Simian Immunodeficiency Virus SIVsab Infection of Rhesus Macaques as a Model of Complete Immunological Suppression with Persistent Reservoirs of Replication-Competent Virus: Implications for Cure Research

Abstract

Simian immunodeficiency virus SIVsab infection is completely controlled in rhesus macaques (RMs) through functional immune responses. We report that in SIVsab-infected RMs, (i) viral replication is controlled to <0 to 3 copies/ml, (ii) about onethird of the virus strains in reservoirs are replication incompetent, and (iii) rebounding virus after CD8؉ cell depletion is replication competent and genetically similar to the original virus stock, suggesting early reservoir seeding. This model permits assessment of strategies aimed at depleting the reservoir without multidrug antiretroviral therapy. The report of one patient that was cured of human immunodeficiency virus (HIV) infection (1) renewed enthusiasm for cure research aimed at understanding the mechanisms of HIV persistence and developing therapeutic strategies to reduce/eliminate viral reservoirs (2). However, virus rebound in the Mississippi baby (3) and the Boston patients (4) pointed to the difficulty of achieving a cure/functional cure of HIV infection and the need to develop new strategies to reach this goal. Multiple limitations to the cure have been identified, including (i) rapid establishment of latently infected cells, (ii) residual viral replication in patients receiving combination antiretroviral therapy (cART), which prevents proper reservoir characterization, and (iii) the existence of anatomic reservoirs (privileged sites of latency insufficiently penetrated by drugs) (5, 6). Due to these limitations, it is generally agreed that a more feasible alternative to an HIV infection cure (i.e., complete eradication of HIV and HIV-infected cells from the body) may be a functional cure (i.e., control of HIV infection without complete HIV eradication: undetectable viremia without ART, no disease progression, no CD4 ϩ T-cell loss, and lack of HIV transmission) (6). This concept is supported by the observation that functional cure has been achieved in a fraction of patients that received long-term ART initiated during acute HIV infection (7).Aside from the general barriers to a cure, there are specific limitations to cure research: (i) ethical problems (therapy cannot be stopped in patients without the risks of virus rebound and the development of viral resistance and increased virus transmission), (ii) technical problems (there is no acceptable biomarker for latently infected cells), and (iii) limited availability of invasive samples from the multiple potential reservoir sites (8). These limitations make it imperative that cure research be performed in analogous and tractable animal models. Currently available models need to be improved for such studies. For example, SIVmac infection of rhesus macaques (RMs) (the most widely used animal model for AIDS research) is more difficult to control with ART than HIV-1 infection in humans, requiring complex combination therapies (9, 10). Furthermore, infection with molecular clones (e.g., simian-human immunodeficiency viruses carrying the reverse transcriptase gene [RT-SHIVs]) does not permit tracking of viral spr...

Cutting Edge: T Regulatory Cell Depletion Reactivates Latent Simian Immunodeficiency Virus (SIV) in Controller Macaques While Boosting SIV-Specific T Lymphocytes

“…SIVsab infection follow-up was performed as described (17, 18). After one and a half year postinfection, when the animals had completely controlled the virus, they were treated twice with Ontak (Ligand Pharmaceutical, La Jolla CA) intravenously (15 μg/kg) for 5 consecutive days at 21 days interval, as reported (20).…”

“…Blood samples were collected prior to Ontak administration and then at 1, 3, 7, 10, 14, 17, 21 days posttreatment (dpt) initiation. Plasma and mononuclear cells were isolated as described (17, 18) for viral load (VL) quantification and flow cytometry.…”

“…Plasma VLs were quantified with an ultrasensitive qPCR assay, as described (17). This assay has a sensitivity of 1 vRNA copies/ml; however, due to frequent sampling which limited the volumes of plasma, assay sensitivity was 5 copies/ml.…”

“…Whole blood was stained for flow cytometry with multiple combinations of the following mAbs: CD3-FITC (SP34) ; CD20-PE (3G8); CD8-PerCP (SK1); CD4-APC (L200); CD25-FITC (2A3); HLA-DR-PerCP (l243); Ki-67-FITC (B56) (all from BD Biosciences) and FoxP3-APC (PCH101) (EBiosciences), as described (17, 18). Data were acquired with a FACSCalibur flow cytometer (BD Immunocytometry Systems) and analyzed with CellQuest software (BD Biosciences).…”

“…Here, we assessed Treg contribution to shaping the SIV reservoir by depleting Tregs in vivo in two spontaneous-controller RMs infected with SIVsab (17, 18). RM treatment with Ontak (recombinant IL-2 coupled with diphtheria toxin) resulted in significant Treg depletion, induced T cell activation and virus reactivation.…”