Camelid VHH-based neutralizing agents (VNAs)　as unconventional and versatile disease therapeutics

Camelid heavy-chain-only VH domains (VHHs) offer an efficient and effective alternative to conventional antibodies. DNAs encoding these unconventional antibodies are more easily cloned and typically express to higher levels than conventional antibodies. Furthermore, recombinant VHH protein products are generally more stable than conventional antibodies, commonly bind the active sites of targeted proteins to neutralize their functions, and are highly amenable to multimerization. Heteromultimers of pathogen-neutralizing VHHs, called VHH-based neutralizing agents or VNAs, are often much more potent and efficacious than monomer VHHs when tested as therapeutics in animal models of many diseases, and permit the targeting of multiple toxins with a single agent. For example, VNAs have proven highly effective in treating infections with Clostridium difficile and enterohemorrhagic E. coli (EHEC), as well as lethal exposures to botulinum neurotoxins, ricin, Shiga toxins and anthrax. VNAs express to high levels in the serum of treated animals following gene therapies such as RNA nanoparticles and adenoviral vectors, and provide prolonged protection from pathogen infections and toxin exposures. VNAs have also been engineered for expression on the surface of red blood cells (RBCs) and the modified RBC/VNAs persisted in blood for as long as normal RBCs, showed virtually no immunogenicity, and provided long-term anti-pathogen protection. Because of their demonstrated stability and versatility, VNAs appear to have particular promise for prevention and treatment of enteric diseases.