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Title: Refocusing antibody responses by chemical modification of vaccine antigens
Author: Schiffner, Torben
ISNI:       0000 0004 5355 4058
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2014
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The envelope glycoprotein (Env) of Human Immunodeficiency Virus 1 (HIV-1) has developed several immune-evasion mechanisms to avoid the induction of neutralising antibodies, including immunodominant non-neutralising epitopes, conformational flexibility of conserved epitopes, and spontaneous subunit dissociation, thus impeding vaccine development. Here, chemical modification of Env-based vaccine antigens is explored to overcome these obstacles. Firstly, covalent fixation of Env by chemical cross-linking was used to stabilise the conformationally flexible structure and prevent subunit dissociation. Cross-linked Env constructs showed reduced binding of many non-neutralising antibodies whilst largely maintaining antibody recognition by broadly neutralising antibodies. Compared to unmodified material, immunisation with some of these cross-linked proteins led to the induction of significantly increased antibody titres targeting the conserved CD4 binding site of Env despite similar overall antibody titres. These refocused antibody responses resulted in increased serum neutralising titres compared to animals receiving unmodified protein. Secondly, an epitope masking strategy was developed to reduce or eliminate the immunogenicity of neutralisation-irrelevant surfaces. This was achieved using site-selective addition of theoretically immunosilent glycoconjugates to lysine residues. Masking of model protein hen egg lysozyme (HEL) led to site-selective loss of antibody binding to the modification sites in vitro, which translated into refocusing of antibody responses from masked to unmasked epitopes in vivo. Mutant HIV-1 and influenza virus surface glycoproteins were designed that had lysine residues removed from close proximity to the respective broadly neutralising epitopes, but added throughout the remaining surface. Masking of these mutant proteins with second-generation glycoconjugates led to predictable perturbations of antibody binding in vitro. However, administration of these modified glycoproteins revealed unexpectedly that the masking glycans were highly immunogenic in vivo. Thus, this strategy may well prove useful if truly non-immunogenic glycoconjugates can be identified. Taken together, these chemical modifications of vaccine antigens may allow focused targeting of specific antigenic regions for increased B cell recognition, and may thus be a valuable tool for vaccine antigen design.
Supervisor: Sattentau, Quentin J. Sponsor: Edward Penley Abraham Research Fund
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Glycobiology ; Biochemistry ; Biology ; Medical sciences ; Biology (medical sciences) ; Disease prevention ; Immunology ; Infectious diseases ; Pathology ; Vaccinology ; Viruses ; Vaccine Design ; Antigenicity ; Immunogenicity ; Envelope Glycoproteins ; Neutralizing Antibody ; Glycosylation ; Protein Modifications ; Glycoconjugates ; Chemical Cross-linking