Intranasal or airborne transmission-mediated delivery of an attenuated SARS-CoV-2 protects Syrian hamsters against new variants

Detection of secretory antibodies in the airway is highly desirable when evaluating mucosal protection by vaccines against a respiratory virus, such as the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We show that intranasal delivery of an attenuated SARS-CoV-2 (Nsp1-K164A/H165A) induces both mucosal and systemic IgA and IgG in male Syrian hamsters. Interestingly, either direct intranasal immunization or airborne transmission-mediated delivery of Nsp1-K164A/H165A in Syrian hamsters offers protection against heterologous challenge with variants of concern (VOCs) including Delta, Omicron BA.1, BA.2.12.1 and BA.5. Vaccinated animals show significant reduction in both tissue viral loads and lung inflammation. Similarly attenuated viruses bearing BA.1 and BA.5 spike boost variant-specific neutralizing antibodies in male mice that were first vaccinated with modified vaccinia virus Ankara vectors (MVA) expressing full-length WA1/2020 Spike protein. Together, these results demonstrate that our attenuated virus may be a promising nasal vaccine candidate for boosting mucosal immunity against future SARS-CoV-2 VOCs.

Intranasal delivery of a rationally attenuated SARS-CoV-2 is immunogenic and protective in Syrian hamsters

Few live attenuated severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines are in pre-clinical or clinical development. We seek to attenuate SARS-CoV-2 (isolate WA1/2020) by removing the polybasic insert within the spike protein and the open reading frames (ORFs) 6-8, and by introducing mutations that abolish non-structural protein 1 (Nsp1)-mediated toxicity. The derived virus (WA1-ΔPRRA-ΔORF6-8-Nsp1^K164A/H165A) replicates to 100- to 1000-fold-lower titers than the ancestral virus and induces little lung pathology in both K18-human ACE2 (hACE2) transgenic mice and Syrian hamsters. Immunofluorescence and transcriptomic analyses of infected hamsters confirm that three-pronged genetic modifications attenuate the proinflammatory pathways more than the removal of the polybasic cleavage site alone. Finally, intranasal administration of just 100 PFU of the WA1-ΔPRRA-ΔORF6-8-Nsp1^K164A/H165A elicits robust antibody responses in Syrian hamsters and protects against SARS-CoV-2-induced weight loss and pneumonia. As a proof-of-concept study, we demonstrate that live but sufficiently attenuated SARS-CoV-2 vaccines may be attainable by rational design.

Long-term immunity in convalescent Syrian hamsters provides protection against new-variant SARS-CoV-2 infection of the lower but not upper respiratory tract

COVID-19 vaccines provide high levels of protection against severe disease and hospitalization due to severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2) infection. Vaccination may be less effective in preventing shedding of infectious viruses from otherwise immune patients. In this study, we describe breakthrough infections and shedding of infectious viruses in convalescent hamsters without significant replication in the lower respiratory tract following reinfection by Alpha and Delta variants despite high levels of circulating antibodies in sera. Using convalescent hamsters with long-term immunity (up to 1 year) following infection by ancestral SARS-CoV-2, we can model aspects of recurring COVID-19 in the context of preexisting immunity.

SARS-CoV-2 B.1.1.7 Infection of Syrian Hamster Does Not Cause More Severe Disease, and Naturally Acquired Immunity Confers Protection

Epidemiological studies have revealed the emergence of multiple severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants of concern (VOC), including the lineage B.1.1.7 that is rapidly replacing old variants. The B.1.1.7 variant has been linked to increased morbidity rates, transmissibility, and potentially mortality. To assess viral fitness in vivo and to address whether the B.1.1.7 variant is capable of immune escape, we conducted infection and reinfection studies in naive and convalescent Syrian hamsters (>10 months old). Nasal wash samples from hamsters infected by a B.1.1.7 variant exhibited slightly higher viral RNA levels but lower infectious titers than those from B.1 (G614) variant-infected hamsters, and the two variants induced comparable lung pathologies in hamsters. Despite a sporadic and transient low-level infection in the nasal cavity, convalescent hamsters that had recovered from a previous USA-WA1 isolate (D614) infection displayed no observable clinical signs or lung pathology following B.1.1.7 rechallenge. Altogether, our study did not find that the B.1.1.7 variant significantly differs from the B.1 variant in pathogenicity in Syrian hamsters and that a heterologous natural infection-induced immunity confers protection against a secondary challenge by the B1.1.7 variant. IMPORTANCE The rapid emergence of several variants of concern of SARS-CoV-2 calls for evaluations of viral fitness and pathogenicity in animal models in order to understand the mechanism of enhanced transmission and the possible increases in morbidity and mortality rates. Here, we demonstrated that immunity naturally acquired through a prior infection with the first-wave variant does confer nearly complete protection against the B.1.1.7 variant in Syrian hamsters upon reexposure. Strikingly, although the B.1.1.7 variant appears to replicate to a higher level in the nose than the ancestral B.1 variant, it does not induce more severe lung pathology in hamsters.

SARS-CoV-2 B.1.1.7 infection of Syrian hamster does not cause more severe disease and is protected by naturally acquired immunity

Epidemiological studies have revealed the emergence of multiple SARS-CoV-2 variants of concern (VOC), including the lineage B.1.1.7 that is rapidly replacing old variants. The B.1.1.7 variant has been linked to increased morbidity rates, transmissibility, and potentially mortality (1). To assess viral fitness in vivo and to address whether the B.1.1.7 variant is capable of immune escape, we conducted infection and re-infection studies in naïve and convalescent Syrian hamsters (>10 months old). Hamsters infected by either a B.1.1.7 variant or a B.1 (G614) variant exhibited comparable viral loads and pathology. Convalescent hamsters that were previously infected by the original D614 variant were protected from disease following B.1.1.7 challenge with no observable clinical signs or lung pathology. Altogether, our study did not find that the B.1.1.7 variant significantly differs from the B.1 variant in pathogenicity in hamsters and that natural infection-induced immunity confers protection against a secondary challenge by the B1.1.7 variant.

The G614 pandemic SARS-CoV-2 variant is not more pathogenic than the original D614 form in adult Syrian hamsters

Dynamic tracking of variant frequencies among viruses circulating in the global pandemic has revealed the emergence and dominance of a D614G mutation in the SARS-CoV-2 spike protein. To address whether pandemic SARS-CoV-2 G614 variant has evolved to become more pathogenic, we infected adult hamsters (>10 months old) with two natural SARS-CoV-2 variants carrying either D614 or G614 spike protein to mimic infection of the adult/elderly human population. Hamsters infected by the two variants exhibited comparable viral loads and pathology in lung tissues as well as similar amounts of virus shed in nasal washes. Altogether, our study does not find that naturally circulating D614 and G614 SARS-CoV-2 variants differ significantly in pathogenicity in hamsters.

SARS-CoV-2 infection induces protective immunity and limits transmission in Syrian hamsters

A critical question in understanding the immunity to SARS-COV-2 is whether recovered patients are protected against re-challenge and transmission upon second exposure. We developed a Syrian hamster model in which intranasal inoculation of just 100 TCID50 virus caused viral pneumonia. Aged hamsters developed more severe disease and even succumbed to SARS-CoV-2 infection, representing the first lethal model using genetically unmodified laboratory animals. After initial viral clearance, the hamsters were re-challenged with 105 TCID50 SARS-CoV-2 and displayed more than 4 log reduction in median viral loads in both nasal washes and lungs in comparison to primary infections. Most importantly, re-challenged hamsters were unable to transmit virus to naïve hamsters, and this was accompanied by the presence of neutralizing antibodies. Altogether, these results show that SARS-CoV-2 infection induces protective immunity that not only prevents re-exposure but also limits transmission in hamsters. These findings may help guide public health policies and vaccine development and aid evaluation of effective vaccines against SARS-CoV-2.

A method for detection of SARS-CoV-2 RNA in healthy human stool: a validation study

Background

Faecal shedding of SARS-CoV-2 has raised concerns about transmission through faecal microbiota transplantation procedures. Validation parameters of authorised tests for SARS-CoV-2 RNA detection in respiratory samples are described in product labelling, whereas the published methods for SARS-CoV-2 detection from faecal samples have not permitted a robust description of the assay parameters. We aimed to develop and validate a test specifically for detection of SARS-CoV-2 in human stool.

Methods

In this validation study, we evaluated performance characteristics of a reverse transcriptase real-time PCR (RT-rtPCR) test for detection of SARS-CoV-2 in human stool specimens by spiking stool with inactivated SARS-CoV-2 material. A modified version of the US Centers for Disease Control and Prevention RT-rtPCR SARS-CoV-2 test was used for detection of viral RNA. Analytical sensitivity was evaluated in freshly spiked stool by testing two-fold dilutions in replicates of 20. Masked samples were tested by a second laboratory to evaluate interlaboratory reproducibility. Short-term (7-day) stability of viral RNA in stool samples was assessed with four different stool storage buffers (phosphate-buffered saline, Cary-Blair medium, Stool Transport and Recovery [STAR] buffer, and DNA/RNA Shield) kept at −80°C, 4°C, and ambient temperature (approximately 21°C). We also tested clinical stool and anal swab specimens from patients who were SARS-CoV-2 positive by nasopharyngeal testing.

Findings

The lower limit of detection of the assay was found to be 3000 viral RNA copies per g of original stool sample, with 100% detection across 20 replicates assessed at this concentration. Analytical sensitivity was diminished by approximately two times after a single freeze-thaw cycle at −80°C. At 100 times the limit of detection, spiked samples were generally stable in all four stool storage buffers tested for up to 7 days, with maximum changes in mean threshold cycle values observed at −80°C storage in Cary-Blair medium (from 29·4 [SD 0·27] at baseline to 30·8 [0·17] at day 7; p<0·0001), at 4°C storage in DNA/RNA Shield (from 28·5 [0·15] to 29·8 [0·09]; p=0·0019), and at ambient temperature in STAR buffer (from 30·4 [0·24] to 32·4 [0·62]; p=0·0083). 30 contrived SARS-CoV-2 samples were tested by a second laboratory and were correctly identified as positive or negative in at least one of two rounds of testing. Additionally, SARS-CoV-2 RNA was detected using this assay in the stool and anal swab specimens of 11 of 23 individuals known to be positive for SARS-CoV-2.

Interpretation

This is a sensitive and reproducible assay for detection of SARS-CoV-2 RNA in human stool, with potential uses in faecal microbiota transplantation donor screening, sewage monitoring, and further research into the effects of faecal shedding on the epidemiology of the COVID-19 pandemic.

Funding

National Institute of Allergy and Infectious Diseases, US National Institutes of Health; Center for Biologics Evaluation and Research, US Food and Drug Administration.

Sclareol attenuates the development of atopic dermatitis induced by 2,4-dinitrochlorobenzene in mice

Context: Atopic dermatitis is a common chronic inflammatory skin disease affecting up to 20% of children and 1% of adults worldwide. Treatment of atopic dermatitis include corticosteroids and immunosuppressants, such as calcineurin inhibitors and methotrexate. However, these treatments often bring about adverse effects including skin atrophy, osteoporosis, skin cancer, and metabolic syndrome. Objective: In this study, we evaluated the therapeutic effects and mechanisms of sclareol, a natural diterpene, on atopic dermatitis (AD)-like skin lesions induced by 2,4-dinitrochlorobenzene (DNCB) in mice. Materials and methods: To evaluate the effect of sclareol in vivo model, BALB/c mice were repeatedly injected intraperitoneally with sclareol (50 and 100 mg/kg) in 2,4-dinitrochlorobenzene (DNCB)-induced AD-like murine model. Major assays were enzyme-linked immunosorbent assay, histological analysis, flow cytometry, western blot analysis. Results: Intraperitoneal administration of sclareol (50 and 100 mg/kg) significantly attenuated AD-like symptoms, such as serum IgE levels, epidermal/dermal hyperplasia, and the numbers of infiltrated mast cells. In addition, systemic sclareol treatments reduced local pro-inflammatory cytokine concentrations, including IL-6, IL-1b, TNF-a, IL-4, IFN-g, and IL-17A, on AD-like lesions. Furthermore, we demonstrated that sclareol also suppressed T cell activation and the capability of cytokine productions (IFN-g, IL-4 and IL-17A) in response to DNCB stimulation. By examining the skin homogenate, we found that sclareol inhibited the AD-like severity likely through suppressions of both NF-kB translocation and phosphorylation of the MAP kinase pathway. Discussion and conclusions: Cumulatively, our results indicate that sclareol induced anti-inflammatory effects against the atopic dermatitis elicited by DNCB. Thus, sclareol is worth of being further evaluated for its potential therapeutic benefits for the clinical treatment of AD.