Transmission, acute HIV-1 infection and the quest for strategies to prevent infection

Fetal immune activation to malaria antigens enhances susceptibility to in vitro HIV infection in cord blood mononuclear cells

Mother-to-child-transmission (MTCT) of human immunodeficiency virus (HIV) remains a significant cause of new HIV infections in many countries. To examine whether fetal immune activation as a consequence of prenatal exposure to parasitic antigens increases the risk of MTCT, cord blood mononuclear cells (CBMCs) from Kenyan and North American newborns were examined for relative susceptibility to HIV infection in vitro. Kenyan CBMCs were 3-fold more likely to be infected with HIV than were North American CBMCs (P=.03). Kenyan CBMCs with recall responses to malaria antigens demonstrated enhanced susceptibility to HIV when compared with Kenyan CBMCs lacking recall responses to malaria (P=.03). CD4(+) T cells from malaria-sensitized newborns expressed higher levels of CD25 and human leukocyte antigen DR ex vivo, which is consistent with increased immune activation. CD4(+) T cells were the primary reservoir of infection at day 4 after virus exposure. Thus, prenatal exposure and in utero priming to malaria may increase the risk of MTCT.

Amyloid-binding small molecules efficiently block SEVI (semen-derived enhancer of virus infection)- and semen-mediated enhancement of HIV-1 infection

Semen was recently shown to contain amyloid fibrils formed from a self-assembling peptide fragment of the protein prostatic acid phosphatase. These amyloid fibrils, termed semen-derived enhancer of virus infection, or SEVI, have been shown to strongly enhance HIV infectivity and may play an important role in sexual transmission of HIV, making them a potential microbicide target. One novel approach to target these fibrils is the use of small molecules known to intercalate into the structure of amyloid fibrils, such as derivatives of thioflavin-T. Here, we show that the amyloid-binding small molecule BTA-EG₆ (the hexa(ethylene glycol) derivative of benzothiazole aniline) is able to bind SEVI fibrils and effectively inhibit both SEVI-mediated and semen-mediated enhancement of HIV infection. BTA-EG₆ also blocks the interactions of SEVI with HIV-1 virions and HIV-1 target cells but does not cause any inflammation or toxicity to cervical epithelial cells. These results suggest that an amyloid-binding small molecule may have utility as a microbicide, or microbicidal supplement, for HIV-1.

R5 clade C SHIV strains with tier 1 or 2 neutralization sensitivity: tools to dissect env evolution and to develop AIDS vaccines in primate models

Background

HIV-1 clade C (HIV-C) predominates worldwide, and anti-HIV-C vaccines are urgently needed. Neutralizing antibody (nAb) responses are considered important but have proved difficult to elicit. Although some current immunogens elicit antibodies that neutralize highly neutralization-sensitive (tier 1) HIV strains, most circulating HIVs exhibiting a less sensitive (tier 2) phenotype are not neutralized. Thus, both tier 1 and 2 viruses are needed for vaccine discovery in nonhuman primate models.

Methodology/Principal Findings

We constructed a tier 1 simian-human immunodeficiency virus, SHIV-1157ipEL, by inserting an “early,” recently transmitted HIV-C env into the SHIV-1157ipd3N4 backbone [1] encoding a “late” form of the same env, which had evolved in a SHIV-infected rhesus monkey (RM) with AIDS. SHIV-1157ipEL was rapidly passaged to yield SHIV-1157ipEL-p, which remained exclusively R5-tropic and had a tier 1 phenotype, in contrast to “late” SHIV-1157ipd3N4 (tier 2). After 5 weekly low-dose intrarectal exposures, SHIV-1157ipEL-p systemically infected 16 out of 17 RM with high peak viral RNA loads and depleted gut CD4⁺ T cells. SHIV-1157ipEL-p and SHIV-1157ipd3N4 env genes diverge mostly in V1/V2. Molecular modeling revealed a possible mechanism for the increased neutralization resistance of SHIV-1157ipd3N4 Env: V2 loops hindering access to the CD4 binding site, shown experimentally with nAb b12. Similar mutations have been linked to decreased neutralization sensitivity in HIV-C strains isolated from humans over time, indicating parallel HIV-C Env evolution in humans and RM.

Conclusions/Significance

SHIV-1157ipEL-p, the first tier 1 R5 clade C SHIV, and SHIV-1157ipd3N4, its tier 2 counterpart, represent biologically relevant tools for anti-HIV-C vaccine development in primates.

Treatment of HIV infection with the CCR5 antagonist maraviroc

IMPORTANCE OF THE FIELD

The emergence of resistance in treatment-experienced HIV patients often limits therapeutic success of the currently available antiretroviral drugs. New drug classes are thus required. Maraviroc is the first chemokine receptor 5 antagonist approved for use in treatment experienced HIV patients with a R5-tropic virus.

AREAS COVERED IN THIS REVIEW

For this review, data from pharmacokinetic, Phase II and III clinical trials were reviewed.

WHAT THE READER WILL GAIN

The objectives of this review were to discuss the pharmacokinetics and clinical efficacy and safety of maraviroc in treatment-experienced and -naive HIV patients with R5-tropic virus. Additionally, tropism testing was discussed.

TAKE HOME MESSAGE

Maraviroc is effective in previously treated patients with R5-tropic virus only. Also, maraviroc will be an attractive option for HIV-1-infected treatment-naive patients with R5-tropic viruses only, once genotypic assays have been validated.

PPARgamma and LXR signaling inhibit dendritic cell-mediated HIV-1 capture and trans-infection

Dendritic cells (DCs) contribute to human immunodeficiency virus type 1 (HIV-1) transmission and dissemination by capturing and transporting infectious virus from the mucosa to draining lymph nodes, and transferring these virus particles to CD4+ T cells with high efficiency. Toll-like receptor (TLR)-induced maturation of DCs enhances their ability to mediate trans-infection of T cells and their ability to migrate from the site of infection. Because TLR-induced maturation can be inhibited by nuclear receptor (NR) signaling, we hypothesized that ligand-activated NRs could repress DC-mediated HIV-1 transmission and dissemination. Here, we show that ligands for peroxisome proliferator-activated receptor gamma (PPARgamma) and liver X receptor (LXR) prevented proinflammatory cytokine production by DCs and inhibited DC migration in response to the chemokine CCL21 by preventing the TLR-induced upregulation of CCR7. Importantly, PPARgamma and LXR signaling inhibited both immature and mature DC-mediated trans-infection by preventing the capture of HIV-1 by DCs independent of the viral envelope glycoprotein. PPARgamma and LXR signaling induced cholesterol efflux from DCs and led to a decrease in DC-associated cholesterol, which has previously been shown to be required for DC capture of HIV-1. Finally, both cholesterol repletion and the targeted knockdown of the cholesterol transport protein ATP-binding cassette A1 (ABCA1) restored the ability of NR ligand treated cells to capture HIV-1 and transfer it to T cells. Our results suggest that PPARgamma and LXR signaling up-regulate ABCA1-mediated cholesterol efflux from DCs and that this accounts for the decreased ability of DCs to capture HIV-1. The ability of NR ligands to repress DC mediated trans-infection, inflammation, and DC migration underscores their potential therapeutic value in inhibiting HIV-1 mucosal transmission.

HIV-1 neutralization profile and plant-based recombinant expression of actinohivin, an Env glycan-specific lectin devoid of T-cell mitogenic activity

The development of a topical microbicide blocking the sexual transmission of HIV-1 is urgently needed to control the global HIV/AIDS pandemic. The actinomycete-derived lectin actinohivin (AH) is highly specific to a cluster of high-mannose-type glycans uniquely found on the viral envelope (Env). Here, we evaluated AH's candidacy toward a microbicide in terms of in vitro anti-HIV-1 activity, potential side effects, and recombinant producibility. Two validated assay systems based on human peripheral blood mononuclear cell (hPBMC) infection with primary isolates and TZM-bl cell infection with Env-pseudotyped viruses were employed to characterize AH's anti-HIV-1 activity. In hPMBCs, AH exhibited nanomolar neutralizing activity against primary viruses with diverse cellular tropisms, but did not cause mitogenicity or cytotoxicity that are often associated with other anti-HIV lectins. In the TZM-bl-based assay, AH showed broad anti-HIV-1 activity against clinically-relevant, mucosally transmitting strains of clades B and C. By contrast, clade A viruses showed strong resistance to AH. Correlation analysis suggested that HIV-1's AH susceptibility is significantly linked to the N-glycans at the Env C2 and V4 regions. For recombinant (r)AH expression, we evaluated a tobacco mosaic virus-based system in Nicotiana benthamiana plants as a means to facilitate molecular engineering and cost-effective mass production. Biochemical analysis and an Env-mediated syncytium formation assay demonstrated high-level expression of functional rAH within six days. Taken together, our study revealed AH's cross-clade anti-HIV-1 activity, apparent lack of side effects common to lectins, and robust producibility using plant biotechnology. These findings justify further efforts to develop rAH toward a candidate HIV-1 microbicide.

High Multiplicity Infection by HIV-1 in Men Who Have Sex with Men

Elucidating virus-host interactions responsible for HIV-1 transmission is important for advancing HIV-1 prevention strategies. To this end, single genome amplification (SGA) and sequencing of HIV-1 within the context of a model of random virus evolution has made possible for the first time an unambiguous identification of transmitted/founder viruses and a precise estimation of their numbers. Here, we applied this approach to HIV-1 env analyses in a cohort of acutely infected men who have sex with men (MSM) and found that a high proportion (10 of 28; 36%) had been productively infected by more than one virus. In subjects with multivariant transmission, the minimum number of transmitted viruses ranged from 2 to 10 with viral recombination leading to rapid and extensive genetic shuffling among virus lineages. A combined analysis of these results, together with recently published findings based on identical SGA methods in largely heterosexual (HSX) cohorts, revealed a significantly higher frequency of multivariant transmission in MSM than in HSX [19 of 50 subjects (38%) versus 34 of 175 subjects (19%); Fisher's exact p = 0.008]. To further evaluate the SGA strategy for identifying transmitted/founder viruses, we analyzed 239 overlapping 5′ and 3′ half genome or env-only sequences from plasma viral RNA (vRNA) and blood mononuclear cell DNA in an MSM subject who had a particularly well-documented virus exposure history 3–6 days before symptom onset and 14–17 days before peak plasma viremia (47,600,000 vRNA molecules/ml). All 239 sequences coalesced to a single transmitted/founder virus genome in a time frame consistent with the clinical history, and a molecular clone of this genome encoded replication competent virus in accord with model predictions. Higher multiplicity of HIV-1 infection in MSM compared with HSX is consistent with the demonstrably higher epidemiological risk of virus acquisition in MSM and could indicate a greater challenge for HIV-1 vaccines than previously recognized.

Understanding the biology of sexual transmission of HIV-1 could contribute importantly to the development of effective prevention measures. However, different routes of virus transmission (vaginal, rectal, penile or oral) and inaccessibility of tissues at or near the time of virus transmission make this goal elusive. Here, we apply single genome amplification and sequencing of plasma HIV-1 and a model of random virus evolution to a cohort of acutely infected men who have sex with men (MSM) and find that MSM are twice as likely as heterosexuals to become infected by multiple viruses as opposed to a single virus. Some MSM subjects were infected by as many as 7 to 10 or more genetically distinct viruses as a consequence of a single exposure event. We go on to molecularly clone the first full-length transmitted/founder subtype B HIV-1 virus and show that it is highly replicative in human CD4+ T-cells but not macrophages. Our study provides the first comparative, quantitative analysis of the multiplicity of HIV-1 infection in the two primary risk groups—MSM and heterosexuals—driving the global pandemic, and we discuss the implications of the findings to HIV-1 vaccine development and prevention research.

The role of antibodies in HIV vaccines

Licensed vaccines against viral diseases generate antibodies that neutralize the infecting virus and protect against infection or disease. Similarly, an effective vaccine against HIV-1 will likely need to induce antibodies that prevent initial infection of host cells or that limit early events of viral dissemination. Such antibodies must target the surface envelope glycoproteins of HIV-1, which are highly variable in sequence and structure. The first subunit vaccines to enter clinical trails were safe and immunogenic but unable to elicit antibodies that neutralized most circulating strains of HIV-1. However, potent virus neutralizing antibodies (NAbs) can develop during the course of HIV-1 infection, and this is the type of antibody response that researchers seek to generate with a vaccine. Thus, current vaccine design efforts have focused on a more detailed understanding of these broadly neutralizing antibodies and their epitopes to inform the design of improved vaccines.

Human immunodeficiency virus-1 inhibition of immunoamphisomes in dendritic cells impairs early innate and adaptive immune responses

Dendritic cells (DCs) in mucosal surfaces are early targets for human immunodeficiency virus-1 (HIV-1). DCs mount rapid and robust immune responses upon pathogen encounter. However, immune response in the early events of HIV-1 transmission appears limited, suggesting that HIV-1 evade early immune control by DCs. We report that HIV-1 induces a rapid shutdown of autophagy and immunoamphisomes in DCs. HIV-1 envelope activated the mammalian target of rapamycin pathway in DCs, leading to autophagy exhaustion. HIV-1-induced inhibition of autophagy in DC increased cell-associated HIV-1 and transfer of HIV-1 infection to CD4(+) T cells. HIV-1-mediated downregulation of autophagy in DCs impaired innate and adaptive immune responses. Immunoamphisomes in DCs engulf incoming pathogens and appear to amplify pathogen degradation as well as Toll-like receptor responses and antigen presentation. The findings that HIV-1 downregulates autophagy and impedes immune functions of DCs represent a pathogenesis mechanism that can be pharmacologically countered with therapeutic and prophylactic implications.

Multiple vaccine-elicited nonneutralizing antienvelope antibody activities contribute to protective efficacy by reducing both acute and chronic viremia following simian/human immunodeficiency virus SHIV89.6P challenge in rhesus macaques

We have shown that following priming with replicating adenovirus type 5 host range mutant (Ad5hr)-human immunodeficiency virus (HIV)/simian immunodeficiency virus (SIV) recombinants, boosting with gp140 envelope protein enhances acute-phase protection against intravenous simian/human immunodeficiency virus (SHIV)(89.6P) challenge compared to results with priming and no boosting or boosting with an HIV polypeptide representing the CD4 binding site of gp120. We retrospectively analyzed antibodies in sera and rectal secretions from these same macaques, investigating the hypothesis that vaccine-elicited nonneutralizing antibodies contributed to the better protection. Compared to other immunized groups or controls, the gp140-boosted group exhibited significantly greater antibody activities mediating antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cell-mediated viral inhibition (ADCVI) in sera and transcytosis inhibition in rectal secretions. ADCC and ADCVI activities were directly correlated with antibody avidity, suggesting the importance of antibody maturation for functionality. Both ADCVI and percent ADCC killing prechallenge were significantly correlated with reduced acute viremia. The latter, as well as postchallenge ADCVI and ADCC, was also significantly correlated with reduced chronic viremia. We have previously demonstrated induction by the prime/boost regimen of mucosal antibodies that inhibit transcytosis of SIV across an intact epithelial cell layer. Here, antibody in rectal secretions was significantly correlated with transcytosis inhibition. Importantly, the transcytosis specific activity (percent inhibition/total secretory IgA and IgG) was strongly correlated with reduced chronic viremia, suggesting that mucosal antibody may help control cell-to-cell viral spread during the course of infection. Overall, the replicating Ad5hr-HIV/SIV priming/gp140 protein boosting approach elicited strong systemic and mucosal antibodies with multiple functional activities associated with control of both acute and chronic viremia.

Syndecan-Fc hybrid molecule as a potent in vitro microbicidal anti-HIV-1 agent

In the absence of a vaccine, there is an urgent need for the development of safe and effective topical microbicides to prevent the sexual transmission of human immunodeficiency virus type 1 (HIV-1). In this study, we proposed to develop a novel class of microbicides using syndecan as the antiviral agent. Specifically, we generated a soluble syndecan-Fc hybrid molecule by fusing the ectodomain of syndecan-1 to the Fc domain of a human IgG. We then tested the syndecan-Fc hybrid molecule for various in vitro microbicidal anti-HIV-1 properties. Remarkably, the syndecan-Fc hybrid molecule possesses multiple attractive microbicidal properties: (i) it blocks HIV-1 infection of primary targets including T cells, macrophages, and dendritic cells (DC); (ii) it exhibits a broad range of antiviral activity against primary HIV-1 isolates, multidrug resistant HIV-1 isolates, HIV-2, and simian immunodeficiency virus (SIV); (iii) it prevents transmigration of HIV-1 through human primary genital epithelial cells; (iv) it prevents HIV-1 transfer from dendritic cells to CD4(+) T cells; (v) it is potent when added 2 h prior to addition of HIV-1 to target cells; (vi) it is potent at a low pH; (vii) it blocks HIV-1 infectivity when diluted in genital fluids; and (viii) it prevents herpes simplex virus infection. The heparan sulfate chains of the syndecan-Fc hybrid molecule are absolutely required for HIV-1 neutralization. Several lines of evidence suggest that the highly conserved Arg298 in the V3 region of gp120 serves as the locus for the syndecan-Fc hybrid molecule neutralization. In conclusion, this study suggests that the syndecan-Fc hybrid molecule represents the prototype of a new generation of microbicidal agents that may have promise for HIV-1 prevention.

HIV-1 sexual transmission: early events of HIV-1 infection of human cervico-vaginal tissue in an optimized ex vivo model

Infection and dissemination of human immunodeficiency virus (HIV)-1 through the female body after vaginal intercourse depends on the activation/differentiation status of mucosal CD4 T cells. In this study, we investigated this status and the susceptibility to HIV-1 infection of human cervico-vaginal tissue ex vivo. We found that virtually all T cells are of the effector memory phenotype with broad CC chemokine receptor 5 (CCR5) expression. As it does in vivo, human cervico-vaginal tissue ex vivo preferentially supports the productive infection of R5 HIV-1 rather than that of X4 HIV-1 in spite of the broad expression of CXC chemokine receptor 4 (CXCR4). X4 HIV-1 replicated only in the few tissues that were enriched in CD27(+)CD28(+) effector memory CD4 T cells. Productive infection of R5 HIV-1 occurred preferentially in activated CD38(+)CD4 T cells and was followed by a similar activation of HIV-1-uninfected (bystander) CD4 T cells that may amplify viral infection. These results provide new insights into the dependence of HIV-1 infection and dissemination on the activation/differentiation of cervico-vaginal lymphocytes.

HIV-associated neurocognitive disorder: pathogenesis and therapeutic opportunities

Human immunodeficiency virus type 1 (HIV) infection presently affects more that 40 million people worldwide, and is associated with central nervous system (CNS) disruption in at least 30% of infected individuals. The use of highly active antiretroviral therapy has lessened the incidence, but not the prevalence of mild impairment of higher cognitive and cortical functions (HIV-associated neurocognitive disorders) as well as substantially reduced a more severe form dementia (HIV-associated dementia). Furthermore, improving neurological outcomes will require novel, adjunctive therapies that are targeted towards mechanisms of HIV-induced neurodegeneration. Identifying such molecular and pharmacological targets requires an understanding of the events preceding irreversible neuronal damage in the CNS, such as actions of neurotoxins (HIV proteins and cellular factors), disruption of ion channel properties, synaptic damage, and loss of adult neurogenesis. By considering the specific mechanisms and consequences of HIV neuropathogenesis, unified approaches for neuroprotection will likely emerge using a tailored, combined, and non-invasive approach.

Relative transmissibility of an R5 clade C simian-human immunodeficiency virus across different mucosae in macaques parallels the relative risks of sexual HIV-1 transmission in humans via different routes

BACKGROUND

Worldwide, approximately 90% of all human immunodeficiency virus (HIV) transmissions occur mucosally; almost all involve R5 strains. Risks of sexual HIV acquisition are highest for rectal, then vaginal, and finally oral exposures.

METHODS

Mucosal lacerations may affect the rank order of susceptibility to HIV but cannot be assessed in humans. We measured relative virus transmissibility across intact mucosae in macaques using a single stock of SHIV-1157ipd3N4, a simian-human immunodeficiency virus encoding a primary R5 HIV clade C env (SHIV-C).

RESULTS

The penetrability of rhesus macaque mucosae differed significantly, with rectal challenge requiring the least virus, followed by vaginal and then oral routes (P = .031, oral vs vaginal; P < .001 rectal vs vaginal). These findings imply that intrinsic mucosal properties are responsible for the differential mucosal permeability. The latter paralleled the rank order reported for humans, with relative risk estimates within the range of epidemiological human studies. To test whether inflammation facilitates virus transmission--as predicted from human studies--we established a macaque model of localized buccal inflammation. Systemic infection occurred across inflamed but not normal buccal mucosa.

CONCLUSION

Our primate data recapitulate virus transmission risks observed in humans, thus establishing R5 SHIV-1157ipd3N4 in macaques as a robust model system to study cofactors involved in human mucosal HIV transmission and its prevention.

Wide variation in the multiplicity of HIV-1 infection among injection drug users

Recent studies indicate that sexual transmission of human immunodeficiency virus type 1 (HIV-1) generally results from productive infection by only one virus, a finding attributable to the mucosal barrier. Surprisingly, a recent study of injection drug users (IDUs) from St. Petersburg, Russia, also found most subjects to be acutely infected by a single virus. Here, we show by single-genome amplification and sequencing in a different IDU cohort that 60% of IDU subjects were infected by more than one virus, including one subject who was acutely infected by at least 16 viruses. Multivariant transmission was more common in IDUs than in heterosexuals (60% versus 19%; odds ratio, 6.14; 95% confidence interval [CI], 1.37 to 31.27; P = 0.008). These findings highlight the diversity in HIV-1 infection risks among different IDU cohorts and the challenges faced by vaccines in protecting against this mode of infection.

How fast could HIV change gene frequencies in the human population?

Infectious diseases have the potential to act as strong forces for genetic selection on the populations they affect. Human immunodeficiency virus (HIV) is a prime candidate to impose such genetic selection owing to the vast number of people it infects and the varying susceptibility of different human leucocyte antigen (HLA) types to HIV disease progression. We have constructed a model of HIV infection that differentiates between these HLA types, and have used reported estimates of the number of people infected with HIV and the different rates of progression to acquired immunodeficiency syndrome (AIDS) to provide a lower bound estimate on the length of time it would take for HIV to impose major genetic change in humans. We find that an HIV infection similar to that currently affecting sub-Saharan Africa could not yet have caused more than a 3 per cent decrease in the proportion of individuals who progress quickly to disease. Such an infection is unlikely to cause major genetic change (defined as a decrease in the proportion of quickly progressing individuals to under 50 per cent of their starting proportion) until 400 years have passed since HIV emergence. However, in very severely affected populations, there is a chance of observing such major genetic changes after another 50 years.

Nanoparticle-based vaginal drug delivery systems for HIV prevention

IMPORTANCE OF THE FIELD

Several strategies are being investigated for the prevention of heterosexual transmission of HIV. Of these, topical vaginal drug delivery systems, microbicides, are being actively pursued. HIV prevention by means of a topical microbicide has several drug delivery challenges. These challenges include the vaginal mucosal barriers and potential degradation of the drugs in the vaginal lumen due to pH and enzymes present. Also, new drugs being evaluated as microbicides have specific mechanisms of action, which in some cases require drug targeting to a specific site of action. Nanoparticles provide a delivery strategy for targeted or controlled delivery to the vagina which can be applied in the field of HIV prevention.

AREAS COVERED IN THE REVIEW

This review summarizes nanoparticulate systems and their use in mucosal delivery to date. The sexual transmission of HIV along with the various targets to prevent transmission are discussed as well as the potential opportunities, challenges and advantages in using a nanoparticle-based approach for microbicidal drug delivery.

WHAT THE READER WILL GAIN

This review provides a general understanding of vaginal drug delivery, its challenges, and nanoparticulate delivery systems. Additionally, insight will be gained as to the limited existing application of this technology to the field of HIV prevention.

TAKE HOME MESSAGE

To date, few studies have been published that exploit nanoparticle-based microbicidal delivery to the vagina. The use of nanoparticles for vaginal drug delivery provides an approach to overcome the existing barriers to success.

Minimum infective dose of HIV for parenteral dosimetry

The probability of HIV-1 transmission in a small blood exposure such as a needlestick injury or an unsafe medical injection has been estimated indirectly. Now that several comparable laboratory simulations have provided data on inoculum volumes for such exposures, the epidemiological evidence supporting these estimates can be validated and qualified using dosimetry. This review of data on infective titre, viral load and injection inoculum volume compares three approaches to HIV dosimetry. Agreement across the three approaches indicates that unsafe medical injections are several times more likely to transmit HIV-1 than needlestick accidents, and that the risk remains substantial if injection equipment is wiped, rinsed or flushed prior to re-use. The 50% infective dose of HIV in blood exposures ranges from one virion (two copies RNA) in primary infection with CCR5 co-receptor using strains of HIV-1 to 65,000 copies HIV-1 RNA in blood from an asymptomatic source patient. The median transmission risks for unsafe intravenous or intramuscular injections using equipment cleaned but not sterilized after use on a symptomatic pre-AIDS patient are 1.8% (95% confidence interval [CI] 0.1-3.2%) and 0.8% (95% CI 0.1-1.4%), respectively.

Dendritic cells derived from hemozoin-loaded monocytes display a partial maturation phenotype that promotes HIV-1 trans-infection of CD4+ T cells and virus replication

Coinfection of HIV-1 patients with Plasmodium falciparum, the etiological agent of malaria, results in a raise of viral load and an acceleration of disease progression. The primary objective of this study was to investigate whether the malarial pigment hemozoin (HZ), a heme by-product of hemoglobin digestion by malaria parasites, can affect HIV-1 transmission by monocytes-derived dendritic cells (DCs) to CD4(+) T cells when HZ is initially internalized in monocytes before their differentiation in DCs. We demonstrate in this study that HZ treatment during the differentiation process induces an intermediate maturation phenotype when compared with immature and fully mature DCs. Furthermore, the DC-mediated transfer of HIV-1 is enhanced in presence of HZ, a phenomenon that may be linked with the capacity of HZ-loaded cells to interact and activate CD4(+) T cells. Altogether our findings suggest a new mechanism that could partially explain the increased HIV-1 virus production during a coinfection with P. falciparum. Understanding the multifaceted interactions between P. falciparum and HIV-1 is an important challenge that could lead to the development of new treatment strategies.

Viral dynamics during primary simian immunodeficiency virus infection: effect of time-dependent virus infectivity

A recent experiment involving simian immunodeficiency virus (SIV) infection of macaques revealed that the infectivity of this virus decreased over the first few months of infection. Based on this observation, we introduce a viral dynamic model in which viral infectivity varies over time. The model is fit to viral load data from eight (donor) monkeys infected by intravaginal inoculation of SIVmac251, three monkeys infected by intravenous inoculation of virus isolated from the donors during the ramp-up phase of acute infection, and three monkeys infected by intravenous inoculation of virus isolated at the viral set-point. Although we only analyze data from 14 monkeys, the new model with time-dependent infectivity seems to fit the data significantly better than a widely used model with constant infectivity (P = 2.44 x 10(-11)). Our results indicate that plasma virus infectivity on average decays approximately 8-fold (95% confidence interval [CI] = 5.1 to 10.3) over the course of acute infection, with the decay occurring exponentially with an average rate of 0.28 day(-1) (95% CI = 0.14 to 0.42 day(-1)). The decay rate in set point plasma virus recipient animals is approximately 16 times slower than in ramp-up plasma virus recipient animals and approximately 6 times slower than in donor animals. Throughout acute infection up to the set-point, the infection rate is higher in ramp-up plasma virus recipient animals than in set-point plasma virus recipient animals. These results show that the infectivity depends upon the source of viral infection.

Modulation of protective immunity against herpes simplex virus via mucosal genetic co-transfer of DNA vaccine with beta2-adrenergic agonist

Cholera toxin, which has been frequently used as mucosal adjuvant, leads to an irreversible activation of adenylyl cyclase, thereby accumulating cAMP in target cells. Here, it was assumed that beta(2)-adrenergic agonist salbutamol may have modulatory functions of immunity induced by DNA vaccine, since beta(2)-adrenergic agonists induce a temporary cAMP accumulation. To test this assumption, the present study evaluated the modulatory functions of salbutamol co-administered with DNA vaccine expressing gB of herpes simplex virus (HSV) via intranasal (i.n.) route. We found that the i.n. co-administration of salbutamol enhanced gB-specific IgG and IgA responses in both systemic and mucosal tissues, but optimal dosages of co-administered salbutamol were required to induce maximal immune responses. Moreover, the mucosal co-delivery of salbutamol with HSV DNA vaccine induced Th2-biased immunity against HSV antigen, as evidenced by IgG isotypes and Th1/Th2-type cytokine production. The enhanced immune responses caused by co-administration of salbutamol provided effective and rapid responses to HSV mucosal challenge, thereby conferring prolonged survival and reduced inflammation against viral infection. Therefore, these results suggest that salbutamol may be an attractive adjuvant for mucosal genetic transfer of DNA vaccine.

Galectin-1 and HIV-1 Infection

Initial binding of human immunodeficiency virus-1 (HIV-1) to its susceptible CD4(+) cells is the limiting step for the establishment of infection as the avidity of viral envelope gp120 for CD4 is not high and the number of viral envelope spikes on the surface is found to be low compared to highly infectious viruses. Several host factors, such as C-type lectins, are listed as being able to enforce or facilitate the crucial interaction of HIV-1 to the susceptible cell. Recent works suggest that a host soluble beta-galactoside-binding lectin, galectin-1, also facilitates both virion binding and the infection of target cells in a manner dependent on lactose but not mannose, suggesting that this soluble galectin can be considered as a host factor that influences HIV-1 pathogenesis. In this chapter, we describe methods used to investigate the potential role of the galectin family in HIV-1-mediated disease progression.

Development of topical microbicides to prevent the sexual transmission of HIV

Women comprise almost 50% of the population of people living with HIV and the majority of these women contracted the virus through sexual transmission in monogamous relationships in the developing world. In these environments, where women are not empowered to protect themselves through the negotiation of condom use, effective means of preventing HIV transmission are urgently needed. In the absence of an approved and effective vaccine, microbicides have become the strategy of choice to provide women with the ability to prevent HIV transmission from their infected partners. Topical microbicides are agents specifically developed and formulated for use in either the vaginal or rectal environment that prevent infection by sexually transmitted infectious organisms, including pathogenic viruses, bacteria and fungi. Although a microbicidal product will have many of the same properties as other anti-infective agents and would be similarly developed through human clinical trials, microbicide development bears its own challenges related to formulation and delivery and the unique environment in which the product must act, as well as the requirement to develop a product that is acceptable to the user. Herein, perspectives based on preclinical and clinical microbicide development experience, which have led to an evolving microbicide development algorithm, will be discussed. This article forms part of a special issue of Antiviral Research marking the 25th anniversary of anti-retroviral drug discovery and development, Vol 85, issue 1, 2010.

HSV type 2 infection increases HIV DNA detection in vaginal tissue of mice expressing human CD4 and CCR5

The goal of this study was to develop an in vivo murine model that can be used to study the influence of HSV-2 on HIV infection. Mice expressing transgenes for human CD4, CCR5, and Cyclin T1 were infected intravaginally with HSV-2 and 3-7 days later infected with HIV. HIV DNA was detected by real-time PCR. The frequency of detection of HIV DNA was significantly higher (65%) in vaginal tissue of HSV-2-infected mice compared to mock-infected mice (35%) when HIV was given 3 days after HSV-2. HSV-2-infected mice also had significantly higher levels of HIV DNA in vaginal tissue. HIV DNA was not detected in vaginal tissue of mice lacking human CD4. Longer periods (5 or 7 days) between infection with HSV-2 and HIV did not increase the frequency of detection or the amount of HIV DNA detected. HIV DNA was also detected in lymph nodes from some of the mice that were infected intravaginally with HSV-2 and HIV. Flow cytometric and mRNA analysis of human CD4 in vaginal tissue suggested that HSV-2 infection increased the number of T cells expressing human CD4 in vaginal tissue. This study provides evidence that HIV infection of cells occurs in the vagina of mice expressing human CD4, CCR5, and Cyclin T1 and that HSV-2 infection increases HIV infection. These findings demonstrate that this model can be used to study the mechanisms responsible for increased susceptibility to HIV in HSV-2-infected persons and for testing preventative treatments.

Spermatozoa capture HIV-1 through heparan sulfate and efficiently transmit the virus to dendritic cells

Semen is the main vector for HIV-1 dissemination worldwide. It contains three major sources of infectious virus: free virions, infected leukocytes, and spermatozoa-associated virions. We focused on the interaction of HIV-1 with human spermatozoa and dendritic cells (DCs). We report that heparan sulfate is expressed in spermatozoa and plays an important role in the capture of HIV-1. Spermatozoa-attached virus is efficiently transmitted to DCs, macrophages, and T cells. Interaction of spermatozoa with DCs not only leads to the transmission of HIV-1 and the internalization of the spermatozoa but also results in the phenotypic maturation of DCs and the production of IL-10 but not IL-12p70. At low values of extracellular pH (∼6.5 pH units), similar to those found in the vaginal mucosa after sexual intercourse, the binding of HIV-1 to the spermatozoa and the consequent transmission of HIV-1 to DCs were strongly enhanced. Our observations support the notion that far from being a passive carrier, spermatozoa acting in concert with DCs might affect the early course of sexual transmission of HIV-1 infection.

Mucosal immunology of the genital and gastrointestinal tracts and HIV-1 infection

The male and female genital tracts are protected by a local immune system that displays features distinguishing them from other mucosal sites. In contrast to the intestinal tract, where locally produced IgA is the dominant Ig, secretions of the male and female genital tract contain predominantly IgG of both local and systemic origin. Genital tract tissues also lack mucosal lymphoepithelial inductive sites analogous to intestinal Peyer's patches; consequently, local immunization or infections with sexually transmitted pathogens induce low immune responses. Human immunodeficiency virus 1 (HIV-1) infection must be primarily considered as a mucosal disease with extensive involvement of the systemic immune compartment. Although the majority of infections is acquired through the genital mucosa, a high rate of virus replication and profound CD4(+) T cell depletion occurs in the intestinal mucosa and other mucosal tissues shortly after infection. Evaluation of HIV-specific antibodies in sera and external secretions, including vaginal washes and semen, unexpectedly revealed a selective lack of IgA responses. Moreover, specific antibody-secreting cells in peripheral blood were of the IgG isotype, even in mucosally infected individuals. Whether humoral responses to previously or newly encountered antigens are compromised in HIV-1-infected persons is under current investigation.

Pharmacotherapy of HIV-1 Infection: Focus on CCR5 Antagonist Maraviroc

Sustained inhibition of HIV-1, the goal of antiretroviral therapy, is often impeded by the emergence of viral drug resistance. For patients infected with HIV-1 resistant to conventional drugs from the viral reverse transcriptase and protease inhibitor classes, the recently approved entry and integration inhibitors effectively suppress HIV-1 and offer additional therapeutic options. Entry inhibitors are particularly attractive because, unlike conventional antiretrovirals, they target HIV-1 extracellularly, thereby sparing cells from both viral- and drug-induced toxicities. The fusion inhibitor enfuvirtide and the CCR5 antagonist maraviroc are the first entry inhibitors licensed for patients with drug-resistant HIV-1, with maraviroc restricted to those infected with CCR5-tropic HIV-1 (R5 HIV-1) only. Vicriviroc (another CCR5 antagonist) is in Phase III clinical trials, whereas the CCR5 antibodies PRO 140 and HGS 004 are in early stages of clinical development. Potent antiviral synergy between maraviroc and CCR5 antibodies, coupled with distinct patterns of resistance, suggest their combinations might be particularly effective in patients. In addition, given that oral administration of maraviroc achieves high drug levels in cervicovaginal fluid, combinations of maraviroc and other CCR5 inhibitors could be effective in preventing HIV-1 transmission. Moreover, since CCR5 antagonists prevent rejection of transplanted organs, maraviroc could both suppress HIV-1 and prolong organ survival for the growing number of HIV-1 patients with kidney or liver failure necessitating organ transplantation. Thus, maraviroc offers an important treatment option for patients with drug-resistant R5 HIV-1, who presently account for >50% of drug-resistance cases.

Detection of HIV-1 RNA/DNA and CD4 mRNA in feces and urine from chronic HIV-1 infected subjects with and without anti-retroviral therapy

HIV-1 infects gut associated lymphoid tissues (GALT) very early after transmission by multiple routes. The infected GALT consequently serves as the major reservoir for HIV-1 infection and could constantly shed HIV-1 and CD4+ T cells into the intestinal lumen. To examine this hypothesis, we monitored HIV-1 RNA/DNA and CD4 mRNA in fecal samples of chronically infected subjects with and without antiretroviral therapy (ART). We compared this to levels of HIV-1 RNA/DNA in urine and blood from the same subjects. Our results show that HIV-1 DNA, RNA and CD4 mRNA were detected in 8%, 19% and 31% respectively, of feces samples from infected subjects with detectable plasma viral load, and were not detected in any of subjects on ART with undetectable plasma viral load. In urine samples, HIV-1 DNA was detected in 24% of infected subjects with detectable plasma viral load and 23% of subjects on ART with undetectable plasma viral load. Phylogenetic analysis of the envelope sequences of HIV-1 revealed distinct virus populations in concurrently collected serum, feces and urine samples from one subject. In addition, our study demonstrated for the first time the presence of CD4 mRNA in fecal specimens of HIV-1 infected subjects, which could be used to assess GALT pathogenesis in HIV-1 infection.

TSLP production by epithelial cells exposed to immunodeficiency virus triggers DC-mediated mucosal infection of CD4+ T cells

Mucosal dendritic cells have been implicated in the capture, storage, and transmission of HIV to CD4(+) T cells as well as in the promotion of HIV replication in activated CD4(+) T cells during the cognate T-cell and DC interaction. We report that HIV induces human genital mucosal epithelial cells to produce thymic stromal lymphopoietin (TSLP) via activation of the NFkappaB signaling pathway. The TSLP secreted by HIV exposed epithelial cells activated DC, which promoted proliferation and HIV-1 replication of co-cultured autologous CD4(+) T cells. In rhesus macaques, we observed dramatic increases in TSLP expression concurrent with an increase in viral replication in the vaginal tissues within the first 2 weeks after vaginal SIV exposure. These data suggest that HIV-mediated TSLP production by mucosal epithelial cells is a critical trigger for DC-mediated amplification of HIV-infection in activated CD4(+) T cells. The cross talk between mucosal epithelial cells and DC, mediated by HIV-induced TSLP, may be an important mechanism for the high rate of HIV infection in women through the vaginal mucosa.

Follicular dendritic cells activate HIV-1 replication in monocytes/macrophages through a juxtacrine mechanism mediated by P-selectin glycoprotein ligand 1

Follicular dendritic cells (FDCs) are located in the lymphoid follicles of secondary lymphoid tissues and play a pivotal role in the selection of memory B lymphocytes within the germinal center, a major site for HIV-1 infection. Germinal centers are composed of highly activated B cells, macrophages, CD4(+)T cells, and FDCs. However, the physiological role of FDCs in HIV-1 replication remains largely unknown. We demonstrate in our current study that FDCs can efficiently activate HIV-1 replication in latently infected monocytic cells via an intercellular communication network mediated by the P-selectin/P-selectin glycoprotein ligand 1 (PSGL-1) interaction. Upon coculture with FDCs, HIV-1 replication was significantly induced in infected monocytic cell lines, primary monocytes, or macrophages. These cocultures were found to synergistically induce the expression of P-selectin in FDCs via NF-kappaB activation and its cognate receptor PSGL-1 in HIV-1-infected cells. Consistent with this observation, we find that this response is significantly blocked by antagonistic Abs against PSGL-1 and almost completely inhibited by PSGL-1 small interfering RNA. Moreover, a selective inhibitor for Syk, which is a downstream effector of PSGL-1, blocked HIV-1 replication in our cultures. We have thus elucidated a novel regulatory mechanism in which FDCs are a potent positive bystander that facilitates HIV-1 replication in adjacent infected monocytic cells via a juxtacrine signaling mechanism.

Polyclonal B cell differentiation and loss of gastrointestinal tract germinal centers in the earliest stages of HIV-1 infection

BACKGROUND

The antibody response to HIV-1 does not appear in the plasma until approximately 2-5 weeks after transmission, and neutralizing antibodies to autologous HIV-1 generally do not become detectable until 12 weeks or more after transmission. Moreover, levels of HIV-1-specific antibodies decline on antiretroviral treatment. The mechanisms of this delay in the appearance of anti-HIV-1 antibodies and of their subsequent rapid decline are not known. While the effect of HIV-1 on depletion of gut CD4(+) T cells in acute HIV-1 infection is well described, we studied blood and tissue B cells soon after infection to determine the effect of early HIV-1 on these cells.

METHODS AND FINDINGS

In human participants, we analyzed B cells in blood as early as 17 days after HIV-1 infection, and in terminal ileum inductive and effector microenvironments beginning at 47 days after infection. We found that HIV-1 infection rapidly induced polyclonal activation and terminal differentiation of B cells in blood and in gut-associated lymphoid tissue (GALT) B cells. The specificities of antibodies produced by GALT memory B cells in acute HIV-1 infection (AHI) included not only HIV-1-specific antibodies, but also influenza-specific and autoreactive antibodies, indicating very early onset of HIV-1-induced polyclonal B cell activation. Follicular damage or germinal center loss in terminal ileum Peyer's patches was seen with 88% of follicles exhibiting B or T cell apoptosis and follicular lysis.

CONCLUSIONS

Early induction of polyclonal B cell differentiation, coupled with follicular damage and germinal center loss soon after HIV-1 infection, may explain both the high rate of decline in HIV-1-induced antibody responses and the delay in plasma antibody responses to HIV-1. Please see later in the article for Editors' Summary.

Genetic identity, biological phenotype, and evolutionary pathways of transmitted/founder viruses in acute and early HIV-1 infection

Identification of full-length transmitted HIV-1 genomes could be instrumental in HIV-1 pathogenesis, microbicide, and vaccine research by enabling the direct analysis of those viruses actually responsible for productive clinical infection. We show in 12 acutely infected subjects (9 clade B and 3 clade C) that complete HIV-1 genomes of transmitted/founder viruses can be inferred by single genome amplification and sequencing of plasma virion RNA. This allowed for the molecular cloning and biological analysis of transmitted/founder viruses and a comprehensive genome-wide assessment of the genetic imprint left on the evolving virus quasispecies by a composite of host selection pressures. Transmitted viruses encoded intact canonical genes (gag-pol-vif-vpr-tat-rev-vpu-env-nef) and replicated efficiently in primary human CD4⁺ T lymphocytes but much less so in monocyte-derived macrophages. Transmitted viruses were CD4 and CCR5 tropic and demonstrated concealment of coreceptor binding surfaces of the envelope bridging sheet and variable loop 3. 2 mo after infection, transmitted/founder viruses in three subjects were nearly completely replaced by viruses differing at two to five highly selected genomic loci; by 12–20 mo, viruses exhibited concentrated mutations at 17–34 discrete locations. These findings reveal viral properties associated with mucosal HIV-1 transmission and a limited set of rapidly evolving adaptive mutations driven primarily, but not exclusively, by early cytotoxic T cell responses.

Targeted delivery of immunogen to primate m cells with tetragalloyl lysine dendrimer

Effective uptake of Ags by specialized M cells of gut-associated lymphoid tissues is an important step in inducing efficient immune responses after oral vaccination. Although stable nontoxic small molecule mimetics of lectins, such as synthetic multivalent polygalloyl derivatives, may have potential in murine M cell targeting, it remains unclear whether synthetic multivalent polygalloyl derivatives effectively target nonhuman and human M cells. In this study, we evaluated the ability of a tetragalloyl derivative, the tetragalloyl-D-lysine dendrimer (TGDK), to target M cells in both in vivo nonhuman primate and in vitro human M-like cell culture models. TGDK was efficiently transported from the lumen of the intestinal tract into rhesus Peyer's patches by M cells and then accumulated in germinal centers. Oral administration of rhesus CCR5-derived cyclopeptide conjugated with TGDK in rhesus macaque resulted in a statistically significant increase in stool IgA response against rhesus CCR5-derived cyclopeptide and induced a neutralizing activity against SIV infection. Furthermore, TGDK was specifically bound to human M-like cells and efficiently transcytosed from the apical side to the basolateral side in the M-like cell model. Thus, the TGDK-mediated vaccine delivery system represents a potential approach for enabling M cell-targeted mucosal vaccines in primates.

Delivery of human immunodeficiency virus vaccine vectors to the intestine induces enhanced mucosal cellular immunity

Effective vaccines for human immunodeficiency virus type 1 (HIV-1) will likely need to stimulate protective immunity in the intestinal mucosa, where HIV-1 infection causes severe CD4(+) T-cell depletion. While replication-competent recombinant adenovirus (rAd) vectors can stimulate adenovirus-specific mucosal immunity after replication, oral delivery of replication-defective rAd vectors encoding specific immunogens has proven challenging. In this study, we have systematically identified barriers to effective gut delivery of rAd vectors and identified sites and strategies to induce potent cellular and humoral immunity. Vector-mediated gene transfer by rAd5 was susceptible to low-pH buffer, gastric and pancreatic proteases, and extracellular mucins. Using ex vivo organ explants, we found that transduction with rAd5 was highest in the ileum and colon among all intestinal segments. Transgene expression was 100-fold higher after direct surgical introduction into the ileum than after oral gavage, with rAd5 showing greater potency than the rAd35 or the rAd41 vector. A single immunization of rAd5 encoding HIV-1 gp140B to the ileum stimulated potent CD8(+) T-cell responses in the intestinal and systemic compartments, and these responses were further enhanced by intramuscular rAd5 boosting. These studies suggest that induction of primary immune responses by rAd5 gut immunization and subsequent systemic boosting elicits potent antigen-specific gut mucosal responses.

Low-dose rectal inoculation of rhesus macaques by SIVsmE660 or SIVmac251 recapitulates human mucosal infection by HIV-1

We recently developed a novel strategy to identify transmitted HIV-1 genomes in acutely infected humans using single-genome amplification and a model of random virus evolution. Here, we used this approach to determine the molecular features of simian immunodeficiency virus (SIV) transmission in 18 experimentally infected Indian rhesus macaques. Animals were inoculated intrarectally (i.r.) or intravenously (i.v.) with stocks of SIVmac251 or SIVsmE660 that exhibited sequence diversity typical of early-chronic HIV-1 infection. 987 full-length SIV env sequences (median of 48 per animal) were determined from plasma virion RNA 1–5 wk after infection. i.r. inoculation was followed by productive infection by one or a few viruses (median 1; range 1–5) that diversified randomly with near starlike phylogeny and a Poisson distribution of mutations. Consensus viral sequences from ramp-up and peak viremia were identical to viruses found in the inocula or differed from them by only one or a few nucleotides, providing direct evidence that early plasma viral sequences coalesce to transmitted/founder viruses. i.v. infection was >2,000-fold more efficient than i.r. infection, and viruses transmitted by either route represented the full genetic spectra of the inocula. These findings identify key similarities in mucosal transmission and early diversification between SIV and HIV-1, and thus validate the SIV–macaque mucosal infection model for HIV-1 vaccine and microbicide research.

Visualizing antigen-specific and infected cells in situ predicts outcomes in early viral infection

In the early stages of viral infection, outcomes depend on a race between expansion of infection and the immune response generated to contain it. We combined in situ tetramer staining with in situ hybridization to visualize, map, and quantify relationships between immune effector cells and their targets in tissues. In simian immunodeficiency virus infections in macaques and lymphocytic choriomeningitis virus infections in mice, the magnitude and timing of the establishment of an excess of effector cells versus targets were found to correlate with the extent of control and the infection outcome (i.e., control and clearance versus partial or poor control and persistent infection). This method highlights the importance of the location, timing, and magnitude of the immune response needed for a vaccine to be effective against agents of persistent infection, such as HIV-1.

HIV/AIDS vaccines: a need for new concepts?

HIV vaccine research is at a crossroads carefully contemplating on the next path. The unexpected results of the Merck vaccine trial, while providing a stunning blow to a field in dire need of a protective vaccine, has also raised several fundamental questions regarding the candidate immunogen itself, preexisting immunity to vaccine vectors, surrogate assays and animal models used for assessing preclinical protective responses, as well as relevant endpoints to be measured in a clinical trial. As a result, the research community is faced with the daunting task of identifying novel vaccine concepts and products to continue the search. This review highlights and addresses some of the scientific and practical concerns.

Localized populations of CD8 MHC class I tetramer SIV-specific T cells in lymphoid follicles and genital epithelium

CD8 T cells play an important role in controlling viral infections. We investigated the in situ localization of simian immunodeficiency virus (SIV)-specific T cells in lymph and genital tissues from SIV-infected macaques using MHC-class I tetramers. The majority of tetramer-binding cells localized in T cell zones and were CD8⁺. Curiously, small subpopulations of tetramer-binding cells that had little to no surface CD8 were detected in situ both early and late post-infection, and in both vaginally and rectally inoculated macaques. These tetramer⁺CD8^low/− cells were more often localized in apparent B cell follicles relative to T cell zones and more often found near or within the genital epithelium than the submucosa. Cells analyzed by flow cytometry showed similar populations of cells. Further immunohistological characterization revealed small populations of tetramer⁺CD20⁻ cells inside B cell follicles and that tetramer⁺ cells did not stain with γδ-TCR nor CD4 antibodies. Negative control tetramer staining indicated that tetramer⁺CD8^low/− cells were not likely NK cells non-specifically binding to MHC tetramers. These findings have important implications for SIV-specific and other antigen-specific T cell function in these specific tissue locations, and suggest a model in which antigen-specific CD8+ T cells down modulate CD8 upon entering B cell follicles or the epithelial layer of tissues, or alternatively a model in which only antigen-specific CD8 T cells that down-modulate CD8 can enter B cell follicles or the epithelium.

Double-stranded RNA analog poly(I:C) inhibits human immunodeficiency virus amplification in dendritic cells via type I interferon-mediated activation of APOBEC3G

Human immunodeficiency virus (HIV) is taken up by and replicates in immature dendritic cells (imDCs), which can then transfer virus to T cells, amplifying the infection. Strategies known to boost DC function were tested for their ability to overcome this exploitation when added after HIV exposure. Poly(I:C), but not single-stranded RNA (ssRNA) or a standard DC maturation cocktail, elicited type I interferon (IFN) and interleukin-12 (IL-12) p70 production and the appearance of unique small (15- to 20-kDa) fragments of APOBEC3G (A3G) and impeded HIV(Bal) replication in imDCs when added up to 60 h after virus exposure. Comparable effects were mediated by recombinant alpha/beta IFN (IFN-alpha/beta). Neutralizing the anti-IFN-alpha/beta receptor reversed poly(I:C)-induced inhibition of HIV replication and blocked the appearance of the small A3G proteins. The poly(I:C)-induced appearance of small A3G proteins was not accompanied by significant differences in A3G mRNA or A3G monomer expression. Small interfering RNA (siRNA) knockdown of A3G could not be used to reverse the poly(I:C)-induced protective effect, since siRNAs nonspecifically activated the DCs, inducing the appearance of the small A3G proteins and inhibiting HIV infection. Notably, the appearance of small A3G proteins coincided with the shift of high-molecular-mass inactive A3G complexes to the low-molecular-mass (LMM) active A3G complexes. The unique immune stimulation by poly(I:C) with its antiviral effects on imDCs marked by the expression of IFN-alpha/beta and active LMM A3G renders poly(I:C) a promising novel strategy to combat early HIV infection in vivo.

HMGB1-dependent triggering of HIV-1 replication and persistence in dendritic cells as a consequence of NK-DC cross-talk

Background

HIV-1 has evolved ways to exploit DCs, thereby facilitating viral dissemination and allowing evasion of antiviral immunity. Recently, the fate of DCs has been found to be extremely dependent on the interaction with autologous NK cells, but the mechanisms by which NK-DC interaction controls viral infections remain unclear. Here, we investigate the impact of NK-DC cross-talk on maturation and functions of HIV-infected immature DCs.

Methodology/Principal Findings

Immature DCs were derived from primary monocytes, cultured in the presence of IL-4 and GM-CSF. In some experiments, DCs were infected with R5-HIV-1_BaL or X4-HIV-1_NDK, and viral replication, proviral HIV-DNA and the frequency of infected DCs were measured. Autologous NK cells were sorted and either kept unstimulated in the presence of suboptimal concentration of IL-2, or activated by a combination of PHA and IL-2. The impact of 24 h NK-DC cross-talk on the fate of HIV-1-infected DCs was analyzed. We report that activated NK cells were required for the induction of maturation of DCs, whether uninfected or HIV-1-infected, and this process involved HMGB1. However, the cross-talk between HIV-1-infected DCs and activated NK cells was functionally defective, as demonstrated by the strong impairment of DCs to induce Th1 polarization of naïve CD4 T cells. This was associated with the defective production of IL-12 and IL-18 by infected DCs. Moreover, the crosstalk between activated NK cells and HIV-infected DCs resulted in a dramatic increase in viral replication and proviral DNA expression in DCs. HMGB1, produced both by NK cells and DCs, was found to play a pivotal role in this process, and inhibition of HMGB1 activity by glycyrrhizin, known to bind specifically to HMGB1, or blocking anti-HMGB1 antibodies, abrogated NK-dependent HIV-1 replication in DCs.

Conclusion

These observations provide evidence for the crucial role of NK-DC cross-talk in promoting viral dissemination, and challenge the question of the in vivo involvement of HMGB1 in the triggering of HIV-1 replication and replenishment of viral reservoirs in AIDS.

SHIV-1157i and passaged progeny viruses encoding R5 HIV-1 clade C env cause AIDS in rhesus monkeys

Background

Infection of nonhuman primates with simian immunodeficiency virus (SIV) or chimeric simian-human immunodeficiency virus (SHIV) strains is widely used to study lentiviral pathogenesis, antiviral immunity and the efficacy of AIDS vaccine candidates. SHIV challenges allow assessment of anti-HIV-1 envelope responses in primates. As such, SHIVs should mimic natural HIV-1 infection in humans and, to address the pandemic, encode HIV-1 Env components representing major viral subtypes worldwide.

Results

We have developed a panel of clade C R5-tropic SHIVs based upon env of a Zambian pediatric isolate of HIV-1 clade C, the world's most prevalent HIV-1 subtype. The parental infectious proviral clone, SHIV-1157i, was rapidly passaged through five rhesus monkeys. After AIDS developed in the first animal at week 123 post-inoculation, infected blood was infused into a sixth monkey. Virus reisolated at this late stage was still exclusively R5 tropic and mucosally transmissible. Here we describe the long-term follow-up of this initial cohort of six monkeys. Two have remained non-progressors, whereas the other four gradually progressed to AIDS within 123–270 weeks post-exposure. Two progressors succumbed to opportunistic infections, including a case of SV40 encephalitis.

Conclusion

These data document the disease progression induced by the first mucosally transmissible, pathogenic R5 non-clade B SHIV and suggest that SHIV-1157i-derived viruses, including the late-stage, highly replication-competent SHIV-1157ipd3N4 previously described (Song et al., 2006), display biological characteristics that mirror those of HIV-1 clade C and support their expanded use for AIDS vaccine studies in nonhuman primates.

Efficacy of Carraguard-based microbicides in vivo despite variable in vitro activity

Anti-HIV microbicides are being investigated in clinical trials and understanding how promising strategies work, coincident with demonstrating efficacy in vivo, is central to advancing new generation microbicides. We evaluated Carraguard® and a new generation Carraguard-based formulation containing the non-nucleoside reverse transcriptase inhibitor (NNRTI) MIV-150 (PC-817). Since dendritic cells (DCs) are believed to be important in HIV transmission, the formulations were tested for the ability to limit DC-driven infection in vitro versus vaginal infection of macaques with RT-SHIV (SIVmac239 bearing HIV reverse transcriptase). Carraguard showed limited activity against cell-free and mature DC-driven RT-SHIV infections and, surprisingly, low doses of Carraguard enhanced infection. However, nanomolar amounts of MIV-150 overcame enhancement and blocked DC-transmitted infection. In contrast, Carraguard impeded infection of immature DCs coincident with DC maturation. Despite this variable activity in vitro, Carraguard and PC-817 prevented vaginal transmission of RT-SHIV when applied 30 min prior to challenge. PC-817 appeared no more effective than Carraguard in vivo, due to the limited activity of a single dose of MIV-150 and the dominant barrier effect of Carraguard. However, 3 doses of MIV-150 in placebo gel at and around challenge limited vaginal infection, demonstrating the potential activity of a topically applied NNRTI. These data demonstrate discordant observations when comparing in vitro and in vivo efficacy of Carraguard-based microbicides, highlighting the difficulties in testing putative anti-viral strategies in vitro to predict in vivo activity. This work also underscores the potential of Carraguard-based formulations for the delivery of anti-viral drugs to prevent vaginal HIV infection.

Stable gene transfer of CCR5 and CXCR4 siRNAs by sleeping beauty transposon system to confer HIV-1 resistance

BACKGROUND

Thus far gene therapy strategies for HIV/AIDS have used either conventional retroviral vectors or lentiviral vectors for gene transfer. Although highly efficient, their use poses a certain degree of risk in terms of viral mediated oncogenesis. Sleeping Beauty (SB) transposon system offers a non-viral method of gene transfer to avoid this possible risk. With respect to conferring HIV resistance, stable knock down of HIV-1 coreceptors CCR5 and CXCR4 by the use of lentiviral vector delivered siRNAs has proved to be a promising strategy to protect cells from HIV-1 infection. In the current studies our aim is to evaluate the utility of SB system for stable gene transfer of CCR5 and CXCR4 siRNA genes to derive HIV resistant cells as a first step towards using this system for gene therapy.

RESULTS

Two well characterized siRNAs against the HIV-1 coreceptors CCR5 and CXCR4 were chosen based on their previous efficacy for the SB transposon gene delivery. The siRNA transgenes were incorporated individually into a modified SB transfer plasmid containing a FACS sortable red fluorescence protein (RFP) reporter and a drug selectable neomycin resistance gene. Gene transfer was achieved by co-delivery with a construct expressing a hyperactive transposase (HSB5) into the GHOST-R3/X4/R5 cell line, which expresses the major HIV receptor CD4 and and the co-receptors CCR5 and CXCR4. SB constructs expressing CCR5 or CXCR4 siRNAs were also transfected into MAGI-CCR5 or MAGI-CXCR4 cell lines, respectively. Near complete downregulation of CCR5 and CXCR4 surface expression was observed in transfected cells. During viral challenge with X4-tropic (NL4.3) or R5-tropic (BaL) HIV-1 strains, the respective transposed cells showed marked viral resistance.

CONCLUSION

SB transposon system can be used to deliver siRNA genes for stable gene transfer. The siRNA genes against HIV-1 coreceptors CCR5 and CXCR4 are able to downregulate the respective cell surface proteins and thus confer resistance against viral infection by restricting viral entry. These studies have demonstrated for the first time the utility of the non-viral SB system in conferring stable resistance against HIV infection and paved the way for the use of this system for HIV gene therapy studies.

Acute Schistosoma mansoni infection increases susceptibility to systemic SHIV clade C infection in rhesus macaques after mucosal virus exposure

Background

Individuals living in sub-Saharan Africa represent 10% of the world's population but almost 2/3 of all HIV-1/AIDS cases. The disproportionate HIV-1 infection rates in this region may be linked to helminthic parasite infections that affect many individuals in the developing world. However, the hypothesis that parasite infection increases an individual's susceptibility to HIV-1 has never been prospectively tested in a relevant in vivo model.

Methodology/Principal Findings

We measured whether pre-existing infection of rhesus monkeys with a parasitic worm would facilitate systemic infection after mucosal AIDS virus exposure. Two groups of animals, one consisting of normal monkeys and the other harboring Schistosoma mansoni, were challenged intrarectally with decreasing doses of R5-tropic clade C simian-human immunodeficiency virus (SHIV-C). Systemic infection occurred in parasitized monkeys at viral doses that remained sub-infectious in normal hosts. In fact, the 50% animal infectious (AID₅₀) SHIV-C dose was 17-fold lower in parasitized animals compared to controls (P<0.001). Coinfected animals also had significantly higher peak viral RNA loads than controls (P<0.001), as well as increased viral replication in CD4⁺ central memory cells (P = 0.03).

Conclusions/Significance

Our data provide the first direct evidence that acute schistosomiasis significantly increases the risk of de novo AIDS virus acquisition, and the magnitude of the effect suggests that control of helminth infections may be a useful public health intervention to help decrease the spread of HIV-1.

To test the hypothesis that infection with helmiths may increase host susceptibility to infection with HIV-1, we quantified the amount of a clade C simian-human immunodeficiency virus needed to infect rhesus macaques that had acute Schistosoma mansoni infections. Compared to control animals exposed to virus alone, monkeys with schistosomiasis required exposure to 17-fold lower levels of virus to become infected. The schistosome-infected monkeys also had significantly higher levels of initial virus replication and loss of a certain subset of memory T cells, both predictors of a more rapid progression to immune dysfunction. These results suggest that worm infections may increase the risk of becoming infected with HIV-1 among individuals with viral exposures. Furthermore, they support the idea that control programs for schistosomiasis and perhaps other parasitic worm infections may also be useful in helping to reduce the spread of HIV/AIDS in developing countries where helminths are endemic.

HIV-1 Transmission, Replication Fitness and Disease Progression

Upon transmission, human immunodeficiency virus type 1 (HIV-1) establishes infection of the lymphatic reservoir, leading to profound depletion of the memory CD4+ T cell population despite the induction of the adaptive immune response. The rapid evolution and association of viral variants having distinct characteristics during different stages of infection, the level of viral burden, and rate of disease progression suggest a role for viral variants in this process. Here, we review the literature on HIV-1 variants and disease and discuss the importance of viral fitness for transmission and disease.

Critical issues in mucosal immunity for HIV-1 vaccine development

Development of a safe and effective vaccine for HIV-1 infection is a critical global priority. However, the nature of host-virus interactions that lead to early immunosuppression and CD4 depletion, HIV-1 diversity, and the inability of the immune system to eliminate the latently infected CD4 pool of cells has to date thwarted successful vaccine development. Moreover, both the initial antibody-inducing vaccine (protein envelope gp120) and cell-mediated vaccine (recombinant adenovirus containing HIV-1 genes) strategies have failed in efficacy trials, and the latter cell-mediated vaccine appeared to have caused enhanced HIV-1 acquisition. Thus basic and translational research to understand why current vaccines have failed and elucidation of new mechanisms of virus control at mucosal surfaces is essential for eventual successful development of a preventive HIV-1 vaccine.

Mucosal immunity and HIV/AIDS vaccines. Report of an International Workshop, 28-30 October 2007

In October 2007, a joint ANRS-NIH workshop was held on “Mucosal immunity and HIV/AIDS vaccines” in Veyrier-du-Lac, France. Goal of the meeting was to discuss recent developments in the understanding of viral entry and dissemination at mucosal surfaces, rationale for designing vaccines to elicit mucosal immune responses by various routes of immunization, and the types of immune responses elicited. Lessons were drawn from existing vaccines against viral mucosal infections, from the recent failure of the Merck Ad5/HIV vaccine and from attempts at mucosal immunization against SIV. This report summarizes the main concepts and conclusions that came out of the meeting.