Mice with humanized-lungs and immune system - an idealized model for COVID-19 and other respiratory illness

Structural and functional characterization of NEMO cleavage by SARS-CoV-2 3CLpro

In addition to its essential role in viral polyprotein processing, the SARS-CoV-2 3C-like protease (3CLpro) can cleave human immune signaling proteins, like NF-κB Essential Modulator (NEMO) and deregulate the host immune response. Here, in vitro assays show that SARS-CoV-2 3CLpro cleaves NEMO with fine-tuned efficiency. Analysis of the 2.50 Å resolution crystal structure of 3CLpro C145S bound to NEMO226-234 reveals subsites that tolerate a range of viral and host substrates through main chain hydrogen bonds while also enforcing specificity using side chain hydrogen bonds and hydrophobic contacts. Machine learning- and physics-based computational methods predict that variation in key binding residues of 3CLpro-NEMO helps explain the high fitness of SARS-CoV-2 in humans. We posit that cleavage of NEMO is an important piece of information to be accounted for, in the pathology of COVID-19.

3D ex vivo tissue platforms to investigate the early phases of influenza A virus- and SARS-CoV-2-induced respiratory diseases

Pandemic outbreaks of viruses such as influenza virus or SARS-CoV-2 are associated with high morbidity and mortality and thus pose a massive threat to global health and economics. Physiologically relevant models are needed to study the viral life cycle, describe the pathophysiological consequences of viral infection, and explore possible drug targets and treatment options. While simple cell culture-based models do not reflect the tissue environment and systemic responses, animal models are linked with huge direct and indirect costs and ethical questions. Ex vivo platforms based on tissue explants have been introduced as suitable platforms to bridge the gap between cell culture and animal models. We established a murine lung tissue explant platform for two respiratory viruses, influenza A virus (IAV) and SARS-CoV-2. We observed efficient viral replication, associated with the release of inflammatory cytokines and the induction of an antiviral interferon response, comparable to ex vivo infection in human lung explants. Endolysosomal entry could be confirmed as a potential host target for pharmacological intervention, and the potential repurposing potentials of fluoxetine and interferons for host-directed therapy previously seen in vitro could be recapitulated in the ex vivo model.

Potential Applications and Perspectives of Humanized Mouse Models

As medical and pharmacological technology advances, new and complex modalities of disease treatment that are more personalized and targeted are being developed. Often these modalities must be validated in the presence of critical components of the human biological system. Given the incongruencies between murine and human biology, as well as the human-tropism of certain drugs and pathogens, the selection of animal models that accurately recapitulate the intricacies of the human biological system becomes more salient for disease modeling and preclinical testing. Immunodeficient mice engrafted with functional human tissues (so-called humanized mice), which allow for the study of physiologically relevant disease mechanisms, have thus become an integral aspect of biomedical research. This review discusses the recent advancements and applications of humanized mouse models on human immune system and liver humanization in modeling human diseases, as well as how they can facilitate translational medicine.

Using in vivo animal models for studying SARS-CoV-2

INTRODUCTION

The search for an animal model capable of reproducing the physiopathology of the COVID-19, and also suitable for evaluating the efficacy and safety of new drugs has become a challenge for many researchers.

AREAS COVERED

This work reviews the current animal models for in vivo tests with SARS-CoV-2 as well as the challenges involved in the safety and efficacy trials.

EXPERT OPINION

Studies have reported the use of nonhuman primates, ferrets, mice, Syrian hamsters, lagomorphs, mink, and zebrafish in experiments that aimed to understand the course of COVID-19 or test vaccines and other drugs. In contrast, the assays with animal hyperimmune sera have only been used in in vitro assays. Finding an animal that faithfully reproduces all the characteristics of the disease in humans is difficult. Some models may be more complex to work with, such as monkeys, or require genetic manipulation so that they can express the human ACE2 receptor, as in the case of mice. Although some models are more promising, possibly the use of more than one animal model represents the best scenario. Therefore, further studies are needed to establish an ideal animal model to help in the development of other treatment strategies besides vaccines.

Structural and functional characterization of NEMO cleavage by SARS-CoV-2 3CLpro.. [PMID: 34816264 PMCID: PMC8609902 DOI: 10.1101/2021.11.11.468228] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

In addition to its essential role in viral polyprotein processing, the SARS-CoV-2 3C-like (3CLpro) protease can cleave human immune signaling proteins, like NF-κB Essential Modulator (NEMO) and deregulate the host immune response. Here, in vitro assays show that SARS-CoV-2 3CLpro cleaves NEMO with fine-tuned efficiency. Analysis of the 2.14 Å resolution crystal structure of 3CLpro C145S bound to NEMO_226–235 reveals subsites that tolerate a range of viral and host substrates through main chain hydrogen bonds while also enforcing specificity using side chain hydrogen bonds and hydrophobic contacts. Machine learning- and physics-based computational methods predict that variation in key binding residues of 3CLpro-NEMO helps explain the high fitness of SARS-CoV-2 in humans. We posit that cleavage of NEMO is an important piece of information to be accounted for in the pathology of COVID-19.

Mouse Models for the Study of SARS-CoV-2 Infection

Mice are an invaluable resource for studying virus-induced disease. They are a small, genetically modifiable animal for which a large arsenal of genetic and immunologic tools is available for evaluation of pathogenesis and potential vaccines and therapeutics. SARS-CoV-2, the betacoronavirus responsible for the COVID-19 pandemic, does not naturally replicate in wild-type mice, due to structural differences between human and mouse ACE2, the primary receptor for SARS-CoV-2 entry into cells. However, several mouse strains have been developed that allow for SARS-CoV-2 replication and clinical disease. Two broad strategies have primarily been deployed for developing mouse strains susceptible to COVID-19-like disease: adding in the human ACE2 gene and adapting the virus to the mouse ACE2 receptor. Both approaches result in mice that develop several of the clinical and pathologic hallmarks of COVID-19, including acute respiratory distress syndrome and acute lung injury. In this review, we describe key acute pulmonary and extrapulmonary pathologic changes seen in COVID-19 patients that mouse models of SARS-CoV-2 infection ideally replicate, the essential development of mouse models for the study of Severe Acute Respiratory Syndrome and Middle Eastern Respiratory Syndrome and the basis of many of the models of COVID-19, and key clinical and pathologic features of currently available mouse models of SARS-CoV-2 infection.

Will Mutations in the Spike Protein of SARS-CoV-2 Lead to the Failure of COVID-19 Vaccines?

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is the causative agent of coronavirus disease 2019 (COVID-19), which has spread worldwide since it was first identified in Wuhan, China, at the end of 2019. With the global transmission of the virus, a large number of SARS-CoV-2 variants have also appeared, especially, emerging strains that have recently been discovered in the United Kingdom (variant 20I/501Y.V1, lineage B.1.1.7), South Africa (variant 20H/501Y.V2, lineage B.1.351), and Brazil (variant 20 J/501Y.V3, and lineage P.1). The common feature of these variants is that they share the N501Y mutation involving the SARS-CoV-2 spike (S) protein, which is precisely the target of most COVID-19 vaccines. Furthermore, mutations such as N501Y, E484K, and K417N in the S protein may affect viral fitness and transmissibility. However, current research on the impact of these variants on COVID-19 vaccines is still lacking. Herein, we briefly explain why most COVID-19 vaccines target the S protein, update the progress of research regarding S protein-related COVID-19 vaccines, review the latest studies concerning the effects of S protein variants on COVID-19 vaccines, and finally, propose certain strategies to deal with SARS-CoV-2 variants.

A SCID mouse-human lung xenograft model of SARS-CoV-2 infection

SARS-CoV-2 infection, which is responsible for the current COVID-19 pandemic, can cause life-threatening pneumonia, respiratory failure and even death. Characterizing SARS-CoV-2 pathogenesis in primary human target cells and tissues is crucial for developing vaccines and therapeutics. However, given the limited access to clinical samples from COVID-19 patients, there is a pressing need for in vitro/in vivo models to investigate authentic SARS-CoV-2 infection in primary human lung cells or tissues with mature structures. The present study was designed to evaluate a humanized mouse model carrying human lung xenografts for SARS-CoV-2 infection in vivo. Methods: Human fetal lung tissue surgically grafted under the dorsal skin of SCID mice were assessed for growth and development after 8 weeks. Following SARS-CoV-2 inoculation into the differentiated lung xenografts, viral replication, cell-type tropism and histopathology of SARS-CoV-2 infection, and local cytokine/chemokine expression were determined over a 6-day period. The effect of IFN-α treatment against SARS-CoV-2 infection was tested in the lung xenografts. Results: Human lung xenografts expanded and developed mature structures closely resembling normal human lung. SARS-CoV-2 replicated and spread efficiently in the lung xenografts with the epithelial cells as the main target, caused severe lung damage, and induced a robust pro-inflammatory response. IFN-α treatment effectively inhibited SARS-CoV-2 replication in the lung xenografts. Conclusions: These data support the human lung xenograft mouse model as a useful and biological relevant tool that should facilitate studies on the pathogenesis of SARS-CoV-2 lung infection and the evaluation of potential antiviral therapies.

Experimental Models of SARS-CoV-2 Infection: Possible Platforms to Study COVID-19 Pathogenesis and Potential Treatments

In December 2019, a novel coronavirus crossed species barriers to infect humans and was effectively transmitted from person to person, leading including vaccines and antiviral drugs that could prevent or limit the burden or transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is a global health priority. It is thus of utmost importance to assess possible therapeutic strategies against SARS-CoV-2 using experimental models that recapitulate aspects of the human disease. Here, we review available models currently being developed and used to study SARS-CoV-2 infection and highlight their application to screen potential therapeutic approaches, including repurposed antiviral drugs and vaccines. Each identified model provides a valuable insight into SARS-CoV-2 cellular tropism, replication kinetics, and cell damage that could ultimately enhance understanding of SARS-CoV-2 pathogenesis and protective immunity. Expected final online publication date for the Annual Review of Pharmacology and Toxicology, Volume 62 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.