Monoclonal Antibodies in Rabies Therapy

Monoclonal antibodies against rabies: current uses in prophylaxis and in therapy

Rabies is a severe viral infection that causes an acute encephalomyelitis, which presents a case fatality of nearly 100% after the manifestation of neurological clinical signs. Rabies can be efficiently prevented with post-exposure prophylaxis (PEP), composed of vaccines and anti-rabies immunoglobulins (RIGs); however, no treatment exists for symptomatic rabies. The PEP protocol faces access and implementation obstacles in resource-limited settings, which could be partially overcome by substituting RIGs for monoclonal antibodies (mAbs). mAbs offer lower production costs, consistent supply availability, long-term storage/stability, and an improved safety profile. Here we summarize the key features of the different available mAbs against rabies, focusing on their application in PEP and highlighting their potential in a novel therapeutic approach.

Development of a mouse monoclonal antibody cocktail for post-exposure rabies prophylaxis in humans

As the demand for rabies post-exposure prophylaxis (PEP) treatments has increased exponentially in recent years, the limited supply of human and equine rabies immunoglobulin (HRIG and ERIG) has failed to provide the required passive immune component in PEP in countries where canine rabies is endemic. Replacement of HRIG and ERIG with a potentially cheaper and efficacious alternative biological for treatment of rabies in humans, therefore, remains a high priority. In this study, we set out to assess a mouse monoclonal antibody (MoMAb) cocktail with the ultimate goal to develop a product at the lowest possible cost that can be used in developing countries as a replacement for RIG in PEP. Five MoMAbs, E559.9.14, 1112-1, 62-71-3, M727-5-1, and M777-16-3, were selected from available panels based on stringent criteria, such as biological activity, neutralizing potency, binding specificity, spectrum of neutralization of lyssaviruses, and history of each hybridoma. Four of these MoMAbs recognize epitopes in antigenic site II and one recognizes an epitope in antigenic site III on the rabies virus (RABV) glycoprotein, as determined by nucleotide sequence analysis of the glycoprotein gene of unique MoMAb neutralization-escape mutants. The MoMAbs were produced under Good Laboratory Practice (GLP) conditions. Unique combinations (cocktails) were prepared, using different concentrations of the MoMAbs that were capable of targeting non-overlapping epitopes of antigenic sites II and III. Blind in vitro efficacy studies showed the MoMab cocktails neutralized a broad spectrum of lyssaviruses except for lyssaviruses belonging to phylogroups II and III. In vivo, MoMAb cocktails resulted in protection as a component of PEP that was comparable to HRIG. In conclusion, all three novel combinations of MoMAbs were shown to have equal efficacy to HRIG and therefore could be considered a potentially less expensive alternative biological agent for use in PEP and prevention of rabies in humans.

Human mortality from endemic canine rabies is estimated to be 55,000 deaths per year in Africa and Asia, yet rabies remains a neglected disease throughout most of these countries. More than 99% of human rabies cases are caused by infections resulting from a dog-bite injury. In the vast majority of human exposures to rabies, patients require post-exposure prophylaxis (PEP), which includes both passive (rabies immunoglobulin, RIG) and active immunization (rabies vaccine). The number of victims requiring PEP has increased exponentially in recent years, and human and equine RIG (HRIG and ERIG) were not sufficiently available in countries where canine rabies is endemic. Rabies virus-neutralizing monoclonal antibodies (MAbs) of mouse (Mo) origin have been identified as promising alternatives to HRIG and ERIG. We have developed and assessed both in vitro and in vivo unique mouse monoclonal antibody (MoMAb) cocktails, which are highly efficacious. Three novel combinations were shown to have an equal or superior efficacy to HRIG and therefore could be considered a potentially less expensive alternative for passive prophylactic use to prevent the development of rabies in humans, particularly where needed most in developing countries.

The development of monoclonal human rabies virus-neutralizing antibodies as a substitute for pooled human immune globulin in the prophylactic treatment of rabies virus exposure

To provide a more defined and safer replacement for the human rabies immune globulin (HRIG) from pooled serum which is currently used for treatment of exposure to rabies virus we have developed a series of human rabies virus-specific monoclonal antibodies. Mouse-human heterohybrid myeloma cells producing rabies virus-specific human monoclonal antibodies were prepared using B cells obtained from volunteers recently-immunized with a commercial rabies virus vaccine (HDCV). Cell lines producing antibody which neutralized the Evelyn-Rokitnicki-Abelseth (ERA) rabies virus strain in vitro were cloned and the resulting monoclonal antibodies characterized for isotype, specificity against a variety of rabies virus isolates, and neutralization capacity. The ability of the monoclonal antibodies to neutralize a variety of rabies virus strains in vitro correlated with their binding specificity for these viruses in an enzyme-linked immunoadsorbant assay (ELISA). A number of these antibodies have proven suitable for the formulation of a prophylactic human monoclonal antibody-based reagent which would provide significant advantages to the HRIG in having defined, reproducible specificity, lessened possibility of contamination with viral pathogens, and consistent availability.