A potent SARS-CoV-2 neutralising nanobody shows therapeutic efficacy in the Syrian golden hamster model of COVID-19 (preprint)

SARS-CoV-2 remains a global threat to human health particularly as escape mutants emerge. There is an unmet need for effective treatments against COVID-19 for which neutralizing single domain antibodies (nanobodies) have significant potential. Their small size and stability mean that nanobodies are compatible with respiratory administration. We report four nanobodies (C5, H3, C1, F2) engineered as homotrimers with pmolar affinity for the receptor binding domain (RBD) of the SARS-CoV-2 spike protein. Crystal structures show C5 and H3 overlap the ACE2 epitope, whilst C1 and F2 bind to a different epitope. Cryo Electron Microscopy shows C5 binding results in an all down arrangement of the Spike protein. C1, H3 and C5 all neutralize the Victoria strain, and the highly transmissible Alpha (B.1.1.7 first identified in Kent, UK) strain and C1 also neutralizes the Beta (B.1.35, first identified in South Africa). Administration of C5-trimer via the respiratory route showed potent therapeutic efficacy in the Syrian hamster model of COVID-19 and separately effective prophylaxis. The molecule was similarly potent by intraperitoneal injection.

Potent SARS-CoV-2 neutralizing antibodies selected from a human antibody library constructed decades ago (preprint)

Combinatorial antibody libraries not only effectively reduce antibody discovery to a numbers game, but enable documentation of the history of antibody responses in an individual. The SARS-CoV-2 pandemic has prompted a wider application of this technology to meet the public health challenge of pandemic threats in the modern era. Herein, we used a combinatorial human antibody library constructed 20 years before the COVID-19 pandemic to discover three highly potent antibodies that selectively bind SARS-CoV-2 spike protein and neutralize authentic SARS-CoV-2 virus. Compared to neutralizing antibodies from COVID-19 patients with generally low somatic hypermutation (SHM), these antibodies contain over 13-22 SHMs, many of which are involved in specific interactions in crystal structures with SARS-CoV-2 spike RBD. The identification of these somatically mutated antibodies in a pre-pandemic library raises intriguing questions about the origin and evolution of human immune responses to SARS-CoV-2.

Plasmablast-derived antibody response to acute SARS-CoV-2 infection in humans (preprint)

Plasmablast responses and derived IgG monoclonal antibodies (MAbs) have been analysed in three COVID-19 patients. An average of 13.7% and 13.0% of plasmablast-derived IgG MAbs were reactive with virus spike glycoprotein or nucleocapsid, respectively. Of thirty-two antibodies specific for the spike glycoprotein, ten recognised the receptor-binding domain (RBD), thirteen were specific for non-RBD epitopes on the S1 subunit, and nine recognised the S2 subunit. A subset of anti-spike antibodies (10 of 32) cross-reacted with other betacoronaviruses tested, five targeted the non-RBD S1, and five targeted the S2 subunit. Of the plasmablast-derived MAbs reacting with nucleocapsid, over half of them (19 of 35) cross-reacted with other betacoronaviruses tested. The cross-reactive plasmablast-derived antibodies harboured extensive somatic mutations, indicative of an expansion of memory B cells upon SARS-CoV-2 infection. We identified 14 of 32 anti-spike MAbs that neutralised SARS-CoV-2 in independent assays at [≤] 133 nM (20 g/ml) (five of 10 anti-RBD, three of 13 anti-non-RBD S1 subunit, six of nine anti-S2 subunit). Six of 10 anti-RBD MAbs showed evidence of blockade of ACE2 binding to RBD, and five of six of these were neutralising. Non-competing pairs of neutralising antibodies were identified, which offer potential templates for the development of prophylactic and therapeutic agents against SARS-CoV-2.

Long Period Modeling SARS-CoV-2 Infection of in Vitro Cultured Polarized Human Airway Epithelium (preprint)

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) replicates throughout human airways. The polarized human airway epithelium (HAE) cultured at an airway-liquid interface (HAE-ALI) is an in vitro model mimicking the in vivo human mucociliary airway epithelium and supports the replication of SARS-CoV-2. However, previous studies only characterized short-period SARS-CoV-2 infection in HAE. In this study, continuously monitoring the SARS-CoV-2 infection in HAE-ALI cultures for a long period of up to 51 days revealed that SARS-CoV-2 infection was long lasting with recurrent replication peaks appearing between an interval of approximately 7-10 days, which was consistent in all the tested HAE-ALI cultures derived from 4 lung bronchi of independent donors. We also identified that SARS-CoV-2 does not infect HAE from the basolateral side, and the dominant SARS-CoV-2 permissive epithelial cells are ciliated cells and goblet cells, whereas virus replication in basal cells and club cells was not detectable. Notably, virus infection immediately damaged the HAE, which is demonstrated by dispersed Zonula occludens-1 (ZO-1) expression without clear tight junctions and partial loss of cilia. Importantly, we identified that SARS-CoV-2 productive infection of HAE requires a high viral load of 2.5 x 105 virions per cm2 of epithelium. Thus, our studies highlight the importance of a high viral load and that epithelial renewal initiates and maintains a recurrent infection of HAE with SARS-CoV-2.