Mouse monoclonal antibody protects against SARS-CoV-2 wild-type, UK and South African variants

Importance of crossNeutralizing antibody The recently emerging variants of Severe Acute Respiratory Syndrome coronavirus 2 (SARS-CoV-2) are the fact that these variants are highly contagious and can evade an immune response to early variants of this virus. It is clear in the light of.

New preprint research treatise submitted to bioRxiv* The server reports on the ability of a set of neutralized mouse antibodies to protect mice from multiple strains of SARS-CoV-2.

Antibody and virus neutralization

Approximately 20 vaccines are approved worldwide for use in combination with several monoclonal antibodies to prevent and treat SARS-CoV-2 infection.

The virus invades the host cell and successfully infects by binding through the virus. Spike protein To angiotensin converting enzyme 2 (ACE2), which is a host cell receptor. The portion of the spike that binds to the receptor, called the receptor binding domain (RBD), forms an attractive target for both therapeutic and prophylactic antibodies.

Neutralizing antibody titers are highly correlated with protection against reinfection, but vaccination takes time to cover the global population, so therapeutic antibodies and drugs to treat and prevent serious illness are urgent. Is needed for.

Currently available monoclonal antibodies (mAbs) have been created against spikes in the original Wuhan variant of the virus. However, the appearance of escape mutations, especially in the RBD region of spikes, threatens the usefulness of these mAbs.

Mutations in RBD can reduce the efficiency of mAbs, as most neutralizing antibodies act by blocking viral entry that targets RBD.

The N-terminal domain (NTD) is another region that is often targeted by new variants because it is neutralized by many antibodies. Therefore, these mutants may be able to evade vaccine-induced antibodies.

Research objectives and details

Researchers from Mount Sinai Medical University Kramer InstituteThe purpose of this study was to evaluate the binding and neutralizing ability of 14 mouse mAbs produced against viral RBD against both RBD and peplomer. They also evaluated the potential of non-neutralized mAbs to reduce viral load.

Third, this study examined the binding of these mAbs to RBD mutants, including point and grouping mutations that define the three major mutants (VOCs) of concern-UK (B1. 1.7), South African (SA) mutant (B.1.351), and Brazilian variant (P.1).

Finally, mAbs were tested for neutralization against UK and SA variants.

How was the result?

Mouse immunoglobulin G (IgG) antibody was produced in hybridoma cells. It was found that all 14 bind to RBD with high affinity, as shown by the very low minimal coupling concentration (MBC).

When tested against full peplomers, most of them bound well, but three had higher MBC compared to RBD. Researchers hypothesize that this may be due to coating of the RBD-binding epitope on the complete spike compared to RBD expressed alone.

Of the 14 mAbs, 10 were specific for SARS-CoV-2RBD, but 4 were also cross-reactive with SARS-CoVRBD.

Six are high when tested with live virus in a microneutralization assay where the ability of the antibody to block viral infection of cultured cells is determined as the reciprocal of the dilution at which the cells remain completely uninfected. Showed the sum ability.

In all six cases, the concentration (IC50) at which 50% of the cells remained free of live virus was very low, 0.1-1 ug / ml. This indicates that these can prevent virus invasion and replication with high dilutions, especially the two with the lowest IC50s.

Decreased viral titer in mice

Researchers tested mAbs for their ability to block viral invasion and reduce viral load in engineered mice expressing the human ACE2 gene. Mice were given mAb 2 hours before SARS-CoV-2.

A plaque reduction neutralization test showed that only 6 mAbs with neutralizing ability could protect animals from viral invasion and replication. Three of the six reduced viral load by 2 logs on day 3, while the other two caused a significantly more significant reduction in viral titers.

On day 5, none of the animals treated with neutralized mAbs showed signs of significant viral presence in the lungs, but two showed residual virus.

Lung condition decreased

Lung tissue was collected on day 4 for histopathology and immunohistochemistry (IHC). This showed some evidence of interstitial pneumonia, probably due to high doses of the virus.

Injections of the adenovirus hACE2 vector showed mild inflammation, but mice treated with the vector and virus had higher inflammation scores. There were no signs of antibody-dependent enhancement enhancement (ADE).

Few nucleoproteins were detected, indicating that all neutralized mAbs prevented the virus from entering the cells and reduced the viral titer in the lungs.

Bind to RBD variant

The study also showed that some variant RBDs, such as K487R and N487R, each lost complete binding of one mAb. Mutants E484K, F486A, and F490K also reduced binding by the third mAb. Grouped mutations in the SA variant RBD also caused loss of binding by the same mAb.

However, five of the mAbs maintained a 50% binding affinity for at least all mutant RBDs, and some showed higher binding than wild-type RBDs. The researchers commented:The ability to bind to all RBDs can be a function of the antibody’s affinity, and if high, it will allow the antibody to maintain its footprint... “

Overall, neutralized mAbs bound to wild-type and mutant RBD at somewhat comparable levels.

Of particular interest is that four of the six neutralized mAbs bound to both wild-type and SA RBD variants, and all six neutralized the UK RBD variant. The latter has only one RBD mutation, N501Y.

Of the four that maintained binding and neutralization of the SA mutant, IC50 increased 2.5 to 5 times that of the wild-type virus or UK mutant.

The loss of neutralization of the SA mutant may be due to poor binding of E484-containing RBD in one mAb and altered spike epitope presentation in the other mAb.

Inhibition of ACE2-RBD binding

Researchers also found by structural analysis of six neutralized mAbs that two of them were unable to form a stable complex with RBD and could not be visualized. Three of them showed overlap with the ACE2 binding site and could explain how they prevented ACE2-RBD binding.

They show that they bind to RBD at different angles and bind to different epitopes.

What is the impact?

This study shows that spike RBD can undergo multiple mutations while retaining its ability to bind to the ACE2 receptor and cause host cell infection.

“”The plasticity of RBD is alarming, as it can be reduced by major changes in RBD. Effectiveness of Additional booster immunization with current and updated vaccines may be needed for future protection.. “

The lack of protection by non-neutralizing mAbs is due to the IgG1 isotype that interferes with the interaction mediated by the effector Fc receptor (FcR) in mice. Therefore, antibodies that do not activate FcR and do not have the ability to neutralize lack a protective effect.

The two antibodies best protected from viral entry are IgG2a, a subtype associated with mouse Fc-Fc interactions, and the hypothesis that antibody binding to the activating effector FcR is key to the protective effect of the antibody. I support.

In humans, IgG2 antibodies interact strongly with FcR, and most antibodies to this virus belong to this isotype.

This study suggests that humanized forms of these neutralized mAbs could be developed as therapeutic agents with potent activity against wild-type viruses as well as UK and SA mutants.

It’s all in a long but excellent title:

“A mouse monoclonal antibody against RBD of SARS-CoV-2 neutralizes real wild-type SARS-CoV-2, B.1.1.7 and B.1.351 viruses and neutralizes in vivo protection in a mouse model. To do.” https://t.co/Lbw4seLU4D

-Dr. Kevin Purcell (@kevinpurcell) April 6, 2021

*Important Notices

bioRxiv publishes unpeer-reviewed preliminary scientific reports and should not be considered definitive, guide clinical / health-related behaviors, or be treated as established information.