Long-acting capsid inhibitor protects macaques from repeat SHIV challenges.

Because no currently available vaccine can prevent HIV infection, pre-exposure prophylaxis (PrEP) with antiretrovirals (ARVs) is an important tool for combating the HIV pandemic1,2. Long-acting ARVs promise to build on the success of current PrEP strategies, which must be taken daily, by reducing the frequency of administration3. GS-CA1 is a small-molecule HIV capsid inhibitor with picomolar antiviral potency against a broad array of HIV strains, including variants resistant to existing ARVs, and has shown long-acting therapeutic potential in a mouse model of HIV infection4. Here we show that a single subcutaneous administration of GS-CA1 provides long-term protection against repeated rectal simian-human immunodeficiency virus (SHIV) challenges in rhesus macaques. Whereas all control animals became infected after 15 weekly challenges, a single 300 mg kg-1 dose of GS-CA1 provided per-exposure infection risk reduction of 97% for 24 weeks. Pharmacokinetic analysis showed a correlation between GS-CA1 plasma concentration and protection from SHIV challenges. GS-CA1 levels greater than twice the rhesus plasma protein-adjusted 95% effective concentration conferred 100% protection in this model. These proof-of-concept data support the development of capsid inhibitors as a novel long-acting PrEP strategy in humans.

Flt3 agonist enhances immunogenicity of arenavirus vector-based simian immunodeficiency virus vaccine in macaques.

Arenaviral vaccine vectors encoding simian immunodeficiency virus (SIV) immunogens are capable of inducing efficacious humoral and cellular immune responses in nonhuman primates. Several studies have evaluated the use of immune modulators to further enhance vaccine-induced T-cell responses. The hematopoietic growth factor Flt3L drives the expansion of various bone marrow progenitor populations, and administration of Flt3L was shown to promote expansion of dendritic cell populations in spleen and blood, which are targets of arenaviral vectors. Therefore, we evaluated the potential of Flt3 signaling to enhance the immunogenicity of arenaviral vaccines encoding SIV immunogens (SIVSME543 Gag, Env, and Pol) in rhesus macaques, with a rhesus-specific engineered Flt3L-Fc fusion protein. In healthy animals, administration of Flt3L-Fc led to a 10- to 100-fold increase in type 1 dendritic cells 7 days after dosing, with no antidrug antibody (ADA) generation after repeated dosing. We observed that administration of Flt3L-Fc fusion protein 7 days before arenaviral vaccine increased the frequency and activation of innate immune cells and enhanced T-cell activation with no treatment-related adverse events. Flt3L-Fc administration induced early innate immune activation, leading to a significant enhancement in magnitude, breadth, and polyfunctionality of vaccine-induced T-cell responses. The Flt3L-Fc enhancement in vaccine immunogenicity was comparable to a combination with αCTLA-4 and supports the use of safe and effective variants of Flt3L to augment therapeutic vaccine-induced T-cell responses.IMPORTANCEInduction of a robust human immunodeficiency virus (HIV)-specific CD4+ and CD8+ T-cell response through therapeutic vaccination is considered essential for HIV cure. Arenaviral vaccine vectors encoding simian immunodeficiency virus (SIV) immunogens have demonstrated strong immunogenicity and efficacy in nonhuman primates. Here, we demonstrate that the immunogenicity of arenaviral vectors encoding SIV immunogens can be enhanced by administration of Flt3L-Fc fusion protein 7 days before vaccination. Flt3L-Fc-mediated increase in dendritic cells led to robust improvements in vaccine-induced T- and B-cell responses compared with vaccine alone, and Flt3L-Fc dosing was not associated with any treatment-related adverse events. Importantly, immune modulation by either Flt3L-Fc or αCTLA-4 led to comparable enhancement in vaccine response. These results indicate that the addition of Flt3L-Fc fusion protein before vaccine administration can significantly enhance vaccine immunogenicity. Thus, safe and effective Flt3L variants could be utilized as part of a combination therapy for HIV cure.

HIV envelope antibodies and TLR7 agonist partially prevent viral rebound in chronically SHIV-infected monkeys.

A key challenge for the development of a cure to HIV-1 infection is the persistent viral reservoir established during early infection. Previous studies using Toll-like receptor 7 (TLR7) agonists and broadly neutralizing antibodies (bNAbs) have shown delay or prevention of viral rebound following antiretroviral therapy (ART) discontinuation in simian-human immunodeficiency virus (SHIV)-infected rhesus macaques. In these prior studies, ART was initiated early during acute infection, which limited the size and diversity of the viral reservoir. Here we evaluated in SHIV-infected rhesus macaques that did not initiate ART until 1 year into chronic infection whether the TLR7 agonist vesatolimod in combination with the bNAb PGT121, formatted either as a human IgG1, an effector enhanced IgG1, or an anti-CD3 bispecific antibody, would delay or prevent viral rebound following ART discontinuation. We found that all 3 antibody formats in combination with vesatolimod were able to prevent viral rebound following ART discontinuation in a subset of animals. These data indicate that a TLR7 agonist combined with antibodies may be a promising strategy to achieve long-term ART-free HIV remission in humans.

Antibody and TLR7 agonist delay viral rebound in SHIV-infected monkeys.

The latent viral reservoir is the critical barrier for the development of a cure for HIV-1 infection. Previous studies have shown direct antiviral activity of potent HIV-1 Env-specific broadly neutralizing antibodies (bNAbs) administered when antiretroviral therapy (ART) was discontinued, but it remains unclear whether bNAbs can target the viral reservoir during ART. Here we show that administration of the V3 glycan-dependent bNAb PGT121 together with the Toll-like receptor 7 (TLR7) agonist vesatolimod (GS-9620) during ART delayed viral rebound following discontinuation of ART in simian-human immunodeficiency virus (SHIV)-SF162P3-infected rhesus monkeys in which ART was initiated during early acute infection. Moreover, in the subset of monkeys that were treated with both PGT121 and GS-9620 and that did not show viral rebound after discontinuation of ART, adoptive transfer studies and CD8-depletion studies also did not reveal virus. These data demonstrate the potential of bNAb administration together with innate immune stimulation as a possible strategy for targeting the viral reservoir.

Publisher Correction: Antibody and TLR7 agonist delay viral rebound in SHIV-infected monkeys.

In Fig. 4b of this Article, the x-axis labels 'PGT121' and 'GS-9620' were inadvertently swapped in both graphs. In Fig. 5a, b, 'TLR7' should have been 'GS-9620'. These figures have been corrected online.

TLR7 agonist, N6-LS and PGT121 delayed viral rebound in SHIV-infected macaques after antiretroviral therapy interruption.

Toll-like receptor 7 (TLR7) agonist and PGT121 (broadly neutralizing antibody, bnAb) administration previously delayed viral rebound and induced SHIV remission. We evaluated the impact of GS-986 (TLR7 agonist) and dual bnAbs on viral rebound after antiretroviral therapy (ART) interruption. Rhesus macaques inoculated with SHIV-1157ipd3N4 were initiated on daily suppressive ART from Day 14 post SHIV inoculation. Active arm animals (n = 8) received GS-986, N6-LS and PGT121 after plasma viral suppression, starting from week 14. GS-986 induced immune activation and SHIV-specific T cell responses but not viral expression in all the active arm animals. After ART interruption, median time to viral rebound was 6 weeks in the active and 3 weeks in the control arm (p = 0.024). In this animal model, the administration of the combination of GS-986 and dual bnAbs was associated with a modest delay in viral rebound. This strategy should be further evaluated to better understand the underlying mechanisms for the induction of virus-specific immune responses and delay in viral rebound.

Therapeutic vaccination of SIV-infected, ART-treated infant rhesus macaques using Ad48/MVA in combination with TLR-7 stimulation.

Globally, 1.8 million children are living with HIV-1. While antiretroviral therapy (ART) has improved disease outcomes, it does not eliminate the latent HIV-1 reservoir. Interventions to delay or prevent viral rebound in the absence of ART would be highly beneficial for HIV-1-infected children who now must remain on daily ART throughout their lifespan. Here, we evaluated therapeutic Ad48-SIV prime, MVA-SIV boost immunization in combination with the TLR-7 agonist GS-986 in rhesus macaque (RM) infants orally infected with SIVmac251 at 4 weeks of age and treated with a triple ART regimen beginning 4 weeks after infection. We hypothesized immunization would enhance SIV-specific T cell responses during ART-mediated suppression of viremia. Compared to controls, vaccinated infants had greater magnitude SIV-specific T cell responses (mean of 3475 vs 69 IFN-γ spot forming cells (SFC) per 106 PBMCs, respectively, P = 0.01) with enhanced breadth of epitope recognition and increased CD8+ and CD4+ T cell polyfunctionality (P = 0.004 and P = 0.005, respectively). Additionally, SIV-specific gp120 antibodies against challenge and vaccine virus strains were significantly elevated following MVA boost (P = 0.02 and P < 0.001, respectively). GS-986 led to expected immune stimulation demonstrated by activation of monocytes and T cells 24 hours post-dose. Despite the vaccine-induced immune responses, levels of SIV DNA in peripheral and lymph node CD4+ T cells were not significantly different from controls and a similar time to viral rebound and viral load set point were observed following ART interruption in both groups. We demonstrate infant RMs mount a robust immunological response to this immunization, but vaccination alone was not sufficient to impact viral reservoir size or modulate rebound dynamics following ART release. Our findings hold promise for therapeutic vaccination as a part of a combination cure approach in children and highlight the importance of a pediatric model to evaluate HIV-1 cure interventions in this unique setting of immune development.

Ad26/MVA therapeutic vaccination with TLR7 stimulation in SIV-infected rhesus monkeys.

The development of immunologic interventions that can target the viral reservoir in HIV-1-infected individuals is a major goal of HIV-1 research. However, little evidence exists that the viral reservoir can be sufficiently targeted to improve virologic control following discontinuation of antiretroviral therapy. Here we show that therapeutic vaccination with Ad26/MVA (recombinant adenovirus serotype 26 (Ad26) prime, modified vaccinia Ankara (MVA) boost) and stimulation of TLR7 (Toll-like receptor 7) improves virologic control and delays viral rebound following discontinuation of antiretroviral therapy in SIV-infected rhesus monkeys that began antiretroviral therapy during acute infection. Therapeutic vaccination with Ad26/MVA resulted in a marked increase in the magnitude and breadth of SIV-specific cellular immune responses in virologically suppressed, SIV-infected monkeys. TLR7 agonist administration led to innate immune stimulation and cellular immune activation. The combination of Ad26/MVA vaccination and TLR7 stimulation resulted in decreased levels of viral DNA in lymph nodes and peripheral blood, and improved virologic control and delayed viral rebound following discontinuation of antiretroviral therapy. The breadth of cellular immune responses correlated inversely with set point viral loads and correlated directly with time to viral rebound. These data demonstrate the potential of therapeutic vaccination combined with innate immune stimulation as a strategy aimed at a functional cure for HIV-1 infection.

Vesatolimod, a Toll-like Receptor 7 Agonist, Induces Immune Activation in Virally Suppressed Adults Living With Human Immunodeficiency Virus-1.

BACKGROUND: Treatment with vesatolimod, an investigational, oral, toll-like receptor 7 (TLR7) agonist, leads to sustained viral remission in some non-human primates when combined with anti-envelope antibodies or therapeutic vaccines. We report results of a Phase Ib study evaluating safety, pharmacokinetics, and pharmacodynamics of vesatolimod in adults living with human immunodeficiency virus (HIV)-1. METHODS: In this double-blind, multicenter, placebo-controlled trial, participants on antiretroviral therapy with screening plasma HIV-1 RNA levels <50 copies/mL were randomized (6:2) to receive 6-10 doses of vesatolimod (1-12 mg) or matching placebo orally every other week in sequential dose-escalation cohorts. The primary study objectives included establishing the safety and virologic effects of vesatolimod (change from baseline in plasma HIV-1 RNA). Pharmacokinetics and pharmacodynamic/immunologic activity were assessed as secondary objectives. RESULTS: A total of 48 individuals were randomly assigned to vesatolimod (n = 36) or placebo (n = 12). Vesatolimod was generally well tolerated, with no study drug-related serious adverse events or adverse events leading to study drug discontinuation. There were no statistically significant changes from baseline in plasma HIV-1 RNA in the vesatolimod groups, compared to placebo.Vesatolimod plasma exposures increased dose proportionally; consistent responses in cytokines, interferon-stimulated gene expression, and lymphocyte activation were observed with increasing dose levels above 4 mg. Peak elevations 24 hours after receipt of a 6 mg dose were >3.9-fold higher for interferon gamma-induced protein 10 (IP-10), interleukin-1 receptor antagonist (IL-1RA), interferon-inducible T-cell alpha chemoattractant (ITAC) when compared to baseline values. CONCLUSIONS: Vesatolimod was well tolerated at doses ranging from 1 to 12 mg. Immune stimulation was observed at doses above 4 mg, providing rationale for future combination trials in people living with HIV. CLINICAL TRIALS REGISTRATION: NCT02858401.

Rapid seeding of the viral reservoir prior to SIV viraemia in rhesus monkeys.

The viral reservoir represents a critical challenge for human immunodeficiency virus type 1 (HIV-1) eradication strategies. However, it remains unclear when and where the viral reservoir is seeded during acute infection and the extent to which it is susceptible to early antiretroviral therapy (ART). Here we show that the viral reservoir is seeded rapidly after mucosal simian immunodeficiency virus (SIV) infection of rhesus monkeys and before systemic viraemia. We initiated suppressive ART in groups of monkeys on days 3, 7, 10 and 14 after intrarectal SIVMAC251 infection. Treatment with ART on day 3 blocked the emergence of viral RNA and proviral DNA in peripheral blood and also substantially reduced levels of proviral DNA in lymph nodes and gastrointestinal mucosa as compared with treatment at later time points. In addition, treatment on day 3 abrogated the induction of SIV-specific humoral and cellular immune responses. Nevertheless, after discontinuation of ART following 24 weeks of fully suppressive therapy, virus rebounded in all animals, although the monkeys that were treated on day 3 exhibited a delayed viral rebound as compared with those treated on days 7, 10 and 14. The time to viral rebound correlated with total viraemia during acute infection and with proviral DNA at the time of ART discontinuation. These data demonstrate that the viral reservoir is seeded rapidly after intrarectal SIV infection of rhesus monkeys, during the 'eclipse' phase, and before detectable viraemia. This strikingly early seeding of the refractory viral reservoir raises important new challenges for HIV-1 eradication strategies.

PD-1 Blockade and TLR7 Activation Lack Therapeutic Benefit in Chronic Simian Immunodeficiency Virus-Infected Macaques on Antiretroviral Therapy.

Antiretroviral therapy (ART) limits human immunodeficiency virus 1 (HIV-1) replication but does not eliminate the long-lived reservoir established shortly after viral acquisition. A successful HIV cure intervention necessitates either elimination or generation of long-term immune control of the persistent viral reservoir. Immune modulating strategies in conjunction with ART hold promise for achieving cure by inducing viral antigen expression and augmenting infected cell killing. Programmed death-1 (PD-1) blockade is a potential means to both activate and eliminate the latent reservoir by restoring exhausted T cell function. We assessed the therapeutic efficacy of PD-1 blockade, Toll-like receptor 7 (TLR7) activation with the agonist vesatolimod, or a combination of the two agents in chronically simian immunodeficiency virus (SIV)-infected macaques suppressed with ART for more than 2 years. Despite achieving extended anti-PD-1 antibody plasma exposure and TLR7-dependent immune activation after multiple administrations, neither individual treatment nor the combination resulted in changes to viral rebound kinetics following ART interruption or reduction in the SIV reservoir size. Our data in the context of other reports demonstrating improved viral control upon PD-1 blockade suggest that its therapeutic utility may be restricted to specific experimental conditions or treatment times during viral pathogenesis.

A Subset of Latency-Reversing Agents Expose HIV-Infected Resting CD4+ T-Cells to Recognition by Cytotoxic T-Lymphocytes.

Resting CD4+ T-cells harboring inducible HIV proviruses are a critical reservoir in antiretroviral therapy (ART)-treated subjects. These cells express little to no viral protein, and thus neither die by viral cytopathic effects, nor are efficiently cleared by immune effectors. Elimination of this reservoir is theoretically possible by combining latency-reversing agents (LRAs) with immune effectors, such as CD8+ T-cells. However, the relative efficacy of different LRAs in sensitizing latently-infected cells for recognition by HIV-specific CD8+ T-cells has not been determined. To address this, we developed an assay that utilizes HIV-specific CD8+ T-cell clones as biosensors for HIV antigen expression. By testing multiple CD8+ T-cell clones against a primary cell model of HIV latency, we identified several single agents that primed latently-infected cells for CD8+ T-cell recognition, including IL-2, IL-15, two IL-15 superagonists (IL-15SA and ALT-803), prostratin, and the TLR-2 ligand Pam3CSK4. In contrast, we did not observe CD8+ T-cell recognition of target cells following treatment with histone deacetylase inhibitors or with hexamethylene bisacetamide (HMBA). In further experiments we demonstrate that a clinically achievable concentration of the IL-15 superagonist 'ALT-803', an agent presently in clinical trials for solid and hematological tumors, primes the natural ex vivo reservoir for CD8+ T-cell recognition. Thus, our results establish a novel experimental approach for comparative evaluation of LRAs, and highlight ALT-803 as an LRA with the potential to synergize with CD8+ T-cells in HIV eradication strategies.

Histone deacetylase inhibitor romidepsin induces HIV expression in CD4 T cells from patients on suppressive antiretroviral therapy at concentrations achieved by clinical dosing.

Persistent latent reservoir of replication-competent proviruses in memory CD4 T cells is a major obstacle to curing HIV infection. Pharmacological activation of HIV expression in latently infected cells is being explored as one of the strategies to deplete the latent HIV reservoir. In this study, we characterized the ability of romidepsin (RMD), a histone deacetylase inhibitor approved for the treatment of T-cell lymphomas, to activate the expression of latent HIV. In an in vitro T-cell model of HIV latency, RMD was the most potent inducer of HIV (EC50 = 4.5 nM) compared with vorinostat (VOR; EC50 = 3,950 nM) and other histone deacetylase (HDAC) inhibitors in clinical development including panobinostat (PNB; EC50 = 10 nM). The HIV induction potencies of RMD, VOR, and PNB paralleled their inhibitory activities against multiple human HDAC isoenzymes. In both resting and memory CD4 T cells isolated from HIV-infected patients on suppressive combination antiretroviral therapy (cART), a 4-hour exposure to 40 nM RMD induced a mean 6-fold increase in intracellular HIV RNA levels, whereas a 24-hour treatment with 1 µM VOR resulted in 2- to 3-fold increases. RMD-induced intracellular HIV RNA expression persisted for 48 hours and correlated with sustained inhibition of cell-associated HDAC activity. By comparison, the induction of HIV RNA by VOR and PNB was transient and diminished after 24 hours. RMD also increased levels of extracellular HIV RNA and virions from both memory and resting CD4 T-cell cultures. The activation of HIV expression was observed at RMD concentrations below the drug plasma levels achieved by doses used in patients treated for T-cell lymphomas. In conclusion, RMD induces HIV expression ex vivo at concentrations that can be achieved clinically, indicating that the drug may reactivate latent HIV in patients on suppressive cART.

Elevated Plasma Viral Loads in Romidepsin-Treated Simian Immunodeficiency Virus-Infected Rhesus Macaques on Suppressive Combination Antiretroviral Therapy.

Replication-competent human immunodeficiency virus (HIV) persists in infected people despite suppressive combination antiretroviral therapy (cART), and it represents a major obstacle to HIV functional cure or eradication. We have developed a model of cART-mediated viral suppression in simian human immunodeficiency virus (SIV) mac239-infected Indian rhesus macaques and evaluated the impact of the histone deacetylase inhibitor (HDACi) romidepsin (RMD) on viremia in vivo. Eight macaques virologically suppressed to clinically relevant levels (<30 viral RNA copies/ml of plasma), using a three-class five-drug cART regimen, received multiple intravenous infusions of either RMD (n = 5) or saline (n = 3) starting 31 to 54 weeks after cART initiation. In vivo RMD treatment resulted in significant transient increases in acetylated histone levels in CD4(+) T cells. RMD-treated animals demonstrated plasma viral load measurements for each 2-week treatment cycle that were significantly higher than those in saline control-treated animals during periods of treatment, suggestive of RMD-induced viral reactivation. However, plasma virus rebound was indistinguishable between RMD-treated and control-treated animals for a subset of animals released from cART. These findings suggest that HDACi drugs, such as RMD, can reactivate residual virus in the presence of suppressive antiviral therapy and may be a valuable component of a comprehensive HIV functional cure/eradication strategy.

Study of marine natural products including resorcyclic acid lactones from Humicola fuscoatra that reactivate latent HIV-1 expression in an in vitro model of central memory CD4+ T cells.

An extract of Humicola fuscoatra (UCSC strain no. 108111A) was shown to reactivate latent HIV-1 expression in an in vitro model of central memory CD4+ T cells. We report the bioassay-guided isolation and structure determination of several resorcyclic acid lactones, including four known compounds, radicicol (1, aka. monorden) and pochonins B (2), C (3), and N (4), and three new analogues, radicicols B-D (5-7). Compounds 1-3 and 5 showed moderate activities in the memory T cell model of HIV-1 latency. Radicicol (1) displayed lower potency in reactivating latent HIV-1 (EC50 = 9.1 µM) relative to the HDAC inhibitors apicidin (EC50 = 0.3 µM), romidepsin (EC50 = 0.003 µM), and SAHA (EC50 = 0.6 µM); however, it achieved equivalent maximum efficacy relative to the positive control compounds (98% of SAHA and romidepsin).

HIV-1 envelope diversity and sensitivity to broadly neutralizing antibodies across stages of acute HIV-1 infection.

We studied the relationship between viral diversity and susceptibility to broadly neutralizing antibodies (bNAbs) in longitudinal plasma and peripheral blood mononuclear cells from 89 people with HIV who initiated antiretroviral therapy (ART) during acute and early HIV-1 infection (AEHI). HIV-1 diversity and predicted bNAb susceptibility were comparable across AEHI. Diversity evolution was not observed during ART, suggesting (pro)viruses at initiation or during treatment may identify individuals with susceptible virus for bNAb interventional trials.

Oral administration of obeldesivir protects nonhuman primates against Sudan ebolavirus.

Obeldesivir (ODV, GS-5245) is an orally administered prodrug of the parent nucleoside of remdesivir (RDV) and is presently in phase 3 trials for COVID-19 treatment. In this work, we show that ODV and its circulating parent nucleoside metabolite, GS-441524, have similar in vitro antiviral activity against filoviruses, including Marburg virus, Ebola virus, and Sudan virus (SUDV). We also report that once-daily oral ODV treatment of cynomolgus monkeys for 10 days beginning 24 hours after SUDV exposure confers 100% protection against lethal infection. Transcriptomics data show that ODV treatment delayed the onset of inflammation and correlated with antigen presentation and lymphocyte activation. Our results offer promise for the further development of ODV to control outbreaks of filovirus disease more rapidly.

New class of HIV-1 integrase (IN) inhibitors with a dual mode of action.

tert-Butoxy-(4-phenyl-quinolin-3-yl)-acetic acids (tBPQA) are a new class of HIV-1 integrase (IN) inhibitors that are structurally distinct from IN strand transfer inhibitors but analogous to LEDGINs. LEDGINs are a class of potent antiviral compounds that interacts with the lens epithelium-derived growth factor (LEDGF) binding pocket on IN and were identified through competition binding against LEDGF. LEDGF tethers IN to the host chromatin and enables targeted integration of viral DNA. The prevailing understanding of the antiviral mechanism of LEDGINs is that they inhibit LEDGF binding to IN, which prevents targeted integration of HIV-1. We showed that in addition to the properties already known for LEDGINs, the binding of tBPQAs to the IN dimer interface inhibits IN enzymatic activity in a LEDGF-independent manner. Using the analysis of two long terminal repeat junctions in HIV-infected cells, we showed that the inhibition by tBPQAs occurs at or prior to the viral DNA 3'-processing step. Biochemical studies revealed that this inhibition operates by compound-induced conformational changes in the IN dimer that prevent proper assembly of IN onto viral DNA. For the first time, tBPQAs were demonstrated to be allosteric inhibitors of HIV-1 IN displaying a dual mode of action: inhibition of IN-viral DNA assembly and inhibition of IN-LEDGF interaction.

Immunogenic arenavirus vector SIV vaccine reduces setpoint viral load in SIV-challenged rhesus monkeys.

HIV affects more than 38 million people worldwide. Although HIV can be effectively treated by lifelong combination antiretroviral therapy, only a handful of patients have been cured. Therapeutic vaccines that induce robust de novo immune responses targeting HIV proteins and latent reservoirs will likely be integral for functional HIV cure. Our study shows that immunization of naïve rhesus macaques with arenavirus-derived vaccine vectors encoding simian immunodeficiency virus (SIVSME543 Gag, Env, and Pol) immunogens is safe, immunogenic, and efficacious. Immunization induced robust SIV-specific CD8+ and CD4+ T-cell responses with expanded cellular breadth, polyfunctionality, and Env-binding antibodies with antibody-dependent cellular cytotoxicity. Vaccinated animals had significant reductions in median SIV viral load (1.45-log10 copies/mL) after SIVMAC251 challenge compared with placebo. Peak viral control correlated with the breadth of Gag-specific T cells and tier 1 neutralizing antibodies. These results support clinical investigation of arenavirus-based vectors as a central component of therapeutic vaccination for HIV cure.

Antiretroviral therapy reveals triphasic decay of intact SIV genomes and persistence of ancestral variants.

The decay kinetics of HIV-1-infected cells are critical to understand virus persistence. We evaluated the frequency of simian immunodeficiency virus (SIV)-infected cells for 4 years of antiretroviral therapy (ART). The intact proviral DNA assay (IPDA) and an assay for hypermutated proviruses revealed short- and long-term infected cell dynamics in macaques starting ART ∼1 year after infection. Intact SIV genomes in circulating CD4+T cells showed triphasic decay with an initial phase slower than the decay of the plasma virus, a second phase faster than the second phase decay of intact HIV-1, and a stable third phase reached after 1.6-2.9 years. Hypermutated proviruses showed bi- or mono-phasic decay, reflecting different selective pressures. Viruses replicating at ART initiation had mutations conferring antibody escape. With time on ART, viruses with fewer mutations became more prominent, reflecting decay of variants replicating at ART initiation. Collectively, these findings confirm ART efficacy and indicate that cells enter the reservoir throughout untreated infection.