High-Definition Mapping of Four Spatially Distinct Neutralizing Epitope Clusters on RiVax, a Candidate Ricin Toxin...

Area of Science:

• Immunology
• Biochemistry
• Vaccinology

Background:

• RiVax, a recombinant ricin toxin A subunit (RTA) antigen, is a safe and immunogenic vaccine candidate.
• RiVax has demonstrated efficacy in protecting non-human primates against ricin toxin exposure.
• Previous studies showed similar serum antibody profiles in humans and macaques immunized with RiVax, but epitope mapping was lacking.

Purpose of the Study:

• To define the specific binding sites (epitopes) on the RiVax antigen recognized by toxin-neutralizing monoclonal antibodies (MAbs).
• To create a high-resolution B cell epitope map of RiVax using advanced mass spectrometry techniques.

Main Methods:

• Hydrogen exchange-mass spectrometry (HX-MS) was employed to analyze the interactions between MAbs and the RiVax antigen.
• Epitope localization was determined by assessing the protection of RiVax regions from hydrogen exchange upon MAb binding.

Main Results:

• Nine toxin-neutralizing MAbs were mapped to four distinct epitope clusters (I-IV) on RiVax.
• Cluster I targeted the immunodominant α-helix B (residues 94-107).
• Other clusters involved various α-helices and β-strands on different surfaces of the RTA molecule.

Conclusions:

• A detailed B cell epitope map of RiVax has been generated.
• This map provides critical insights into the structural basis of the antibody response to the RiVax vaccine.
• The findings will facilitate the development of improved assays for analyzing vaccine-induced immunity across species.