Isolation and characterization of IgG3 glycan-targeting antibodies with exceptional cross-reactivity for diverse viral families.

Broadly reactive antibodies that target sequence-diverse antigens are of interest for vaccine design and monoclonal antibody therapeutic development because they can protect against multiple strains of a virus and provide a barrier to evolution of escape mutants. Using LIBRA-seq (linking B cell receptor to antigen specificity through sequencing) data for the B cell repertoire of an individual chronically infected with human immunodeficiency virus type 1 (HIV-1), we identified a lineage of IgG3 antibodies predicted to bind to HIV-1 Envelope (Env) and influenza A Hemagglutinin (HA). Two lineage members, antibodies 2526 and 546, were confirmed to bind to a large panel of diverse antigens, including several strains of HIV-1 Env, influenza HA, coronavirus (CoV) spike, hepatitis C virus (HCV) E protein, Nipah virus (NiV) F protein, and Langya virus (LayV) F protein. We found that both antibodies bind to complex glycans on the antigenic surfaces. Antibody 2526 targets the stem region of influenza HA and the N-terminal domain (NTD) region of SARS-CoV-2 spike. A crystal structure of 2526 Fab bound to mannose revealed the presence of a glycan-binding pocket on the light chain. Antibody 2526 cross-reacted with antigens from multiple pathogens and displayed no signs of autoreactivity. These features distinguish antibody 2526 from previously described glycan-reactive antibodies. Further study of this antibody class may aid in the selection and engineering of broadly reactive antibody therapeutics and can inform the development of effective vaccines with exceptional breadth of pathogen coverage.

Structures of Langya Virus Fusion Protein Ectodomain in Pre- and Postfusion Conformation.

Langya virus (LayV) is a paramyxovirus in the Henipavirus genus, closely related to the deadly Nipah (NiV) and Hendra (HeV) viruses, that was identified in August 2022 through disease surveillance following animal exposure in eastern China. Paramyxoviruses present two glycoproteins on their surface, known as attachment and fusion proteins, that mediate entry into cells and constitute the primary antigenic targets for immune response. Here, we determine cryo-electron microscopy (cryo-EM) structures of the uncleaved LayV fusion protein (F) ectodomain in pre- and postfusion conformations. The LayV-F protein exhibits pre- and postfusion architectures that, despite being highly conserved across paramyxoviruses, show differences in their surface properties, in particular at the apex of the prefusion trimer, that may contribute to antigenic variability. While dramatic conformational changes were visualized between the pre- and postfusion forms of the LayV-F protein, several domains remained invariant, held together by highly conserved disulfides. The LayV-F fusion peptide (FP) is buried within a highly conserved, hydrophobic interprotomer pocket in the prefusion state and is notably less flexible than the rest of the protein, highlighting its "spring-loaded" state and suggesting that the mechanism of pre-to-post transition must involve perturbations to the pocket and release of the fusion peptide. Together, these results offer a structural basis for how the Langya virus fusion protein compares to its Henipavirus relatives and propose a mechanism for the initial step of pre- to postfusion conversion that may apply more broadly to paramyxoviruses. IMPORTANCE The Henipavirus genus is quickly expanding into new animal hosts and geographic locations. This study compares the structure and antigenicity of the Langya virus fusion protein to other henipaviruses, which have important vaccine and therapeutic development implications. Furthermore, the study proposes a new mechanism to explain the early steps of the fusion initiation process that can be more broadly applied to the Paramyxoviridae family.

Structural Studies of Henipavirus Glycoproteins.

Henipaviruses are a genus of emerging pathogens that includes the highly virulent Nipah and Hendra viruses that cause reoccurring outbreaks of disease. Henipaviruses rely on two surface glycoproteins, known as the attachment and fusion proteins, to facilitate entry into host cells. As new and divergent members of the genus have been discovered and structurally characterized, key differences and similarities have been noted. This review surveys the available structural information on Henipavirus glycoproteins, complementing this with information from related biophysical and structural studies of the broader Paramyxoviridae family of which Henipaviruses are members. The process of viral entry is a primary focus for vaccine and drug development, and this review aims to identify critical knowledge gaps in our understanding of the mechanisms that drive Henipavirus fusion.

Functional HIV-1/HCV cross-reactive antibodies isolated from a chronically co-infected donor.

Despite prolific efforts to characterize the antibody response to human immunodeficiency virus type 1 (HIV-1) and hepatitis C virus (HCV) mono-infections, the response to chronic co-infection with these two ever-evolving viruses is poorly understood. Here, we investigate the antibody repertoire of a chronically HIV-1/HCV co-infected individual using linking B cell receptor to antigen specificity through sequencing (LIBRA-seq). We identify five HIV-1/HCV cross-reactive antibodies demonstrating binding and functional cross-reactivity between HIV-1 and HCV envelope glycoproteins. All five antibodies show exceptional HCV neutralization breadth and effector functions against both HIV-1 and HCV. One antibody, mAb688, also cross-reacts with influenza and coronaviruses, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We examine the development of these antibodies using next-generation sequencing analysis and lineage tracing and find that somatic hypermutation established and enhanced this reactivity. These antibodies provide a potential future direction for therapeutic and vaccine development against current and emerging infectious diseases. More broadly, chronic co-infection represents a complex immunological challenge that can provide insights into the fundamental rules that underly antibody-antigen specificity.