Human influenza A and B viruses cause annual epidemics of the flu worldwide. Neuraminidase inhibitors such as Tamiflu are less effective in treating IBV than IAV. Monoclonal antibodies against IBV have been developed, but they have limited effectiveness. Given these limitations, researchers conducted studies using an in vivo plasmablast enrichment technique to isolate a human monoclonal antibody capable of neutralizing IBVs in vitro and that also protects against lethal IBV challenges in vivo.
Peripheral blood mononuclear cells from human donors were mixed with IBV hemagglutinin, a surface protein involved in viral attachment to host cells and the release of viral genome into the cytoplasm. This served to activate antigen-specific cells, then the cells were transplanted into mouse spleens for the expansion and differentiation of the peripheral blood mononuclear cells into plasmablasts. The plasmoblasts were isolated from the mouse spleens using FACS and underwent IgG cloning. Antibody clone screening by ELISA uncovered an antibody, 46B8, that was able to neutralize all eleven IBV strains tested. Using a cell-cell fusion assay (with HeLa cells incubated with antibody), the researchers observed that 46B8 blocks membrane fusion.
They also conducted a conformational change assay using ﬂow cytometry. The results suggest that 46B8 blocks IBV infection by preventing hemagglutinin conformational changes during membrane fusion. In vitro assays were performed using a lung epithelial cell line (target cells) infected with wild-type or mutant IBV viruses and incubated with NK effector cells and 46B8, as well as negative and positive control antibodies. The ability of 46B8 antibody to induce antibody-dependent cellular cytotoxicity was observed by performing assays involving the activation of NK cells from human donor blood (by measuring a marker of cytokine production) and observing target cell lysis (by measuring lactate dehydrogenase release).
Mice were treated with 46B8, control IgG, Tamiflu, or a combined treatment with Tamiflu and a sub-efficacious dose of 46B8. There was 100% mortality of mice treated with control IgG, while treatment with 46B8 conferred 100% protection. Mice co-treated with the 46B8-Tamiflu combination improved the outcome better than either alone. The results suggest that 46B8 could be the basis for the development of new vaccines against IBV, late treatment of infection, and/or combination therapy with Tamiflu.
Chai, N., Swem, L., Park, S., Nakamura, G., Chiang, N., & Estevez, A. et al. (2017). A broadly protective therapeutic antibody against influenza B virus with two mechanisms of action. Nature Communications, 8, 14234. doi:10.1038/ncomms14234