Neutralizing activity and protective immunity to ricin toxin conferred by B subunit (RTB)-specific Fab fragments

Yermakova, Anastasiya; Mantis, Nicholas J.

doi:10.1016/j.toxicon.2013.04.005

Cited by 14 publications

(31 citation statements)

References 33 publications

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“…We speculate that RTB-B7 likely recognizes a conformation-dependent epitope based on its poor binding in Western blot analysis. 4 We have recently reported that there are two types (I and II) of RTB-specific neutralizing mAbs (1,15). Type I neutralizers are postulated to prevent RTB from binding to its receptors, thereby inhibiting toxin internalization.…”

Section: Discussionmentioning

confidence: 99%

“…Recent high profile incidents involving ricin-laden envelopes addressed to members of the United States Congress and the President have accelerated efforts by the Department of Defense and the National Institutes of Health to develop countermeasures against the toxin (10,11). We and others have produced a large collection of RTA-and RTB-specific murine and chimeric mouse-human mAbs with toxin-neutralizing activity in vitro and in vivo (1,(12)(13)(14)(15)(16). Although many of these mAbs have therapeutic potential, funding agencies are increasing moving away from the "one bug, one drug" model of biodefense therapeutics to more broad-based platform technologies that can provide rapid onset against similarly acting biothreat agents.…”

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confidence: 99%

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Stepwise Engineering of Heterodimeric Single Domain Camelid VHH Antibodies That Passively Protect Mice from Ricin Toxin

Vance

Tremblay

Mantis

et al. 2013

Journal of Biological Chemistry

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130

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Background:We sought to engineer highly efficacious agents that neutralize ricin toxin. Results: We identified monomeric single-chain camelid V H domains (V H Hs) capable of neutralizing ricin in vitro and engineered heterodimeric V H Hs that neutralized ricin in vivo. Conclusion: Stepwise engineering of V H Hs resulted in highly potent ricin toxin-neutralizing antibodies. Significance: This study highlights the potential use of a V H H platform as a strategy for therapeutics against diverse biological toxins.

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Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Stepwise Engineering of Heterodimeric Single Domain Camelid VHH Antibodies That Passively Protect Mice from Ricin Toxin

Vance

Tremblay

Mantis

et al. 2013

Journal of Biological Chemistry

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130

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“…For example, SylH3 is a potent inhibitor of ricin-receptor interactions but only marginally effective at neutralizing ricin when pre-bound to cell surfaces, while 24B11 only partially inhibits toxin-receptor interactions but is highly effective at neutralizing ricin when toxin is pre-bound to cells [27], [28]. In an effort to better characterize RTB-B7, we first examined its ability to inhibit ricin from binding to the surrogate receptor ASF.…”

Section: Resultsmentioning

confidence: 99%

“…Surface-bound 24B11 is subsequently endocytosed as a toxin:antibody complex and interferes with retrograde transport of ricin to the TGN [27]. We have also reported that SylH3 and 24B11 Fab fragments were as effective as the full length IgGs at neutralizing ricin in vitro and in vivo , indicating that in the case of SylH3 and 24B11, neither bivalency nor Fc-domains are necessary determinants of toxin-neutralizing activity [28].…”

Section: Introductionmentioning

confidence: 99%

Differential Neutralizing Activities of a Single Domain Camelid Antibody (VHH) Specific for Ricin Toxin’s Binding Subunit (RTB)

et al. 2014

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Ricin, a member of the A-B family of ribosome-inactivating proteins, is classified as a Select Toxin by the Centers for Disease Control and Prevention because of its potential use as a biothreat agent. In an effort to engineer therapeutics for ricin, we recently produced a collection of alpaca-derived, heavy-chain only antibody VH domains (VHH or “nanobody”) specific for ricin’s enzymatic (RTA) and binding (RTB) subunits. We reported that one particular RTB-specific VHH, RTB-B7, when covalently linked via a peptide spacer to different RTA-specific VHHs, resulted in heterodimers like VHH D10/B7 that were capable of passively protecting mice against a lethal dose challenge with ricin. However, RTB-B7 itself, when mixed with ricin at a 1∶10 toxin:antibody ratio did not afford any protection in vivo, even though it had demonstrable toxin-neutralizing activity in vitro. To better define the specific attributes of antibodies associated with ricin neutralization in vitro and in vivo, we undertook a more thorough characterization of RTB-B7. We report that RTB-B7, even at 100-fold molar excess (toxin:antibody) was unable to alter the toxicity of ricin in a mouse model. On the other hand, in two well-established cytotoxicity assays, RTB-B7 neutralized ricin with a 50% inhibitory concentration (IC50) that was equivalent to that of 24B11, a well-characterized and potent RTB-specific murine monoclonal antibody. In fact, RTB-B7 and 24B11 were virtually identical when compared across a series of in vitro assays, including adherence to and neutralization of ricin after the toxin was pre-bound to cell surface receptors. RTB-B7 differed from both 24B11 and VHH D10/B7 in that it was relatively less effective at blocking ricin attachment to receptors on host cells and was not able to form high molecular weight toxin:antibody complexes in solution. Whether either of these activities is important in ricin toxin neutralizing activity in vivo remains to be determined.

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“…For example, neutralization of anthrax toxin is modulated by FcR-mediated clearance though the action of specific IgG subclasses [91,92]. In the case of ricin toxin, the contribution of Fc-mediated neutralizing activity in vivo remains up for debate [84,87,93]. Indeed, very little is known about the exact mechanisms by which ricin is neutralized in vivo .…”

Section: F Key Challenges Moving Forward In Ricin Toxin Vaccine Devementioning

confidence: 99%

Progress and challenges associated with the development of ricin toxin subunit vaccines

Vance

Mantis

2016

Expert Review of Vaccines

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Summary The past several years have seen major advances in the development of a safe and efficacious ricin toxin vaccine, including the completion of two Phase I clinical trials with two different recombinant A subunit (RTA)-based vaccines: RiVax™ and RVEc™ adsorbed to aluminum salt adjuvant, as well as a non-human primate study demonstrating that parenteral immunization with RiVax elicits a serum antibody response that was sufficient to protect against a lethal dose aerosolized ricin exposure. One of the major obstacles moving forward is assessing vaccine efficacy in humans, when neither ricin-specific serum IgG endpoint titers nor toxin-neutralizing antibody levels are accepted as definitive predictors of protective immunity. In this review we summarize ongoing efforts to leverage recent advances in our understanding of RTA-antibody interactions at the structural level to develop novel assays to predict vaccine efficacy in humans.

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Neutralizing activity and protective immunity to ricin toxin conferred by B subunit (RTB)-specific Fab fragments

Cited by 14 publications

References 33 publications

Stepwise Engineering of Heterodimeric Single Domain Camelid VHH Antibodies That Passively Protect Mice from Ricin Toxin

Stepwise Engineering of Heterodimeric Single Domain Camelid VHH Antibodies That Passively Protect Mice from Ricin Toxin

Differential Neutralizing Activities of a Single Domain Camelid Antibody (VHH) Specific for Ricin Toxin’s Binding Subunit (RTB)

Progress and challenges associated with the development of ricin toxin subunit vaccines

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