Bispecific antibodies for SARS-CoV-2 variant neutralization

By Dr. Chinta SidharthanReviewed by Lexie CornerMar 14 2025

It has been five years since the onset of the coronavirus disease 2019 (COVID-19) pandemic. Many monoclonal antibody therapies have lost effectiveness against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) due to the emergence of variants with novel mutations.

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Developing new treatment strategies and innovative antibodies capable of neutralizing these resistant strains remains a pressing concern.

A recent study published in Science Translational Medicine introduced a bispecific antibody that effectively neutralizes highly mutated SARS-CoV-2 variants, including XBB.1.5.

By combining two distinct antibody types, this approach enhances viral targeting and improves efficacy against emerging strains resistant to conventional treatments.

Challenges in antibody-based COVID-19 therapies

Since the emergence of SARS-CoV-2, vaccines and monoclonal antibody therapies have played a crucial role in reducing morbidity and mortality. The rapid development and deployment of these interventions helped control infections worldwide.

However, continued viral mutations, particularly in the spike protein, have compromised the effectiveness of many existing antibody-based treatments.

The rise of Omicron subvariants, such as XBB.1.5, has further challenged traditional monoclonal antibody strategies by allowing the virus to evade immune recognition. Conventional monoclonal antibodies primarily target the receptor-binding domain (RBD) of the spike protein, but mutations in this region reduce their efficacy.

Bispecific antibodies, engineered to bind two distinct viral sites simultaneously, offer an alternative approach that enhances neutralization while reducing the likelihood of escape mutations. However, despite promising early findings, gaps remain in understanding their real-world effectiveness.

This study aimed to address these challenges by designing and testing a bispecific antibody against emerging SARS-CoV-2 variants such as XBB.1.5.

Development of a bispecific antibody

To evaluate the efficacy of bispecific antibodies against highly mutated SARS-CoV-2 variants, researchers designed a novel bispecific antibody, CoV2-biRN5, by combining two monoclonal antibodies, C1596 and C952.

One antibody targets the N-terminal domain (NTD), while the other binds the RBD. This dual-targeting strategy was hypothesized to improve neutralization potency and limit viral escape.

The study began with in vitro experiments assessing CoV2-biRN5's binding affinity and neutralization potential using enzyme-linked immunosorbent assays (ELISA) and biolayer interferometry. Pseudovirus neutralization assays were performed to evaluate its ability to prevent viral entry into host cells. Deep mutational scanning was used to assess resistance and identify potential escape mutations.

For in vivo analysis, the bispecific antibody was tested in a mouse model expressing human angiotensin-converting enzyme 2 (hACE2). Mice received the antibody either prophylactically (before exposure) or therapeutically (after infection).

Following viral challenge with SARS-CoV-2 XBB.1.5, lung tissue samples were collected three days post-infection to quantify viral ribonucleic acid (RNA) load using quantitative reverse transcription polymerase chain reaction (qRT-PCR).

Pharmacokinetic studies examined antibody stability, circulation time, and clearance rates in vivo. Researchers monitored antibody persistence through serum analysis and compared treatment groups using statistical methods.

Key insights

CoV2-biRN5 demonstrated strong neutralization activity against SARS-CoV-2 variants, including XBB.1.5. In vitro assays confirmed high binding affinity to both the NTD and RBD regions and showed enhanced viral inhibition compared to conventional monoclonal antibodies. Pseudovirus neutralization assays indicated broad-spectrum activity against emerging variants.

In the mouse model, prophylactic administration of CoV2-biRN5 resulted in a significant reduction in lung viral load. The therapeutic group also showed reduced viral levels, though the effect was slightly lower than in the prophylactic setting. Mice treated with CoV2-biRN5 exhibited reduced disease severity compared to untreated controls.

Deep mutational scanning revealed a low frequency of viral escape mutations (<0.05%), suggesting that the targeted epitopes remain highly conserved. This finding indicates a reduced likelihood of immune evasion compared to single-target monoclonal antibodies. Although this study focused on a single antibody pairing, the results support further exploration of alternative combinations to enhance resilience against future variants.

Implications and future research

This study highlights the potential of bispecific antibodies in addressing SARS-CoV-2 variants that evade existing treatments. By targeting multiple viral sites, CoV2-biRN5 offers a promising strategy for long-term immune protection.

Future research should focus on optimizing bispecific antibody combinations, expanding testing to additional variants, and evaluating clinical efficacy in human trials.

Understanding antibody persistence and immune system interactions will be crucial for developing durable therapeutic solutions. If validated in clinical settings, bispecific antibodies could provide a valuable tool for managing future SARS-CoV-2 variants and improving pandemic preparedness.

Journal reference

Rubio, A. A., Baharani, Viren A, Dadonaite, B., Parada, M., Abernathy, M. E., Wang, Z., Lee, Y. E., Eso, M. R., Phung, J., Ramos, I., Chen, T., Gina, E. N., Bloom, J. D., Bieniasz, P. D., Nussenzweig, M. C., Barnes, C. O. (2025). Bispecific antibodies targeting the N-terminal and receptor binding domains potently neutralize SARS-CoV-2 variants of concern. Science Translational Medicine. DOI:10.1126/scitranslmed.adq5720, https://www.science.org/doi/10.1126/scitranslmed.adq5720