Controlling HIV pathogenesis: the role of the noncytotoxic anti-HIV response of CD8+ T cells

Identification of differentially expressed genes, pathways, and immune infiltration in diabetes

This study aimed to perform exhaustive bioinformatic analysis by using GSE29221 micro-array maps obtained from healthy controls and Type 2 Diabetes (T2DM) patients. Raw data are downloaded from the Gene Expression Omnibus database and processed by the limma package in R software to identify Differentially Expressed Genes (DEGs). Gene ontology functional analysis and Kyoto Gene Encyclopedia and Genome Pathway analysis are performed to determine the biological functions and pathways of DEGs. A protein interaction network is constructed using the STRING database and Cytoscape software to identify key genes. Finally, immune infiltration analysis is performed using the Cibersort method. This study has implications for understanding the underlying molecular mechanism of T2DM and provides potential targets for further research.

CD8+ T cells promote HIV latency by remodeling CD4+ T cell metabolism to enhance their survival, quiescence, and stemness

HIV infection persists during antiretroviral therapy (ART) due to a reservoir of latently infected cells that harbor replication-competent virus and evade immunity. Previous ex vivo studies suggested that CD8+ T cells from people with HIV may suppress HIV expression via non-cytolytic mechanisms, but the mechanisms responsible for this effect remain unclear. Here, we used a primary cell-based in vitro latency model and demonstrated that co-culture of autologous activated CD8+ T cells with HIV-infected memory CD4+ T cells promoted specific changes in metabolic and/or signaling pathways resulting in increased CD4+ T cell survival, quiescence, and stemness. Collectively, these pathways negatively regulated HIV expression and ultimately promoted the establishment of latency. As shown previously, we observed that macrophages, but not B cells, promoted latency in CD4+ T cells. The identification of CD8-specific mechanisms of pro-latency activity may favor the development of approaches to eliminate the viral reservoir in people with HIV.

STING Ligand-Mediated Priming of Functional CD8+ T Cells Specific for HIV-1-Protective Epitopes from Naive T Cells

Functional HIV-1-specific CD8+ T cells primed from naive T cells are expected to act as effector T cells in a "shock-and-kill" therapeutic strategy for an HIV-1 cure since less functional HIV-1-specific CD8+ T cells are elicited from memory T cells in HIV-1-infected individuals on combined antiretroviral therapy (cART). CD8+ T cells specific for HIV-1 conserved and protective epitopes are candidates for such T cells. We investigated the priming with STING ligand of CD8+ T cells specific for HLA-B*52:01 or HLA-C*12:02-restricted protective epitopes from naive T cells. STING ligand 3'3'-cGAMP effectively primed CD8+ T cells specific for 3 of 4 HLA-B*52:01-restricted epitopes but failed to prime those specific for all 3 HLA-C*12:02-restricted epitopes from the naive T cells of HIV-1-uninfected individuals having an HLA-B*52:01-C*12:02 protective haplotype. These HLA-B*52:01-restricted CD8+ T cells had a strong ability to suppress HIV-1 replication and expressed a high level of cytolytic effector molecules. The viral suppression ability of these T cells was significantly correlated with the expression level of perforin and showed a trend for a positive correlation with the expression level of CD107a. The present study highlighted the priming with STING ligand of functional CD8+ T cells specific for protective epitopes, which T cells would contribute as effector T cells to a shock-and-kill therapy. IMPORTANCE The current "shock-and-kill" therapeutic strategy for HIV cure has been directed toward eliminating latent viral reservoirs by reactivation of latent reservoirs with latency-reversing agents followed by eradication of these cells by immune-mediated responses. Although HIV-1-specific T cells are expected to eradicate viral reservoirs, the function of these T cells is reduced in HIV-1-infected individuals with long-term cART. Therefore, priming of HIV-1-specific T cells with high function from naive T cells is to be expected in these individuals. In this study, we demonstrated the priming with STING ligand 3'3'-cGAMP of CD8+ T cells specific for HIV-1-protective epitopes from naive T cells. cGAMP primed CD8+ T cells specific for 3 HLA-B*52:01-restricted protective epitopes, which cells expressed a high level of cytolytic effector molecules and effectively suppressed HIV-1 replication. The present study suggested that the priming with STING ligand of functional CD8+ T cells specific for protective epitopes would be useful in a therapy for an HIV-1 cure.

Potential Utility of Natural Killer Cells for Eliminating Cells Harboring Reactivated Latent HIV-1 Following the Removal of CD8+ T Cell-Mediated Pro-Latency Effect(s)

An impediment to curing HIV-1 infection is the persistence of latently infected cells in ART-treated people living with HIV (PLWH). A key strategy for curing HIV-1 infection is to activate transcription and translation of latent virus using latency reversing agents (LRAs) and eliminate cells harboring reactivated virus via viral cytopathic effect or immune clearance. In this review, we provide an overview of available LRAs and their use in clinical trials. Furthermore, we describe recent data suggesting that CD8⁺ T cells promote HIV-1 latency in the context of ART, even in the presence of LRAs, which might at least partially explain the clinical inefficiency of previous “shock and kill” trials. Here, we propose a novel cure strategy called “unlock, shock, disarm, and kill”. The general premise of this strategy is to shut down the pro-latency function(s) of CD8⁺ T cells, use LRAs to reverse HIV-1 latency, counteract anti-apoptotic molecules, and engage natural killer (NK) cells to mediate the killing of cells harboring reactivated latent HIV-1.

The CD8+ T Cell Noncytotoxic Antiviral Responses

The CD8+ T cell noncytotoxic antiviral response (CNAR) was discovered during studies of asymptomatic HIV-infected subjects more than 30 years ago. In contrast to CD8+ T cell cytotoxic lymphocyte (CTL) activity, CNAR suppresses HIV replication without target cell killing. This activity has characteristics of innate immunity: it acts on all retroviruses and thus is neither epitope specific nor HLA restricted. The HIV-associated CNAR does not affect other virus families. It is mediated, at least in part, by a CD8+ T cell antiviral factor (CAF) that blocks HIV transcription. A variety of assays used to measure CNAR/CAF and the effects on other retrovirus infections are described. Notably, CD8+ T cell noncytotoxic antiviral responses have now been observed with other virus families but are mediated by different cytokines. Characterizing the protein structure of CAF has been challenging despite many biologic, immunologic, and molecular studies. It represents a low-abundance protein that may be identified by future next-generation sequencing approaches. Since CNAR/CAF is a natural noncytotoxic activity, it could provide promising strategies for HIV/AIDS therapy, cure, and prevention.

Plasma Cytokine Levels As Predictors of Global and Domain-Specific Human Immunodeficiency Virus-Associated Neurocognitive Impairment in Treatment-Naive Individuals

Central nervous system dysfunction, associated with human immunodeficiency virus (HIV) infection, remains a significant clinical concern, affecting at least 50% of infected people. Imbalances in cytokine expression levels have been linked to HIV-associated neurocognitive disorders. The aim of this study was to evaluate plasma cytokine levels as predictor neurocognitive impairment in HIV infection using a multiplex profiling kit. Stepwise regression model was used to identify cytokine biomarkers of overall and domain-specific cognitive performance. Higher interleukin (IL)-2 (β = 0.04; P = 0.001) and eotaxin (β = 0.01; P = 0.017) were predictors of global neurocognitive, whereas higher IL-5 (β = 0.005; P = 0.007) was negative predictor of global cognitive deficit. IL-2 was a negative predictor of most cognitive domain functions, including recall (β = 0.24; P = 0.005), recognition (β = 0.04; P = 0.026), mental control (β = 0.38; P = 0.005), symbol search (β = -0.55; P = 0.001), and digital symbol (β = -0.79; P = 0.019). IL-6 was associated with 3 impaired domains, mental processing (β = -0.468; P = 0.027), recognition (β = -0.044; P = 0.012), and learning (β = 0.02668; P = 0.020) These results show that plasma cytokines/chemokines may serve as markers of neurocognitive impairment in HIV infection.

Innate, non-cytolytic CD8+ T cell-mediated suppression of HIV replication by MHC-independent inhibition of virus transcription

MHC-I-restricted, virus-specific cytotoxic CD8+ T cells (CTLs) may control human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) replication via the recognition and killing of productively infected CD4+ T cells. Several studies in SIV-infected macaques suggest that CD8+ T cells may also decrease virus production by suppressing viral transcription. Here, we show that non-HIV-specific, TCR-activated non-cytolytic CD8+ T cells suppress HIV transcription via a virus- and MHC-independent immunoregulatory mechanism that modulates CD4+ T cell proliferation and activation. We also demonstrate that this CD8+ T cell-mediated effect promotes the survival of infected CD4+ T cells harboring integrated, inducible virus. Finally, we used RNA sequencing and secretome analyses to identify candidate cellular pathways that are involved in the virus-silencing mediated by these CD8+ T cells. This study characterizes a previously undescribed mechanism of immune-mediated HIV silencing that may be involved in the establishment and maintenance of the reservoir under antiretroviral therapy and therefore represent a major obstacle to HIV eradication.

Baboon CD8 T cells suppress SIVmac infection in CD4 T cells through contact-dependent production of MIP-1α, MIP-1β, and RANTES

Simian immunodeficiency virus (SIV) infection in rhesus macaques is often characterized by high viremia and CD4 T cell depletion. By contrast, SIV infection in African nonhuman primate natural hosts is typically nonpathogenic despite active viral replication. Baboons are abundant in Africa and have a geographical distribution that overlaps with natural hosts, but they do not harbor SIVs. Previous work has demonstrated baboons are resistant to chronic SIV infection and/or disease in vivo but the underlying mechanisms remain unknown. Using in vitro SIVmac infections, we sought to identify SIV restriction factors in baboons by comparing observations to the pathogenic rhesus macaque model. SIVmac replicated in baboon PBMC but had delayed kinetics compared to rhesus PBMC. However, SIVmac replication in baboon and rhesus isolated CD4 cells were similar to the kinetics seen for rhesus PBMC, demonstrating intracellular restriction factors do not play a strong role in baboon inhibition of SIVmac replication. Here, we show CD8 T cells contribute to the innate SIV-suppressive activity seen in naïve baboon PBMC. As one mechanism of restriction, we identified higher production of MIP-1α, MIP-1β, and RANTES by baboon PBMC. Contact between CD4 and CD8 T cells resulted in maximum production of these chemokines and suppression of viral replication, whereas neutralization of CCR5-binding chemokines in baboon PBMC increased viral loads. Our studies indicate baboon natural restriction of SIVmac replication is largely dependent on CD4-extrinsinc mechanisms mediated, in part, by CD8 T cells.

CD8+ lymphocyte control of SIV infection during antiretroviral therapy

CD8⁺ lymphocytes play an important role in suppressing in vivo viral replication in HIV infection. However, both the extent to which and the mechanisms by which CD8⁺ lymphocytes contribute to viral control are not completely understood. A recent experiment depleted CD8⁺ lymphocytes in simian immunodeficiency virus (SIV)-infected rhesus macaques (RMs) on antiretroviral treatment (ART) to study the role of CD8⁺ lymphocytes. CD8⁺ lymphocytes depletion resulted in temporary plasma viremia in all studied RMs. Viral control was restored when CD8⁺ lymphocytes repopulated. We developed a viral dynamic model to fit the viral load (VL) data from the CD8 depletion experiment. We explicitly modeled the dynamics of the latent reservoir and the SIV-specific effector cell population including their exhaustion and their potential cytolytic and noncytolytic functions. We found that the latent reservoir significantly contributes to the size of the peak VL after CD8 depletion, while drug efficacy plays a lesser role. Our model suggests that the overall CD8⁺ lymphocyte cytolytic killing rate is dynamically changing depending on the levels of antigen-induced effector cell activation and exhaustion. Based on estimated parameters, our model suggests that before ART or without ART the overall CD8 cytolytic killing rate is small due to exhaustion. However, after the start of ART, the overall CD8 cytolytic killing rate increases due to an expansion of SIV-specific CD8 effector cells. Further, we estimate that the cytolytic killing rate can be significantly larger than the cytopathic death rate in some animals during the second phase of ART-induced viral decay. Lastly, our model provides a new explanation for the puzzling findings by Klatt et al. and Wong et al. that CD8 depletion done immediately before ART has no noticeable effect on the first phase viral decay slope seen after ART initiation Overall, by incorporating effector cells and their exhaustion, our model can explain the effects of CD8 depletion on VL during ART, reveals a detailed dynamic role of CD8⁺ lymphocytes in controlling viral infection, and provides a unified explanation for CD8 depletion experimental data.

CD8⁺ lymphocytes play an important role in suppressing in vivo viral replication in HIV infection. However, both the extent to which and the mechanisms by which CD8⁺ lymphocytes contribute to viral control are not completely understood. By mathematically modeling data from a recent CD8 depletion experiment done in antiretroviral (ART) treated animals, our results suggest that the overall CD8⁺ lymphocyte cytolytic killing rate is dynamically changing depending on the levels of antigen-induced effector cell activation and exhaustion, i.e. before ART or without ART the overall CD8 cytolytic killing rate is small due to exhaustion. However, after the start of ART, the overall CD8 cytolytic killing rate increases due to an expansion of SIV-specific CD8 effector cells. By incorporating effector cells and their exhaustion, our model explains the effects on viral load of CD8 depletion done before ART or during ART, reveals a detailed dynamic role of CD8⁺ lymphocytes in controlling viral infection, and provides a unified explanation for CD8 depletion experimental data.

Variable Effect of HIV Superinfection on Clinical Status: Insights From Mathematical Modeling

HIV superinfection (infection of an HIV positive individual with another strain of the virus) has been shown to result in a deterioration of clinical status in multiple case studies. However, superinfection with no (or positive) clinical outcome might easily go unnoticed, and the typical effect of superinfection is unknown. We analyzed mathematical models of HIV dynamics to assess the effect of superinfection under various assumptions. We extended the basic model of virus dynamics to explore systematically a set of model variants incorporating various details of HIV infection (homeostatic target cell dynamics, bystander killing, interference competition between viral clones, multiple target cell types, virus-induced activation of target cells). In each model, we identified the conditions for superinfection, and investigated whether and how successful invasion by a second viral strain affects the level of uninfected target cells. In the basic model, and in some of its extensions, the criteria for invasion necessarily entail a decrease in the equilibrium abundance of uninfected target cells. However, we identified three novel scenarios where superinfection can substantially increase the uninfected cell count: (i) if the rate of new infections saturates at high infectious titers (due to interference competition or cell-autonomous innate immunity); or when the invading strain is more efficient at infecting activated target cells, but less efficient at (ii) activating quiescent cells or (iii) inducing bystander killing of these cells. In addition, multiple target cell types also allow for modest increases in the total target cell count. We thus conclude that the effect of HIV superinfection on clinical status might be variable, complicated by factors that are independent of the invasion fitness of the second viral strain.

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

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

Vaccination with Combination DNA and Virus-Like Particles Enhances Humoral and Cellular Immune Responses upon Boost with Recombinant Modified Vaccinia Virus Ankara Expressing Human Immunodeficiency Virus Envelope Proteins

Heterologous prime boost with DNA and recombinant modified vaccinia virus Ankara (rMVA) vaccines is considered as a promising vaccination approach against human immunodeficiency virus (HIV-1). To further enhance the efficacy of DNA-rMVA vaccination, we investigated humoral and cellular immune responses in mice after three sequential immunizations with DNA, a combination of DNA and virus-like particles (VLP), and rMVA expressing HIV-1 89.6 gp120 envelope proteins (Env). DNA prime and boost with a combination of VLP and DNA vaccines followed by an rMVA boost induced over a 100-fold increase in Env-specific IgG antibody titers compared to three sequential immunizations with DNA and rMVA. Cellular immune responses were induced by VLP-DNA and rMVA vaccinations at high levels in CD8 T cells, CD4 T cells, and peripheral blood mononuclear cells secreting interferon (IFN)-γ, and spleen cells producing interleukin (IL)-2, 4, 5 cytokines. This study suggests that a DNA and VLP combination vaccine with MVA is a promising strategy in enhancing the efficacy of DNA-rMVA vaccination against HIV-1.

Viral-specific T-cell response in hemorrhagic cystitis after haploidentical donor stem cell transplantation

Viral hemorrhagic cystitis (HC) after hematopoietic stem cell transplantation (HSCT) can be devastating. Standard treatment modalities have not been well established, but immune reconstitution may be necessary for sustained viral clearance. We studied five pediatric patients who developed viral HC after haplo-identical HSCT. All patients developed virus-specific CD4- and CD8-positive T cells, and the emergence of these viral-specific T cells was temporally associated with successful viral clearance.

Timing of CD8 T cell effector responses in viral infections

CD8 T cell or cytotoxic T lymphocyte (CTL) responses are an important branch of the immune system in the fight against viral infections. The dynamics of anti-viral CTL responses have been characterized in some detail, both experimentally and with mathematical models. An interesting experimental observation concerns the timing of CTL responses. A recent study reported that in pneumonia virus of mice the effector CTL tended to arrive in the lung only after maximal virus loads had been achieved, an observation that seems at first counterintuitive because prevention of pathology would require earlier CTL-mediated activity. A delay in CTL-mediated effector activity has also been quoted as a possible explanation for the difficulties associated with CTL-based vaccines. This paper uses mathematical models to show that in specific parameter regimes, delayed CTL effector activity can be advantageous for the host in the sense that it can increase the chances of virus clearance. The increased ability of the CTL to clear the infection, however, is predicted to come at the cost of acute pathology, giving rise to a trade-off, which is discussed in the light of evolutionary processes. This work provides a theoretical basis for understanding the described experimental observations.

The CD8+ cell non-cytotoxic antiviral response affects RNA polymerase II-mediated human immunodeficiency virus transcription in infected CD4+ cells

A CD8+ cell non-cytotoxic antiviral response (CNAR), mediated by a CD8+ cell antiviral factor (CAF), is associated with a long-term healthy state in human immunodeficiency virus (HIV) infection. CNAR/CAF reduces viral transcription without a known effect on specific viral sequences in the HIV genome. In studies to define the mechanism involved in the block in viral transcription, we now report that transcription from the HIV-LTR reporter is reduced in infected CD4+ cells upon treatment with CAF. In agreement with this observation, the amount of RNA polymerase II (RNAPII) on the HIV promoter and other viral regions was strongly diminished in HIV-infected CD4+ cells co-cultivated with CNAR-expressing CD8+ cells. These results demonstrate further that CNAR/CAF has a specific role in regulating HIV transcription and a step during the preinitiation complex assembly appears to be sensitive to CNAR/CAF.

TOE1 is an inhibitor of HIV-1 replication with cell-penetrating capability

Target of Egr1 (TOE1) is a nuclear protein localized primarily in nucleoli and Cajal bodies that was identified as a downstream target of the immediate early gene Egr1. TOE1 displays a functional deadenylation domain and has been shown to participate in spliceosome assembly. We report here that TOE1 can function as an inhibitor of HIV-1 replication and show evidence that supports a direct interaction of TOE1 with the viral specific transactivator response element as part of the inhibitory mechanism. In addition, we show that TOE1 can be secreted by activated CD8(+) T lymphocytes and can be cleaved by the serine protease granzyme B, one of the main components of cytotoxic granules. Both full-length and cleaved TOE1 can spontaneously cross the plasma membrane and penetrate cells in culture, retaining HIV-1 inhibitory activity. Antiviral potency of TOE1 and its cell-penetrating capability have been identified to lie within a 35-amino-acid region containing the nuclear localization sequence.

Dispelling myths and focusing on notable concepts in HIV pathogenesis

Since the discovery of HIV over three decades ago, major efforts have been made to control and perhaps eliminate HIV infection worldwide. During these studies, certain myths or misconceptions about this infectious disease have been emphasized and other potentially beneficial concepts have received less attention. A true long-term solution to HIV infection merits an appreciation of alternative ideas and findings that could be beneficial in the ultimate control of HIV/AIDS. Here, I discuss six issues and call for more attention to the science of HIV and well-designed clinical trials.

Modeling T cell responses to antigenic challenge

T cell responses are a crucial part of the adaptive immune system in the fight against infections. This article discusses the use of mathematical models for understanding the dynamics of cytotoxic T lymphocyte (CTL) responses against viral infections. Complementing experimental research, mathematical models have been very useful for exploring new hypotheses, interpreting experimental data, and for defining what needs to be measured to improve understanding. This review will start with minimally parameterized models of CTL responses, which have generated some valuable insights into basic dynamics and correlates of control. Subsequently, more biological complexity is incorporated into this modeling framework, examining different mechanisms of CTL expansion, different effector activities, and the influence of T cell help. Models and results are discussed in the context of data from specific infections.

The CD8 antiviral factor (CAF) can suppress HIV-1 transcription from the long terminal repeat (LTR) promoter in the absence of elements upstream of the CATATAA box

Background

The CD8 Antiviral Factor (CAF) suppresses viral transcription from the HIV-1 Long Terminal Repeat (LTR) promoter in a non-cytolytic manner. However, the region on the LTR upon which CAF acts is unknown. Our objective was to determine the region on the LTR upon which CAF acts to suppress HIV-1 transcription.

Methods

Serial deletions of the LTR from the 5’ end and inactivating point mutations were made.

Results

Serial deletions of the LTR from the 5’ end indicated the importance of a short ~120 bp segment, containing the 3 SpI sites, CATA box (used by HIV-1 instead of the TATA box) and TAR region, in the suppressive process. Introduction of deletions or inactivating point mutations in the SpI sites or deletion of the TAR region did not abolish CAF-mediated transcriptional suppression. Yet, CAF-mediated transcriptional suppression was still retained in the HIV-1 CATA-TAR segment.

Conclusion

CAF is able to suppress transcription from the LTR lacking all the elements upstream of the CATA box. Our results suggest that the HIV-1 CATA box may be responsible for CAF-mediated suppression of transcription from the HIV-1 LTR.

Inhibition of R5-tropic HIV type-1 replication in CD4⁺ natural killer T cells by γδ T lymphocytes

After the development of highly active anti-retroviral therapy, it became clear that the majority of emergent HIV-1 is macrophage-tropic and infects CD4⁺, CCR5-expressing cells (R5-tropic). There are three distinct cell populations, R5-tropic, HIV-1-susceptible CD4⁺ cells: (i) natural killer T (NKT) cells, (ii) dendritic cells and macrophages, and (iii) tissue-associated T cells residing primarily at mucosal surfaces. We have confirmed that CD4⁺ NKT cells derived from peripheral blood mononuclear cells (PBMCs) predominantly express CCR5 rather than CXCR4, whereas the reverse is true for CD4⁺ T cells derived from circulating PBMCs, and that R5-tropic HIV-1 expands efficiently in the CD4⁺ NKT cells. Moreover, when PBMCs depleted of CD8α⁺ cells were stimulated in the presence of α-galactosylceramide (α-GalCer) and R5-tropic HIV-1 [NL(AD8)], the production of HIV-1 virions was not suppressed, whereas, similar to the untreated PBMCs, depletion of CD8β⁺ cells from PBMCs significantly inhibited virion production. These findings suggest that CD8αα⁺ but not CD8αβ⁺ cells may have the ability to inhibit R5-tropic HIV-1 replication in CD4⁺ NKT cells. Here, we show that co-culturing R5-tropic HIV-1-infected CD4⁺ NKT cells with CD8αα⁺ γδ T cells, in particular Vγ1Vδ1 cells, but not with CD8αα⁺ NKT cells or CD8αα⁺ dendritic cells, inhibits HIV-1 replication mainly by secreting chemokines, such as macrophage inflammatory proteins 1α and 1β and RANTES. Collectively, these results indicate the importance of CD8αα⁺ γδ T cells in the control of R5-tropic HIV-1 replication and persistence in CD4⁺ NKT cells.

Ability of CD8+T Cell Anti-Feline Immunodeficiency Virus Activity Correlated with Peripheral CD4+T Cell Counts and Plasma Viremia

In the host defense mechanism against feline immunodeficiency virus (FIV) infection, CD8(+) T cells specifically attack virus-infected cells and suppress the replication of the virus in a non-cytolytic manner by secreting soluble factors. In this study, we measured CD8(+) T cell anti-FIV activity in 30 FIV-infected cats. We investigated its relationship with the number of peripheral blood lymphocytes, particularly the CD4(+) T cell and CD8(+) T cell counts, and the relationship between anti-FIV activity and the number of T cells of CD8alpha(+)beta(lo) and CD8alpha(+)beta(-) phenotypes. A clearly significant correlation was observed between anti-FIV activity and the number of CD4(+) T cells. A weaker anti-FIV activity was associated with a greater decrease in the number of CD4(+) T cells. However, there was no significant correlation between anti-FIV activity and the number of B or CD8(+) T cells. Compared with SPF cats, FIV-infected cats had significantly higher CD8alpha(+)beta(lo) T cell and CD8alpha(+)beta(-) T cell counts, but, no significant correlation was observed between these cell counts and anti-FIV activity. This anti-FIV activity significantly correlated with plasma viremia, which was detected in cats with a weak anti-FIV activity. These results suggest that the anti-FIV activity of CD8(+) T cells plays an important role in plasma viremia and the maintenance of CD4(+) T cells in the body. It is unlikely that CD8alpha(+)beta(lo) or CD8alpha(+)beta(-) T cells appearing after FIV infection represent a phenotype of CD8(+) cells with anti-FIV activity.

Can non-lytic CD8+ T cells drive HIV-1 escape?

The CD8+ T cell effector mechanisms that mediate control of HIV-1 and SIV infections remain poorly understood. Recent work suggests that the mechanism may be primarily non-lytic. This is in apparent conflict with the observation that SIV and HIV-1 variants that escape CD8+ T cell surveillance are frequently selected. Whilst it is clear that a variant that has escaped a lytic response can have a fitness advantage compared to the wild-type, it is less obvious that this holds in the face of non-lytic control where both wild-type and variant infected cells would be affected by soluble factors. In particular, the high motility of T cells in lymphoid tissue would be expected to rapidly destroy local effects making selection of escape variants by non-lytic responses unlikely. The observation of frequent HIV-1 and SIV escape poses a number of questions. Most importantly, is the consistent observation of viral escape proof that HIV-1- and SIV-specific CD8+ T cells lyse infected cells or can this also be the result of non-lytic control? Additionally, the rate at which a variant strain escapes a lytic CD8+ T cell response is related to the strength of the response. Is the same relationship true for a non-lytic response? Finally, the potential anti-viral control mediated by non-lytic mechanisms compared to lytic mechanisms is unknown. These questions cannot be addressed with current experimental techniques nor with the standard mathematical models. Instead we have developed a 3D cellular automaton model of HIV-1 which captures spatial and temporal dynamics. The model reproduces in vivo HIV-1 dynamics at the cellular and population level. Using this model we demonstrate that non-lytic effector mechanisms can select for escape variants but that outgrowth of the variant is slower and less frequent than from a lytic response so that non-lytic responses can potentially offer more durable control.

The interplay between viruses and the immune system cannot always be studied with current experimental techniques or commonly used mathematical models. Consequently, many important questions remain unanswered. The questions we wished to address fall into this category. Recent evidence strongly suggests that CD8+ T cells control SIV, and potentially HIV-1, primarily by secreting anti-viral factors rather than by killing infected cells. However, this does not seem compatible with the common observation that HIV and SIV evolve to escape the immune response. Soluble anti-viral factors, like RANTES which protects uninfected cells from infection, would be expected to inhibit both wild-type and variant virus. Furthermore, the high speed and motility of T cells in lymphoid tissue will increase homogeneity and again decrease the likelihood that an escape variant can have a selective advantage in the face of non-lytic control. We wanted to understand whether viral escape is proof that HIV-1- and SIV-specific CD8+ T cells kill infected cells, determine the factors that facilitate viral escape, and investigate the comparative efficiency of lytic and non-lytic responses in controlling viral infections. Here we develop an elaborate but robust computational framework that captures T cell kinetics and spatial interactions in lymphoid tissue to addresses these important questions.

CD8(+) lymphocytes suppress human immunodeficiency virus 1 replication by secreting type I interferons

CD8(+) cells can suppress human immunodeficiency virus 1 (HIV-1) replication by releasing soluble factors. In 26 years of intensive research efforts, the identity of the major CD8(+) cell antiviral factor has remained elusive. To investigate the mechanism for this antiviral immune response, we performed gene expression analyses on primary CD4(+) cells that were exposed to HIV-suppressing CD8(+) cells or CD8(+) cell-conditioned medium having HIV-suppressing activity. These experiments revealed increased levels of multiple genes stimulated by type I interferons (IFN; eg, IFN-α and IFN-β). Further evaluation revealed that primary CD8(+) cells, particularly those from elite controllers and other asymptomatic HIV-1-infected individuals, secrete IFN, and this response directly contributes to the in vitro suppression of HIV replication in CD4(+) cells. This novel immune response, likely mediated by memory CD8(+) T cells, may play an important role in a wide variety of viral infections, cancers, and autoimmune diseases.

Modeling of HIV-1 infection: insights to the role of monocytes/macrophages, latently infected T4 cells, and HAART regimes

A novel dynamic model covering five types of cells and three connected compartments, peripheral blood (PB), lymph nodes (LNs), and the central nervous system (CNS), is here proposed. It is based on assessment of the biological principles underlying the interactions between the human immunodeficiency virus type I (HIV-1) and the human immune system. The simulated results of this model matched the three well-documented phases of HIV-1 infection very closely and successfully described the three stages of LN destruction that occur during HIV-1 infection. The model also showed that LNs are the major location of viral replication, creating a pool of latently infected T4 cells during the latency period. A detailed discussion of the role of monocytes/macrophages is made, and the results indicated that infected monocytes/macrophages could determine the progression of HIV-1 infection. The effects of typical highly active antiretroviral therapy (HAART) drugs on HIV-1 infection were analyzed and the results showed that efficiency of each drug but not the time of the treatment start contributed to the change of the turnover of the disease greatly. An incremental count of latently infected T4 cells was made under therapeutic simulation, and patients were found to fail to respond to HAART therapy in the presence of certain stimuli, such as opportunistic infections. In general, the dynamics of the model qualitatively matched clinical observations very closely, indicating that the model may have benefits in evaluating the efficacy of different drug therapy regimens and in the discovery of new monitoring markers and therapeutic schemes for the treatment of HIV-1 infection.

Unbiased analysis of TCRα/β chains at the single-cell level in human CD8+ T-cell subsets

T-cell receptor (TCR) α/β chains are expressed on the surface of CD8⁺ T-cells and have been implicated in antigen recognition, activation, and proliferation. However, the methods for characterization of human TCRα/β chains have not been well established largely because of the complexity of their structures owing to the extensive genetic rearrangements that they undergo. Here we report the development of an integrated 5′-RACE and multiplex PCR method to amplify the full-length transcripts of TCRα/β at the single-cell level in human CD8⁺ subsets, including naive, central memory, early effector memory, late effector memory, and effector phenotypic cells. Using this method, with an approximately 47% and 62% of PCR success rate for TCRα and for TCRβ chains, respectively, we were able to analyze more than 1,000 reads of transcripts of each TCR chain. Our comprehensive analysis revealed the following: (1) chimeric rearrangements of TCRδ-α, (2) control of TCRα/β transcription with multiple transcriptional initiation sites, (3) altered utilization of TCRα/β chains in CD8⁺ subsets, and (4) strong association between the clonal size of TCRα/β chains and the effector phenotype of CD8⁺ T-cells. Based on these findings, we conclude that our method is a useful tool to identify the dynamics of the TCRα/β repertoire, and provides new insights into the study of human TCRα/β chains.

THE IMPACT OF THE CD8+ CELL NON-CYTOTOXIC ANTIVIRAL RESPONSE (CNAR) AND CYTOTOXIC T LYMPHOCYTE (CTL) ACTIVITY IN A CELL-TO-CELL SPREAD MODEL FOR HIV-1 WITH A TIME DELAY

In this paper, neglecting the effects of free virus, we consider a simple model of cell-to-cell spread of HIV-1. We discuss the impact of the CD8+ cell non-cytotoxic anti-viral response (CNAR) and cytotoxic T lymphocyte (CTL) activity on infection by HIV-1. Two types of models are considered: the ordinary differential equation (ODE) model and the discrete time delay differential equation (DDE) system. The steady states of the ODE model are globally asymptotically stable respectively under two threshold criteria. In the DDE model, the global stability of the infected steady state of the ODE model becomes only ultimately stable. Moreover, at a certain interval of the time delay, the DDE model will produce Hopf bifurcation or periodic solutions. The introduction of CTL and CNAR will change the values of these steady states and induce fluctuations in the cell concentration. It also affects the critical value of the time delay and is of utility in the interpretation of typical HIV-dynamics data resulting from clinical trials. The DDE model produces sustained infective oscillations in some real parameter values, which is different from the result of the similar cell-free viral spread model with delay.

Elevated CD8 counts during HAART are associated with HIV virologic treatment failure

OBJECTIVE

To evaluate whether elevated CD8 counts are associated with increased risk of virologic treatment failure in HIV-infected individuals.

DESIGN

Retrospective cohort study.

METHODS

US Military HIV Natural History Study participants who initiated highly active antiretroviral therapy (HAART) in 1996-2008 had 6- and 12-month post-HAART HIV RNA <400 copies per milliliter, ≥ 2 subsequent HIV viral loads and a baseline CD8 count were eligible (n = 817). Baseline was 12 months after the start of HAART, virologic failure (VF) was defined as confirmed HIV RNA ≥ 400 copies per milliliter, and CD8 counts ≥ 1200 cells per cubic millimeter were considered elevated. Cox models were used to examine the effect of baseline and time-updated CD8 counts on VF.

RESULTS

There were 216 failures for a rate of 5.6 per 100 person-years [95% confidence interval (CI): 4.9 to 6.4]. Among those initiating HAART in 2000-2008, the participants with elevated baseline CD8 counts had significantly greater risk of VF compared with those with baseline CD8 counts ≤ 600 cells per cubic millimeter [hazard ratio (HR) = 2.68, 95% CI: 1.13 to 6.35]. The participants with elevated CD8 counts at >20% of previous 6-month follow-up visits had a greater risk of failure at the current visit than those who did not (HR = 1.53, 95% CI: 1.14 to 2.06). Those with CD8 counts that increased after the start of HAART had a greater risk of failure than those with CD8 counts that decreased or remained the same (HR = 1.59, 95% CI: 1.19 to 2.13).

CONCLUSIONS

Initial or serial elevated CD8 counts while on HAART or an increase in CD8 counts from HAART initiation may be early warnings for future treatment failure.

Why don't CD8+ T cells reduce the lifespan of SIV-infected cells in vivo?

In January 2010 two groups independently published the observation that the depletion of CD8+ cells in SIV-infected macaques had no detectable impact on the lifespan of productively infected cells. This unexpected observation led the authors to suggest that CD8+ T cells control SIV viraemia via non-lytic mechanisms. However, a number of alternative plausible explanations, compatible with a lytic model of CD8+ T cell control, were proposed. This left the field with no consensus on how to interpret these experiments and no clear indication whether CD8+ T cells operated primarily via a lytic or a non-lytic mechanism. The aim of this work was to investigate why CD8+ T cells do not appear to reduce the lifespan of SIV-infected cells in vivo.

Several studies have shown a role for CD8+ T cells in controlling SIV-infection. However, early last year two groups independently showed that depletion of CD8+ lymphocytes did not result in a measurable increase in the lifespan of productively infected cells, suggesting that direct cell killing may not be the major mechanism of antiviral activity by CD8+ lymphocytes. We investigated whether the lack of an effect on lifespan of infected cells indeed excludes a lytic role for CD8+ cells and whether a non-lytic effect of CD8+ cells, for instance by preventing new infections or blocking production of free virions, better explains the similar death rates of SIV-infected cells in animals with and without CD8+ lymphocytes. We found that, even though lytic models of CD8+ cell function are compatible with the absence of an effect of CD8+ cells on the lifespan of productively infected cells, the most likely mechanism of CD8-control in SIV-infection is via a non-lytic mechanism.

Transfection optimization for primary human CD8+ cells

Electroporation, a non-virus-mediated gene transfection method, has traditionally had poor outcomes with low gene transfection efficiency and poor cellular viability, particularly in primary human lymphocytes. Herein we have optimized the electroporation conditions for primary CD8+ cells resulting in a maximum rate of 81.3%, and a mean transfection efficiency of 59.6%. After removal of dead cells, the viability of transfected primary CD8+ cells was greater than 90%, similar to untransfected controls. Using this procedure, primary human CD8+ cells transfected with an interferon α8 plasmid produced fluids that inhibited HIV-1 replication by > 95%. This transfection protocol is useful for transfection of other primary blood cells, such as CD4+ T cells, and for studying the function of genes in primary human blood cells instead of cell lines. The transfection procedure also has potential application in gene therapy clinical trials to treat diseases utilizing transfected primary human cells.

HIV vaccines: progress to date

The quest for an effective and safe HIV-1 vaccine has been and still is the aspiration of many scientists and clinicians worldwide. Until recently, the hopes for an effective vaccine were thwarted by the disappointing results and early termination in September 2007 of the STEP study, which saw a subgroup of male vaccine recipients at an increased risk of HIV-1 infection, and the failure of earlier trials of vaccines based on recombinant envelope proteins to provide any level of protection. The results of the STEP study raised important questions in the field of HIV vaccines, including the use of recombinant adenovirus vectors as immunogens, the rationale for the development of T-cell-based vaccines and the development pathway for these vaccines, in terms of assessment of immunogenicity and the challenge models used. The study of neutralizing antibodies has demonstrated that the induction of high-titre, broadly neutralizing antibodies in the majority of recipients is likely to be highly problematic. However, the results of the RV144 Thai trial released in September 2009 have brought new optimism to the field. This study employed envelope-based immunogens delivered as a priming vaccination with a recombinant poxvirus vector and boosting with recombinant proteins. This regimen provided modest protection to HIV-1 infection in a low-risk population. Although the correlates of protection are currently unknown, extensive studies are underway to try to determine these. Neutralizing antibodies were not induced in the RV144 study; however, considerable titres of binding antibodies to HIV-1 viral envelope (Env) were. It is speculated that these antibodies may have provided a means of protection by a mechanism such as antibody-dependent cell-mediated cytotoxicity. In addition, no CD8+ T-cell responses were induced, but robust CD4+ T-cell responses were, and correlates of protection are being sought by analysing the quality of this aspect of the vaccine-induced immune response. The current paradigm for an optimal HIV-1 vaccine is to design immunogens and vaccination protocols that allow the induction of both broadly neutralizing humoral and broadly reactive and effective cell-mediated immunity, to act at sites of possible infection and post-infection, respectively. However, this is challenged by the results of the RV144 trial as neither of these responses were induced but modest protection was observed. Understanding the biology and immunopathology of HIV-1 early following infection, its modes of transmission and the human immune system's response to the virus should aid in the rational design of vaccines of increased efficacy.

Active lytic infection of human primary tonsillar B cells by KSHV and its noncytolytic control by activated CD4+ T cells

Kaposi sarcoma-associated herpesvirus (KSHV) is a B-lymphotropic virus whose primary site of replication is the oropharynx. KSHV can infect both T and B cells from primary tonsillar explant cultures. However, T cells do not support lytic replication, while B cells spontaneously produce substantial amounts of infectious virus. Here, we provide evidence for a mechanism by which activated T cells may promote or stabilize latency of KSHV infection in B cells. When mixed cultures of B cells and activated T cells were exposed to KSHV, little spontaneous virus production was observed. Removing T cells from the mix or treating the mixed culture with immune suppressants enhanced virus production. Adding back activated T cells to purified infected B cells efficiently suppressed KSHV production, primarily due to CD4(+) T cells. This suppressive activity required T cell activation and direct cell-cell contact, but not prior exposure to KSHV antigen. Suppression was not MHC restricted and did not result in killing of the target cell. We therefore propose that oropharyngeal T cells activated by a variety of stimuli can recognize ligands on infected target B cells, leading to signaling events that prevent spontaneous lytic activation and promote latent infection in this compartment.

Natural suppression of human immunodeficiency virus type 1 replication is mediated by transitional memory CD8+ T cells

HIV replication is suppressed in vitro by a CD8(+) cell noncytotoxic antiviral response (CNAR). This activity directly correlates with an asymptomatic clinical state. The objective of this study was to identify the phenotype of CD8(+) cell subsets having strong CNAR activity. CD8(+) cell subset frequencies and CNAR levels were measured for human immunodeficiency virus (HIV)-uninfected individuals and three groups of HIV type 1 (HIV-1)-infected individuals: asymptomatic individuals with low-level viremia (vHIV), antiretroviral-drug-treated subjects with undetectable virus levels (TxHIV), and therapy-naïve aviremic elite controllers (EC). CD8(+) cells from the vHIV individuals exhibited the highest HIV-suppressing activity and had elevated frequencies of CD45RA(-) CD27(+) and PD-1(+) (CD279(+)) cells. Functional assessments of CD8(+) cells sorted into distinct subsets established that maximal CNAR activity was mediated by CD45RA(-) CCR7(-) CD27(+) and PD-1(+) CD8(+) cells. T cell receptor (TCR) repertoire profiles of CD8(+) cell subsets having strong CNAR activity exhibited increased perturbations in comparison to those of inactive subsets. Together, these studies suggest that CNAR is driven by HIV replication and that this antiviral activity is associated with oligoclonally expanded activated CD8(+) cells expressing PD-1 and having a transitional memory cell phenotype. The findings better describe the identity of CD8(+) cells showing CNAR and should facilitate the evaluation of this important immune response in studies of HIV pathogenesis, resistance to infection, and vaccine development.

Secretion of MIP-1β and MIP-1α by CD8(+) T-lymphocytes correlates with HIV-1 inhibition independent of coreceptor usage

CD8(+) T-lymphocytes can utilize noncytolytic mechanisms to suppress HIV-1 replication through the secretion of soluble factors. The secretion of MIP-1β, MIP-1α, IP-10, MIG, IL-1α, and interferon gamma correlated most strongly with soluble noncytolytic suppression (p<0.0001). Since the noncytolytic response is impaired by histone hyperacetylation, we examined the ability of histone hyperacetylation to alter the expression of immune-related genes. MIP-1α and IP-10 were also among the genes that were down-regulated by histone hyperacetylation. We define a multifactorial cytokine profile of CD8(+) T-lymphocytes capable of mediating noncytolytic suppression of CXCR4-tropic HIV-1 replication.

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.

Immunomodulation of caprine lentiviral infection by interleukin-16

Interleukin-16 (IL-16) is a proinflammatory cytokine produced by a variety of cells including lymphocytes, macrophages, mast cells, and eosinophils. We have shown in our previous studies increased expression of IL-16 mRNA and protein in caprine arthritis-encephalitis virus (CAEV)-infected goats blood. In this study, we determined the immunomodulatory effects of IL-16 in vitro using cells derived from CAEV infected and uninfected goats. Human recombinant IL-16 (rhIL-16) significantly increased chemotaxis of peripheral blood mononuclear cells (PBMCs) of both control and CAEV-infected goats. Pretreatment of PBMC with anti-goat CD4 monoclonal antibody inhibited IL-16-induced chemotaxis of PBMC of control and infected goats suggesting that IL-16 exerts its action in goats primarily by binding to CD4. The CAEV proviral DNA was less in caprine monocytes treated with rhIL-16 infected in vitro with CAEV. These data suggest inhibitory effect of IL-16 on viral integration. Flow cytometric studies indicated a trend toward IL-16-induced increased expression of lymphocyte activation markers. Combined with our previously reported data, these experiments suggest that increased IL-16 expression during CAEV infection may inhibit viral integration.

Noncytotoxic suppression of human immunodeficiency virus type 1 transcription by exosomes secreted from CD8+ T cells

CD8(+) T cells display a noncytotoxic activity that suppresses transcription of human immunodeficiency virus type 1 (HIV-1) in an antigen-independent and major histocompatibility complex-unrestricted manner. To date, the precise cellular and molecular factors mediating this CD8(+) T-cell effector function remain unsolved. Despite evidence indicating the dependence of the activity on cell-cell contact, the possibility of a membrane-mediated activity that represses transcription from the viral promoter remains unexplored. We therefore investigated whether this inhibition of HIV-1 transcription might be elicited by a membrane-bound determinant. Using a CD8(+) T-cell line displaying potent noncytotoxic HIV-1 suppression activity, we have identified a membrane-localized HIV-1-suppressing activity that is concomitantly secreted as 30- to 100-nm endosome-derived tetraspanin-rich vesicles known as exosomes. Purified exosomes from CD8(+) T-cell culture supernatant noncytotoxically suppressed CCR5-tropic (R5) and CXCR4-tropic (X4) replication of HIV-1 in vitro through a protein moiety. Similar antiviral activity was also found in exosomes isolated from two HIV-1-infected subjects. The antiviral exosomes specifically inhibited HIV-1 transcription in both acute and chronic models of infection. Our results, for the first time, indicate the existence of an antiviral membrane-bound factor consistent with the hallmarks defining noncytotoxic CD8(+) T-cell suppression of HIV-1.

Lentivirus-induced immune dysregulation

FIV/HIV infections are associated with an early robust humoral and cellular anti-viral immune response followed by a progressive immune suppression that eventually results in AIDS. Several mechanisms responsible for this immune dysfunction have been proposed including cytokine dysregulation, immunologic anergy and apoptosis, and inappropriate activation of immune regulatory cells. Studies on FIV infection provide evidence for all three. Cytokine alterations include decreases in IL2 and IL12 production and increases in IFNgamma and IL10 in FIV(+) cats compared to normal cats. The elevated IL10:IL12 ratio is associated with the inability of FIV(+) cats to mount a successful immune response to secondary pathogens. Additionally, chronic antigenic (FIV) stimulation results in an increase in the percent of activated T cells expressing B7 and CTLA4 co-stimulatory molecules in infected cats. The expression of these molecules is associated with T cells that are undergoing apoptosis in the lymph nodes. As ligation of CTLA4 by B7 transduces a signal for induction of anergy, one can speculate that the activated T cells are capable of T cell-T cell interactions resulting in anergy and apoptosis. The inability of CD4(+) cells from FIV(+) cats to produce IL2 in response to recall antigens and the gradual loss of CD4(+) cell numbers could be due to B7-CTLA4 interactions. The chronic antigenemia may also lead to activation of CD4(+)CD25(+) T regulatory cells. Treg cells from FIV(+) cats are chronically activated and inhibit the mitogen-induced proliferative response of CD4(+)CD25(-) by down-regulating IL2 production. Although Treg cell activation can be antigen-specific, the suppressor function is not, and thus activated Treg cells would suppress responses to secondary pathogens as well as to FIV. Concomitant with the well-known virus-induced immune suppression is a progressive immune hyper-activation. Evidence for immune hyper-activation includes polyclonal B cell responses, gradual replacement of naïve CD4(+) and CD8(+) T cell phenotypes with activation phenotypes (CD62L(-), B7(+), CTLA4(+)), and the chronic activation of CD4(+)CD25(+) Treg cells. Thus lentivirus infections lead to severe immune dysregulation manifested as both chronic immune suppression and chronic immune activation. FIV infection of cats provides a number of advantages over other lentivirus infections as a model to study this immune dysregulation. It is a natural infection that has existed in balance with the cat's immune system for thousands of years. As such, the natural history and pathogenesis provides an excellent model to study the long-term relationships between AIDS lentivirus and host immune system function/dysregulation.

Derivation of infectious HIV-1 molecular clones with LTR mutations: sensitivity to the CD8+ cell noncytotoxic anti-HIV response

CD8(+) cells from healthy, asymptomatic HIV-1-infected individuals can inhibit HIV-1 replication in naturally or acutely infected CD4(+) cells in the absence of cell killing. This CD8(+) cell noncytotoxic anti-HIV response (CNAR) is mediated by a soluble CD8(+) cell antiviral factor (CAF). CNAR/CAF inhibits HIV-1 replication by blocking viral RNA transcription. HIV transcription is regulated by a variety of cis-acting DNA sequence elements within the proviral long terminal repeat (LTR). We hypothesized that one of the HIV-1 LTR proviral DNA sequence elements that binds host cell transcriptional factors is involved in this antiviral activity. To assess this possibility, we constructed full-length infectious HIV-1 molecular clones with mutations in the LTR elements NFAT, AP-1, IL-2 homology region, and the downstream ISRE. We also tested full-length infectious molecular clones that had deletions of either the NF-kappaB or Sp1 sites of the LTR or lacked functional Tat and TAR elements. Viruses generated from these molecular clones were used to acutely infect CD4(+) cells that subsequently were either co-cultured with CD8(+) cells from individuals that exhibited strong CNAR or cultured with CAF-containing fluids. The replication of all of the mutant HIV-1 viruses tested was substantially reduced in the presence of CNAR/CAF. These findings suggest that other regions in the viral LTR or other host cell processes are involved in the transcriptional block elicited by CNAR/CAF.

[Adaptive cell immune response against the hepatitis C virus infection]

Hepatitis C virus (HCV) infects around 175 million people worldwide and is one of the leading causes of chronic liver disease. Less than one third of patients infected with HCV are able to spontaneously clear the virus during acute infection, while most patients evolve to chronic infection. Control of viral replication has been associated to the cellular component of the host immune response. It is not fully understood what distinguish a successful cellular immune response. An integral interpretation of the numerous experimental findings may allow a better understanding of the immune mechanisms involved in the inability of the immune system to successfully control chronic HCV infection.

Vaccination against the feline immunodeficiency virus: the road not taken

Natural infection of domestic cats by the feline immunodeficiency virus (FIV) causes acquired immunodeficiency syndrome (AIDS). FIV is genetically related to human immunodeficiency virus (HIV), and the clinical and biological features of infections caused by feline and human viruses in their respective hosts are highly analogous. Although the obstacles to vaccinating against FIV and HIV would seem to be of comparable difficulty, a licensed vaccine against feline AIDS is already in widespread use in several countries. While this seemingly major advance in prevention of AIDS would appear to be highly instructive for HIV vaccine development, its message has not been heeded by investigators in the HIV field. This review endeavours to relate what has been learned about vaccination against feline AIDS, and to suggest what this may mean for HIV vaccine development.

Proinflammatory and type 1 cytokine expression in cervical mucosa during HIV-1 and human papillomavirus infection

Suppression of immune activation and increased inflammation are prevalent during viral infection. To investigate the role of inflammation in HIV transmission, we studied the infectious and inflammatory milieu in cervical mucosa from HIV-1- and human papillomavirus (HPV)-coinfected and HPV-monoinfected women. The numbers of cytokine-, chemokine-, and p24-expressing cells were determined using in situ imaging analysis and intracellular staining of p24 antigen. Significantly higher expression of the proinflammatory cytokines, interleukin (IL)-1alpha/beta, was seen in cervical tissue from HIV/HPV-coinfected as compared with HPV-monoinfected tissues, whereas IL-2- and interferon (IFN)-gamma-expressing cells were higher in HPV-monoinfected tissues. IL-10 was low in both groups, whereas IL-4 was significantly higher in HPV-monoinfected and HIV/HPV-coinfected tissues than in HIV/HPV-negative controls. RANTES and macrophage inflammatory protein (MIP)-1beta but not MIP-1alpha were significantly higher in the genital tract of HIV/HPV-coinfected as compared with HPV-monoinfected individuals and controls. HIV/HPV-coinfected tissues had a higher level of human leukocyte antigen D-related (HLA-DR)-expressing dendritic cells (DCs). There was a positive correlation between the number of CD4(+) and CD8(+) T cells as well as CD1a, IL-1alpha, and RANTES expression and p24 antigen-expressing cells in the HIV/HPV-coinfected tissues. These findings suggest the persistence of immune activation and inflammation in the genital tract of women with HPV monoinfection and in HIV-infected women coinfected with HPV.

Clarification of how HIV-1 DNA and protein immunizations may be better used to obtain HIV-1-specific mucosal and systemic immunity

More focused research on a mucosal HIV-1 vaccine is needed urgently. An increasing amount of collected data, using heterologous multimodality prime-booster strategies, suggest that an efficient and protective HIV-1 vaccine must generate broad, long-lasting HIV-specific CD8(+) cytotoxic T-lymphocyte and neutralizing antibody responses. In the mucosa, these responses would be most effective if a preferential stimulus of HIV-1 neutralizing secretory immunoglobulin A and G were obtained. The attractive property of mucosal immunization is the obtained mucosal and systemic immunity, whereas systemic immunization induces a more limited immunity, predominantly in systemic sites. These objectives will require new vaccine regimens, such as multiclade HIV DNA and protein vaccines (nef, tat, gag and env expressed in DNA plasmids) delivered onto mucosal surfaces with needle-free delivery methods, such as nasal drop, as well as oral and rectal/vaginal delivery, and should merit clinical trials.