Dissertation submitted to the Faculty of Health Sciences, University of the Witwatersrand,
Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Medicine.
Johannesburg, 2012 / Introduction:
Most new HIV-1 infections world-wide are caused by subtype C viruses. The C3V4 region, including
the alpha2-helix and V4 loop, has been identified as a major target for autologous neutralising
antibodies in subtype C infections. Factors associated with the immunogenicity of this region, and
the mechanisms of escape from anti-C3V4 responses have not been described, although charge
changes in the alpha2-helix have been proposed to mediate neutralisation escape.
Methods:
Seventeen HIV-1 subtype C infected individuals were classified as C3V4 responders or nonresponders
using chimeric viruses in env-pseudotyped neutralisation assays. Longitudinal sequences
obtained from C3V4 responders were used to identify putative neutralisation escape mutations. The
role of these mutations in mediating escape was investigated using site-directed mutagenesis.
Results:
The C3V4 region was confirmed as a major target in HIV-1 subtype C infections. The development of
an anti-C3V4 response was associated with shorter V4 loops and fewer potential N-linked glycans
(PNGs) in the C3V4 region. Anti-C3V4 responses were associated with higher autologous
neutralising titres. Neutralisation escape from an anti-C3V4 response was rarely mediated by charge
changes in the alpha2-helix and generally occurred through mutations in other structurally proximal
regions of the envelope. This study confirmed the use of glycan shuffling as a predominant escape
pathway. In three individuals multiple mechanisms of escape were identified and in two other cases
escape mutations within the C3V4 and structurally proximal regions clustered at opposite termini of
the alpha2-helix, inconsistent with the surface area of a single epitope.
Conclusion:
A more exposed and accessible C3V4 region was more likely to elicit an anti-C3V4 response. The
highly immunogenic nature of this region may contribute to the higher overall neutralisation titres in
subtype C infections. Distinct clusters of mutations may suggest the existence of two “sub-epitopes”
within the C3V4 domain that warrant further investigation. These findings emphasise the
adaptability and plasticity of the C3V4 region in the context of viral evasion of host defences.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/13796 |
| Date | January 2012 |
| Creators | Bhiman, Jinal Nomathemba |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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