Quantification of regional aerosol deposition patterns as a function of aerodynamic particle size in rhesus macaques using PET/CT imaging

Influence of mesh nebulizer characteristics on aerosol delivery in non-human primates

Non-Human Primates (NHPs) are particularly relevant for preclinical studies during the development of inhaled biologics. However, aerosol inhalation in NHPs is difficult to evaluate due to a low lung deposition fraction and high variability. The objective of this study was to evaluate the influence of mesh nebulizer parameters to improve lung deposition in macaques. We developed a humidified heated and ventilated anatomical 3D printed macaque model of the upper respiratory tract to reduce experiments with animals. The model was compared to in vivo deposition using 2D planar scintigraphy imaging in NHPs and demonstrated good predictivity. Next, the anatomical model was used to evaluate the position of the nebulizer on the mask, the aerosol particle size and the aerosol flow rate on the lung deposition. We showed that placing the mesh-nebulizer in the upper part of the mask and in proximal position to the NHP improved lung delivery prediction. The lower the aerosol size and the lower the aerosol flow rate, the better the predicted aerosol deposition. In particular, for 4.3 ± 0.1 µm in terms of volume mean diameter, we obtained 5.6 % ± 0.2 % % vs 19.2 % ± 2.5 % deposition in the lung model for an aerosol flow rate of 0.4 mL/min vs 0.03 mL/min and achieved 16 % of the nebulizer charge deposited in the lungs of macaques. Despite the improvement of lung deposition efficiency in macaques, its variability remained high (6-21 %).

Refined semi-lethal aerosol H5N1 influenza model in cynomolgus macaques for evaluation of medical countermeasures

Highly pathogenic avian influenza A H5N1 viruses cause high mortality in humans and have pandemic potential. Effective vaccines and treatments against this threat are urgently needed. Here, we have refined our previously established model of lethal H5N1 infection in cynomolgus macaques. An inhaled aerosol virus dose of 5.1 log10 plaque-forming unit (pfu) induced a strong febrile response and acute respiratory disease, with four out of six macaques succumbing after challenge. Vaccination with three doses of adjuvanted seasonal quadrivalent influenza vaccine elicited low but detectable neutralizing antibody to H5N1. All six vaccinated macaques survived four times the 50% lethal dose of aerosolized H5N1, while four of six unvaccinated controls succumbed to disease. Although vaccination did not protect against severe influenza, vaccinees had reduced respiratory dysfunction and lower viral load in airways compared to controls. We anticipate that our macaque model will play a vital role in evaluating vaccines and antivirals against influenza pandemics.

Aerosol Particle Size Influences the Infectious Dose and Disease Severity in a Golden Syrian Hamster Model of Inhalational COVID-19

Background: Significant evidence suggests that SARS-CoV-2 can be transmitted via respiratory aerosols, which are known to vary as a function of respiratory activity. Most animal models examine disease presentation following inhalation of small-particle aerosols similar to those generated during quiet breathing or speaking. However, despite evidence that particle size can influence dose-infectivity relationships and disease presentation for other microorganisms, no studies have examined the infectivity of SARS-CoV-2 contained in larger particle aerosols similar to those produced during coughing, singing, or talking. Therefore, the aim of the present study was to assess the influence of aerodynamic diameter on the infectivity and virulence of aerosols containing SARS-CoV-2 in a hamster model of inhalational COVID-19. Methods: Dose-response relationships were assessed for two different aerosol particle size distributions, with mass median aerodynamic diameters (MMADs) of 1.3 and 5.2 μm in groups of Syrian hamsters exposed to aerosols containing SARS-CoV-2. Results: Disease was characterized by viral shedding in oropharyngeal swabs, increased respiratory rate, decreased activity, and decreased weight gain. Aerosol particle size significantly influenced the median doses to induce seroconversion and viral shedding, with both increasing ∼30-fold when the MMAD was increased. In addition, disease presentation was dose-dependent, with seroconversion and viral shedding occurring at lower doses than symptomatic disease characterized by increased respiratory rate and decreased activity. Conclusions: These results suggest that aerosol particle size may be an important factor influencing the risk of COVID-19 transmission and needs to be considered when developing animal models of disease. This result agrees with numerous previous studies with other microorganisms and animal species, suggesting that it would be generally translatable across different species. However, it should be noted that the absolute magnitude of the observed shifts in the median doses obtained with the specific particle sizes utilized herein may not be directly applicable to other species.

Broadly neutralizing humanized SARS-CoV-2 antibody binds to a conserved epitope on Spike and provides antiviral protection through inhalation-based delivery in non-human primates

The COVID-19 pandemic represents a global challenge that has impacted and is expected to continue to impact the lives and health of people across the world for the foreseeable future. The rollout of vaccines has provided highly anticipated relief, but effective therapeutics are required to further reduce the risk and severity of infections. Monoclonal antibodies have been shown to be effective as therapeutics for SARS-CoV-2, but as new variants of concern (VoC) continue to emerge, their utility and use have waned due to limited or no efficacy against these variants. Furthermore, cumbersome systemic administration limits easy and broad access to such drugs. As well, concentrations of systemically administered antibodies in the mucosal epithelium, a primary site of initial infection, are dependent on neonatal Fc receptor mediated transport and require high drug concentrations. To reduce the viral load more effectively in the lung, we developed an inhalable formulation of a SARS-CoV-2 neutralizing antibody binding to a conserved epitope on the Spike protein, ensuring pan-neutralizing properties. Administration of this antibody via a vibrating mesh nebulization device retained antibody integrity and resulted in effective distribution of the antibody in the upper and lower respiratory tract of non-human primates (NHP). In comparison with intravenous administration, significantly higher antibody concentrations can be obtained in the lung, resulting in highly effective reduction in viral load post SARS-CoV-2 challenge. This approach may reduce the barriers of access and uptake of antibody therapeutics in real-world clinical settings and provide a more effective blueprint for targeting existing and potentially emerging respiratory tract viruses.

Quantitative Imaging Metrics for the Assessment of Pulmonary Pathophysiology: An Official American Thoracic Society and Fleischner Society Joint Workshop Report

Multiple thoracic imaging modalities have been developed to link structure to function in the diagnosis and monitoring of lung disease. Volumetric computed tomography (CT) renders three-dimensional maps of lung structures and may be combined with positron emission tomography (PET) to obtain dynamic physiological data. Magnetic resonance imaging (MRI) using ultrashort-echo time (UTE) sequences has improved signal detection from lung parenchyma; contrast agents are used to deduce airway function, ventilation-perfusion-diffusion, and mechanics. Proton MRI can measure regional ventilation-perfusion ratio. Quantitative imaging (QI)-derived endpoints have been developed to identify structure-function phenotypes, including air-blood-tissue volume partition, bronchovascular remodeling, emphysema, fibrosis, and textural patterns indicating architectural alteration. Coregistered landmarks on paired images obtained at different lung volumes are used to infer airway caliber, air trapping, gas and blood transport, compliance, and deformation. This document summarizes fundamental "good practice" stereological principles in QI study design and analysis; evaluates technical capabilities and limitations of common imaging modalities; and assesses major QI endpoints regarding underlying assumptions and limitations, ability to detect and stratify heterogeneous, overlapping pathophysiology, and monitor disease progression and therapeutic response, correlated with and complementary to, functional indices. The goal is to promote unbiased quantification and interpretation of in vivo imaging data, compare metrics obtained using different QI modalities to ensure accurate and reproducible metric derivation, and avoid misrepresentation of inferred physiological processes. The role of imaging-based computational modeling in advancing these goals is emphasized. Fundamental principles outlined herein are critical for all forms of QI irrespective of acquisition modality or disease entity.

Nipah Virus Aerosol Challenge of Three Distinct Particle Sizes in Nonhuman Primates

Aerosol and inhalational studies of high-consequence pathogens allow researchers to study the disease course and effects of biologicals transmitted through aerosol in a laboratory-controlled environment. Inhalational studies involving Nipah virus with small (1-3 μm), intermediate (6-8 μm), and large particles (10-14 μm) were explored in African green nonhuman primates to determine if the subsequent disease course more closely recapitulated what is observed in Nipah virus human disease. The aerosol procedures outlined describe the different equipment/techniques used to generate the three particle sizes and control the site of particle deposition within this animal model.

Imaging drug delivery to the lungs: Methods and applications in oncology

Direct delivery to the lung via inhalation is arguably one of the most logical approaches to treat lung cancer using drugs. However, despite significant efforts and investment in this area, this strategy has not progressed in clinical trials. Imaging drug delivery is a powerful tool to understand and develop novel drug delivery strategies. In this review we focus on imaging studies of drug delivery by the inhalation route, to provide a broad overview of the field to date and attempt to better understand the complexities of this route of administration and the significant barriers that it faces, as well as its advantages. We start with a discussion of the specific challenges for drug delivery to the lung via inhalation. We focus on the barriers that have prevented progress of this approach in oncology, as well as the most recent developments in this area. This is followed by a comprehensive overview of the different imaging modalities that are relevant to lung drug delivery, including nuclear imaging, X-ray imaging, magnetic resonance imaging, optical imaging and mass spectrometry imaging. For each of these modalities, examples from the literature where these techniques have been explored are provided. Finally the different applications of these technologies in oncology are discussed, focusing separately on small molecules and nanomedicines. We hope that this comprehensive review will be informative to the field and will guide the future preclinical and clinical development of this promising drug delivery strategy to maximise its therapeutic potential.

Detailed comparative analysis of environmental microparticle deposition characteristics between human and monkey nasal cavities using a surface mapping technique

Inhaled particulate matter is associated with nasal diseases such as allergic rhinitis, rhinosinusitis and neural disorders. Its health risks on humans are usually evaluated by measurements on monkeys as they share close phylogenetic relationship. However, the reliability of cross-species toxicological extrapolation is in doubt due to physiological and anatomical variations, which greatly undermine the reliability of these expensive human surrogate models. This study numerically investigated in-depth microparticle transport and deposition characteristics on human and monkey (Macaca fuscata) nasal cavities that were reconstructed from CT-images. Deposition characteristics of 1-30μm particles were investigated under resting and active breathing conditions. Similar trends were observed for total deposition efficiencies and a single correlation using Stokes Number was fitted for both species and both breathing conditions, which is convenient for monkey-human extrapolation. Regional deposition patterns were carefully compared using the surface mapping technique. Deposition patterns of low, medium and high inertial particles, classified based on their total deposition efficiencies, were further analyzed in the 3D view and the mapped 2D view, which allows locating particle depositions on specific nasal regions. According to the particle intensity contours and regional deposition profiles, the major differences were observed at the vestibule and the floor of the nasal cavity, where higher deposition intensities of medium and high inertial particles were shown in the monkey case than the human case. Comparisons of airflow streamlines indicated that the cross-species variations of microparticle deposition patterns are mainly contributed by two factors. First, the more oblique directions of monkey nostrils result in a sharper airflow turn in the vestibule region. Second, the monkey's relatively narrower nasal valves lead to higher impaction of medium and high inertial particles on the nasal cavity floor. The methods and findings in this study would contribute to an improved cross-species toxicological extrapolation between human and monkey nasal cavities.

Comparison of Dose-Response Relationships for Two Isolates of SARS-CoV-2 in a Nonhuman Primate Model of Inhalational COVID-19

Background: As the COVID-19 pandemic has progressed, numerous variants of SARS-CoV-2 have arisen, with several displaying increased transmissibility. Methods: The present study compared dose-response relationships and disease presentation in nonhuman primates infected with aerosols containing an isolate of the Gamma variant of SARS-CoV-2 to the results of our previous study with the earlier WA-1 isolate of SARS-CoV-2. Results: Disease in Gamma-infected animals was mild, characterized by dose-dependent fever and oronasal shedding of virus. Differences were observed in shedding in the upper respiratory tract between Gamma- and WA-1-infected animals that have the potential to influence disease transmission. Specifically, the estimated median doses for shedding of viral RNA or infectious virus in nasal swabs were approximately 10-fold lower for the Gamma variant than the WA-1 isolate. Given that the median doses for fever were similar, this suggests that there is a greater difference between the median doses for viral shedding and fever for Gamma than for WA-1 and potentially an increased range of doses for Gamma over which asymptomatic shedding and disease transmission are possible. Conclusions: These results complement those of previous studies, which suggested that differences in exposure dose may help to explain the range of clinical disease presentations observed in individuals with COVID-19, highlighting the importance of public health measures designed to limit exposure dose, such as masking and social distancing. The dose-response data provided by this study are important to inform disease transmission and hazard modeling, as well as to inform dose selection in future studies examining the efficacy of therapeutics and vaccines in animal models of inhalational COVID-19.

Seroconversion and fever are dose-dependent in a nonhuman primate model of inhalational COVID-19

While evidence exists supporting the potential for aerosol transmission of SARS-CoV-2, the infectious dose by inhalation remains unknown. In the present study, the probability of infection following inhalation of SARS-CoV-2 was dose-dependent in a nonhuman primate model of inhalational COVID-19. The median infectious dose, assessed by seroconversion, was 52 TCID50 (95% CI: 23-363 TCID50), and was significantly lower than the median dose for fever (256 TCID50, 95% CI: 102-603 TCID50), resulting in a group of animals that developed an immune response post-exposure but did not develop fever or other clinical signs of infection. In a subset of these animals, virus was detected in nasopharyngeal and/or oropharyngeal swabs, suggesting that infected animals without signs of disease are able to shed virus and may be infectious, which is consistent with reports of asymptomatic spread in human cases of COVID-19. These results suggest that differences in exposure dose may be a factor influencing disease presentation in humans, and reinforce the importance of public health measures that limit exposure dose, such as social distancing, masking, and increased ventilation. The dose-response data provided by this study are important to inform disease transmission and hazard modeling, and, ultimately, mitigation strategies. Additionally, these data will be useful to inform dose selection in future studies examining the efficacy of therapeutics and vaccines against inhalational COVID-19, and as a baseline in healthy, young adult animals for assessment of the importance of other factors, such as age, comorbidities, and viral variant, on the infectious dose and disease presentation.

Recommendations for Standardizing Thorax PET-CT in Non-Human Primates by Recent Experience from Macaque Studies

Despite the possibilities of routine clinical measures and assays on readily accessible bio-samples, it is not always essential in animals to investigate the dynamics of disease longitudinally. In this regard, minimally invasive imaging methods provide powerful tools in preclinical research. They can contribute to the ethical principle of gathering as much relevant information per animal as possible. Besides, with an obvious parallel to clinical diagnostic practice, such imaging platforms are potent and valuable instruments leading to a more refined use of animals from a welfare perspective. Non-human primates comprise highly relevant species for preclinical research to enhance our understanding of disease mechanisms and/or the development of improved prophylactic or therapeutic regimen for various human diseases. In this paper, we describe parameters that critically affect the quality of integrated positron emission tomography and computed tomography (PET-CT) in non-human primates. Lessons learned are exemplified by results from imaging experimental infectious respiratory disease in macaques; specifically tuberculosis, influenza, and SARS-CoV-2 infection. We focus on the thorax and use of 18F-fluorodeoxyglucose as a PET tracer. Recommendations are provided to guide various stages of PET-CT-supported research in non-human primates, from animal selection, scan preparation, and operation, to processing and analysis of imaging data.

The Use of Large-Particle Aerosol Exposure to Nipah Virus to Mimic Human Neurological Disease Manifestations in the African Green Monkey

Nipah virus (NiV) is an emerging virus associated with outbreaks of acute respiratory disease and encephalitis. To develop a neurological model for NiV infection, we exposed 6 adult African green monkeys to a large-particle (approximately 12 μm) aerosol containing NiV (Malaysian isolate). Brain magnetic resonance images were obtained at baseline, every 3 days after exposure for 2 weeks, and then weekly until week 8 after exposure. Four of six animals showed abnormalities reminiscent of human disease in brain magnetic resonance images. Abnormalities ranged from cytotoxic edema to vasogenic edema. The majority of lesions were small infarcts, and a few showed inflammatory or encephalitic changes. Resolution or decreased size in some lesions resembled findings reported in patients with NiV infection. Histological lesions in the brain included multifocal areas of encephalomalacia, corresponding to known ischemic foci. In other regions of the brain there was evidence of vasculitis, with perivascular infiltrates of inflammatory cells and rare intravascular fibrin thrombi. This animal model will help us better understand the acute neurological features of NiV infection and develop therapeutic approaches for managing disease caused by NiV infection.

Peripheral immune response in the African green monkey model following Nipah-Malaysia virus exposure by intermediate-size particle aerosol

The ability to appropriately mimic human disease is critical for using animal models as a tool for understanding virus pathogenesis. In the case of Nipah virus (NiV), infection of humans appears to occur either through inhalation, contact with or consumption of infected material. In two of these circumstances, respiratory or sinusoidal exposure represents a likely route of infection. In this study, intermediate-size aerosol particles (~7 μm) of NiV-Malaysia were used to mimic potential routes of exposure by focusing viral deposition in the upper respiratory tract. Our previous report showed this route of exposure extended the disease course and a single animal survived the infection. Here, analysis of the peripheral immune response found minimal evidence of systemic inflammation and depletion of B cells during acute disease. However, the animal that survived infection developed an early IgM response with rapid development of neutralizing antibodies that likely afforded protection. The increase in NiV-specific antibodies correlated with an expansion of the B cell population in the survivor. Cell-mediated immunity was not clearly apparent in animals that succumbed during the acute phase of disease. However, CD4+ and CD8+ effector memory cells increased in the survivor with correlating increases in cytokines and chemokines associated with cell-mediated immunity. Interestingly, kinetic changes of the CD4+ and CD8bright T cell populations over the course of acute disease were opposite from animals that succumbed to infection. In addition, increases in NK cells and basophils during convalescence of the surviving animal were also evident, with viral antigen found in NK cells. These data suggest that a systemic inflammatory response and "cytokine storm" are not major contributors to NiV-Malaysia pathogenesis in the AGM model using this exposure route. Further, these data demonstrate that regulation of cell-mediated immunity, in addition to rapid production of NiV specific antibodies, may be critical for surviving NiV infection.

Exposure to bioaerosols at open dumpsites: A case study of bioaerosols exposure from activities at Olusosun open dumpsite, Lagos Nigeria

Activities associated with the open dumping of municipal solid waste has the potential for greater impact on the environment and public health compared to other forms of waste-to-land treatment of such wastes. However, there is a lack of quantitative data on the exposure to bioaerosols from open dumpsites, hence impeding the development of effective interventions that would reduce the risk of respiratory symptoms among scavengers and waste workers at such dumpsites. This study investigated exposure to bioaerosols at Olusosun open dumpsite, Lagos Nigeria using three methodologies; (1) Conducting a cross-sectional survey on the respiratory health of the population on the dumpsite, (2) Measuring bioaerosol concentrations in the ambient air by measuring four bioaerosols indicator groups (total bacteria, gram-negative bacteria, Aspergillus fumigatus and total fungi) using a Anderson six stage impactor sampler, (3) Measuring activity related exposures to bioaerosols using an SKC button personal sampler. After a cross sectional health survey of 149 participants (waste workers, scavengers, middlemen, food vendors and business owners), smokers reported higher symptoms of chronic cough (21%) and chronic phlegm (15%) compared to non-smokers (chronic cough 15%, chronic phlegm 13%). Years of work > 5 years showed no statistically significant association with chronic phlegm (OR 1.2, 95% CI 0.4-3.4; p > 0.05) or asthma (OR 1.8, 95% CI 0.6-5.2; p > 0.05). At the 95th percentile, the concentration of total bacteria was the highest (2189 CFU/m³), then gram negative bacteria (2188 CFU/m³), total fungi (843 CFU/m³) and Aspergillus fumigatus (441 CFU/m³) after ambient air sampling. A comparison of the data showed that the activity-based sampling (undertaken using body worn personal sampler) had higher bioaerosols concentrations (10⁴ -10⁶ CFU/m³), i.e. 2-3 logs higher than those recorded from static ambient air sampling. Bioaerosol exposure was highest during scavenging activities compared to waste sorting and site supervision. Particle size distributions showed that 41%, 46%, 76% and 63% of total bacteria, gram-negative bacteria, Aspergillus fumigatus and total fungi respectively were of respirable sizes and would therefore be capable of penetrating deep into the respiratory system, posing a greater human health risk. This study has shown that exposure to bioaerosols can be associated with activities undertaken at open dumpsites and may contribute to the high prevalence of the chronic respiratory symptoms among the workers in such environments.

Studies of Radioaerosol Deposition in the Respiratory Tract

Deposition of aerosols in the respiratory tract can be quantitatively and qualitatively studied by scintigraphy. The most commonly used radionuclide for this purpose is technetium-99m. The effects of various factors on particle deposition have been investigated by using radiolabeled aerosols in the past decade. Most of these studies were in vivo but some were in vitro or ex vivo. The factors examined include particle size, formulation, inhaler design, inhalation flowrate, body posture, and gravity. They have been shown to influence pulmonary deposition, nasal high flow nebulization, and intranasal delivery. A thorough understanding of the various factors is required for the advancement of respiratory-drug delivery. Scintigraphy is a powerful technique that can assist in this regard.

Aerosol exposure to intermediate size Nipah virus particles induces neurological disease in African green monkeys

Nipah virus (NiV) infection can lead to severe respiratory or neurological disease in humans. Transmission of NiV has been shown to occur through contact with virus contaminated fomites or consumption of contaminated food. Previous results using the African green monkey (AGM) model of NiV infection identified aspects of infection that, while similar to humans, don’t fully recapitulate disease. Previous studies also demonstrate near uniform lethality that is not consistent with human NiV infection. In these studies, aerosol exposure using an intermediate particle size (7μm) was used to mimic potential human exposure by facilitating virus deposition in the upper respiratory tract. Computed tomography evaluation found some animals developed pulmonary parenchymal disease including consolidations, ground-glass opacities, and reactive adenopathy. Despite the lack of neurological signs, magnetic resonance imaging identified distinct brain lesions in three animals, similar to those previously reported in NiV-infected patients. Immunological characterization of tissues collected at necropsy suggested a local pulmonary inflammatory response with increased levels of macrophages in the lung, but a limited neurologic response. These data provide the first clear evidence of neurological involvement in the AGM that recapitulates human disease. With the development of a disease model that is more representative of human disease, these data suggest that NiV infection in the AGM may be appropriate for evaluating therapeutic countermeasures directed at virus-induced neuropathogenesis.

The development of effective therapeutic approaches to the treatment of human diseases requires an understanding of the disease process induced by an infectious agent. Historically the development of medical countermeasures for highly pathogenic viruses required the use of a uniformly lethal animal model. While this approach is useful in some regards, it frequently does not provide a true indication of the disease process. In the work presented here, the approach was to use a virus exposure method that mimicked a potential route of human exposure and used a dose that might be more representative of one a human would receive. Using this method and advanced medical imaging techniques, we were able to demonstrate an extended disease course with mixed respiratory and neurological disease like that seen in humans. This study also found that the response to infection in the lungs was inflammatory and that the disease in the brain was limited despite clear evidence of lesions. These data support the development of animal models that mimic human disease and allow for the identification of potential therapeutic approaches that target the disease process rather than only the virus.