HIV and drug misuse in the Edinburgh cohort

The Edinburgh cohort of intravenous drug users (IVDUs) became infected with HIV between 1983 and 1984. Before the era of effective therapy, many of these infected IVDUs displayed cognitive impairments on progressing to AIDS and were found to have HIV encephalitis (HIVE). Full autopsies were conducted on these patients, providing an opportunity to study the intersecting pathology of pure HIVE and drug use. High proviral load in the brain correlated well with the presence of giant cells and HIV p24 positivity. In presymptomatic HIV infection, IVDUs were found to have a lymphocytic infiltrate in the central nervous system (CNS). Apart from the expected microglial activation in the presence of HIV infection of the CNS, drug use in its own right was found to be associated with microglial activation. Examination of HIV-negative IVDUs revealed a number of neuropathologic features, including microglial activation, which may underpin HIV-related pathology in the CNS. HIV isolated from different regions of the brain was exclusively of R5-tropic type throughout the course of infection. Detailed studies of p17 and V3 sequences suggest that viral sequestration occurs in the CNS before the onset of AIDS and that increasing diversity of HIV variants within the brain is associated with increasing severity of HIVE. Because brain isolates have proved to be different from those in lymphoid tissue (and blood), it is likely that selective neuroadaptive pressures operate before HIVE supervenes. Drug abuse may be synergistic in this process through activation of microglia, breakdown of the blood-brain barrier, and direct neurotoxicity. Collections of clinically well-characterized HIV-infected tissues such as those in the Edinburgh Brain Bank are a vital resource to support ongoing studies of viral pathogenesis in the CNS and interactions with drug abuse.     

Gene therapy strategies: can we eradicate HIV?

Despite the tremendous advances in antiretroviral combination therapy over the last decade, eradication of HIV from the infected organism is still an elusive goal. Lifelong therapy is associated with potential long-term toxicity, adherence problems, and development of drug resistance. Thus, gene therapy approaches targeting viral eradication are still attractive. Here a number of studies have failed to show a clear clinical benefit yet. Current approaches were mainly limited by a low number of transduced cells and genotoxicity. The use of new vector systems and the right choice of target cells and improved transduction protocols may overcome these obstacles. Recent reports on the use of newly developed transgenes either allowing for an enrichment of transduced cells by an in vivo selection advantage or restoration of a functional immune system which is resistant to HIV infection nourished the hope for continuous progress in this field. Indeed the intriguing finding that HIV seems to be eradicated in an individual case study after stem cell transplantation with a mutant coreceptor (CCR5 delta 32 deletion) underlines the proof of the concept.     

Can antiretroviral therapy ever be stopped?

A pool of latently infected CD4+ T cells is established within the first few weeks of HIV infection. Because these memory T cells are inactive, the viral DNA integrated into their chromosomes remains invisible to immune surveillance and to antiretrovirals. Research shows that this reservoir of infected memory T cells does not decay in a clinically meaningful time frame--that is, within 60 years--in patients being treated with potent combination antiretrovirals. Even a hypothetical regimen that prevents any new infection of cells would not hasten the decay of this latent reservoir. Treatments that activate this reservoir have been studied in patients with suppressed viremia, but such interventions are highly toxic and have not succeeded so far. Studying rare individuals who manage to control activation of these latent cells may provide important clues to long-term control of HIV infection.     

Enfuvirtide, the first fusion inhibitor to treat HIV infection

Entry inhibitors are a new class of drugs for the treatment of HIV infection. Enfuvirtide is the first compound of this family to be approved for clinical use. It blocks HIV fusion to host cells. It is a synthetic peptide that mimics an HR2 fragment of gp41, blocking the formation of a six-helix bundle structure which is critical in the fusion process. Enfuvirtide is a good therapeutic option as rescue therapy in combination with other active antiretrovirals and works against different HIV-1 variants, including all group M subtypes and group O. However, it is not active against HIV-2. The main mechanism of resistance to enfuvirtide depends of the selection of changes in a 10-amino acid domain between residues 36 to 45 in the HR1 region of gp41. Single and double mutations in this region have been shown to result in high-level resistance to enfuvirtide. A negative impact of enfuvirtide-resistance mutations on viral fitness has been postulated, since resistance mutations tend to disappear soon after drug discontinuation and because immunologic benefits have been noticed despite virologic failure in patients undergoing enfuvirtide treatment.     

Tat-regulated expression of RNA interference: Triggers for the treatment of HIV infection

HIV infection is a lifelong problem requiring continual medication for suppressing viral replication. Current strategies of antiretroviral drug combinations have proven effective in prolonging the time from infection to the symptoms of AIDS. Nevertheless, chemotherapy is not without its problems, which include toxicities and eventual emergence of virus mutants that are resistant to current antiretrovirals. Gene therapy refers to the introduction of effector oligonucleotides to transiently or stably alter gene expression or the delivery and expression of an exogenous gene within a specific target cell. A number of studies have demonstrated effective silencing/inhibition of HIV-1 replication by using RNA-based effector oligonucleotides for RNA interference. In this study, we have taken advantage of lentiviral vector-mediated delivery of anti-HIV short hairpin RNA for the treatment of HIV infection in hematopoietic cells.     

Evaluation of a flow cytometric model for monitoring HIV antigen expression in vitro.

Using flow cytometry, monoclonal antibodies to the HIV proteins p24, gp41 and p17 were evaluated for their ability to detect HIV antigens associated with HIV-infected T cells. Mixtures containing varying ratios of HIV-infected and uninfected cells were subjected to analysis with these monoclonal antibodies. In most cases, the monoclonal antibodies identified the correct ratio of HIV-infected cells to uninfected cells in the mixtures tested. An HIV anti-p24 monoclonal antibody was selected for further studies. Flow cytometric analysis was performed on various populations of cells including uninfected, acutely infected and chronically infected cells. Based on cell population fluorescence intensity three distinct regions were identified. In the first region were cells having low level fluorescence that were considered negative for HIV antigens, a profile detected in uninfected cells, and in the majority of cells in the first days following acute HIV infection. In the second region were those cells exhibiting strong fluorescence such as chronically infected cells or acutely infected cells several days after infection. A third region was identified containing cells that were intermediate in fluorescence intensity. Cells exhibiting intermediate intensity fluorescence appeared to have low concentrations of HIV p24 antigen associated with them either through viral adsorption and uptake or through low level virus expression. These intermediate region cells appeared in the early stages following acute infection, and also when chronically infected cells and uninfected cells were permeabilized together, suggesting a 'leaching' of HIV proteins from highly infected cells to uninfected cells. This leaching type of phenomenon could present problems in determining gating parameters for positive cells since uninfected cells that have associated HIV antigens exhibit higher fluorescence intensity than uninfected cells.     

Role of HIV phenotypic assays in the management of HIV infection

Contemporary phenotypic assays such as the PhenoSense HIV assay are more straightforward to interpret than genotyping results because they do not require the expert interpretation of complex mutation patterns. The drug susceptibility data provides information for the clinician to select a treatment regimen effective against the predominant viral population circulating in the patient's blood. Compared to traditional phenotypic assays, the PhenoSense HIV assay uses a virus vector and a luciferase reporter gene to provide a quick and sensitive measure of viral replication. The main use of phenotypic assays at present is to identify those antiretroviral drugs that still retain activity against the patient's virus. Phenotypic assays are useful to provide guidance after treatment failure and to select a proper combination of drugs prior to initiation of therapy. They are also useful to detect transmission of resistance virus and to monitor HIV patients during early viral rebound. In essence, phenotypic testing provides information to target antiretroviral therapy against the predominant HIV variant in the patient for a prolonged suppression of viral replication, decreased mortality, and lower health-care costs.     

Peripheral blood monocytes derived from HIV+ individuals mediate antibody-dependent cellular cytotoxicity (ADCC)

Monocytes/macrophages serve a number of immunologic functions and play a major role in the host defense against infection. Abnormal functions of monocytes have been reported in AIDS and HIV+ individuals. A recent report from our laboratory demonstrated that peripheral blood monocytes (PBM) derived from AIDS patients were de novo "activated" as assessed by direct cell-mediated cytotoxicity (CMC) and secretion of cytotoxic factors and tumor necrosis factor-alpha (TNF alpha). Thus, both the direct cytotoxicity as well as the antibody-dependent cellular cytotoxicity (ADCC) exerted by the monocytes may contribute to the destruction of HIV-infected/coated cells and the immunopathogenesis of AIDS. The present study investigated the ability of HIV+ PBM to mediate ADCC against antibody-coated target cells in an 18-hr 51Cr release assay. Initial studies examined ADCC using a macrophage resistant target Raji and rabbit anti-Raji serum. The results show that the majority of PBM from HIV+ individuals mediate ADCC activity while the majority of PBM from normal healthy controls was not cytotoxic. While activation of PBM with recombinant interferon-gamma (rIFN-gamma) enhances the ADCC activity of normal PBM, treatment of HIV+ PBM with IFN-gamma resulted in significant enhancement of ADCC. Both untreated and treated PBM from HIV+ individuals had significantly higher ADCC than PBM from normal individuals. Of interest, a significant ADCC activity was found by PBM derived from two HIV- high risk individuals whether untreated or treated with rIFN-gamma. The ADCC results with RAJI target cells prompted us to investigate whether ADCC can also be obtained using HIV-infected T4+ cells. We selected a macrophage and TNF resistant T4+ CEM cell line as target for ADCC. The target was coated with inactivated HIV and pooled human anti-HIV serum was used. Studies with a few HIV+ individuals demonstrate that significant ADCC is obtained with PBM from HIV+ individuals but little or no ADCC by normal PBM and the ADCC was specific for HIV. The ADCC was also significantly enhanced by treatment of PBM with rIFN-gamma. The results of this study clearly indicate that PBM from HIV+ individuals are endowed with the capacity to mediate ADCC against HIV-infected/coated cells and thus, we postulate that PBM may play a direct role in vivo in lysis or suppression of HIV-coated/infected cells and in the pathogenesis of AIDS.     

1141180267Mechanism of HIV transmission across female primary genital epithelial cells

Our lab is utilizing human primary genital epithelial cultures to investigate the mechanism of HIV transmission across the female genital mucosa. Primary endometrial epithelial cells (ECs) grown on matrigel- coated cell inserts were used for HIV infection studies. EC's were infected with cell- free or cell- associated R5 and X4 virus strains. Infections were performed in the presence or absence of the appropriate macrophage (U937) or T-cell (Jurkat) target cell- line in basolateral compartments of cultures. Virus was quantified from supernatants using p24 ELISA. U373-CXCR4 and CCR5 magi cell lines were utilized to measure infectious virus and tropism. Sybrgreen real time PCR was used to detect viral RNA in cell lysates. Infectious HIV particles were found only in basolateral supernatants of EC's infected with X4 strains of HIV in the presence of appropriate target cells. This indicated that EC's may not be productively infected, but were only able to transmit HIV in the presence of target cells. These results were supported by the detection of higher levels of gag gene (CT-15) in X4 target cells compared to EC's (CT-25) using real-time PCR. No infectious virus was present in primary EC's infected with cell-free R5 strain, although gag gene product was detected by real time PCR in both R5 target cells as well as EC's. P24 levels in supernatants were not indicative of infectious virus. Our data indicates that R5 and X4 virus strains have differential abilities to cross the female genital mucosa to infect target cells. The presence of target cells appears to be critical for the production of infectious HIV particles under these culture conditions. These studies are providing important information regarding the ability of HIV-1 to cross the female genital mucosa.     

High proportion of PD‐1‐expressing CD4+ T cells in adipose tissue constitutes an immunomodulatory microenvironment that may support HIV persistence

We and others have demonstrated that adipose tissue is a reservoir for HIV. Evaluation of the mechanisms responsible for viral persistence may lead to ways of reducing these reservoirs. Here, we evaluated the immune characteristics of adipose tissue in HIV‐infected patients receiving antiretroviral therapy (ART) and in non‐HIV‐infected patients. We notably sought to determine whether adipose tissue's intrinsic properties and/or HIV induced alteration of the tissue environment may favour viral persistence. ART‐controlled HIV infection was associated with a difference in the CD4/CD8 T‐cell ratio and an elevated proportion of Treg cells in subcutaneous adipose tissue. No changes in Th1, Th2 and Th17 cell proportions or activation markers expression on T cell (Ki‐67, HLA‐DR) could be detected, and the percentage of CD69‐expressing resident memory CD4⁺ T cells was not affected. Overall, our results indicate that adipose‐tissue‐resident CD4⁺ T cells are not extensively activated during HIV infection. PD‐1 was expressed by a high proportion of tissue‐resident memory CD4⁺ T cells in both HIV‐infected patients and non‐HIV‐infected patients. Our findings suggest that adipose tissue's intrinsic immunomodulatory properties may limit immune activation and thus may strongly contribute to viral persistence.     

A new approach to an AIDS vaccine: creating antibodies to HIV vif will enable apobec3G to turn HIV-infection into a benign problem

For a decade, attempts to produce a vaccine that prevents HIV infection have been fruitless, and fresh approaches are required. Apobec3G is a natural defensin and a cytidine deaminase. Apobec3G induces a high rate of dC to dU mutation in the first minus strand of cDNA, causing degradation throughout the HIV genome that renders the virus effete. The viral infectivity factor (vif) of HIV is essential for efficient replication of that virus. Vif binds to apobec3G and induces its polyubiquitination, which enables HIV to evade apobec3G. This suggests that a vif-based vaccine which induced anti-vif antibodies, would prevent the neutralizing action of vif upon apobec3G. Then, with HIV-vif ineffective, apobec3G could act without hindrance to create a less aggressive, non-lethal HIV infection. Mutated vif impedes HIV infection. Slow progressors with vif 132S had 4-fold lower viral loads than those with vif 132R; and introducing vif 132S into HIV-1 caused a 5-fold decrease in viral replication. And in the absence of vif, HIV virions accumulate multiple defects in structural, enzymatic, and regulatory viral proteins. The success of a vif-based vaccine depends upon (1) a vif-antibody response, and (2) vif antibodies entering the cells that harbor HIV. First, antibodies to vif have been seen in frequencies ranging between 25% and 100% in patients infected with HIV-1. Second, transport of anti-vif antibodies into cells might occur via several mechanisms. Likeliest is that in viremic persons, antibodies would attach to cell-free virions which would piggyback the antibodies into CD4+ cells. Alternatively, a fusion protein between vif and a cell-surface receptor, e.g., CD4 or CCR5, might be used as vaccine antigen. Also, anti-vif antibodies might internalize after ligation of HIV virions budding on the cell surface, in the same way as monoclonal antibodies against porcine pseudorabies virus induced viral glycoproteins on the cell surface to internalize. Finally, monoclonal antibodies, using unknown mechanisms to enter cells, have been effective against several other intracellular pathogens. In summary, HIV-vif might be effective in a vaccine intended to ameliorate either preexisting or subsequent HIV infection.     

T cell anergy and activation are associated with suboptimal humoral responses to measles revaccination in HIV‐infected children on anti‐retroviral therapy in Nairobi,Kenya

HIV‐infected children are less capable of mounting and maintaining protective humoral responses to vaccination against measles compared to HIV‐uninfected children. This poses a public health challenge in countries with high HIV burdens. Administration of anti‐retroviral therapy (ART) and revaccinating children against measles is one approach to increase measles immunity in HIV‐infected children, yet it is not effective in all cases. Immune anergy and activation during HIV infection are factors that could influence responses to measles revaccination. We utilized a flow cytometry‐based approach to examine whether T cell anergy and activation were associated with the maintenance of measles‐specific immunoglobulin (Ig)G antibodies generated in response to measles revaccination in a cohort of HIV‐infected children on ART in Nairobi, Kenya. Children who sustained measles‐specific IgG for at least 1 year after revaccination displayed significantly lower programmed cell death 1 (PD‐1) surface expression on CD8⁺ T cells on a per‐cell basis and exhibited less activated CD4⁺ T cells compared to those unable to maintain detectable measles‐specific antibodies. Children in both groups were similar in age and sex, CD4⁺ T cell frequency, duration of ART treatment and HIV viral load at enrolment. These data suggest that aberrant T cell anergy and activation are associated with the impaired ability to sustain an antibody response to measles revaccination in HIV‐infected children on ART.     

Broadly Neutralizing Antibodies for HIV Eradication

Passive transfer of antibodies has long been considered a potential treatment modality for infectious diseases, including HIV. Early efforts to use antibodies to suppress HIV replication, however, were largely unsuccessful, as the antibodies that were studied neutralized only a relatively narrow spectrum of viral strains and were not very potent. Recent advances have led to the discovery of a large portfolio of human monoclonal antibodies that are broadly neutralizing across many HIV-1 subtypes and are also substantially more potent. These antibodies target multiple different epitopes on the HIV envelope, thus allowing for the development of antibody combinations. In this review, we discuss the application of broadly neutralizing antibodies (bNAbs) for HIV treatment and HIV eradication strategies. We highlight bNAbs that target key epitopes, such as the CD4 binding site and the V2/V3-glycan-dependent sites, and we discuss several bNAbs that are currently in the clinical development pipeline.     

Protective humoral immune responses to the human immunodeficiency virus induced in immunized pigs: a possible source of therapeutic immunoglobulin preparations.

The human immunodeficiency virus (HIV-1) induces progressive and fatal disease in infected hosts. Initially the human immune response appears to control HIV infection. This hypothesis is supported by the long latency period observed during HIV infection prior to development of the active disease state. Similarly the observation of fetal protection from HIV infection in some pregnant women who have high titered neutralizing antibody responses to the virus underscores the importance of the humoral response to HIV in limiting infection. Therefore antibody replacement therapy is likely to provide substantial clinical benefits in this and other infected populations. However, currently there is no safe source for human antibodies with the desired protective qualities necessary for passive immune therapies. For a passive immune therapy to be valid it must protect against a diverse collection of viral isolates. Such a task is likely to require a complex mixture of human antibodies or human substitute antibodies which are available in large quantities and target conserved regions of the viral envelope, such that protection from diverse isolates are realized. Porcine products have been used extensively in many human therapeutic replacement regimens. Their use is primarily due to genetic similarity of the two species at the amino acid level which results in a high acceptance of grafted prosthetics and excellent tolerance of repeatedly administered biologicals. Accordingly we have examined the immunoglobulin responses to the Human Immunodeficiency Virus (HIV-1) of the Yorkshire mixed breed pig. Immunized animals developed significant humoral immunity as judged by ELISA, Western blot, radioimmunoprecipitation, flow microfluorimetry as well as in functional assays including neutralization and syncytia inhibition. The high neutralizing activity obtained and the immunological similarity between human and porcine immunoglobulin suggests that further investigation into the use of porcine immunoglobulin as human replacement antibodies for the therapeutic treatment of HIV is warranted.     

Inhibition of human immunodeficiency virus infection in monocytes by monoclonal antibodies against leukocyte adhesion molecules.

CD4 is the surface receptor for HIV envelope. Some evidence exists, however, that other cell surface receptors may be involved in viral entry subsequent to the initial binding of gp120 to CD4. Antibodies to leukocyte integrin LFA-1, a major component of intercellular adhesive interactions, have been shown to inhibit HIV-induced syncytia formation. Using a stringent system for in vitro HIV infection of human leukocytes, we examine the ability of some monoclonal antibodies (mAb) against various adhesion-related molecules to block or partially inhibit productive viral replication. HIV-1 infection of target monocytes or T cells by cell-free virus was blocked completely or partially by some mAb that prevent cell-cell interactions (CD4, HLA-DR, LFA-1, LFA-3), but not by others (ICAM-1, MAC-1, gp150.95, CD2, CD3, CD14). The capacity for mAb to block HIV infection appears to be epitope-specific, and does not relate to the ability to block homotypic adhesion. HIV transmission from infected cells was more difficult to block than was infection by cell-free virus. Adhesion molecules may be involved in facilitating early stages of HIV infection, following gp120/CD4 binding but prior to viral integration, in a manner distinct from cell-cell adhesion.     

Targeted lysis of HIV-infected cells by natural killer cells armed and triggered by a recombinant immunoglobulin fusion protein: implications for immunotherapy

Natural killer (NK) cells play an important role in both innate and adaptive antiviral immune responses. The adaptive response typically requires that virus-specific antibodies decorate infected cells which then direct NK cell lysis through a CD16 mediated process termed antibody-dependent cellular cytotoxicity (ADCC). In this report, we employ a highly polymerized chimeric IgG1/IgA immunoglobulin (Ig) fusion protein that, by virtue of its capacity to extensively crosslink CD16, activates NK cells while directing the lysis of infected target cells. We employ HIV as a model system, and demonstrate that freshly isolated NK cells preloaded with an HIV gp120-specific chimeric IgG1/IgA fusion protein efficiently lyse HIV-infected target cells at picomolar concentrations. NK cells pre-armed in this manner retain the capacity to kill targets over an extended period of time. This strategy may have application to other disease states including various viral infections and cancers.     

Biological significance of the antibody response to HIV antigens expressed on the cell surface

Summary Human antibodies to HIV antigens expressed on the surface of infected cells may inhibit cell fusion with uninfected CD 4-positive cells and mediate killing of the infected cells by effector cells bearing the Fc receptor.Sequential sera from ten HIV-antibody seroconverted men, of which five progressed to ARC or AIDS (CDC stage IV) during the follow-up period of two years, were tested for the ability to inhibit CD 4-dependent cell fusion, (CFI) and to mediate antibody-dependent cellular cytotoxicity (ADCC).Nine patients developed HIV-specific ADCC and seven CFI-antibodies using the HIV strain HTLV-IIIB as target antigen. These antibodies appeared approximately at the same time 2–12 months after primary infection, defined as antibody seroconversion or antigenaemia. ADCC antibodies were detectable at higher titers as compared to CFI-antibodies. All sera of asymptomatic individuals (CDC stage II and III) were CFI antibody positive and had a higher mean ADCC titer as compared to sera from patients progressing to AIDS or ARC.ADCC and CFI antibodies coincided in some cases in the complete absence of core antibodies. Because the relationship between ADCC and CFI was not exclusive it is concluded that distinct domains of the HIV envelope induce natural antibodies mediating ADCC and CFI.