Structural conservation of Lassa virus glycoproteins and recognition by neutralizing antibodies

Abstract

Lassa fever is an acute hemorrhagic fever caused by the zoonotic Lassa virus (LASV). The LASV glycoprotein complex (GPC) mediates viral entry and is the sole target for neutralizing antibodies. Immunogen design is complicated by the metastable nature of recombinant GPCs and the antigenic differences amongst LASV lineages. Despite the sequence diversity of GPC, structures of most lineages are lacking. We present the development and characterization of prefusion-stabilized, trimeric GPCs of LASV lineages II, V, and VI, revealing structural conservation despite sequence diversity. High-resolution structures and biophysical characterization of GPC in complex with GP1-A antibodies reveal their neutralization mechanisms. Finally, we present the isolation and characterization of a novel trimer-preferring neutralizing antibody belonging to the GPC-B competition group with an epitope that spans adjacent protomers and includes the fusion peptide. Our work provides molecular detail information on LASV antigenic diversity and will guide efforts to design pan-LASV vaccines.

Defining bottlenecks and opportunities for Lassa virus neutralization by structural profiling of vaccine-induced polyclonal antibody responses

“…Recent studies have shown multiple conformations of LASV's fusion peptide are possible, with unbound (whether by matriglycan or antibodies) GPCs residing flexibly in the space between the HR1a helix, HR1d helix, and the HR2 loop. 30,31 We note that binding by FP-1 seems to promote the fusion peptide conformation where residues 260-268 extend towards the interior trimeric interface, as has been observed when GPC is bound by other NAbs such as 25.10C and 37.7H. While we are yet unable to confirm, it is reasonable to suspect that FP-1 would have the potential to mature towards a neutralizing phenotype as has been reported with many GPC-B mAbs.…”

“…27,28 Since then, methods have been described to stabilize the trimeric conformation of prefusion GPC in the absence of a trimer-stabilizing mAb. [29][30][31] We previously demonstrated that prefusion GPC trimers are stabilized by genetic fusion to the trimeric scaffold I53-50A. 30,31 These fusion proteins, known as GPC-I53-50A, have not only proven to be a useful reagent for characterizing and isolating GPC-specific antibodies but also were able to induce NAb responses in rabbits.…”

“…[29][30][31] We previously demonstrated that prefusion GPC trimers are stabilized by genetic fusion to the trimeric scaffold I53-50A. 30,31 These fusion proteins, known as GPC-I53-50A, have not only proven to be a useful reagent for characterizing and isolating GPC-specific antibodies but also were able to induce NAb responses in rabbits. 30,31 Protective immunity to LASV infection has been attributed to cell-mediated responses 5 with severe infections often associated with poor T-cell responses to the GPC and nucleoprotein.…”

“…30,31 These fusion proteins, known as GPC-I53-50A, have not only proven to be a useful reagent for characterizing and isolating GPC-specific antibodies but also were able to induce NAb responses in rabbits. 30,31 Protective immunity to LASV infection has been attributed to cell-mediated responses 5 with severe infections often associated with poor T-cell responses to the GPC and nucleoprotein. 14,32,33 NAb responses appear to play a limited role in curbing acute infection as they generally appear months after viral clearance.…”

“…39 Nevertheless, numerous potent NAbs have been isolated from convalescent individuals and the mechanism of action for several of these NAbs has been elucidated. 15,[27][28][29]31,40,41 Cocktails of isolated NAbs have shown great promise as therapeutics in animal models. For example, Arevirumab-3, a cocktail of NAbs 8.9F, 37.2D and 12.1F, shows protection in non-human primates after LASV challenge.…”