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Title: The impact of sequence diversity on the glycan shield of HIV-1 immunogens
Author: Seabright, Gemma Elizabeth
ISNI:       0000 0004 7966 4319
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2019
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Vaccine strategies for the human immunodeficiency virus type 1 (HIV-1) focus on the mimicry of its envelope spike (Env), due to its exposed location on the viral membrane and role in mediating infection. However, the virus has evolved to minimise the immunogenicity of Env, notably through extremely high sequence variability and the shielding of conserved protein epitopes by an extensive array of host-derived, immunologically 'self' N-linked glycans. Despite this, a subset of infected individuals eventually develop broadly neutralising antibodies that can recognise these glycans. Defining the composition of glycan epitopes on both viral Env and candidate immunogens is therefore a major research focus for HIV-1 vaccine design. Using recombinant, soluble mimics of Env, this thesis sought to determine the impact of protein sequence on the processing of the glycan shield. This was addressed on three levels: the impact of virally-encoded sequence diversity, the impact of engineered stabilising mutations, and the impact of mutations affecting glycosylation sites. Despite the extensive diversity displayed by the Env sequence, many features of the glycan shield were remarkably conserved. Mutations affecting glycosylation sites, however, did impact the fine processing of nearby sites. Additionally, the glycan composition of Env mimics could be subtly altered using glycan-dependent broadly neutralising antibodies, either during the expression or purification stages. The latter effect appeared to be sequence-specific. Although recombinant, soluble Env proteins are good structural and antigenic mimics of native, viral Env, the extent to which their glycan shields resemble that of infectious viruses is unknown. To that end, the glycosylation of a candidate immunogen was compared to that of sequence-matched Env derived from infectious virions. The glycan processing of key broadly neutralising antibody epitopes was largely conserved between virus and immunogen. However, there were subtle differences at some sites, with the viral material typically displaying elevated glycan processing. Given that recombinant Env constructs are good mimics of the viral glycan shield, they are likely also inherently immunoquiescent. Accordingly, this thesis also explored a strategy to boost the immunogenicity of the glycan shield, using yeast to decorate a soluble Env immunogen with 'non-self' glycan structures. Overall, features of the Env glycan shield are largely conserved between virus and immunogens, and across multiple genotypes, supporting it as a suitable target for HIV-1 vaccine design.
Supervisor: Crispin, Max ; Wormald, Mark Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: HIV-1 glycan shield