K18-hACE2 mice develop respiratory disease resembling severe COVID-19

Abstract

SARS-CoV-2 emerged in late 2019 and resulted in the ongoing COVID-19 pandemic. Several animal models have been rapidly developed that recapitulate the asymptomatic to moderate disease spectrum. Now, there is a direct need for additional small animal models to study the pathogenesis of severe COVID-19 and for fast-tracked medical countermeasure development. Here, we show that transgenic mice expressing the human SARS-CoV-2 receptor (angiotensin-converting enzyme 2 [hACE2]) under a cytokeratin 18 promoter (K18) are susceptible to SARS-CoV-2 and that infection resulted in a dose-dependent lethal disease course. After inoculation with either 104 TCID50 or 105 TCID50, the SARS-CoV-2 infection resulted in rapid weight loss in both groups and uniform lethality in the 105 TCID50 group. High levels of viral RNA shedding were observed from the upper and lower respiratory tract and intermittent shedding was observed from the intestinal tract. Inoculation with SARS-CoV-2 resulted in upper and lower respiratory tract infection with high infectious virus titers in nasal turbinates, trachea and lungs. The observed interstitial pneumonia and pulmonary pathology, with SARS-CoV-2 replication evident in pneumocytes, were similar to that reported in severe cases of COVID-19. SARS-CoV-2 infection resulted in macrophage and lymphocyte infiltration in the lungs and upregulation of Th1 and proinflammatory cytokines/chemokines. Extrapulmonary replication of SARS-CoV-2 was observed in the cerebral cortex and hippocampus of several animals at 7 DPI but not at 3 DPI. The rapid inflammatory response and observed pathology bears resemblance to COVID-19. Additionally, we demonstrate that a mild disease course can be simulated by low dose infection with 102 TCID50 SARS-CoV-2, resulting in minimal clinical manifestation and near uniform survival. Taken together, these data support future application of this model to studies of pathogenesis and medical countermeasure development.

Neuroinvasion and neurotropism by SARS-CoV-2 variants in the K18-hACE2 mouse

“…With the higher infectious dose (10 4 PFU) or with IAV pre-infection, we observed widespread extensive viral antigen expression and involvement of the spinal cord. This suggests some dose dependence of virus spread in the CNS, as it was suspected in another study (Yinda et al, 2021), and an effect of prior damage in the respiratory tract (Clark et al, 2021). At the same time, we and others found virus in the olfactory epithelium and in neurons in the olfactory bulb (Carossino et al, 2021;Kumari et al, 2021).…”

“…In the mice, the inflammatory processes were only mild and more pronounced in frontal regions like caudoputamen and the thalamus/hypothalamus region as well as the hippocampal area. Further vascular lesions apart from vasculitis/endotheliitis, like ischemic infarcts (Kantonen et al, 2020;Song et al, 2021) or microthrombi (Fabbri et al, 2020) that seem to be frequent in fatal human COVID-19 cases, are obviously not a regular feature in this mouse model, since only two studies reported occasional microthrombi in the brain (Yinda et al, 2021;Zheng et al, 2021). This could be due to the lack of endothelial cell infection in the brain of the mice, whereas it was seen in association with fresh ischemic infarcts in the brain of a COVID-19 patient (Meinhardt et al, 2021;Song et al, 2021).…”

“…Similar to a previous study (Oladunni et al, 2020), we observed a mild non-suppurative, macrophage and T cell driven encephalitis (perivascular infiltrates and occasional vasculitis) in all mice that harbored viral antigen in the brains at 7 dpi. This appeared to be slightly more intense with more extensive neuronal virus antigen expression in animals that had received the higher viral dose (10 4 PFU) or had been preinfected with IAV, suggesting some dependence on the infectious dose or easier access to the brain with pre-existing damage due to IAV infection (Clark et al, 2021;Yinda et al, 2021). Transcriptional investigations also confirmed the inflammatory state of the brain, demonstrating an increase in infammatory cytokines and chemokines (IL-6, TNF-α, IFN-γ, IL-1β, MIP-1α.MIP-2, IP-10) in the brain of infected mice (Oladunni et al, 2020;Kumari et al, 2021).…”

Safe and effective two-in-one replicon-and-VLP minispike vaccine for COVID-19: Protection of mice after a single immunization

“…To assess the protective capacity of the VSV replicon we used transgenic K18-hACE2 C57BL/6 mice, which were previously shown to develop respiratory disease resembling severe COVID-19 [76]. Five mice each were immunized as before with VSVΔG-minispike-eGFP or VSVΔG-eGFP control and challenged intranasally with 10 4 TCID50 of SARS-CoV-2 Wetzlar, either following prime immunization or homologous boost immunization (Fig 7A).…”

ACE2-lentiviral transduction enables mouse SARS-CoV-2 infection and mapping of receptor interactions

“…Expression of hACE2 in mice via a transgene allows SARS-CoV-2 infection and provides mouse models that recapitulate aspects of COVID-19. In such models hACE2 is expressed under control of various promoters, including K18 (6–12), mACE2 (13, 14), HFH4 (15), or chicken β-actin (16). These mouse models all differ in various aspects including level of virus replication, disease manifestations and tissue tropisms (3), but do not provide a simple mechanism whereby genetically modified (GM) or knock-out mice can be exploited for SARS-CoV-2/COVID-19 research.…”