Conformation-Dependent High-Affinity Potent Ricin-Neutralizing Monoclonal Antibodies

Abstract

Ricin is a potential biothreat agent with no approved antidote available for ricin poisoning. The aim of this study was to develop potent antibody-based antiricin antidotes. Four strong ricin resistant hybridoma clones secreting antiricin monoclonal antibodies (mAbs) were developed. All four mAbs are bound to conformational epitopes of ricin toxin B (RTB) with high affinity (K D values from 2.55 to 36.27 nM). RTB not only triggers cellular uptake of ricin, but also facilitates transport of the ricin toxin A (RTA) from the endoplasmic reticulum to the cytosol, where RTA exerts its toxic activity. The four mAbs were found to have potent ricin-neutralizing capacities and synergistic effects among them as determined by an in vitro neutralization assay. In vivo protection assay demonstrated that all four mAbs had strong efficacy against ricin challenges. D9 was found to be exceptionally effective. Intraperitoneal (i.p.) administration of D9, at a dose of 5 μg, 6 weeks before or 6 hours after an i.p. challenge with 5 × LD50 of ricin was able to protect or rescue 100% of the mice, indicating that mAb D9 is an excellent candidate to be developed as a potent antidote against ricin poisoning for both prophylactic and therapeutic purposes.

A Humanized Monoclonal Antibody Cocktail to Prevent Pulmonary Ricin Intoxication

“…There are a large number of RT-specific MAbs from mice and NHPs described in the literature that have been shown to be able to passively protect mice against RT challenge [34][35][36][37][38][39][40][41][42]. It is unclear whether the PB10/SylH3 cocktail is any more potent that other possible combinations of MAbs described, since systematic comparisons have not been conducted, although certainly the two MAbs are the best within our collection [10].…”

Opportunities and Challenges of Therapeutic Monoclonal Antibodies as Medical Countermeasures for Biodefense

“…If the antibody binds to the pathogen or toxin at the right location, the antibody will efficiently block the entry of pathogen or toxin into cells; otherwise, the blockage will only be partial or null. For example, a recently developed anti-ricin mAb showed extremely high efficacy since it binds to the part of ricin which is responsible for binding to the cell surface to initiate ricin entry into cells [45]. Only a small amount of antibody (0.25 mg/kg) was required for complete protection against lethal ricin challenge [26,[45][46][47].…”

Monoclonal Antibody Combinations that Present Synergistic Neutralizing Activity: A Platform for Next-Generation Anti-Toxin Drugs

“…The RTB subunit of ricin contains two galactose binding sites that function independently and are distant from one another [ 34 , 73 ]. Hu et al generated four MAbs directed against the RTB subunit and found that all of them bound to conformational epitopes with a high affinity.…”