A team of researchers has developed bispecific antibodies that target both the N-terminal domain and receptor-binding domain of the SARS-CoV-2 spike protein, demonstrating strong neutralization against Omicron variants that have evaded previous monoclonal antibody therapies.

In a new study, published in Science Translational Medicine, the researchers reported the creation of novel bispecific antibodies (bsAbs), termed CoV2-biRNs, that retained neutralization potency against all tested Omicron variants, including XBB.1.5, BA.2.86, and JN.1.

"Given C1596's favorable binding profile, we designed a series of bispecific antibodies (bsAbs), termed CoV2-biRNs, that featured both N-terminal domain (NTD) and receptor-binding domain (RBD) specificities," the study authors detailed. "Two of the C1596-inclusive bsAbs, CoV2-biRN5 and CoV2-biRN7, retained potent in vitro neutralization activity against all Omicron variants tested, including XBB.1.5, BA.2.86, and JN.1, contrasting the diminished potency of parental antibodies delivered as monotherapies or as a cocktail," they added.

The researchers initially characterized monoclonal antibodies (mAbs) targeting the NTD of the spike protein, with specific focus on antibodies binding outside the antigenic "site i" supersite, which has been subject to significant immune pressure in previous variants. Among these, antibody C1596 displayed exceptional breadth of binding across SARS-CoV-2 variants.

Structural analysis using cryo-electron microscopy revealed that C1596 bound a quaternary epitope spanning three domains within a single spike protomer: the NTD, RBD, and subdomain 1 (SD1). This binding profile appeared to contribute to C1596's resilience against mutations found in circulating variants.

The researchers then created several bispecific constructs combining C1596 with C952, an RBD-specific antibody. Among these constructs, CoV2-biRN5 and CoV2-biRN7, which feature tandem single-chain variable fragments (scFvs) with C1596 positioned at the N-terminus, demonstrated the most robust neutralization activity, with IC50 values below 10 ng/mL against all Omicron variants tested.

The prophylactic efficacy of CoV2-biRN5 was also evaluated in K18-hACE2 transgenic mice challenged with SARS-CoV-2 XBB.1.5. Mice receiving 5 mg/kg of CoV2-biRN5 intraperitoneally 24 hours prior to viral challenge showed a statistically significant 1,500-fold reduction in viral load in lung tissue compared with untreated controls (P = .006).

Deep mutational scanning revealed that mutations conferring resistance to CoV2-biRN5 were found in less than 0.01% of all SARS-CoV-2 sequences available in the GISAID database, suggesting that the epitope targeted by these bispecific antibodies remains under minimal selective pressure.

"Our data support the potential use of NTD-RBD bsAbs as a therapeutic strategy against emerging SARS-CoV-2 VOCs," the study authors concluded.

The research may provide a potential approach for developing antibody therapeutics against current and future SARS-CoV-2 variants, especially for immunocompromised patients who remain vulnerable to COVID-19 infections despite the availability of vaccines.

Full disclosures can be found in the study.