Potent SARS-CoV-2 neutralizing antibodies with therapeutic effects in two animal models

Overcoming antibody-resistant SARS-CoV-2 variants with bispecific antibodies constructed using non-neutralizing antibodies

A current challenge is the emergence of SARS-CoV-2 variants, such as BQ.1.1 and XBB.1.5, that can evade immune defenses, thereby limiting antibody drug effectiveness. Emergency-use antibody drugs, including the widely effective bebtelovimab, are losing their benefits. One potential approach to address this issue are bispecific antibodies which combine the targeting abilities of two antibodies with distinct epitopes. We engineered neutralizing bispecific antibodies in the IgG-scFv format from two initially non-neutralizing antibodies, CvMab-6 (which binds to the receptor-binding domain [RBD]) and CvMab-62 (targeting a spike protein S2 subunit epitope adjacent to the known anti-S2 antibody epitope). Furthermore, we created a bispecific antibody by incorporating the scFv of bebtelovimab with our anti-S2 antibody, demonstrating significant restoration of effectiveness against bebtelovimab-resistant BQ.1.1 variants. This study highlights the potential of neutralizing bispecific antibodies, which combine existing less effective anti-RBD antibodies with anti-S2 antibodies, to revive the effectiveness of antibody therapeutics compromised by immune-evading variants.

Characterization of a neutralizing antibody that recognizes a loop region adjacent to the receptor-binding interface of the SARS-CoV-2 spike receptor-binding domain

Although the global crisis caused by the coronavirus disease 2019 (COVID-19) pandemic is over, the global epidemic of the disease continues. Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the cause of COVID-19, initiates infection via the binding of the receptor-binding domain (RBD) of its spike protein to the human angiotensin-converting enzyme II (ACE2) receptor, and this interaction has been the primary target for the development of COVID-19 therapeutics. Here, we identified neutralizing antibodies against SARS-CoV-2 by screening mouse monoclonal antibodies and characterized an antibody, CSW1-1805, that targets a narrow region at the RBD ridge of the spike protein. CSW1-1805 neutralized several variants in vitro and completely protected mice from SARS-CoV-2 infection. Cryo-EM and biochemical analyses revealed that this antibody recognizes the loop region adjacent to the ACE2-binding interface with the RBD in both a receptor-inaccessible "down" state and a receptor-accessible "up" state and could stabilize the RBD conformation in the up-state. CSW1-1805 also showed different binding orientations and complementarity determining region properties compared to other RBD ridge-targeting antibodies with similar binding epitopes. It is important to continuously characterize neutralizing antibodies to address new variants that continue to emerge. Our characterization of this antibody that recognizes the RBD ridge of the spike protein will aid in the development of future neutralizing antibodies.IMPORTANCESARS-CoV-2 cell entry is initiated by the interaction of the viral spike protein with the host cell receptor. Therefore, mechanistic findings regarding receptor recognition by the spike protein help uncover the molecular mechanism of SARS-CoV-2 infection and guide neutralizing antibody development. Here, we characterized a SARS-CoV-2 neutralizing antibody that recognizes an epitope, a loop region adjacent to the receptor-binding interface, that may be involved in the conformational transition of the receptor-binding domain (RBD) of the spike protein from a receptor-inaccessible "down" state into a receptor-accessible "up" state, and also stabilizes the RBD in the up-state. Our mechanistic findings provide new insights into SARS-CoV-2 receptor recognition and guidance for neutralizing antibody development.

Diminished neutralizing activity against the XBB1.5 strain in 55.9% of individuals post 6 months COVID-19 mRNA booster vaccination: insights from a pseudovirus assay on 1,353 participants in the Fukushima vaccination community survey, Japan

This study investigates the neutralizing activity against the XBB1.5 variant and the ancestral strain in a population post-bivalent vaccination using a pseudo virus assay validated with authentic virus assay. While bivalent booster vaccination and past infections enhanced neutralization against the XBB 1.5 strain, individuals with comorbidities showed reduced responses. The study suggests the need for continuous vaccine updates to address emerging SARS-CoV-2 variants and highlights the importance of monitoring real-world immune responses.

SARS-CoV-2 induces inflammation and intracranial infection through the olfactory epithelium-olfactory bulb pathway in non-human primates

We examined the histopathological changes in the olfactory mucosa of cynomolgus and rhesus macaque models of SARS-CoV-2 infection. SARS-CoV-2 infection induced severe inflammatory changes in the olfactory mucosa. A major histocompatibility complex (MHC) class II molecule, HLA-DR was expressed in macrophage and supporting cells, and melanocytes were increased in olfactory mucosa. Supporting cells and olfactory neurons were infected, and SARS-CoV-2 N protein was detected in the axons of olfactory neurons and in olfactory bulbs. Viral RNA was detected in olfactory bulbs and brain tissues. The olfactory epithelium-olfactory bulb pathway may be important as a route for intracranial infection by SARS-CoV-2.

Novel Omicron Variants Enhance Anchored Recognition of TMEM106B: A New Pathway for SARS-CoV-2 Cellular Invasion

The recent discovery that TMEM106B serves as a receptor mediating ACE2-independent SARS-CoV-2 entry into cells deserves attention, especially in the background of the frequent emergence of mutant strains. Here, the structure-dynamic features of this novel pathway are dissected deeply. Our investigation revealed that the large loop (RBD@471-491) could anchor TMEM106B, which was then firmly locked by another loop (RBD@444-451). The novel and widely disseminated Omicron variants (BA.2.86/EG.5.1) affect the anchoring recognition of proteins, with BA.2.86 being more likely to impact cells with limited or undetectable ACE2 expression. The large loop of the EG.5.1 variant captures TMEM106B poorly due to impaired electrostatic complementarity. Furthermore, we emphasize that antibody design against these two loops could enhance the protection of ACE2 low-expressing cells according to the alanine scanning mutagenesis of multiple antibodies. We hope this study will provide a novel perspective for the prevention and treatment against this new viral invasion pathway.

Boosted production of antibodies that neutralized different SARS-CoV-2 variants in a COVID-19 convalescent following messenger RNA vaccination - a case study

Vaccinated convalescents do not develop severe COVID-19 after infection with new SARS-CoV-2 variants. We questioned how messenger RNA (mRNA) vaccination of convalescents provides protection from emerging virus variants. From the cohort of 71 convalescent plasma donors, we identified a patient who developed immune response to infection with SARS-CoV-2 variant of 20A clade and who subsequently received mRNA vaccine encoding spike (S) protein of strain of 19A clade. We showed that vaccination increased the production of immune cells and anti-S antibodies in the serum. Serum antibodies neutralized not only 19A and 20A, but also 20B, 20H, 21J, and 21K virus variants. One of the serum antibodies (100F8) completely neutralized 20A, 21J, and partially 21K strains. 100F8 was structurally similar to published Ab188 antibody, which recognized non-conserved epitope on the S protein. We proposed that 100F8 and other serum antibodies of the patient which recognized non- and conserved epitopes of the S protein, could have additive or synergistic effects to neutralize various virus variants. Thus, mRNA vaccination could be beneficial for convalescents because it boosts production of neutralizing antibodies with broad-spectrum activity.

Glycyrrhiza glabra L. Extracts and Other Therapeutics against SARS-CoV-2 in Central Eurasia: Available but Overlooked

In Central Eurasia, the availability of drugs that are inhibitors of the SARS-CoV-2 virus and have proven clinical efficacy is still limited. The aim of this study was to evaluate the activity of drugs that were available in Kazakhstan during the acute phase of the epidemic against SARS-CoV-2. Antiviral activity is reported for Favipiravir, Tilorone, and Cridanimod, which are registered drugs used for the treatment of respiratory viral infections in Kazakhstan. A licorice (Glycyrrhiza glabra) extract was also incorporated into this study because it offered an opportunity to develop plant-derived antivirals. The Favipiravir drug, which had been advertised in local markets as an anti-COVID cure, showed no activity against SARS-CoV-2 in cell cultures. On the contrary, Cridanimod showed impressive high activity (median inhibitory concentration 66 μg/mL) against SARS-CoV-2, justifying further studies of Cridanimod in clinical trials. Tilorone, despite being in the same pharmacological group as Cridanimod, stimulated SARS-CoV-2 replication in cultures. The licorice extract inhibited SARS-CoV-2 replication in cultures, with a high median effective concentration of 16.86 mg/mL. Conclusions: The synthetic, low-molecular-weight compound Cridanimod suppresses SARS-CoV-2 replication at notably low concentrations, and this drug is not toxic to cells at therapeutic concentrations. In contrast to its role as an inducer of interferons, Cridanimod is active in cells that have a genetic defect in interferon production, suggesting a different mechanism of action. Cridanimod is an attractive drug for inclusion in clinical trials against SARS-CoV-2 and, presumably, other coronaviruses. The extract from licorice shows low activity against SARS-CoV-2. At the same time, high doses of 2 g/kg of this plant extract show little or no acute toxicity in animal studies; for this reason, licorice products can still be considered for further development as a safe, orally administered adjunctive therapy.

Potent neutralizing broad-spectrum antibody against SARS-CoV-2 generated from dual-antigen-specific B cells from convalescents

Several antibody therapeutics have been developed against SARS-CoV-2; however, they have attenuated neutralizing ability against variants. In this study, we generated multiple broadly neutralizing antibodies from B cells of convalescents, by using two types of receptor-binding domains, Wuhan strain and the Gamma variant as bait. From 172 antibodies generated, six antibodies neutralized all strains prior to the Omicron variant, and the five antibodies were able to neutralize some of the Omicron sub-strains. Structural analysis showed that these antibodies have a variety of characteristic binding modes, such as ACE2 mimicry. We subjected a representative antibody to the hamster infection model after introduction of the N297A modification, and observed a dose-dependent reduction of the lung viral titer, even at a dose of 2 mg/kg. These results demonstrated that our antibodies have certain antiviral activity as therapeutics, and highlighted the importance of initial cell-screening strategy for the efficient development of therapeutic antibodies.