Quantification of HIV-1 latency reversal in resting CD4+ T cells from patients on suppressive antiretroviral therapy

Significance A pool of latently infected resting CD4+ T cells in patients on antiretroviral therapy is a major barrier to a cure for HIV-1. Clinical trials are underway to assess whether small molecules can “kick” HIV-1 out of latency, but the potency of such latency reversing agents has not been evaluated at the level of single proviruses. Using a unique quantitative system, we found that the histone deacetylase inhibitor vorinostat (suberoylanilide hydroxamic acid), which is being investigated clinically, did not induce unspliced cellular viral RNA or lead to virion production from the large majority of proviruses in resting CD4+ T cells. Our results demonstrate that more potent interventions will likely be necessary to reduce the size of the latent reservoir. Reversal of proviral latency is being pursued as a curative strategy for HIV-1 infection. Recent clinical studies of in vivo administration of the histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA; vorinostat) show increases in unspliced cellular HIV-1 RNA levels in resting CD4+ T cells. A critical unknown, however, is the proportion of latent proviruses that can be transcriptionally reactivated by SAHA or T-cell activation. In this study, we quantified the fraction of HIV-1 proviruses in resting CD4+ T cells from patients on suppressive antiretroviral therapy that were reactivated ex vivo with SAHA or antibodies to CD3/CD28. At concentrations of SAHA achieved clinically, only 0.079% of proviruses in resting CD4+ T cells were reactivated to produce virions, compared with 1.5% of proviruses in cells treated with anti-CD3/CD28 antibodies after correcting for spontaneous virion production in the medium control. A significant positive correlation (ρ = 0.67, P < 0.001) was found between levels of virions in the supernatant and unspliced cellular HIV-1 RNA following anti-CD3/CD28 treatment, but not following SAHA treatment (ρ = 0.21, P = 0.99). These results reveal that the majority of HIV-1 proviruses are not reactivated by current therapeutic approaches and that more effective means of reversing proviral latency will likely be required to deplete HIV-1 reservoirs.

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