Hepatitis A Virus Infection in Cynomolgus Monkeys Confounds the Safety Evaluation of a Drug Candidate

In a 3-month toxicity study in cynomolgus monkeys at a European contract laboratory, animals were infected with HAV, initially resulting in hepatic injury being incorrectly attributed to the test compound. Elevated serum ALT/AST/GLDH (5- to 10-fold) were noted in individual animals from all groups including controls, with no apparent dose, exposure, or time-related relationship. Liver histopathology revealed minimal to slight inflammatory cell accumulation in periportal zones of most animals, and minimal to slight hepatocyte degeneration/necrosis in 10/42 animals from all groups. As these findings were more pronounced in 6 drug-treated animals, including 2/6 in the low dose group, the draft report concluded: "treatment-related hepatotoxicity at all dose levels precluded determination of a NOAEL." However, the unusual pattern of hepatotoxicity suggested a factor other than drug exposure might have caused the hepatic effects. Therefore, snap-frozen liver samples were tested for hepatitis viruses using a PCR method. Tests for hepatitis B, C, and E virus were negative; however, 20/42 samples were positive for hepatitis A virus (HAV). Infection was strongly associated with increased serum ALT/GLDH, and/or hepatocyte degeneration/necrosis. Re-evaluation of the study in light of these data concluded that the hepatic injury was not drug-related. A subsequent 6-month toxicology study in HAV-vaccinated cynomolgus monkeys confirmed the absence of hepatotoxicity. Identification of HAV infection supported progression of the drug candidate into later clinical trials. Although rarely investigated, subclinical HAV infection has occasionally been reported in laboratory primates, including those used for toxicology studies and it may be more prevalent than the literature indicates.

Pathologic characteristics of infectious diseases in macaque monkeys used in biomedical and toxicologic studies

Nonhuman primates (NHPs), which have many advantages in scientific research and are often the only relevant animals to use in assessing the safety profiles and biological or pharmacological effects of drug candidates, including biologics. In scientific or developmental experiments, the immune systems of animals can be spontaneously compromised possibly due to background infection, experimental procedure-associated stress, poor physical condition, or intended or unintended mechanisms of action of test articles. Under these circumstances, background, incidental, or opportunistic infections can seriously can significantly complicate the interpretation of research results and findings and consequently affect experimental conclusions. Pathologists and toxicologists must understand the clinical manifestations and pathologic features of infectious diseases and the effects of these diseases on animal physiology and experimental results in addition to the spectrum of infectious diseases in healthy NHP colonies. This review provides an overview of the clinical and pathologic characteristics of common viral, bacterial, fungal, and parasitic infectious diseases in NHPs, especially macaque monkeys, as well as methods for definitive diagnosis of these diseases. Opportunistic infections that can occur in the laboratory setting have also been addressed in this review with examples of cases of infection disease manifestation that was observed or influenced during safety assessment studies or under experimental conditions.

Bacterial Genotype, Carrier Risk Factors, and an Antimicrobial Stewardship Approach Relevant to Methicillin-resistant Staphylococcus aureus Prevalence in a Population of Macaques Housed in a Research Facility

Methicillin-resistant Staphylococcus aureus (MRSA) remains a significant problem for human and animal health and can negatively affect the health status of macaques and other nonhuman primates (NHP) in research colonies. However, few publications provide guidance on the prevalence, genotype, or risk factors for macaques with MRSA and even fewer on how to effectively respond to MRSA once identified in a population. After having a clinical case of MRSA in a rhesus macaque, we sought to determine the MRSA carrier prevalence, risk factors, and genotypes of MRSA in a population of research NHPs. Over a 6-wk period in 2015, we collected nasal swabs from 298 NHPs. MRSA was isolated from 28% (n = 83). We then reviewed each macaque's medical record for a variety of variables including animal housing room, sex, age, number of antibiotic courses, number of surgical interventions, and SIV status. Analysis of these data suggests that MRSA carriage is associated with the room location, age of the animal, SIV status, and the number of antibiotic courses. We used multilocus sequence typing and spa typing on a subset of MRSA and MSSA isolates to determine whether the MRSA present in NHPs was comparable with common human strains. Two MRSA sequence types were predominant: ST188 and a novel MRSA genotype, neither of which is a common human isolate in the United States. We subsequently implemented antimicrobial stewardship practices (significantly reducing antimicrobial use) and then resampled the colony in 2018 and found that MRSA carriage had fallen to 9% (26/285). These data suggest that, as in humans, macaques may have a high carrier status of MRSA despite low clinically apparent disease. Implementing strategic antimicrobial stewardship practices resulted in a marked reduction in MRSA carriage in the NHP colony, highlighting the importance of limiting antimicrobial use when possible.

Fungal Rhinosinusitis Caused by a Curvularia sp. Infection in a Female Sumatran Orangutan: A Case Report

Mycotic nasal cavity and paranasal sinus infections in non-human primates (NHPs) are relatively uncommon diseases of the upper respiratory tract. This case study describes the clinical and pathological features as well as the diagnostic techniques and interventions applied to treat the associated disease. A 23-year-old primiparous female Sumatran orangutan residing at Perth Zoo in Western Australia developed intermittent episodes of right-sided epistaxis. An ulcerative nasal mass was identified from a diagnostic endoscopy. The mass was initially biopsied and showed the morphological characteristics of a dematiaceous fungal organism upon a histological examination. There were prominent mucosal and submucosal granulomatous infiltrates containing histocytes, giant cells, and lymphocytes admixed with fewer numbers of neutrophils and eosinophils surrounding the fungal organism. The organism was identified as Curvularia sp. by the fungal characteristics associated with the histopathology, culture growth, and PCR analysis. The mass was subsequently removed with endoscopic sinus surgery (ESS) and the orangutan was medically treated with itraconazole for several months. The recovery was uneventful and the orangutan returned to full health.

Immunosuppression Profile of CFZ533 (Iscalimab), a Non-Depleting Anti-CD40 Antibody, and the Presence of Opportunistic Infections in a Rhesus Monkey Toxicology Study

CFZ533 (iscalimab) is a nondepleting anti-CD40 antibody intended for inhibition of transplant organ rejection and treatment of autoimmune diseases. In a safety assessment in rhesus monkeys, CFZ533 was administered for 13 weeks up to 150 mg/kg/week subcutaneously. CFZ533 was shown previously to completely inhibit primary and secondary T-cell-dependent antibody responses. CD40 is expressed on B cells, antigen-presenting cells, and endothelial and epithelial cells, but is not expressed on T cells. Here, we demonstrate the complete suppression of germinal center formation in lymphoid organs. CFZ533 was well tolerated and did not cause any dose-limiting toxicity. However, the histological evaluation revealed increased numbers of CD4⁺ and CD8⁺ T cells in the T-cell-rich areas of lymph nodes enlarged in response to observed adenovirus and Cryptosporidium infections which suggest that T-cell immune function was unaffected. Background infections appear as the condition leading to unraveling the differential immunosuppressive effects by CFZ533. The presence of T cells at lymph nodes draining sites of infections corroborates the immunosuppressive mechanism, which is different from calcineurin-inhibiting drugs. Furthermore, CFZ533 did not show any hematological or microscopic evidence of thromboembolic events in rhesus monkeys, which were previously shown to respond with thromboembolism to treatment with anti-CD154 antibodies.

Selected Resources for Pathology Evaluation of Nonhuman Primates in Nonclinical Safety Assessment

Humans and nonhuman primates (NHPs) share numerous anatomical and physiological characteristics, thereby explaining the importance of NHPs as essential animal models for translational medicine and nonclinical toxicity testing. Researchers, toxicologic pathologists, toxicologists, and regulatory reviewers must be familiar with normal and abnormal NHP biological traits when designing, performing, and interpreting data sets from NHP studies. The current compilation presents a list of essential books, journal articles, and websites that provide context to safety assessment and research scientists working with NHP models. The resources used most frequently by the authors have been briefly annotated to permit readers to rapidly ascertain their applicability to particular research endeavors. The references are aimed primarily for toxicologic pathologists working with cynomolgus and rhesus macaques and common marmosets in efficacy and safety assessment studies.

International Harmonization of Nomenclature and Diagnostic Criteria (INHAND): Non-proliferative and Proliferative Lesions of the Non-human Primate (M. fascicularis)

The INHAND (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions Project (www.toxpath.org/inhand.asp) is a joint initiative of the Societies of Toxicologic Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP) and North America (STP) to develop an internationally accepted nomenclature for proliferative and nonproliferative lesions in laboratory animals. The purpose of this publication is to provide a standardized nomenclature for classifying microscopic lesions observed in most tissues and organs from the nonhuman primate used in nonclinical safety studies. Some of the lesions are illustrated by color photomicrographs. The standardized nomenclature presented in this document is also available electronically on the internet (http://www.goreni.org/). Sources of material included histopathology databases from government, academia, and industrial laboratories throughout the world. Content includes spontaneous lesions as well as lesions induced by exposure to test materials. Relevant infectious and parasitic lesions are included as well. A widely accepted and utilized international harmonization of nomenclature for lesions in laboratory animals will provide a common language among regulatory and scientific research organizations in different countries and increase and enrich international exchanges of information among toxicologists and pathologists.

Research Relevant Conditions and Pathology in Nonhuman Primates

Biomedical research involving animal models continues to provide important insights into disease pathogenesis and treatment of diseases that impact human health. In particular, nonhuman primates (NHPs) have been used extensively in translational research due to their phylogenetic proximity to humans and similarities to disease pathogenesis and treatment responses as assessed in clinical trials. Microscopic changes in tissues remain a significant endpoint in studies involving these models. Spontaneous, expected (ie, incidental or background) histopathologic changes are commonly encountered and influenced by species, genetic variations, age, and geographical origin of animals, including exposure to infectious or parasitic agents. Often, the background findings confound study-related changes, because numbers of NHPs used in research are limited by animal welfare and other considerations. Moreover, background findings in NHPs can be exacerbated by experimental conditions such as treatment with xenobiotics (eg, infectious morphological changes related to immunosuppressive therapy). This review and summary of research-relevant conditions and pathology in rhesus and cynomolgus macaques, baboons, African green monkeys, common marmosets, tamarins, and squirrel and owl monkeys aims to improve the interpretation and validity of NHP studies.

Phosphatidylinositol 3-Kinase δ Inhibitor-Induced Immunomodulation and Secondary Opportunistic Infection in the Cynomolgus Monkey (Macaca fascicularis)

Phosphatidylinositol 3-kinases (PI3Ks) regulate intracellular signaling events for multiple cell surface receptors. Phosphatidylinositol 3-kinase δ, 1 of 4 class I PI3K isoforms, is primarily found in leukocytes and regulates immune cell functions. Here, we report changes in the immune and digestive systems that were associated with AMG2519493, a highly selective small-molecule PI3Kδ inhibitor. Following 1- or 3-month oral repeat dosing in the cynomolgus monkey, changes were observed in circulating B cells, lymphoid tissues (spleen, lymph nodes, gut-associated lymphoid tissue, tonsil), and the digestive tract. Decreased circulating B cells and lymphoid cellularity in B cell-rich zones in lymphoid tissues were attributed to the intended pharmacologic activity of AMG2519493. Dose- and duration-dependent digestive system toxicity was characterized by inflammation in the large intestine and secondary opportunistic infections restricted to the digestive tract. Digestive tract changes were associated with moribundity and mortality at high-dose levels, and the effect level decreased with increased duration of exposure. These observations demonstrate the role of PI3Kδ in regulation of the immune system and of host resistance to opportunistic infections of the digestive tract.

Biologic Immunomodulatory Drugs and Infection in the Respiratory Tract of Nonhuman Primates

Though rare due to measures and practices to control the risk, infections can occur in research and toxicology studies, especially in nonhuman primates (NHPs) exposed to xenobiotics, particularly immunomodulatory drugs. With such xenobiotics, immunocompromised or immunosuppressed animals will not be able to mount a protective response to infection by an opportunistic pathogen (bacteria, virus, parasite, or fungus) that might otherwise be nonpathogenic and remain clinically asymptomatic in immunocompetent animals. The respiratory tract is one of the most commonly affected systems in clinic, but also in toxicology studies. Pulmonary inflammation will be the main finding associated with opportunistic infections and may cause overt clinical disease with even early sacrifice or death, and may compromise or complicate the pathology evaluation. It is important to properly differentiate the various features of infection, to be aware of the range of possible opportunistic pathogens and how they may impact the interpretation of pathology findings. This review will present the most common bacterial, viral, parasitic, and fungal infections observed in the respiratory tract in NHPs during research and/or toxicology studies.

Epidemiological and molecular characterization of a novel adenovirus of squirrel monkeys after fatal infection during immunosuppression

Adenoviruses are a frequent cause of acute upper respiratory tract infections that can also cause disseminated disease in immunosuppressed patients. We identified a novel adenovirus, squirrel monkey adenovirus 1 (SqMAdV-1), as the cause of fatal infection in an immunocompromised squirrel monkey (Saimiri boliviensis) at the Keeling Center for Comparative Medicine and Research (KCCMR). Sequencing of SqMAdV-1 revealed that it is most closely related (80.4 % pairwise nucleotide identity) to the titi monkey (Plecturocebus cupreus) adenovirus (TMAdV). Although identified in the titi monkey, TMAdV is highly lethal in these monkeys, and they are not thought to be the natural host. While SqMAdV-1 is similar to other primate adenoviruses in size and genomic characteristics, a nucleotide polymorphism at the expected stop codon of the DNA polymerase gene results in a 126 amino acid extension at the carboxy terminus, a feature not previously observed among other primate adenoviruses. PCR testing and partial sequencing of 95 archived faecal samples from other squirrel monkeys (Saimiri boliviensis and Saimiri sciureus) housed at the KCCMR revealed the presence of three distinct, and apparently endemic species of adenoviruses. A grouping of ten squirrel monkey adenovirus variants has high similarity to SqMAdV-1. A single adenovirus variant (designated SqMAdV-3), detected in five monkeys, has similarity to tufted capuchin (Sapajus apella) adenoviruses. The largest group of adenovirus variants detected (designated SqMAdV-2.0-2.16) has very high similarity (93-99 %) to the TMAdV, suggesting that squirrel monkeys may be the natural host of the TMAdV.

Applied Institutional Approaches for the Evaluation and Management of Zoonoses in Contemporary Laboratory Animal Research Facilities

Zoonoses, diseases transmitted between animals and humans, have been a concern in laboratory animal medicine for decades. Exposure to zoonotic organisms not only poses health risks to personnel and research animals but may also affect research integrity. Early laboratory animal programs were ineffective at excluding and preventing transmission of zoonotic diseases: the health status of the animals were often unknown, endemic diseases occurred frequently, housing conditions were less controlled, and veterinary care programs were decentralized. Over time, these conditions improved, but despite this, zoonotic diseases remain a contemporary concern. To reduce the incidence of zoonoses, management should perform an accurate risk assessment that takes into account the type of research performed, animal species used, animal sources, and housing conditions. Specific research practices, such as the use of biological materials, can also affect the risk assessment and should be considered. Once identified, the characteristics of significant zoonotic organisms can be examined. In addition, personnel attitudes and training, facility design and management, equipment availability, personal protective equipment used, standard operating procedures, and the institution’s vermin control program can impact the risk assessment. The effectiveness of the occupational health and safety program at managing risks of zoonoses should also be examined. Risk assessment, in the context of zoonotic disease prevention, is a complex exercise and is most effective when a team approach is used and includes research, husbandry, veterinary, and biosafety personnel.

Bacterial endocarditis and increased cardiac troponin I levels in a brown howler monkey (Alouatta guariba clamitans) with an interventricular septal defect

A brown howler monkey (Alouatta guariba clamitans) was presented with lethargy, hyporexia, cough and heart murmur. The complementary tests and necropsy revealed pleuropneumonia, bacterial endocarditis and interventricular septal defect. To the best of our knowledge, this is the first report of increased cardiac troponin I levels in this species.

Molecular Localization Techniques in the Diagnosis and Characterization of Nonhuman Primate Infectious Diseases

Molecular localization techniques remain important diagnostic and research tools for the pathologist evaluating nonhuman primate tissues. In situ hybridization and immunohistochemistry protocols have been developed for many important pathogens of nonhuman primates, including RNA and DNA viruses, prions, and bacterial, protozoal, and fungal pathogens. Such techniques will remain critical in defining the impact and relevance of novel agents on animal health and disease. A comparative pathology perspective often provides valuable insight to the best strategy for reagent development and can also facilitate interpretation of molecular localization patterns. Such a perspective is grounded in a firm understanding of microbe-host pathobiology. This review summarizes current molecular localization protocols used in the diagnosis of selected primate infectious diseases.

Meeting report: Emerging respiratory viral infections and nonhuman primate case reports

A workshop on Emerging Respiratory Viral Infections and Spontaneous Diseases in nonhuman primates was sponsored by the concurrent Annual Meetings of the American College of Veterinary Pathologists and the American Society for Veterinary Clinical Pathology, held December 1-5, 2012, in Seattle, Washington. The session had platform presentations from Drs Karen Terio, Thijs Kuiken, Guy Boivin, and Robert Palermo that focused on naturally occurring influenza, human respiratory syncytial virus, and metapneumovirus in wild and zoo-housed great apes; the molecular biology and pathology of these viral respiratory diseases in nonhuman primate (NHP) models; and the therapeutic and vaccine approaches to prevention and control of these emerging respiratory viral infections. These formal presentations were followed by presentations of 14 unique case studies of rare or newly observed spontaneous lesions in NHPs (see online files for access to digital whole-slide images corresponding to each case report at http://scanscope.com/ACVP%20Slide%20Seminars/2012/Primate%20Pathology/view.apml). The session was attended by meeting participants that included students, pathology trainees, and experienced pathologists from academia and industry with an interest in respiratory and spontaneous diseases of NHPs.

Men, primates, and germs: an ongoing affair

Humans and nonhuman primates are phylogenetically (i.e., genetically) related and share pathogens that can jump from one species to another. The specific strategies of three groups of pathogens for crossing the species barrier among primates will be discussed. In Africa, gorillas and chimpanzees have succumbed for years to simultaneous epizootics (i.e.. "multi-emergence") of Ebola virus in places where they are in contact with Chiropters, which could be animal reservoirs of these viruses. Human epidemics often follow these major outbreaks. Simian immunodeficiency viruses (SIVs) have an ancient history of coevolution and many interspecific exchanges with their natural hosts. Chimpanzee and gorilla SIVs have crossed the species barrier at different times and places, leading to the emergence of HIV-1 and HIV-2. Other retroviruses, such as the Simian T-Lymphotropic Viruses and Foamiviruses, have also a unique ancient or recent history of crossing the species barrier. The identification of gorilla Plasmodium parasites that are genetically close to P. falciparum suggests that gorillas were the source of the deadly human P. falciparum. Nonhuman plasmodium species that can infect humans represent an underestimated risk.

Mucocutaneous candidiasis in a mandrill (Mandrillus sphinx)

An adult male mandrill (Mandrillus sphinx) suffered from chronic ulceration of the facial and gluteal skin and the oral and nasal mucosa. The ulcers were resistant to therapy and led to deterioration in the general condition of the animal. Microscopical examination revealed a severe, chronic, multifocal, granulomatous and eosinophilic dermatitis and panniculitis. There was also stomatitis and rhinitis with numerous intralesional fungal elements. These organisms were identified by immunohistochemistry, transmission electron microscopy, polymerase chain reaction and fungal culture as Candida albicans. Species identification was confirmed by MALDI-TOF mass spectrometry. A specific predisposing immunosuppressive factor for the deep chronic mucocutaneous candidiasis was not identified; however, social stress and/or a primary defect in cell-mediated immunity could not be excluded as possible causes for a predisposing immunodeficiency in the animal.

Specific pathogen-free status alters immunophenotype in rhesus macaques: implications for the study of simian immunodeficiency virus

The repertoire of viruses to which research primates are exposed, even in the absence of clinical disease, may contribute to experimental confounding. In this study we examined whether standard specific pathogen-free (SPF) rhesus macaques exposed to a wider spectrum of enzootic viruses and expanded SPF macaques derived to exclude a greater number of viral agents would display alterations in immune activation or immune cell populations. Given the impact of immunophenotype on human immunodeficiency virus (HIV) progression and the importance of the simian immunodeficiency virus (SIV) model for the study of HIV pathogenesis, we elected to additionally examine the impact of SPF status on the capacity of peripheral blood mononuclear cells (PBMCs) to support SIV replication. The expanded SPF group displayed significant immune alterations including increased serum interleukin (IL)-15 and a greater in vitro elaboration of GM-CSF, IL1ra, VEGF, IL-10, IL12/23, and MIP-1b. Consistent with reduced viral antigenic exposure in expanded SPF macaques, decreased CD4(+) and CD8(+) transitional and effector memory (T(EM)) cell populations were observed. Expanded SPF PBMC cultures also demonstrated an increased peak (192.61 ng/ml p27) and area under the curve in in vitro SIV production (1968.64 ng/ml p27) when compared to standard SPF macaques (99.32 ng/ml p27; p=0.03 and 915.17 ng/ml p27; p=0.03, respectively). In vitro SIV replication did not correlate with CD4(+) T(EM) cell counts but was highly correlated with serum IL-15 in the subset of animals examined. Findings suggest that an altered immunophenotype associated with the maintenance of primates under differing levels of bioexclusion has the potential to impact the outcome of SIV studies and models for which the measurement of immunologic endpoints is critical.

Laboratory diagnosis of malaria in nonhuman primates

Nonhuman primates (NHPs) are commonly used for biomedical research because of the high level of gene homology that underlies physiologic similarity to human beings. Malaria parasites of the genus Plasmodium cause one of the most frequent parasitic diseases of NHPs originating from tropical and subtropical areas and as such represent a significant research confounder. Malaria in NHPs presents a diagnostic challenge especially to those laboratories that see no more than a few malaria cases per year in NHPs. The accurate and timely diagnosis of malaria infection in NHPs facilitates the appropriate treatment of individuals infected with the malaria parasites. Conventional microscopy based on the examination of Giemsa-stained thick and thin blood films remains the mainstay of laboratory diagnosis of malaria infection because of the high diagnostic sensitivity and specificity and also the capability for Plasmodium species identification and parasite counts. This procedure is recognized as technically difficult and time-consuming, requiring considerable training to obtain the necessary skills. In the past few years, efforts to replace the traditional but tedious reading of blood films have led to different techniques for the detection of malaria parasites, including fluorescence microscopy, detection of intraleukocytic hemozoin or malaria pigment using automated blood cell analyzers, immunochromatographic rapid diagnostic tests based on malaria antigen detection, and PCR assays. These techniques offer new approaches for diagnosing malaria in NHPs. This review focuses on the available laboratory diagnostic tools for malaria in NHPs.

Emerging and reemerging infectious diseases of nonhuman primates in the laboratory setting

Despite numerous advances in the diagnosis and control of infectious diseases of nonhuman primates in the laboratory setting, a number of infectious agents continue to plague colonies. Some, such as measles virus and Mycobacterium tuberculosis, cause sporadic outbreaks despite well-established biosecurity protocols, whereas others, such as retroperitoneal fibromatosis-associated herpesvirus, have only recently been discovered, often as a result of immunosuppressive experimental manipulation. Owing to the unique social housing requirements of nonhuman primates, importation of foreign-bred animals, and lack of antemortem diagnostic assays for many new diseases, elimination of these agents is often difficult or impractical. Recognition of these diseases is therefore essential because of their confounding effects on experimental data, impact on colony health, and potential for zoonotic transmission. This review summarizes the relevant pathology and pathogenesis of emerging and reemerging infectious diseases of laboratory nonhuman primates.

Overview of known non-human primate pathogens with potential to affect colonies used for toxicity testing

The increased demand for non-human primates (NHPs) in biomedical research has resulted in alternative sources of animals being used, which has allowed for importation of animals with varying background incidences of bacterial, viral, parasitic, and fungal pathogens. This can be of minimal consequence when animals from different sources are kept isolated. However, when NHPs from different sources with varying incidences of primary and opportunistic pathogens are mixed, there can be a rapid spread of these pathogens and an increase in the seroconversion of susceptible animals. If this process occurs during the conduct of a study, interpretation of that study can be confounded. Furthermore, NHPs imported from areas enzootic for pathogens such as Plasmodium or with high incidences of human diseases such as measles and tuberculosis can introduce diseases that can be a threat to colony health, have zoonotic risk, and can severely impact study outcome. Thus, knowledge of the common primary and opportunistic NHP infections, as well as reemerging pathogens, enables the toxicologist to use information on disease status for pre-study animal selection and intelligent study design. This is particularly important when immunomodulatory compounds are being investigated. Moreover, the toxicologic pathologist well versed in the common spontaneous infections, opportunistic pathogens, and background lesions in NHPs is able to assess possible drug-related effects in drug safety studies. This review identifies the common primary and opportunistic pathogens, as well as newly emerging infections of NHPs, that can directly or indirectly affect colony health and the interpretation of drug safety studies.

Simian retroviruses: infection and disease--implications for immunotoxicology research in primates

Non-human primates have assumed an important role in preclinical safety assessment studies, particularly in the evaluation of biopharmaceutical and immunomodulatory therapies. Naturally occurring simian retrovirus infections may adversely affect the suitability of primates for use in such studies. Various species of non-human primates are the natural hosts for six exogenous retroviruses, representing five genera within the family Retroviridae. Retroviruses establish persistent infections with a broad spectrum of pathogenic potential, ranging from nonpathogenic to highly pathogenic, depending on the variety of the host, virus, and environmental factors. In the context of immunotoxicology, in which the research objective is to specifically evaluate the effect of drugs or biologics on the immune system, the immune modulatory effects of simian retroviruses, which may be subtle or profound, may introduce significant confounding into the studies of immunotoxic effects utilizing non-human primates. Latent or subclinical retrovirus infections are common and research-related procedures may lead to virus reactivation or overt disease. Adverse effects of undetected retrovirus infections on preclinical research include the loss of experimental subjects (and potentially of statistical power) due to increased morbidity and mortality, virus-induced clinical abnormalities, histologic lesions, alteration of physiologic parameters and biologic responses, and interference with in vitro assays and/or cytolytic destruction of primary cell cultures. The aim of this review is to provide an overview of the key biological, clinical, and pathological features of several important simian retroviruses, with emphasis on viruses infecting macaques and other primate species commonly used in preclinical research, and a discussion of the implications of these infections for immunotoxicology and other preclinical research in primates. Adequate pre-study retrovirus screening is essential to exclude retrovirus-infected primates from research protocols.

Opportunistic infections in non-human primates exposed to immunomodulatory biotherapeutics: considerations and case examples

Immunomodulatory biotherapeutics are most often evaluated for safety preclinically by way of repeat dose toxicity studies in non-human primates. Since immunomodulation is expected with this class of therapeutics, and since non-human primates share many opportunistic or latent infectious agents with humans, non-human primates in these toxicity studies may present with opportunistic or recrudescent infections that would be of concern if they occurred clinically in humans. In such instances, it is suggested that non-clinical safety assessment scientists consider a series of key questions that aim to clarify the relationship of the findings to the biotherapeutic under study and the expected predictivity of the findings to the human clinical setting. In this review, relevant case examples are considered comprising (i) gammaherpesviruses-mediated B-lymphocyte proliferation associated with a T-lymphocyte depleting fusion protein; (ii) increased plasmodial hemoparasite burdens associated with a monoclonal antibody inhibitory to T-lymphocyte trafficking and macrophage function, and (iii) the expected predictivity of non-human primate models for the occurrence of encephalic polyomavirus infections.

Bacterial infections in cynomolgus monkeys given small molecule immunomodulatory antagonists

Opportunistic infections (OIs) during the course of non-clinical toxicity studies can serve as a clinical indicator of immunosuppression. In monkeys, severity may be magnified since the possibility for fecal-oral and cage-to-cage transmission of bacteria exists, reserve capacity is low, and clinical signs of infection are not easily detected until the infectious process is well underway. This review summarizes a case study presented at the HESI-ILSI ITC-Sponsored workshop on Naturally Occurring Infections in Non-human Primates and Immunotoxicity Implications. It gives an overview on the impact of bacterial infections in monkeys on the development and regulatory assessment of three closely-related representative small molecule immunomodulatory (anti-inflammatory) drug candidates all inhibiting the same drug target. The infections, which sometimes progressed to bacteremia and death, originally manifested in the skin, upper respiratory tract, gastrointestinal tract, and less frequently as soft tissue abscesses. Infections were sporadic and not observed in all studies despite coverage of equivalent or higher systemic exposures or longer durations of treatment. To address concerns regarding inconsistency in the presentation and type of findings and their potential relationship to infection, steps were taken to identify causative agents (via culture, microscopy), implement various intervention and treatment regimens (supportive care, antibiotics, drug holiday), demonstrate reversibility of clinical and immune effects, and study major immune components/mechanisms affected (cytokine/stress protein profiling, immune cell phenotyping, and humoral/innate immune cell function tests). Appropriate diagnosis and characterization of the infection was critical to discrimination of these findings as a secondary pharmacologic effect rather than a direct drug-related target organ effect, and also guided clinical protocol design and regulatory acceptance.

Carcinogenicity assessments of biotechnology-derived pharmaceuticals: a review of approved molecules and best practice recommendations

An important safety consideration for developing new therapeutics is assessing the potential that the therapy will increase the risk of cancer. For biotherapeutics, traditional two-year rodent bioassays are often not scientifically applicable or feasible. This paper is a collaborative effort of industry toxicologists to review past and current practice regarding carcinogenicity assessments of biotherapeutics and to provide recommendations. Publicly available information on eighty marketed protein biotherapeutics was reviewed. In this review, no assessments related to carcinogenicity or tumor growth promotion were identified for fifty-one of the eighty molecules. For the twenty-nine biotherapeutics in which assessments related to carcinogenicity were identified, various experimental approaches were employed. This review also discusses several key principles to aid in the assessment of carcinogenic potential, including (1) careful consideration of mechanism of action to identify theoretical risks, (2) careful investigation of existing data for indications of proliferative or immunosuppressive potential, and (3) characterization of any proliferative or immunosuppressive signals detected. Traditional two-year carcinogenicity assays should not be considered as the default method for assessing the carcinogenicity potential of biotherapeutics. If experimentation is considered warranted, it should be hypothesis driven and may include a variety of experimental models. Ultimately, it is important that preclinical data provide useful guidance in product labeling.

Impact of infections and normal flora in nonhuman primates on drug development

Preclinical safety studies that are required for the marketing approval of a pharmaceutical include single and repeat dose studies in rodent and nonrodent species. The use of nonhuman primates (NHPs), primarily macaques, as the nonrodent species has increased in recent years, in part due to the increase in development of biopharmaceuticals and immunomodulatory agents. Depending on the source of the macaques, they may vary in genetic background, normal flora, and/or the incidence of preexisting pathogens and inflammatory conditions. As the use of alternative sources of macaques rises to meet the increased demand for these animals in biomedical research, the toxicologic pathologist should be well versed in NHP pathology to adequately assess potential drug-related effects in the context of these variations. Such knowledge is particularly important in studies involving immunomodulatory drugs as the toxicologic pathologist should anticipate which type(s) of infections are most likely to arise depending on which arm of the immune system is modulated. The purpose of this review is to discuss the immunosuppressive (e.g., simian type D retrovirus, simian immunodeficiency virus) and opportunistic viruses (e.g., cytomegalovirus, adenovirus, simian virus 40, rhesus rhadinovirus, and lymphocryptovirus), primary and opportunistic bacteria (e.g., Campylobacter spp., Shigella flexneri, Yersinia enterocolitica, Moraxella catarrhalis, Mycobacterium avium complex, enteropathogenic Escherichia coli), and parasites (e.g., Plasmodium spp., Schistosoma spp., Strongyloides fulleborni) that have had the most profound impact on the interpretation of drug safety studies and/or that may reemerge as alternative sources of NHPs are used for drug safety studies.