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The capacity of HIV-1 to replicate during optimal antiretroviral therapy (ART) is challenging to assess directly. To gain greater sensitivity to detect evolution on ART, we used a nonhuman primate (NHP) model providing precise control over the level of pre-ART evolution and more comprehensive analyses than are possible with clinical samples. We infected 21 rhesus macaques (RMs) with the barcoded virus SIVmac239M and initiated ART early to minimize baseline genetic diversity. RMs were treated for 285–1200 days. We used several tests of molecular evolution to compare 1352 near-full-length (nFL) SIV DNA single genome sequences from PBMCs, lymph nodes, and spleen obtained near the time of ART initiation and those present after long-term ART, none of which showed significant changes to the SIV DNA population during ART in any animal. To investigate the possibility of ongoing replication in unsampled putative tissue sanctuaries during ART, we discontinued treatment in four animals and confirmed that none of the 336 nFL SIV RNA sequences obtained from rebound plasma viremia showed evidence of evolution. The rigorous nature of our analyses reinforced the emerging consensus of a lack of appreciable ongoing replication on effective ART and validates the relevance of this NHP model for cure studies. Precluding continued HIV-1 replication during antiretroviral therapy (ART) is critical for the design of curative strategies. Using a SIV rhesus macaque model to increase sensitivity of detection, the authors here demonstrate a lack of ongoing replication on ART. [ABSTRACT FROM AUTHOR]

Human immunodeficiency virus 1 (HIV-1) infection is initiated by binding of the viral envelope glycoprotein (Env) to the cell-surface receptor CD41–4. Although high-resolution structures of Env in a complex with the soluble domains of CD4 have been determined, the binding process is less understood in native membranes5–13. Here we used cryo-electron tomography to monitor Env–CD4 interactions at the membrane–membrane interfaces formed between HIV-1 and CD4-presenting virus-like particles. Env–CD4 complexes organized into clusters and rings, bringing the opposing membranes closer together. Env–CD4 clustering was dependent on capsid maturation. Subtomogram averaging and classification revealed that Env bound to one, two and finally three CD4 molecules, after which Env adopted an open state. Our data indicate that asymmetric HIV-1 Env trimers bound to one and two CD4 molecules are detectable intermediates during virus binding to host cell membranes, which probably has consequences for antibody-mediated immune responses and vaccine immunogen design.HIV-1 Env trimers bound to one, two and three CD4 molecules are observed at membrane–membrane interfaces between HIV-1 and CD4-decorated virus-like particles. [ABSTRACT FROM AUTHOR]

SIVmac239 infection of macaques is a favored model of human HIV infection. However, the SIVmac239 envelope (Env) trimer structure, glycan occupancy, and the targets and ability of neutralizing antibodies (nAbs) to protect against SIVmac239 remain unknown. Here, we report the isolation of SIVmac239 nAbs that recognize a glycan hole and the V1/V4 loop. A high-resolution structure of a SIVmac239 Env trimer-nAb complex shows many similarities to HIV and SIVcpz Envs, but with distinct V4 features and an extended V1 loop. Moreover, SIVmac239 Env has a higher glycan shield density than HIV Env that may contribute to poor or delayed nAb responses in SIVmac239-infected macaques. Passive transfer of a nAb protects macaques from repeated intravenous SIVmac239 challenge at serum titers comparable to those described for protection of humans against HIV infection. Our results provide structural insights for vaccine design and shed light on antibody-mediated protection in the SIV model. SIVmac239 infection of macaques is a favored model of human HIV infection, but antibody-mediated protection for SIVmac239 is insufficiently understood. Here, Zhao and Berndsen et al isolated nAbs and confirmed protection against SIVmac239 infection in passive transfer studies in macaques. The nAb was used to provide the first high-resolution structure of a rhesus SIV trimer by CryoEM. Analysis of the glycosylation pattern of this SIV trimer suggests a denser glycan shield on Env for rhesus SIV compared to chimpanzee SIV or HIV-1, which partially explains the poor nAb response of rhesus macaques to SIVmac239 infection. [ABSTRACT FROM AUTHOR]

Antiretroviral therapy (ART) is not curative due to the persistence of a reservoir of HIV-infected cells, particularly in tissues such as lymph nodes, with the potential to cause viral rebound after treatment cessation. In this study, fingolimod (FTY720), a lysophospholipid sphingosine-1-phosphate receptor modulator is administered to SIV-infected rhesus macaques at initiation of ART to block the egress from lymphoid tissues of natural killer and T-cells, thereby promoting proximity between cytolytic cells and infected CD4+ T-cells. When compared with the ART-only controls, FTY720 treatment during the initial weeks of ART induces a profound lymphopenia and increases frequencies of CD8+ T-cells expressing perforin in lymph nodes, but not their killing capacity; FTY720 also increases frequencies of cytolytic NK cells in lymph nodes. This increase of cytolytic cells, however, does not limit measures of viral persistence during ART, including intact proviral genomes. After ART interruption, a subset of animals that initially receives FTY720 displays a modest delay in viral rebound, with reduced plasma viremia and frequencies of infected T follicular helper cells. Further research is needed to optimize the potential utility of FTY720 when coupled with strategies that boost the antiviral function of T-cells in lymphoid tissues. Although antiretroviral therapy (ART) is able to successfully suppress plasma viremia in most people living with HIV, ART withdrawal typically results in viral replication and rebound. Authors investigate the effect, in terms of delay in viral replication, and immune cell dynamics in lymphoid tissue, of fingolimod (FTY720) administration at the time of ART initiation in SIV-infected rhesus macaques. [ABSTRACT FROM AUTHOR]

Unlike HIV infection, which progresses to AIDS absent suppressive anti-retroviral therapy, nonpathogenic infections in natural hosts, such African green monkeys, are characterized by a lack of gut microbial translocation and robust secondary lymphoid natural killer cell responses resulting in an absence of chronic inflammation and limited SIV dissemination in lymph node B-cell follicles. Here we report, using the pathogenic model of antiretroviral therapy-treated, SIV-infected rhesus macaques that sequential interleukin-21 and interferon alpha therapy generate terminally differentiated blood natural killer cells (NKG2a/clowCD16+) with potent human leukocyte antigen-E-restricted activity in response to SIV envelope peptides. This is in contrast to control macaques, where less differentiated, interferon gamma-producing natural killer cells predominate. The frequency and activity of terminally differentiated NKG2a/clowCD16+ natural killer cells correlates with a reduction of replication-competent SIV in lymph node during antiretroviral therapy and time to viral rebound following analytical treatment interruption. These data demonstrate that African green monkey-like natural killer cell differentiation profiles can be rescued in rhesus macaques to promote viral clearance in tissues. Infection of African green monkeys with SIV is associated with reduced pathogenicity. Here the authors explore the requirement of differentiated NK cell populations in a pathogenic Rhesus macaque model of SIV infection and show administration of IL-21 and IFNα rescues terminally differentiated NK cells, similarly to what found in African green monkeys, and limits the SIV reservoir in antiretroviral therapy treated macaques. [ABSTRACT FROM AUTHOR]

Human immunodeficiency virus (HIV) persists indefinitely in individuals with HIV who receive antiretroviral therapy (ART) owing to a reservoir of latently infected cells that contain replication-competent virus1–4. Here, to better understand the mechanisms responsible for latency persistence and reversal, we used the interleukin-15 superagonist N-803 in conjunction with the depletion of CD8+ lymphocytes in ART-treated macaques infected with simian immunodeficiency virus (SIV). Although N-803 alone did not reactivate virus production, its administration after the depletion of CD8+ lymphocytes in conjunction with ART treatment induced robust and persistent reactivation of the virus in vivo. We found viraemia of more than 60 copies per ml in all macaques (n = 14; 100%) and in 41 out of a total of 56 samples (73.2%) that were collected each week after N-803 administration. Notably, concordant results were obtained in ART-treated HIV-infected humanized mice. In addition, we observed that co-culture with CD8+ T cells blocked the in vitro latency-reversing effect of N-803 on primary human CD4+ T cells that were latently infected with HIV. These results advance our understanding of the mechanisms responsible for latency reversal and lentivirus reactivation during ART-suppressed infection. The interleukin-15 superagonist N-803, combined with the depletion of CD8+ lymphocytes, induced a robust and persistent reactivation of the virus in vivo in both antiretroviral-therapy-treated SIV-infected macaques and HIV-infected humanized mice. [ABSTRACT FROM AUTHOR]

Women globally need access to multipurpose prevention technologies (MPTs) that prevent human immunodeficiency virus (HIV), sexually transmitted infections that increase HIV acquisition/transmission risk, and unintended pregnancy. Seeking an MPT with activity against HIV, herpes simplex virus-2 (HSV-2), and human papillomavirus (HPV), we developed a prototype intravaginal ring (IVR), the MZCL IVR, which released the antiviral agents MIV-150, zinc acetate, and carrageenan (MZC for short) and the contraceptive levonorgestrel (LNG). Previously, we showed that an MZC gel has potent activity against immunodeficiency viruses, HSV-2, and HPV and that the MZCL (MZC with LNG) IVR releases all four components in macaques in vivo at levels associated with efficacy. Vaginal fluid from treated macaques has in vitro activity against HIV, HSV-2, and HPV. Herein, we assessed the ability of the MZCL IVR to protect macaques against repeated co-challenge with HSV-2 and SHIV-RT (simian immunodeficiency virus [SIV] containing the reverse transcriptase gene from HIV) and prevent hormonal cycling. We evaluated in vivo drug release in co-challenged macaques by measuring drug levels in blood and vaginal fluid and residual drug levels in used IVRs. The MZCL IVR significantly prevented SHIV-RT infection, reduced HSV-2 vaginal shedding, and prevented cycling. No non-nucleoside HIV reverse transcriptase inhibitor (NNRTI)-resistant SHIV was detected in macaques that became infected after continuous exposure to MZC from the IVR. Macaques wearing the MZCL IVR also had carrageenan levels in vaginal fluid expected to protect from HPV (extrapolated from mice) and LNG levels in blood associated with contraceptive efficacy. The MZCL IVR is a promising MPT candidate that warrants further development. [ABSTRACT FROM AUTHOR]

Highly potent and broadly neutralizing anti-HIV-1 antibodies (bNAbs) have been used to prevent and treat lentivirus infections in humanized mice, macaques, and humans. In immunotherapy experiments, administration of bNAbs to chronically infected animals transiently suppresses virus replication, which invariably returns to pre-treatment levels and results in progression to clinical disease. Here we show that early administration of bNAbs in a macaque simian/human immunodeficiency virus (SHIV) model is associated with very low levels of persistent viraemia, which leads to the establishment of T-cell immunity and resultant long-term infection control. Animals challenged with SHIVAD8-EO by mucosal or intravenous routes received a single 2-week course of two potent passively transferred bNAbs (3BNC117 and 10-1074 (refs 13, 14)). Viraemia remained undetectable for 56-177 days, depending on bNAb half-life in vivo. Moreover, in the 13 treated monkeys, plasma virus loads subsequently declined to undetectable levels in 6 controller macaques. Four additional animals maintained their counts of T cells carrying the CD4 antigen (CD4+) and very low levels of viraemia persisted for over 2 years. The frequency of cells carrying replication-competent virus was less than 1 per 106 circulating CD4+ T cells in the six controller macaques. Infusion of a T-cell-depleting anti-CD8β monoclonal antibody to the controller animals led to a specific decline in levels of CD8+ T cells and the rapid reappearance of plasma viraemia. In contrast, macaques treated for 15 weeks with combination anti-retroviral therapy, beginning on day 3 after infection, experienced sustained rebound plasma viraemia when treatment was interrupted. Our results show that passive immunotherapy during acute SHIV infection differs from combination anti-retroviral therapy in that it facilitates the emergence of potent CD8+ T-cell immunity able to durably suppress virus replication. [ABSTRACT FROM AUTHOR]

Neutralizing antibodies can confer immunity to primate lentiviruses by blocking infection in macaque models of AIDS. However, earlier studies of anti-human immunodeficiency virus type 1 (HIV-1) neutralizing antibodies administered to infected individuals or humanized mice reported poor control of virus replication and the rapid emergence of resistant variants. A new generation of anti-HIV-1 monoclonal antibodies, possessing extraordinary potency and breadth of neutralizing activity, has recently been isolated from infected individuals. These neutralizing antibodies target different regions of the HIV-1 envelope glycoprotein including the CD4-binding site, glycans located in the V1/V2, V3 and V4 regions, and the membrane proximal external region of gp41 (refs 9, 10, 11, 12, 13, 14). Here we have examined two of the new antibodies, directed to the CD4-binding site and the V3 region (3BNC117 and 10-1074, respectively), for their ability to block infection and suppress viraemia in macaques infected with the R5 tropic simian-human immunodeficiency virus (SHIV)-AD8, which emulates many of the pathogenic and immunogenic properties of HIV-1 during infections of rhesus macaques. Either antibody alone can potently block virus acquisition. When administered individually to recently infected macaques, the 10-1074 antibody caused a rapid decline in virus load to undetectable levels for 4-7 days, followed by virus rebound during which neutralization-resistant variants became detectable. When administered together, a single treatment rapidly suppressed plasma viraemia for 3-5 weeks in some long-term chronically SHIV-infected animals with low CD4+ T-cell levels. A second cycle of anti-HIV-1 monoclonal antibody therapy, administered to two previously treated animals, successfully controlled virus rebound. These results indicate that immunotherapy or a combination of immunotherapy plus conventional antiretroviral drugs might be useful as a treatment for chronically HIV-1-infected individuals experiencing immune dysfunction. [ABSTRACT FROM AUTHOR]

The acquired immunodeficiency syndrome (AIDS)-causing lentiviruses human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) effectively evade host immunity and, once established, infections with these viruses are only rarely controlled by immunological mechanisms. However, the initial establishment of infection in the first few days after mucosal exposure, before viral dissemination and massive replication, may be more vulnerable to immune control. Here we report that SIV vaccines that include rhesus cytomegalovirus (RhCMV) vectors establish indefinitely persistent, high-frequency, SIV-specific effector memory T-cell (TEM) responses at potential sites of SIV replication in rhesus macaques and stringently control highly pathogenic SIVMAC239 infection early after mucosal challenge. Thirteen of twenty-four rhesus macaques receiving either RhCMV vectors alone or RhCMV vectors followed by adenovirus 5 (Ad5) vectors (versus 0 of 9 DNA/Ad5-vaccinated rhesus macaques) manifested early complete control of SIV (undetectable plasma virus), and in twelve of these thirteen animals we observed long-term (≥1 year) protection. This was characterized by: occasional blips of plasma viraemia that ultimately waned; predominantly undetectable cell-associated viral load in blood and lymph node mononuclear cells; no depletion of effector-site CD4+ memory T cells; no induction or boosting of SIV Env-specific antibodies; and induction and then loss of T-cell responses to an SIV protein (Vif) not included in the RhCMV vectors. Protection correlated with the magnitude of the peak SIV-specific CD8+ T-cell responses in the vaccine phase, and occurred without anamnestic T-cell responses. Remarkably, long-term RhCMV vector-associated SIV control was insensitive to either CD8+ or CD4+ lymphocyte depletion and, at necropsy, cell-associated SIV was only occasionally measurable at the limit of detection with ultrasensitive assays, observations that indicate the possibility of eventual viral clearance. Thus, persistent vectors such as CMV and their associated TEM responses might significantly contribute to an efficacious HIV/AIDS vaccine. [ABSTRACT FROM AUTHOR]

Manifestations of viral infections can differ between women and men, and marked sex differences have been described in the course of HIV-1 disease. HIV-1–infected women tend to have lower viral loads early in HIV-1 infection but progress faster to AIDS for a given viral load than men. Here we show substantial sex differences in the response of plasmacytoid dendritic cells (pDCs) to HIV-1. pDCs derived from women produce markedly more interferon-α (IFN-α) in response to HIV-1–encoded Toll-like receptor 7 (TLR7) ligands than pDCs derived from men, resulting in stronger secondary activation of CD8+ T cells. In line with these in vitro studies, treatment-naive women chronically infected with HIV-1 had considerably higher levels of CD8+ T cell activation than men after adjusting for viral load. These data show that sex differences in TLR-mediated activation of pDCs may account for higher immune activation in women compared to men at a given HIV-1 viral load and provide a mechanism by which the same level of viral replication might result in faster HIV-1 disease progression in women compared to men. Modulation of the TLR7 pathway in pDCs may therefore represent a new approach to reduce HIV-1–associated pathology. [ABSTRACT FROM AUTHOR]

Although there has been great progress in treating human immunodeficiency virus 1 (HIV-1) infection, preventing transmission has thus far proven an elusive goal. Indeed, recent trials of a candidate vaccine and microbicide have been disappointing, both for want of efficacy and concerns about increased rates of transmission. Nonetheless, studies of vaginal transmission in the simian immunodeficiency virus (SIV)–rhesus macaque (Macacca mulatta) model point to opportunities at the earliest stages of infection in which a vaccine or microbicide might be protective, by limiting the expansion of infected founder populations at the portal of entry. Here we show in this SIV–macaque model, that an outside-in endocervical mucosal signalling system, involving MIP-3α (also known as CCL20), plasmacytoid dendritic cells and CCR5+ cell-attracting chemokines produced by these cells, in combination with the innate immune and inflammatory responses to infection in both cervix and vagina, recruits CD4+ T cells to fuel this obligate expansion. We then show that glycerol monolaurate—a widely used antimicrobial compound with inhibitory activity against the production of MIP-3α and other proinflammatory cytokines—can inhibit mucosal signalling and the innate and inflammatory response to HIV-1 and SIV in vitro, and in vivo it can protect rhesus macaques from acute infection despite repeated intra-vaginal exposure to high doses of SIV. This new approach, plausibly linked to interfering with innate host responses that recruit the target cells necessary to establish systemic infection, opens a promising new avenue for the development of effective interventions to block HIV-1 mucosal transmission. [ABSTRACT FROM AUTHOR]

The rapid onset of massive, systemic viral replication during primary HIV or simian immunodeficiency virus (SIV) infection and the immune evasion capabilities of these viruses pose fundamental problems for vaccines that depend upon initial viral replication to stimulate effector T cell expansion and differentiation. We hypothesized that vaccines designed to maintain differentiated effector memory T cell (TEM cell) responses at viral entry sites might improve efficacy by impairing viral replication at its earliest stage, and we have therefore developed SIV protein-encoding vectors based on rhesus cytomegalovirus (RhCMV), the prototypical inducer of life-long TEM cell responses. RhCMV vectors expressing SIV Gag, Rev-Tat-Nef and Env persistently infected rhesus macaques, regardless of preexisting RhCMV immunity, and primed and maintained robust, SIV-specific CD4+ and CD8+ TEM cell responses (characterized by coordinate tumor necrosis factor, interferon-γ and macrophage inflammatory protein-1β expression, cytotoxic degranulation and accumulation at extralymphoid sites) in the absence of neutralizing antibodies. Compared to control rhesus macaques, these vaccinated rhesus macaques showed increased resistance to acquisition of progressive SIVmac239 infection upon repeated limiting-dose intrarectal challenge, including four macaques who controlled rectal mucosal infection without progressive systemic dissemination. These data suggest a new paradigm for AIDS vaccine development—vaccines capable of generating and maintaining HIV-specific TEM cells might decrease the incidence of HIV acquisition after sexual exposure. [ABSTRACT FROM AUTHOR]

Envelope glycoprotein (Env) spikes on AIDS retroviruses initiate infection of host cells and are therefore targets for vaccine development. Though crystal structures for partial Env subunits are known, the structure and distribution of native Env spikes on virions is obscure. We applied cryoelectron microscopy tomography to define ultrastructural details of spikes. Virions of wild-type human immunodeficiency virus 1 (HIV-1) and a mutant simian immunodeficiency virus (SIV) had ∼14 and ∼73 spikes per particle, respectively, with some clustering of HIV-1 spikes. Three-dimensional averaging showed that the surface glycoprotein (gp120) ‘head’ of each subunit of the trimeric SIV spike contains a primary mass, with two secondary lobes. The transmembrane glycoprotein ‘stalk’ of each trimer is composed of three independent legs that project obliquely from the trimer head, tripod-like. Reconciling available atomic structures with the three-dimensional whole spike density map yields insights into the orientation of Env spike structural elements and possible structural bases of their functions. [ABSTRACT FROM AUTHOR]

The International AIDS Vaccine Initiative has established a consortium to elucidate mechanisms of protection conferred by live attenuated simian immunodeficiency virus vaccines in monkeys. Here, the strategies defining key components of the protective immune response elicited by these vaccines are discussed. [ABSTRACT FROM AUTHOR]

Engendering cytotoxic T-lymphocyte (CTL) responses is likely to be an important goal of HIV vaccines. However, CTLs select for viral variants that escape immune detection. Maintenance of such escape variants in human populations could pose an obstacle to HIV vaccine development. We first observed that escape mutations in a heterogeneous simian immunodeficiency virus (SIV) isolate were lost upon passage to new animals. We therefore infected macaques with a cloned SIV bearing escape mutations in three immunodominant CTL epitopes, and followed viral evolution after infection. Here we show that each mutant epitope sequence continued to evolve in vivo, often re-establishing the original, CTL-susceptible sequence. We conclude that escape from CTL responses may exact a cost to viral fitness. In the absence of selective pressure upon transmission to new hosts, these original escape mutations can be lost. This suggests that some HIV CTL epitopes will be maintained in human populations. [ABSTRACT FROM AUTHOR]

Dendritic cells and macrophages can process extracellular antigens for presentation by MHC-I molecules. This exogenous pathway may have a crucial role in the activation of CD8+ cytotoxic T lymphocytes during human viral infections. We show here that HIV-1 epitopes derived from incoming virions are presented through the exogenous MHC-I pathway in primary human dendritic cells, and to a lower extent in macrophages, leading to cytotoxic T-lymphocyte activation in the absence of viral protein synthesis. Exogenous antigen presentation required adequate virus-receptor interactions and fusion of viral and cellular membranes. These results provide new insights into how anti-HIV cytotoxic T lymphocytes can be activated and have implications for anti-HIV vaccine design. [ABSTRACT FROM AUTHOR]

Eight different protocols were compared for their ability to raise protection against immunodeficiency virus challenges in rhesus macaques. The most promising containment of challenge infections was achieved by intradermal DNA priming followed by recombinant fowl pox virus booster immunizations. This containment did not require neutralizing antibody and was active for a series of challenges ending with a highly virulent virus with a primary isolate envelope heterologous to the immunizing strain. [ABSTRACT FROM AUTHOR]

An Amendment to this paper has been published and can be accessed via a link at the top of the paper. [ABSTRACT FROM AUTHOR]

Human immunodeficiency virus (HIV) pre-exposure prophylaxis (PrEP) strategies with proven in vivo efficacy rely on antiretroviral drugs, creating the potential for drug resistance and complicated treatment options in individuals who become infected. Moreover, on-demand products are currently missing from the PrEP development portfolio. Griffithsin (GRFT) is a non-antiretroviral HIV entry inhibitor derived from red algae with an excellent safety profile and potent activity in vitro. When combined with carrageenan (CG), GRFT has strong activity against herpes simplex virus-2 (HSV-2) and human papillomavirus (HPV) in vitro and in vivo. Here, we report that GRFT/CG in a freeze-dried fast dissolving insert (FDI) formulation for on-demand use protects rhesus macaques from a high dose vaginal SHIV SF162P3 challenge 4 h after FDI insertion. Furthermore, the GRFT/CG FDI also protects mice vaginally against HSV-2 and HPV pseudovirus. As a safe, potent, broad-spectrum, on-demand non-antiretroviral product, the GRFT/CG FDI warrants clinical development. Safety and efficacy remain important challenges for non-antiretroviral-based microbicides. Here, Derby et al. show that a Griffithsin-Carrageenan fast dissolving vaginal insert provides on-demand protection against SHIV infections in macaques, paving the way for the development of pre-exposure prophylaxis on-demand products. [ABSTRACT FROM AUTHOR]

A review is presented of an article by Deng et alia appearing on page 381 of the issue which contributes to the effort in defeating human immunodeficiency virus (HIV) infection by documenting obstacles to HIV cure and suggesting a possible strategy for overcoming the virus' strength.

Discusses the challenges in developing an effective AIDS vaccine. Aim of most vaccines that offer protection against viruses; Vaccination strategies; Assessment of the efficacy of the vaccines.

A correction to the article titled "Effector memory T cell responses are associated with protection of rhesus monkeys from mucosal simian immunodeficiency virus challenge," by Scott G. Hansen and colleagues that was published in the 2009 issue is presented.

A correction to the article "Effector memory T cell responses are associated with protection of rhesus monkeys from mucosal simian immunodeficiency virus challenge" that was published in the April 6, 2009 issue is presented.