SARS-CoV-2 Rapidly Adapts in Aged BALB/c Mice and Induces Typical Pneumonia

Abstract

Age is a risk factor for coronavirus disease 2019 (COVID-19) associated morbidity and mortality in humans; hence, in this study, we compared the course of severe acute respiratory syndrome–coronavirus 2 (SARS-CoV-2) infection in young and aged BALB/c mice. We found that SARS-CoV-2 isolates replicated in the respiratory tracts of 12-month-old (aged) mice and caused pathological features of pneumonia upon intranasal infection. In contrast, rapid viral clearance was observed 5 days following infection in 2-month-old (young) mice with no evidence of pathological changes in the lungs. Infection with SARS-CoV-2 elicited significantly upregulated production of cytokines, especially interleukin 6 and interferon gamma, in aged mice; whereas this response was much weaker in young mice. Subsequent challenge of infected aged BALB/c mice with SARS-CoV-2 resulted in neutralized antibody responses, a significantly reduced viral burden in the lungs, and inflammation mitigation. Deep sequencing showed a panel of mutations potentially associated with the enhanced infection in aged BALB/c mice, such as the Q498H mutations which are located at the receptor binding domain (RBD) of the spike (S) protein. We further found that the isolates can not only multiply in the respiratory tract of mice but also cause disease in aged mice. Overall, viral replication and rapid adaption in aged BALB/c mice were associated with pneumonia, confirming that the age-related susceptibility to SARS-CoV-2 in mice resembled that in humans. Importance Aged BALB/c model are in use as a model of disease caused by SARS-CoV-2. Our research demonstrated SARS-CoV-2 can rapidly adapt in aged BALB/c mice through causing mutations at the RBD of the S protein. Moreover, SARS-CoV-2-infected aged BALB/c mice indicated that alveolar damage, interstitial pneumonia, and inflammatory immune responses were similar to the clinical manifestations of human infections. Therefore, our aged BALB/c challenge model will be useful for further understanding the pathogenesis of SARS-CoV-2 and for testing vaccines and antiviral agents.

Emerging SARS-CoV-2 variants expand species tropism to rodents

“…In particular, our results indicate that B.1.1.7-infected mice and rats can shed infectious virus particles in the respiratory tract for approximately 4 to 7 days after infection, which may contaminate the environment and become a persistent source of human infection. Importantly, SARS-CoV-2 adaptation in mice occurs rapidly, with mouse-adapting mutations usually developing within 1-to-10 passages 18,[23][24][25] . These mutations will result in even more robust SARS-CoV-2 replication in rodents and may further facilitate virus dissemination.…”

But Mouse, you are not alone: On some severe acute respiratory syndrome coronavirus 2 variants infecting mice

“…Further details are provided under Supplementary Methods for Molecular Modelling. We then compared our insilico findings with experimental results reported by different research groups with mouse adapted strains/isolates [6][7][8]13,[21][22][23][24][25][26][27][28][29] and VOC 14,[30][31][32][33][34] (Table 1). Taken together, we were able to gain valuable insights into the likely effects of different mutations of consequence.…”

“…It is unsurprising that the latter variants requiring two or more changes were rarely observed in situ regardless of their high in vitro affinity scores from Starr et al 38 From the above and Table 3, we see that in silico analysis can provide valuable insights to interpret and bridge in vitro, in vivo and in situ observations on the RBD position 501. A similar analysis is possible with the alternative essential mutation for mouse adaptation at RBD position 498, where the in vitro affinity enhancement order is H498, Y498, F498 and W498 according to Starr et al 38 Of these, H498 (on its own) and Y498 (with enhancing RBD mutations) have been shown to result in mouse adaptation in vivo (Table 1); 7,8,[23][24][25][26][27][28] Q498R was also reported once, unusually in combination with N501Y, isolated from mouse lung after 30 passages. However, in situ observations of these variants have been limited to R498 ( 15occurrences) and H498 (3 occurrences) so far.…”

Design of Peptide Vaccine for COVID19: CD8+ and CD4+ T cell epitopes from SARS-CoV-2 open-reading-frame protein variants

“…In order to safely test the predicted vaccine constructs in pre-clinical studies, we also predicted mouse MHC affinity to our top CD8 epitopes. Mouse models are useful for the evaluation of antiviral targets as they share features with humans and two mouse strains - BALB/CJ and C57BL/6 have been reported as good models for SARS-CoV-2 [14, 15].…”