Vaccine and antiviral development against SARS-CoV-2 infection or COVID-19 disease would benefit from validated small animal models. Here, we show that transgenic mice expressing human angiotensin-converting enzyme 2 (hACE2) by the human cytokeratin 18 promoter (K18 hACE2) represent a susceptible rodent model. K18 hACE2 transgenic mice succumbed to SARS-CoV-2 infection by day 6, with virus detected in lung airway epithelium and brain. K18 ACE2 transgenic mice produced a modest TH1/2/17 cytokine storm in the lung and spleen that peaked by day 2, and an extended chemokine storm that was detected in both lungs and brain. This chemokine storm was also detected in the brain at day 6. K18 hACE2 transgenic mice are, therefore, highly susceptible to SARS-CoV-2 infection and represent a suitable animal model for the study of viral pathogenesis, and for identification and characterization of vaccines (prophylactic) and antivirals (therapeutics) for SARS-CoV-2 infection and associated severe COVID-19 disease.

The pandemic of coronavirus disease 2019 (COVID-19) has reached nearly 240 million cases, caused nearly 5 million deaths worldwide as of October 2021, and has raised an urgent need for the development of novel drugs and therapeutics to prevent the spread and pathogenesis of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). To achieve this goal, an animal model that recapitulates the features of human COVID-19 disease progress and pathogenesis is greatly needed.

In the last two decades, multi (MDR), extensively (XDR), extremely (XXDR) and total (TDR) drug-resistant Mycobacterium tuberculosis (M.tb) strains have emerged as a threat to public health worldwide, stressing the need to develop new tuberculosis (TB) prevention and treatment strategies. It is estimated that in the next 35 years, drug-resistant TB will kill around 75 million people and cost the global economy $16.7 trillion. Indeed, the COVID-19 pandemic alone may contribute with the development of 6.3 million new TB cases due to lack of resources and enforced confinement in TB endemic areas. Evolution of drug-resistant M.tb depends on numerous factors, such as bacterial fitness, strain’s genetic background and its capacity to adapt to the surrounding environment, as well as host-specific and environmental factors. Whole-genome transcriptomics and genome-wide association studies in recent years have shed some insights into the complexity of M.tb drug resistance and have provided a better understanding of its underlying molecular mechanisms. In this review, we will discuss M.tb phenotypic and genotypic changes driving resistance, including changes in cell envelope components, as well as recently described intrinsic and extrinsic factors promoting resistance emergence and transmission. We will further explore how drug-resistant M.tb adapts differently than drug-susceptible strains to the lung environment at the cellular level, modulating M.tb–host interactions and disease outcome, and novel next generation sequencing (NGS) strategies to study drug-resistant TB.

Murine models of Mycobacterium tuberculosis infection are essential tools in drug discovery. Here we describe a fast standardized 9-day acute assay intended to measure the efficacy of drugs against M. tuberculosis growing in the lungs of immunocompetent mice. This assay is highly reproducible, allows good throughput, and was validated for drug lead optimization using isoniazid, rifampin, ethambutol, pyrazinamide, linezolid, and moxifloxacin.The appearance of clinical resistance to first-line drugs (8) and the long treatments have prompted a renewed effort in tuberculosis drug discovery. Efficacy in animal models is a key criterion for selection of compounds. In order to address its complexity, tuberculosis can be deconstructed by modeling specific pathological characteristics of the human infection separately (15). Assays designed to measure the ability of a drug to kill Mycobacterium tuberculosis actively replicating in the lungs can be easily modeled in mice (12) and are relevant because most fatalities are caused by lung infections. The model using C57BL/6 (B6) gamma interferon (IFN-␥)-disrupted mice (GKO) and low-dose aerosol infection (9) is particularly well suited for the objective above since (i) the lungs are the primary infected organs, (ii) antitubercular efficacy is almost exclusively due to drug action, since GKO mice do not mount an effective adaptive immune response (6), and (iii) the model is reproducible and sensitive (9). However, this model requires 30 days from infection to sacrifice, and GKO mice are relatively expensive animals. In order to overcome these drawbacks, a fast therapeutic-efficacy assay against replicating M. tuberculosis H37Rv in the lungs of wild-type B6 mice was developed and standardized.The assay should (i) allow significant bacterial growth after lung infection, (ii) enable detection of drug exposures that kill bacteria in lungs, (iii) minimize the duration of the assay, and (iv) maximize the duration of treatment. Bacterial growth of about 2 logs over the initial inoculum was determined to be a level that would provide enough dynamic range to detect statistically significant growth inhibition. Infection was initiated by nonsurgical intratracheal instillation of M. tuberculosis H37Rv. In brief, mice were anesthetized with 3% isoflurane and intubated with a metal probe (catalog number 27134;

Vaccine and antiviral development against SARS-CoV-2 infection or COVID-19 disease currently lacks a validated small animal model. Here, we show that transgenic mice expressing human angiotensin converting enzyme 2 (hACE2) by the human cytokeratin 18 promoter (K18 hACE2) represent a susceptible rodent model. K18 hACE2-transgenic mice succumbed to SARS-CoV-2 infection by day 6, with virus detected in lung airway epithelium and brain. K18 ACE2-transgenic mice produced a modest TH1/2/17 cytokine storm in the lung and spleen that peaked by day 2, and an extended chemokine storm that was detected in both lungs and brain. This chemokine storm was also detected in the brain at day 4. K18 hACE2-transgenic mice are, therefore, highly susceptible to SARS-CoV-2 infection and represent a suitable animal model for the study of viral pathogenesis, and for identification and characterization of vaccines (prophylactic) and antivirals (therapeutics) for SARS-CoV-2 infection and associated severe COVID-19 disease.