Botulinum Neurotoxins and Botulism: A Novel Therapeutic Approach

Specific treatment is not available for human botulism. Current remedial mainstay is the passive administration of polyclonal antibody to botulinum neurotoxin (BoNT) derived from heterologous species (immunized animal or mouse hybridoma) together with supportive and symptomatic management. The antibody works extracellularly, probably by blocking the binding of receptor binding (R) domain to the neuronal receptors; thus inhibiting cellular entry of the holo-BoNT. The antibody cannot neutralize the intracellular toxin. Moreover, a conventional antibody with relatively large molecular size (150 kDa) is not accessible to the enzymatic groove and, thus, cannot directly inhibit the BoNT zinc metalloprotease activity. Recently, a 15–20 kDa single domain antibody (VHH) that binds specifically to light chain of BoNT serotype A was produced from a humanized-camel VH/VHH phage display library. The VHH has high sequence homology (>80%) to the human VH and could block the enzymatic activity of the BoNT. Molecular docking revealed not only the interface binding between the VHH and the toxin but also an insertion of the VHH CDR3 into the toxin enzymatic pocket. It is envisaged that, by molecular linking the VHH to a cell penetrating peptide (CPP), the CPP-VHH fusion protein would be able to traverse the hydrophobic cell membrane into the cytoplasm and inhibit the intracellular BoNT. This presents a novel and safe immunotherapeutic strategy for botulism by using a cell penetrating, humanized-single domain antibody that inhibits the BoNT by means of a direct blockade of the groove of the menace enzyme

Immunodominance of LipL3293–272 peptides revealed by leptospirosis sera and therapeutic monoclonal antibodies

Background/Purpose: Leptospirosis is a neglected zoonosis, imposing significant human and veterinary public health burdens. In this study, recombinant LipL3293–147 and LipL32148–184 middle domain of LipL3293–184, and LipL32171–214, and LipL32215–272 of c-terminal LipL32171–272 truncations were defined for immunodominance of the molecule during Leptospira infections revealed by leptospirosis sera. Results: IgM-dominant was directed to highly surface accessible LipL32148–184 and Lipl32171–214. IgG dominance of LipL32148–184 revealed by rabbit anti-Leptospira sera and convalescent leptospirosis paired sera were mapped to highly accessible surface of middle LipL32148–184 truncation whereas two LipL32148–184 and LipL32215–272 truncations were IgG-dominant when revealed by single leptospirosis sera. The IgM-dominant of LipL32148–214 and IgG-dominant LipL32148–184 peptides have highly conserved amino acids of 70% identity among pathogenic and intermediate Leptospira species and were mapped to the highly surface accessible area of LipL32 molecule that mediated interaction of host components. IgG dominance of two therapeutic epitopes located at LipL32243–253 and LipL32122–130 of mAbLPF1 and mAbLPF2, respectively has been shown less IgG-dominant (<30%), located outside IgG-dominant regions characterized by leptospirosis paired sera. Conclusion: The IgM- and IgG-dominant LipL32 could be further perspectives for immunodominant LipL32-based serodiagnosis and LipL32 epitope-based vaccine. Keywords: Leptospira spp., LipL32, IgM-dominant LipL32 peptide, IgG-dominant LipL32 peptide, Therapeutic LipL32 epitope

Human single-chain antibodies that neutralize homologous and heterologous strains and clades of influenza a virus subtype H5N1

Background Human antibodies that interfere with the biological activity of haemagglutinins (HAs) of influenza viruses have high potential as an antiviral agent. Methods Human single-chain antibody fragments (HuScFv) to recombinant and native HAs of the influenza virus H5N1 subtype were produced using a human antibody phage display library with the intention to increase the therapeutic arsenal against this highly pathogenic virus. Results The HuScFv inhibited HA activity and neutralized infectivity of both homologous and heterologous strains and clades of the H5N1 subtype in Madin–Darby canine kidney cell cultures. Intraperitoneally injected HuScFv also mediated immunotherapeutic protection in mice that were intranasally challenged with highly pathogenic H5N1 viruses belonging to different strains and clades. Conclusions Our data indicate that it might be worth pursuing these HuScFv further for future consideration as candidates for influenza intervention and treatment. </jats:sec