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HIV persistence on antiretroviral therapy- the role of homeostatic proliferation and T-cell trafficking
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posted on 22.02.2017by Khoury, Gabriela
Combination antiretroviral therapy (cART) reduces HIV-related morbidity and mortality however it is not curative and needs to be taken life-long. This is largely due to HIV persistence in long lived latently infected CD4+ T-cells. In this thesis we hypothesised that persistence of latently infected CD4+ T-cells in HIV-infected subjects on cART is influenced by multiple factors including CD4+ T-cell differentiation, homeostatic proliferation, T-cell trafficking and immune activation (IA).
The role of naïve CD4+ T-cells as a reservoir was investigated both in vitro and in vivo. In vitro, naïve CD4+ T-cells were relatively resistant to HIV infection, despite these findings, integrated HIV DNA, cell-associated unspliced (CA-US) HIV-RNA and 2-LTR circles were all detected in naïve CD4+ T-cells during long term suppressive cART. In a longitudinal cohort of individuals receiving long-term suppressive cART, CD31+ naïve CD4+ T-cells were a stable reservoir of HIV likely to be maintained via homeostatic proliferation. Together these data demonstrated that naïve CD4+ T-cells are an important reservoir during cART.
CD4+ T-cell subsets that express specific chemokine receptors (CKR) such as CXCR3 and CCR6 have the capacity to home to specific locations including the gut associated lymphoid tissue (GALT) and sites of inflammation. Quantification of the reservoir within different central memory (CM) CD4+ T-cells expressing CXCR3 and/or CCR6 revealed that CXCR3+CCR6+ subset were preferentially infected compared to other subsets (n=20, p<0.001). The relationship between HIV persistence and expression of CKR, CCR7, CXCR3, CCR6, CCR5 and CXCR5, plus their chemokine (CK) ligands during cART was further assessed. CKR expression was statistically significantly associated with current CD4+ T-cell count and multiple markers of IA but no association was demonstrated with integrated or total HIV DNA. Inverse associations were demonstrated between the frequency of CCR5+ (p=0.030) and CXCR3+ (p=0.001) CD4+ T-cells with 2-LTR circles, independent of current and nadir CD4+ T-cell counts. The enrichment of HIV in CXCR3+CCR6+ CM CD4+ T-cells in combination with their capacity to traffic to the GALT potentially explains the high frequency of infected cells at this site.
The role of IA in HIV persistence on cART was examined in CD4+ T-cells isolated from blood, lymph node (LN) and GALT. The GALT was enriched for integrated HIV DNA (p<0.001) and CA-US HIV RNA (p=0.029) which were both positively associated with the high proportion of PD-1+ CD4+ T-cells in this site. A statistically significant positive association was observed between activated CD8+ T-cells and all markers of HIV persistence in both the LN and GALT. Reduced ARV penetration within these tissue sites might allow for ongoing viral replication, a likely driver of chronic immune activation and inflammation during cART, or ongoing infection of resting CD4+ T-cells.
CD4+ T-cells are a diverse population and HIV persists in both naïve and memory CD4+ T-cell subsets in individuals receiving suppressive cART. HIV persistence on cART is a consequence of multiple factors that are important for CD4+ T-cell homeostasis including differentiation, trafficking and activation. The complexity of HIV persistence on cART, suggests a diverse number of strategies will be required to eliminate latency.