Respiratory Syncytial Virus-Neutralizing Monoclonal Antibodies Motavizumab and Palivizumab Inhibit Fusion

Abstract

Respiratory syncytial virus (RSV) is a major cause of virus-induced respiratory disease and hospitalization in infants. Palivizumab, an RSV-neutralizing monoclonal antibody, is used clinically to prevent serious RSV-related respiratory disease in high-risk infants. Motavizumab, an affinity-optimized version of palivizumab, was developed to improve protection against RSV. These antibodies bind RSV F protein, which plays a role in virus attachment and mediates fusion. Determining how these antibodies neutralize RSV is important to help guide development of new antibody drugs against RSV and, potentially, other viruses. This study aims to uncover the mechanism(s) by which palivizumab and motavizumab neutralize RSV. Assays were developed to test the effects of these antibodies at distinct steps during RSV replication. Pretreatment of virus with palivizumab or motavizumab did not inhibit virus attachment or the ability of F protein to interact with the target cell membrane. However, pretreatment of virus with either of these antibodies resulted in the absence of detectable viral transcription. These results show that palivizumab and motavizumab act at a point after F protein initiates interaction with the cell membrane and before virus transcription. Palivizumab and motavizumab also inhibited F protein-mediated cell-to-cell fusion. Therefore, these results strongly suggest that these antibodies block both cell-to-cell and virus-to-cell fusion, since these processes are likely similar. Finally, palivizumab and motavizumab did not reduce viral budding. Based on models developed from numerous studies of viral fusion proteins, our results indicate that these antibodies may prevent conformational changes in F protein required for the fusion process.

Structural basis for immunization with postfusion respiratory syncytial virus fusion F glycoprotein (RSV F) to elicit high neutralizing antibody titers

“…RSV F helices α5 and α6 form the epitope bound by neutralizing antibodies Palivizumab and Motavizumab. These antibodies bind cell surface-expressed, full-length, likely prefusion RSV F (23) and inhibit RSV cell entry and F-mediated cell-cell fusion (24), presumably by preventing conformational changes in F. The structure of a complex between the Motavizumab Fab and a 24-residue RSV F peptide that includes α5 and α6 has been reported (17). Comparison between this structure and the postfusion RSV F structure reveals a close match between the α5-α6 helices (rmsd for 23 α-carbon atoms = 0.52 Å; Fig.…”

Antibody-Induced Internalization of the Human Respiratory Syncytial Virus Fusion Protein

“…For some MAbs, it is shown that neutralization results from blocking virus fusion with host cell membranes by fixing RSV F proteins in their prefusion conformation (14,52). Interestingly, their neutralizing activity may be directed against not only virions but also virus-infected cells, since cell-to-cell fusion can be inhibited by MAbs like palivizumab and motavizumab (52). In this study, flow-cytometric analysis showed that all RSV F-specific MAbs tested had the ability to decrease surface expression of RSV F proteins, which may impact cell-to-cell fusion.…”

Hydrolyzable Tannins (Chebulagic Acid and Punicalagin) Target Viral Glycoprotein-Glycosaminoglycan Interactions To Inhibit Herpes Simplex Virus 1 Entry and Cell-to-Cell Spread

“…Viral attachment to cell surface was assessed at 4°C, which allows for HSV-1 binding but excludes entry (41), using cellular enzyme-linked immunosorbent assay (ELISA), as well as flow cytometry. The ELISA binding assay was performed as previously described with some modifications (2,31). Briefly, 96-well plates were seeded with A549 cells (2 ϫ 10 4 cells per well) and allowed to grow overnight.…”