Nonhuman primate models for islet transplantation in type 1 diabetes research

Insulin-dependent diabetes mellitus is an autoimmune disease that causes a progressive destruction of the pancreatic beta cells. As a result, the patient requires exogenous insulin to maintain normal blood glucose levels. Both the pancreas and the islets of Langerhans have been transplanted successfully in humans and in animal models, resulting in full normalization of glucose homeostasis. However, insulin independence, transient or persistent, was documented in only a small fraction of cases until recently. The chronic immunosuppression required to avoid immunological rejection appears to be toxic to the islets and adds the risk of lymphoproliferative disease reported earlier. For islet transplantation to become the method of choice, it is essential first to identify islet-friendly immunosuppressive regimens and/or to develop methods that induce donor-specific tolerance and improve islet isolation and transplantation protocols. Indeed, researchers have already successfully allografted islets in the presence of nonsteroidal immunosuppression in a process known as the Edmonton protocol. An alternative method, gene therapy, could replace these other methods and better meet the insulin requirement of an individual without requiring pancreatic or islet transplantation. This alternative, however, requires animal models to develop and test clinical protocols and to demonstrate the feasibility of preclinical trials. Nonhuman primates are ideally suited to achieve these goals. The efforts toward developing a nonhuman primate diabetic model with demonstrable insulin dependence are discussed and include pancreatic and islet transplant trials to reverse the diabetic state and achieve insulin independence. Also described are the various protocols that have been tested in primates to circumvent immunosuppression by using tolerance induction strategies in lieu of immunosuppression, thus exploring the field of donor-specific tolerance that extends beyond islet transplantation.     

Nonhuman primate models of menopause workshop

The Nonhuman Primate Models of Menopause Workshop was held on the National Institutes of Health campus in January 2001. The purpose of this workshop, sponsored by the National Institute on Aging, was to review what is known about the female reproductive aging process in various species of monkeys (particularly rhesus, baboons, cynomolgus, and chimpanzees), including hormone profiles during the menopausal transition, occurrence of hot flashes, extent of age-related and menopause-associated changes in hormone levels on metabolism, bone loss, and impaired cardiovascular and cognitive function. Many aspects of the female reproductive aging process appear to be concordant between humans and these monkey species, but several important features may be species-specific. Those features that appear to parallel human menopause and aging include general similarity of hormone profiles across the menopausal transition, progression to cycle termination through irregular cycles, declining fertility with age, age-related gains in weight and percentage body fat content (with tendencies toward insulin resistance and glucose intolerance), increased low-density lipoprotein cholesterol and decreased high-density lipoprotein cholesterol, declines in serum dehydroepiandrosterone, similarities in temperature-regulation systems, protective responses to estrogen replacement following ovariectomy in terms of bone metabolism, lipid profiles, and cognitive changes. Important differences include relatively short postmenopausal life span, timing in menopause-related changes in hormone secretion, and seasonal menstrual cycles. In addition, the question of whether ovariectomy in young adults is an appropriate model for the consequences of natural or surgical menopause in middle-aged and older adults is unresolved, and the numbers of older female animals available for research on menopause are very limited. The use of animal models is seen by workshop participants to be crucial for a mechanistic understanding of the human menopausal process and its connections to postmenopausal health problems; however, extensive in-depth and broad-based research is required to determine if nonhuman primates are appropriate models of human menopause.     

Nonhuman primate models of Parkinson's disease

Nonhuman primate (NHP) models of Parkinson's disease (PD) play an essential role in the understanding of PD pathophysiology and the assessment of PD therapies. NHP research enabled the identification of environmental risk factors for the development of PD. Electrophysiological studies in NHP models of PD identified the neural circuit responsible for PD motor symptoms, and this knowledge led to the development of subthalamic surgical ablation and deep brain stimulation. Similar to human PD patients, parkinsonian monkeys are responsive to dopamine replacement therapies and present complications associated with their long-term use, a similarity that facilitated the assessment of new symptomatic treatments, such as dopaminergic agonists. New generations of compounds and novel therapies that use directed intracerebral delivery of drugs, cells, and viral vectors benefit from preclinical evaluation in NHP models of PD. There are several NHP models of PD, each with characteristics that make it suitable for the study of different aspects of the disease or potential new therapies. Investigators who use the models and peer scientists who evaluate their use need information about the strengths and limitations of the different PD models and their methods of evaluation. This article provides a critical review of available PD monkey models, their utilization, and how they compare to emerging views of PD as a multietiologic, multisystemic disease. The various models are particularly useful for representing different aspects of PD at selected time points. This conceptualization provides clues for the development of new NHP models and facilitates the clinical translation of findings. As ever, successful application of any model depends on matching the model to the scientific question to be answered. Adequate experimental designs, with multiple outcome measures of clinical relevance and an appropriate number of animals, are essential to minimize the limitations of models and increase their predictive clinical validity.     

Nonhuman primate models of intrauterine cytomegalovirus infection

Congenital human cytomegalovirus (HCMV) infection has long been recognized as a threat to the developing fetus, even though studies have shown that only a subset of congenital infections results in clinical signs of disease. Among the estimated 8000 children who develop sequelae from congenital CMV infection each year in the United States alone, most suffer permanent developmental defects within the central nervous system. Because there is currently no approved vaccine for HCMV, and anti-HCMV drugs are not administered to gravid women with congenital infection because of potential toxicity to the fetus, there is a clear clinical need for effective strategies that minimize infection in the mother, transplacental transmission of the virus, and/or fetal disease. Animal models provide a method to understand the mechanisms of HCMV persistence and pathogenesis, and allow for testing of novel strategies that limit prenatal infection and disease. The rhesus macaque model is especially well suited for these tasks because monkeys and humans share strong developmental, immunological, anatomical, and biochemical similarities due to their close phylogenetic relationship. This nonhuman primate model provides an invaluable system to accelerate the clinical development of promising new therapies for the treatment of human disease. This review addresses salient findings with the macaque model as they relate to HCMV infection and potential avenues of discovery, including studies of intrauterine CMV infection. The complexity of the natural history of HCMV is discussed, along with the ethical and logistical issues associated with studies during pregnancy, the recent contributions of animal research in this field of study, and future prospects for increasing our understanding of immunity against HCMV disease.     

Nonhuman primate models and the failure of the Merck HIV-1 vaccine in humans

The adenovirus type 5 (Ad5)-based vaccine developed by Merck failed to either prevent HIV-1 infection or suppress viral load in subsequently infected subjects in the STEP human Phase 2b efficacy trial. Analogous vaccines had previously also failed in the simian immunodeficiency virus (SIV) challenge-rhesus macaque model. In contrast, vaccine protection studies that used challenge with a chimeric simian-human immunodeficiency virus (SHIV89.6P) in macaques did not predict the human trial results. Ad5 vector-based vaccines did not protect macaques from infection after SHIV89.6P challenge but did cause a substantial reduction in viral load and a preservation of CD4+ T cell counts after infection, findings that were not reproduced in the human trials. Although the SIV challenge model is incompletely validated, we propose that its expanded use can help facilitate the prioritization of candidate HIV-1 vaccines, ensuring that resources are focused on the most promising candidates. Vaccine designers must now develop T cell vaccine strategies that reduce viral load after heterologous challenge.     

Old world nonhuman primate models of type 2 diabetes mellitus

Type 2 diabetes mellitus is a major health problem of increasing incidence. To better study the pathogenesis and potential therapeutic agents for this disease, appropriate animal models are needed. Old World nonhuman primates (NHPs) are a useful animal model of type 2 diabetes; like humans, the disease is most common in older, obese animals. Before developing overt diabetes, NHPs have a period of obesity-associated insulin resistance that is initially met with compensatory insulin secretion. When either a relative or absolute deficiency in pancreatic insulin production occurs, fasting glucose concentrations begin to increase and diabetic signs become apparent. Pathological changes in pancreatic islets are also similar to those seen in human diabetics. Initially there is hyperplasia of the islets with abundant insulin production typically followed by replacement of islets with islet-associated amyloid. Diabetic NHPs have detrimental changes in plasma lipid and lipoprotein concentrations, lipoprotein composition, and glycation, which may contribute to progression of atherosclerosis. As both the prediabetic condition (similar to metabolic syndrome in humans) and overt diabetes become better defined in monkeys, their use in pharmacological studies is increasing. Likely due to their genetic similarity to humans and the similar characteristics of the disease in NHPs, NHPs have been used to study recently developed agonists of the peroxisome proliferators-activated receptors. Importantly, agonists of the different receptor subclasses elicit similar responses in both humans and NHPs. Thus, Old World NHPs are a valuable animal model of type 2 diabetes to study disease progression, associated risk factors, and potential new treatments.     

Immunological models of type 1 diabetes

Type 1 diabetes mellitus is a serious health problem that affects several million new people each year. Although it is recognized that type 1 diabetes results from an autoimmune destruction of the insulin-producing beta-cells in the pancreatic islets of Langerhans, its etiopathogenesis is still not well understood. A certain genetic phenotype seems to be required, but it is not sufficient per se to trigger diabetes development. Numerous studies have pointed to the role of infectious agents as important environmental factors in breaking 'self'-tolerance and triggering activation of autoreactive T cells. Activated T cells, in turn, destroy target cells harboring the corresponding tissue-specific self-antigen, causing organ damage and loss of function. Several theories have been proposed to explain how environmental factors can initiate and/or perpetuate autoimmunity towards pancreatic beta-cells.     

Nonhuman primate infections after organ transplantation

Nonhuman primates, primarily rhesus macaques (Macaca mulatta), cynomolgus macaques (Macaca fascicularis), and baboons (Papio spp.), have been used extensively in research models of solid organ transplantation, mainly because the nonhuman primate (NHP) immune system closely resembles that of the human. Nonhuman primates are also frequently the model of choice for preclinical testing of new immunosuppressive strategies. But the management of post-transplant nonhuman primates is complex, because it often involves multiple immunosuppressive agents, many of which are new and have unknown effects. Additionally, the resulting immunosuppression carries a risk of infectious complications, which are challenging to diagnose. Last, because of the natural tendency of animals to hide signs of weakness, infectious complications may not be obvious until the animal becomes severely ill. For these reasons the diagnosis of infectious complications is difficult among post-transplant NHPs. Because most nonhuman primate studies in organ transplantation are quite small, there are only a few published reports concerning infections after transplantation in nonhuman primates. Based on our survey of these reports, the incidence of infection in NHP transplant models is 14%. The majority of reports suggest that many of these infections are due to reactivation of viruses endemic to the primate species, such as cytomegalovirus (CMV), polyomavirus, and Epstein-Barr virus (EBV)-related infections. In this review, we address the epidemiology, pathogenesis, role of prophylaxis, clinical presentation, and treatment of infectious complications after solid organ transplantation in nonhuman primates.     

Circulating sphingolipid biomarkers in models of type 1 diabetes

Alterations in lipid metabolism may contribute to diabetic complications. Sphingolipids are essential components of cell membranes and have essential roles in homeostasis and in the initiation and progression of disease. However, the role of sphingolipids in type 1 diabetes remains largely unexplored. Therefore, we sought to quantify sphingolipid metabolites by LC-MS/MS from two animal models of type 1 diabetes (streptozotocin-induced diabetic rats and Ins2(Akita) diabetic mice) to identify putative therapeutic targets and biomarkers. The results reveal that sphingosine-1-phosphate (So1P) is elevated in both diabetic models in comparison to respective control animals. In addition, diabetic animals demonstrated reductions in plasma levels of omega-9 24:1 (nervonic acid)-containing ceramide, sphingomyelin, and cerebrosides. Reduction of 24:1-esterfied sphingolipids was also observed in liver and heart. Nutritional stress via a high-fat diet also reduced 24:1 content in the plasma and liver of mice, exacerbating the decrease in some cases where diabetes was also present. Subcutaneous insulin corrected both circulating So1P and 24:1 levels in the murine diabetic model. Thus, changes in circulating sphingolipids, as evidenced by an increase in bioactive So1P and a reduction in cardio- and neuro-protective omega-9 esterified sphingolipids, may serve as biomarkers for type 1 diabetes and represent novel therapeutic targets.     

Nonhuman primate transgenesis: progress and prospects

The nonhuman primate is used extensively in biomedical research owing to its close similarities to human physiology and human disease pathophysiology. Recently, several groups have initiated efforts to genetically manipulate nonhuman primates to address complex questions concerning primate-specific development and physiological adaptation. Primates pose unique challenges to transgenesis and, although this field is still in its infancy, the potential for obtaining new insights into primate physiology and gene function is unprecedented. This review focuses on the methods and potential applications of genetically altered nonhuman primates in biomedical research.     

非人灵长类糖尿病动物模型研究进展

糖尿病是继心血管疾病和肿瘤之后的另一种严重危害人类健康的重要慢性疾病,据世界卫生组织(WHO)报道,2009年全世界约有2.2亿糖尿病患者。对糖尿病发病机理的研究、预防和诊断、治疗药物的筛选和评价都需要合适的动物模型。在已报道的糖尿病动物模型中,非人灵长类动物糖尿病病程、病症与人类的糖尿病最为相似。该文从糖尿病动物模型的来源归纳了目前报道的主要的非人灵长类糖尿病模型,重点介绍了猕猴、食蟹猴和树鼩糖尿病模型及其特征,并对该领域的发展提出了一些思考。     

Myeloid-derived suppressor cells prevent type 1 diabetes in murine models

Effective immunotherapy for type 1 diabetes (T1D) relies on active induction of peripheral tolerance. Myeloid-derived suppressor cells (MDSCs) play a critical role in suppressing immune responses in various pathologic settings via multiple mechanisms, including expansion of regulatory T cells (Tregs). In this study, we investigated whether MDSCs could act as APCs to induce expansion of Ag-specific Tregs, suppress T cell proliferation, and prevent autoimmune T1D development. We found that MDSC-mediated expansion of Tregs and T cell suppression required MHC-dependent Ag presentation. A murine T1D model was established in INS-HA/RAG(-/-) mice in which animals received CD4-HA-TCR transgenic T cells via adoptive transfer. We found a significant reduction in the incidence of diabetes in recipients receiving MDSC plus HA, but not OVA peptide, leading to 75% diabetes-free mice among the treated animals. To test further whether MDSCs could prevent diabetes onset in NOD mice, nondiabetic NOD/SCID mice were injected with inflammatory T cells from diabetic NOD mice. MDSCs significantly prevented diabetes onset, and 60% of MDSC-treated mice remained diabetes free. The pancreata of treated mice showed significantly lower levels of lymphocyte infiltration in islet and less insulitis compared with that of the control groups. The protective effects of MDSCs might be mediated by inducing anergy in autoreactive T cells and the development of CD4(+)CD25(+)Foxp3(+) Tregs. Thist study demonstrates a remarkable capacity of transferred MDSCs to downregulate Ag-specific autoimmune responses and prevent diabetes onset, suggesting that MDSCs possess great potential as a novel cell-based tolerogenic therapy in the control of T1D and other autoimmune diseases.     

Nonhuman primate quarantine: its evolution and practice

Nonhuman primates (NHPs) are imported to the United States for use in research, domestic breeding, and propagation of endangered populations in zoological gardens. During the past 60 years, individuals responsible for NHP importation programs have observed morbidity and mortality typically associated with infectious disease outbreaks. These outbreaks have included infectious agents such as tuberculosis, Herpesvirus sp., simian hemorrhagic fever, and filovirus infections such as the Ebola and Marburg viruses. Some outbreaks have affected both animal and human populations. These epizootics are attributable to a variety of factors, including increased population density, exposure of na?ve populations to new infectious agents, and stress. The practice of quarantining animals arriving in the United States was first applied by individual research programs to improve animal health and ensure the quality of animals entering research programs. The development of government regulations for nonhuman primate quarantine accompanied the recognition that imported NHPs could pose a risk to public health. This article briefly reviews the history of US NHP importation and the factors behind the development of NHP quarantine regulations. The focus is on regulations concerned with infectious disease, public health, and the health of domestic primate colonies. These regulations have had the dual benefit of protecting public health as well as reducing animal morbidity and mortality during importation and quarantine. We review current practices and facilities for nonhuman primate quarantine and identify challenges for the future.     

The effects of diabetes and aminoguanidine treatment on endothelial function in a primate model of type 1 diabetes

Abnormalities of endothelial function have been demonstrated in diabetes and are thought to play a role in the pathogenesis of diabetic complications. The aims of this study were to determine whether aminoguanidine, an inhibitor of glycation, can prevent endothelial and microcirculation abnormalities in a primate model of type 1 diabetes. Male baboons (Papio hamadryas) were assigned to one of the four groups: control, diabetes, control treated with aminoguanidine or diabetes treated with aminoguanidine. Diabetes was induced by streptozocin (60 mg/kg) and treated with once daily injection of insulin. Aminoguanidine was given subcutaneously (10 mg/kg), once a day. Diabetic animals had a mean duration of diabetes of 8.9 +/- 3.4 years and HbA1c of 8.9 +/- 1.1%. Microvascular function was measured by laser Doppler velocimetry, with examination of endothelium-dependent increase in skin blood flow (SkBF) following iontophoresis of acetylcholine (ACh) and endothelium-independent increase in SkBF in response to the nitric oxide (NO) donor sodium nitroprusside (SNP). Multiple regression analysis identified diabetes (P = 0.049) and aminioguanidine treatment (P = 0.026) as significant determinants of ACh response. The diabetic baboons treated with aminoguanidine had less Ach-mediated SkBF response compared with controls (1.39 +/- 0.32 vs. 2.26 +/- 0.61, F = 3.3, P = 0.04), but there was no difference between groups in SkBF response to SNP. We conclude that endothelial dysfunction can be demonstrated in this primate model of type 1 diabetes at a stage when overt diabetic complications are not present. This occurred in the absence of insulin resistance or significant hypercholesterolemia. Administration of aminoguanidine from the onset of diabetes was not able to prevent this abnormality and in fact aggravated the endothelial response. Effects of aminoguanidine on NO synthase may contribute to this phenomenon.     

Nonhuman primates are relevant models for research in hematology, immunology and virology

Nonhuman primates have been used for biomedical research for several decades. They have proved to be models that are relevant to humans because of the high level of gene homology which underlies physiological and biochemical similarities. The similarity of monkeys to humans has been used to investigate pathophysiological mechanisms in hematology, immunology and virology. New therapeutic procedures can be assessed in primates by using materials, in particular pharmacological reagents, and methods designed for humans. The relevance of these models also relies on the use of species-specific pathogens and the availability of recombinant, homologous cytokines. The introduction of more and more sophisticated cell and gene therapy protocols in hematopoietic cell transplantation and immunotherapy requires the development of preclinical trials similar to clinical settings. For several decades now, baboons and cynomolgus/rhesus monkeys have been the most useful primate models in experimental hematology, and this has contributed to numerous therapeutic advances. Primate models of AIDS have been developed to study the pathogenesis, transmission and immune responses to infection, and to test vaccines and drugs. Primate research should be restricted in quantity, and mainly designed with the aim of removing uncertainty as to the safety and clinical benefit to the patient, of new biomedical protocols.