Infectious Diseases: Recombinant Antitoxins

Many bacterial toxin diseases are treated using antitoxin therapies. Typically, antitoxins are the antisera obtained from large animals immunized with inactivated toxin. More recently, antitoxin therapies for some toxin-mediated diseases, such as our treatment for Shiga toxins, contain antitoxin monoclonal Abs (mAbs). Antisera and mAbs can be difficult to produce economically at scale, usually require long development times and often have problematic quality control, shelf-life and safety issues. The Department of Infectious Disease and Global Health is developing a novel recombinant antitoxin platform that would radically change current approaches to antitoxin therapies. The department's antitoxin strategy should permit rapid development and commercialization of safe, effective antitoxin products with low development and production costs and long shelf lives.

Recombinant Antitoxin Project

The Department of Infectious Disease and Global Health's strategy for antitoxin development (see Mukherjee et al) employs two components; a VHH-based neutralizing agent (VNA) and an effector antibody (efAb) to promote clearance. The VNA consists of two or more VHH agents that each bind and neutralize their target(s) at two non-overlapping sites. Because of the multivalent binding, VNAs are extremely effective at neutralizing the pathogenicity of their target toxin. Each VHH consists of the 14 kDa VH region of a heavy-chain-only Ab derived from alpacas immunized with the target antigen. VNAs are easily produced in microbial host expression systems and are abundantly expressed and secreted from mammalian cells. A single injection of an adenovirus engineered to promote expression of a VNA targeting botulinum neurotoxin (BoNT) fully protects mice from intoxication for several months. The VNAs typically are engineered to contain two copies of a peptide epitopic ‘tag’ which is recognized by an anti-tag mAb called the ‘effector Ab’ (efAb). When VNAs are co-administered with efAb, they promote the decoration of each pathogenic target molecule with four molecules of efAb. Decoration of biomolecules with three or more Ab molecules promotes rapid serum clearance of the targeted biomolecule through the liver. The same efAb can be universally employed by all VHH-based therapies simply by incorporating the appropriate tags into the VNAs. We have demonstrated in several animal model systems that dramatic improvements in therapeutic efficacy can be achieved when neutralization and clearance mechanisms are combined to treat toxin-mediated diseases. Furthermore, we can target multiple toxins with a single VNA consisting of additional toxin neutralizing VHH components produced as a heteromultimer.

This project is funded by NIH NIAID through the New England Regional Center of Excellence (NERCE) for Biodefense and Emerging Infectious Diseases Research. Currently the department is working on the development of recombinant antitoxin agents for the treatment of botulism, C. difficile infection (CDI), hemolytic uremic syndrome (HUS), anthrax and ricin toxin exposure. These projects are being performed in collaborations with Dr. Stephen Leppla at the NIH (anthrax), Dr. Nicholas Mantis at the NY State Department of Health (ricin). The department is also collaborating with Dr. David Curiel at Washington University in St. Louis to develop a genetic delivery vehicle for VNAs using adenovirus vectors.

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