COVID-19 vaccination recruits and matures cross-reactive antibodies to conserved epitopes in endemic coronavirus Spike proteins

The COVID-19 pandemic has triggered the first widespread vaccination campaign against a coronavirus. Most vaccinated subjects are naive to SARS-CoV-2, however almost all have previously encountered other coronaviruses (CoVs) and the role of this immunity in shaping the vaccine response remains uncharacterized. Here we use longitudinal samples and highly-multiplexed serology to identify mRNA-1273 vaccine-induced antibody responses against a range of CoV Spike epitopes and in both phylogenetically conserved and non-conserved regions. Whereas reactivity to SARS-CoV-2 epitopes showed a delayed but progressive increase following vaccination, we observed distinct kinetics for the endemic CoV homologs at two conserved sites in Spike S2: these became detectable sooner, and decayed at later timepoints. Using homolog-specific depletion and alanine-substitution experiments, we show that these distinctly-evolving specificities result from cross-reactive antibodies as they mature against rare, polymorphic residues within these epitopes. Our results reveal mechanisms for the formation of antibodies with broad reactivity against CoVs.

FXa cleaves the SARS-CoV-2 spike protein and blocks cell entry to protect against infection with inferior effects in B.1.1.7 variant

The ongoing coronavirus disease 2019 (COVID-19) pandemic is caused by infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Human natural defense mechanisms against SARS-CoV-2 are largely unknown. Serine proteases (SPs) including furin and TMPRSS2 cleave SARS-CoV-2 spike protein, facilitating viral entry. Here, we show that FXa, a SP for blood coagulation, is upregulated in COVID-19 patients compared to non-COVID-19 donors and exerts anti-viral activity. Mechanistically, FXa cleaves the SARS-CoV-2 spike protein, which prevents its binding to ACE2, and thus blocks viral entry. Furthermore, the variant B.1.1.7 with several mutations is dramatically resistant to the anti-viral effect of FXa compared to wild-type SARA-CoV-2 in vivo and in vitro. The anti-coagulant rivaroxaban directly inhibits FXa and facilitates viral entry, whereas the indirect inhibitor fondaparinux does not. In a lethal humanized hACE2 mouse model of SARS-CoV-2, FXa prolonged survival while combination with rivaroxaban but not fondaparinux abrogated this protection. These preclinical results identify a previously unknown SP function and associated anti-viral host defense mechanism and suggest caution in considering direct inhibitors for prevention or treatment of thrombotic complications in COVID-19 patients.

The K18-hACE2 Transgenic Mouse Model Recapitulates Non-Severe and Severe COVID-19 in Response to Infectious Dose of SARS-CoV-2 Virus

A comprehensive analysis and characterization of a SARS-CoV-2 infection model that mimics non-severe and severe COVID-19 in humans is warranted for understating the virus and developing preventive and therapeutic agents. Here, we characterized the K18-hACE2 mouse model expressing human (h)ACE2 in mice, controlled by the human keratin 18 (K18) promoter, in epithelia, including airway epithelial cells where SARS-CoV-2 infections typically start. We found that intranasal inoculation with higher viral doses (2x103 and 2x104 PFU) of SARS-CoV-2 caused lethality of all mice and severe damage of various organs, including lungs, liver, and kidney, while lower doses (2x101 and 2x102 PFU) led to less severe tissue damage and some mice recovered from the infection. In this humanized hACE2 mouse model, SARS-CoV-2 infection damaged multiple tissues, with a dose-dependent effect in most tissues. Similar damage was observed in biopsy samples from COVID-19 patients. Finally, the mice that recovered after infection with a low dose of virus also survived rechallenge with a high dose of virus. Compared to other existing models, the K18-hACE2 model seems to be the most sensitive COVID-19 model reported to date. Our work expands the information available about this model to include analysis of multiple infectious doses and various tissues with comparison to human biopsy samples from COVID-19 patients. In conclusion, the K18-hACE2 mouse model recapitulates both severe and non-severe COVID-19 in humans and can provide insight into disease progression and the efficacy of therapeutics for preventing or treating COVID-19. ImportanceThe pandemic of COVID-19 has reached 112,589,814 cases and caused 2,493,795 deaths worldwide as of February 23, 2021, has raised an urgent need for development of novel drugs and therapeutics to prevent the spread and pathogenesis of 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 this study, we have comprehensively characterized a mouse model of SARS-CoV-2 infection using K18-hACE2 transgenic mice. We infected the mice with low and high doses of SARS-CoV-2 virus to study the pathogenesis and survival in response to different infection patterns. Moreover, we compared the pathogenesis of the K18-hACE2 transgenic mice with that of the COVID-19 patients to show that this model could be a useful tool for the development of anti-viral drugs and therapeutics.

The Effect of Minnelide against SARS-CoV-2 in a Murine Model

Severe acute respiratory syndrome coronavirus 2, SARS-CoV-2, is the causative agent of coronavirus disease 2019, COVID-19, and the current COVID-19 pandemic. Even as more vaccine candidates are released, more treatment options are critically needed. Here, we investigated the use of Minnelide, a water soluble pro-drug with anti-inflammatory properties, for the treatment of COVID-19. To do this, k18-hACE2 mice were infected with SARS-CoV-2 or given PBS control intranasally. The next day mice were either treated daily with low dose (0.0025mg/day) or high dose Minnelide (0.005mg/day), or given vehicle control intraperitoneal. Mice were weighed daily, and sacrificed at day 6 and 10 post-infection to analyze viral burden, cytokine response, and pathology. We observed a reduction in viral load in the lungs of Minnelide-treated mice infected with SARS-CoV-2 at day 10 post-infection compared to day 6 post-infection. All SARS-CoV-2 infected non-treated mice were moribund six days post-infection while treatment with Minnelide extended survival for both low (60% survival) and high (100% survival) dose treated mice ten days post-infection. Interestingly, cytokine analysis demonstrated a significant reduction in IL-6 (lung and heart) and D-dimer (serum) in high dose treated SARS-CoV-2 infected mice compared to mice infected with SARS-CoV-2 alone at day 6 post-infection. Additionally, histology analysis revealed that Minnelide treatment significantly improved lung pathology ten days post-infection with SARS-CoV-2 with all the mice exhibiting normal lung tissue with thin alveolar septa and no inflammatory cells. Overall, our study exhibits potential for the use of Minnelide to improve survival in COVID-19 patients.