View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Elsevier - Publisher Connector Cell Stem Cell Forum Strategies for Improving Animal Models for Regenerative Medicine Jose Cibelli,1 Marina E. Emborg,2 Darwin J. Prockop,3 Michael Roberts,4 Gerald Schatten,5 Mahendra Rao,6 John Harding,7 and Oleg Mirochnitchenko7,* 1Michigan State University, Cellular Reprogramming Laboratory, Department of Animal Science, B270 Anthony Hall, East Lansing, MI 48824, USA 2University of Wisconsin-Madison, Department of Medical Physics and Wisconsin National Primate Research Center, 1223 Capitol Court, Madison, WI 53715, USA 3Texas A&M Health Science Center, College of Medicine Institute for Regenerative Medicine at Scott and White, Department of Medicine, 5701 Airport Road, Module C, Temple, TX 76502, USA 4University of Missouri, 240b C.S. Bond Life Sciences Center, 1201 East Rollins Street, Columbia, MO 65211-7310, USA 5University of Pittsburgh, Department of Cell Biology and Physiology, S362 Biomedical Science Towers, 3500 Terrace Street, Pittsburgh, PA 15261, USA 6Center for Regenerative Medicine, National Institutes of Health, 50 South Drive, Suite 1140, Bethesda, MD 20892, USA 7Division of Comparative Medicine/ORIP/DPCPSI/OD, National Institutes of Health, 6701 Democracy Boulevard, Suite 943/950, Bethesda, MD 20892, USA *Correspondence: [email protected] http://dx.doi.org/10.1016/j.stem.2013.01.004 The field of regenerative medicine is moving toward translation to clinical practice. However, there are still knowledge gaps and safety concerns regarding stem cell-based therapies. Improving large animal models and methods for transplantation, engraftment, and imaging should help address these issues, facilitating eventual use of stem cells in the clinic. Introduction to cancer and renal failure. They are examples of a large animal model In this Forum, we discuss the current relatively obese and hypertensive due to currently being used to study human status, challenges, and major directions the constant access to food. In compar- genetic diseases (review in Kuzmuk and for future development of animal models ison to humans, mice have small body Schook, 2011). Even without genetic to facilitate the use of stem cells in size, short lifespan, and substantially modification, minipigs and full-size regenerative medicine. The variety of different physiology. Significant progress breeds have been widely used for stem cell sources and a wide spectrum has been made in the creation and use studying infectious diseases, cardiovas- of potential applications make the devel- of humanized mice. There are, how- cular disease and atherosclerosis, wound opment of universal recommendations ever, disadvantages to using the current healing, digestive processes, diabetes, and guiding principles very challenging, strains, including complications in repro- ophthalmology, and some cancers, as yet certain common themes and ducing standard chimeras, limitations well as providing organs for xenotrans- possible solutions are emerging that in choices of human cell types that can plantation. The value of pigs as biomed- can increase the predictive validity of be used for xenotransplantation, residual ical models has been enhanced over the animal models for regenerative medicine. host immunoreactivity, and problems last decade by targeting specific genomic This report is based on discussions that with translating conditioning regiments sites for modification. Swine disease took place at a recent NIH workshop between species. The evolutionary dis- models created by targeted genetic engi- on this topic (http://dpcpsi.nih.gov/orip/ tance between donor and recipient neering include those for cystic fibrosis, documents/summary_of_the_improving_ animals will also affect the survival of Alzheimer’s and Huntington’s disease, animal_models.pdf). transplanted stem cells due to species retinitis pigmentosa, hyperlipoproteine- differences in trophic properties of mia, and muscular dystrophy. Recently, Animal Models for Stem Cell-Based tissues. creation of humanized pigs has been re- Regenerative Medicine: Mice Larger animal species, which were crit- ported (Suzuki et al., 2012), as well as versus Large Animal Models ical for developing hematopoietic stem improved preclinical disease models suit- The discovery of mouse embryonic stem cell therapies, often have an enhanced able for testing stem cell therapies in pigs cells (ESCs) in 1981 revolutionized the ability to predict clinical efficacy relative (Giraud et al., 2011; McCall et al., 2012). study of developmental biology, and to mice. The utilization of large animal Most of this work has been enhanced mice are now used extensively to study models is expected to increase and, through access to the swine genome stem cell biology. However, there are limi- therefore, further development of large sequence and the use of inbred tations to their application as models for animal stem cell technologies will also minipigs (http://www.nsrrc.missouri.edu/ regenerative medicine. Mouse models be required. It will be critical to select strainavail.asp). Work in swine will do not reproduce in full certain human the large animal that is most appropriate complement nonhuman primate research disease conditions. For example, labora- for each potential therapy in humans. for neurological treatments when ana- tory mice are insulin resistant and prone The pig has emerged as one of the best lyzing recovery of fine motor skills or Cell Stem Cell 12, March 7, 2013 ª2013 Elsevier Inc. 271 Cell Stem Cell Forum impact on cognitive function. This related to safety, efficiency, and differen- certain cellular abnormalities of the corre- would be facilitated by equivalent tiation potential. sponding cells from patients with various advances in primate transgenesis, like Several problems remain before the Mendelian disorders. The ability to model the recent monkey models of Hunting- potential of nonrodent animal iPSCs can low-penetrance phenotypes, late-onset ton’s disease. be realized. Cell lines must be character- disorders, and genetically complex disor- Major challenges remain, however, for ized in more detail, chimerism tested, ders, however, remains to be proved. using large animals in stem cell research. and reprogramming increased in effi- Animal model systems may help solve For example, there is limited availability ciency and speed in order to enhance some of these problems because trans- of species-specific reagents, such as genome integrity. Cell surface markers plantation experiments can be performed antibodies and growth factors, and can be inconsistent among various lines using the animal as a host. The use of fully annotated expression microarrays. and cell populations may be heteroge- allogeneic iPSCs in animal model systems Authenticated ESCs have been difficult neous, probably reflecting different or xenotransplantation of human stem to generate from large domestic species, stages of reprogramming. Efficient deri- cells in immunocompromised or human- such as dog, swine, cattle, sheep, and vation of animal iPSC lines requires ized animals should facilitate analysis of goats. This has been obviated in part by further development of technologies for disease phenotypes that require cellular creation of induced pluripotent stem cells generating the cells, preferentially avoid- interactions in the tissues. Animal iPSCs (iPSCs) from these species by standard ing gene integration and potential risks can have certain advantages for testing reprogramming technologies. There is of tumorigenesis. hypotheses regarding the influence of a lack of centralized resources where An important aspect of animal studies is environmental or epigenetic components cells can be characterized and stored, the ability to test immune responses to of disease first identified in cell culture. reagents made available, and databases iPSCs and their derivatives. A number of The effects of exposures and genomic maintained for the wider biomedical animal studies have reported that iPSCs modifications can be tested at the level community. If these barriers can be over- can form teratomas and other types of of the tissue, organ, and the whole animal, come, well-characterized large animal tumors in immunodeficient, allogeneic, preserving interactions among distinct stem cells can provide an appropriate syngeneic, and xenogeneic recipients cell types in vivo. Use of animal systems choice of animal models for particular due to the inability of the host to re- also facilitates experimental design by human disease conditions and medical ject teratoma-inducing cells. The innate providing controls with matching genetic applications. These studies will comple- immune system appears capable of background, age, gender, and exposure ment the use of mice, leading to more dealing with small numbers of undifferen- history. comprehensive studies that can then be tiated iPSCs that might be present in applied to humans. grafts, despite efforts to eliminate them. Improving Stem Cell The ability of adaptive and innate immune Transplantation: Engraftment and Animal Induced Pluripotent Stem reactions to weaken engraftment of syn- Imaging Cells as Emerging Models for geneic stem cell transplants is another Two different approaches can be taken Human Therapeutic Applications important aspect of the host reaction for stem cell-based therapies. The first is The field of stem cell research experi- that can affect the efficiency of cell transplantation, in which stem cells, or enced