A human immunodeficiency virus (HIV) infection cure requires an understanding of the cellular and anatomical sites harboring virus that contribute to viral rebound upon treatment interruption. Despite antiretroviral therapy (ART), HIVassociated neurocognitive disorders (HAND) are reported in HIV-infected individuals on ART. Biomarkers for macrophage activation and neuronal damage in cerebrospinal fluid (CSF) of HIV-infected individuals demonstrate continued effects of HIV in brain and suggest that the central nervous system (CNS) may serve as a viral reservoir. Using a simian immunodeficiency virus (SIV)/macaque model for HIV encephalitis and AIDS, we evaluated whether infected cells persist in brain despite ART. Eight SIV-infected pig-tailed macaques were virally suppressed with ART, and plasma and CSF viremia levels were analyzed longitudinally. To assess whether virus persisted in brain macrophages (BrMΦ) in these macaques, we used a macrophage quantitative viral outgrowth assay (MΦ-QVOA), PCR, and in situ hybridization (ISH) to measure the frequency of infected cells and the levels of viral RNA and DNA in brain. Viral RNA in brain tissue of suppressed macaques was undetectable, although viral DNA was detected in all animals. The MΦ-QVOA demonstrated that the majority of suppressed animals contained latently infected BrMΦ. We also showed that virus produced in the MΦ-QVOAs was replication competent, suggesting that latently infected BrMΦ are capable of reestablishing productive infection upon treatment interruption. This report provides the first confirmation of the presence of replication-competent SIV in BrM_ of ART-suppressed macaques and suggests that the highly debated issue of viral latency in macrophages, at least in brain, has been addressed in SIV-infected macaques treated with ART. IMPORTANCE Resting CD4+ T cells are currently the only cells that fit the definition of a latent reservoir. However, recent evidence suggests that HIV/SIV-infected macrophages persist despite ART. Markers of macrophage activation and neuronal damage are observed in the CSF of HIV-infected individuals and of SIV-infected macaques on suppressive ART regimens, suggesting that the CNS has continued virus infection and latent infection. A controversy exists as to whether brain macrophages represent a latent source of replication-competent virus capable of reestablishing infection upon treatment interruption. In this study, we demonstrated the presence of the latent macrophage reservoir in brains of SIV-infected ART-treated macaques and analyzed the reservoir using our established outgrowth assay to quantitate macrophages harboring replication-competent SIV genomes. Our results support the idea of the existence of other latent reservoirs in addition to resting CD4+ T cells and underscore the importance of macrophages in developing strategies to eradicate HIV.
Bibliographical noteFunding Information:
This research has been facilitated by the infrastructure and resources provided by the Johns Hopkins University Center for AIDS Research, an NIH funded program (1P30AI094189).
and macrophages; therefore, this study may not be directly comparable to studies of other phenotypically restricted animal models or HIV-infected subjects. The detection of virus in the CSF of virally suppressed patients (7, 8) is a strong indication of the presence of HIV-infected cells in human brain. However, precise quantitation of viable, blood-free, infected brain cells from human patients remains difficult despite the availability of well-characterized HIV brain from the National NeuroAIDS Tissue Consortium (NNTC; supported by the National Institute of Mental Health [NIMH]). Procedural obstacles, such as those represented by time of sample acquisition and blood CD4+ T cell contamination due to lack of perfusion, complicate the interpretation of results. Our model and the BrMΦ QVOA provide an experimental protocol for quantitating and understanding mechanisms of viral latency in brain, as well as for examining the establishment and role of viral reservoirs in the CNS.
© 2017 Avalos et al.
Copyright 2017 Elsevier B.V., All rights reserved.
- Human immunodeficiency virus
- Simian immunodeficiency virus