Integrated workflow for production and in vitro characterization of equine anti-SARS-CoV-2 hyperimmune serum with epitope mapping.

Integrated production and characterization of horse-derived antibodies against SARS-CoV-2 reveal effective immune responses and identify viral regions targeted by these antibodies.

### Study Overview

• Researchers developed a comprehensive process to produce, analyze, and map antibodies raised in horses against SARS-CoV-2, the virus causing COVID-19.
• The integrated workflow linked antibody production, their neutralization capacity, and epitope mapping to understand which viral regions are targeted by these polyclonal antibodies.

### Antigen Preparation and Validation

• The viral material used for immunization was prepared by inactivating SARS-CoV-2 with a chemical called β-propiolactone under strict Biosafety Level 3 (BSL-3) conditions to ensure safety.
• Post-inactivation testing showed no cytopathic effects or viral plaques, confirming the virus lost its ability to replicate.
• Despite inactivation, the virus maintained antigenic integrity, meaning its key proteins were still recognizable by antibodies.
• This was confirmed by the binding of IgG antibodies from people vaccinated or previously infected with SARS-CoV-2.
• Western blot analyses detected major structural proteins—the spike and nucleocapsid—in different molecular forms, consistent with known viral protein behavior.

### Immunization and Antibody Production in Horses

• Horses were sequentially immunized with the inactivated whole virus to induce strong humoral immune responses.
• Antibody titers (concentration) significantly increased, with up to a 16-fold rise following booster immunizations.
• This demonstrated successful induction and enhancement of the immune response in the horses over time.

### Purification and Characterization of Antibodies

• From the horse sera, the F(ab’)₂ antibody fragments—portions of IgG that bind antigen but lack the Fc region—were purified.
• Purity of the F(ab’)₂ preparation was estimated at 80.4% through densitometry analysis, indicating efficient purification.
• ELISA tests showed these antibody fragments retained strong binding to the viral antigens, confirming functional activity after purification.

### Neutralization Capacity Assessment

• The purified antibodies were tested in a Plaque Reduction Neutralization Test (PRNT), a sensitive assay measuring the ability to block viral infection.
• The antibodies showed potent neutralization with a PRNT₅₀ (50% plaque reduction titer) of 1:97,000, highlighting strong capability to inhibit SARS-CoV-2 infection in vitro.

### Advantages of Using Whole Inactivated Virus as Immunogen

• Using chemically inactivated whole virus preserves the complete structural complexity of the virus, exposing multiple epitopes to the immune system.
• This approach contrasts with recombinant protein immunization, which usually targets fewer, specific proteins.
• The broad antibody response induced can recognize diverse viral epitopes, potentially improving effectiveness against virus variants.
• The workflow can be safely carried out in BSL-3 labs, allowing rapid adaptation for emerging infectious diseases.

### Epitope Mapping and Applications

• This study experimentally identified multiple linear immunogenic peptides on the virus that are recognized by the generated antibodies.
• These identified epitopes provide detailed antibody-binding profiles, valuable for designing diagnostics or therapeutic tools.
• Knowledge of targeted viral regions can help in immunobiotechnology developments and enhance understanding of immune responses.

### Summary

• The research successfully integrated production of equine antibodies, their functional neutralization analysis, and precise epitope mapping against SARS-CoV-2.
• The methodology combines safety, effectiveness, and adaptability, proposing an alternative to recombinant protein-based antibody generation strategies.
• These findings support potential utility in developing affordable, scalable antibody therapies and diagnostic reagents for COVID-19 and possibly other infectious diseases.