The Veterinary Journal 198 (2013) 34–42

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Review

Veterinary applications of induced pluripotent stem cells: Regenerative medicine and models for disease? Alberto Cebrian-Serrano a, Tom Stout b, Andras Dinnyes a,c,d,⇑ a

}, Hungary Biotalentum Ltd., Aulich Lajos u. 26, H-2100 Gödöllo Department of Equine Sciences, Faculty of Veterinary Medicine, Utrecht University, 3584 CL Utrecht, The Netherlands c Department of Farm Animal Health, Faculty of Veterinary Medicine, Utrecht University, 3584 CL Utrecht, The Netherlands d }, Hungary Molecular Animal Biotechnology Laboratory, Szent Istvan University, 2100 Gödöllo b

a r t i c l e

i n f o

Article history: Accepted 26 March 2013

Keywords: Induced pluripotent stem cell Veterinary Animal models Regenerative medicine Reprogramming

a b s t r a c t Induced pluripotent stem cells (iPSCs) can now be derived from a tissue biopsy and represent a promising new platform for disease modelling, drug and toxicity testing, biomarker development and cell-based therapies for regenerative medicine. In regenerative medicine, large animals may represent the best models for man, and thereby provide invaluable systems in which to test the safety and the potential of iPSCs. Hence, testing iPSCs in veterinary species may serve a double function, namely, developing therapeutic products for regenerative medicine in veterinary patients while providing valuable background information for human clinical trials. The production of iPSCs from livestock or wild species is attractive because it could improve efficiency and reduce costs in various fields, such as transgenic animal generation and drug development, preservation of biological diversity, and because it also offers an alternative to xenotransplantation for in vivo generation of organs. Although the technology of cellular reprogramming using the so-called ‘Yamanaka factors’ is in its peak expectation phase and many concerns still need to be addressed, the rapid technical progress suggests that iPSCs could contribute significantly to novel therapies in veterinary and biomedical practice in the near future. This review provides an overview of the potential applications of iPSCs in veterinary medicine. Ó 2013 Elsevier Ltd. All rights reserved.

Introduction The generation of induced pluripotent stem cells (iPSCs) by the enforced expression of a small number of embryonic transcription factors in adult mammalian cells launched a new field of stem cell research. From the outset, iPSCs have generated enormous interest. In particular, it was anticipated that iPSCs would share most of the advantages of embryonic stem cells (ESCs), while overcoming some of their most important limitations (Robinton and Daley, 2012). From a veterinary perspective, the successful derivation of iPSC lines from many important domestic animal species in recent years (Fig. 1) represents a significant milestone. In particular, the reprogramming technology is expected to increase the accessibility of stem cells and their many potential uses in veterinary science and practice (Fig. 2). Moreover, domestic animals may help fill the considerable gaps between experiments in laboratory animals, especially mice, and clinical trials in humans; in fact, bridging this

⇑ Corresponding author at: Biotalentum Ltd., Aulich Lajos u. 26, H-2100 Gödöllo}, Hungary. Tel.: + 36 20 510 9632. E-mail address: [email protected] (A. Dinnyes). 1090-0233/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.tvjl.2013.03.028

gap may become a major application for domestic animal iPSC research in the near future. While there are great expectations for iPSC technology, sceptics have rightly warned that similarly high expectations for ESCs and somatic cell nuclear transfer (SCNT) are still largely unfulfilled despite years of basic research. On the other hand, the rapid rate of progress currently being made within the iPSC field is fundamentally different to the more laborious progress witnessed for ESCs and SCNT. This suggests that iPSC technology has a higher likelihood of becoming a clinical reality in the foreseeable future. Indeed, treatments based on iPSCs are already moving towards clinical practice; the RIKEN Centre for Developmental Biology in Kobe and the California Institute for Regenerative Medicine (CIRM) are awaiting administrative approval to launch human clinical trials using iPSCs to cure macular degeneration and dystrophic epidermolysis bullosa, respectively. As a spin-off these trials may generate techniques by which iPSC therapy can be used to treat some forms of blindness or skin disease in veterinary patients. The aim of this review is to provide an overview of the potential applications of iPSCs in veterinary medicine, highlighting recently published articles and indicating connections between these publications and potential applications.

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22 20

2012

18

2011 2010

16

2009

14

2008

12 10 8 6

4 2 0

Pigs

Non Human Primates

Dogs

Cattle

Sheep

Horse

Goat

Drill and White rhinoceros

Buffalo

Snow leopard

Fig. 1. Number of articles on large animal induced pluripotent stem cells published in a recent period (2008–2012). Pig: Esteban et al. (2009), Ezashi et al. (2009, 2011), Wu et al. (2009), Telugu et al. (2010), West et al. (2010), Montserrat et al. (2011, 2012), Nowak-Imialek et al. (2011), Zhou et al. (2011), Aravalli et al. (2012), Cheng et al. (2012), Fujishiro et al. (2013), Gu et al. (2012), Hall et al. (2012), Kues et al. (2013), Liu et al. (2012b), Tang et al. (2012), Templin et al. (2012), Yang et al. (2012). Non human primates: Liu et al. (2008), Tomioka et al. (2010), Wu et al. (2010), Zhong et al. (2011a,b), Chan et al. (2010), Deleidi et al. (2011), Zhu et al. (2011), Gori et al. (2012), and Torrez et al. (2012). Dog: Shimada et al. (2010), Lee et al. (2011), Luo et al. (2011), Koh et al. (2012), and Whitworth et al. (2012). Cattle: Han et al. (2011), Huang et al. (2011), Sumer et al. (2011), and Cao et al. (2012). Sheep: Bao et al. (2011), Li et al. (2011), Liu et al. (2012a), and Sartori et al. (2012). Horse: Nagy et al. (2011), Breton et al. (2013), and Hackett et al., 2012. Goat: Ren et al. (2011). Drill and white rhinoceros: Ben-Nun et al. (2011). Buffalo: Deng et al. (2012). Snow leopard: Verma et al. (2012).

Fig. 2. Potential veterinary applications of induced pluripotent stem cell technology.

Historical background Two milestones paved the way for the recent breakthroughs in iPSC technology in mammals. First, the isolation over 30 years ago of pluripotent stem cells from the inner cell mass of a mouse blastocyst, and their maintenance in the pluripotent state during in vitro culture (Evans and Kaufman, 1981). These cells, which are generally referred to as ESCs, showed two unique and invaluable characteristics, namely, the ability for unlimited self-renewal and the capacity to differentiate into tissues of all three major lineages (endoderm, ectoderm and mesoderm). The second major milestone in the development of mammalian genetic reprogramming methods was the discovery that terminally differentiated mammalian somatic cells could be reprogrammed to the totipotent state by an oocyte, and subsequently used to create ‘cloned’ embryos capable of generating grossly normal live offspring. The production of ‘Dolly the sheep’ by SNCT was

undoubtedly the most famous example of this breakthrough (Wilmut et al., 1997).

Induced pluripotent stem cell discovery In an attempt to identify the major transcriptional regulators capable of reprogramming adult cells to the pluripotent state, Takahashi and Yamanaka (2006) examined the effect of transfecting cells with various combinations of 24 genes associated with the induction of pluripotency in somatic cells. To their surprise, the reprogramming of adult cells to pluripotency could be achieved by the transfection and co-overexpression of only four of these genes (OCT4, SOX2, cMYC and KLF4; the ‘Yamanaka factors’). Soon after this breakthrough, similar cells, termed iPSCs, were derived in other laboratories (Fig. 3). Most significantly, their pluripotency was confirmed when it was shown that they could be used to

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Fig. 3. Flowchart for induced pluripotent stem cell therapeutic development.

generate germ-line chimeric mice (Maherali et al., 2007; Okita et al., 2007; Wernig et al., 2007), and ‘exclusively iPSC’ mice, following injection into tetraploid blastocysts (Kang et al., 2009). At the same time, the first report of human iPSCs (hiPSCs), generated from adult fibroblasts, was published (Takahashi et al., 2007). To date, validated iPSCs have been derived from a broad range of somatic cell types (Stadtfeld and Hochedlinger, 2010). Interestingly, in all species in which iPS cell derivation has been verified, the over-expression of the Yamanaka factors alone, or together with a minimal number of additional factors, has been sufficient to reprogram somatic cells (Fig. 1). This suggests that mammalian cell pluripotency is governed by a pan-species, largely conserved network of primary transcription factors. However, full pluripotency (i.e. germ-line transmission via chimaeras in which presumptive pluripotent cells were incorporated) has not been achieved in many species, indicating that there are subtle, but important between-species differences in the regulation of pluripotency.

Induced pluripotent stem cells: Towards a biomedical application Modelling disease in vitro offers a cheap and ethically more acceptable initial approach to developing novel therapies. Using cell reprogramming technology, patient-specific hiPSC lines have been generated for at least 45 monogenetic or multi-factorial human diseases (Robinton and Daley, 2012). In addition, the first validated infectious disease model (hepatitis C) was recently established with human hepatocyte-like cells derived from iPSCs (Schwartz et al., 2012). Nevertheless, an effective in vitro model for a disease of interest has been achieved in only a few cases, primarily because differentiated iPSCs can fail to recapitulate the critical pathological defects in vitro. The second step in the development of clinical applications for iPSC therapy did not take long to appear, and involved the jump from the Petri-dish to a whole-animal (mouse) model. The

transplantation of differentiated iPSCs into mice affected with variants of human diseases has allowed not only for the study of disease development and pathogenesis, but also for monitoring the successful treatment and, in some cases, subsequent development of potential cures (Table 1). How close are we to being able to initiate iPSC-based therapies in clinical practice? In this respect, it is important to bear in mind that iPSCs represent an entirely novel product and, therefore, several key issues need to be addressed before clinical trials can be contemplated. For example, the reprogramming process (especially when performed via retroviral transduction) has the potential to alter both the genomic and epigenomic state of the iPSCs, tending to push them towards tumorigenicity and away from the generation of normally differentiated daughter cells capable of forming functional target tissues. In addition, the immune tolerance of recipients to autologous iPSC transplantation has been questioned (Barrilleaux and Knoepfler, 2011). To avoid repeating the mistakes made with gene therapy, many researchers in the iPSC field have recommended additional basic research, efficiency and safety testing in animal models before

Table 1 Diseases treated by induced pluripotent stem cell transplantation in murine models. Diseases

Reference

Neuronal

Spinal cord injury Parkinson’s disease

Haematological

Sickle cell anaemia Haemophilia A Limb ischemia Acute myocardial infarction Peripheral vascular disease Diabetes Liver regeneration

Cardiovascular

Hormonal Hepatic

Tsuji et al. (2010) Wernig et al. (2008) and Swistowski et al. (2010) Hanna et al. (2007) Xu et al. (2009) Lian et al. (2010) Nelson et al. (2009) Rufaihah et al. (2011) Alipio et al. (2010) Liu et al. (2011)

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moving iPSCs into the clinical arena (Hyun et al., 2008; Wilson, 2009). The report of a donor cell-derived brain tumour following neural ESC transplantation (Amariglio et al., 2009) confirms the need to advance with caution when considering the use of iPSCs in patients. In this regard, it is no coincidence that the clinical trials at the RIKEN Centre and CIRM involve iPSC therapy in external organs with a relatively simple structure and easy accessibility for monitoring. Moreover, since larger steps equate with larger risks, potential breakthrough treatments may be ethically difficult to justify for human clinical trials, while being acceptable for wellplanned veterinary clinical trials. Indeed, veterinary medicine is becoming more and more like human medicine in terms of the technology of treatments offered and the high standards of care and post-therapy monitoring, all of which may help justify the testing of iPSC therapies relevant to the species in question, with the added potential spin-off of providing novel data that can be extrapolated to man. Clearly iPSCs have tremendous promise in domestic animals for future regenerative therapies of well-defined diseases or injuries that cannot be adequately remedied with existing treatment modalities.

Potential use of induced pluripotent stem cells in veterinary medicine Adult stem cells (ASCs) may offer great therapeutic potential for a number of companion animal diseases due to their regenerationpromoting properties. In particular, mesenchymal stem cell (MSCs) therapies have been applied in horses and dogs for the treatment of traumatic or degenerative musculoskeletal diseases (Fortier and Travis, 2011). In addition, promising results have been reported following the use of ASCs to treat other chronic diseases, such as liver and cardiac failure, diabetes, blood and bone marrow disease in companion animals (Gattegno-Ho et al., 2012). Nevertheless, the potential therapeutic applications of ASCs are limited because only a very small fraction of the total population of cells isolated can be characterized as ASCs, and their potential for ex vivo expansion and differentiation is limited (Fortier and Travis, 2011). There are several reasons to believe that iPSCs should be a better base cell for regenerative medicine compared to other stem cell types. For example, iPSCs can be readily isolated from a skin biopsy, simplifying the generation of patient-specific pluripotent stem cells and raising the possibility of establishing stores of customized iPSCs. In addition, the use of patient-specific iPSCs in cell-based therapy should reduce the risks of immunological complications post-transplantation, and therefore avoid the need for chronic administration of immunosuppressive drugs to prevent rejection. Additionally, iPSCs have proven to be an effective base for producing MSCs (Lian et al., 2010) and chondrocytes both in vitro and in vivo (Wei et al., 2012). By combining iPSC therapy with targeted gene-repair strategies, it may be possible to remedy genetic defects (Robinton and Daley, 2012), thereby offering substantial potential benefits for the treatment of some inherited diseases in companion animals (Sewell et al., 2007). The studies listed in Table 1 have provided valuable proof of principle that iPSC therapy has real potential for treating a broad range of companion animal disorders that are currently untreatable, or for which treatment options are restricted by costs and availability of suitable materials or tissue (e.g. organs for transplantation). Nevertheless, only a few cell types have been differentiated from domestic animal iPSCs to date, and only one in companion animals (Lee et al., 2011). The first challenge remains therefore the development of reliable, directed-differentiation protocols for companion animal iPSCs. Deriving and testing patient-specific iPSCs is a time-consuming and expensive process (current estimates are 6 months and tens of

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thousands of pounds). Even so, the University of Kyoto plans to produce, from fetal blood cells, a bank of hiPSC lines for therapeutic use that are a good enough match to be immunotolerated by 80% of the population (Cyranoski, 2012). Similarly, the establishment of banks of iPSC lines in valuable domestic or wild species could provide an off-the-shelf source of stem cells for therapeutic use in conditions such as musculoskeletal injuries, bone marrow disorders, leukaemia and following high dose chemotherapy. In terms of providing safe iPSCs for clinical uses, methods of avoiding exogenous genetic or epigenomic modifications to the target cells during cellular reprogramming have become the focus of intense research efforts. In this respect, Robinton and Daley (2012) described several novel reprogramming methods that limit the potentially harmful effects of ‘leaky transgene expression’ and insertional mutagenesis. In this vein, it would be useful to develop rapid, standard and accurate protocols for screening iPSC lines for genetic and epigenetic abnormalities, and for improving the efficiency of reprogramming. Moreover, since the possible tumorigenicity of undifferentiated iPSCs is higher than those of differentiated cells (Goldring et al., 2011), and because differentiated iPSCs are in any case preferred for regenerative medicine purposes, it is of utmost importance to develop appropriate protocols for producing pure populations of safe, differentiated cells for clinical use. Use of induced pluripotent stem cells for drug development and screening Pharmacological products used to preserve health and increase the longevity of companion animals or livestock have huge potential clinical and economic significance. Although current attention on iPSCs has focussed on their potential use in cell replacement therapies, iPSCs also have the potential to transform the way in which drugs are discovered, validated and screened for likely efficacy or toxicity. Drug discovery and development is an expensive and relatively inefficient process (Rubin, 2008). A reliable in vitro model is a vital element of the drug discovery process, since it allows for more efficient selection of novel compounds for development. One potential benefit of iPSC technology is that it may allow for the creation of a library of animal cell lines that covers the major genetic and epigenetic variants within a species. The use of such cell lines in screening assays should help to drive more efficient and predictive drug discovery and toxicity studies. In particular, availability of hepatocyte-like cells derived from iPSCs, as reported for the pig by Aravalli et al. (2012), would be of great value for studying drug toxicity and metabolism. The use of iPSCs for drug toxicity screening could also prove a significant benefit in the case of endangered species. Despite the extremely high value of rare species, only few drugs have been confirmed safe and effective in these species and the use of several therapeutic drugs can carry significant risks. The derivation of iPSCs from such species to develop fit-for-purpose in vitro toxicology assays could be a useful tool for modelling the pharmacology and predicting the toxicity of desirable drugs. Large animal models Although the mouse is still by far the most commonly used animal in biomedical research, studies into cell regeneration and gene therapy in laboratory rodents probably provide only limited insight into many human diseases. By contrast, preclinical studies in carefully selected domestic animals may be more enlightening with respect to several aspects of physiology and pathology (Plews et al., 2012) (Table 2). In addition, the use of naturally occurring disease in domestic animals, such as cancer or other chronic diseases, offers an invaluable comparative model for research.

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Non-human primates (NHPs) NHPs represent an extremely valuable potential biomedical model because of their close phylogenetic relationship to man. Making use of existing transgenic monkey models, iPSCs have recently been derived from transgenic Huntington’s disease (HD) monkeys and differentiated in vitro into neuronal cell types with typical HD-like features (Chan et al., 2010). Such studies may yield attractive in vitro and in vivo platforms for investigating HD pathogenesis and therapy. The use of NHPs in research can be emotive, ethically questionable, expensive, and not widely available. The use of mice in an initial clinical trial to test the therapeutic effects of NHP-derived iPSCs may be a useful alternative to reduce and optimize the use of NHPs for scientific purposes. In this regard, Zhu et al. (2011) produced insulin-producing cells from rhesus monkey iPSCs and demonstrated their functionality (insulin secretion) in approximately 50% of mice receiving a transplant. Similarly, Zhong et al. (2011b) demonstrated the utility of introducing two apoptosisinducing genes in both in vitro and in vivo mouse models, to control the cell fates of macaque iPSCs without interfering with their pluripotency and capacity for self-renewal. These suicide genes were designed to eliminate or reduce the risk of teratomaformation or the proliferation of other oncogenically transformed clones, and may therefore increase the safety of iPSC therapy. Taking a first step towards the establishment of histocompatible stem cell banks, Deleidi et al. (2011) described the generation of a collection of histocompatible iPSCs from macaque skin fibroblasts. Moreover, they were able to differentiate iPSCs in vitro into midbrain-like dopaminergic neurons. Similarly, after transplantation into a rodent Parkinson’s disease model, iPSCs were integrated into the striatum and promoted behavioural recovery without tumour formation or significant immunological complications. Pig Pigs are attractive alternatives to NHPs because they present fewer ethical dilemmas and lower economic costs. Biologically and anatomically, pigs are relatively similar to humans, and are therefore a meaningful model in many fields of medicine, including transplant biology, immunology, and cardiovascular surgery (Kues and Niemann, 2004). It is therefore no coincidence that the pig is the large animal on which the most iPSC publications have been reported to date. In 2009, three independent laboratories reported almost simultaneously the generation of pig iPSCs (piPSCs) (Esteban et al., 2009; Ezashi et al., 2009; Wu et al., 2009) (Fig. 1). Subsequently, novel reprogramming strategies have been published in an attempt to bypass transgene-integration; these include virus-free techniques for generating piPSCs by using episomal plasmid (extra-chromosomal) vectors (Telugu et al., 2010; Montserrat et al., 2011). However, clonal lines examined in both cases showed either signs of vector integration or persistence of episomal plasmids. Another strategy, reported recently by Montserrat et al. (2012) and Liu et al. (2012b), reduced the number of transcription factors used for piPSC induction to reduce the risk of integration of exogenous genes. Sox2, Klf4 and c-Myc, and Oct4 and Klf4 in combination with specific small molecules, respectively, were sufficient to generate piPSCs. Interestingly, in both studies published by Montserrat et al. (2011, 2012), piPSCs were generated without the use of feeder cells, therefore approaching xeno-free conditions. Zhou et al. (2011) used the pig as a model for retinal stem cell transplantation. They differentiated piPSCs in vitro into the rod photoreceptor lineage; after transplantation, engrafted cells were able to integrate into the outer layer of the retina. Similarly, Templin et al. (2012) used a novel imaging approach to monitor

a pig model of myocardial infarction; human hiPSCs, carrying a sodium iodide symporter for transgene imaging, were transplanted and visualized successfully for up to 15 weeks. Moreover, 12– 15 weeks after cell injection, immunohistochemistry demonstrated that the hiPSC-derived cells had adopted phenotypes for lining numerous vessels in the injected heart regions, without teratoma or other tumour formation. Gu et al. (2012) differentiated piPSCs into endothelial cells and transplanted them into mice from a myocardial infarction model and concluded that the improved cardiac function observed might be due to paracrine stimulation of piPSC-derived endothelial cells. Cardiomyocyte-like cells (Montserrat et al., 2011), neuron-like, astrocyte-like, oligodendrocyte-like (Yang et al., 2012) and hepatocyte-like cells (Aravalli et al., 2012) have been successfully derived using other in vitro differentiation protocols for piPSCs. It also appears that the generation of transgenic pigs using iPSC technology is a viable objective. West et al. (2010) reported the generation of chimeric pigs by the introduction of iPSCs into porcine embryos. The chimeric piglets developed normally and showed a high level of piPSC integration into tissues, and, in a later study, no indications of tumour formation (West et al., 2011). Moreover, a piPSC germ-line contribution was confirmed by the live birth of two transgenic piglets. Subsequently, Fujishiro et al. (2013) studied the incorporation of piPSCs into porcine embryos, although the frequency of chimera formation was quite low. Various transgenic pigs have the potential to provide useful targets in which to test iPSC efficacy to treat specific diseases, such as Alzheimer’s disease, HD, retinitis pigmentosa, spinal muscular atrophy and diabetes. It is generally believed that Oct4 is essential for the maintenance of pluripotency in mammalian cells. Recently, Nowak-Imialek et al. (2011) derived piPSCs from a transgenic pig carrying a molecular imaging protein coupled to Oct4 as a pluripotency marker. Such techniques may be helpful for monitoring reprogramming and the differentiation status of cell lines, as well as to increase our knowledge and understanding of these processes. Dog The dog is often advocated as a logical model for studying hereditary and chronic diseases. Although biotechnological techniques and tools for the dog are less well developed than for other species, recent developments such as the derivation of canine iPSCs by four different research groups in the last 2 years (Fig. 1) have confirmed increasing interest in stem cell technology in this species. Furthermore, autologous iPSCs were recently transplanted into the myocardial wall of dogs to examine the potential for myocardial infarct treatment (Lee et al., 2011). These authors used molecular imaging of stem cell populations to successfully track the distribution, migration, engraftment, survival, proliferation, and differentiation of the iPSCs. In the same study, differentiated functional endothelial cells were derived from canine iPSCs and their therapeutic potential was demonstrated successfully in murine models of hind-limb ischemia and myocardial infarction. Other domestic animals To our knowledge, preclinical studies with iPSCs from other large animals, such as the sheep, cow, and horse, have not yet been published. However, the availability of iPSCs from these species may lead to the development of alternative animal models. For example, the sheep is considered a cheap and easy-to-handle animal species and has been used to study respiratory diseases and their treatment. In addition to studies in which iPSCs were derived

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A. Cebrian-Serrano et al. / The Veterinary Journal 198 (2013) 34–42 Table 2 Reports of large animal pre-clinical models involving induced pluripotent stem cells. Species

Reference

Disease modelled

Advance reported

Application

Rhesus macaque

Zhong et al. (2011b) Zhu et al. (2011)

None

Use of suicide genes to safeguard induced pluripotent stem cells (iPSCs) and their derivatives

Diabetes

Derivation of rhesus monkey iPSCs? Differentiation into pancreatic insulin-producing cells? Transplanted into mouse model for diabetes ? 50% animals regulate blood glucose to a normal level Derivation of pig iPSCs? Differentiation into rod photoreceptors? Transplanted into the retina of pigs without rod photoreceptors? After 3 weeks, rod photoreceptor cells were evident Derivation of dog iPSCs? Differentiation into endothelial cells? Imaging their integration into dog and murine models. Demonstrated the therapeutic potential of these cells in murine models Generation of a collection of histocompatible iPSCs from macaque skin fibroblasts? differentiated in vitro into midbrain-like dopaminergic neurons? transplanted into mouse model of Parkinson’s? promoted behavioural recovery Derivation of pig iPSCs and differentiation into endothelial cells? transplantation into mouse models of myocardial infarction? improved cardiac function after myocardial infarction via paracrine activation Derivation of human iPSCs carrying a sodium iodide symporter transgene imaging? transplantation in pig models of myocardial infarction? assessment of cell survival, engraftment and distribution during long term (15 weeks)? Human iPSC-derived endothelial cells contributed to vascularisation

Eliminate potential teratoma-initiating iPSCs or oncogenic transformed clones in iPSCrelated cellular therapy Investigating the efficacy and safety of iPSC derived insulin-producing cells

Rhesus monkey

Pig

Dog

Zhou et al. (2011) Lee et al. (2011)

Retina injury or disease Cardiovascular disease

Cynomolgus macaque

Deleidi et al. (2011)

Parkinson’s disease

Pig

Gu et al. (2012)

Cardiovascular disease

Pig (with human iPSCs)

Templin et al. (2012)

Cardiovascular disease

from sheep (Fig. 1), Sartori et al. (2012) reported that ovine iPSCs could contribute to live-born chimeric lambs, although at a low level of incorporation. Moreover, Liu et al. (2012a) observed that ovine iPSCs injected into sheep embryos could contribute to the inner cell mass of the resulting blastocysts. The horse is considered an ideal animal model for testing cell therapy for musculoskeletal injuries such as cartilage damage or degeneration, since the structure and matrix composition of weight-bearing tendons and nature of joint and tendon injuries in the horse closely resemble those in man, and the tissues have to sustain great loads (Nagy et al., 2011). Other potential applications The discovery that almost any somatic cell from any species can be reprogrammed to pluripotency led to a flood of proposed biotechnological and therapeutic applications. It is useful therefore to consider alternative potential applications of iPSCs in veterinary science.

A foundation for future studies of retinal stem cell transplantation in a swine model Validating pre-clinical iPSC imaging in large animal models

Resource for future preclinical investigations in the field of regenerative medicine Neuronal cell therapy with iPSCs Using iPSCs for the treatment of ischemic heart disease

The feasibility of repeated long term in vivo imaging of viability and tissue distribution of cellular grafts in large animals

able for transplantation to human patients. Indeed, Kobayashi et al. (2010) demonstrated that it is possible to take xenotransplantation to another level. They generated rat organs (pancreas) in a mutant mouse strain, in which a gene necessary for pancreas formation was missing, by injecting iPSCs from a rat into a blastocyst of the mutant mouse strain. This experiment constitutes proof of principle for interspecific blastocyst complementation as a technique for the in vivo generation of organs derived from donor iPSCs in a xenogenic environment. While there are still numerous ethical and safety barriers to be addressed, injecting iPSCs into pig blastocysts could underlie novel future techniques for generating human organs. An alternative strategy to fill this demand is the development of bioartificial organs. iPSCs may have a significant role to play here although, considering the complexity of the micro-architecture of organs required for normal physiological function, numerous technical issues need to be addressed before there is any prospect of generating functional organs ex vivo. Reproductive applications

Transgenic animal generation The iPSC technology may have a major advantage over SCNT for genetic manipulation in large animals. iPSCs are capable of efficiently generating chimeric animals and the modified cells can theoretically be transmitted via the germ-line, although many improvements are needed to achieve this goal reliably. The sequencing of the genome has now been completed for the dog, cow and horse, and is in progress for the pig and sheep. Based on such databases, our ability to specify genetic modifications in large animal species will improve significantly, enabling more accurate representations of human diseases and development of more efficient food producers with reduced environmental impact. In vivo organ generation Pigs with multiple genetic modifications appear to be the most promising route to generating an abundant source of organs suit-

The ability of iPSCs to generate germ cells in vitro could provide a means of studying the molecular basis of germ-line establishment and could offer new therapeutic approaches for infertility, novel contraceptive development, and improved genetic selection. It has been reported that mouse iPSCs derived from adult mouse hepatocytes can be induced to differentiate into presumptive germ cells and oocyte-like cells (Imamura et al., 2010; Niu et al., 2013). In addition, expression of female gamete specific markers has been reported in embryonic bodies formed in vitro from bovine iPSCs (Cao et al., 2012). Biodiversity preservation In a world where one in every four animal species is threatened by extinction,1 there is a pressing need to preserve biodiversity. 1

See: http://www.iucn.org.

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However, progress has been slow, mainly because assisted reproductive techniques have not always been easy to adapt to wildlife, and cloning by SCNT technology has not generally been considered acceptable or desirable as a tool for animal conservation purposes. iPSCs derived from endangered species could represent novel approaches for improving assisted reproduction and for studying genetic diversity; this would be especially interesting in wild species for which no suitable domestic animal model is available. The deriving of gametes or embryos (directly) from iPSCs would also benefit livestock and wildlife species. Present, past and future efforts to preserve genetic material from endangered and threatened species in a genetic resource bank could allow future generation of offspring with the iPSC technology from stored material. With this potential in mind, two recent studies generated iPSCs from three endangered species (Fig. 1). Conclusions The production of iPSCs for domestic animal species is an exciting reality with preliminary biomedical applications. The use of large animals to model novel treatments for humans may provide evidence for the feasibility of iPSC-based therapy. At the same time, iPSC studies in domestic species could improve our understanding of the potential benefits of iPSCs in veterinary medicine. Novel therapeutics are already being tested for humans through the application of iPSC technology, and it seems reasonable to expect that the same will happen for domestic and wild species. Conflict of interest statement None of the authors of this paper has a financial or personal relationship with other people or organisations that could inappropriately influence or bias the content of the paper. Acknowledgement This project was supported by EU FP7 (AniStem, PIAP-GA-2011286264 and PartnErS, PIAP-GA-2008-218205). References Alipio, Z., Liao, W., Roemer, E.J., Waner, M., Fink, L.M., Ward, D.C., Ma, Y., 2010. Reversal of hyperglycemia in diabetic mouse models using induced-pluripotent stem (iPS)-derived pancreatic b-like cells. Proceedings of the National Academy of Sciences of the United States of America 107, 13426–13431. Amariglio, N., Hirshberg, A., Scheithauer, B.W., Cohen, Y., Loewenthal, R., Trakhtenbrot, L., Paz, N., Koren-Michowitz, M., Waldman, D., Leider-Trejo, L., et al., 2009. Donor-derived brain tumor following neural stem cell transplantation in an ataxia telangiectasia patient. PLoS Medicine 6, e1000029. Aravalli, R.N., Cressman, E.N., Steer, C.J., 2012. Hepatic differentiation of porcine induced pluripotent stem cells in vitro. The Veterinary Journal 194, 369–374. Bao, L., He, L., Chen, J., Wu, Z., Liao, J., Rao, L., Ren, J., Li, H., Zhu, H., Qian, L., et al., 2011. Reprogramming of ovine adult fibroblasts to pluripotency via druginducible expression of defined factors. Cell Research 21, 600–608. Barrilleaux, B., Knoepfler, P.S., 2011. Inducing iPSCs to escape the dish. Cell Stem Cell 9, 103–111. Ben-Nun, I.F., Montague, S.C., Houck, M.L., Tran, H.T., Garitaonandia, I., Leonardo, T.R., Wang, Y.C., Charter, S.J., Laurent, L.C., Ryder, O.A., Loring, J.F., 2011. Induced pluripotent stem cells from highly endangered species. Nature Methods 8, 829– 831. Breton, A., Sharma, R., Diaz, A.C., Parham, A.G., Graham, A., Neil, C., Whitelaw, C.B., Milne, E., Donadeu, F.X., 2013. Derivation and characterization of induced pluripotent stem cells from equine fibroblasts. Stem Cells and Development 22, 611–621. Cao, H., Yang, P., Pu, Y., Sun, X., Yin, H., Zhang, Y., Zhang, Y., Li, Y., Liu, Y., Fang, F., et al., 2012. Characterization of bovine induced pluripotent stem cells by lentiviral transduction of reprogramming factor fusion proteins. International Journal of Biological Sciences 8, 498–511. Chan, A.W., Cheng, P.H., Neumann, A., Yang, J.J., 2010. Reprogramming Huntington monkey skin cells into pluripotent stem cells. Cellular Reprogramming 12, 509– 517.

Cheng, D., Li, Z., Liu, Y., Gao, Y., Wang, H., 2012. Kinetic analysis of porcine fibroblast reprogramming toward pluripotency by defined factors. Cellular Reprogramming 14, 312–323. Cyranoski, D., 2012. Stem-cell pioneer banks on future therapies. Nature News 488, 139. Deleidi, M., Hargus, G., Hallett, P., Osborn, T., Isacson, O., 2011. Development of histocompatible primate-induced pluripotent stem cells for neural transplantation. Stem Cells 29, 1052–1063. Deng, Y., Liu, Q., Luo, C., Chen, S., Li, X., Wang, C., Liu, Z., Lei, X., Zhang, H., Sun, H., et al., 2012. Generation of induced pluripotent stem cells from buffalo (Bubalus bubalis) fetal fibroblasts with buffalo defined factors. Stem Cells and Development 21, 2485–2494. Esteban, M.A., Xu, J., Yang, J., Peng, M., Qin, D., Li, W., Jiang, Z., Chen, J., Deng, K., Zhong, M., et al., 2009. Generation of induced pluripotent stem cell lines from Tibetan miniature pig. Journal of Biological Chemistry 284, 17634–17640. Evans, M.J., Kaufman, M.H., 1981. Establishment in culture of pluripotential cells from mouse embryos. Nature 292, 154–156. Ezashi, T., Telugu, B.P., Alexenko, A.P., Sachdev, S., Sinha, S., Roberts, R.M., 2009. Derivation of induced pluripotent stem cells from pig somatic cells. Proceedings of the National Academy of Sciences of the United States of America 106, 10993–10998. Ezashi, T., Matsuyama, H., Telugu, B.P., Roberts, R.M., 2011. Generation of colonies of induced trophoblast cells during standard reprogramming of porcine fibroblasts to induced pluripotent stem cells. Biology of Reproduction 85, 779–787. Fortier, L.A., Travis, A.J., 2011. Stem cells in veterinary medicine. Stem Cell Research and Therapy 2, 9. Fujishiro, S.H., Nakano, K., Mizukami, Y., Azami, T., Arai, Y., Matsunari, H., Ishino, R., Nishimura, T., Watanabe, M., Abe, T., et al., 2013. Generation of naive-like porcine-induced pluripotent stem cells capable of contributing to embryonic and fetal development. Stem Cells and Development 22, 473–482. Gattegno-Ho, D., Argyle, S.A., Argyle, D.J., 2012. Stem cells and veterinary medicine: Tools to understand diseases and enable tissue regeneration and drug discovery. The Veterinary Journal 191, 19–27. Goldring, C.E., Duffy, P.A., Benvenisty, N., Andrews, P.W., Ben-David, U., Eakins, R., French, N., Hanley, N.A., Kelly, L., Kitteringham, N.R., et al., 2011. Assessing the safety of stem cell therapeutics. Cell Stem Cell 8, 618–628. Gori, J.L., Chandrasekaran, D., Kowalski, J.P., Adair, J.E., Beard, B.C., D’Souza, S.L., Kiem, H.P., 2012. Efficient generation, purification, and expansion of CD34+ hematopoietic progenitor cells from nonhuman primate-induced pluripotent stem cells. Blood 120, e35–e44. Gu, M., Nguyen, P.K., Lee, A.S., Xu, D., Hu, S., Plews, J.R., Han, L., Huber, B.C., Lee, W.H., Gong, Y., et al., 2012. Microfluidic single-cell analysis shows that porcine induced pluripotent stem cell-derived endothelial cells improve myocardial function by paracrine activation. Circulation Research 111, 882–893. Hackett, C.H., Greve, L., Novakofski, K.D., Fortier, L.A., 2012. Comparison of genespecific DNA methylation patterns in equine induced pluripotent stem cell lines with cells derived from equine adult and fetal tissues. Stem Cells and Development 21, 1803–1811. Hall, V.J., Kristensen, M., Rasmussen, M.A., Ujhelly, O., Dinnyes, A., Hyttel, P., 2012. Temporal repression of endogenous pluripotency genes during reprogramming of porcine induced pluripotent stem cells. Cellular Reprogramming 14, 204– 216. Han, X., Han, J., Ding, F., Cao, S., Lim, S.S., Dai, Y., Zhang, R., Zhang, Y., Lim, B., Li, N., 2011. Generation of induced pluripotent stem cells from bovine embryonic fibroblast cells. Cell Research 21, 1509–1512. Hanna, J., Wernig, M., Markoulaki, S., Sun, C., Meissner, A., Cassady, J.P., Beard, C., Brambrink, T., Wu, L., Townes, T.M., Jaenisch, R., 2007. Treatment of sickle cell anemia mouse model with iPS cells generated from autologous skin. Science 318, 1920–1923. Huang, B., Li, T., Alonso-Gonzalez, L., Gorre, R., Keatley, S., Green, A., Turner, P., Kallingappa, P.K., Verma, V., Oback, B., 2011. A virus-free poly-promoter vector induces pluripotency in quiescent bovine cells under chemically defined conditions of dual kinase inhibition. PLoS ONE 6, e24501. Hyun, I., Lindvall, O., Ahrlund-Richter, L., Cattaneo, E., Cavazzana-Calvo, M., Cossu, G., De Luca, M., Fox, I.J., Gerstle, C., Goldstein, R.A., et al., 2008. New ISSCR guidelines underscore major principles for responsible translational stem cell research. Cell Stem Cell 3, 607–609. Imamura, M., Aoi, T., Tokumasu, A., Mise, N., Abe, K., Yamanaka, S., Noce, T., 2010. Induction of primordial germ cells from mouse induced pluripotent stem cells derived from adult hepatocytes. Molecular Reproduction and Development 77, 802–811. Kang, L., Wang, J., Zhang, Y., Kou, Z., Gao, S., 2009. IPS cells can support full-term development of tetraploid blastocyst-complemented embryos. Cell Stem Cell 5, 135–138. Kobayashi, T., Yamaguchi, T., Hamanaka, S., Kato-Itoh, M., Yamazaki, Y., Ibata, M., Sato, H., Lee, Y.S., Usui, J., Knisely, A.S., et al., 2010. Generation of rat pancreas in mouse by interspecific blastocyst injection of pluripotent stem cells. Cell 142, 787–799. Koh, S., Thomas, R., Tsai, S., Bischoff, S., Lim, J.H., Breen, M., Olby, N.J., Piedrahita, J., 2012. Growth requirements and chromosomal instability of induced pluripotent stem cells generated from adult canine fibroblasts. Stem Cells and Development doi. http://dx.doi.org/10.1089/scd.2012.0393. Kues, W.A., Niemann, H., 2004. The contribution of farm animals to human health. Trends in Biotechnology 22, 286–294. Kues, W.A., Herrmann, D., Barg-Kues, B., Haridoss, S., Nowak-Imialek, M., Buchholz, T., Streeck, M., Grebe, A., Grabundzija, I., Merkert, S., et al., 2013. Derivation and

A. Cebrian-Serrano et al. / The Veterinary Journal 198 (2013) 34–42 characterization of sleeping beauty transposon-mediated porcine induced pluripotent stem cells. Stem Cells and Development 22, 124–135. Lee, A.S., Xu, D., Plews, J.R., Nguyen, P.K., Nag, D., Lyons, J.K., Han, L., Hu, S., Lan, F., Liu, J., et al., 2011. Preclinical derivation and imaging of autologously transplanted canine induced pluripotent stem cells. Journal of Biological Chemistry 286, 32697–32704. Li, Y., Cang, M., Lee, A.S., Zhang, K., Liu, D., 2011. Reprogramming of sheep fibroblasts into pluripotency under a drug-inducible expression of mouse-derived defined factors. PLoS ONE 6, e15947. Lian, Q., Zhang, Y., Zhang, J., Zhang, H.K., Wu, X., Zhang, Y., Lam, F.F., Kang, S., Xia, J.C., Lai, W., et al., 2010. Functional mesenchymal stem cells derived from human induced pluripotent stem cells attenuate limb ischemia in mice. Circulation 121, 1113–1123. Liu, H., Zhu, F., Yong, J., Zhang, P., Hou, P., Li, H., Jiang, W., Cai, J., Liu, M., Cui, K., et al., 2008. Generation of induced pluripotent stem cells from adult rhesus monkey fibroblasts. Cell Stem Cell 3, 587–590. Liu, H., Kim, Y., Sharkis, S., Marchionni, L., Jang, Y.Y., 2011. In vivo liver regeneration potential of human induced pluripotent stem cells from diverse origins. Science Translational Medicine 3, 82ra39. Liu, J., Balehosur, D., Murray, B., Kelly, J.M., Sumer, H., Verma, P.J., 2012a. Generation and characterization of reprogrammed sheep induced pluripotent stem cells. Theriogenology 77, 338–346. Liu, K., Ji, G., Mao, J., Liu, M., Wang, L., Chen, C., Liu, L., 2012b. Generation of porcineinduced pluripotent stem cells by using OCT4 and KLF4 porcine factors. Cellular Reprogramming 14, 505–513. Luo, J., Suhr, S.T., Chang, E.A., Wang, K., Ross, P.J., Nelson, L.L., Venta, P.J., Knott, J.G., Cibelli, J.B., 2011. Generation of leukemia inhibitory factor and basic fibroblast growth factor-dependent induced pluripotent stem cells from canine adult somatic cells. Stem Cells and Development 20, 1669–1678. Maherali, N., Sridharan, R., Xie, W., Utikal, J., Eminli, S., Arnold, K., Stadtfeld, M., Yachechko, R., Tchieu, J., Jaenisch, R., et al., 2007. Directly reprogrammed fibroblasts show global epigenetic remodeling and widespread tissue contribution. Cell Stem Cell 1, 55–70. Montserrat, N., Bahima, E.G., Batlle, L., Hafner, S., Rodrigues, A.M., Gonzalez, F., Izpisua Belmonte, J.C., 2011. Generation of pig iPS cells: A model for cell therapy. Journal of Cardiovascular Translational Research 4, 121–130. Montserrat, N., de Onate, L., Garreta, E., Gonzalez, F., Adamo, A., Eguizabal, C., Hafner, S., Vassena, R., Izpisua Belmonte, J.C., 2012. Generation of feeder-free pig induced pluripotent stem cells without Pou5f1. Cell Transplantation 21, 815–825. Nagy, K., Sung, H.K., Zhang, P., Laflamme, S., Vincent, P., Agha-Mohammadi, S., Woltjen, K., Monetti, C., Michael, I.P., Smith, L.C., Nagy, A., 2011. Induced pluripotent stem cell lines derived from equine fibroblasts. Stem Cell Reviews 7, 693–702. Nelson, T.J., Martinez-Fernandez, A., Yamada, S., Perez-Terzic, C., Ikeda, Y., Terzic, A., 2009. Repair of acute myocardial infarction by human stemness factors induced pluripotent stem cells. Circulation 120, 408–416. Niu, Z., Hu, Y., Chu, Z., Yu, M., Bai, Y., Wang, L., Hua, J., 2013. Germ-like cell differentiation from induced pluripotent stem cells (iPSCs). Cell Biochemistry and Function 31, 12–19. Nowak-Imialek, M., Kues, W.A., Petersen, B., Lucas-Hahn, A., Herrmann, D., Haridoss, S., Oropeza, M., Lemme, E., Scholer, H.R., Carnwath, J.W., Niemann, H., 2011. Oct4-enhanced green fluorescent protein transgenic pigs: A new large animal model for reprogramming studies. Stem Cells and Development 20, 1563–1575. Okita, K., Ichisaka, T., Yamanaka, S., 2007. Generation of germline-competent induced pluripotent stem cells. Nature 448, 313–317. Plews, J.R., Gu, M., Longaker, M.T., Wu, J.C., Plews, J.R., Gu, M., Longaker, M.T., Wu, J.C., 2012. Large animal induced pluripotent stem cells as pre-clinical models for studying human disease. Journal of Cellular and Molecular Medicine 16, 1196– 1202. Ren, J., Pak, Y., He, L., Qian, L., Gu, Y., Li, H., Rao, L., Liao, J., Cui, C., Xu, X., et al., 2011. Generation of hircine-induced pluripotent stem cells by somatic cell reprogramming. Cell Research 21, 849–853. Robinton, D.A., Daley, G.Q., 2012. The promise of induced pluripotent stem cells in research and therapy. Nature 481, 295–305. Rubin, L.L., 2008. Stem cells and drug discovery: The beginning of a new era? Cell 132, 549–552. Rufaihah, A.J., Huang, N.F., Jamé, S., Lee, J.C., Nguyen, H.N., Byers, B., De, A., Okogbaa, J., Rollins, M., Reijo-Pera, R., et al., 2011. Endothelial cells derived from human iPSCS increase capillary density and improve perfusion in a mouse model of peripheral arterial disease. Arteriosclerosis, Thrombosis, and Vascular Biology 31, e.72–e.79. Sartori, C., DiDomenico, A.I., Thomson, A.J., Milne, E., Lillico, S.G., Burdon, T.G., Whitelaw, C.B., 2012. Ovine-induced pluripotent stem cells can contribute to chimeric lambs. Cellular Reprogramming 14, 8–19. Schwartz, R.E., Trehan, K., Andrus, L., Sheahan, T.P., Ploss, A., Duncan, S.A., Rice, C.M., Bhatia, S.N., 2012. Modeling hepatitis C virus infection using human induced pluripotent stem cells. Proceedings of the National Academy of Sciences of the United States of America 109, 2544–2548. Sewell, A.C., Haskins, M.E., Giger, U., 2007. Inherited metabolic disease in companion animals: Searching for nature’s mistakes. The Veterinary Journal 2007, 252–259. Shimada, H., Nakada, A., Hashimoto, Y., Shigeno, K., Shionoya, Y., Nakamura, T., 2010. Generation of canine induced pluripotent stem cells by retroviral transduction and chemical inhibitors. Molecular Reproduction and Development 77, 2.

41

Stadtfeld, M., Hochedlinger, K., 2010. Induced pluripotency: History, mechanisms, and applications. Genes and Development 24, 2239–2263. Sumer, H., Liu, J., Malaver-Ortega, L.F., Lim, M.L., Khodadadi, K., Verma, P.J., 2011. NANOG is a key factor for induction of pluripotency in bovine adult fibroblasts. Journal of Animal Science 89, 2708–2716. Swistowski, A., Peng, J., Liu, Q., Mali, P., Rao, M.S., Cheng, L., Zeng, X., 2010. Efficient generation of functional dopaminergic neurons from human induced pluripotent stem cells under defined conditions. Stem Cells 28, 1893–1904. Takahashi, K., Yamanaka, S., 2006. Induction of pluripotent stem cells from mouse embryonic and adult fibroblast cultures by defined factors. Cell 126, 663–676. Takahashi, K., Tanabe, K., Ohnuki, M., Narita, M., Ichisaka, T., Tomoda, K., Yamanaka, S., 2007. Induction of pluripotent stem cells from adult human fibroblasts by defined factors. Cell 131, 861–872. Tang, L., Yin, Y., Zhou, H., Song, G., Fan, A., Tang, B., Shi, W., Li, Z., 2012. Proliferative capacity and pluripotent characteristics of porcine adult stem cells derived from adipose tissue and bone marrow. Cellular Reprogramming 14, 342–352. Telugu, B.P., Ezashi, T., Roberts, R.M., 2010. Porcine induced pluripotent stem cells analogous to naive and primed embryonic stem cells of the mouse. International Journal of Developmental Biology 54, 1703–1711. Templin, C., Zweigerdt, R., Schwanke, K., Olmer, R., Ghadri, J.R., Emmert, M.Y., Muller, E., Kuest, S.M., Cohrs, S., Schibli, R., et al., 2012. Transplantation and tracking of human-induced pluripotent stem cells in a pig model of myocardial infarction: Assessment of cell survival, engraftment, and distribution by hybrid single photon emission computed tomography/computed tomography of sodium iodide symporter transgene expression. Circulation 126, 430–439. Tomioka, I., Maeda, T., Shimada, H., Kawai, K., Okada, Y., Igarashi, H., Oiwa, R., Iwasaki, T., Aoki, M., Kimura, T., et al., 2010. Generating induced pluripotent stem cells from common marmoset (Callithrix jacchus) fetal liver cells using defined factors, including Lin28. Genes to Cells: Devoted to Molecular and Cellular Mechanisms 15, 959–969. Torrez, L.B., Perez, Y., Yang, J., Zur Nieden, N.I., Klassen, H., Liew, C.G., 2012. Derivation of neural progenitors and retinal pigment epithelium from common marmoset and human pluripotent stem cells. Stem Cells International 2012, 417865. Tsuji, O., Miura, K., Okada, Y., Fujiyoshi, K., Mukaino, M., Nagoshi, N., Kitamura, K., Kumagai, G., Nishino, M., Tomisato, S., et al., 2010. Therapeutic potential of appropriately evaluated safe-induced pluripotent stem cells for spinal cord injury. Proceedings of the National Academy of Sciences of the United States of America 107, 12704–12709. Verma, R., Holland, M.K., Temple-Smith, P., Verma, P.J., 2012. Inducing pluripotency in somatic cells from the snow leopard (Panthera uncia), an endangered felid. Theriogenology 77, 220–228.e2. Wei, Y., Zeng, W., Wan, R., Wang, J., Zhou, Q., Qiu, S., Singh, S.R., 2012. Chondrogenic differentiation of induced pluripotent stem cells from osteoarthritic chondrocytes in alginate matrix. European Cells and Materials 23, 1–12. Wernig, M., Meissner, A., Foreman, R., Brambrink, T., Ku, M., Hochedlinger, K., Bernstein, B.E., Jaenisch, R., 2007. In vitro reprogramming of fibroblasts into a pluripotent ES-cell-like state. Nature 448, 318–324. Wernig, M., Zhao, J.P., Pruszak, J., Hedlund, E., Fu, D., Soldner, F., Broccoli, V., Constantine-Paton, M., Isacson, O., Jaenisch, R., 2008. Neurons derived from reprogrammed fibroblasts functionally integrate into the fetal brain and improve symptoms of rats with Parkinson’s disease. Proceedings of the National Academy of Sciences of the United States of America 105, 5856–5861. West, F.D., Terlouw, S.L., Kwon, D.J., Mumaw, J.L., Dhara, S.K., Hasneen, K., Dobrinsky, J.R., Stice, S.L., 2010. Porcine induced pluripotent stem cells produce chimeric offspring. Stem Cells and Development 19, 1211–1220. West, F.D., Uhl, E.W., Liu, Y., Stowe, H., Lu, Y., Yu, P., Gallegos-Cardenas, A., Pratt, S.L., Stice, S.L., 2011. Brief report: Chimeric pigs produced from induced pluripotent stem cells demonstrate germline transmission and no evidence of tumor formation in young pigs. Stem Cells 29, 1640–1643. Whitworth, D.J., Ovchinnikov, D.A., Wolvetang, E.J., 2012. Generation and characterization of LIF-dependent canine induced pluripotent stem cells from adult dermal fibroblasts. Stem Cells and Development 21, 2288–2297. Wilmut, I., Schnieke, A.E., McWhir, J., Kind, A.J., Campbell, K.H., 1997. Viable offspring derived from fetal and adult mammalian cells. Nature 385, 810–813. Wilson, J.M., 2009. Medicine. A history lesson for stem cells. Science 324, 727–728. Wu, Z., Chen, J., Ren, J., Bao, L., Liao, J., Cui, C., Rao, L., Li, H., Gu, Y., Dai, H., et al., 2009. Generation of pig induced pluripotent stem cells with a drug-inducible system. Journal of Molecular Cell Biology 1, 46–54. Wu, Y., Zhang, Y., Mishra, A., Tardif, S.D., Hornsby, P.J., 2010. Generation of induced pluripotent stem cells from newborn marmoset skin fibroblasts. Stem Cell Research 4, 180–188. Xu, D., Alipio, Z., Fink, L.M., Adcock, D.M., Yang, J., Ward, D.C., Ma, Y., 2009. Phenotypic correction of murine hemophilia A using an iPS cell-based therapy. Proceedings of the National Academy of Sciences of the United States of America 106, 808–813. Yang, J.Y., Mumaw, J.L., Liu, Y., Stice, S.L., West, F.D., 2012. SSEA4 positive pig induced pluripotent stem cells are primed for differentiation into neural cells. Cell Transplantation. http://dx.doi.org/10.3727/096368912X657279. Zhong, B., Trobridge, G.D., Zhang, X., Watts, K.L., Ramakrishnan, A., Wohlfahrt, M., Adair, J.E., Kiem, H.P., 2011a. Efficient generation of nonhuman primate induced pluripotent stem cells. Stem Cells and Development 20, 795–807. Zhong, B., Watts, K.L., Gori, J.L., Wohlfahrt, M.E., Enssle, J., Adair, J.E., Kiem, H.P., 2011b. Safeguarding nonhuman primate iPS cells with suicide genes. Molecular Therapy: The Journal of the American Society of Gene Therapy 19, 1667–1675.

42

A. Cebrian-Serrano et al. / The Veterinary Journal 198 (2013) 34–42

Zhou, L., Wang, W., Liu, Y., de Castro, J.F., Ezashi, T., Telugu, B.P.V.L., Roberts, R.M., Kaplan, H.J., Dean, D.C., 2011. Differentiation of induced pluripotent stem cells of swine into rod photoreceptors and their integration into the retina. Stem Cells 29, 972–980.

Zhu, F.F., Zhang, P.B., Zhang, D.H., Sui, X., Yin, M., Xiang, T.T., Shi, Y., Ding, M.X., Deng, H., 2011. Generation of pancreatic insulin-producing cells from rhesus monkey induced pluripotent stem cells. Diabetologia 54, 2325–2336.