Characterization of inducible reservoirs of HIV-1

Combination antiretroviral therapy for HIV-1 suppresses viral replication, but is not curative. HIV-1 remains detectable in those on suppressive therapy as cellular proviral DNA and cellular HIV-1 RNA in peripheral blood mononuclear cells (PBMC), and as low-level plasma viremia. A long-lived reservoir of intact proviruses is also retained in the resting CD4+ T cell population. This population of long-lived, latently infected cells is believed to cause life-long persistence of HIV-1. To deplete latently infected cells, a “kick and kill” strategy has been proposed, in which HIV-1 is “kicked” out of proviral latency by small molecule latency reversing agents, leading to the “kill” from viral cytopathic effects or immune mediated clearance. Recent ex vivo and in vivo studies have concluded that histone deacetylase inhibitors, protein kinase C agonists and Brd4 inhibitors can effect HIV-1 latency reversal. We evaluated this proposed strategy at the level of individual proviruses using a limiting dilution assay, and found that currently used latency reversal agents are not potent activators of HIV-1 latency compared with T cell activation. These latency reversal agents also do not lead to significant depletions of the HIV-1 reservoir in resting CD4+ T cells. We also sought to better understand relationships between molecular biomarkers of HIV-1 persistence and the size of the inducible reservoir. We found that as the frequency of infected cells and their transcriptional activity in PBMC increases, the size of the inducible reservoir also increases. Spontaneous virion production from resting CD4+ T cells and PBMC was also associated with low-level viremia. We also found that the magnitude of the inducible reservoir, and the levels of infectious virus, were higher in total CD4+ T cells compared with resting CD4+ T cells. Finally, we also found that the size of the inducible reservoir was significantly correlated with the magnitude of viral outgrowth from total and resting CD4+ T cells. Overall, these findings demonstrate that more potent latency reversing agents will be required to reduce the size of the latent reservoir, and suggest that measures of the infectious and inducible reservoirs in those on long-term antiretroviral therapy can be greatly simplified