Myeloid and CD4 T Cells Comprise the Latent Reservoir in Antiretroviral Therapy-Suppressed SIVmac251-Infected Macaques

Abstract

Human immunodeficiency virus (HIV) eradication or long-term suppression in the absence of antiretroviral therapy (ART) requires an understanding of all viral reservoirs that could contribute to viral rebound after ART interruption. CD4 T cells (CD4s) are recognized as the predominant reservoir in HIV type 1 (HIV-1)-infected individuals. However, macrophages are also infected by HIV-1 and simian immunodeficiency virus (SIV) during acute infection and may persist throughout ART, contributing to the size of the latent reservoir. We sought to determine whether tissue macrophages contribute to the SIVmac251 reservoir in suppressed macaques. Using cell-specific quantitative viral outgrowth assays (CD4-QVOA and MΦ-QVOA), we measured functional latent reservoirs in CD4s and macrophages in ART-suppressed SIVmac251-infected macaques. Spleen, lung, and brain in all suppressed animals contained latently infected macrophages, undetectable or low-level SIV RNA, and detectable SIV DNA. Silent viral genomes with potential for reactivation and viral spread were also identified in blood monocytes, although these cells might not be considered reservoirs due to their short life span. Additionally, virus produced in the MΦ-QVOA was capable of infecting healthy activated CD4s. Our results strongly suggest that functional latent reservoirs in CD4s and macrophages can contribute to viral rebound and reestablishment of productive infection after ART interruption. These findings should be considered in the design and implementation of future HIV cure strategies. IMPORTANCE This study provides further evidence that the latent reservoir is comprised of both CD4+ T cells and myeloid cells. The data presented here suggest that CD4+ T cells and macrophages found throughout tissues in the body can contain replication-competent SIV and contribute to rebound of the virus after treatment interruption. Additionally, we have shown that monocytes in blood contain latent virus and, though not considered a reservoir themselves due to their short life span, could contribute to the size of the latent reservoir upon entering the tissue and differentiating into long-lived macrophages. These new insights into the size and location of the SIV reservoir using a model that is heavily studied in the HIV field could have great implications for HIV-infected individuals and should be taken into consideration with the development of future HIV cure strategies.

HIV-1 Persistence and Chronic Induction of Innate Immune Responses in Macrophages

“…Additional support for macrophages as tissue reservoirs comes from studies of experimental SIV-infections of NHPs. For instance, macrophages isolated from various tissues of SIV-infected animals harbor replication competent viruses, as determined by the quantitative viral outgrowth assay (QVOA) [22,23]. Utilizing TCR beta as a marker of T cell contamination in macrophage preparations, these authors concluded that contribution of contaminated or phagocytosed infected T cells in the QVOA is negligible [22,23].…”

“…For instance, macrophages isolated from various tissues of SIV-infected animals harbor replication competent viruses, as determined by the quantitative viral outgrowth assay (QVOA) [22,23]. Utilizing TCR beta as a marker of T cell contamination in macrophage preparations, these authors concluded that contribution of contaminated or phagocytosed infected T cells in the QVOA is negligible [22,23]. Macrophage tropic HIV-1 that can infect cells with low CD4 expression has been isolated from cerebrospinal fluid (CSF) of a patient on suppressive cART, suggesting production of HIV particles from replicating CNS reservoirs, that are most likely macrophages/microglia [24].…”

“…Thus, it remains formally possible that HIV-infected microglia might persist for the lifespan of the infected individual. In fact, recent QVOA studies optimized for myeloid cells demonstrated the presence of replication competent infectious viruses in microglia from SIV-infected cART-suppressed macaques [22,23,37]. Although macrophages have been postulated to harbor HIV-1 as transcriptionally silent provirus or unintegrated DNA (see the review in [38]), frequency and mode of HIV-1 latency in tissue-resident macrophages in patients on therapy are largely unknown.…”

Targeted immuno-antiretroviral HIV therapeutic approach to provide dual protection and boosts cellular immunity: A proof-of-concept study

“…To achieve this we formulated CCR5 targeting ARV loaded nanoformulation with the potential to block HIV entrance and promote cellular immunity against HIV infection, specifically in memory CD4+ T-cells as they commit themselves to provide antiviral immunity as latent HIV-1 reservoir (34). Alongside memory CD4+ T-cells, the myeloid lineage, such as monocytes/macrophages, are believed to be other potential HIV-1 sanctuaries (35, 36). Our hypothesis is the novel CCR5 targeted ARV nanoformulation approach could combine different strategies to ensure dual protection against HIV to the CCR5+ cell types.…”

μ-Lat: A Mouse Model to Evaluate Human Immunodeficiency Virus Eradication Strategies

“…This general approach is highly versatile and should allow for a broad range of infected cell types to be examined in vivo. For example, HIV latency in the myeloid compartment is likely critical to viral persistence (35,(66)(67)(68)(69), and multiple reports suggest this compartment may respond quite differently to curative approaches, as compared to lymphoid reservoirs (70,71). It may be fruitful to inject the U1 HIV chronically-infected promonocytic cell line (72) into NSG mice to examine LRA responses in myeloid cells.…”