Mathematical Modeling Predicts that Increased HSV-2 Shedding in HIV-1 Infected Persons Is Due to Poor Immunologic Control in Ganglia and Genital Mucosa

<div><p>A signature feature of HIV infection is poor control of herpes virus infections, which reactivate from latency and cause opportunistic infections. While the general mechanism underlying this observation is deficient CD4+T-cell function, it is unknown whether increased severity of herpes virus infections is due primarily to poor immune control in latent or lytic sites of infection, or whether CD4+ immunodeficiency leads to more critical downstream deficits in humoral or cell-mediated immunologic responses. Here we compare genital shedding patterns of herpes simplex virus-2 (HSV-2) in 98 HIV infected and 98 HIV uninfected men matched on length of infection, HSV-1 serostatus and nationality. We demonstrate that high copy HSV-2 shedding is more frequent in HIV positive men, particularly in participants with CD4+ T-cell count <200/μL. Genital shedding is more frequent due to higher rate of shedding episodes, as well as a higher proportion of prolonged shedding episodes. Peak episode viral load was not found to differ between HIV infected and uninfected participants regardless of CD4+ T-cell count. We simulate a mathematical model which recapitulates these findings and identifies that rate of HSV-2 release from neural tissue increases, duration of mucosal cytolytic immune protection decreases, and cell-free viral lifespan increases in HIV infected participants. These results suggest that increased HSV-2 shedding in HIV infected persons may be caused by impaired immune function in both latent and lytic tissue compartments, with deficits in clearance of HSV-2 infected cells and extracellular virus.</p></div

Episode characteristics.

<p>Rate outcomes were compared by arm between persons using generalized estimating equations with a log link. Continuous outcomes were compared using generalized estimating models with an identity link. Significant differences are noted in bold and are limited to differences in episode rate and episode duration. All other episode characteristics are equivalent across cohorts.</p

Mathematical model fit to quantitative shedding rate and episode rate.

<p>Ten mathematical model simulations of HSV-2 shedding (thin colored lines) in reference to empirical shedding data (median marked with black dot and 95% CI with black horizontal bars). Quantitative shedding per swab for <b>(A)</b> HIV negative, and HIV positive men with <b>(B)</b> CD4+ T-cells >500/μL, <b>(C)</b> 200-499/μL and <b>(D)</b> <200/μL.</p

Immunologic determinants of increased HSV-2 shedding in HIV-1 infected men.

<p>Parameter sets represent the top 50 (5%) model fits for each group. Boxplots whiskers are inclusive of the full range of values. The box includes interquartile range and a median line. <b>(A)</b> HSV-2 release rate from ganglia to the genital tract, <b>(B)</b> Genital T-cell decay rate, <b>(C)</b> Genital HSV-2 DNA clearance rate and <b>(D)</b> Number of infected cells needed to stimulate half-maximal genital T-cell expansion. All comparisons are with Mann Whitney rank tests. Of note, genital T-cell levels in the model are intended as a surrogate measure of cytolytic immune potential.</p

HSV-2 shedding episode characteristics in HIV-1 negative and positive men with CD4+ T-cells count <200/μL.

<p>500 simulated episodes with parameters optimized for HIV negative (orange) and HIV positive men with CD4+ T-cells <200/μL (teal). Boxplots whiskers are inclusive of 90% of values and dots are simulations outside of this range. The box includes interquartile range and a median line. <b>(A)</b> Genital T-cell density in model region of episode initiation, <b>(B)</b> Peak HSV DNA copy number, <b>(C)</b> Number of infected regions per shedding episode, <b>(D)</b> Episode duration. Comparisons for each of the episode characteristics were not statistically significant with non-parametric Mann Whitney rank tests. However, simulations with CD4+ T-cells <200/μL had higher proportions of episodes involving more than 50 regions <b>(C)</b> and lasting more than 10 and 20 days <b>(D)</b>.</p

Increased HSV-2 shedding rate, episode rate and episode duration in HIV infected men.

<p>Frequency histograms of HSV-2 shedding in cohorts of HIV negative (orange), and HIV positive men with CD4+ T-cells >500/μL (magenta), 200-499/μL (green) and <200/μL (teal). (<b>A)</b> Quantitative shedding per swab; <b>(B)</b> Shedding episode classification scheme (adapted from reference 4; (<b>C)</b> Annualized episode rate; (<b>D)</b> Duration, (<b>E)</b> First positive viral load, (F<b>)</b> Peak positive viral load & (<b>G)</b> Last positive viral load per episode.</p

Clinical cohort characteristics.

<p>Clinical cohort characteristics.</p

Parameter ranges used for model fitting.

<p>Varied parameters were selected from uniform distributions. Fixed parameters were derived from prior model fitting or literature search <b>(Methods).</b></p

Individual determinants of increased HSV-2 shedding rate.

<p>Critical model predictors of shedding rate in 10-year simulations with 1000 parameter sets. Curves in all panels indicate best fit with a polynomial model while dots are single simulations. <b>(A)</b> HSV-2 release rate from ganglia to the genital tract (R² = 0.17), <b>(B)</b> Genital T-cell decay rate (R² = 0.29), <b>(C)</b> HSV-2 DNA clearance rate (R² = 0.30), predict shedding rate to various degrees. Genital T-cell levels in the model are intended as a surrogate measure of cytolytic immune potential.</p

Incidence of maternal postpartum adverse events, by study arm.

<p>Incidence of maternal postpartum adverse events, by study arm.</p