Nanobodies® with in vitro neutralizing activity protect mice against H5N1 influenza virus infection

F.M. CARDOSO; L. I. IBAÑEZ; A. HULTBERG; N. TEMPERTON; P. VANLANDSCHOOT; X. SAELENS

Amsterdam

Congreso; 1st Antivirals Congress 2010; 2010

Elsevier

Influenza A virus infections impose recurrent and global disease burden. Although a number of small drug antiviral therapeutics against influenza is available, their impact is limited, in particular in cases of severe complications resulting from influenza. Here we assessed the protective potential of llama-derived immunoglobulin single variable domains (VHH domains or VHHs), called Nanobodies® against H5N1 virus. We first demonstrated that intranasal administration of these VHH domains is an effective way to suppress challenge with a homologous influenza A virus and this route of VHH delivery was used throughout the study. Administration of bivalent VHH up to 72 hours prior to H5N1 virus challenge strongly reduced viral replication in the lungs. Interestingly, a 500 ng dose of bivalent VHH given 24 hours prior to challenge with 1 LD50 of H5N1 virus, completely abrogated viral replication. Furthermore, mice treated with 60 ug of bivalent VHH survived a 4 LD50 challenge with H5N1 virus and displayed no signs of morbidity while all mice in the control groups died. We demonstrated that intranasal administration of bivalent VHH up to 48 hours after challenge with H5N1 virus strongly reduced viral replication in the lungs and significantly delayed time to death compared to controls, when a severe challenge dose was applied. Finally we identified two HA amino acid residues involved in binding with the neutralizing H5N1-HA-specific VHH antibodies described here; based on the 3-dimensional structure of H5 HA, the VHH epitope maps to site B. Since VHH domains are easy to produce, have a small size and are highly stable, these molecules represent a promising, novel therapeutic against influenza.