In Vivo Efficacy of SYN023, an Anti-Rabies Monoclonal Antibody Cocktail, in Post-Exposure Prophylaxis Animal Models

Development of novel canine phage display-derived neutralizing monoclonal antibody fragments against rabies virus from immunized dogs

Animal rabies is a potentially fatal infectious disease in mammals, especially dogs. Currently, the number of rabies cases in pet dogs is increasing in several regions of Thailand. However, no passive postexposure prophylaxis (PEP) has been developed to combat rabies infection in animals. As monoclonal antibodies (MAbs) are promising biological therapies for postinfection, we developed a canine-neutralizing MAb against rabies virus (RABV) via the single-chain variable fragment (scFv) platform. Immunized phage-displaying scFv libraries were constructed from PBMCs via the pComb3XSS system. Diverse canine VHVLκ and VHVLλ libraries containing 2.4 × 108 and 1.3 × 106 clones, respectively, were constructed. Five unique clones that show binding affinity with the RABV glycoprotein were then selected, of which K9RABVscFv1 and K9RABVscFv16 showed rapid fluorescent foci inhibition test (RFFIT) neutralizing titers above the human protective level of 0.5 IU/ml. Finally, in silico docking predictions revealed that the residues on the CDRs of these neutralizing clones interact mainly with similar antigenic sites II and III on the RABV glycoprotein. These candidates may be used to develop complete anti-RABV MAbs as a novel PEP protocol in pet dogs and other animals.

Development of a reporter gene assay for antibody dependent cellular cytotoxicity activity determination of anti-rabies virus glycoprotein antibodies

Rabies is a viral disease that is nearly 100% fatal once clinical signs and symptoms develop. Post-exposure prophylaxis can efficiently prevent rabies, and antibody (Ab) induction by vaccination or passive immunization of human rabies immunoglobulin (HRIG) or monoclonal antibodies (mAbs) play an integral role in prevention against rabies. In addition to their capacity to neutralize viruses, antibodies exert their antiviral effects by antibody-dependent cellular cytotoxicity (ADCC), which plays an important role in antiviral immunity and clearance of viral infections. For antibodies against rabies virus (RABV), evaluation of ADCC activity was neglected. Here, we developed a robust cell-based reporter gene assay (RGA) for the determination of the ADCC activity of anti-RABV antibodies using CVS-N2c-293 cells, which stably express the glycoprotein (G) of RABV strain CVS-N2c as target cells, and Jurkat cells, which stably express FcγRⅢa and nuclear factor of activated T cells (NFAT) reporter gene as effector cells (Jurkat/NFAT-luc/FcγRⅢa cells). The experimental parameters were carefully optimized, and the established ADCC assay was systematically validated according to the International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH) Q2 guideline. We also evaluated the ADCC activity of anti-RABV antibodies, including mAbs, HRIG, and vaccine induced antisera, and found that all test antibodies exhibited ADCC activity with varied strengths. The established RGA provides a novel method for evaluating the ADCC of anti-RABV antibodies.

Advances in the progress of monoclonal antibodies for rabies

Rabies is a highly fatal zoonotic disease caused by the rabies virus invading the central nervous system. When suspected of exposure to the rabies virus, post-exposure prophylaxis should be administered as soon as possible. Monoclonal antibodies (mAbs) neutralizing the rabies virus could be better in human rabies post-exposure prophylaxis than equine or human rabies immune globulin in terms of supply, cost, and efficacy. This article reviews anti-rabies mAbs produced by multiple techniques, and the results of clinical trials for anti-rabies mAbs cocktails recognizing non-overlapping epitopes are also discussed.

[New aspects of rabies control]

Rabies still causes about 60,000 human deaths per year, mainly in poor populations in Africa and Asia. However, since Louis Pasteur developed the first vaccine 130 years ago, prophylactic measures have been considerably improved and simplified. They now consist of the vaccine combined with purified rabies immunoglobulins of equine or human origin. In general, however, post-exposure prophylaxis protocols are long and expensive. Furthermore, the immunoglobulins used for associated serotherapy are costly and not widely available in developing countries. Approaches have been developed to deal with these two issues that offer hope for a paradigm shift for the benefit of exposed populations. Finally, mass rabies vaccination in dogs, which are the most cost-effective measure for preventing rabies in humans, are difficult to implement and sometimes have moderate effectiveness. The identification and analysis of the epidemiological drivers conditioning the circulation of the virus in dog populations allow a better understanding of the key control points that need to be associated with these campaigns for a better efficacy.