# Discovery and molecular mechanism of potent neutralizing antibody from humanized mice with respiratory syncytial virus

## TL;DR

Researchers discovered a powerful antibody from humanized mice that neutralizes RSV and could lead to better treatments and vaccines.

## Contribution

The study reports the first isolation of RSV-neutralizing antibodies from humanized mice and identifies a unique epitope for broad-spectrum activity.

## Key findings

- PR306007 neutralizes both RSV-A and B subgroups with superior potency.
- Cryo-EM reveals PR306007 binds to a unique epitope overlapping antigenic sites II and V of the F protein.
- PR306007 shows strong in vivo antiviral activity and prophylactic potential in animal models.

## Abstract

Respiratory syncytial virus (RSV) is a leading cause of lower respiratory tract infections among infants and older adults, posing a significant threat to global public health. The prophylactic use of neutralizing antibodies (nAbs) underscores the need to understand elite RSV antibody neutralization mechanisms, which is fundamental for developing next-generation therapies with enhanced potency and broader activity. In this study, we utilized H2L2 transgenic mice encoding human immunoglobulin variable regions for immunization and successfully screened multiple antibodies with significant neutralizing activity using the Beacon Optofluidic system. One of these antibodies, PR306007, exhibited significantly superior broad-spectrum neutralization against both RSV-A and B subgroups. Cryo-electron microscopy (Cryo-EM) structural analysis revealed that PR306007 binds to a unique epitope that overlaps with antigenic sites II and V of the F protein, with its primary binding regions located at the base of the α6 and α7 helices of site II, and residues S173 and N175 of site V. This binding mode offers valuable insights into enhanced neutralization activity and potentially reduces the risk of emerging immune evasive mutants. Furthermore, PR306007 showed potent in vivo antiviral activity against RSV infection and demonstrated good efficacy against both lower and upper respiratory tract infections, making it a promising prophylactic candidate for broad prevention. These findings provide new insights for the future development of RSV vaccines or nAbs.

Respiratory syncytial virus (RSV) poses a significant burden on global public health, presenting a serious health threat to infants, young children, the elderly, and other vulnerable populations, including individuals with immunodeficiencies. The ongoing development of neutralizing antibodies against RSV not only holds substantial scientific value but also promises widespread clinical applications. In this study, we reported for the first time the isolation of the neutralizing antibodies against RSV from immunized humanized mice. The neutralizing antibody PR306007 exhibits potent activity against both RSV-A and B subgroups. We elucidated the cryo-electron microscopy structure of PR306007, a potent activity and broad-spectrum neutralizing antibody, in complex with the RSV pre-F antigen. Through structural and sequence analyses, we revealed that PR306007 bound to a unique epitope across the antigenic sites II and V of the F protein. Notably, the heavy chain gene of PR306007 is encoded by IGHV1–8, which is relatively rare within the known repertoire of antiviral antibody lineages. Furthermore, PR306007 demonstrated effective prophylactic effect in animal experiments, underscoring its potential as a broad-spectrum therapeutic against RSV. These findings offer valuable insights and guidance for the development of next-generation therapies and vaccines.