Diverse effects of interferon alpha on the establishment and reversal of HIV latency.

HIV latency is the major barrier to a cure for people living with HIV (PLWH) on antiretroviral therapy (ART) because the virus persists in long-lived non-proliferating and proliferating latently infected CD4+ T cells. Latently infected CD4+ T cells do not express viral proteins and are therefore not visible to immune mediated clearance. Therefore, identifying interventions that can reverse latency and also enhance immune mediated clearance is of high interest. Interferons (IFNs) have multiple immune enhancing effects and can inhibit HIV replication in activated CD4+ T cells. However, the effects of IFNs on the establishment and reversal of HIV latency is not understood. Using an in vitro model of latency, we demonstrated that plasmacytoid dendritic cells (pDC) inhibit the establishment of HIV latency through secretion of type I IFNα, IFNß and IFNω but not IFNε or type III IFNλ1 and IFNλ3. However, once latency was established, IFNα but no other IFNs were able to efficiently reverse latency in both an in vitro model of latency and CD4+ T cells collected from PLWH on suppressive ART. Binding of IFNα to its receptor expressed on primary CD4+ T cells did not induce activation of the canonical or non-canonical NFκB pathway but did induce phosphorylation of STAT1, 3 and 5 proteins. STAT5 has been previously demonstrated to bind to the HIV long terminal repeat and activate HIV transcription. We demonstrate diverse effects of interferons on HIV latency with type I IFNα; inhibiting the establishment of latency but also reversing HIV latency once latency is established.

Combination Immune Checkpoint Blockade to Reverse HIV Latency.

In people living with HIV on antiretroviral therapy, HIV latency is the major barrier to a cure. HIV persists preferentially in CD4+ T cells expressing multiple immune checkpoint (IC) molecules, including programmed death (PD)-1, T cell Ig and mucin domain-containing protein 3 (TIM-3), lymphocyte associated gene 3 (LAG-3), and T cell immunoreceptor with Ig and ITIM domains (TIGIT). We aimed to determine whether these and other IC molecules have a functional role in maintaining HIV latency and whether blocking IC molecules with Abs reverses HIV latency. Using an in vitro model that establishes latency in both nonproliferating and proliferating human CD4+ T cells, we show that proliferating cells express multiple IC molecules at high levels. Latent infection was enriched in proliferating cells expressing PD-1. In contrast, nonproliferating cells expressed IC molecules at significantly lower levels, but latent infection was enriched in cells expressing PD-1, TIM-3, CTL-associated protein 4 (CTLA-4), or B and T lymphocyte attenuator (BTLA). In the presence of an additional T cell-activating stimulus, staphylococcal enterotoxin B, Abs to CTLA-4 and PD-1 reversed HIV latency in proliferating and nonproliferating CD4+ T cells, respectively. In the absence of staphylococcal enterotoxin B, only the combination of Abs to PD-1, CTLA-4, TIM-3, and TIGIT reversed latency. The potency of latency reversal was significantly higher following combination IC blockade compared with other latency-reversing agents, including vorinostat and bryostatin. Combination IC blockade should be further explored as a strategy to reverse HIV latency.

Myeloid Dendritic Cells Induce HIV Latency in Proliferating CD4+ T Cells.

HIV latency occurs predominantly in long-lived resting CD4+ T cells; however, latent infection also occurs in T cell subsets, including proliferating CD4+ T cells. We compared the establishment and maintenance of latent infection in nonproliferating and proliferating human CD4+ T cells cocultured with syngeneic myeloid dendritic cells (mDC). Resting CD4+ T cells were labeled with the proliferation dye eFluor 670 and cultured alone or with mDC, plasmacytoid dendritic cells, or monocytes in the presence of staphylococcal enterotoxin B (SEB). Cells were cultured for 24 h and infected with CCR5-tropic enhanced GFP (EGFP) reporter HIV. Five days postinfection, nonproductively infected EGFP- CD4+ T cells that were either nonproliferating (eFluor 670hi) or proliferating (eFluor 670lo) were sorted and cultured for an additional 7 d (day 12) with IL-7 and antiretrovirals. At day 5 postinfection, sorted, nonproductively infected T cells were stimulated with anti-CD3/CD28, and induced expression of EGFP was measured to determine the frequency of latent infection. Integrated HIV in these cells was confirmed using quantitative PCR. By these criteria, latent infection was detected at day 5 and 12 in proliferating T cells cocultured with mDC and monocytes but not plasmacytoid dendritic cells, where CD4+ T cells at day 12 were poor. At day 5 postinfection, nonproliferating T cells expressing SEB-specific TCR Vß-17 were enriched in latent infection compared with non-SEB-specific TCR Vß-8.1. Together, these data show that both nonproliferating and proliferating CD4+ T cells can harbor latent infection during SEB-stimulated T cell proliferation and that the establishment of HIV latency in nonproliferating T cells is linked to expression of specific TCR that respond to SEB.

Mechanisms of CD8+ T cell-mediated suppression of HIV/SIV replication.

In this article, we summarize the role of CD8+ T cells during natural and antiretroviral therapy (ART)-treated HIV and SIV infections, discuss the mechanisms responsible for their suppressive activity, and review the rationale for CD8+ T cell-based HIV cure strategies. Evidence suggests that CD8+ T cells are involved in the control of virus replication during HIV and SIV infections. During early HIV infection, the cytolytic activity of CD8+ T cells is responsible for control of viremia. However, it has been proposed that CD8+ T cells also use non-cytolytic mechanisms to control SIV infection. More recently, CD8+ T cells were shown to be required to fully suppress virus production in ART-treated SIV-infected macaques, suggesting that CD8+ T cells are involved in the control of virus transcription in latently infected cells that persist under ART. A better understanding of the complex antiviral activities of CD8+ T cells during HIV/SIV infection will pave the way for immune interventions aimed at harnessing these functions to target the HIV reservoir.

Antibody-Mediated CD4 Depletion Induces Homeostatic CD4+ T Cell Proliferation without Detectable Virus Reactivation in Antiretroviral Therapy-Treated Simian Immunodeficiency Virus-Infected Macaques.

A major barrier to human immunodeficiency virus (HIV) eradication is the long-term persistence of latently infected CD4+ T cells harboring integrated replication-competent virus. It has been proposed that the homeostatic proliferation of these cells drives long-term reservoir persistence in the absence of virus reactivation, thus avoiding cell death due to either virus-mediated cytopathicity or immune effector mechanisms. Here, we conducted an experimental depletion of CD4+ T cells in eight antiretroviral therapy (ART)-treated, simian immunodeficiency virus (SIV)-infected rhesus macaques (RMs) to determine whether the homeostatically driven CD4+ T-cell proliferation that follows CD4+ T-cell depletion results in reactivation of latent virus and/or expansion of the virus reservoir. After administration of the CD4R1 antibody, we observed a CD4+ T cell depletion of 65 to 89% in peripheral blood and 20 to 50% in lymph nodes, followed by a significant increase in CD4+ T cell proliferation during CD4+ T cell reconstitution. However, this CD4+ T cell proliferation was not associated with detectable increases in viremia, indicating that the homeostatic activation of CD4+ T cells is not sufficient to induce virus reactivation from latently infected cells. Interestingly, the homeostatic reconstitution of the CD4+ T cell pool was not associated with significant changes in the number of circulating cells harboring SIV DNA compared to results for the first postdepletion time point. This study indicates that, in ART-treated SIV-infected RMs, the homeostasis-driven CD4+ T-cell proliferation that follows experimental CD4+ T-cell depletion occurs in the absence of detectable reactivation of latent virus and does not increase the size of the virus reservoir as measured in circulating cells.IMPORTANCE Despite successful suppression of HIV replication with antiretroviral therapy, current treatments are unable to eradicate the latent virus reservoir, and treatment interruption almost invariably results in the reactivation of HIV even after decades of virus suppression. Homeostatic proliferation of latently infected cells is one mechanism that could maintain the latent reservoir. To understand the impact of homeostatic mechanisms on virus reactivation and reservoir size, we experimentally depleted CD4+ T cells in ART-treated SIV-infected rhesus macaques and monitored their homeostatic rebound. We find that depletion-induced proliferation of CD4+ T cells is insufficient to reactivate the viral reservoir in vivo Furthermore, the proportion of SIV DNA+ CD4+ T cells remains unchanged during reconstitution, suggesting that the reservoir is resistant to this mechanism of expansion at least in this experimental system. Understanding how T cell homeostasis impacts latent reservoir longevity could lead to the development of new treatment paradigms aimed at curing HIV infection.

The role of antigen presenting cells in the induction of HIV-1 latency in resting CD4(+) T-cells.

BACKGROUND: Combination antiretroviral therapy (cART) is able to control HIV-1 viral replication, however long-lived latent infection in resting memory CD4(+) T-cells persist. The mechanisms for establishment and maintenance of latent infection in resting memory CD4(+) T-cells remain unclear. Previously we have shown that HIV-1 infection of resting CD4(+) T-cells co-cultured with CD11c(+) myeloid dendritic cells (mDC) produced a population of non-proliferating T-cells with latent infection. Here we asked whether different antigen presenting cells (APC), including subpopulations of DC and monocytes, were able to induce post-integration latent infection in resting CD4(+) T-cells, and examined potential cell interactions that may be involved using RNA-seq. RESULTS: mDC (CD1c(+)), SLAN(+) DC and CD14(+) monocytes were most efficient in stimulating proliferation of CD4(+) T-cells during syngeneic culture and in generating post-integration latent infection in non-proliferating CD4(+) T-cells following HIV-1 infection of APC-T cell co-cultures. In comparison, plasmacytoid DC (pDC) and B-cells did not induce latent infection in APC-T-cell co-cultures. We compared the RNA expression profiles of APC subpopulations that could and could not induce latency in non-proliferating CD4(+) T-cells. Gene expression analysis, comparing the CD1c(+) mDC, SLAN(+) DC and CD14(+) monocyte subpopulations to pDC identified 53 upregulated genes that encode proteins expressed on the plasma membrane that could signal to CD4(+) T-cells via cell-cell interactions (32 genes), immune checkpoints (IC) (5 genes), T-cell activation (9 genes), regulation of apoptosis (5 genes), antigen presentation (1 gene) and through unknown ligands (1 gene). CONCLUSIONS: APC subpopulations from the myeloid lineage, specifically mDC subpopulations and CD14(+) monocytes, were able to efficiently induce post-integration HIV-1 latency in non-proliferating CD4(+) T-cells in vitro. Inhibition of key pathways involved in mDC-T-cell interactions and HIV-1 latency may provide novel targets to eliminate HIV-1 latency.