Structure-Based Immunogen Design for Nipah and other Paramyxoviruses
Rebecca J. Loomis, Guillaume B.E. Stewart-Jones, John R. Mascola and Barney S. Graham Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD, USA
Introduction: All members of the Paramyxoviridae and Pneumoviridae have two membrane glycoproteins, the attachment (H, HN or G) and the fusion (F) proteins involved in receptor binding and viral entry, respectively. While parenterally-administered live-attenuated viral vaccines can elicit protective immune responses to measles and mumps, this strategy has failed for other paramyxoviruses. Paramyxoviruses and Pneumoviruses utilize a type I fusion glycoprotein that transitions between a metastable prefusion conformation and a stable postfusion conformation to merge viral and cellular membranes. Structure-based stabilization of RSV F in its prefusion conformation has been shown to induce high levels of RSV-neutralizing activity in vaccine animals models and in a clinical trial.
Methods: We engineered soluble prefusion-stabilized versions of the F glycoprotein from numerous paramyxoviruses. We are characterizing structurally and testing for immunogenicity in animal models.
Results: Antigenic and electron microscopy analysis of prefusion-stabilized Nipah virus (NiV) F variants showed introduction of various combinations of non-natural disulfide bonds, cavity-filling mutations and proline additions resulted in improved protein expression and NiV F glycoproteins that bound a prefusion-specific neutralizing antibody. A postfusion NiV F glycoprotein also expressed well, but did not the bind the prefusion-specific antibody. None of the prefusion stabilizing mutations for NiV F are shared with those identified to stabilize prefusion RSV F, despite similar F protein structures. NiV prefusion F variants were structurally evaluated and elicited neutralizing antibodies in immunized mice. Prefusion-stabilized NiV F-induced superior neutralizing activity compared to postfusion F, similar to what was seen with RSV F. Additionally, we are using homology design for prefusion F stabilized variants of Hendra and Cedar, two other henipaviruses.
Conclusions: Stabilizing class I fusion glycoproteins in their prefusion native conformation preserves neutralization-sensitive epitopes and may represent a general solution for designing vaccine antigens for many enveloped viruses including paramyxoviruses, some of which are considered high risk for pandemic outbreaks.
Credits: None available.
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