Persistence of drug-resistant HIV-1 after a structured treatment interruption and its impact on treatment response.

OBJECTIVE: Among treated patients with drug-resistant viremia, structured treatment interruptions often result in the re-emergence of drug-susceptible HIV-1. Theoretically, this may allow for a more durable response to salvage therapy. We therefore studied the long-term treatment outcome to antiretroviral therapy in a cohort of patients who had previously interrupted therapy, focusing on the determinants of treatment success versus failure.
DESIGN: A prospective observational study of the response to antiretroviral therapy in patients resuming therapy after a treatment interruption. Virological and immunological studies were performed every month for 3 months and then every 3 months.
RESULTS: Twenty-four patients underwent a structured treatment interruption and resumed therapy after a variable period of time (median 20 weeks). The median duration of treatment after the treatment interruption was 109 weeks. A transient virological response was observed in all patients who resumed a regimen containing no drug to which their pre-interruption virus was fully susceptible. Virus isolated during virological failure was genotypically and phenotypically identical to the pre-interruption virus, exhibited reduced replicative capacity, and replicated at levels similar to the pre-interruption baseline. In contrast, durable viral suppression (< 200 copies/ml) was observed in patients who initiated a regimen containing only one drug to which their pre-interruption virus was fully susceptible. Despite viral suppression, the pre-interruption drug-resistant virus population remained detectable in two patients.
CONCLUSION: Although drug-resistant HIV-1 persists at low levels during and after the interruption of therapy, durable suppression of this virus population may be achieved with a combination regimen containing only one fully active agent.