A Mouse Model of SARS-CoV-2 induced Acute Lung Injury (ALI) in Standard Laboratory Mice

Due to their zoonotic nature coronaviruses are poised for emergence into new species. Most recently, SARS-CoV-2 emerged into humans in Wuhan, China to cause a worldwide pandemic leading to significant morbidity, mortality and economic losses. As SARS-CoV-2 cannot infect standard laboratory mice there is an urgent need for small animal models that accurately reflect the spectrum of disease symptoms observed in humans. We used an in vivo passaging strategy to further adapt a SARS-CoV-2 virus variant that was genetically engineered to allow for efficient binding of the viral spike protein to the mACE2 receptor for entry. After 10 passages we recovered a virus (SARS-CoV-2 MA10) that is able to cause significant morbidity and mortality in young adult BALB/c mice. Additionally, aged BALB/c mice exhibited an increase in disease phenotypes as it has been observed in humans. Histopathological and lung function analyses revealed that morbidity and mortality in those models is caused by a decrease in lung function including hallmarks of acute lung injury (ALI) and acute respiratory distress symptoms (ARDS). Furthermore, we challenged C57BL/6J mice with SARS-CoV-2 MA10, which are the most commonly used inbred mouse strain and serve as the genetic backbone for the majority of genetically engineered mice. We observed an attenuated disease phenotype giving the field the opportunity to analyze increase as well as decrease of pathogenicity. We then showed that SARS-CoV-2 is an ideal model to test medical counter measurements including clinical parameters of disease. Mice vaccinated with VRPs expressing the spike protein were protected from weight loss and decreased lung function. Overall, we generated and characterized a new mouse adapted SARS-CoV-2 model that mirrors multiple aspects of COVID-19 disease seen in humans including age-related increase in morbidity and mortality, targeting of cells in upper and lower respiratory tract, and respiratory dysfunction. Thus, our model fulfills the urgent need for a small animal model that provides robust parameters to evaluate medical counter measurements such as vaccines and antivirals.

冠状病毒具备人畜共患（zoonotic）属性，极易实现跨物种传播并感染新宿主。近期，严重急性呼吸综合征冠状病毒2型（SARS-CoV-2）于中国武汉实现人际传播，引发全球大流行，造成了大量发病、死亡及经济损失。由于SARS-CoV-2无法感染普通实验小鼠，当前亟需能够精准复刻人类感染后全部疾病症状谱的小型动物模型。本研究采用体内传代策略，对一株经基因工程改造、可使病毒刺突蛋白（spike protein）高效结合小鼠血管紧张素转换酶2（mACE2）受体以介导病毒入侵的SARS-CoV-2变异株开展进一步适应性进化。经过10轮传代后，我们获得了一株可在年轻成年BALB/c小鼠中引发显著发病与死亡的病毒毒株（SARS-CoV-2 MA10）。此外，老年BALB/c小鼠的疾病表型更为严重，这与人类感染后的病情变化趋势一致。组织病理学与肺功能分析显示，该模型小鼠的发病与死亡源于肺功能损伤，具体表现为急性肺损伤（ALI）与急性呼吸窘迫综合征（ARDS）的典型病理特征。此外，我们使用SARS-CoV-2 MA10毒株攻毒C57BL/6J小鼠——这是目前最常用的近交系小鼠品系，也是绝大多数基因工程小鼠的遗传背景品系。本研究观察到该品系小鼠的疾病表型呈减毒特征，这为领域内研究病原体致病力的增强与减弱提供了可行模型。随后我们证实，该模型可用于评估各类新型冠状病毒肺炎（COVID-19）医疗防治对策，包括疾病相关临床参数的检测。接种了表达刺突蛋白的病毒样颗粒（VRPs）疫苗的小鼠，可免受体重下降与肺功能损伤的影响。综上，本研究构建并鉴定了一株新的鼠适应性SARS-CoV-2模型，该模型可精准复刻人类感染COVID-19后的多种病理特征：包括年龄相关的发病与死亡风险升高、上下呼吸道细胞靶向感染以及呼吸功能障碍。因此，本研究所构建的模型填补了当前的迫切需求，可提供稳定可靠的检测参数以评估疫苗、抗病毒药物等各类COVID-19医疗防治对策。