐grade hiPSCs, (2) scale‐up and differentiation of clinical‐grade hiPSCs into β cells in clinically compliant conditions and (3) mandatory quality control and product release criteria necessitated by various regulatory bodies to approve the use of the cell‐based products.

Two Sets of Compound Complex Driving for High Efficiency of Nonintegration Reprogramming of Human Fibroblasts

Currently, plentiful chemical-assisted methods have been applied for mouse induced pluripotent stem cells (iPSCs). It has been reported that small-molecule compounds can only reprogram mouse embryonic fibroblasts into mouse chemically induced pluripotent stem cells (mouse CiPSCs). However, human CiPSCs have not been reported. Therefore, it is still necessary to search for safer chemically assisted human pluripotent stem cells, which might realize the potential of human iPSCs. Here, we developed two sets of chemical cocktails to greatly improve the induction efficiency of human nonintegrated iPSCs, including the 4 compound mixture (4M) and the 5 compound mixture (4MI). These two sets of complex driving strategies might greatly improve the reprogramming efficiency to generate integration-free iPSCs.

Induced Pluripotent Stem Cells (iPSCs) and Gene Therapy: A New Era for the Treatment of Neurological Diseases

To date, gene therapy has employed viral vectors to deliver therapeutic genes. However, recent progress in molecular and cell biology has revolutionized the field of stem cells and gene therapy. A few years ago, clinical trials started using stem cell replacement therapy, and the induced pluripotent stem cells (iPSCs) technology combined with CRISPR-Cas9 gene editing has launched a new era in gene therapy for the treatment of neurological disorders. Here, we summarize the latest findings in this research field and discuss their clinical applications, emphasizing the relevance of recent studies in the development of innovative stem cell and gene editing therapeutic approaches. Even though tumorigenicity and immunogenicity are existing hurdles, we report how recent progress has tackled them, making engineered stem cell transplantation therapy a realistic option.

Elimination of residual undifferentiated induced pluripotent stem cells (iPSCs) using irradiation for safe clinical applications of iPSC-derived cardiomyocytes

A major concern in the clinical application of induced pluripotent stem cells (iPSCs) is the prevention of tumorigenesis after implantation. Stem cells with high proliferative and differentiation potential are sensitive to radiation. Therefore, we hypothesized that irradiation may selectively eliminate residual undifferentiated human iPSCs (hiPSCs) in a cell population containing differentiated cardiomyocytes derived from hiPSCs (hiPSCs-CMs) and thus reduce tumorigenicity in vivo. hiPSC-CMs were irradiated with X-rays, after which the cell proliferation, apoptosis, morphology, and gene expression were analyzed. The gene expression of Lin28A, Nanog, Oct3/4, and SRY-box 2 was significantly lower in the irradiation group than in the control group. Irradiated hiPSC-CMs showed no change in proliferation potency and morphology compared to untreated hiPSC-CMs. Furthermore, irradiation did not induce apoptosis of differentiated cardiomyocytes. No significant difference in the gene expression of cardiac-specific markers, including α-myosin heavy chain, cardiac troponin T, and NK2 Homeobox 5, was observed between the groups. Tumorigenicity tests using NOG mice showed less frequent tumor formation in the irradiation group than in the control group. Irradiation of hiPSC-CMs significantly reduced the number of undifferentiated hiPSC and the tumor formation, while minimizing any adverse effects on hiPSC-CMs, thereby enabling safe hiPSC-based treatment.

Comparing the Therapeutic Potential of Stem Cells and their Secretory Products in Regenerative Medicine

Cell therapy involves the transplantation of human cells to replace or repair the damaged tissues and modulate the mechanisms underlying disease initiation and progression in the body. Nowadays, many different types of cell-based therapy are developed and used to treat a variety of diseases. In the past decade, cell-free therapy has emerged as a novel approach in regenerative medicine after the discovery that the transplanted cells exerted their therapeutic effect mainly through the secretion of paracrine factors. More and more evidence showed that stem cell-derived secretome, i.e., growth factors, cytokines, and extracellular vesicles, can repair the injured tissues as effectively as the cells. This finding has spurred a new idea to employ secretome in regenerative medicine. Despite that, will cell-free therapy slowly replace cell therapy in the future? Or are these two modes of treatment still needed to address different diseases and conditions? This review provides an indepth discussion about the values of stem cells and secretome in regenerative medicine. In addition, the safety, efficacy, advantages, and disadvantages of using these two modes of treatment in regenerative medicine are also critically reviewed.

Induced Pluripotent Stem Cells (iPSCs) Provide a Potentially Unlimited T Cell Source for CAR-T Cell Development and Off-the-Shelf Products

Chimeric antigen receptor T (CAR-T) cell therapy has been increasingly conducted for cancer patients in clinical settings. Progress in this therapeutic approach is hampered by the lack of a solid manufacturing process, T lymphocytes, and tumor-specific antigens. T cell source used in CAR-T cell therapy is derived predominantly from the patient's own T lymphocytes, which makes this approach impracticable to patients with progressive diseases and T leukemia. The generation of autologous CAR-T cells is time-consuming due to the lack of readily available T lymphocytes and is not applicable for third-party patients. Pluripotent stem cells, such as human induced pluripotent stem cells (hiPSCs), can provide an unlimited T cell source for CAR-T cell development with the potential of generating off-the-shelf T cell products. T-iPSCs (iPSC-derived T cells) are phenotypically defined, expandable, and as functional as physiological T cells. The combination of iPSC and CAR technologies provides an exciting opportunity to oncology and greatly facilitates cell-based therapy for cancer patients. However, T-iPSCs, in combination with CARs, are at the early stage of development and need further pre-clinical and clinical studies. This review will critically discuss the progress made in iPSC-derived T cells and provides a roadmap for the development of CAR iPSC-derived T cells and off-the-shelf T-iPSCs.

Cell surface markers for immunophenotyping human pluripotent stem cell-derived cardiomyocytes

Human pluripotent stem cells (hPSC) self-renew and represent a potentially unlimited source for the production of cardiomyocytes (CMs) suitable for studies of human cardiac development, drug discovery, cardiotoxicity testing, and disease modelling and for cell-based therapies. However, most cardiac differentiation protocols yield mixed cultures of atrial-, ventricular-, and pacemaker-like cells at various stages of development, as well as non-CMs. The proportions and maturation states of these cell types result from disparities among differentiation protocols and time of cultivation, as well as hPSC reprogramming inconsistencies and genetic background variations. The reproducible use of hPSC-CMs for research and therapy is therefore limited by issues of cell population heterogeneity and functional states of maturation. A validated method that overcomes issues of cell heterogeneity is immunophenotyping coupled with live cell sorting, an approach that relies on accessible surface markers restricted to the desired cell type(s). Here we review current progress in unravelling heterogeneity in hPSC-cardiac cultures and in the identification of surface markers suitable for defining cardiac identity, subtype specificity, and maturation states.

Method for selective ablation of undifferentiated human pluripotent stem cell populations for cell-based therapies

Human pluripotent stem cells (PSCs), which are composed of embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), provide an opportunity to advance cardiac cell therapy-based clinical trials. However, an important hurdle that must be overcome is the risk of teratoma formation after cell transplantation due to the proliferative capacity of residual undifferentiated PSCs in differentiation batches. To tackle this problem, we propose the use of a minimal noncardiotoxic doxorubicin dose as a purifying agent to selectively target rapidly proliferating stem cells for cell death, which will provide a purer population of terminally differentiated cardiomyocytes before cell transplantation. In this study, we determined an appropriate in vitro doxorubicin dose that (a) eliminates residual undifferentiated stem cells before cell injection to prevent teratoma formation after cell transplantation and (b) does not cause cardiotoxicity in ESC-derived cardiomyocytes (CMs) as demonstrated through contractility analysis, electrophysiology, topoisomerase activity assay, and quantification of reactive oxygen species generation. This study establishes a potentially novel method for tumorigenic-free cell therapy studies aimed at clinical applications of cardiac cell transplantation.

Single-cell sequencing reveals the potential oncogenic expression atlas of human iPSC-derived cardiomyocytes

Human induced pluripotent stem cells (iPSCs) are important source for regenerative medicine. However, the links between pluripotency and oncogenic transformation raise safety issues. To understand the characteristics of iPSC-derived cells at single-cell resolution, we directly reprogrammed two human iPSC lines into cardiomyocytes and collected cells from four time points during cardiac differentiation for single-cell sequencing. We captured 32,365 cells and identified five molecularly distinct clusters that aligned well with our reconstructed differentiation trajectory. We discovered a set of dynamic expression events related to the upregulation of oncogenes and the decreasing expression of tumor suppressor genes during cardiac differentiation, which were similar to the gain-of-function and loss-of-function patterns during oncogenesis. In practice, we characterized the dynamic expression of the TP53 and Yamanaka factor genes (OCT4, SOX2, KLF4 and MYC), which were widely used for human iPSCs lines generation; and revealed the co-occurrence of MYC overexpression and TP53 silencing in some of human iPSC-derived TNNT2+ cardiomyocytes. In summary, our oncogenic expression atlas is valuable for human iPSCs application and the single-cell resolution highlights the clues potentially associated with the carcinogenic risk of human iPSC-derived cells.

Summary: The single-cell expression atlas in the cardiomyocytes generated from human iPSCs provide potential carcinogenic information for the clinical application of human iPSC-derived cells.

Quality assessment tests for tumorigenicity of human iPS cell-derived cartilage

Articular cartilage damage does not heal spontaneously and causes joint dysfunction. The implantation of induced pluripotent stem cell (iPSC)-derived cartilage (iPS-Cart) is one candidate treatment to regenerate the damaged cartilage. However, concerns of tumorigenicity are associated with iPS-Cart, because the iPSC reprogramming process and long culture time for cartilage induction could increase the chance of malignancy. We evaluated the tumorigenic risks of iPS-Cart using HeLa cells as the reference. Spike tests revealed that contamination with 100 HeLa cells in 150 mg of iPS-Cart accelerated the cell growth rate. On the other hand, 150 mg of iPS-Cart without HeLa cells reached growth arrest and senescence after culture, suggesting less than 100 tumorigenic cells, assuming they behave like HeLa cells, contaminated iPS-Cart. The implantation of 10,000 or fewer HeLa cells into joint surface defects in the knee joint of nude rat did not cause tumor formation. These in vitro and in vivo studies collectively suggest that the implantation of 15 g or less iPS-Cart in the knee joint does not risk tumor formation if assuming that the tumorigenic cells in iPS-Cart are equivalent to HeLa cells and that nude rat knee joints are comparable to human knee joints in terms of tumorigenicity. However, considering the limited immunodeficiency of nude rats, the clinical amount of iPS-Cart for implantation needs to be determined cautiously.

Accuracy of spiked cell counting methods for designing a pre-clinical tumorigenicity study model

Background

Evaluations for the tumorigenicity of transplantation of stem cell products is mandatory for clinical application. It is of importance to establish a system to accurately quantify contaminated tumorigenic cells regardless of the format of stem cell product. In the present report, we aimed to examine the accuracy of the quantification of tumorigenic cell numbers with commonly used 2 methods, quantitative polymerase chain reaction (qPCR) and flow cytometry (FCM) using experimental models of stem cell products spiked with tumorigenic cells.

Methods

Human mesenchymal stem cells (hMSCs) and melanoma Mewo-Luc cells constitutively expressing luciferase were used. We stained Mewo-Luc cells with a cell linker then spiked onto hMSC suspensions and hMSC sheets. We validated the accuracy of 10-fold serial dilution technique for Mewo-Luc cell suspension using a Coulter counter. The samples spiked with Mewo-Luc cells were subjected to qPCR and FCM analyses, respectively for the quantification of Mewo-Luc cells.

Results

Ten-fold serial dilutions of Mewo-Luc cells were performed accurately with small deviation. In samples spiked with or less than 100 cells in hMSC suspensions, and samples spiked with or less than 1,000 cells in hMSC sheets showed significantly higher cell numbers in calculations by FCM, respectively (suspensions; qPCR vs FCM: 100 cells: 59 ± 25 vs 232 ± 35 cells, p = 0.022/10 cells: 21 ± 7 vs 114 ± 27 cells, p = 0.030, sheets; qPCR vs FCM: 1,000 cells: 1723 ± 258 vs 5810 ± 878 cells, p = 0.012/100 cells: 110 ± 18 vs 973 ± 232 cells, p = 0.012/10 cells: 20 ± 6 vs 141 ± 36 cells, p = 0.030).

Conclusion

Differences in accuracy between quantification methods should be considered in designing a tumorigenicity study model.

Ultrasensitive and rapid quantification of rare tumorigenic stem cells in hPSC-derived cardiomyocyte populations

The ability to detect rare human pluripotent stem cells (hPSCs) in differentiated populations is critical for safeguarding the clinical translation of cell therapy, as these undifferentiated cells have the capacity to form teratomas in vivo. The detection of hPSCs must be performed using an approach compatible with traceable manufacturing of therapeutic cell products. Here, we report a novel microfluidic approach, stem cell quantitative cytometry (SCQC), for the quantification of rare hPSCs in hPSC-derived cardiomyocyte (CM) populations. This approach enables the ultrasensitive capture, profiling, and enumeration of trace levels of hPSCs labeled with magnetic nanoparticles in a low-cost, manufacturable microfluidic chip. We deploy SCQC to assess the tumorigenic risk of hPSC-derived CM populations in vivo. In addition, we isolate rare hPSCs from the differentiated populations using SCQC and characterize their pluripotency.

RNA-Based Strategies for Cardiac Reprogramming of Human Mesenchymal Stromal Cells

Multipotent adult mesenchymal stromal cells (MSCs) could represent an elegant source for the generation of patient-specific cardiomyocytes needed for regenerative medicine, cardiovascular research, and pharmacological studies. However, the differentiation of adult MSC into a cardiac lineage is challenging compared to embryonic stem cells or induced pluripotent stem cells. Here we used non-integrative methods, including microRNA and mRNA, for cardiac reprogramming of adult MSC derived from bone marrow, dental follicle, and adipose tissue. We found that MSC derived from adipose tissue can partly be reprogrammed into the cardiac lineage by transient overexpression of GATA4, TBX5, MEF2C, and MESP1, while cells isolated from bone marrow, and dental follicle exhibit only weak reprogramming efficiency. qRT-PCR and transcriptomic analysis revealed activation of a cardiac-specific gene program and up-regulation of genes known to promote cardiac development. Although we did not observe the formation of fully mature cardiomyocytes, our data suggests that adult MSC have the capability to acquire a cardiac-like phenotype when treated with mRNA coding for transcription factors that regulate heart development. Yet, further optimization of the reprogramming process is mandatory to increase the reprogramming efficiency.

Current Challenges of iPSC-Based Disease Modeling and Therapeutic Implications

Induced pluripotent stem cell (iPSC)-based disease modelling and the cell replacement therapy approach have proven to be very powerful and instrumental in biomedical research and personalized regenerative medicine as evidenced in the past decade by unraveling novel pathological mechanisms of a multitude of monogenic diseases at the cellular level and the ongoing and emerging clinical trials with iPSC-derived cell products. iPSC-based disease modelling has sparked widespread enthusiasm and has presented an unprecedented opportunity in high throughput drug discovery platforms and safety pharmacology in association with three-dimensional multicellular organoids such as personalized organs-on-chips, gene/base editing, artificial intelligence and high throughput "omics" methodologies. This critical review summarizes the progress made in the past decade with the advent of iPSC discovery in biomedical applications and regenerative medicine with case examples and the current major challenges that need to be addressed to unleash the full potential of iPSCs in clinical settings and pharmacology for more effective and safer regenerative therapy.