Addition of N-glycosylation sites on the globular head of the H5 hemagglutinin induces the escape of highly pathogenic avian influenza A H5N1 viruses from vaccine-induced immunity

Abstract

Highly pathogenic avian influenza A H5N1 viruses remain endemic in poultry in several countries and still constitute a pandemic threat. Since the early 20th century, we experienced four influenza A pandemics. H3N2 and H1N1pdm09 viruses that respectively emerged during 1968 and 2009 pandemics are still responsible for seasonal epidemics. These viruses evolve regularly by substitutions in antigenic sites of the hemagglutinin (HA), which prevent neutralization by antibodies directed against previous strains (antigenic drift). For seasonal H3N2 viruses, an addition of N-glycosylation sites (glycosites) on H3 contributed to this drift. Here, we questioned whether additional glycosites on H5 could induce an escape of H5N1 virus from neutralization, as it was observed for seasonal H3N2 viruses. Seven H5N1 mutants were produced by adding glycosites on H5. The most glycosylated virus escaped from neutralizing antibodies, in vitro and in vivo. Furthermore, a single additional glycosite was responsible for this escape.

Antigenic diversity of H5 highly pathogenic avian influenza viruses of clade 2.3.4.4 isolated in Asia

“…Among the viruses that we tested in the present study, Pf/HK (H5N1) and A/Muscovy duck/Vietnam/OIE‐559/2011 (H5N1) has this substitution (Table ). The viruses that carried threonine 160 were predicted to possess an N‐linked oligosaccharide chain at position 158 . The acquisition of oligosaccharide chain contributes to antigenic drift, so single immunized antisera against Kum/1‐7 (H5N8) and mtA32/2 were prepared to observe slight antigenic differences and to evaluate the importance of amino acid position 160 in the HA for the antigenicity of Kum/1‐7 (H5N8).…”

“…In particular, the H5 HA possesses a relatively conserved asparagine residue in position 158; therefore, threonine 160 contributes to the glycosylation on position 158 in several H5 viruses. The mutant selected by mAb A32/2, mtA32/2, carried threonine 160 and it was predicted to possess an N‐linked oligosaccharide chain on position 158 . This oligosaccharide chain should shield the antigenic site, so the acquisition of glycosylation sites in the HA may allow escape from antibodies .…”

Production of complex viral glycoproteins in plants as vaccine immunogens

“…These glycans are host-derived and are considered 'self-antigens', enabling the virus to mask vulnerable epitopes with a poorly immunogenic shield Julien et al, 2013;McGuire et al, 2013;Sok et al, 2016;Wei et al, 2003). Similarly, influenza HA also contains multiple glycosylation sites which appear to have been increasing since 1918, presumably to enable the virus to escape from neutralizing antibodies (Herve et al, 2015;Job et al, 2013;Skehel et al, 1984;Wei et al, 2010). Despite reports that glycan occupancy may be lower in plant-produced proteins than in other production platforms, Medicago's plant-produced HA was reported to contain glycans at all six potential N-glycan sites in the extracellular portion of the protein (Le Mauff et al, 2015;Ward et al, 2014).…”

Live poultry vaccines against highly pathogenic avian influenza viruses

“…The immunization with inactivated virus did not prevent virus shedding in birds after being challenged by HPAIVs [5][6][7][8]. Therefore, the inactivated vaccines successfully protected layers and broiler chickens from disease and prevented the decrease in egg production but did not prevent the spread of the virus.…”