Chimerization and characterization of a monoclonal antibody with potent neutralizing activity across multiple influenza A H5N1 clades

• Monoclonal antibody (MAb) 9F4 has potent neutralizing activity across multiple influenza A H5N1 clades.
• MAb 9F4 was converted from mouse IgG2b to mouse-human chimeric IgG1 and IgA1 forms.
• Activity of MAb 9F4 was retained to varying degrees by the chimeric MAb forms.

The persistent evolution and circulation of highly pathogenic avian influenza H5N1 viruses pose a serious threat to global heath and hamper pandemic preparedness through conventional vaccine strategies. Combination passive immunotherapy using non-competing neutralizing antibodies has been proposed as a viable alternative to provide broad protection against drift variants. This necessitates the pre-pandemic production and characterization of potently neutralizing monoclonal antibodies (MAbs). One such antibody, MAb 9F4 was shown to provide heterologous protection against multiple H5N1 clade viruses, including one of the recently designated subclades, namely 2.3.4, through binding to a novel epitope, warranting its further development and characterization as a therapeutic candidate. In this study, the conversion of MAb 9F4 from mouse IgG2b to mouse-human chimeric (xi) IgG1 and IgA1 was achieved. These chimeric MAb versions were found to retain high degrees of binding and neutralizing activity against H5N1. The demonstration that xi-IgA1-9F4 retains a fairly high level of neutralizing activity, which is ∼10-fold lower than the corresponding xi-IgG1 isotype, suggests that this MAb could be further developed and engineered for intranasal administration.