Transplanted terminally differentiated induced pluripotent stem cells are accepted by immune mechanisms similar to self-tolerance

iPSC modification strategies to induce immune tolerance

Human pluripotent stem cells (hPSCs) hold great promise in regenerative medicine. However, immune rejections remain one of the major obstacles to stem cell therapy. Though conventional immunosuppressants are available in clinics, the side effects prevent the wide application of hPSCs derivatives, compromising both survival rate and quality of life. In recent years, a myriad of strategies aimed at inducing immune tolerance specifically by engineering stem cells has been introduced to society. One strategy involves human leukocyte antigen (HLA) deletion through gene editing, affording allografts the capability to evade the host immune system. Another strategy involves immune cloak, which is the focus of this review, with emphasis on the overexpression of immune checkpoints and the blocking of immune cytotoxic pathways. Nevertheless, co-transplantation with mesenchymal stem cells (MSCs) and enhanced MSCs confers immune privilege to engraftments. This review summarizes recent studies on the intricacies of immune tolerance induction by engineering stem cells. In addition, we endeavor to deliberate upon the safety and limitations associated with this promising and potential therapeutic modality.

Pluripotent stem cell-derived cardiomyocyte transplantation: marching from bench to bedside

Cardiovascular diseases such as myocardial infarction, heart failure, and cardiomyopathy, persist as a leading global cause of death. Current treatment options have inherent limitations, particularly in terms of cardiac regeneration due to the limited regenerative capacity of adult human hearts. The transplantation of pluripotent stem cell-derived cardiomyocytes (PSC-CMs) has emerged as a promising and potential solution to address this challenge. This review aims to summarize the latest advancements and prospects of PSC-CM transplantation (PCT), along with the existing constraints, such as immune rejection and engraftment arrhythmias, and corresponding solutions. Encompassing a comprehensive range from fundamental research findings and preclinical experiments to ongoing clinical trials, we hope to offer insights into PCT from bench to bedside.

Bone Tissue Engineering: From Biomaterials to Clinical Trials

Bone tissue engineering is a promising field that aims to rebuild the bone tissue using biomaterials, cells, and signaling molecules. Materials like natural and synthetic polymers, inorganic materials, and composite materials are used to create scaffolds that mimic the hierarchical microstructure of bone. Stem cells, particularly mesenchymal stem cells (MSCs), play a crucial role in bone tissue engineering by promoting tissue regeneration and modulating the immune response. Growth factors like bone morphogenetic proteins (BMPs), vascular endothelial growth factor (VEGF), and platelet-derived growth factor (PDGF) are utilized to accelerate bone regeneration. Clinical applications include treating nonunion and mal-union fractures, osteonecrosis, orthopedic surgery, dental applications, and spinal cord injuries. Recent advances in the field include nanotechnology, 3D printing, bioprinting techniques, gene editing technologies, and microfluidic devices for drug testing. However, challenges remain, such as standardization of protocols, large-scale biomaterial production, personalized medicine approaches, cost-effectiveness, and regulatory issues. Current clinical trials are investigating the safety and efficacy of various bone tissue engineering approaches, with the potential to modernize patient care by providing more adequate treatments for bone defects and injuries.

Human iPSC-Derived Endothelial Cells Exhibit Reduced Immunogenicity in Comparison With Human Primary Endothelial Cells

Human induced pluripotent stem cell (iPSC)-derived endothelial cells (ECs) have emerged as a promising source of autologous cells with great potential to produce novel cell therapy for ischemic vascular diseases. However, their clinical application still faces numerous challenges including safety concerns such as the potential aberrant immunogenicity derived from the reprogramming process. This study investigated immunological phenotypes of iPSC-ECs by a side-by-side comparison with primary human umbilical vein ECs (HUVECs). Three types of human iPSC-ECs, NIBSC8-EC generated in house and two commercial iPSC-ECs, alongside HUVECs, were examined for surface expression of proteins of immune relevance under resting conditions and after cytokine activation. All iPSC-EC populations failed to express major histocompatibility complex (MHC) Class II on their surface following interferon-gamma (IFN-γ) treatment but showed similar basal and IFN-γ-stimulated expression levels of MHC Class I of HUVECs. Multiple iPSC-ECs also retained constitutive and tumor necrosis factor-alpha (TNF-α)-stimulated expression levels of intercellular adhesion molecule-1 (ICAM-1) like HUVECs. However, TNF-α induced a differential expression of E-selectin and vascular cell adhesion molecule-1 (VCAM-1) on iPSC-ECs. Furthermore, real-time monitoring of proliferation of human peripheral blood mononuclear cells (PBMCs) cocultured on an endothelial monolayer over 5 days showed that iPSC-ECs provoked distinct dynamics of PBMC proliferation, which was generally decreased in alloreactivity and IFN-γ-stimulated proliferation of PBMCs compared with HUVECs. Consistently, in the conventional mixed lymphocyte reaction (MLR), the proliferation of total CD3+ and CD4+ T cells after 5-day cocultures with multiple iPSC-EC populations was largely reduced compared to HUVECs. Last, multiple iPSC-EC cocultures secreted lower levels of proinflammatory cytokines than HUVEC cocultures. Collectively, iPSC-ECs manifested many similarities, but also some disparities with a generally weaker inflammatory immune response than primary ECs, indicating that iPSC-ECs may possibly exhibit hypoimmunogenicity corresponding with less risk of immune rejection in a transplant setting, which is important for safe and effective cell therapies.

Emerging Diabetes Therapies: Regenerating Pancreatic β Cells

The incidence of diabetes mellitus (DM) is steadily increasing annually, with 537 million diabetic patients as of 2021. Restoring diminished β cell mass or impaired islet function is crucial in treating DM, particularly type 1 DM. However, the regenerative capacity of islet β cells, which primarily produce insulin, is severely limited, and natural regeneration is only observed in young rodents or children. Hence, there is an urgent need to develop advanced therapeutic approaches that can regenerate endogenous β cells or replace them with stem cell (SC)-derived or engineered β-like cells. Current strategies for treating insulin-dependent DM mainly include promoting the self-replication of endogenous β cells, inducing SC differentiation, reprogramming non-β cells into β-like cells, and generating pancreatic-like organoids through cell-based intervention. In this Review, we discuss the current state of the art in these approaches, describe associated challenges, propose potential solutions, and highlight ongoing efforts to optimize β cell or islet transplantation and related clinical trials. These effective cell-based therapies will generate a sustainable source of functional β cells for transplantation and lay strong foundations for future curative treatments for DM.

Neoantigen-augmented iPSC cancer vaccine combined with radiotherapy promotes antitumor immunity in poorly immunogenic cancers

Although irradiated induced-pluripotent stem cells (iPSCs) as a prophylactic cancer vaccine elicit an antitumor immune response, the therapeutic efficacy of iPSC-based cancer vaccines is not promising due to their insufficient antigenicity and the immunosuppressive tumor microenvironment. Here, we found that neoantigen-engineered iPSC cancer vaccines can trigger neoantigen-specific T cell responses to eradicate cancer cells and increase the therapeutic efficacy of RT in poorly immunogenic colorectal cancer (CRC) and triple-negative breast cancer (TNBC). We generated neoantigen-augmented iPSCs (NA-iPSCs) by engineering AAV2 vector carrying murine neoantigens and evaluated their therapeutic efficacy in combination with radiotherapy. After administration of NA-iPSC cancer vaccine and radiotherapy, we found that ~60% of tumor-bearing mice achieved a complete response in microsatellite-stable CRC model. Furthermore, splenocytes from mice treated with NA-iPSC plus RT produced high levels of IFNγ secretion in response to neoantigens and had a greater cytotoxicity to cancer cells, suggesting that the NA-iPSC vaccine combined with radiotherapy elicited a superior neoantigen-specific T-cell response to eradicate cancer cells. The superior therapeutic efficacy of NA-iPSCs engineered by mouse TNBC neoantigens was also observed in the syngeneic immunocompetent TNBC mouse model. We found that the risk of spontaneous lung and liver metastasis was dramatically decreased by NA-iPSCs plus RT in the TNBC animal model. Altogether, these results indicated that autologous iPSC cancer vaccines engineered by neoantigens can elicit a high neoantigen-specific T-cell response, promote tumor regression, and reduce the risk of distant metastasis in combination with local radiotherapy.

Dysregulation of Immune Tolerance to Autologous iPSCs and Their Differentiated Derivatives

Induced pluripotent stem cells (iPSCs), capable of differentiating into any cell type, are a promising tool for solving the problem of donor organ shortage. In addition, reprogramming technology makes it possible to obtain a personalized, i.e., patient-specific, cell product transplantation of which should not cause problems related to histocompatibility of the transplanted tissues and organs. At the same time, inconsistent information about the main advantage of autologous iPSC-derivatives - lack of immunogenicity - still casts doubt on the possibility of using such cells beyond immunosuppressive therapy protocols. This review is devoted to immunogenic properties of the syngeneic and autologous iPSCs and their derivatives, as well as to the reasons for dysregulation of their immune tolerance.

Stem Cell-Based Strategies: The Future Direction of Bioartificial Liver Development

Acute liver failure (ALF) results from severe liver damage or end-stage liver disease. It is extremely fatal and causes serious health and economic burdens worldwide. Once ALF occurs, liver transplantation (LT) is the only definitive and recommended treatment; however, LT is limited by the scarcity of liver grafts. Consequently, the clinical use of bioartificial liver (BAL) has been proposed as a treatment strategy for ALF. Human primary hepatocytes are an ideal cell source for these methods. However, their high demand and superior viability prevent their widespread use. Hence, finding alternatives that meet the seed cell quality and quantity requirements is imperative. Stem cells with self-renewing, immunogenic, and differentiative capacities are potential cell sources. MSCs and its secretomes encompass a spectrum of beneficial properties, such as anti-inflammatory, immunomodulatory, anti-ROS (reactive oxygen species), anti-apoptotic, pro-metabolomic, anti-fibrogenesis, and pro-regenerative attributes. This review focused on the recent status and future directions of stem cell-based strategies in BAL for ALF. Additionally, we discussed the opportunities and challenges associated with promoting such strategies for clinical applications.

Induced pluripotent stem cell-derived exosomes attenuate vascular remodelling in pulmonary arterial hypertension by targeting HIF-1α and Runx2

AIMS

Pulmonary arterial hypertension (PAH) is characterized by extensive pulmonary arterial remodelling. Although mesenchymal stem cell (MSC)-derived exosomes provide protective effects in PAH, MSCs exhibit limited senescence during in vitro expansion compared with the induced pluripotent stem cells (iPSCs). Moreover, the exact mechanism is not known.

METHODS AND RESULTS

In this study, we used murine iPSCs generated from mouse embryonic fibroblasts with triple factor (Oct4, Klf4, and Sox2) transduction to determine the efficacy and action mechanism of iPSC-derived exosomes (iPSC-Exo) in attenuating PAH in rats with monocrotaline (MCT)-induced pulmonary hypertension. Both early and late iPSC-Exo treatment effectively prevented the wall thickening and muscularization of pulmonary arterioles, improved the right ventricular systolic pressure, and alleviated the right ventricular hypertrophy in MCT-induced PAH rats. Pulmonary artery smooth muscle cells (PASMC) derived from MCT-treated rats (MCT-PASMC) developed more proliferative and pro-migratory phenotypes, which were attenuated by the iPSC-Exo treatment. Moreover, the proliferation and migration of MCT-PASMC were reduced by iPSC-Exo with suppression of PCNA, cyclin D1, MMP-1, and MMP-10, which are mediated via the HIF-1α and P21-activated kinase 1/AKT/Runx2 pathways.

CONCLUSION

IPSC-Exo are effective at reversing pulmonary hypertension by reducing pulmonary vascular remodelling and may provide an iPSC-free therapy for the treatment of PAH.

Expression of Major Histocompatibility Complex during Neuronal Differentiation of Somatic Cell Nuclear Transfer-Human Embryonic Stem Cells

Human pluripotent stem cells (hPSCs) such as human embryonic stem cells (hESCs), induced pluripotent stem cells, and somatic cell nuclear transfer (SCNT)-hESCs can permanently self-renew while maintaining their capacity to differentiate into any type of somatic cells, thereby serving as an important cell source for cell therapy. However, there are persistent challenges in the application of hPSCs in clinical trials, where one of the most significant is graft rejection by the patient immune system in response to human leukocyte antigen (HLA) mismatch when transplants are obtained from an allogeneic (non-self) cell source. Homozygous SCNT-hESCs (homo-SCNT-hESCs) were used to simplify the clinical application and to reduce HLA mismatch. Here, we present a xeno-free protocol that confirms the efficient generation of neural precursor cells in hPSCs and also the differentiation of dopaminergic neurons. Additionally, there was no difference when comparing the HLA expression patterns of hESC, homo-SCNT-hESCs and hetero-SCNT-hESCs. We propose that there are no differences in the differentiation capacity and HLA expression among hPSCs that can be cultured in vitro. Thus, it is expected that homo-SCNT-hESCs will possess a wider range of applications when transplanted with neural precursor cells in the context of clinical trials.

Evaluation of the safety and efficiency of cytotoxic T cell therapy sensitized by tumor antigens original from T-ALL-iPSC in vivo

Background

Since RNA sequencing has shown that induced pluripotent stem cells (iPSCs) share a common antigen profile with tumor cells, cancer vaccines that focus on iPSCs have made promising progress in recent years. Previously, we showed that iPSCs derived from leukemic cells of patients with primary T cell acute lymphoblastic leukemia (T-ALL) have a gene expression profile similar to that of T-ALL cell lines.

Methods

Mice with T-ALL were treated with dendritic and T (DC-T) cells loaded with intact and complete antigens from T-ALL-derived iPSCs (T-ALL-iPSCs). We evaluated the safety and antitumor efficiency of autologous tumor-derived iPSC antigens by flow cytometry, cytokine release assay, acute toxicity experiments, long-term toxicity experiments, and other methods.

Results

Our results indicate that complete tumor antigens from T-ALL-iPSCs could inhibit the growth of inoculated tumors in immunocompromised mice without causing acute and long-term toxicity.

Conclusion

T-ALL-iPSC-based treatment is safe and can be used as a potential strategy for leukemia immunotherapy.

Application of Induced Pluripotent Stem Cells in Malignant Solid Tumors

In the past decade, induced pluripotent stem cells (iPSCs) technology has significantly progressed in studying malignant solid tumors. This technically feasible reprogramming techniques can reawaken sequestered dormant regions that regulate the fate of differentiated cells. Despite the evolving therapeutic modalities for malignant solid tumors, treatment outcomes have not been satisfactory. Recently, scientists attempted to apply induced pluripotent stem cell technology to cancer research, from modeling to treatment. Induced pluripotent stem cells derived from somatic cells, cancer cell lines, primary tumors, and individuals with an inherited propensity to develop cancer have shown great potential in cancer modeling, cell therapy, immunotherapy, and understanding tumor progression. This review summarizes the evolution of induced pluripotent stem cells technology and its applications in malignant solid tumor. Additionally, we discuss potential obstacles to induced pluripotent stem cell technology.

Corneal Endothelial-like Cells Derived from Induced Pluripotent Stem Cells for Cell Therapy

Corneal endothelial dysfunction is one of the leading causes of corneal blindness, and the current conventional treatment option is corneal transplantation using a cadaveric donor cornea. However, there is a global shortage of suitable donor graft material, necessitating the exploration of novel therapeutic approaches. A stem cell-based regenerative medicine approach using induced pluripotent stem cells (iPSCs) offers a promising solution, as they possess self-renewal capabilities, can be derived from adult somatic cells, and can be differentiated into all cell types including corneal endothelial cells (CECs). This review discusses the progress and challenges in developing protocols to induce iPSCs into CECs, focusing on the different media formulations used to differentiate iPSCs to neural crest cells (NCCs) and subsequently to CECs, as well as the characterization methods and markers that define iPSC-derived CECs. The hurdles and solutions for the clinical application of iPSC-derived cell therapy are also addressed, including the establishment of protocols that adhere to good manufacturing practice (GMP) guidelines. The potential risks of genetic mutations in iPSC-derived CECs associated with long-term in vitro culture and the danger of potential tumorigenicity following transplantation are evaluated. In all, this review provides insights into the advancement and obstacles of using iPSC in the treatment of corneal endothelial dysfunction.

Genetic Engineering of Immune Evasive Stem Cell-Derived Islets

Genome editing has the potential to revolutionize many investigative and therapeutic strategies in biology and medicine. In the field of regenerative medicine, one of the leading applications of genome engineering technology is the generation of immune evasive pluripotent stem cell-derived somatic cells for transplantation. In particular, as more functional and therapeutically relevant human pluripotent stem cell-derived islets (SCDI) are produced in many labs and studied in clinical trials, there is keen interest in studying the immunogenicity of these cells and modulating allogeneic and autoimmune immune responses for therapeutic benefit. Significant experimental work has already suggested that elimination of Human Leukocytes Antigen (HLA) expression and overexpression of immunomodulatory genes can impact survival of a variety of pluripotent stem cell-derived somatic cell types. Limited work published to date focuses on stem cell-derived islets and work in a number of labs is ongoing. Rapid progress is occurring in the genome editing of human pluripotent stem cells and their progeny focused on evading destruction by the immune system in transplantation models, and while much research is still needed, there is no doubt the combined technologies of genome editing and stem cell therapy will profoundly impact transplantation medicine in the future.

Development of the T-ALLiPSC-based therapeutic cancer vaccines for T-cell acute lymphoblastic leukemia

The T-cell acute lymphoblastic leukemia (T-ALL) is a kind of hematological malignancy in children. Despite the significant improvement in the cure rate of T-ALL upon treatment with chemotherapy regimens, steroids, and allotransplantation there are relapses. This study focuses on the tumor-specific therapeutic vaccines derived from the induced pluripotent stem cells (iPSC) to address the issue of T-ALL recurrence. Patient-derived tumor cells and healthy donor cells were reprogrammed into the iPSCs and the RNA-seq data of the T-ALL-iPSCs and H-iPSCs were analyzed. In vitro, the whole-cell lysate antigens of iPSCs were prepared to induce the dendritic cells (DC) maturation, which in turn stimulated the tumor-specific T cells to kill the T-ALL tumor cells (Jurkat, CCRF-CEM, MOLT-4). The cytotoxic T lymphocyte stimulated by the DC-loaded T-ALL-iPSC-derived antigens showed specific cytotoxicity against the T-ALL cells in vitro. In conclusion, the T-ALL-iPSC-based therapeutic cancer vaccine can elicit a specific anti-tumor effect on T-ALL.

Human iPSC-Derived Renal Cells Change Their Immunogenic Properties during Maturation: Implications for Regenerative Therapies

The success of human induced pluripotent stem cell (hiPSC)-based therapy critically depends on understanding and controlling the immunological effects of the hiPSC-derived transplant. While hiPSC-derived cells used for cell therapy are often immature with post-grafting maturation, immunological properties may change, with adverse effects on graft tolerance and control. In the present study, the allogeneic and autologous cellular immunity of hiPSC-derived progenitor and terminally differentiated cells were investigated in vitro. In contrast to allogeneic primary cells, hiPSC-derived early renal progenitors and mature renal epithelial cells are both tolerated not only by autologous but also by allogeneic T cells. These immune-privileged properties result from active immunomodulation and low immune visibility, which decrease during the process of cell maturation. However, autologous and allogeneic natural killer (NK) cell responses are not suppressed by hiPSC-derived renal cells and effectively change NK cell activation status. These findings clearly show a dynamic stage-specific dependency of autologous and allogeneic T and NK cell responses, with consequences for effective cell therapies. The study suggests that hiPSC-derived early progenitors may provide advantageous immune-suppressive properties when applied in cell therapy. The data furthermore indicate a need to suppress NK cell activation in allogeneic as well as autologous settings.

Skeletal muscle differentiation of human iPSCs meets bioengineering strategies: perspectives and challenges

Although skeletal muscle repairs itself following small injuries, genetic diseases or severe damages may hamper its ability to do so. Induced pluripotent stem cells (iPSCs) can generate myogenic progenitors, but their use in combination with bioengineering strategies to modulate their phenotype has not been sufficiently investigated. This review highlights the potential of this combination aimed at pushing the boundaries of skeletal muscle tissue engineering. First, the overall organization and the key steps in the myogenic process occurring in vivo are described. Second, transgenic and non-transgenic approaches for the myogenic induction of human iPSCs are compared. Third, technologies to provide cells with biophysical stimuli, biomaterial cues, and biofabrication strategies are discussed in terms of recreating a biomimetic environment and thus helping to engineer a myogenic phenotype. The embryonic development process and the pro-myogenic role of the muscle-resident cell populations in co-cultures are also described, highlighting the possible clinical applications of iPSCs in the skeletal muscle tissue engineering field.

The Potential Applications of Stem Cells for Cancer Treatment

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Scientists encounter many obstacles in traditional cancer therapies, including the side effects on the healthy cells, drug resistance, tumor relapse, the short half-life of employed drugs in the blood circulation, and the improper delivery of drugs toward the tumor site. The unique traits of stem cells (SCs) such as self-renewal, differentiation, tumor tropism, the release of bioactive molecules, and immunosuppression have opened a new window for utilizing SCs as a novel tool in cancer treatment. In this regard, engineered SCs can secrete anti-cancer proteins or express enzymes used in suicide gene therapy which locally induce apoptosis in neoplastic cells via the bystander effect. These cells also stand as proper candidates to serve as careers for drug-loaded nanoparticles or to play suitable hosts for oncolytic viruses. Moreover, they harbor great potential to be employed in immunotherapy and combination therapy. However, tactful strategies should be devised to allow easier transplantation and protection of SCs from in vivo immune responses. In spite of the great hope concerning SCs application in cancer therapy, there are shortcomings and challenges to be addressed. This review tends to elaborate on recent advances on the various applications of SCs in cancer therapy and existing challenges in this regard.

Evidence of Antitumor and Antimetastatic Potential of Induced Pluripotent Stem Cell-Based Vaccines in Cancer Immunotherapy

Cancer is maintained by the activity of a rare population of self-renewing "cancer stem cells" (CSCs), which are resistant to conventional therapies. CSCs over-express several proteins shared with induced pluripotent stem cells (iPSCs). We show here that allogenic or autologous murine iPSCs, combined with a histone deacetylase inhibitor (HDACi), are able to elicit major anti-tumor responses in a highly aggressive triple-negative breast cancer, as a relevant cancer stemness model. This immunotherapy strategy was effective in preventing tumor establishment and efficiently targeted CSCs by inducing extensive modifications of the tumor microenvironment. The anti-tumoral effect was correlated with the generation of CD4+, CD8+ T cells, and CD44+ CD62L- CCR7low CD127low T-effector memory cells, and the reduction of CD4+ CD25+FoxP3+ Tregs, Arg1⁺ CD11b+ Gr1+, and Arg1⁺ and CD11b+ Ly6+ myeloid-derived suppressor cell populations within the tumor. The anti-tumoral effect was associated with a reduction in metastatic dissemination and an improvement in the survival rate. These results demonstrate for the first time the clinical relevance of using an off-the-shelf allogeneic iPSC-based vaccine combined with an HDACi as a novel pan-cancer anti-cancer immunotherapy strategy against aggressive tumors harboring stemness features with high metastatic potential.

The Potential of Induced Pluripotent Stem Cells to Advance the Treatment of Pancreatic Ductal Adenocarcinoma

Simple Summary

Despite improvements in the treatment of several cancer types, the extremely poor prognosis of pancreatic cancer patients has remained unchanged over the last decades. Therefore, new therapeutic regimens for pancreatic cancer are highly needed. In this review, we will discuss the potential of induced pluripotent stem cells (iPSCs) to generate representative pancreatic cancer models that can aid the development of novel diagnostics and therapeutic strategies. Furthermore, the potential of iPSCs as pancreatic cancer vaccines or as a basis for cellular therapies will be discussed. With promising preclinical results and ongoing clinical trials, the potential of iPSCs to further the treatment of pancreatic cancer is being explored and, in turn, will hopefully provide additional therapies to increase the poor survival rates of this patient population.

Abstract

Advances in the treatment of pancreatic ductal adenocarcinoma (PDAC) using neoadjuvant chemoradiotherapy, chemotherapy, and immunotherapy have had minimal impact on the overall survival of patients. A general lack of immunogenic features and a complex tumor microenvironment (TME) are likely culprits for therapy refractoriness in PDAC. Induced pluripotent stem cells (iPSCs) should be explored as a means to advance the treatment options for PDAC, by providing representative in vitro models of pancreatic cancer development. In addition, iPSCs could be used for tailor-made cellular immunotherapies or as a source of tumor-associated antigens in the context of vaccination.

Computational tools for analyzing single-cell data in pluripotent cell differentiation studies

Single-cell technologies are revolutionizing the ability of researchers to infer the causes and results of biological processes. Although several studies of pluripotent cell differentiation have recently utilized single-cell sequencing data, other aspects related to the optimization of differentiation protocols, their validation, robustness, and usage are still not taking full advantage of single-cell technologies. In this review, we focus on computational approaches for the analysis of single-cell omics and imaging data and discuss their use to address many of the major challenges involved in the development, validation, and use of cells obtained from pluripotent cell differentiation.

[Hepatic organoids: What are the challenges?]

The study and understanding of liver organogenesis have allowed the development of protocols for pluripotent stem cells differentiation to overcome the lack of primary cells, providing an almost unlimited source of liver cells. However, as their differentiation in conventional 2D culture systems has shown serious limits, hepatic organoids derived from human pluripotent stem cells represent a promising alternative. These complex and organized structures, containing one or more cell types, make it possible to recapitulate in vitro some of the organ functions, thus enabling numerous applications such as the study of the liver development, the mass production of functional liver cells for transplantation or the development of bioartificial livers, as well as the in vitro modeling of hepatic pathologies allowing high throughput applications in drug screening or toxicity studies. Economic and ethical issues must also be taken into account before using these organoids in therapeutic applications.

Advanced Techniques and Awaited Clinical Applications for Human Pluripotent Stem Cell Differentiation into Hepatocytes

Liver transplantation is currently the only curative treatment for several liver diseases such as acute liver failure, end-stage liver disorders, primary liver cancers, and certain genetic conditions. Unfortunately, despite improvements to transplantation techniques, including live donor transplantation, the number of organs available remains insufficient to meet patient needs. Hepatocyte transplantation has enabled some encouraging results as an alternative to organ transplantation, but primary hepatocytes are little available and cannot be amplified using traditional two-dimensional culture systems. Indeed, although recent studies have tended to show that three-dimensional culture enables long-term hepatocyte culture, it is still agreed that, like most adult primary cell types, hepatocytes remain refractory to in vitro expansion. Because of their exceptional properties, human pluripotent stem cells (hPSCs) can be amplified indefinitely and differentiated into any cell type, including liver cells. While many teams have worked on hepatocyte differentiation, there has been a consensus that cells obtained after hPSC differentiation have more fetal than adult hepatocyte characteristics. New technologies have been used to improve the differentiation process in recent years. This review discusses the technical improvements made to hepatocyte differentiation protocols and the clinical approaches developed to date and anticipated in the near future.

Immunological considerations and challenges for regenerative cellular therapies

The central goal of regenerative medicine is to replace damaged or diseased tissue with cells that integrate and function optimally. The capacity of pluripotent stem cells to produce unlimited numbers of differentiated cells is of considerable therapeutic interest, with several clinical trials underway. However, the host immune response represents an important barrier to clinical translation. Here we describe the role of the host innate and adaptive immune responses as triggers of allogeneic graft rejection. We discuss how the immune response is determined by the cellular therapy. Additionally, we describe the range of available in vitro and in vivo experimental approaches to examine the immunogenicity of cellular therapies, and finally we review potential strategies to ameliorate immune rejection. In conclusion, we advocate establishment of platforms that bring together the multidisciplinary expertise and infrastructure necessary to comprehensively investigate the immunogenicity of cellular therapies to ensure their clinical safety and efficacy.

A Concise Review on Induced Pluripotent Stem Cell-Derived Cardiomyocytes for Personalized Regenerative Medicine

The induced pluripotent stem cells (iPSCs) are derived from somatic cells by using reprogramming factors such as Oct4, Sox2, Klf4, and c-Myc (OSKM) or Oct4, Sox2, Nanog and Lin28 (OSNL). They resemble embryonic stem cells (ESCs) and have the ability to differentiate into cell lineage of all three germ-layer, including cardiomyocytes (CMs). The CMs can be generated from iPSCs by inducing embryoid bodies (EBs) formation and treatment with activin A, bone morphogenic protein 4 (BMP4), and inhibitors of Wnt signaling. However, these iPSC-derived CMs are a heterogeneous population of cells and require purification and maturation to mimic the in vivo CMs. The matured CMs can be used for various therapeutic purposes in regenerative medicine by cardiomyoplasty or through the development of tissue-engineered cardiac patches. In recent years, significant advancements have been made in the isolation of iPSC and their differentiation, purification, and maturation into clinically usable CMs. Newer small molecules have also been identified to substitute the reprogramming factors for iPSC generation as well as for direct differentiation of somatic cells into CMs without an intermediary pluripotent state. This review provides a concise update on the generation of iPSC-derived CMs and their application in personalized cardiac regenerative medicine. It also discusses the current limitations and challenges in the application of iPSC-derived CMs. Graphical abstract.

A Concise Review: The Role of Stem Cells in Cancer Progression and Therapy

The properties of cancer stem cells (CSCs) have recently gained attention as an avenue of intervention for cancer therapy. In this review, we highlight some of the key roles of CSCs in altering the cellular microenvironment in favor of cancer progression. We also report on various studies in this field which focus on transformative properties of CSCs and their influence on surrounding cells or targets through the release of cellular cargo in the form of extracellular vesicles. The findings from these studies encourage the development of novel interventional therapies that can target and prevent cancer through efficient, more effective methods. These methods include targeting immunosuppressive proteins and biomarkers, promoting immunization against tumors, exosome-mediated CSC conversion, and a focus on the quiescent properties of CSCs and their role in cancer progression. The resulting therapeutic benefit and transformative potential of these novel approaches to stem cell-based cancer therapy provide a new direction in cancer treatment, which can focus on nanoscale, molecular properties of the cellular microenvironment and establish a more precision medicine-oriented paradigm of treatment.

Fit-For-All iPSC-Derived Cell Therapies and Their Evaluation in Humanized Mice With NK Cell Immunity

Human induced pluripotent stem cells (iPSCs) can be limitlessly expanded and differentiated into almost all cell types. Moreover, they are amenable to gene manipulation and, because they are established from somatic cells, can be established from essentially any person. Based on these characteristics, iPSCs have been extensively studied as cell sources for tissue grafts, blood transfusions and cancer immunotherapies, and related clinical trials have started. From an immune-matching perspective, autologous iPSCs are perfectly compatible in principle, but also require a prolonged time for reaching the final products, have high cost, and person-to-person variation hindering their common use. Therefore, certified iPSCs with reduced immunogenicity are expected to become off-the-shelf sources, such as those made from human leukocyte antigen (HLA)-homozygous individuals or genetically modified for HLA depletion. Preclinical tests using immunodeficient mice reconstituted with a human immune system (HIS) serve as an important tool to assess the human alloresponse against iPSC-derived cells. Especially, HIS mice reconstituted with not only human T cells but also human natural killer (NK) cells are considered crucial. NK cells attack so-called “missing self” cells that do not express self HLA class I, which include HLA-homozygous cells that express only one allele type and HLA-depleted cells. However, conventional HIS mice lack enough reconstituted human NK cells for these tests. Several measures have been developed to overcome this issue including the administration of cytokines that enhance NK cell expansion, such as IL-2 and IL-15, the administration of vectors that express those cytokines, and genetic manipulation to express the cytokines or to enhance the reconstitution of human myeloid cells that express IL15R-alpha. Using such HIS mice with enhanced human NK cell reconstitution, alloresponses against HLA-homozygous and HLA-depleted cells have been studied. However, most studies used HLA-downregulated tumor cells as the target cells and tested in vitro after purifying human cells from HIS mice. In this review, we give an overview of the current state of iPSCs in cell therapies, strategies to lessen their immunogenic potential, and then expound on the development of HIS mice with reconstituted NK cells, followed by their utilization in evaluating future universal HLA-engineered iPSC-derived cells.

Generation of inner ear sensory neurons using blastocyst complementation in a Neurog1+/--deficient mouse

This research is the first to produce induced pluripotent stem cell-derived inner ear sensory neurons in the Neurog1^+/− heterozygote mouse using blastocyst complementation. Additionally, this approach corrected non-sensory deficits associated with Neurog1 heterozygosity, indicating that complementation is specific to endogenous Neurog1 function. This work validates the use of blastocyst complementation as a tool to create novel insight into the function of developmental genes and highlights blastocyst complementation as a potential platform for generating chimeric inner ear cell types that can be transplanted into damaged inner ears to improve hearing.

Selection of different endothelialization modes and different seed cells for tissue-engineered vascular graft

Tissue-engineered vascular grafts (TEVGs) have enormous potential for vascular replacement therapy. However, thrombosis and intimal hyperplasia are important problems associated with TEVGs especially small diameter TEVGs (<6 mm) after transplantation. Endothelialization of TEVGs is a key point to prevent thrombosis. Here, we discuss different types of endothelialization and different seed cells of tissue-engineered vascular grafts. Meanwhile, endothelial heterogeneity is also discussed. Based on it, we provide a new perspective for selecting suitable types of endothelialization and suitable seed cells to improve the long-term patency rate of tissue-engineered vascular grafts with different diameters and lengths.

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The material, diameter and length of tissue-engineered vascular graft are all key factors affecting its long-term patency.

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Endothelialization strategies should consider the different diameters and lengths of tissue-engineered vascular grafts.

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Cell heterogeneity and tissue heterogeneity should be considered in the application of seed cells.

Non-immunogenic Induced Pluripotent Stem Cells, a Promising Way Forward for Allogenic Transplantations for Neurological Disorders

Neurological disorder is a general term used for diseases affecting the function of the brain and nervous system. Those include a broad range of diseases from developmental disorders (e.g., Autism) over injury related disorders (e.g., stroke and brain tumors) to age related neurodegeneration (e.g., Alzheimer's disease), affecting up to 1 billion people worldwide. For most of those disorders, no curative treatment exists leaving symptomatic treatment as the primary mean of alleviation. Human induced pluripotent stem cells (hiPSC) in combination with animal models have been instrumental to foster our understanding of underlying disease mechanisms in the brain. Of specific interest are patient derived hiPSC which allow for targeted gene editing in the cases of known mutations. Such personalized treatment would include (1) acquisition of primary cells from the patient, (2) reprogramming of those into hiPSC via non-integrative methods, (3) corrective intervention via CRISPR-Cas9 gene editing of mutations, (4) quality control to ensure successful correction and absence of off-target effects, and (5) subsequent transplantation of hiPSC or pre-differentiated precursor cells for cell replacement therapies. This would be the ideal scenario but it is time consuming and expensive. Therefore, it would be of great benefit if transplanted hiPSC could be modulated to become invisible to the recipient's immune system, avoiding graft rejection and allowing for allogenic transplantations. This review will focus on the current status of gene editing to generate non-immunogenic hiPSC and how these cells can be used to treat neurological disorders by using cell replacement therapy. By providing an overview of current limitations and challenges in stem cell replacement therapies and the treatment of neurological disorders, this review outlines how gene editing and non-immunogenic hiPSC can contribute and pave the road for new therapeutic advances. Finally, the combination of using non-immunogenic hiPSC and in vivo animal modeling will highlight the importance of models with translational value for safety efficacy testing; before embarking on human trials.

The Potentials and Pitfalls of Using Adult Stem Cells in Cancer Treatment

Stem cells play a pivotal role in the developmental stages of an organism and in adulthood as well. Therefore, it is not surprising that stem cells constitute a focus of extensive research. Indeed, several decades of stem cell research have tremendously increased our knowledge on the mechanistic understandings of stem cell biology. Interestingly, revealing the fundamental principles of stem cell biology has also fostered its application for therapeutic purposes. Many of the attributes that the stem cells possess, some of which are unique, allow multifaceted exploitation of stem cells in the treatment of various diseases. Cancer, the leading cause of mortality worldwide, is one of the disease groups that has been benefited by the potentials of therapeutic applications of the stem cells. While the modi operandi of how stem cells contribute to cancer treatment are many-sided, two major principles can be conceived. One mode involves harnessing the regenerative power of the stem cells to promote the generation of blood-forming cells in cancer patients after cytotoxic regimens. A totally different kind of utility of stem cells has been exercised in another mode where the stem cells can potentially deliver a plethora of anti-cancer therapeutics in a tumor-specific manner. While both these approaches can improve the treatment of cancer patients, there exist several issues that warrant further research. This review summarizes the basic principles of the utility of the stem cells in cancer treatment along with the current trends and pinpoints the major obstacles to focus on in the future for further improvement.

Xenogeneic and Stem Cell-Based Therapy for Cardiovascular Diseases: Genetic Engineering of Porcine Cells and Their Applications in Heart Regeneration

Cardiovascular diseases represent a major health concern worldwide with few therapy options for ischemic injuries due to the limited regeneration potential of affected cardiomyocytes. Innovative cell replacement approaches could facilitate efficient regenerative therapy. However, despite extensive attempts to expand primary human cells in vitro, present technological limitations and the lack of human donors have so far prevented their broad clinical use. Cell xenotransplantation might provide an ethically acceptable unlimited source for cell replacement therapies and bridge the gap between waiting recipients and available donors. Pigs are considered the most suitable candidates as a source for xenogeneic cells and tissues due to their anatomical and physiological similarities with humans. The potential of porcine cells in the field of stem cell-based therapy and regenerative medicine is under intensive investigation. This review outlines the current progress and highlights the most promising approaches in xenogeneic cell therapy with a focus on the cardiovascular system.

Recent progress in translational engineered in vitro models of the central nervous system

The complexity of the human brain poses a substantial challenge for the development of models of the CNS. Current animal models lack many essential human characteristics (in addition to raising operational challenges and ethical concerns), and conventional in vitro models, in turn, are limited in their capacity to provide information regarding many functional and systemic responses. Indeed, these challenges may underlie the notoriously low success rates of CNS drug development efforts. During the past 5 years, there has been a leap in the complexity and functionality of in vitro systems of the CNS, which have the potential to overcome many of the limitations of traditional model systems. The availability of human-derived induced pluripotent stem cell technology has further increased the translational potential of these systems. Yet, the adoption of state-of-the-art in vitro platforms within the CNS research community is limited. This may be attributable to the high costs or the immaturity of the systems. Nevertheless, the costs of fabrication have decreased, and there are tremendous ongoing efforts to improve the quality of cell differentiation. Herein, we aim to raise awareness of the capabilities and accessibility of advanced in vitro CNS technologies. We provide an overview of some of the main recent developments (since 2015) in in vitro CNS models. In particular, we focus on engineered in vitro models based on cell culture systems combined with microfluidic platforms (e.g. 'organ-on-a-chip' systems). We delve into the fundamental principles underlying these systems and review several applications of these platforms for the study of the CNS in health and disease. Our discussion further addresses the challenges that hinder the implementation of advanced in vitro platforms in personalized medicine or in large-scale industrial settings, and outlines the existing differentiation protocols and industrial cell sources. We conclude by providing practical guidelines for laboratories that are considering adopting organ-on-a-chip technologies.

Strategies for Cancer Immunotherapy Using Induced Pluripotency Stem Cells-Based Vaccines

Despite improvements in cancer therapy, metastatic solid tumors remain largely incurable. Immunotherapy has emerged as a pioneering and promising approach for cancer therapy and management, and in particular intended for advanced tumors unresponsive to current therapeutics. In cancer immunotherapy, components of the immune system are exploited to eliminate cancer cells and treat patients. The recent clinical successes of immune checkpoint blockade and chimeric antigen receptor T cell therapies represent a turning point in cancer treatment. Despite their potential success, current approaches depend on efficient tumor antigen presentation which are often inaccessible, and most tumors turn refractory to current immunotherapy. Patient-derived induced pluripotent stem cells (iPSCs) have been shown to share several characteristics with cancer (stem) cells (CSCs), eliciting a specific anti-tumoral response when injected in rodent cancer models. Indeed, artificial cellular reprogramming has been widely compared to the biogenesis of CSCs. Here, we will discuss the state-of-the-art on the potential implication of cellular reprogramming and iPSCs for the design of patient-specific immunotherapeutic strategies, debating the similarities between iPSCs and cancer cells and introducing potential strategies that could enhance the efficiency and therapeutic potential of iPSCs-based cancer vaccines.

Tumorigenic and Immunogenic Properties of Induced Pluripotent Stem Cells: a Promising Cancer Vaccine

Induced pluripotent stem cells (iPSCs) are mainly characterized by their unlimited proliferation abilities and potential to develop into almost any cell type. The creation of this technology has been of great interest to many scientific fields, especially regenerative biology. However, concerns about the safety of iPSC application in transplantation have arisen due to the tumorigenic and immunogenic properties of iPSCs. This review will briefly introduce the developing history of somatic reprogramming and applications of iPSC technology in regenerative medicine. In addition, the review will highlight two challenges to the efficient usage of iPSCs and the underlying mechanisms of these challenges. Finally, the review will discuss the expanding application of iPSC technology in cancer immunotherapy as a potential cancer vaccine and its advantages in auxiliary treatment compared with oncofetal antigen-based and embryonic stem cell (ESC)-based vaccines.

The H-Y Antigen in Embryonic Stem Cells Causes Rejection in Syngeneic Female Recipients

Pluripotent stem cells are promising candidates for cell-based regenerative therapies. To avoid rejection of transplanted cells, several approaches are being pursued to reduce immunogenicity of the cells or modulate the recipient's immune response. These include gene editing to reduce the antigenicity of cell products, immunosuppression of the host, or using major histocompatibility complex-matched cells from cell banks. In this context, we have investigated the antigenicity of H-Y antigens, a class of minor histocompatibility antigens encoded by the Y chromosome, to assess whether the gender of the donor affects the cell's antigenicity. In a murine transplant model, we show that the H-Y antigen in undifferentiated embryonic stem cells (ESCs), as well as ESC-derived endothelial cells, provokes T- and B cell responses in female recipients.

Myogenic progenitor cells derived from human induced pluripotent stem cell are immune-tolerated in humanized mice

It is still unclear if immune responses will compromise the large‐scale utilization of human induced pluripotent stem cells (hiPSCs)‐derived cell therapies. To answer this question, we used humanized mouse models generated by the adoptive transfer of peripheral blood mononuclear cells or the cotransplantation of hematopoietic stem cells and human thymic tissue. Using these mice, we evaluated the engraftment in skeletal muscle of myoblasts derived either directly from a muscle biopsy or differentiated from hiPSCs or fibroblasts. Our results showed that while allogeneic grafts were mostly rejected and highly infiltrated with human T cells, engraftment of autologous cells was tolerated. We also observed that hiPSC‐derived myogenic progenitor cells (MPCs) are not targeted by autologous T cells and natural killer cells in vitro. These findings suggest that the reprogramming and differentiation procedures we used are not immunogenic and that hiPSC‐derived MPCs will be tolerated in the presence of a competent human immune system.

Breakthrough concepts in immune-oncology: Cancer vaccines at the bedside

Clinical approval of the immune checkpoint blockade (ICB) agents for multiple cancer types has reinvigorated the long-standing work on cancer vaccines. In the pre-ICB era, clinical efforts focused on the Ag, the adjuvants, the formulation, and the mode of delivery. These translational efforts on therapeutic vaccines range from cell-based (e.g., dendritic cells vaccine Sipuleucel-T) to DNA/RNA-based platforms with various formulations (liposome), vectors (Listeria monocytogenes), or modes of delivery (intratumoral, gene gun, etc.). Despite promising preclinical results, cancer vaccine trials without ICB have historically shown little clinical activity. With the anticipation and expansion of combinatorial immunotherapeutic trials with ICB, the cancer vaccine field has entered the personalized medicine arena with recent advances in immunogenic neoantigen-based vaccines. In this article, we review the literature to organize the different cancer vaccines in the clinical space, and we will discuss their advantages, limits, and recent progress to overcome their challenges. Furthermore, we will also discuss recent preclinical advances and clinical strategies to combine vaccines with checkpoint blockade to improve therapeutic outcome and present a translational perspective on future directions.

Human iPS Cells Loaded with MnO2-Based Nanoprobes for Photodynamic and Simultaneous Enhanced Immunotherapy Against Cancer

HIGHLIGHTS

MnO₂@Ce6 nanoprobes-loaded-iPS cells (iPS-MnO₂@Ce6) were developed for enhanced photodynamic and immunotherapy against cancer. Under the guidance of multi-mode real-time imaging, iPS-MnO₂@Ce6 achieved an enhanced photodynamic therapeutic effect and stimulated a strong anti-tumor immune response in the tumor-bearing mouse.

ABSTRACT

How to trigger strong anti-tumor immune responses has become a focus for tumor therapy. Here, we report the human-induced pluripotent stem cells (iPSs) to deliver MnO₂@Ce6 nanoprobes into tumors for simultaneous photodynamic therapy (PDT) and enhanced immunotherapy. Ce6 photosensitizer was attached on manganese dioxide (MnO₂) nanoparticles, and resultant MnO₂@Ce6 nanoprobes were delivered into mitomycin-treated iPSs to form iPS-MnO₂@Ce6 nanoprobes. The iPS-MnO₂@Ce6 actively targeted in vivo tumors, the acidic microenvironment triggered interaction between MnO₂ and H₂O₂, released large quantities of oxygen, alleviated hypoxia in tumor. Upon PDT, singlet oxygen formed, broken iPSs released tumor-shared antigens, which evoked an intensive innate and adaptive immune response against the tumor, improving dendritic cells matured, effector T cells, and natural killer cells were activated. Meanwhile, regulatory T cells were reduced, and then the immune response induced by iPS-MnO₂@Ce6 was markedly stronger than the immune reaction induced by MnO₂@Ce6 (P < 0.05). The iPS-MnO₂@Ce6 markedly inhibited tumor growth and metastasis and reduced mortality in mice models with tumor. Human iPSs loaded with MnO₂-based nanoprobes are a promising strategy for simultaneous PDT and enhanced immunotherapy against tumor and own clinical translational prospect. [Image: see text]

ELECTRONIC SUPPLEMENTARY MATERIAL

The online version of this article (10.1007/s40820-020-00452-y) contains supplementary material, which is available to authorized users.

Accept or Reject: The Role of Immune Tolerance in the Development of Stem Cell Therapies and Possible Future Approaches

In 2011, Goldring and colleagues published a review article describing the potential safety issues of novel stem cell-derived treatments. Immunogenicity and immunotoxicity of the administered cell product were considered risks in the light of clinical experience of transplantation. The relative immunogenicity of mesenchymal stem cells, embryonic stem cells (ESCs), and induced pluripotent stem cells (iPSCs) was being addressed through in vitro and in vivo models. But the question arose as to whether the implanted cells needed to be identical to the recipient in every respect, including epigenetically, to evade immune recognition? If so, this set a high bar which may preclude use of many cells derived from iPSCs which have vestiges of a fetal phenotype and epigenetic memory of their cell of origin. However, for autologous iPSCs, the immunogenicity reduces once the surface antigen expression profile becomes close to that of the parent somatic cells. Therefore, a cell product containing incompletely differentiated cells could be more immunogenic. The properties of the administered cells, the immune privilege of the administration site, and the host immune status influence graft success or failure. In addition, the various approaches available to characterize potential immunogenicity of a cell therapy will be discussed.

Coreceptor blockade targeting CD4 and CD8 allows acceptance of allogeneic human pluripotent stem cell grafts in humanized mice

We have previously demonstrated that short-term coreceptor blockade with non-lytic monoclonal antibodies enables the long-term survival of fully allogeneic embryonic stem cell (ESC) transplants in mice. Here, we describe the use of Hu-PBL humanized mice to determine whether short-term coreceptor blockade with humanized anti-human CD4 and CD8 antibodies can achieve the same outcome towards human ESC derivatives. While control Hu-PBL mice rejected allogeneic hESC-derived transplants within weeks, mice treated with coreceptor blocking antibodies held their grafts for 7 weeks, the duration of the study. Rejection in the control mice was associated with demonstrable infiltrates of human CD45 white blood cells, predominantly of CD8 T-cells, whereas anti-CD4, but not anti-CD8 antibody treated mice showed remarkably reduced lymphocyte infiltration and prolonged allograft survival, indicating that the CD4⁺ T-cells were crucial to the rejection process. Our results give support to the principle that short-term blockade of T-cell co-receptors can achieve long-term acceptance of regenerative cell transplants in humans.

The Challenge of Bringing iPSCs to the Patient

The implementation of induced pluripotent stem cells (iPSCs) in biomedical research more than a decade ago, resulted in a huge leap forward in the highly promising area of personalized medicine. Nowadays, we are even closer to the patient than ever. To date, there are multiple examples of iPSCs applications in clinical trials and drug screening. However, there are still many obstacles to overcome. In this review, we will focus our attention on the advantages of implementing induced pluripotent stem cells technology into the clinics but also commenting on all the current drawbacks that could hinder this promising path towards the patient.

Application of Human Induced Pluripotent Stem Cells in Generating Tissue-Engineered Blood Vessels as Vascular Grafts

In pace with the advancement of tissue engineering during recent decades, tissue-engineered blood vessels (TEBVs) have been generated using primary seed cells, and their impressive success in clinical trials have demonstrated the great potential of these TEBVs as implantable vascular grafts in human regenerative medicine. However, the production, therapeutic efficacy, and readiness in emergencies of current TEBVs could be hindered by the accessibility, expandability, and donor-donor variation of patient-specific primary seed cells. Alternatively, using human induced pluripotent stem cells (hiPSCs) to derive seed vascular cells for vascular tissue engineering could fundamentally address this current dilemma in TEBV production. As an emerging research field with a promising future, the generation of hiPSC-based TEBVs has been reported recently with significant progress. Simultaneously, to further promote hiPSC-based TEBVs into vascular grafts for clinical use, several challenges related to the safety, readiness, and structural integrity of vascular tissue need to be addressed. Herein, this review will focus on the evolution and role of hiPSCs in vascular tissue engineering technology and summarize the current progress, challenges, and future directions of research on hiPSC-based TEBVs.

Functions of p53 in pluripotent stem cells

Pluripotent stem cells (PSCs) are capable of unlimited self-renewal in culture and differentiation into all functional cell types in the body, and thus hold great promise for regenerative medicine. To achieve their clinical potential, it is critical for PSCs to maintain genomic stability during the extended proliferation. The critical tumor suppressor p53 is required to maintain genomic stability of mammalian cells. In response to DNA damage or oncogenic stress, p53 plays multiple roles in maintaining genomic stability of somatic cells by inducing cell cycle arrest, apoptosis, and senescence to prevent the passage of genetic mutations to the daughter cells. p53 is also required to maintain the genomic stability of PSCs. However, in response to the genotoxic stresses, a primary role of p53 in PSCs is to induce the differentiation of PSCs and inhibit pluripotency, providing mechanisms to maintain the genomic stability of the self-renewing PSCs. In addition, the roles of p53 in cellular metabolism might also contribute to genomic stability of PSCs by limiting oxidative stress. In summary, the elucidation of the roles of p53 in PSCs will be a prerequisite for developing safe PSC-based cell therapy.

Induced pluripotent stem cells as a novel cancer vaccine

Introduction: Although many current cancer therapies are effective, the mortality rate globally is unacceptably high. Cancer remains the second leading cause of death worldwide after heart disease and has caused nearly 10 million deaths in 2018. Additionally, current preventive therapies for cancer are underdeveloped, undermining the quality of life of high-risk individuals. Therefore, new treatment options for targeting cancer are urgently needed. In a recent study, researchers adopted an autologous iPSC-based vaccine to present a broad spectrum of tumor antigens to the immune system and succeeded in orchestrating a strong prophylactic immunity towards multiple types of cancer in mice. Areas covered: In this review, we provide an overview of how cancer develops, the role of immune surveillance in cancer progression, the current status and challenges of cancer immunotherapy as well as the genetic overlap between pluripotent stem cells and cancer cells. Finally, we discuss the rationale for an autologous iPSC-based vaccine and its applications in murine cancer models. Expert opinion: The autologous iPSC-based vaccine is a promising preventive and therapeutic strategy for fighting various types of cancers. Continuing efforts and clinical/translational follow-up studies may bring an autologous iPSC-based cancer vaccination approach from bench to bedside.

Human iPSC banking: barriers and opportunities

The introduction of induced pluripotent stem cells (iPSCs) has opened up the potential for personalized cell therapies and ushered in new opportunities for regenerative medicine, disease modeling, iPSC-based drug discovery and toxicity assessment. Over the past 10 years, several initiatives have been established that aim to collect and generate a large amount of human iPSCs for scientific research purposes. In this review, we compare the construction and operation strategy of some iPSC banks as well as their ongoing development. We also introduce the technical challenges and offer future perspectives pertaining to the establishment and management of iPSC banks.

Conversion of human fibroblasts into multipotent cells by cell-penetrating peptides

The potential application of human induced pluripotent stem cells (hiPSCs) brings great expectations to regenerative medicine. However, several safety concerns, such as oncogenic transformation, remain. A number of methods have been developed to produce hiPSCs with potentially reduced risks. Cell-penetrating peptides (CPPs) are expected to improve the efficiency of nonviral reprogramming by delivering biologically active molecules into cells. Here, we show that the transfection of CPPs alone into normal adult human fibroblasts generated embryonic body (EB)-like cell clusters in the absence of reprogramming factors. The CPP-generated cell clusters were positive for a set of multipotency markers and differentiated into endodermal, ectodermal, and mesodermal cells in vitro. These results suggest that CPPs converted normal human adult somatic cells into multipotent cells. Moreover, we show that CPPs dissociated histone deacetylase 1 and lysine-specific demethylase 1 from the promoter/enhancer regions of reprogramming factors to reactivate their expression. This is the first report of an easy and quick method for somatic cell reprogramming by CPPs and a novel mechanism of reprogramming. The potential application of CPP-generated multipotent cells resolves several concerns, especially safety issues, in regenerative medicine.

De novo mutations in mitochondrial DNA of iPSCs produce immunogenic neoepitopes in mice and humans

The utility of autologous induced pluripotent stem cell (iPSC) therapies for tissue regeneration depends on reliable production of immunologically silent functional iPSC derivatives. However, rejection of autologous iPSC-derived cells has been reported, although the mechanism underlying rejection is largely unknown. We hypothesized that de novo mutations in mitochondrial DNA (mtDNA), which has far less reliable repair mechanisms than chromosomal DNA, might produce neoantigens capable of eliciting immune recognition and rejection. Here we present evidence in mice and humans that nonsynonymous mtDNA mutations can arise and become enriched during reprogramming to the iPSC stage, long-term culture and differentiation into target cells. These mtDNA mutations encode neoantigens that provoke an immune response that is highly specific and dependent on the host major histocompatibility complex genotype. Our results reveal that autologous iPSCs and their derivatives are not inherently immunologically inert for autologous transplantation and suggest that iPSC-derived products should be screened for mtDNA mutations.