Journal of virology 2018 04 11() pii 10.1128/JVI.02225-17
HIV infection requires lifelong antiretroviral therapy because of the persistence of latently infected CD4+ T cells. Induction of viral expression from latently infected cells occurs following T cell receptor (TCR) activation but not all latently infected cells respond to TCR stimulation. We compared two models of latently infected cells using an enhanced green fluorescent protein (EGFP) reporter virus to infect CCL19 treated resting CD4+ (rCD4) T cells (pre-activation latency) or activated CD4+ T cells that returned to a resting state (post-activation latency). We isolated latently infected cells by sorting for EGFP- cells after infection. These cells were cultured with antivirals and stimulated with anti-CD3/anti-CD28, mitogens, latency reversing agents (LRA) as well as co-cultured with monocytes and anti-CD3. Spontaneous EGFP expression was more frequent in post-activation than pre-activation latency. Stimulation of latently infected cells with monocytes/anti-CD3 resulted in an increase in EGFP expression compared to unstimulated controls using the pre-activation latency model but led to a reduction in EGFP expression in the post-activation latency model. The reduced EGFP expression was not associated with a reduction in viral DNA or the levels of T cell proliferation but depended on direct contact between monocytes and T cells. Monocytes added to the post-activation latency model during the establishment of latency reduced spontaneous viral expression suggesting that monocyte-T cell interactions at an early time point post infection can maintain HIV latency. This direct comparison of pre- and post- activation latency suggests that effective strategies needed to reverse latency will depend on how latency is established. One strategy being evaluated to eliminate latently infected cells that persist in HIV-infected individuals on antiretroviral therapy (ART) is to activate HIV expression or production with the goal of inducing virus mediated cytolysis or immune mediated clearance of the infected cells. The gold standard for activation of latent virus is T cell receptor stimulation with anti-CD3/anti-CD28. However, this stimulus only activates a small proportion of latently infected cells. We show clear differences in the response of latently infected cells to activating stimuli based on how latent infection is established, an observation that may potentially explain the persistence of non-induced intact proviruses in HIV-infected individuals on ART.