ACE2 mimetic antibody potently neutralizes all SARS-CoV-2 variants and fully protects in XBB.1.5 challenged monkeys (preprint)

The rapid evolution of SARS-CoV-2 to variants with improved transmission efficiency and reduced sensitivity to vaccine-induced humoral immunity has abolished the protective effect of licensed therapeutic human monoclonal antibodies (mAbs). To fill this unmet medical need and protect vulnerable patient populations, we isolated the P4J15 mAb from a previously infected, vaccinated donor, with <20 ng/ml neutralizing activity against all Omicron variants including the latest XBB.2.3 and EG.1 sub-lineages. Structural studies of P4J15 in complex with Omicron XBB.1 Spike show that the P4J15 epitope shares ~93% of its buried surface area with the ACE2 contact region, consistent with an ACE2 mimetic antibody. Although SARS-CoV-2 mutants escaping neutralization by P4J15 were selected in vitro, these displayed lower infectivity, poor binding to ACE2, and the corresponding "escape" mutations are accordingly rare in public sequence databases. Using a SARS-CoV-2 XBB.1.5 monkey challenge model, we show that P4J15 confers complete prophylactic protection. We conclude that the P4J15 mAb has potential as a broad-spectrum anti-SARS-CoV-2 drug.

SARS-CoV-2 Omicron potently neutralized by a novel antibody with unique Spike binding properties (preprint)

The SARS-CoV-2 Omicron variant exhibits very high levels of transmission, pronounced resistance to authorized therapeutic human monoclonal antibodies and reduced sensitivity to vaccine-induced immunity. Here we describe P2G3, a human monoclonal antibody (mAb) isolated from a previously infected and vaccinated donor, which displays picomolar-range neutralizing activity against Omicron BA.1, BA.1.1, BA.2 and all other current variants, and is thus markedly more potent than all authorized or clinically advanced anti-SARS-CoV-2 mAbs. Structural characterization of P2G3 Fab in complex with the Omicron Spike demonstrates unique binding properties to both down and up spike trimer conformations at an epitope that partially overlaps with the receptor-binding domain (RBD), yet is distinct from those bound by all other characterized mAbs. This distinct epitope and angle of attack allows P2G3 to overcome all the Omicron mutations abolishing or impairing neutralization by other anti-SARS-COV-2 mAbs, and P2G3 accordingly confers complete prophylactic protection in the SARS-CoV-2 Omicron monkey challenge model. Finally, although we could isolate in vitro SARS-CoV2 mutants escaping neutralization by P2G3 or by P5C3, a previously described broadly active Class 1 mAb, we found these viruses to be lowly infectious and their key mutations extremely rare in the wild, and we could demonstrate that P2G3/P5C3 efficiently cross-neutralized one another's escapees. We conclude that this combination of mAbs has great prospects in both the prophylactic and therapeutic settings to protect from Omicron and other VOCs.

A Highly Potent Antibody Effective Against SARS-CoV-2 Variants of Concern (preprint)

Control of the ongoing SARS-CoV-2 pandemic is endangered by the emergence of viral variants with increased transmission efficiency, resistance to marketed therapeutic antibodies and reduced sensitivity to vaccine-induced immunity. Here, we screened B cells from COVID-19 donors and identified P5C3, a highly potent and broadly neutralizing monoclonal antibody with picomolar neutralizing activity against all SARS-CoV-2 variants of concern (VOC) identified to date. Structural characterization of P5C3 Fab in complex with the Spike demonstrates a neutralizing activity defined by a large buried surface area, highly overlapping with the receptor-binding domain (RBD) surface necessary for ACE2 interaction. We further demonstrate that P5C3 showed complete prophylactic protection in the SARS-CoV-2 infected hamster challenge model. These results indicate that P5C3 opens exciting perspectives either as a prophylactic agent in immunocompromised individuals with poor response to vaccination or as combination therapy in SARS-CoV-2-infected individuals.Funding: This CARE project has received funding from the Innovative MedicinesInitiative 2 Joint Undertaking (JU) under grant agreement No 101005077. The JU receives support from the European Union’s Horizon 2020 research and innovation program and EFPIA and BILL & MELINDA GATES FOUNDATION, GLOBAL HEALTH DRUG DISCOVERYINSTITUTE, UNIVERSITY OF DUNDEE. Furthermore, funding was also provided through the Lausanne University Hospital, through the Swiss Vaccine Research Institute to G.P., and through the EPFL COVID fund to D.T.Conflict of Interest: None to declare. Ethical Approval: Study design and use of subject samples were approved by the Institutional Review Board of the Lausanne University Hospital and the ‘Commission d’éthique du Canton de Vaud’ (CER-VD).

A multiplexed high-throughput neutralization assay reveals a lack of activity against multiple variants after SARS-CoV-2 infection (preprint)

The detection of SARS-CoV-2-specific antibodies in the serum of an individual indicates prior infection or vaccination. However, it provides limited insight into the protective nature of this immune response. Neutralizing antibodies recognizing the viral Spike are far more revealing, yet their measurement traditionally requires virus- and cell-based systems that are costly, time-consuming, poorly flexible and potentially biohazardous. Here we present a cell-free quantitative neutralization assay based on the competitive inhibition of trimeric SARS-CoV-2 Spike protein binding to the angiotensin converting enzyme 2 (ACE2) viral receptor. This high-throughput method matches the performance of the gold standard live virus infectious assay, as verified with a panel of 206 seropositive donors with varying degrees of infection severity and virus-specific IgG titers, achieving 96.7% sensitivity and 100% specificity. Furthermore, it allows for the parallel assessment of neutralizing activities against multiple SARS-CoV-2 Spike variants of concern (VOC), which is otherwise unpredictable even in individuals displaying robust neutralizing antibody responses. Profiling serum samples from 59 hospitalized COVID-19 patients, we found that although most had high activity against the 2019-nCoV Spike and to a lesser extent the B.1.1.7 variant, only 58% could efficiently neutralize a Spike derivative containing mutations present in the B.1.351 variant. In conclusion, we have developed an assay that has proven its clinical relevance in the large-scale evaluation of effective neutralizing antibody responses to VOC after natural infection and that can be applied to the characterization of vaccine-induced antibody responses and of the potency of human monoclonal antibodies. Once sentence summaryMultiplexed cell-free neutralization assay for quantitative assessment of serum antibody responses against Spike mutations in SARS-COV-2 variants

Qualitative Changes in the SARS-CoV-2 Antibody Response in the Post-Infection Phase Impact the estimates of infections in Population-Based Seroprevalence Studies (preprint)

We have determined SARS-CoV-2-specific antibody responses in a cohort of 96 individuals with acute infection and in 578 individuals enrolled in a seroprevalence population study in Switzerland including three groups, i.e. subjects with previous RT-PCR confirmed SARS-CoV-2 infections (n=90), positive patient contacts (n=177) and random selected subjects (n=311). SARS-CoV-2 antibody responses specific to the Spike (S), in the monomeric and native trimeric forms, and/or the nucleocapsid (N) proteins were equally sensitive in the acute infection phase. Interestingly, as compared to anti-S antibody responses, those against the N protein appear to wane in the post-infection and substantially underestimated the proportion of SARS-CoV-2 infections in the groups of patient positive contacts, i.e. 10.9 to 32.2% reduction and in the random selected general population, i.e. up to 45% reduction. The overall reduction in seroprevalence targeting only anti-N IgG antibodies for the total cohort ranged from 9.4 to 31%. Of note, the use of the S protein in its native trimer form was more sensitive as compared to monomeric S proteins. These results indicate that the assessment of anti-S IgG antibody responses against the native trimeric S protein should be implemented to estimate SARS-CoV-2 infections in population-based seroprevalence studies.