The Baboon (Papio spp.) as a model of human Ebola virus infection

Utilizing non-human primate models to combat recent COVID-19/SARS-CoV-2 and viral infectious disease outbreaks

In recent times, global viral outbreaks and diseases, such as COVID-19 (SARS-CoV-2), Zika (ZIKV), monkeypox (MPOX), Ebola (EBOV), and Marburg (MARV), have been extensively documented. Swiftly deciphering the mechanisms underlying disease pathogenesis and devising vaccines or therapeutic interventions to curtail these outbreaks stand as paramount imperatives. Amidst these endeavors, animal models emerge as pivotal tools. Among these models, non-human primates (NHPs) hold a position of particular importance. Their proximity in evolutionary lineage and physiological resemblances to humans render them a primary model for comprehending human viral infections. This review encapsulates the pivotal role of various NHP species-such as rhesus macaques (Macaca mulatta), cynomolgus macaques (Macaca fascicularis), african green monkeys (Chlorocebus sabaeus/aethiops), pigtailed macaques (Macaca nemestrina/Macaca leonina), baboons (Papio hamadryas/Papio anubis), and common marmosets (Callithrix jacchus)-in investigations pertaining to the abovementioned viral outbreaks. These NHP models play a pivotal role in illuminating key aspects of disease dynamics, facilitating the development of effective countermeasures, and contributing significantly to our overall understanding of viral pathogenesis.

Filoviruses: Scientific Gaps and Prototype Pathogen Recommendation

Viruses in the family Filoviridae, including the commonly known Ebola (EBOV) and Marburg (MARV) viruses, can cause severe hemorrhagic fever in humans and nonhuman primates. Sporadic outbreaks of filovirus disease occur in sub-Saharan Africa with reported case fatality rates ranging from 25% to 90%. The high mortality and increasing frequency and magnitude of recent outbreaks along with the increased potential for spread from rural to urban areas highlight the importance of pandemic preparedness for these viruses. Despite their designation as high-priority pathogens, numerous scientific gaps exist in critical areas. In this review, these gaps and an assessment of potential prototype pathogen candidates are presented for this important virus family.

Zebrafish-based platform for emerging bio-contaminants and virus inactivation research

Emerging bio-contaminants such as viruses have affected health and environment settings of every country. Viruses are the minuscule entities resulting in severe contagious diseases like SARS, MERS, Ebola, and avian influenza. Recent epidemic like the SARS-CoV-2, the virus has undergone mutations strengthen them and allowing to escape from the remedies. Comprehensive knowledge of viruses is essential for the development of targeted therapeutic and vaccination treatments. Animal models mimicking human biology like non-human primates, rats, mice, and rabbits offer competitive advantage to assess risk of viral infections, chemical toxins, nanoparticles, and microbes. However, their economic maintenance has always been an issue. Furthermore, the redundancy of experimental results due to aforementioned aspects is also in examine. Hence, exploration for the alternative animal models is crucial for risk assessments. The current review examines zebrafish traits and explores the possibilities to monitor emerging bio-contaminants. Additionally, a comprehensive picture of the bio contaminant and virus particle invasion and abatement mechanisms in zebrafish and human cells is presented. Moreover, a zebrafish model to investigate the emerging viruses such as coronaviridae and poxviridae has been suggested.

Molecular Approaches for the Validation of the Baboon as a Nonhuman Primate Model for the Study of Zika Virus Infection

Nonhuman primates (NHP) are particularly important for modeling infections with viruses that do not naturally replicate in rodent cells. Zika virus (ZIKV) has been responsible for sporadic epidemics, but in 2015 a disseminated outbreak of ZIKV resulted in the World Health Organization declaring it a global health emergency. Since the advent of this last epidemic, several NHP species, including the baboon, have been utilized for modeling and understanding the complications of ZIKV infection in humans; several health issues related to the outcome of infection have not been resolved yet and require further investigation. This study was designed to validate, in baboons, the molecular signatures that have previously been identified in ZIKV-infected humans and macaque models. We performed a comprehensive molecular analysis of baboons during acute ZIKV infection, including flow cytometry, cytokine, immunological, and transcriptomic analyses. We show here that, similar to most human cases, ZIKV infection of male baboons tends to be subclinical, but is associated with a rapid and transient antiviral interferon-based response signature that induces a detectable humoral and cell-mediated immune response. This immunity against the virus protects animals from challenge with a divergent ZIKV strain, as evidenced by undetectable viremia but clear anamnestic responses. These results provide additional support for the use of baboons as an alternative animal model to macaques and validate omic techniques that could help identify the molecular basis of complications associated with ZIKV infections in humans.

Comparative Analysis of Cellular Immune Responses in Conventional and SPF Olive Baboons (Papio anubis)

Olive baboons (P. anubis) have provided a useful model of human diseases and conditions, including cardiac, respiratory, and infectious diseases; diabetes; and involving genetics, immunology, aging, and xenotransplantation. The development of a immunologically defined SPF baboons has advanced research further, especially for studies involving the immune system and immunosuppression. In this study, we compare normal immunologic changes of PBMC subsets, and their function in age-matched conventional and SPF baboons. Our results revealed that both groups have comparable numbers of different lymphocyte subsets, but phenotypic differences in central and effector memory T-cell subsets are more pronounced in CD4+ T cells. Despite equal proportions of CD3+ T cells among the conventional and SPF baboons, PBMC from the conventional group showed greater proliferative responses to phytohemagglutinin and pokeweed mitogen and higher numbers of IFNγ-producing cells after stimulation with concanavalin A or pokeweed mitogen, whereas plasma levels of the inflammatory cytokine TNFα were significantly higher in SPF baboons. Exposure of PBMC from conventional baboons to various Toll-like (TLR) ligands, including TLR3, TLR4, and TLR8, yielded increased numbers of IFNγ producing cells, whereas PBMC from SPF baboons stimulated with TLR5 or TLR6 ligand had more IFNγ-producing cells. These findings suggest that although lymphocyte subsets share many phenotypic and functional similarities in conventional and SPF baboons, specific differences in the immune function of lymphocytes could differentially influence the quality and quantity of their innate and adaptive immune responses. These differences should be considered in interpreting experimental outcomes, specifically in studies measuring immunologic endpoints.

Characterization of Ebola Virus Disease (EVD) in Rhesus Monkeys for Development of EVD Therapeutics

Recent Ebola virus (EBOV) outbreaks in West Africa and the Democratic Republic of the Congo have highlighted the urgent need for approval of medical countermeasures for treatment and prevention of EBOV disease (EVD). Until recently, when successes were achieved in characterizing the efficacy of multiple experimental EVD therapeutics in humans, the only feasible way to obtain data regarding potential clinical benefits of candidate therapeutics was by conducting well-controlled animal studies. Nonclinical studies are likely to continue to be important tools for screening and development of new candidates with improved pharmacological properties. Here, we describe a natural history study to characterize the time course and order of progression of the disease manifestations of EVD in rhesus monkeys. In 12 rhesus monkeys exposed by the intramuscular route to 1000 plaque-forming units of EBOV, multiple endpoints were monitored for 28 days following exposure. The disease progressed rapidly with mortality events occurring 7–10 days after exposure. Key disease manifestations observed consistently across the infected animals included, but were not limited to, viremia, fever, systemic inflammation, coagulopathy, lymphocytolysis, renal tubular necrosis with mineralization, and hepatocellular degeneration and necrosis.

Optimization of culture conditions for the derivation and propagation of baboon (Papio anubis) induced pluripotent stem cells

Induced pluripotent stem cells (iPSCs) offer the possibility of cell replacement therapies using patient-matched cells to treat otherwise intractable diseases and debilitations. To successfully realize this potential, several factors must be optimized including i) selection of the appropriate cell type and numbers to transplant, ii) determination of the means of transplantation and the location into which the transplanted cells should be delivered, and iii) demonstration of the safety and efficacy of the cell replacement protocol to mitigate each targeted disease state. A majority of diseases or debilitations likely to be targeted by cell-based therapeutic approaches represent complex conditions or physiologies manifest predominantly in primates including humans. Nonhuman primates afford the most clinically relevant model system for biomedical studies and testing of cell-based therapies. Baboons have 92% genomic similarity with humans overall and especially significant similarities in their immunogenetic system, rendering this species a particularly valuable model for testing procedures involving cell transplants into living individuals. To maximize the utility of the baboon model, standardized protocols must be developed for the derivation of induced pluripotent stem cells from living adults and the long-term maintenance of these cells in culture. Here we tested four commercially available culture systems (ReproFF, mTeSR1, E8 and Pluristem) for competence to maintain baboon iPSCs in a pluripotent state over multiple passages, and to support the derivation of new lines of baboon iPSCs. Of these four media only Pluristem was able to maintain baboon pluripotency as assessed by morphological characteristics, immunocytochemistry and RT-qPCR. Pluristem also facilitated the derivation of new lines of iPSCs from adult baboon somatic cells, which had previously not been accomplished. We derived multiple iPS cell lines from adult baboon peripheral blood mononuclear cells cultured in Pluristem. These were validated by expression of the pluripotency markers OCT4, NANOG, SOX2, SSEA4 and TRA181, as well as the ability to differentiate into tissues from all three germ layers when injected into immunocompromised mice. These findings further advance the utility of the baboon as an ideal preclinical model system for optimizing iPS cell-based, patient-specific replacement therapies in humans.

Apnea induction for invasive lung function testing in infant olive baboons: Comparison of intravenous propofol versus hyperventilation

BACKGROUND

In various types of pulmonary research, pulmonary function testing (PFT) is performed to quantify the severity of lung disease. Induction of apnea and positive pressure ventilation are required for accurate PFT measurements in non-cooperative subjects. We compared two methods of apnea induction in infant olive baboons (Papio anubis).

METHODS

Pulmonary function testing results were compared during apnea induced by hyperventilation (CO₂ washout) vs. intravenous propofol (1 dose 10 mg/kg). PFT was evaluated using a hot-wire pneumotachometer incorporated within an Avea ventilator in nine 1-month-old baboons.

RESULTS

Propofol induced apnea faster and more reliably. In both groups, PFT values passed the statistical equivalence test and were not significantly different (Student's t-test). There was a trend toward less data variability after propofol administration.

CONCLUSIONS

Intravenous propofol was non-inferior to CO₂ washout for apnea induction in infant olive baboons. Propofol induced apnea faster and more reliably and yielded less variable PFT results.

Assessment of listing and categorisation of animal diseases within the framework of the Animal Health Law (Regulation (EU) No 2016/429): Ebola virus disease

Ebola virus disease has been assessed according to the criteria of the Animal Health Law (AHL), in particular criteria of Article 7 on disease profile and impacts, Article 5 on the eligibility of Ebola virus disease to be listed, Article 9 for the categorisation of Ebola virus disease according to disease prevention and control rules as in Annex IV and Article 8 on the list of animal species related to Ebola virus disease. The assessment has been performed following a methodology composed of information collection and compilation, expert judgement on each criterion at individual and, if no consensus was reached before, also at collective level. The output is composed of the categorical answer, and for the questions where no consensus was reached, the different supporting views are reported. Details on the methodology used for this assessment are explained in a separate opinion. According to the assessment performed, Ebola virus disease can be considered eligible to be listed for Union intervention as laid down in Article 5(3) of the AHL. The disease would comply with the criteria as in Sections 4 and 5 of Annex IV of the AHL, for the application of the disease prevention and control rules referred to in points (d) and (e) of Article 9(1). The animal species to be listed for Ebola virus disease according to Article 8(3) criteria are some species of non‐human primates, pigs and rodents as susceptible species and some species of fruit bats as reservoir, as indicated in the present opinion.

Animal Models of Ebolavirus Infection

Ebola virus is a highly pathogenic member of the family Filoviridae that causes a severe hemorrhagic disease in humans and NHP. The 2013-2016 West African outbreak has increased interest in the development and refinement of animal models of Ebola virus disease. These models are used to test countermeasures and vaccines, gain scientific insights into the mechanisms of disease progression and transmission, and study key correlates of immunology. Ebola virus is classified as a BSL4 pathogen and Category A agent, for which the United States government requires preparedness in case of bioterrorism. Rodents, such as Syrian golden hamsters (Mesocricetus auratus), mice (Mus musculus), and guinea pigs (Cavia porcellus), are the most common research species. However, NHP, especially macaques, are favored for Ebola virus disease research due to similarities with humans regarding the pathogenesis, clinical presentation, laboratory findings, and causes of fatality. To satisfy the regulatory requirements for approval of countermeasures against high-consequence pathogens, the FDA instituted the Animal Rule, which permits efficacy studies in animal models in place of human clinical data when such studies are not feasible or ethical. This review provides a comprehensive summary of various animal models and their use in Ebola virus disease research.

Differentiation and Characterization of Dopaminergic Neurons From Baboon Induced Pluripotent Stem Cells

: The progressive death of dopamine producing neurons in the substantia nigra pars compacta is the principal cause of symptoms of Parkinson's disease (PD). Stem cells have potential therapeutic use in replacing these cells and restoring function. To facilitate development of this approach, we sought to establish a preclinical model based on a large nonhuman primate for testing the efficacy and safety of stem cell-based transplantation. To this end, we differentiated baboon fibroblast-derived induced pluripotent stem cells (biPSCs) into dopaminergic neurons with the application of specific morphogens and growth factors. We confirmed that biPSC-derived dopaminergic neurons resemble those found in the human midbrain based on cell type-specific expression of dopamine markers TH and GIRK2. Using the reverse transcriptase quantitative polymerase chain reaction, we also showed that biPSC-derived dopaminergic neurons express PAX6, FOXA2, LMX1A, NURR1, and TH genes characteristic of this cell type in vivo. We used perforated patch-clamp electrophysiology to demonstrate that biPSC-derived dopaminergic neurons fired spontaneous rhythmic action potentials and high-frequency action potentials with spike frequency adaption upon injection of depolarizing current. Finally, we showed that biPSC-derived neurons released catecholamines in response to electrical stimulation. These results demonstrate the utility of the baboon model for testing and optimizing the efficacy and safety of stem cell-based therapeutic approaches for the treatment of PD.

SIGNIFICANCE

Functional dopamine neurons were produced from baboon induced pluripotent stem cells, and their properties were compared to baboon midbrain cells in vivo. The baboon has advantages as a clinically relevant model in which to optimize the efficacy and safety of stem cell-based therapies for neurodegenerative diseases, such as Parkinson's disease. Baboons possess crucial neuroanatomical and immunological similarities to humans, and baboon pluripotent stem cells can be differentiated into functional neurons that mimic those in the human brain, thus laying the foundation for the utility of the baboon model for evaluating stem cell therapies.

Ebola virus disease and the veterinary perspective

Ebola virus disease (EVD) is a potentially fatal haemorrhagic disease of humans. The last and most serious outbreak of Ebola virus (EBOV) started in December 2013 in West Africa and also affected other continents. Animals such as fruit bats and non-human primates are potential sources of EBOV. This review highlights the clinical features of EVD in humans and animals and addresses the public health implications of EVD outbreaks from the veterinary perspective.

Animal models for ebolavirus countermeasures discovery: what defines a useful model?

INTRODUCTION

Ebolaviruses are highly pathogenic filoviruses, which cause disease in humans and nonhuman primates (NHP) in Africa. The Zaire ebolavirus outbreak in 2014, which continues to greatly affect Western Africa and other countries to which the hemorrhagic fever was exported due to travel of unsymptomatic yet infected individuals, was complicated by the lack of available licensed vaccines or therapeutics to combat infection. After almost a year of research at an increased pace to find and test vaccines and therapeutics, there is now a deeper understanding of the available disease models for ebolavirus infection. Demonstration of vaccine or therapeutic efficacy in NHP models of ebolavirus infection is crucial to the development and eventual licensure of ebolavirus medical countermeasures, so that safe and effective countermeasures can be accelerated into human clinical trials.

AREAS COVERED

The authors describe ebolavirus hemorrhagic fever (EHF) disease in various animal species: mice, guinea pigs, hamsters, pigs and NHP, to include baboons, marmosets, rhesus and cynomolgus macaques, as well as African green monkeys. Because the NHP models are supremely useful for therapeutics and vaccine testing, emphasis is placed on comparison of these models, and their use as gold-standard models of EHF.

EXPERT OPINION

Animal models of EHF varying from rodents to NHP species are currently under evaluation for their reproducibility and utility for modeling infection in humans. Complete development and licensure of therapeutic agents and vaccines will require demonstration that mechanisms conferring protection in NHP models of infection are predictive of protective responses in humans, for a given countermeasure.

[Haemostasis dysregulation in filovirus infections]

Filoviruses are responsible for highly lethal infections. Those viruses are found in intertropical areas of Africa and Asia where they circulate in their supposed natural reservoir, fruit bats. During filovirus outbreaks and depending on the strains, various modifications in hemostasis have been observed in patients. The disseminated intravascular coagulation identified in these infections is multicausal and involves both viral factors and abnormal physiological responses. In this review we will describe the mechanisms responsible for these disturbances and we will highlight some aspects of the basis of filovirus high pathogenicity.

Animal models of viral hemorrhagic fever

The term "viral hemorrhagic fever" (VHF) designates a syndrome of acute febrile illness, increased vascular permeability and coagulation defects which often progresses to bleeding and shock and may be fatal in a significant percentage of cases. The causative agents are some 20 different RNA viruses in the families Arenaviridae, Bunyaviridae, Filoviridae and Flaviviridae, which are maintained in a variety of animal species and are transferred to humans through direct or indirect contact or by an arthropod vector. Except for dengue, which is transmitted among humans by mosquitoes, the geographic distribution of each type of VHF is determined by the range of its animal reservoir. Treatments are available for Argentine HF and Lassa fever, but no approved countermeasures have been developed against other types of VHF. The development of effective interventions is hindered by the sporadic nature of most infections and their occurrence in geographic regions with limited medical resources. Laboratory animal models that faithfully reproduce human disease are therefore essential for the evaluation of potential vaccines and therapeutics. The goal of this review is to highlight the current status of animal models that can be used to study the pathogenesis of VHF and test new countermeasures.

Acellular pertussis vaccines protect against disease but fail to prevent infection and transmission in a nonhuman primate model

Pertussis is a highly contagious respiratory illness caused by the bacterial pathogen Bordetella pertussis. Pertussis rates in the United States have been rising and reached a 50-y high of 42,000 cases in 2012. Although pertussis resurgence is not completely understood, we hypothesize that current acellular pertussis (aP) vaccines fail to prevent colonization and transmission. To test our hypothesis, infant baboons were vaccinated at 2, 4, and 6 mo of age with aP or whole-cell pertussis (wP) vaccines and challenged with B. pertussis at 7 mo. Infection was followed by quantifying colonization in nasopharyngeal washes and monitoring leukocytosis and symptoms. Baboons vaccinated with aP were protected from severe pertussis-associated symptoms but not from colonization, did not clear the infection faster than naïve animals, and readily transmitted B. pertussis to unvaccinated contacts. Vaccination with wP induced a more rapid clearance compared with naïve and aP-vaccinated animals. By comparison, previously infected animals were not colonized upon secondary infection. Although all vaccinated and previously infected animals had robust serum antibody responses, we found key differences in T-cell immunity. Previously infected animals and wP-vaccinated animals possess strong B. pertussis-specific T helper 17 (Th17) memory and Th1 memory, whereas aP vaccination induced a Th1/Th2 response instead. The observation that aP, which induces an immune response mismatched to that induced by natural infection, fails to prevent colonization or transmission provides a plausible explanation for the resurgence of pertussis and suggests that optimal control of pertussis will require the development of improved vaccines.

Olive baboons: a non-human primate model for testing dengue virus type 2 replication

OBJECTIVE

This study evaluated the use of a non-human primate, the olive baboon (Papio anubis), as a model of dengue infection. Olive baboons closely resemble humans genetically and physiologically and have been used extensively for assessing novel vaccine formulations.

METHODS

Two doses of dengue virus type 2 (DENV-2) were tested in baboons: 10(3) and 10(4) pfu. Similarly, African green monkeys received the same quantity of virus and acted as positive controls.

RESULTS

Following exposure, high levels of viremia were detected in both animal species. There was a trend to detect more days of viremia and more homogeneous viral titers in animals receiving the low viral dose. In addition, baboons infected with the virus generally exhibited positive virus isolation 1 day later than African green monkeys. Humoral responses consisting of antiviral and neutralizing antibodies were detected in all animals after infection.

CONCLUSIONS

We conclude that baboons provide an alternative non-human primate species for experimental DENV-2 infection and we recommend their use for further tests of vaccines, administering the lowest dose assayed: 10(3) pfu.