The decay of the latent reservoir of replication-competent HIV-1 is inversely correlated with the extent of residual viral replication during prolonged anti-retroviral therapy

Replication-competent HIV-1 can be isolated from infected patients despite prolonged plasma virus suppression by anti-retroviral treatment(1-3). Recent studies have identified resting, memory CDC T lymphocytes as a long-lived latent reservoir of HIV-1 (refs. 4,5). Cross-sectional analyses indicate that the reservoir is rather small, between 10(3) and 10(7) cells per patient(5,6). In individuals whose plasma viremia levels are well suppressed by anti-retroviral therapy, peripheral blood mononuclear cells containing replication-competent HIV-1 were found to decay with a mean half-life of approximately 6 months(7), close to the decay characteristics of memory lymphocytes in humans and monkeys(8-10). In contrast, little decay was found in a less-selective patient population(11). We undertook this study to address this apparent discrepancy. Using a quantitative micro-culture assay, we demonstrate here that the latent reservoir decays with a mean half-life of 6.3 months in patients who consistently maintain plasma HIV-1 RNA levels of fewer than 50 copies/ml. Slower decay rates occur in individuals who experience intermittent episodes of plasma viremia. Our findings indicate that the persistence of the latent reservoir of HIV-1 despite prolonged treatment is due not only to its slow intrinsic decay characteristics but also to the inability of current drug regimens to completely block HIV-1 replication.