Background: Structured treatment interruptions have been proposed as a strategy to minimize the cost and toxicity of long-term HAART while also providing a mechanism to enhance HIV-1-specific immunity. Prior studies have reported a rapid rebound in viremia and a significant increase in the latent reservoir in resting CD4+ T cells following STI, but the nature of this increase in the reservoir has not been fully characterized.

Methods: We studied 5 patients who had treatment interruptions. Resting CD+ T cells were purified from PBMC during and after treatment interruptions. These cells were then cultured under limiting dilution and the frequency of latently infected cells was determined.

Results: There was a rebound in viremia in all 5 patients with a median peak viral load of 288,000 copies/mL. The median frequency of latently infected cells present at peak measured viremia was 456 infectious units per million, a value similar to that seen in primary HIV-1 disease. Following the re-initiation of HAART, the frequency of latently infected cells dropped by 2 logs and approached baseline levels in the 2 patients who had pre-STI  measurements.

Conclusions: This rapid rate of decay suggests that cells in the labile pre-integration phase of latency predominate when HAART is discontinued and that treatment interruptions do not dramatically increase the size of the stable reservoir for HIV-1.