Lactobacilli Expressing Variable Domain of Llama Heavy-Chain Antibody Fragments (Lactobodies) Confer Protection against Rotavirus-Induced Diarrhea

Background. Rotavirus-induced diarrhea poses a worldwide medical problem in causing substantial morbidity and mortality among children in developing countries. We therefore developed a system for passive immunotherapy in which recombinant lactobacilli constitutively express neutralizing variable domain of llama heavy-chain (VHH) antibody fragments against rotavirus. Methods. VHH were expressed in Lactobacillus paracasei, in both secreted and cell surface–anchored forms. Electron microscopy was used to investigate the binding efficacy of VHH-expressing lactobacilli. To investigate the in vivo function of VHH-expressing lactobacilli, a mouse pup model of rotavirus infection was used. Results. Efficient binding of the VHH antibody fragments to rotavirus was shown by enzyme-linked immu-nosorbent assay and scanning electron microscopy. VHH fragments expressed by lactobacilli conferred a significant reduction in infection in cell cultures. When administered orally, lactobacilli-producing surface-expressed VHH markedly shortened disease duration, severity, and viral load in a mouse model of rotavirus-induced diarrhea when administered both fresh and in a freeze-dried form. Conclusions. Transformed lactobacilli may form the basis of a novel form of prophylactic treatment against rotavirus infections and other diarrheal diseases. Rotavirus is the most common cause of diarrhea i