SYN023, a novel humanized monoclonal antibody cocktail, for post-exposure prophylaxis of rabies

Abstract

Rabies is a neglected zoonotic disease that is preventable in humans by appropriate post-exposure prophylaxis (PEP). However, current PEP relies on polyclonal immune globulin products purified from pooled human (HRIG) or equine (ERIG) plasma that are either in chronic shortage or in association with safety concerns. Here, we present the development of an antibody cocktail, SYN023, made of two novel monoclonal antibodies (MAb) CTB011 and CTB012 that could serve as safer and more cost-effective alternatives to the current RIG products. Both CTB011 and CTB012 are humanized MAbs that bind to non-overlapping epitopes on the rabies virus (RABV) glycoprotein (G) with sub-nanomolar affinities. Sequence analysis revealed that many of the critical residues in binding are highly conserved across different species of lyssaviruses. When combined at a 1:1 ratio, CTB011/CTB012 exhibited neutralization capabilities equivalent or superior to HRIG against 10 North American street RABV isolates in vitro and 15 prevalent Chinese RABV strains in animal models. Finally, SYN023, at a dosage of 0.03 mg/kg, was able to offer the same degree of protection as standard HRIG administration (20 IU/kg) in Syrian hamsters challenged with a highly virulent bat (Tadarida brasiliensis) RABV variant. Taken together, the high-potency and broad-spectrum neutralization demonstrated by SYN023 make it an effective candidate for human rabies PEP consideration.

Conflict of interest statement

The authors SR and ES are listed as inventors on a patent application (WO2013174003 A1 "Compositions and methods related to prevention and treatment of rabies infection") covering the subject matter of the study. Specifically, the compositions of the antibodies discussed in the manuscript, CTB011 and CTB012, constitute major claims of the patent. Data for Figs 1, S2 and S3 of this manuscript was also described in the patent. This does not alter the authors' adherence to PLOS NTD policies on sharing data and materials. Authors TYC, SR, LC, and ET are funded and employed by Synermore Biologics Co., Ltd. The authors ES and CER are employees at Beijing Cotimes Biotech Co., Ltd. and Lyssa LLC respectively. The authors ES and CER are employees at Beijing Cotimes Biotech Co., Ltd. and Lyssa LLC, respectively.

Figures

Fig 1. In vivo neutralizing activity of anti-RABV MAb cocktail compared with polyclonal HRIG.

HRIG at 20 IU/kg or 3D11E3/7G11A3 cocktail (RVNA) at 0.5 mg/kg were administered in conjunction with rabies vaccine to RABV (BD06)-infected Syrian hamsters at 24 h or 72 h post infection. Vaccine was administered on Days 0, 3, 7, 14, and 28. Hamster mortality and morbidity were monitored daily. Vaccine (Vac) only and untreated groups were included as negative controls.

Fig 2. Binding affinities of CTB011 and CTB012 as measured by cell-based ELISA.

Fig 3. Competitive ELISA between CTB011 and CTB012.

0.1 μg of biotin-labeled CTB011 and CTB012 competed against unlabeled CTB011, CTB012, and LR004, an irrelevant antibody, over the concentration range of 0–20 μg/mL. Either diluted vaccine at 100 μL/well (A) or CVS-11 infected BSR cells (B) was coated as antigen.

Fig 4. Complement-dependent cytotoxicity of MAbs CTB011, CTB012, and SYN023.

CVS-11 infected BSR cells (A) and non-infected BSR cells (B).

Fig 5. Rabies immune globulin post-exposure protection in a Syrian hamster model.

Groups of Syrian hamsters were injected with 50 LD50 of a bat (Tadarida brasiliensis) RABV. At 24 hours post-infection, SYN023 at 0.03, 0.1, 0.3, 1.0 mg/kg and HRIG at 20 IU/mL was injected along with anti-rabies vaccine into the same sites as infection. Additional doses of vaccines were administered on Days 3, 7, and 14. The morbidity and mortality of the hamsters were monitored for up to 35 days post-infection. Numbers of surviving hamsters for each group are plotted in this graph by day. Vaccine only and saline treated groups were included as negative controls.