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Martínez-Falguera D, Iborra-Egea O, Gálvez-Montón C. iPSC Therapy for Myocardial Infarction in Large Animal Models: Land of Hope and Dreams. Biomedicines 2021; 9:1836. [PMID: 34944652 PMCID: PMC8698445 DOI: 10.3390/biomedicines9121836] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2021] [Revised: 11/30/2021] [Accepted: 12/01/2021] [Indexed: 02/07/2023] Open
Abstract
Myocardial infarction is the main driver of heart failure due to ischemia and subsequent cell death, and cell-based strategies have emerged as promising therapeutic methods to replace dead tissue in cardiovascular diseases. Research in this field has been dramatically advanced by the development of laboratory-induced pluripotent stem cells (iPSCs) that harbor the capability to become any cell type. Like other experimental strategies, stem cell therapy must meet multiple requirements before reaching the clinical trial phase, and in vivo models are indispensable for ensuring the safety of such novel therapies. Specifically, translational studies in large animal models are necessary to fully evaluate the therapeutic potential of this approach; to empirically determine the optimal combination of cell types, supplementary factors, and delivery methods to maximize efficacy; and to stringently assess safety. In the present review, we summarize the main strategies employed to generate iPSCs and differentiate them into cardiomyocytes in large animal species; the most critical differences between using small versus large animal models for cardiovascular studies; and the strategies that have been pursued regarding implanted cells' stage of differentiation, origin, and technical application.
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Affiliation(s)
- Daina Martínez-Falguera
- Faculty of Medicine, University of Barcelona (UB), 08036 Barcelona, Spain;
- ICREC Research Program, Germans Trias i Pujol Health Research Institute, Can Ruti Campus, 08916 Badalona, Spain;
- Heart Institute (iCor), Germans Trias i Pujol University Hospital, 08916 Badalona, Spain
| | - Oriol Iborra-Egea
- ICREC Research Program, Germans Trias i Pujol Health Research Institute, Can Ruti Campus, 08916 Badalona, Spain;
- Heart Institute (iCor), Germans Trias i Pujol University Hospital, 08916 Badalona, Spain
| | - Carolina Gálvez-Montón
- ICREC Research Program, Germans Trias i Pujol Health Research Institute, Can Ruti Campus, 08916 Badalona, Spain;
- Heart Institute (iCor), Germans Trias i Pujol University Hospital, 08916 Badalona, Spain
- CIBERCV, Instituto de Salud Carlos III, 28029 Madrid, Spain
- Institut d’Investigació Biomèdica de Bellvitge-IDIBELL, L’Hospitalet de Llobregat, 08908 Barcelona, Spain
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Kasendra M, Troutt M, Broda T, Bacon WC, Wang TC, Niland JC, Helmrath MA. Intestinal organoids: roadmap to the clinic. Am J Physiol Gastrointest Liver Physiol 2021; 321:G1-G10. [PMID: 33950707 PMCID: PMC8321798 DOI: 10.1152/ajpgi.00425.2020] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/16/2020] [Revised: 04/29/2021] [Accepted: 05/03/2021] [Indexed: 01/31/2023]
Abstract
Recent advances in intestinal organoid research, along with encouraging preclinical proof-of-concept studies, have revealed significant therapeutic potential for induced pluripotent stem cell (iPSC)-derived organoids in the healing and replacement of severely injured or diseased bowel (Finkbeiner et al. Biol Open 4: 1462-1472, 2015; Kitano et al. Nat Commun 8: 765, 2017; Cruz-Acuna et al. Nat Cell Biol 19: 1326-1335, 2017). To fully realize the tremendous promise of stem cell organoid-based therapies, careful planning aligned with significant resources and efforts must be devoted demonstrating their safety and efficacy to meet critical regulatory requirements. Early recognition of the inherent preclinical and clinical obstacles that occur with the novel use of pluripotent stem cell-derived products will accelerate their bench-to-bedside translation (Neofytou et al. J Clin Invest 125: 2551-2557, 2015; O'Brien et al. Stem Cell Res Ther 6: 146, 2015; Ouseph et al. Cytotherapy 17: 339-343, 2015). To overcome many of these hurdles, a close and effective collaboration is needed between experts from various disciplines, including basic and clinical research, product development and manufacturing, quality assurance and control, and regulatory affairs. Therefore, the purpose of this article is to outline the critical areas and challenges that must be addressed when transitioning laboratory-based discovery, through an investigational new drug (IND) application to first-in-human clinical trial, and to encourage investigators to consider the required regulatory steps from the earliest stage of the translational process. The ultimate goal is to provide readers with a draft roadmap that they could use while navigating this exciting cell therapy space.
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Affiliation(s)
- Magdalena Kasendra
- Center for Stem Cell and Organoid Medicine, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio
- Division of Pediatric General and Thoracic Surgery, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio
| | - Misty Troutt
- Center for Stem Cell and Organoid Medicine, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio
- Division of Pediatric General and Thoracic Surgery, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio
| | - Taylor Broda
- Center for Stem Cell and Organoid Medicine, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio
- Division of Pediatric General and Thoracic Surgery, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio
| | - W Clark Bacon
- Center for Stem Cell and Organoid Medicine, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio
- Division of Pediatric General and Thoracic Surgery, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio
| | - Timothy C Wang
- Division of Digestive and Liver Diseases, Columbia University Medical Center, New York City, New York
| | - Joyce C Niland
- Department of Diabetes and Cancer Discovery Science, City of Hope, Duarte, California
| | - Michael A Helmrath
- Center for Stem Cell and Organoid Medicine, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio
- Division of Pediatric General and Thoracic Surgery, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio
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Zou Y, Wang G, Xu Y, Bai Y. Comparative study of the proliferative ability of skeletal muscle satellite cells under microwave irradiation in fractures with titanium alloy internal fixation in rabbits. Exp Ther Med 2018; 16:4357-4366. [PMID: 30542384 PMCID: PMC6257569 DOI: 10.3892/etm.2018.6812] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2016] [Accepted: 05/11/2017] [Indexed: 11/06/2022] Open
Abstract
The aim of the present study was to investigate the proliferation of skeletal muscle satellite cells (MSCs) under different amounts of microwave irradiation in fractures with titanium alloy internal fixation. A total of 45 male New Zealand adult white rabbits were used to establish a femoral shaft fracture and titanium alloy internal fixation model. The rabbits were randomly divided into the control group (group A) and the experimental groups (groups B and C). For 15 days, groups B and C were exposed to microwave treatment (25 or 50 W, respectively) for 10 min per day. The quadriceps femoris muscle was used for the isolation and culture of MSCs in vitro. The cultured cells were identified using cellular immunohistochemical staining. Transmission electron microscopy was used to observe mitochondrial ultrastructure damage, MTT assays were used to detect cell viability and cell cycle phases were analyzed by flow cytometry. The results revealed that, following 48 or 72 h of culture, cell viability was significantly greater in group B compared with group A, and was significantly lower in group C compared with group A (P<0.05). Compared with group A, the percentage of the cell population in the G0/G1 phase in group B was significantly decreased (P<0.05) and the proportion in the S and G2/M phases was increased (P<0.05). These results were reversed in group C; the percentage of cells in the S and G2/M phases was significantly lower (P<0.05) and in the G0/G1 phase was significantly higher (P<0.05) than in group A. These results suggested that in the healing of fractures with titanium, the proliferation of MSCs is significantly affected by microwave radiation in a dose-dependent manner.
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Affiliation(s)
- Yuzhen Zou
- Department of Rehabilitation, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai 200233, P.R. China
| | - Gang Wang
- Department of Rehabilitation, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai 200233, P.R. China
| | - Yiming Xu
- Department of Rehabilitation, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai 200233, P.R. China
| | - Yuehong Bai
- Department of Rehabilitation, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai 200233, P.R. China
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Cen P, Chen J, Hu C, Fan L, Wang J, Li L. Noninvasive in-vivo tracing and imaging of transplanted stem cells for liver regeneration. Stem Cell Res Ther 2016; 7:143. [PMID: 27664081 PMCID: PMC5035504 DOI: 10.1186/s13287-016-0396-y] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Terminal liver disease is a major cause of death globally. The only ultimate therapeutic approach is orthotopic liver transplant. Because of the innate defects of organ transplantation, stem cell-based therapy has emerged as an effective alternative, based on the capacity of stem cells for multilineage differentiation and their homing to injured sites. However, the disease etiology, cell type, timing of cellular graft, therapeutic dose, delivery route, and choice of endpoints have varied between studies, leading to different, even divergent, results. In-vivo cell imaging could therefore help us better understand the fate and behaviors of stem cells to optimize cell-based therapy for liver regeneration. The primary imaging techniques in preclinical or clinical studies have consisted of optical imaging, magnetic resonance imaging, radionuclide imaging, reporter gene imaging, and Y chromosome-based fluorescence in-situ hybridization imaging. More attention has been focused on developing new or modified imaging methods for longitudinal and high-efficiency tracing. Herein, we provide a descriptive overview of imaging modalities and discuss recent advances in the field of molecular imaging of intrahepatic stem cell grafts.
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Affiliation(s)
- Panpan Cen
- Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases; State Key Laboratory for Diagnosis and Treatment of Infectious Diseases, School of Medicine; First Affiliated Hospital; Zhejiang University, Hangzhou, 310006, China
| | - Jiajia Chen
- Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases; State Key Laboratory for Diagnosis and Treatment of Infectious Diseases, School of Medicine; First Affiliated Hospital; Zhejiang University, Hangzhou, 310006, China
| | - Chenxia Hu
- Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases; State Key Laboratory for Diagnosis and Treatment of Infectious Diseases, School of Medicine; First Affiliated Hospital; Zhejiang University, Hangzhou, 310006, China
| | - Linxiao Fan
- Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases; State Key Laboratory for Diagnosis and Treatment of Infectious Diseases, School of Medicine; First Affiliated Hospital; Zhejiang University, Hangzhou, 310006, China
| | - Jie Wang
- Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases; State Key Laboratory for Diagnosis and Treatment of Infectious Diseases, School of Medicine; First Affiliated Hospital; Zhejiang University, Hangzhou, 310006, China
| | - Lanjuan Li
- Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases; State Key Laboratory for Diagnosis and Treatment of Infectious Diseases, School of Medicine; First Affiliated Hospital; Zhejiang University, Hangzhou, 310006, China.
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Rojas SV, Meier M, Zweigerdt R, Eckardt D, Rathert C, Schecker N, Schmitto JD, Rojas-Hernandez S, Martin U, Kutschka I, Haverich A, Martens A. Multimodal Imaging for In Vivo Evaluation of Induced Pluripotent Stem Cells in a Murine Model of Heart Failure. Artif Organs 2016; 41:192-199. [DOI: 10.1111/aor.12728] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2015] [Revised: 01/18/2016] [Accepted: 01/19/2016] [Indexed: 12/23/2022]
Affiliation(s)
- Sebastian V. Rojas
- Department of Cardiothoracic; Transplantation and Vascular Surgery, Hannover Medical School
- Leibniz Research Laboratories for Biotechnology and Artificial Organs-REBIRTH-Cluster of Excellence; Hannover Medical School
| | - Martin Meier
- Central Animal Laboratory; Hannover Medical School; Hannover
| | - Robert Zweigerdt
- Leibniz Research Laboratories for Biotechnology and Artificial Organs-REBIRTH-Cluster of Excellence; Hannover Medical School
| | | | - Christian Rathert
- Leibniz Research Laboratories for Biotechnology and Artificial Organs-REBIRTH-Cluster of Excellence; Hannover Medical School
| | - Natalie Schecker
- Leibniz Research Laboratories for Biotechnology and Artificial Organs-REBIRTH-Cluster of Excellence; Hannover Medical School
| | - Jan D. Schmitto
- Department of Cardiothoracic; Transplantation and Vascular Surgery, Hannover Medical School
| | - Sara Rojas-Hernandez
- Department of Anaesthesiology and Intensive Care Medicine; Hannover Medical School; Hannover Germany
| | - Ulrich Martin
- Leibniz Research Laboratories for Biotechnology and Artificial Organs-REBIRTH-Cluster of Excellence; Hannover Medical School
| | - Ingo Kutschka
- Department of Cardiothoracic; Transplantation and Vascular Surgery, Hannover Medical School
| | - Axel Haverich
- Department of Cardiothoracic; Transplantation and Vascular Surgery, Hannover Medical School
- Leibniz Research Laboratories for Biotechnology and Artificial Organs-REBIRTH-Cluster of Excellence; Hannover Medical School
| | - Andreas Martens
- Department of Cardiothoracic; Transplantation and Vascular Surgery, Hannover Medical School
- Leibniz Research Laboratories for Biotechnology and Artificial Organs-REBIRTH-Cluster of Excellence; Hannover Medical School
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Mahmoudi M, Tachibana A, Goldstone AB, Woo YJ, Chakraborty P, Lee KR, Foote CS, Piecewicz S, Barrozo JC, Wakeel A, Rice BW, Bell III CB, Yang PC. Novel MRI Contrast Agent from Magnetotactic Bacteria Enables In Vivo Tracking of iPSC-derived Cardiomyocytes. Sci Rep 2016; 6:26960. [PMID: 27264636 PMCID: PMC4893600 DOI: 10.1038/srep26960] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2015] [Accepted: 05/09/2016] [Indexed: 11/17/2022] Open
Abstract
Therapeutic delivery of human induced pluripotent stem cell (iPSC)-derived cardiomyocytes (iCMs) represents a novel clinical approach to regenerate the injured myocardium. However, methods for robust and accurate in vivo monitoring of the iCMs are still lacking. Although superparamagnetic iron oxide nanoparticles (SPIOs) are recognized as a promising tool for in vivo tracking of stem cells using magnetic resonance imaging (MRI), their signal persists in the heart even weeks after the disappearance of the injected cells. This limitation highlights the inability of SPIOs to distinguish stem cell viability. In order to overcome this shortcoming, we demonstrate the use of a living contrast agent, magneto-endosymbionts (MEs) derived from magnetotactic bacteria for the labeling of iCMs. The ME-labeled iCMs were injected into the infarcted area of murine heart and probed by MRI and bioluminescence imaging (BLI). Our findings demonstrate that the MEs are robust and effective biological contrast agents to track iCMs in an in vivo murine model. We show that the MEs clear within one week of cell death whereas the SPIOs remain over 2 weeks after cell death. These findings will accelerate the clinical translation of in vivo MRI monitoring of transplanted stem cell at high spatial resolution and sensitivity.
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Affiliation(s)
- Morteza Mahmoudi
- Division of Cardiovascular Medicine, Stanford University, Stanford, CA, USA
- Nanotechnology Research Center, Faculty of Pharmacy, Tehran University of Medical Sciences, Tehran, Iran
| | - Atsushi Tachibana
- Division of Cardiovascular Medicine, Stanford University, Stanford, CA, USA
| | - Andrew B. Goldstone
- Department of Cardiothoracic Surgery, Stanford University, Stanford, CA, USA
| | - Y. Joseph Woo
- Department of Cardiothoracic Surgery, Stanford University, Stanford, CA, USA
| | | | - Kayla R. Lee
- Bell Biosystems Inc., San Francisco, CA 94107, USA
| | | | | | | | - Abdul Wakeel
- Bell Biosystems Inc., San Francisco, CA 94107, USA
| | | | | | - Phillip C. Yang
- Division of Cardiovascular Medicine, Stanford University, Stanford, CA, USA
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Roberts RM, Yuan Y, Genovese N, Ezashi T. Livestock models for exploiting the promise of pluripotent stem cells. ILAR J 2016; 56:74-82. [PMID: 25991700 DOI: 10.1093/ilar/ilv005] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Livestock species are widely used as biomedical models. Pigs, in particular, are beginning to have a significant role in regenerative medicine for testing the applicability, success, and safety of grafts derived from induced pluripotent stem cells. Animal testing must always be performed before any clinical trials are performed in humans, and pigs may sometimes be the species of choice because of their physiological and anatomical similarities to humans. Induced pluripotent stem cells (iPSC) have been generated with some success from livestock species by a variety of reprogramming procedures, but authenticated embryonic stem cells (ESC) have not. There are now several studies in which porcine iPSC have been tested for their ability to provide functional grafts in pigs. Pigs have also served as recipients for grafts derived from human iPSC. There have also been recent advances in creating pigs with severe combined immunodeficiency (SCID). Like SCID mice, these pigs are expected to be graft tolerant. Additionally, chimeric, partially humanized pigs could be sources of human organs. Another potential application of pluripotent stem cells from livestock is for the purpose of differentiating the cells into skeletal muscle, which, in turn, could be used either to produce cultured meat or to engraft into damaged muscle. None of these technologies has advanced to a stage that they have become mainstream, however. Despite the value of livestock models in regenerative medicine, only a limited number of institutions are able to use these animals.
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Affiliation(s)
- R Michael Roberts
- R. Michael Roberts, DPhil, is a Curators' Professor in the Division of Animal Sciences and Department of Biochemistry at the University of Missouri. Ye Yuan, PhD, is a research scientist; Nicholas Genovese, PhD, is a postdoctoral fellow; and Toshihiko Ezashi, DVM, PhD, is a research associate professor in the Division of Animal Sciences at the University of Missouri
| | - Ye Yuan
- R. Michael Roberts, DPhil, is a Curators' Professor in the Division of Animal Sciences and Department of Biochemistry at the University of Missouri. Ye Yuan, PhD, is a research scientist; Nicholas Genovese, PhD, is a postdoctoral fellow; and Toshihiko Ezashi, DVM, PhD, is a research associate professor in the Division of Animal Sciences at the University of Missouri
| | - Nicholas Genovese
- R. Michael Roberts, DPhil, is a Curators' Professor in the Division of Animal Sciences and Department of Biochemistry at the University of Missouri. Ye Yuan, PhD, is a research scientist; Nicholas Genovese, PhD, is a postdoctoral fellow; and Toshihiko Ezashi, DVM, PhD, is a research associate professor in the Division of Animal Sciences at the University of Missouri
| | - Toshihiko Ezashi
- R. Michael Roberts, DPhil, is a Curators' Professor in the Division of Animal Sciences and Department of Biochemistry at the University of Missouri. Ye Yuan, PhD, is a research scientist; Nicholas Genovese, PhD, is a postdoctoral fellow; and Toshihiko Ezashi, DVM, PhD, is a research associate professor in the Division of Animal Sciences at the University of Missouri
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Schwanke K, Merkert S, Kempf H, Hartung S, Jara-Avaca M, Templin C, Göhring G, Haverich A, Martin U, Zweigerdt R. Fast and efficient multitransgenic modification of human pluripotent stem cells. Hum Gene Ther Methods 2014; 25:136-53. [PMID: 24483184 DOI: 10.1089/hgtb.2012.248] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Human pluripotent stem cells (hPSCs) represent a prime cell source for pharmacological research and regenerative therapies because of their extensive expansion potential and their ability to differentiate into essentially all somatic lineages in vitro. Improved methods to stably introduce multiple transgenes into hPSCs will promote, for example, their preclinical testing by facilitating lineage differentiation and purification in vitro and the subsequent in vivo monitoring of respective progenies after their transplantation into relevant animal models. To date, the establishment of stable transgenic hPSC lines is still laborious and time-consuming. Current limitations include the low transfection efficiency of hPSCs via nonviral methods, the inefficient recovery of genetically engineered clones, and the silencing of transgene expression. Here we describe a fast, electroporation-based method for the generation of multitransgenic hPSC lines by overcoming the need for any preadaptation of conventional hPSC cultures to feeder-free conditions before genetic manipulation. We further show that the selection for a single antibiotic resistance marker encoded on one plasmid allowed for the stable genomic (co-)integration of up to two additional, independent expression plasmids. The method thereby enables the straightforward, nonviral generation of valuable multitransgenic hPSC lines in a single step. Practical applicability of the method is demonstrated for antibiotic-based lineage enrichment in vitro and for sodium iodide symporter transgene-based in situ cell imaging after intramyocardial cell infusion into explanted pig hearts.
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Affiliation(s)
- Kristin Schwanke
- 1 Leibniz Research Laboratories for Biotechnology and Artificial Organs (LEBAO) , Department of Cardiac, Thoracic, Transplantation, and Vascular Surgery, 30625 Hannover, Germany
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Abstract
The field of regenerative medicine is approaching translation to clinical practice, and significant safety concerns and knowledge gaps have become clear as clinical practitioners are considering the potential risks and benefits of cell-based therapy. It is necessary to understand the full spectrum of stem cell actions and preclinical evidence for safety and therapeutic efficacy. The role of animal models for gaining this information has increased substantially. There is an urgent need for novel animal models to expand the range of current studies, most of which have been conducted in rodents. Extant models are providing important information but have limitations for a variety of disease categories and can have different size and physiology relative to humans. These differences can preclude the ability to reproduce the results of animal-based preclinical studies in human trials. Larger animal species, such as rabbits, dogs, pigs, sheep, goats, and non-human primates, are better predictors of responses in humans than are rodents, but in each case it will be necessary to choose the best model for a specific application. There is a wide spectrum of potential stem cell-based products that can be used for regenerative medicine, including embryonic and induced pluripotent stem cells, somatic stem cells, and differentiated cellular progeny. The state of knowledge and availability of these cells from large animals vary among species. In most cases, significant effort is required for establishing and characterizing cell lines, comparing behavior to human analogs, and testing potential applications. Stem cell-based therapies present significant safety challenges, which cannot be addressed by traditional procedures and require the development of new protocols and test systems, for which the rigorous use of larger animal species more closely resembling human behavior will be required. In this article, we discuss the current status and challenges of and several major directions for the future development of large animal models to facilitate advances in stem cell-based regenerative medicine.
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