Abstract

Antigenic mimicry is a fundamental tenet of structure-based vaccinology. 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 minimize the immunogenicity of conserved epitopes on the envelope spike. This principle is starkly illustrated by the presence of an extensive array of host-derived glycans, which act to shield the underlying protein from antibody recognition. Despite these hurdles, a subset of HIV-infected individuals eventually develop broadly neutralizing antibodies that recognize these virally presented glycans. Effective HIV-1 immunogens are therefore likely to involve some degree of mimicry of both the protein and glycan components of Env. As such, considerable efforts have been made to characterize the structure of the envelope spike and its glycan shield. This review summarizes the recent progress made in this field, with an emphasis on our growing understanding of the factors shaping the glycan shield of Env derived from both virus and soluble immunogens. We argue that recombinant mimics of the envelope spike are currently capable of capturing many features of the native viral glycan shield. Finally, we explore strategies through which the immunogenicity of Env glycans may be enhanced in the development of future immunogens.

Highlights

  • Please note that where the full-text provided on King's Research Portal is the Author Accepted Manuscript or Post-Print version this may differ from the final Published version

  • The importance of the glycan shield in human immunodeficiency virus type 1 (HIV-1) vaccine design has recently been underlined by Wagh et al, who observed that the development of bnAbs in infected individuals correlated with the completeness of the glycan shield at transmission [76]

  • It is widely acknowledged that a protective HIV-1 vaccine will be based on the mimicry of the HIV-1 envelope spike, the sole target for bnAbs raised during infection

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Summary

Challenges facing HIV-1 vaccine design

Vaccines typically contain or mimic parts or all of a pathogen, such as an attenuated strain or recombinant soluble surface protein, to prime the immune system to produce an effective response upon future exposure to that pathogen. A subset of HIV-1 infected patients are able to generate antibodies of sufficient breadth and potency to neutralise the vast majority of circulating HIV-1 isolates [11,12,13] These broadly neutralising antibodies (bnAbs) are unable to clear the virus from the infected individual, they are able to protect non-human primates [14,15,16,17,18,19,20,21,22,23,24,25] and humanised mice [26,27,28,29,30,31,32] from viral challenge when passively administered. We discuss the strategies being explored with the aim of boosting the immunogenicity of Env-based vaccines

The antibody response
The glycan shield
Instability of the viral spike
Protein mimicry in vaccine design
Display of bnAb epitopes by viral spike mimetics
Structure and development of broadly neutralising antibodies
Glycan mimicry in vaccine design
Understanding Env glycosylation processing
Immunogen mimicry of viral glycosylation
Glycan clustering and the intrinsic mannose patch
Protein structure and the trimer associated mannose patch
Cell-specific glycosylation
Membrane tethering
Signal peptide
Occupancy
Considerations for immunogen manufacture
Understanding the nature of glycan-dependent bnAb epitopes
Beyond antigenic mimicry
Mimicry of glycan epitopes: chemical approaches
Mimicry of glycan epitopes: biological approaches
Mimicking bnAb development in natural infection
Findings
Conclusions

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