Investigation of a panel of monoclonal antibodies and polyclonal sera against anthrax toxins resulted in identification of an anti-lethal factor antibody with disease-enhancing characteristics

- Disease enhancing characteristics were studied in mouse model and in cell line for anti-lethal factor polyclonal antisera.
- A single chain variable fragment (scFv) and monoclonal antibodies against lethal factor of B. anthracis were developed.
- Anthrax toxin neutralization capability and disease enhancement characteristics of these antibodies were studied.
- Anthrax pathogenesis in animal model was studied after passive immunization with these antibodies (individually or in combination).
- It was concluded that the combination of disease enhancing antibodies with protective antibody abrogated the disease enhancing character.

Hybridomas were created using spleen of mice that were actively immunized with rLFn (recombinant N-terminal domain of lethal factor). Later on, separate group of mice were immunized with rLFn to obtain a polyclonal control for passive immunization studies of monoclonal antibodies. This led to the identification of one cohort of rLFn-immnized mice that harboured disease-enhancing polyclonal antibodies. At the same time, the monoclonal antibodies secreted by all the hybridomas were being tested. Two hybridomas secreted monoclonal antibodies (H10 and H8) that were cross-reactive with EF (edema factor) and LF (lethal factor), while the other two hybridomas secreted LF-specific antibodies (H7 and H11). Single chain variable fragment (LETscFv) was derived from H10 hybridoma. H11 was found to have disease-enhancing property. Combination of H11 with protective monoclonal antibodies (H8 and H10) reduced its disease enhancing nature. This in vitro abrogation of disease-enhancement provides the proof of concept that in polyclonal sera the disease enhancing character of a fraction of antibodies is overshadowed by the protective nature of the rest of the antibodies generated on active immunization.