The National Institute of Allergy and Infectious Diseases (NIAID) is supporting efforts to develop a recombinant subunit vaccine against the Category B agent ricin toxin. The current focus is on the toxin's 267- amino acid enzymatic A subunit (RTA). To date, vaccine design has been aimed at making point mutations and site-specific deletions in RTA to attenuate its enzymatic activity so that it is safe for use in humans. Very little attention has been paid to how these mutations may affect B-cell epitopes on RTA that are critical for eliciting protective immunity. It is known that neutralizing antibodies consttute only a very small fraction of the total antibody pool elicited by RTA immunization. The overwhelming antibody response is made up of non- neutralizing and toxin-enhancing antibodies. This fact may explain the relative ineffectiveness of the current lead vaccine candidate to elicit detectable serum neutralizing activity despite high titer anti-toxin antibodies Because serum neutralizing antibody titers are the singular correlate of immunity to ricin, it is essential that RTA-based subunit vaccine stimulate measurable serum neutralizing activities. Unfortunately, in the absence of a comprehensive B-cell epitope map of RTA it is not possible to engineer derivatives RTA in which key protective B-cell epitopes are preserved, while epitopes that give rise to non-neutralizing (or even deleterious) antibodies are eliminated. This applicatio proposes to generate a comprehensive and high-resolution B-cell epitope map of RTA. This will be accomplished using a unique collection of resources, including a large panel of RTA-specific mAbs, as well as a collection of RTA derivatives with mutations in all of the known immunodominant regions of the protein. The proposed research project is significant in that the resulting B-cell epitope map will be used in conjunction with the available structural information about RTA to design novel antigens in which targets of neutralizing antibodies are preserved and presented in a context designed to most effectively elicit protective immunity.

Public Health Relevance

The proposed project will aid in the development of a vaccine against ricin toxin, one of the most deadly toxins known to mankind, and a potential biothreat agent.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Small Research Grants (R03)
Project #
Application #
Study Section
Vaccines Against Microbial Diseases (VMD)
Program Officer
Baqar, Shahida
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
Wadsworth Center
United States
Zip Code
Rudolph, Michael J; Vance, David J; Cheung, Jonah et al. (2014) Crystal structures of ricin toxin's enzymatic subunit (RTA) in complex with neutralizing and non-neutralizing single-chain antibodies. J Mol Biol 426:3057-68
Herrera, Cristina; Vance, David J; Eisele, Leslie E et al. (2014) Differential neutralizing activities of a single domain camelid antibody (VHH) specific for ricin toxin's binding subunit (RTB). PLoS One 9:e99788
O'Hara, Joanne M; Kasten-Jolly, Jane C; Reynolds, Claire E et al. (2014) Localization of non-linear neutralizing B cell epitopes on ricin toxin's enzymatic subunit (RTA). Immunol Lett 158:7-13
Yermakova, Anastasiya; Klokk, Tove Irene; Cole, Richard et al. (2014) Antibody-mediated inhibition of ricin toxin retrograde transport. MBio 5:e00995
Yermakova, Anastasiya; Mantis, Nicholas J (2013) Neutralizing activity and protective immunity to ricin toxin conferred by B subunit (RTB)-specific Fab fragments. Toxicon 72:29-34
O'Hara, Joanne M; Mantis, Nicholas J (2013) Neutralizing monoclonal antibodies against ricin's enzymatic subunit interfere with protein disulfide isomerase-mediated reduction of ricin holotoxin in vitro. J Immunol Methods 395:71-8
Greene, Christopher J; Chadwick, Chrystal M; Mandell, Lorrie M et al. (2013) LT-IIb(T13I), a non-toxic type II heat-labile enterotoxin, augments the capacity of a ricin toxin subunit vaccine to evoke neutralizing antibodies and protective immunity. PLoS One 8:e69678