Anti-SARS-CoV-2 antibodies administered by NTD protect against lethal infection

As the world struggles with the onset of severe respiratory coronavirus 2 (SARS-CoV-2) syndrome, responsible for more than 1.6 million deaths and 76 million diseases worldwide, -researchers trying to find out what the symptoms of lethality, infectivity and protection are. Such data would help in the dissemination and development of immunosuppressive and curative antivirals and vaccines. A new introduction recently appeared on the bioRxiv * server describes the high level of protection provided by antibodies targeting the N-terminal domain (NTD) of the virus.

Most antibody studies on this virus have focused on cloned single B cells, and their antibodies scavenged for binding and neutralizing activity. in vitro. These indicate the presence of several spike-initiated spike-induced epitopes of monoclonal antibodies (mAbs), mainly those that bind to the viral receptor binding domain (RBD).

On the other hand, little attention has been paid to the epitopes identified by circulating antibodies in convalescent plasma, and in particular IgG antibodies produced by plasma cells. However, these are a key component of the neutral immune response, and it is important to understand that plasma cells and B cells recognize different epitopes and appear at different times. This is why anti-SARS-CoV-2 or RBD B spike cells appear at high frequencies along with the presence of powerful neutral antibodies, while plasma neutralization activity remains low.

Study details

Blood samples were obtained from four 2019 coronavirus infections (COVID-19). They were all convalescents, having been shown to be COVID-19 by reverse-transcriptase polymerase chain reaction (RT PCR). They were all 11-19 days from the onset of the symptom.

The researchers found that 84% of polyclonal IgG antibodies target the ectodomine spike epitopes (S-ECD) that are outside the receptor binding domain (RBD), including the IgG lines plasma most abundant in the four samples. Plasma IgG response was oligoclonal in all cases, with sequences 6–22. Just one line made up nearly a fifth of the entire antibody repertoire.

This agrees with earlier studies, showing that most mAbs connect to regions of the spike outside the RBD. The Seq IgG device used here is known to capture 70% of circulating antibodies, and 85% of the most abundant antibodies.

NTD antibodies have strong neutralizing activity

In one patient who recovered from just two days of symptoms and had the lowest plasma-neutralizing titers, the researchers detected six IgG sequences, four of which made up more than 5% of the total antibody set. S-ECD. However, the top two alone made up> 70%, and the top four (1 anti-S2, 2 anti-NTD and 1 anti-RBD) made up ~ 94% of the plasma antibodies Total S-ECD. The top two peaks also reflected widespread diversity within each line.

Of these, mAbs CM29-CM32 were the most extended clones in the top four series. CM29, CM30 and CM31 specifically identified the S2 spike subunit, the NTD and the RBD, respectively. The most powerful neutralizing activity was seen with CM30, with CM32 just slightly less power. The latter is aimed at the RBD. The other two, CM29 and CM31, showed minimal neutralization activity.

In mice, only CM30, the main IgG against NTD, demonstrated the ability of the mice to protect against disease at low and high doses. CM32 did not protect against infection with a low dose of the virus or reduced viral loads in the lungs. CM29 was also not immune but reduced viral loads in the lungs, possibly because it stimulates antibody-dependent cell phagocytosis (ADCP) activity. CM31 showed a shift toward viral titers in the lung.

Total protection, with unstable viral titers in the lung, at high viral doses, was also provided by a combination of CM29 – CM31. Thus, if one strong plasma mAb targeting an epitope outside the RBD is present, it overcomes the lack of protection due to the other IgGs in the polyclonal response.

In other patients with more severe and prolonged illness, the top 12 layers are associated with non-RBD epitopes outside the S-ECD, accounting for more than 80% of the total. The most numerous responded against the S2 subterranean. They also saw three mAbs against NTD, which bound the S-ECD at nanomolar ties, and had strong neutral activity against the virus at sub-micromolar titers. These mAbs protected mice against fatal infection and reduced viral titers in the lungs. The most powerful of these is CM25, which has “potential similar to, or higher, clinical level antibodies targeting the RBD. ”

Thus, the anti-NTD antibody was sufficient to protect against SARS-CoV-2 infection.

Anti-NTD antibodies encoded in IGHV1-24

IGHV refers to the variable division of the variable domain of heavy immunoglobulin chains. The IGHV1-24 is a germline antibody gene that is expressed at low levels in health but at ten times higher levels by COVID-19, in B cells and plasmablasts. These antibodies were found to target only S-ECD epitopes outside the RBD.

The three mAbs of anti-NTD from the less severe patient had very similar sequences, four others from peripheral B cells and another non-neutral antibody against the virus, for immune receptors on the variable regions of the heavy chains. Symbolic mutations were very few or absent, however, in this region, including three glutamate residues and one phenylalanine in specific locations. These are unique residues found only in IGHV1-24.

NTD connection occurs at heavy chain

Binding between the IGHV1-24 NTD-reactive antibody bonds with the spike is controlled by interactions with the heavy layer, making up 89% of the total interface area.

Effects

This molecular proteomics study of the SARS-CoV-2-targeted antibodies showed an oligoclonal plasma antibody response, mainly directed to non-RBD epitopes of the S-ECD.

Our report is the first demonstration of the ability of anti-NTD antibodies to provide protection in vivo and is the first demonstration of convergent antibody identification of a spike epitope residing outside the RBD, which is together identifying alternative pathways for virus neutralization, the intent of disease, and providing a rationale for therapeutic interventions based on non-RBD spike epitopes. ”

* Important message

bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be seen as final, guiding health-related clinical / behavioral practice, or treatment as established information