Abstract
Respiratory Syncytial Virus (RSV) is an important viral agent causing severe respiratory tract disease in infants and children as well as in the elderly and immunocompromised individuals. The lack of a safe and effective RSV vaccine represents a major unmet medical need. RSV fusion (F) surface glycoprotein was modified and cloned into a baculovirus vector for efficient expression in Sf9 insect cells. Recombinant RSV F was glycosylated and cleaved into covalently linked F2 and F1 polypeptides that formed homotrimers. RSV F extracted and purified from insect cell membranes assembled into 40 nm protein nanoparticles composed of multiple RSV F oligomers arranged in the form of rosettes. The immunogenicity and protective efficacy of purified RSV F nanoparticles was compared to live and formalin inactivated RSV in cotton rats. Immunized animals induced neutralizing serum antibodies, inhibited virus replication in the lungs, and had no signs of disease enhancement in the respiratory track of challenged animals. RSV F nanoparticles also induced IgG competitive for binding of palivizumab neutralizing monoclonal antibody to RSV F antigenic site II. Antibodies to this epitope are known to protect against RSV when passively administered in high risk infants. Together these data provide a rational for continued development a recombinant RSV F nanoparticle vaccine candidate.
Highlights
Respiratory syncytial virus (RSV) is the most common cause of acute lower respiratory infection in infants and young children, and a major disease burden in the elderly
RSV F is produced as a precursor (F0) that is cleaved at Arg109 and Arg136 by cellular furin to three fragments, a shorter F2 polypeptide at the N-terminus covalently linked by two disulfides to a longer F1 polypeptide with an 18 amino acid fusion domain at the N-terminus and a hydrophobic membrane spanning region near the C-terminus; the intervening 27 amino acid fragment is released
No RSV F was detected in Sf9 cells infected with a baculovirus expressing clone 7 where both furin cleavage sites and the intervening 27 amino acid peptide sequences were deleted
Summary
Respiratory syncytial virus (RSV) is the most common cause of acute lower respiratory infection in infants and young children, and a major disease burden in the elderly. Neutralizing monoclonal antibodies palivizumab and motavizumab bind to RSV F antigenic site II (Asn258 - Val278) [8] and have been shown to protect against both lower and upper respiratory RSV disease in high risk and term infants [9,10] The structures of the RSV F epitope polypeptides that bind these neutralizing antibodies are larger than the linear peptide and palivizumab binds with nanomolar and motavizumab picomolar affinity to RSV F [11,12,13]. Preserving RSV F tertiary and quaternary structures may be important in the development of an RSV F vaccine to preserve the native conformation of this important neutralizing region
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