The transmitted HIV-1 subtype C: characterization of the transmitted/founder full-length virus genome and the influence of early immune selective pressure on virus replication

• Main Author: Abrahams, Melissa-Rose Hilda
• Other Authors: Williamson, Carolyn
• Format: Doctoral Thesis
• Language: English
• Published: University of Cape Town 2015
• Online Access: http://hdl.handle.net/11427/12712

Includes bibliographical references. === The identification of targets of early immune responses associated with control of HIV-1 infection will inform immunogen design for vaccine interventions. The early evolution of transmitted/founder subtype C virus sequences was investigated to determine the location and frequency of immune selection, and the impact of early immune escape mutations on viral replicative capacity. Single-genome amplified env sequences from 26 acutely-infected women were evaluated for conformance to a model of random evolution to elucidate multiplicity of infection. Near fulllength genome sequences from the first six months of infection were generated for five women and sites evolving under immune selection were mapped. CD8+ cytotoxic Tlymphocyte escape mutations in HLA-B-restricted epitopes were introduced into infectious molecular clones of cognate transmitted/founder viruses by site-directed mutagenesis and their impact on viral replicative fitness was evaluated using parallel replication assays. In 77% of women (n=20) a single transmitted/founder variant established infection and two to five variants in the remaining 23% (n=6). Near full-length genome sequencing in five women confirmed single variant/low-diversity transmission and identified fifty-five genome regions evolving under immune selection, 40% of which was attributed to CD8+ cytotoxic Tlymphocyte pressure, 35% to antibody-mediated pressure, 16% to reversion and 9% could not be classified. The rate of sequence diversification and number of sites evolving under immune selection was highest in nef. The majority of evolving CD8+ cytotoxic T-lymphocyte epitopes (82%) contained shuffling/toggling mutations. A novel B*15:10-associated mutation, A164T, combined with a V85A Pol mutation reduced viral replication capacity in one individual. In a second individual, the attenuating HLA-B*58:01-associated mutation, T242N, enhanced viral replication capacity due to pre-existing compensatory polymorphisms in the transmitted/founder virus. A third individual, who had extremely rapid disease progression, was infected with the virus with the highest replication capacity. This thesis describes the complex nature of early immune selection and escape in transmitted/founder viruses. Although attenuating escape mutations were identified in viruses from two individuals, this was not associated with clinical benefit. The extensive variability of epitopes evolving under early selection may implicate many early immune targets as poor candidates for vaccine immunogens; however some early targets may be useful if clinical benefit is conferred through attenuating escape mutations.