Development and clinical application of a novel ex vivo assay to assess genital HIV susceptibility

A better understanding of the biological factors that promote heterosexual HIV acquisition in the female genital tract (FGT) may inform HIV prevention efforts. The mucosal cellular targets of HIV are not well defined and proposed cellular and molecular correlates include the HIV co-receptor CCR5 and markers of immune activation, including CD69. I established a novel ex vivo HIV entry assay for mucosal studies to enable assessment of ex vivo HIV infection in freshly isolated and unstimulated endocervical CD4+ T cells. HIV susceptibility was enhanced in cervix-derived CD4+ T cells compared to blood. Cervical CCR5+, CD69+, α4β7+ or α4β1+ CD4+ T cells were preferential HIV targets, however, the homing integrins α4β7 or α4β1 did not mediate direct binding to the HIV env or HIV entry into CD4+ T cells, suggesting that α4β7 and α4β1 are unlikely to be HIV entry receptors. Next, I tested whether ex vivo HIV entry predicts subsequent heterosexual HIV acquisition. Ideally, this would be done using fresh genital samples, but these are usually not available. Hence, I performed a nested, retrospective, blinded, case-control study in blood CD4+ T cells obtained from HIV-uninfected South African female participants enrolled in the CAPRISA 004 clinical trial. Virus entry into blood CD4+ T cell subsets did not predict subsequent HIV acquisition, possibly due to the compartmentalization of immune factors in the genital mucosa. One such compartmentalized factor in the FGT is the bacterial microbiota, which is dominated in the majority of women by lactobacilli, while a shift towards diverse gram-negative anaerobic species, defined (based on Gram stain) as bacterial vaginosis (BV), is associated with increased HIV acquisition in women. To investigate underlying biological mechanisms that may increase HIV acquisition risk in women with BV, I assessed the impact of BV treatment using the current standard of care, oral metronidazole, on genital immunology and HIV susceptibility. BV treatment reduced endocervical CD4+ T cell susceptibility to HIV and genital IL-1 levels; however, an unexpected increase in several chemokines previously associated with increased HIV risk suggests that more studies are needed before the treatment and/or prevention of asymptomatic BV can be recommended for HIV prevention.Ph.D