Purified Immunoglobulin F(ab′)2 Protects Mice and Rhesus Monkeys against Lethal Ricin Intoxication

Objective: Ricin is a highly toxic ribosome-inactivating lectin derived from castor beans. To date, no antidote is available to treat ricin-poisoned patients, and the development of a safe and effective antidote is urgently needed. Methods: First, ricin was prepared and used to construct a mouse model and a rhesus monkey model of ricin intoxication. Second, pepsin-digested F(ab′)2 fragments of serum IgG from horses injected with Freund’s-adjuvanted purified ricin were prepared. Third, the protective efficacy was evaluated in mouse and rhesus monkey models of lethal ricin intoxication. Results: The purity quotient of the prepared ricin and F(ab′)2 fragments exceeded 90% and 85% in the mouse and monkey models, respectively. The LD50 of ricin in mice and rhesus monkeys was 2.7 and 9 μg/kg, respectively. A quantity of 6.25 and 1.85 mg/kg F(ab′)2 was sufficient to treat lethal ricin intoxication in the mice and rhesus monkeys, respectively. Finally, the effect of this therapeutic antibody on peripheral blood immune cells was examined by analysis of peripheral blood immune cells through single cell sequencing. The underlying mechanism was found to involve restraining neutrophil activation, proliferation, and differentiation. Conclusion: Purified F(ab′)2 fragments administered with needle-free devices fully protect mice and rhesus monkeys against lethal doses of ricin intoxication.