SARS-CoV-2 BA.2.86 enters lung cells and evades neutralizing antibodies with high efficiency.

BA.2.86, a recently identified descendant of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron BA.2 sublineage, contains ∼35 mutations in the spike (S) protein and spreads in multiple countries. Here, we investigated whether the virus exhibits altered biological traits, focusing on S protein-driven viral entry. Employing pseudotyped particles, we show that BA.2.86, unlike other Omicron sublineages, enters Calu-3 lung cells with high efficiency and in a serine- but not cysteine-protease-dependent manner. Robust lung cell infection was confirmed with authentic BA.2.86, but the virus exhibited low specific infectivity. Further, BA.2.86 was highly resistant against all therapeutic antibodies tested, efficiently evading neutralization by antibodies induced by non-adapted vaccines. In contrast, BA.2.86 and the currently circulating EG.5.1 sublineage were appreciably neutralized by antibodies induced by the XBB.1.5-adapted vaccine. Collectively, BA.2.86 has regained a trait characteristic of early SARS-CoV-2 lineages, robust lung cell entry, and evades neutralizing antibodies. However, BA.2.86 exhibits low specific infectivity, which might limit transmissibility.

The Omicron variant is highly resistant against antibody-mediated neutralization: Implications for control of the COVID-19 pandemic.

The rapid spread of the SARS-CoV-2 Omicron variant suggests that the virus might become globally dominant. Further, the high number of mutations in the viral spike protein raised concerns that the virus might evade antibodies induced by infection or vaccination. Here, we report that the Omicron spike was resistant against most therapeutic antibodies but remained susceptible to inhibition by sotrovimab. Similarly, the Omicron spike evaded neutralization by antibodies from convalescent patients or individuals vaccinated with the BioNTech-Pfizer vaccine (BNT162b2) with 12- to 44-fold higher efficiency than the spike of the Delta variant. Neutralization of the Omicron spike by antibodies induced upon heterologous ChAdOx1 (Astra Zeneca-Oxford)/BNT162b2 vaccination or vaccination with three doses of BNT162b2 was more efficient, but the Omicron spike still evaded neutralization more efficiently than the Delta spike. These findings indicate that most therapeutic antibodies will be ineffective against the Omicron variant and that double immunization with BNT162b2 might not adequately protect against severe disease induced by this variant.

SARS-CoV-2 variants B.1.351 and P.1 escape from neutralizing antibodies.

The global spread of SARS-CoV-2/COVID-19 is devastating health systems and economies worldwide. Recombinant or vaccine-induced neutralizing antibodies are used to combat the COVID-19 pandemic. However, the recently emerged SARS-CoV-2 variants B.1.1.7 (UK), B.1.351 (South Africa), and P.1 (Brazil) harbor mutations in the viral spike (S) protein that may alter virus-host cell interactions and confer resistance to inhibitors and antibodies. Here, using pseudoparticles, we show that entry of all variants into human cells is susceptible to blockade by the entry inhibitors soluble ACE2, Camostat, EK-1, and EK-1-C4. In contrast, entry of the B.1.351 and P.1 variant was partially (Casirivimab) or fully (Bamlanivimab) resistant to antibodies used for COVID-19 treatment. Moreover, entry of these variants was less efficiently inhibited by plasma from convalescent COVID-19 patients and sera from BNT162b2-vaccinated individuals. These results suggest that SARS-CoV-2 may escape neutralizing antibody responses, which has important implications for efforts to contain the pandemic.

Acquisition of a multibasic cleavage site does not increase MERS-CoV entry into Calu-3 human lung cells.

Human-to-human transmission of the highly pathogenic Middle East respiratory syndrome coronavirus (MERS-CoV) is currently inefficient. However, there is concern that the virus might mutate and thereby increase its transmissibility and thus pandemic potential. The pandemic SARS-CoV-2 depends on a highly cleavable furin motif at the S1/S2 site of the viral spike (S) protein for efficient lung cell entry, transmission, and pathogenicity. Here, by employing pseudotyped particles, we investigated whether augmented cleavage at the S1/S2 site also increases MERS-CoV entry into Calu-3 human lung cells. We report that polymorphism T746K at the S1/S2 cleavage site or optimization of the furin motif increases S protein cleavage but not lung cell entry. These findings suggest that, unlike what has been reported for SARS-CoV-2, a highly cleavable S1/S2 site might not augment MERS-CoV infectivity for human lung cells.IMPORTANCEThe highly cleavable furin motif in the spike protein is required for robust lung cell entry, transmission, and pathogenicity of SARS-CoV-2. In contrast, it is unknown whether optimization of the furin motif in the spike protein of the pre-pandemic MERS-CoV increases lung cell entry and allows for robust human-human transmission. The present study indicates that this might not be the case. Thus, neither a naturally occurring polymorphism that increased MERS-CoV spike protein cleavage nor artificial optimization of the cleavage site allowed for increased spike-protein-driven entry into Calu-3 human lung cells.

The SARS-CoV-2 Delta-Omicron Recombinant Lineage (XD) Exhibits Immune-Escape Properties Similar to the Omicron (BA.1) Variant.

Recently, a recombinant SARS-CoV-2 lineage, XD, emerged that harbors a spike gene that is largely derived from the Omicron variant BA.1 in the genetic background of the Delta variant. This finding raised concerns that the recombinant virus might exhibit altered biological properties as compared to the parental viruses and might pose an elevated threat to human health. Here, using pseudotyped particles, we show that ACE2 binding and cell tropism of XD mimics that of BA.1. Further, XD and BA.1 displayed comparable sensitivity to neutralization by antibodies induced upon vaccination with BNT162b2/Comirnaty (BNT) or BNT vaccination followed by breakthrough infection. Our findings reveal important biological commonalities between XD and Omicron BA.1 host cell entry and its inhibition by antibodies.

Virological Traits of the SARS-CoV-2 BA.2.87.1 Lineage.

Transmissibility and immune evasion of the recently emerged, highly mutated SARS-CoV-2 BA.2.87.1 are unknown. Here, we report that BA.2.87.1 efficiently enters human cells but is more sensitive to antibody-mediated neutralization than the currently dominating JN.1 variant. Acquisition of adaptive mutations might thus be needed for efficient spread in the population.

Rapid spread of the SARS-CoV-2 JN.1 lineage is associated with increased neutralization evasion.

In July/August 2023, the highly mutated severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) BA.2.86 lineage emerged and its descendant JN.1 is on track to become the dominant SARS-CoV-2 lineage globally. Compared to the spike (S) protein of the parental BA.2.86 lineage, the JN.1 S protein contains one mutation, L455S, which may affect receptor binding and antibody evasion. Here, we performed a virological assessment of the JN.1 lineage employing pseudovirus particles bearing diverse SARS-CoV-2 S proteins. Using this strategy, it was found that S protein mutation L455S confers increased neutralization resistance but reduces ACE2 binding capacity and S protein-driven cell entry efficiency. Altogether, these data suggest that the benefit of increased antibody evasion outweighs the reduced ACE2 binding capacity and further enabled the JN.1 lineage to effectively spread in the human population.

Entorhinal grid-like codes and time-locked network dynamics track others navigating through space.

Navigating through crowded, dynamically changing environments requires the ability to keep track of other individuals. Grid cells in the entorhinal cortex are a central component of self-related navigation but whether they also track others' movement is unclear. Here, we propose that entorhinal grid-like codes make an essential contribution to socio-spatial navigation. Sixty human participants underwent functional magnetic resonance imaging (fMRI) while observing and re-tracing different paths of a demonstrator that navigated a virtual reality environment. Results revealed that grid-like codes in the entorhinal cortex tracked the other individual navigating through space. The activity of grid-like codes was time-locked to increases in co-activation and entorhinal-cortical connectivity that included the striatum, the hippocampus, parahippocampal and right posterior parietal cortices. Surprisingly, the grid-related effects during observation were stronger the worse participants performed when subsequently re-tracing the demonstrator's paths. Our findings suggests that network dynamics time-locked to entorhinal grid-cell-related activity might serve to distribute information about the location of others throughout the brain.

Functional analysis of polymorphisms at the S1/S2 site of SARS-CoV-2 spike protein.

Several SARS-CoV-2 variants emerged that harbor mutations in the surface unit of the viral spike (S) protein that enhance infectivity and transmissibility. Here, we analyzed whether ten naturally-occurring mutations found within the extended loop harboring the S1/S2 cleavage site of the S protein, a determinant of SARS-CoV-2 cell tropism and pathogenicity, impact S protein processing and function. None of the mutations increased but several decreased S protein cleavage at the S1/S2 site, including S686G and P681H, the latter of which is found in variants of concern B.1.1.7 (Alpha variant) and B.1.1.529 (Omicron variant). None of the mutations reduced ACE2 binding and cell-cell fusion although several modulated the efficiency of host cell entry. The effects of mutation S686G on viral entry were cell-type dependent and could be linked to the availability of cathepsin L for S protein activation. These results show that polymorphisms at the S1/S2 site can modulate S protein processing and host cell entry.

No evidence for increased cell entry or antibody evasion by Delta sublineage AY.4.2.

Since the beginning of the COVID-19 pandemic, multiple SARS-CoV-2 variants have emerged. While some variants spread only locally, others, referred to as variants of concern, disseminated globally and became drivers of the pandemic. All SARS-CoV-2 variants harbor mutations relative to the virus circulating early in the pandemic, and mutations in the viral spike (S) protein are considered of particular relevance since the S protein mediates host cell entry and constitutes the key target of the neutralizing antibody response. As a consequence, mutations in the S protein may increase SARS-CoV-2 infectivity and enable its evasion of neutralizing antibodies. Furthermore, mutations in the S protein can modulate viral transmissibility and pathogenicity.

Host Cell Entry and Neutralization Sensitivity of SARS-CoV-2 Lineages B.1.620 and R.1.

The spike (S) protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) facilitates viral entry into host cells and is the key target for neutralizing antibodies. The SARS-CoV-2 lineage B.1.620 carries fifteen mutations in the S protein and is spread in Africa, the US and Europe, while lineage R.1 harbors four mutations in S and infections were observed in several countries, particularly Japan and the US. However, the impact of the mutations in B.1.620 and R.1 S proteins on antibody-mediated neutralization and host cell entry are largely unknown. Here, we report that these mutations are compatible with robust ACE2 binding and entry into cell lines, and they markedly reduce neutralization by vaccine-induced antibodies. Our results reveal evasion of neutralizing antibodies by B.1.620 and R.1, which might have contributed to the spread of these lineages.

Evidence for an ACE2-Independent Entry Pathway That Can Protect from Neutralization by an Antibody Used for COVID-19 Therapy.

SARS-CoV-2 variants of concern (VOC) acquired mutations in the spike (S) protein, including E484K, that confer resistance to neutralizing antibodies. However, it is incompletely understood how these mutations impact viral entry into host cells. Here, we analyzed how mutations at position 484 that have been detected in COVID-19 patients impact cell entry and antibody-mediated neutralization. We report that mutation E484D markedly increased SARS-CoV-2 S-driven entry into the hepatoma cell line Huh-7 and the lung cell NCI-H1299 without augmenting ACE2 binding. Notably, mutation E484D largely rescued Huh-7 but not Vero cell entry from blockade by the neutralizing antibody Imdevimab and rendered Huh-7 cell entry ACE2-independent. These results suggest that the naturally occurring mutation E484D allows SARS-CoV-2 to employ an ACE2-independent mechanism for entry that is largely insensitive against Imdevimab, an antibody employed for COVID-19 therapy. IMPORTANCE The interaction of the SARS-CoV-2 spike protein (S) with the cellular receptor ACE2 is considered essential for infection and constitutes the key target for antibodies induced upon infection and vaccination. Here, using a surrogate system for viral entry, we provide evidence that a naturally occurring mutation can liberate SARS-CoV-2 from ACE2-dependence and that ACE2-independent entry may protect the virus from neutralization by an antibody used for COVID-19 therapy.

SARS-CoV-2 Omicron sublineages show comparable cell entry but differential neutralization by therapeutic antibodies.

The Omicron variant of SARS-CoV-2 evades antibody-mediated neutralization with unprecedented efficiency. At least three Omicron sublineages have been identified-BA.1, BA.2, and BA.3-and BA.2 exhibits increased transmissibility. However, it is currently unknown whether BA.2 differs from the other sublineages regarding cell entry and antibody-mediated inhibition. Here, we show that BA.1, BA.2, and BA.3 enter and fuse target cells with similar efficiency and in an ACE2-dependent manner. However, BA.2 was not efficiently neutralized by seven of eight antibodies used for COVID-19 therapy, including Sotrovimab, which robustly neutralized BA.1. In contrast, BA.2 and BA.3 (but not BA.1) were appreciably neutralized by Cilgavimab, which could constitute a treatment option. Finally, all sublineages were comparably and efficiently neutralized by antibodies induced by BNT162b2 booster vaccination after previous two-dose homologous or heterologous vaccination. Collectively, the Omicron sublineages show comparable cell entry and neutralization by vaccine-induced antibodies but differ in susceptibility to therapeutic antibodies.

SARS-CoV-2 variants C.1.2 and B.1.621 (Mu) partially evade neutralization by antibodies elicited upon infection or vaccination.

Rapid spread of SARS-CoV-2 variants C.1.2 and B.1.621 (Mu variant) in Africa and the Americas, respectively, as well as a high number of mutations in the viral spike proteins raised concerns that these variants might pose an elevated threat to human health. Here, we show that C.1.2 and B.1.621 spike proteins mediate increased entry into certain cell lines but do not exhibit increased ACE2 binding. Further, we demonstrate that C.1.2 and B.1.621 are resistant to neutralization by bamlanivimab but remain sensitive to inhibition by antibody cocktails used for COVID-19 therapy. Finally, we show that C.1.2 and B.1.621 partially escape neutralization by antibodies induced upon infection and vaccination, with escape of vaccine-induced antibodies being as potent as that measured for B.1.351 (Beta variant), which is known to be highly neutralization resistant. Collectively, C.1.2 and B.1.621 partially evade control by vaccine-induced antibodies, suggesting that close monitoring of these variants is warranted.

SARS-CoV-2 mutations acquired in mink reduce antibody-mediated neutralization.

Transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) from humans to farmed mink has been observed in Europe and the US. In the infected animals, viral variants arose that harbored mutations in the spike (S) protein, the target of neutralizing antibodies, and these variants were transmitted back to humans. This raised concerns that mink might become a constant source of human infection with SARS-CoV-2 variants associated with an increased threat to human health and resulted in mass culling of mink. Here, we report that mutations frequently found in the S proteins of SARS-CoV-2 from mink are mostly compatible with efficient entry into human cells and its inhibition by soluble angiotensin-converting enzyme 2 (ACE2). In contrast, mutation Y453F reduces neutralization by an antibody with emergency use authorization for coronavirus disease 2019 (COVID-19) therapy and sera/plasma from COVID-19 patients. These results suggest that antibody responses induced upon infection or certain antibodies used for treatment might offer insufficient protection against SARS-CoV-2 variants from mink.

B.1.617.2 enters and fuses lung cells with increased efficiency and evades antibodies induced by infection and vaccination.

The Delta variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), B.1.617.2, emerged in India and has spread to over 80 countries. B.1.617.2 replaced B.1.1.7 as the dominant virus in the United Kingdom, resulting in a steep increase in new infections, and a similar development is expected for other countries. Effective countermeasures require information on susceptibility of B.1.617.2 to control by antibodies elicited by vaccines and used for coronavirus disease 2019 (COVID-19) therapy. We show, using pseudotyping, that B.1.617.2 evades control by antibodies induced upon infection and BNT162b2 vaccination, although to a lesser extent as compared to B.1.351. We find that B.1.617.2 is resistant against bamlanivimab, a monoclonal antibody with emergency use authorization for COVID-19 therapy. Finally, we show increased Calu-3 lung cell entry and enhanced cell-to-cell fusion of B.1.617.2, which may contribute to augmented transmissibility and pathogenicity of this variant. These results identify B.1.617.2 as an immune evasion variant with increased capacity to enter and fuse lung cells.

SARS-CoV-2 variant B.1.617 is resistant to bamlanivimab and evades antibodies induced by infection and vaccination.

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants threatens efforts to contain the coronavirus disease 2019 (COVID-19) pandemic. The number of COVID-19 cases and deaths in India has risen steeply, and a SARS-CoV-2 variant, B.1.617, is believed to be responsible for many of these cases. The spike protein of B.1.617 harbors two mutations in the receptor binding domain, which interacts with the angiotensin converting enzyme 2 (ACE2) receptor and constitutes the main target of neutralizing antibodies. Therefore, we analyze whether B.1.617 is more adept in entering cells and/or evades antibody responses. B.1.617 enters two of eight cell lines tested with roughly 50% increased efficiency and is equally inhibited by two entry inhibitors. In contrast, B.1.617 is resistant against bamlanivimab, an antibody used for COVID-19 treatment. B.1.617 evades antibodies induced by infection or vaccination, although less so than the B.1.351 variant. Collectively, our study reveals that antibody evasion of B.1.617 may contribute to the rapid spread of this variant.