Structural basis of Omicron neutralization by affinity-matured public antibodies

The SARS-CoV-2 Omicron1 Variant of Concern (B.1.1.529) has spread rapidly in many countries. With a spike that is highly diverged from that of the pandemic founder, it escapes most available monoclonal antibody therapeutics2,3 and erodes vaccine protection4. A public class of IGHV3-53-using SARS-CoV-2 neutralizing antibodies5,6 typically fails to neutralize variants carrying mutations in the receptor-binding motif7-11, including Omicron. As antibodies from this class are likely elicited in most people following SARS-CoV-2 infection or vaccination, their subsequent affinity maturation is of particular interest. Here, we isolated IGHV3-53-using antibodies from an individual seven months after infection and identified several antibodies capable of broad and potent SARS-CoV-2 neutralization, extending to Omicron without loss of potency. By introducing select somatic hypermutations into a germline-reverted form of one such antibody, CAB-A17, we demonstrate the potential for commonly elicited antibodies to develop broad cross-neutralization through affinity maturation. Further, we resolved the structure of CAB-A17 Fab in complex with Omicron spike at an overall resolution of 2.6 [A] by cryo-electron microscopy and defined the structural basis for this breadth. Thus, public SARS-CoV-2 neutralizing antibodies can, without modified spike vaccines, mature to cross-neutralize exceptionally antigenically diverged SARS-CoV-2 variants.

A bispecific monomeric nanobody induces SARS-COV-2 spike trimer dimers

Antibodies binding to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike have therapeutic promise, but emerging variants show the potential for virus escape. This emphasizes the need for therapeutic molecules with distinct and novel neutralization mechanisms. Here we isolated a nanobody that interacts simultaneously with two RBDs from different spike trimers of SARS-CoV-2, rapidly inducing the formation of spike trimer-dimers leading to the loss of their ability to attach to the host cell receptor, ACE2. We show that this nanobody potently neutralizes SARS-CoV-2, including the B.1.351 variant, and cross-neutralizes SARS-CoV. Furthermore, we demonstrate the therapeutic potential of the nanobody against SARS-CoV-2 and the B.1.351 variant in a human ACE2 transgenic mouse model. This naturally elicited bispecific monomeric nanobody establishes a novel strategy for potent inactivation of viral antigens and represents a promising antiviral against emerging SARS-CoV-2 variants.

Selection, biophysical and structural analysis of synthetic nanobodies that effectively neutralize SARS-CoV-2

The coronavirus SARS-CoV-2 is the cause of the ongoing COVID-19 pandemic. Therapeutic neutralizing antibodies constitute a key short-to-medium term approach to tackle COVID-19. However, traditional antibody production is hampered by long development times and costly production. Here, we report the rapid isolation and characterization of nanobodies from a synthetic library, known as sybodies (Sb), that target the receptor-binding domain (RBD) of the SARS-CoV-2 spike protein. Several binders with low nanomolar affinities and efficient neutralization activity were identified of which Sb23 displayed high affinity and neutralized pseudovirus with an IC50 of 0.6 {micro}g/ml. A cryo-EM structure of the spike bound to Sb23 showed that Sb23 binds competitively in the ACE2 binding site. Furthermore, the cryo-EM reconstruction revealed a novel conformation of the spike where two RBDs are in the up ACE2-binding conformation. The combined approach represents an alternative, fast workflow to select binders with neutralizing activity against newly emerging viruses.

An alpaca nanobody neutralizes SARS-CoV-2 by blocking receptor interaction

SARS-CoV-2 is the etiologic agent of COVID-19, currently causing a devastating pandemic for which pharmacological interventions are urgently needed. The virus enters host cells through an interaction between the spike glycoprotein and the angiotensin converting enzyme 2 (ACE2) receptor. Directly preventing this interaction presents an attractive possibility for suppressing SARS-CoV-2 replication. Here we report the isolation and characterization of an alpaca-derived single domain antibody fragment, Ty1, that specifically targets the receptor binding domain (RBD) of the SARS-CoV-2 spike, directly preventing ACE2 engagement. The nanobody binds with high affinity in the low nM range to the RBD, occluding ACE2. A cryo-electron microscopy structure of the bound complex at 2.9 Å resolution reveals that Ty1 binds to an epitope on the RBD accessible in both the ‘up’ and ‘down’ conformations and that Ty1 sterically hinders RBD-ACE2 binding. This 12.8 kDa nanobody does not need an Fc domain to neutralize SARS-CoV-2, and can be expressed in high quantities in bacteria, presenting opportunities for manufacturing at scale. Ty1 is therefore an excellent candidate as an intervention against COVID-19.Competing Interest StatementThe authors have declared no competing interest.View Full Text

Case report: association of combined nonarteritic anterior ischemic optic neuropathy (NAION) and obstruction of cilioretinal artery with overdose of Viagra.

AIMS: We report on a case of combined nonarteritic anterior ischemic optic neuropathy (NAAION) and cilioretinal artery occlusion resulting from misuse of sildenafil citrate (Viagra Pfizer Pharmaceuticals, New York, NY). DESIGN: This is an observational case report. METHODS: A 54-year-old white man developed blindness in his left eye after an overdose of Viagra. He was examined and fully evaluated. RESULTS: Ocular examinations revealed a left relative afferent pupillary defect and a left combined NAAION and obstruction of the ipsilateral cilioretinal artery. CONCLUSIONS: Although ocular side-effects of Viagra are rare, they are potentially blinding. Patients should be warned about the side-effects and against misuse of this agent.