Antigenic mapping and functional characterization of human New World hantavirus neutralizing antibodies

Abstract

Hantaviruses are high-priority emerging pathogens carried by rodents and transmitted to humans by aerosolized excreta or, in rare cases, person-to-person contact. While sporadic in North and South America, many infections occur in Europe and Asia, with mortality ranging from 1 to 40% depending on the hantavirus species. There are currently no FDA-approved vaccines or therapeutics for hantaviruses, and the only treatment for infection is supportive care for respiratory or kidney failure. Additionally, the humoral immune response to hantavirus infection is incompletely understood, especially the location of major antigenic sites on the viral glycoproteins and conserved neutralizing epitopes. Here, we report antigenic mapping and functional characterization for four neutralizing hantavirus antibodies. The broadly neutralizing antibody SNV-53 targets an interface between Gn/Gc, neutralizes through fusion inhibition and cross-protects against the Old World hantavirus species Hantaan virus when administered pre- or post-exposure. Another broad antibody, SNV-24, also neutralizes through fusion inhibition but targets domain I of Gc and demonstrates weak neutralizing activity across hantavirus species. ANDV-specific, neutralizing antibodies (ANDV-5 and ANDV-34) neutralize through attachment blocking and protect against hantavirus cardiopulmonary syndrome (HCPS) in animals but target two different antigenic faces on the head domain of Gn. Determining the antigenic sites for neutralizing antibodies will contribute to further therapeutic development for hantavirus-related diseases and inform the design of new broadly protective hantavirus vaccines.

Structural and mechanistic basis of neutralization by a pan-hantavirus protective antibody

“…Neutralization escape from ADI-42898 in a VSV-based assay occurred through the acquisition of an N-linked glycan at different locations in the Gn H capping loop masking this antigenic site, as also observed for SNV-53 ( 28 ). Such sequons in the capping loop have not been reported previously for rodent-borne hantaviruses ( 13 ), raising the possibility that they are not compatible with the formation of the highly interconnected (Gn/Gc) 4 surface lattice thought to be required for the budding of hantavirus particles (as opposed to VSVs bearing hantavirus Gn/Gc, which encode their own budding machinery) ( 7 ).…”

“…SNV-53’s lateral angle of attack, which resembles that of previously described Gc-targeting antibodies ( 23 ), raises the possibility that it can only engage lattice-free sites on virions, whereas ADI-42898’s more vertical angle of attack may allow it to bind Gn/Gc tetramers in both continuous and incomplete lattices. Although a high-resolution structure of an SNV-53:Gn/Gc complex is not yet available, current evidence also suggests that ADI-42898 contacts sequences in Gc with overall higher sequence conservation across hantaviruses than does SNV-53 ( 18 , 28 ).…”

“…This long prodrome complicates attempts to extrapolate the results of antibody protection studies in the acute and highly lethal ANDV challenge model in Syrian hamsters to protective efficacy in humans. This is especially the case for nearly all of the studies reported to date, in which doses of antibody were administered no later than 3 days after infection (18,19,21,28). In a single in vivo study, Syrian hamsters were administered two doses of an antibody cocktail at days 8 and 10 after a lethal intranasal ANDV challenge; this high-antibody dose treatment at a late stage of disease resulted in survival of only half of the animals (39).…”

“…Other recent work has identified a human nAb, SNV-53, elicited by infection with an NWH (SNV), which selectively targets Gn/Gc complexes but not either subunit alone ( 28 ). Genetic and low-resolution structural evidence are consistent with the hypothesis that the nAb SNV-53 recognizes an antigenic site resembling that of ADI-42898 in comprising the Gn H capping loop and the adjacent Gc fusion loops.…”

“…Despite these similarities, however, ADI-42898 and SNV-53 appear to differ in their relative angle of approach to their epitopes. Specifically, SNV-53 engages its epitope from a steeper angle relative to the central axis of the spike than does ADI-42898, projecting its constant regions laterally and causing them to clash with adjacent Gn/Gc spikes in the higher-order surface lattice on viral particles ( 28 ). SNV-53’s lateral angle of attack, which resembles that of previously described Gc-targeting antibodies ( 23 ), raises the possibility that it can only engage lattice-free sites on virions, whereas ADI-42898’s more vertical angle of attack may allow it to bind Gn/Gc tetramers in both continuous and incomplete lattices.…”