Objectives: HIV viral load (VL) testing using polymerase chain reaction is a mainstay of treatment monitoring but is technically demanding, time-consuming, and costly. We investigated whether antibody measurements can detect VL rebound, leveraging a recent analytic treatment interruption (ATI) study, NCT03225118.

Methods: We tested longitudinal specimens in N = 22 ATI participants (91% male, 38-61 year age range, 2.1-15.9 years VL suppression pre-ATI) using limiting antigen (LAg) antibody assays, measured as normalized optical density (ODn). We used Bayesian inference to fit linear mixed-effects models, including the time between first detectable VL and ODn increase, the time between peak VL and peak ODn, and the ODn rate of change after VL re-suppression.

Results: LAg ODn increased 4.36 weeks (95% confidence interval [CI]: 3.58, 5.79) after treatment interruption and 2.78 weeks (95% CI: 1.94, 4.15) after VL became detectable. ODn peaked 1.03 weeks (95% CI: 0.25, 1.93) after VL peaked, increasing 1.70 fold (95% CI: 1.39, 2.08) compared with pre-interruption levels. After VL re-suppression, ODn declined by -0.015 units per week (95% CI: -0.017, -0.013) over 1 year of follow-up.

Conclusion: LAg antibody levels increased in all participants 2-4 weeks after VL detection during treatment interruption. Longitudinal antibody measurements could support facile, rapid, and low-cost HIV treatment monitoring.