Thymic volume predicts CD4 T-cell decline in HIV-infected adults under prolonged treatment interruption

Objective: To analyze the predictive capacity of thymic volume in CD4 T-cell loss after treatment interruption in HIV-infected patients with high nadir CD4 count. Methods: Thirty-nine HIV-infected patients with CD4 counts greater than or equal to 500 cells/mu L, nadir CD4 counts greater than or equal to 250 cells/mu L, and plasma viral loads less than 50 copies/mL for at least the past 12 months began a treatment interruption program. The event of interest for this study was the decrease of CD4 count below 350 cells/mu L. Kaplan-Meier curves were used for all time-to-event analyses, and log-rank tests were used for comparison between groups in the univariate analysis. All variables with statistical association with CD4 T-cell loss were analyzed using multivariate Cox proportional hazards regression models. Results: Twenty-three percent of the patients had a decrease in CD4 count to less than 350 cells/mu L. In the univariate analysis, only thymic volume was statistically significant with this event (P = 0.02). Nadir CD4 count nearly reached statistical significance. However, age, sex, HCV coinfection, CD4 count, T-cell receptor excision circle-bearing cells, and early viral load rebound did not show statistical differences. Thymic volume and CD4 T-cell loss were independently associated using Cox proportional hazards regression model (P = 0.04; relative risk, 0.76; 95% confidence interval, 0.59-0.99). Conclusions: In this study, we demonstrate for the first time that thymic volume predicts CD4 T-cell loss in patients with nadir CD4 count greater than or equal to 250 cells/mu L under treatment interruption.