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

Rabies immune globulin (RIG) is an indispensable component of rabies post-exposure prophylaxis (PEP) because it provides passive immunity to prevent this otherwise inescapably fatal disease in Category III exposed patients. Even with decades of development, RIG products are still criticized for their high cost, lot-to-lot variation, and potential safety issues. They remain largely unattainable in most developing regions of the world, where demand is highest. In recent years, monoclonal antibodies (MAbs) have become widely accepted as safer and more cost-effective alternatives to RIG products. As an example, SYN023 is a 1:1 cocktail of two humanized anti-rabies MAbs previously shown to display extensive neutralizing capabilities. Here, we further assessed the efficacy of SYN023 in animal models of rabies, and found that SYN023 afforded protection equal to a standard dose of human RIG (HRIG) at 0.03 mg/kg in Syrian hamsters and 0.1 mg/kg in beagles. Potential interference with vaccine-induced immunity was analyzed for the MAbs at these concentrations. While individual MAbs did not interfere with vaccine response, SYN023 at dosages of 0.1 mg/kg and above resulted in reduced neutralizing antibody titers similar to HRIG. Thus, the in vivo characterization of SYN023 supports its utility in human rabies PEP as an efficacious alternative to RIG products.