A bivalent ChAd nasal vaccine protects against SARS-CoV-2 BQ.1.1 and XBB.1.5 infection and disease in mice and hamsters (preprint)

We previously described a nasally delivered monovalent adenoviral-vectored SARS-CoV-2 vaccine (ChAd-SARS-CoV-2-S, targeting Wuhan-1 spike [S]; iNCOVACC) that is currently used in India as a primary or booster immunization. Here, we updated the mucosal vaccine for Omicron variants by creating ChAd-SARS-CoV-2-BA.5-S, which encodes for a pre-fusion and surface-stabilized S protein of the BA.5 strain, and then tested monovalent and bivalent vaccines for efficacy against circulating variants including BQ.1.1 and XBB.1.5. Whereas monovalent ChAd-vectored vaccines effectively induced systemic and mucosal antibody responses against matched strains, the bivalent ChAd-vectored vaccine elicited greater breadth. However, serum neutralizing antibody responses induced by both monovalent and bivalent vaccines were poor against the antigenically distant XBB.1.5 Omicron strain and did not protect in passive transfer experiments. Nonetheless, nasally delivered bivalent ChAd-vectored vaccines induced robust antibody and spike-specific memory T cell responses in the respiratory mucosa, and conferred protection against WA1/2020 D614G and Omicron variants BQ.1.1 and XBB.1.5 in the upper and lower respiratory tracts of both mice and hamsters. Our data suggest that a nasally delivered bivalent adenoviral-vectored vaccine induces protective mucosal and systemic immunity against historical and emerging SARS-CoV-2 strains without requiring high levels of serum neutralizing antibody.

THE EFFECT OF THE MEASLES, MUMPS AND RUBELLA VACCINE ON INNATE AND ADAPTIVE IMMUNE RESPONSES IN PERSONS RECEIVING A SARS-COV-2 mRNA VACCINE.A SUB-STUDY OF THE CROWN CORONATION TRIAL (preprint)

ABSTRACT Vaccination elicits a complex combination of immune responses. Immune memory formation is observed not only in the antibody responses of B-cells, but also in the T-cell response. Moreover, some live attenuated vaccines such as measles-containing vaccines can induces heterologous protection, likely through induction of memory characteristics in the innate immune response. Little is known about the immunological interaction that may occur when different vaccines are administered soon after one another, especially in relation to the novel COVID-19 vaccines. The aim of this study was to compare the innate and adaptive immune responses between persons randomized to receive either a MMR or a placebo (0.9% NaCl) injection prior to their SARS-CoV-2 mRNA vaccination. We compared: i) the cytokine and chemokine production (tumor necrosis factor [TNF]-, interleukin [IL]-1{beta}, IL-6, IL-10, IL-17, IL-22, interferon [IFN]- and IFN-{gamma}) after in-vitro stimulation of peripheral blood mononuclear cells (PBMCs) with heterologous stimuli (severe acute respiratory syndrome coronavirus [SARS-CoV]-2, measles mumps and rubella [MMR] vaccine, Toll-like receptor [TLR]-3 ligand, TLR-7/8 ligand, or TLR-4 ligand), and ii) the SARS-CoV-2 neutralizing antibody responses. Ninety-five participants in the CROWN CORONATION trial (NCT04333732; a randomized control trial comparing MMR to placebo for prevention of COVID-19) agreed to an additional single blood sample collection for this immunological study. Samples were collected around 196 (SD 22) days after administration of MMR or placebo, and around 105 (SD 27) days after their second SARS-CoV-2 mRNA vaccine injection. Twenty-four percent of participants were older than fifty and sixty-seven percent were female. The median TNF- response to stimulation with MMR was 8315.3 pg/mL in the MMR group and 4340.5 pg/mL in the placebo group; adjusted median difference (95% CI) 3012.5 (-4734.1; -323.5); p=0.017. No other significant differences were noted in the cytokine and chemokine responses between treatment groups. The SARS-CoV-2 neutralization assay geometric mean (SD) IC50 in the MMR group was 507.6 (2.6) and in the placebo group was 515.7 (2.2); ratio of geometric means (95% CI) 1.0 (0.7; 1.5). Pre-exposure to MMR vaccine was generally not associated with changes in cytokine and chemokine responses of stimulated PBMCs at 105 (27) days after SARS-CoV-2 mRNA vaccination. MMR vaccination led only to an increase of TNF- production in response to an additional ex-vivo stimulation with the MMR vaccine. The SARS-CoV-2 neutralization IC50 values did not differ between MMR and placebo groups. Further studies using a repeated measures design would be better suited to explore or rule-out any short-lived vaccine response and vaccine-vaccine immunological interaction.

The highly conserved stem-loop II motif is important for the lifecycle of astroviruses but dispensable for SARS-CoV-2 (preprint)

The stem-loop II motif (s2m) is an RNA element present in viruses from divergent viral families, including astroviruses and coronaviruses, but its functional significance is unknown. We created deletions or substitutions of the s2m in astrovirus VA1 (VA1), classic human astrovirus 1 (HAstV1) and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). For VA1, recombinant virus could not be rescued upon partial deletion of the s2m or substitutions of G-C base pairs. Compensatory substitutions that restored the G-C base-pair enabled recovery of VA1. For HAstV1, a partial deletion of the s2m resulted in decreased viral titers compared to wild-type virus, and reduced activity in a replicon system. In contrast, deletion or mutation of the SARS-CoV-2 s2m had no effect on the ability to rescue the virus, growth in vitro, or growth in Syrian hamsters. Our study demonstrates the importance of the s2m is virus-dependent.

A public vaccine-induced human antibody protects against SARS-CoV-2 and emerging variants (preprint)

The emergence of antigenically distinct severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants with increased transmissibility is a public health threat. Some of these variants show substantial resistance to neutralization by SARS-CoV-2 infection- or vaccination-induced antibodies, which principally target the receptor binding domain (RBD) on the virus spike glycoprotein. Here, we describe 2C08, a SARS-CoV-2 mRNA vaccine-induced germinal center B cell-derived human monoclonal antibody that binds to the receptor binding motif within the RBD. 2C08 broadly neutralizes SARS-CoV-2 variants with remarkable potency and reduces lung inflammation, viral load, and morbidity in hamsters challenged with either an ancestral SARS-CoV-2 strain or a recent variant of concern. Clonal analysis identified 2C08-like public clonotypes among B cell clones responding to SARS-CoV-2 infection or vaccination in at least 20 out of 78 individuals. Thus, 2C08-like antibodies can be readily induced by SARS-CoV-2 vaccines and mitigate resistance by circulating variants of concern.

Human neutralizing antibodies against SARS-CoV-2 require intact Fc effector functions and monocytes for optimal therapeutic protection (preprint)

SARS-CoV-2 has caused the global COVID-19 pandemic. Although passively delivered neutralizing antibodies against SARS-CoV-2 show promise in clinical trials, their mechanism of action in vivo is incompletely understood. Here, we define correlates of protection of neutralizing human monoclonal antibodies (mAbs) in SARS-CoV-2-infected animals. Whereas Fc effector functions are dispensable when representative neutralizing mAbs are administered as prophylaxis, they are required for optimal protection as therapy. When given after infection, intact mAbs reduce SARS-CoV-2 burden and lung disease in mice and hamsters better than loss-of-function Fc variant mAbs. Fc engagement of neutralizing antibodies mitigates inflammation and improves respiratory mechanics, and transcriptional profiling suggests these phenotypes are associated with diminished innate immune signaling and preserved tissue repair. Immune cell depletions establish that neutralizing mAbs require monocytes for therapeutic efficacy. Thus, potently neutralizing mAbs require Fc effector functions for maximal therapeutic benefit during therapy to modulate protective immune responses and mitigate lung disease.

6-Thioguanine blocks SARS-CoV-2 replication by inhibition of PLpro protease activities (preprint)

A recently emerged betacoronavirus, SARS-CoV-2, has led to a global health crisis that calls for the identification of effective therapeutics for COVID-19 disease. Coronavirus papain-like protease (PLpro) is an attractive drug target as it is essential for viral polyprotein cleavage and for deconjugation of ISG15, an antiviral ubiquitin-like protein. We show here that 6-Thioguanine (6-TG) inhibits SARS-CoV-2 PLpro-catalyzed viral polyprotein cleavage and ISG15 deconjugation in cells and inhibits replication of SARS-CoV-2 in Vero-E6 cells and Calu3 cells at submicromolar levels. As a well-characterized FDA-approved orally delivered drug, 6-TG represents a promising therapeutic for COVID-19 and other emerging coronaviruses.One Sentence Summary A repurposed drug that targets an essential enzymatic activity of SARS-CoV-2 represents a promising COVID-19 therapeutic.Competing Interest StatementThe authors have declared no competing interest.View Full Text