The latent reservoir for HIV-1 in resting memory CD4+ T cells is a major barrier to eradication. In vitro models involving transformed cell lines have been used to search for small molecules that reactivate latent HIV-1. Histone deacetylase (HDAC) inhibitors can reverse HIV-1 latent infection. Most studies on HDAC inhibitors have been performed in cell line models that differ in important aspects from the resting CD4+ T cells that harbour latent HIV-1 in vivo. Therefore, we evaluated the potency and kinetics of HDAC inhibitors in a primary cell model of HIV-1 latency that involves resting CD4+ T cells.

A green fluorescent protein (GFP)-expressing reporter virus NL4-3-Δ6-drGFP was used to generate latent infection in Bcl-2-transduced primary CD4+ T cells. Seventeen HDAC inhibitors were tested in this primary cell model. The effects of these HDAC inhibitors on the reactivation of latent HIV-1 were determined and compared with anti-CD3 and anti-CD28 co-stimulation.

In Bcl-2-transduced primary CD4+ T cells, short-term treatment with HDAC inhibitors resulted in very limited reactivation of latent HIV-1, while prolonged treatment greatly enhanced drug efficacy. The effects of HDAC inhibitors in reactivating latent HIV-1 correlated with their inhibitory effects on class I HDACs. Importantly, HIV-1 reactivated by HDAC inhibitors can quickly re-establish latent infection upon drug removal.

We identified unique features of HDAC inhibitor-induced reactivation of latent HIV-1 in primary CD4+ T cells. Our findings may be useful for the design of eradication trials.