HIV-1 latency in actively dividing human T cell lines

We set out to develop a new in vitro HIV-1 latency model system using the doxycycline (dox)-inducible HIV-rtTA variant. Stable cell clones were generated with a silent HIV-1 provirus, which can subsequently be activated by dox-addition. Surprisingly, only a minority of the cells was able to induce viral gene expression and a spreading infection, eventhough these experiments were performed with the actively dividing SupT1 T cell line. These latent proviruses are responsive to TNFα treatment and alteration of the DNA methylation status with 5-Azacytidine or genistein, but not responsive to the regular T cell activators PMA and IL2. Follow-up experiments in several T cell lines and with wild-type HIV-1 support these findings.We describe the development of a new in vitro model for HIV-1 latency and discuss the advantages of this system. The data suggest that HIV-1 proviral latency is not restricted to resting T cells, but rather an intrinsic property of the virus.With the introduction of highly active antiretroviral therapy (HAART) against HIV-1 it has become possible to stably reduce the viral load below the detection limit in most patients (reviewed in [1]). Current therapies target various steps of the virus replication cycle but can only prevent new infections, without an impact on already infected cells or the integrated provirus. Clearance of infected cells is possible only by cell death or recognition by the host immune system. Consequently, HIV-1 can persist in long-lived reservoirs of different cell types. These cellular reservoirs may differ in the magnitude of viral latency, ranging from low-level virus production that does not trigger immune recognition to truly latent proviruses [2-7]. Viral infection of resting and quiescent cells can lead to a pre-integration complex that fails either to complete reverse transcription or to integrate. These complexes are stable for only a few days and are therefore not important for long term latency [8-11]. Another compo