Human monoclonal antibodies neutralizing influenza virus A/H1N1pdm09 and seasonal A/H1N1 strains – Distinct Ig gene repertoires with a similar action mechanism

Abstract

Influenza virus causes acute respiratory infection in humans, and is a major public health concern globally. Antibodies play a central role in host protection against influenza virus. We isolated human monoclonal antibodies (hMAb) 206-2-4 and 201-6-8 by a human hybridoma protocol that neutralized various but distinct influenza virus (IFV) A/H1N1 strains, including 2009 pandemic strains. The half-inhibitory concentration of 206-2-4 and 201-6-8 against A/H1N1pdm09 strains was 2-100ng/mL and 5-20μg/mL, respectively. Prophylactic and therapeutic potencies of 206-2-4 were demonstrated in a mouse model of IFV infection at i.p. dosages of 0.25 and 2.5mg/kg, respectively, suggesting that 206-2-4 is one of the most potent hnMAbs against IFV reported thus far. The Ig genes of 206-2-4 and 201-6-8 were originated from distinct germ line repertoires, and accompanied by 63 and 23 somatic hypermutations, respectively. The hemagglutination inhibitory activity indicated that the mechanism of neutralization was to interfere the virus-receptor interaction. The binding epitope of the two antibodies was mapped to hemagglutinin 1 (HA1) amino acid residues 111-120. Additional interaction between the antibody and the HA1 globular head was necessary for neutralization. Such hnMAbs bearing distinct binding epitope have been rarely reported. The potency is likely due to the coverage of a wide surface area of HA protein by these hnMABs. IFV is a highly variable. Our knowledge on the mechanisms by which these cross-reactive hnMAbs function should help design a novel immunogen for the development of a vaccine effective against broader spectrum of IFV strains.

Dangerous Pathogens as a Potential Problem for Public Health

“…The reason may be high virus variability, which is caused by antigenic drift of surface glycoproteins. This allows the virus to avoid pre-existing immunity and common influenza vaccines, which do not provide comprehensive protection [170]. The influenza virus infects 5-15% of the worldwide population annually, causing 3-5 million cases of illness and approximately 500,000 deaths [171,172].…”

Targeting Viral Surface Proteins through Structure-Based Design

“…As the head domain contains the receptor-binding site, most neutralizing antibodies target this region to block the virus from binding to the host cell receptors [ 138 ]. Given this immunologic pressure, epitopes at the globular head are continuously mutating to avoid antibody recognition.…”

Structural Insights for Anti-Influenza Vaccine Design

“…Most HA-specific antibody responses upon initial influenza virus infection or vaccination target the globular head domain, which is therefore considered immune-dominant [ 10 , 26 , 67 , 79 , 111 , 123 ]. To date, the antibody against the HA head domain can be detected in the classical hemagglutination inhibition assay (HI) [ 43 , 64 ]. However, given that the HA head domain is highly variable among different virus strains and undergoes constant changes in antigenic drift, the majority of head specific antibodies are only effective against well-matched circulating virus strains and provide little or no effect against drifted seasonal and possible pandemic viruses [ 92 ].…”