Impairment of Gag-specific CD8(+) T-cell function in mucosal and systemic compartments of simian immunodeficiency virus mac251- and simian-human immunodeficiency virus KU2-infected macaques

Differential Inhibitory Receptor Expression on T Cells Delineates Functional Capacities in Chronic Viral Infection

Inhibitory receptors have been extensively described for their importance in regulating immune responses in chronic infections and cancers. Blocking the function of inhibitory receptors such as PD-1, CTLA-4, 2B4, Tim-3, and LAG-3 has shown promise for augmenting CD8 T cell activity and boosting pathogen-specific immunity. However, the prevalence of inhibitory receptors on CD4 T cells and their relative influence on CD4 T cell functionality in chronic HIV infection remains poorly described. We therefore determined and compared inhibitory receptor expression patterns of 2B4, CTLA-4, LAG-3, PD-1, and Tim-3 on virus-specific CD4 and CD8 T cells in relation to their functional T cell profile. In chronic HIV infection, inhibitory receptor distribution differed markedly between cytokine-producing T cell subsets with, gamma interferon (IFN-γ)- and tumor necrosis factor alpha (TNF-α)-producing cells displaying the highest and lowest prevalence of inhibitory receptors, respectively. Blockade of inhibitory receptors differentially affected cytokine production by cells in response to staphylococcal enterotoxin B stimulation. CTLA-4 blockade increased IFN-γ and CD40L production, while PD-1 blockade strongly augmented IFN-γ, interleukin-2 (IL-2), and TNF-α production. In a Friend retrovirus infection model, CTLA-4 blockade in particular was able to improve control of viral replication. Together, these results show that inhibitory receptor distribution on HIV-specific CD4 T cells varies markedly with respect to the functional subset of CD4 T cells being analyzed. Furthermore, the differential effects of receptor blockade suggest novel methods of immune response modulation, which could be important in the context of HIV vaccination or therapeutic strategies.IMPORTANCE Inhibitory receptors are important for limiting damage by the immune system during acute infections. In chronic infections, however, their expression limits immune system responsiveness. Studies have shown that blocking inhibitory receptors augments CD8 T cell functionality in HIV infection, but their influence on CD4 T cells remains unclear. We assessed the expression of inhibitory receptors on HIV-specific CD4 T cells and their relationship with T cell functionality. We uncovered differences in inhibitory receptor expression depending on the CD4 T cell function. We also found differences in functionality of CD4 T cells following blocking of different inhibitory receptors, and we confirmed our results in a Friend virus retroviral model of infection in mice. Our results show that inhibitory receptor expression on CD4 T cells is linked to CD4 T cell functionality and could be sculpted by blockade of specific inhibitory receptors. These data reveal exciting possibilities for the development of novel treatments and immunotherapeutics.

Dysregulation of Systemic and Mucosal Humoral Responses to Microbial and Food Antigens as a Factor Contributing to Microbial Translocation and Chronic Inflammation in HIV-1 Infection

HIV-1 infection is associated with an early and profound depletion of mucosal memory CD4+ T cells, a population that plays an indispensable role in the regulation of isotype switching and transepithelial transport of antibodies. In this study, we addressed whether the depletion of CD4+ T cell in HIV-1-infected individuals results in altered humoral responses specific to antigens encountered at mucosal surfaces. Comprehensive protein microarray of systemic humoral responses to intestinal microbiota demonstrated reduced IgG responses to antigens derived from Proteobacteria and Firmicutes but not Bacteroidetes. Importantly, intestinal secretions of antiretroviral therapy-treated HIV-1-infected individuals exhibited a significant elevation of IgM levels and decreased IgA/IgM and IgG/IgM ratios of antibodies specific to a variety of microbial and food antigens. The presented findings indicate reduced competence of mucosal B cells for class switch recombination from IgM to other isotypes limiting their capacity to react to changing antigenic variety in the gut lumen. Decreased availability of microbiota-specific IgA and IgG may be an important factor contributing to the translocation of microbial antigens across the intestinal mucosal barrier and their systemic dissemination that drives chronic inflammation in HIV-1-infected individuals.

The TB-specific CD4(+) T cell immune repertoire in both cynomolgus and rhesus macaques largely overlap with humans

Non-human primate (NHP) models of tuberculosis (TB) immunity and pathogenesis, especially rhesus and cynomolgus macaques, are particularly attractive because of the high similarity of the human and macaque immune systems. However, little is known about the MHC class II epitopes recognized in macaques, thus hindering the establishment of immune correlates of immunopathology and protective vaccination. We characterized immune responses in rhesus macaques vaccinated against and/or infected with Mycobacterium tuberculosis (Mtb), to a panel of antigens currently in human vaccine trials. We defined 54 new immunodominant CD4(+) T cell epitopes, and noted that antigens immunodominant in humans are also immunodominant in rhesus macaques, including Rv3875 (ESAT-6) and Rv3874 (CFP10). Pedigree and inferred restriction analysis demonstrated that this phenomenon was not due to common ancestry or inbreeding, but rather presentation by common alleles, as well as, promiscuous binding. Experiments using a second cohort of rhesus macaques demonstrated that a pool of epitopes defined in the previous experiments can be used to detect T cell responses in over 75% of individual monkeys. Additionally, 100% of cynomolgus macaques, irrespective of their latent or active TB status, responded to rhesus and human defined epitope pools. Thus, these findings reveal an unexpected general repertoire overlap between MHC class II epitopes recognized in both species of macaques and in humans, showing that epitope pools defined in humans can also be used to characterize macaque responses, despite differences in species and antigen exposure. The results have general implications for the evaluation of new vaccines and diagnostics in NHPs, and immediate applicability in the setting of macaque models of TB.

Animal models for viral infection and cell exhaustion

PURPOSE OF REVIEW

Despite eliciting an early antiviral T cell response, HIV-specific T cells are unable to prevent disease progression, partly because of their loss of effector functions, known as T cell exhaustion. Restoring this T cell functionality represents a critical step for regaining immunological control of HIV-1 replication, and may be fundamental for the development of a functional cure for HIV. In this context, the use of animal models is invaluable for evaluating the efficacy and mechanisms of novel therapeutics aimed at reinvigorating T cell functions.

RECENT FINDINGS

Although nonhuman primates continue to be a mainstay for studying HIV pathogenesis and therapies, recent advances in humanized mouse models have improved their ability to recapitulate the features of cell exhaustion during HIV infection. Targeting coinhibitory receptors in HIV-infected and simian immunodeficiency virus (SIV)-infected animals has resulted in viral load reductions, presumably by reinvigorating the effector functions of T cells. Additionally, studies combining programmed death-1 (PD-1) blockade with suppressive antiretroviral therapy provide further support to the use of coinhibitory receptor blockades in restoring T cell function by delaying viral load rebound upon antiretroviral therapy interruption. Future in-vivo studies should build on recent in-vitro data, supporting the simultaneous targeting of multiple regulators of cell exhaustion.

SUMMARY

In this review, we describe the most recent advances in the use of animal models for the study of cell exhaustion following HIV/SIV infection. These findings suggest that the use of animal models is increasingly critical in translating immunotherapeutics into clinical practice.

Acute HIV infection: it takes more than guts

PURPOSE OF REVIEW

To understand the cellular and molecular mechanisms of acute HIV pathogenesis.

RECENT FINDINGS

Recent studies have given us new insights into the mechanisms of acute HIV pathogenesis by demonstrating the 'systemic' destruction of the CD4 memory T cell compartment. This destruction occurs well before the emergence of a strong and broad immune response, highlighting the failure of the immune response to contain early viral infection and destruction. However, recent data also suggest that very few founder populations of cells are infected early, at the portal of entry, making them ideal targets for vaccine-induced immune responses that may aid in the effective control of early infection and transmission.

SUMMARY

HIV causes a massive destruction of memory CD4 T cells during the early acute phase of infection. This destruction proceeds largely in the absence of emerging antiviral immune responses, and severely disables the ability of the immune system to generate secondary immune responses. Early preservation of the memory CD4 compartment by shifting emphasis of antiretroviral therapeutic strategies to early treatment, and development of vaccines that can induce strong and broad immune responses, will be critical to prevent the destructive effects of early HIV infection.

The magnitude and kinetics of the mucosal HIV-specific CD8+ T lymphocyte response and virus RNA load in breast milk

BACKGROUND

The risk of postnatal HIV transmission is associated with the magnitude of the milk virus load. While HIV-specific cellular immune responses control systemic virus load and are detectable in milk, the contribution of these responses to the control of virus load in milk is unknown.

METHODS

We assessed the magnitude of the immunodominant GagRY11 and subdominant EnvKY9-specific CD8+ T lymphocyte response in blood and milk of 10 A*3002+, HIV-infected Malawian women throughout the period of lactation and correlated this response to milk virus RNA load and markers of breast inflammation.

RESULTS

The magnitude and kinetics of the HIV-specific CD8+ T lymphocyte responses were discordant in blood and milk of the right and left breast, indicating independent regulation of these responses in each breast. However, there was no correlation between the magnitude of the HIV-specific CD8+ T lymphocyte response and the milk virus RNA load. Further, there was no correlation between the magnitude of this response and markers of breast inflammation.

CONCLUSIONS

The magnitude of the HIV-specific CD8+ T lymphocyte response in milk does not appear to be solely determined by the milk virus RNA load and is likely only one of the factors contributing to maintenance of low virus load in milk.

Mucosal immunity and HIV-1 infection: applications for mucosal AIDS vaccine development

Natural transmission of human immunodeficiency virus type 1 (HIV-1) occurs through gastrointestinal and vaginal mucosa. These mucosal tissues are major reservoirs for initial HIV replication and amplification, and the sites of rapid CD4(+) T cell depletion. In both HIV-infected humans and SIV-infected macaques, massive loss of CD4(+) CCR5(+) memory T cells occurs in the gut and vaginal mucosa within the first 10-14 days of infection. Induction of local HIV-specific immune responses by vaccines may facilitate effective control of HIV or SIV replication at these sites. Vaccines that induce mucosal responses, in particular CD8(+) cytotoxic T lymphocytes (CTL), have controlled viral replication at mucosal sites and curtailed systemic dissemination. Thus, there is strong justification for development of next generation vaccines that induce mucosal immune effectors against HIV-1 including CD8(+) CTL, CD4(+) T helper cells and secretory IgA. In addition, further understanding of local innate mechanisms that impact early viral replication will greatly inform future vaccine development. In this review, we examine the current knowledge concerning mucosal AIDS vaccine development. Moreover, we propose immunization strategies that may be able to elicit an effective immune response that can protect against AIDS as well as other mucosal infections.

Sex steroid hormones, hormonal contraception, and the immunobiology of human immunodeficiency virus-1 infection

Worldwide, an increasing number of women use oral or injectable hormonal contraceptives. However, inadequate information is available to aid women and health care professionals in weighing the potential risks of hormonal contraceptive use in individuals living with HIV-1 or at high risk of infection. Numerous epidemiological studies and challenge studies in a rhesus macaque model suggest that progesterone-based contraceptives increase the risk of HIV-1 infection in humans and simian immunodeficiency virus (SIV) infection in macaques, accelerate disease progression, and increase viral shedding in the genital tract. However, because several other studies in humans have not observed any effect of exogenously administered progesterone on HIV-1 acquisition and disease progression, the issue continues to be a topic of intense research and ongoing discussion. In contrast to progesterone, systemic or intravaginal treatment with estrogen efficiently protects female rhesus macaques against the transmission of SIV, likely by enhancing the natural protective properties of the lower genital tract mucosal tissue. Although the molecular and cellular mechanisms underlying the effect of sex steroid hormones on HIV-1 and SIV acquisition and disease progression are not well understood, progesterone and estrogen are known to regulate a number of immune mechanisms that may exert an effect on retroviral infection. This review summarizes current knowledge of the effects of various types of sex steroid hormones on immune processes involved in the biology of HIV-1 infection.

Local replication of simian immunodeficiency virus in the breast milk compartment of chronically-infected, lactating rhesus monkeys

Breast milk transmission remains a major mode of infant HIV acquisition, yet anatomic and immunologic forces shaping virus quasispecies in milk are not well characterized. In this study, phylogenic analysis of envelope sequences of milk SIV variants revealed groups of nearly identical viruses, indicating local virus production. However, comparison of the patterns and rates of CTL escape of blood and milk virus demonstrated only subtle differences between the compartments. These findings suggest that a substantial fraction of milk viruses are produced by locally-infected cells, but are shaped by cellular immune pressures similar to that in the blood.

Mucosa and vaccine-induced immune protection in nonhuman primates

PURPOSE OF REVIEW

The purpose of this article is to review some of the recent progress in the development of HIV vaccines that induce immune responses in mucosal tissues that may correlate with protection of the mucosal CD4 T cell compartment.

RECENT FINDINGS

Mucosal tissues are the primary sites for viral entry and the resident CD4 T cells serve as readily available target cells for active infection. Viral entry is associated with a massive destruction of these cells. The resident CD4 cells are memory T cells and hence play an important role in the generation of secondary immune responses. Protecting these CD4 T cells is critical for controlling viral infection and for preserving immune competence. Numerous mucosal vaccine regimens currently under development have been shown to induce both B and T cell responses in mucosal tissues. Though induction of neutralizing antibodies still remains an elusive goal, the demonstration that antibodies can have a protective role through alternative mechanisms offers hope that humoral responses can be harnessed to yield a protective response in mucosal tissues.

SUMMARY

The mucosal immune system is highly compartmentalized and hence immunization regimens need to target mucosal tissues to be successful in inducing protective immune responses in mucosal tissues.

Evaluation of antiretrovirals in animal models of HIV infection

Animal models of HIV infection have played an important role in the development of antiretroviral drugs. Although each animal model has its limitations and never completely mimics HIV infection of humans, a carefully designed study allows experimental approaches that are not feasible in humans, but that can help to better understand disease pathogenesis and to provide proof-of-concept of novel intervention strategies. While rodent and feline models are useful for initial screening, further testing is best done in non-human primate models, such as simian immunodeficiency virus (SIV) infection of macaques, because they share more similarities with HIV infection of humans. In the early years of the HIV pandemic, non-human primate models played a relatively minor role in the antiretroviral drug development process. Since then, a better understanding of the disease and the development of better drugs and assays to monitor antiviral efficacy have increased the usefulness of the animal models. In particular, non-human primate models have provided proof-of-concept for (i) the benefits of chemoprophylaxis and early treatment, (ii) the preclinical efficacy of novel drugs such as tenofovir, (iii) the virulence and clinical significance of drug-resistant viral mutants, and (iv) the role of antiviral immune responses during drug therapy. Ongoing comparison of results obtained in animal models with those observed in human studies will further validate and improve these animal models so they can continue to help advance our scientific knowledge and to guide clinical trials. This article forms part of a special issue of Antiviral Research marking the 25th anniversary of antiretroviral drug discovery and development, Vol 85, issue 1, 2010.

The efficacy of T cell-mediated immune responses is reduced by the envelope protein of the chimeric HIV-1/SIV-KB9 virus in vivo

Gp120 is a critical component of the envelope of HIV-1. Its role in viral entry is well described. In view of its position on the viral envelope, gp120 is a part of the retrovirus that immune cells encounter first and has the potential to influence antiretroviral immune responses. We propose that high levels of gp120 are present in tissues and may contribute to the failure of the immune system to fully control and ultimately clear the virus. Herein, we show for the first time that lymphoid tissues from acutely HIV-1/SIV (SHIV)-KB9-infected macaques contain deposits of gp120 at concentrations that are high enough to induce suppressive effects on T cells, thus negatively regulating the antiviral CTL response and contributing to virus survival and persistence. We also demonstrate that SHIV-KB9 gp120 influences functional T cell responses during SHIV infection in a manner that suppresses degranulation and cytokine secretion by CTLs. Finally, we show that regulatory T cells accumulate in lymphoid tissues during acute infection and that they respond to gp120 by producing TGFbeta, a known suppressant of cytotoxic T cell activity. These findings have significant implications for our understanding of the contribution of non-entry-related functions of HIV-1 gp120 to the pathogenesis of HIV/AIDS.

Potent simian immunodeficiency virus-specific cellular immune responses in the breast milk of simian immunodeficiency virus-infected, lactating rhesus monkeys

Breast milk transmission of HIV is a leading cause of infant HIV/AIDS in the developing world. Remarkably, only a small minority of breastfeeding infants born to HIV-infected mothers contract HIV via breast milk exposure, raising the possibility that immune factors in the breast milk confer protection to the infants who remain uninfected. To model HIV-specific immunity in breast milk, lactation was pharmacologically induced in Mamu-A*01(+) female rhesus monkeys. The composition of lymphocyte subsets in hormone-induced lactation breast milk was found to be similar to that in natural lactation breast milk. Hormone-induced lactating monkeys were inoculated i.v. with SIVmac251 and CD8(+) T lymphocytes specific for two immunodominant SIV epitopes, Gag p11C and Tat TL8, and SIV viral load were monitored in peripheral blood and breast milk during acute infection. The breast milk viral load was 1-2 logs lower than plasma viral load through peak and set point of viremia. Surprisingly, whereas the kinetics of the SIV-specific cellular immunity in breast milk mirrored that of the blood, the peak magnitude of the SIV-specific CD8(+) T lymphocyte response in breast milk was more than twice as high as the cellular immune response in the blood. Furthermore, the appearance of the SIV-specific CD8(+) T lymphocyte response in breast milk was associated with a reduction in breast milk viral load, and this response remained higher than that in the blood after viral set point. This robust viral-specific cellular immune response in breast milk may contribute to control of breast milk virus replication.

Generation of functionally active HIV-1 specific CD8+ CTL in intestinal mucosa following mucosal, systemic or mixed prime-boost immunization

Gastrointestinal and vaginal mucosa are major sites of entry in natural HIV infection and therefore the preferred sites to elicit high-avidity CD8+ CTL by vaccination. We directly compare systemic and mucosal immunization in mice after DNA priming and boosting with rgp160 env expressed either in MVA or Ad for their ability to induce mucosal as well as systemic HIV-specific CTL. The optimal CTL response in the gut mucosa was observed after priming with the HIV-1 gp160 env DNA vaccine and boosting with rMVA or rAd encoding the same envelope gene all administered intrarectally (IR). Maximum levels of high-avidity CD8+ T cells were seen in intestinal lamina propria following this regimen. When the prime and boost routes were distinct, the delivery site of the boost had a greater impact than the DNA priming. IM DNA prime and IR rMVA boost were more effective than IR DNA prime and IM rMVA boost for eliciting mucosal CD8+ T-cell avidity. A systemic DNA-prime-followed by systemic rMVA boost induced high levels of high-avidity CD8+ T cells systemically, but responses were undetectable in mucosal sites. A single systemic immunization with rMVA was sufficient to induce high-avidity IFN-gamma secreting CD8+ T cells in systemic organs, whereas a single mucosal immunization with rMVA was not sufficient to elicit high-avidity CD8+ T cells in mucosa. Thus, a heterologous mucosal DNA prime-viral vectored boost strategy was needed. The requirement for a heterologous DNA prime-recombinant viral boost strategy for generation of high-avidity CD8+ T cells in mucosal sites in mice may be more stringent than for the induction of high-avidity CD8+ T cells in systemic compartments.

Enhancement of human immunodeficiency virus (HIV)-specific CD8+ T cells in cerebrospinal fluid compared to those in blood among antiretroviral therapy-naive HIV-positive subjects

During untreated human immunodeficiency virus type 1 (HIV-1) infection, virus-specific CD8(+) T cells partially control HIV replication in peripheral lymphoid tissues, but host mechanisms of HIV control in the central nervous system (CNS) are incompletely understood. We characterized HIV-specific CD8(+) T cells in cerebrospinal fluid (CSF) and peripheral blood among seven HIV-positive antiretroviral therapy-naïve subjects. All had grossly normal brain magnetic resonance imaging and spectroscopy and normal neuropsychometric testing. Frequencies of epitope-specific CD8(+) T cells by direct tetramer staining were on average 2.4-fold higher in CSF than in blood (P = 0.0004), while HIV RNA concentrations were lower. Cells from CSF were readily expanded ex vivo and responded to a broader range of HIV-specific human leukocyte antigen class I restricted optimal peptides than did expanded cells from blood. HIV-specific CD8(+) T cells, in contrast to total CD8(+) T cells, in CSF and blood were at comparable maturation states, as assessed by CD45RO and CCR7 staining. The strong relationship between higher T-cell frequencies and lower levels of viral antigen in CSF could be the result of increased migration to and/or preferential expansion of HIV-specific T cells within the CNS. This suggests an important role for HIV-specific CD8(+) T cells in control of intrathecal viral replication.

High frequencies of polyfunctional HIV-specific T cells are associated with preservation of mucosal CD4 T cells in bronchoalveolar lavage

The mechanisms underlying the massive gastrointestinal tract CD4 T-cell depletion in human immunodeficiency virus (HIV) infection are not well understood nor is it clear whether similar depletion is manifest at other mucosal surfaces. Studies of T-cell and virus dynamics in different anatomical sites have begun to illuminate the pathogenesis of HIV-associated disease. Here, we studied depletion and HIV infection frequencies of CD4 T cells from the gastrointestinal tract, bronchoalveolar lavage (BAL), and blood with the frequencies and functional profiles of HIV-specific T cells in these anatomically distinct sites in HIV-infected individuals. The major findings to emerge were as follows: (i) depletion of gastrointestinal CD4 T cells is associated with high frequencies of infected CD4 T cells; (ii) HIV-specific T cells are present at low frequencies in the gastrointestinal tract compared to blood; (iii) BAL CD4 T cells are not massively depleted during the chronic phase; (iv) infection frequencies of BAL CD4 T cells are similar to those in blood; (v) significantly higher frequencies and increased functionality of HIV-specific T cells were observed in BAL compared to blood. Taken together, these data suggest mechanisms for mucosal CD4 T-cell depletion and interventions that might circumvent global depletion of mucosal CD4 T cells.

HIV infection and the gastrointestinal immune system

There has recently been a resurgence of interest in the gastrointestinal pathology observed in patients infected with HIV. The gastrointestinal tract is a major site of HIV replication, which results in massive depletion of lamina propria CD4 T cells during acute infection. Highly active antiretroviral therapy leads to incomplete suppression of viral replication and substantially delayed and only partial restoration of gastrointestinal CD4 T cells. The gastrointestinal pathology associated with HIV infection comprises significant enteropathy with increased levels of inflammation and decreased levels of mucosal repair and regeneration. Assessment of gut mucosal immune system has provided novel directions for therapeutic interventions that modify the consequences of acute HIV infection.

Selective induction of cell-mediated immunity and protection of rhesus macaques from chronic SHIV(KU2) infection by prophylactic vaccination with a conserved HIV-1 envelope peptide-cocktail

Infection of Indian-origin rhesus macaques by the simian human immunodeficiency virus (SHIV) is considered to be a suitable preclinical model for directly testing efficacy of vaccine candidates based on the HIV-1 envelope. We used this model for prophylactic vaccination with a peptide-cocktail comprised of highly conserved HIV-1 envelope sequences immunogenic/antigenic in macaques and humans. Separate groups of macaques were immunized with the peptide-cocktail by intravenous and subcutaneous routes using autologous dendritic cells (DC) and Freund's adjuvant, respectively. The vaccine elicited antigen specific IFN-gamma-producing cells and T-cell proliferation, but not HIV-neutralizing antibodies. The vaccinated animals also exhibited efficient cross-clade cytolytic activity against target cells expressing envelope proteins corresponding to HIV-1 strains representative of multiple clades that increased after intravenous challenge with pathogenic SHIV(KU2). Virus-neutralizing antibodies were either undetectable or present only transiently at low levels in the control as well as vaccinated monkeys after infection. Significant control of plasma viremia leading to undetectable levels was achieved in majority of vaccinated monkeys compared to mock-vaccinated controls. Monkeys vaccinated with the peptide-cocktail using autologous DC, compared to Freund's adjuvant, and the mock-vaccinated animals, showed significantly higher IFN-gamma production, higher levels of vaccine-specific IFN-gamma producing CD4(+) cells and significant control of plasma viremia. These results support DC-based vaccine delivery and the utility of the conserved HIV-1 envelope peptide-cocktail, capable of priming strong cell-mediated immunity, for potential inclusion in HIV vaccination strategies.

Early establishment and antigen dependence of simian immunodeficiency virus-specific CD8+ T-cell defects

Differentiation and survival defects of human immunodeficiency virus (HIV)-specific CD8(+) T cells may contribute to the failure of HIV-specific CD8(+) T cells to control HIV replication. It is not known, however, whether simian immunodeficiency virus (SIV)-infected rhesus macaques show comparable defects in these virus-specific CD8(+) T cells or when such defects are established during infection. Peripheral blood cells from acutely and chronically infected rhesus macaques were stained ex vivo for memory subpopulations and examined by in vitro assays for apoptosis sensitivity. We show here that SIV-specific CD8(+) T cells from chronically SIV infected rhesus macaques show defects comparable to those observed in HIV infection, namely, a skewed CD45RA(-) CD62L(-) effector memory phenotype, reduced Bcl-2 levels, and increased levels of spontaneous and CD95-induced apoptosis of SIV-specific CD8(+) T cells. Longitudinal studies showed that the survival defects and phenotype are established early in the first few weeks of SIV infection. Most importantly, they appear to be antigen driven, since most probably the loss of epitope recognition due to viral escape results in the reversal of the phenotype and reduced apoptosis sensitivity, something we observed also for animals treated with antiretroviral therapy. These findings further support the use of SIV-infected rhesus macaques to investigate the phenotypic changes and apoptotic defects of HIV-specific CD8(+) T cells and indicate that such defects of HIV-specific CD8(+) T cells are the result of chronic antigen stimulation.

A novel functional CTL avidity/activity compartmentalization to the site of mucosal immunization contributes to protection of macaques against simian/human immunodeficiency viral depletion of mucosal CD4+ T cells

The presence of high-avidity CTLs in the right compartment can greatly affect clearance of a virus infection (for example, AIDS viral infection of and dissemination from mucosa). Comparing mucosal vs systemic immunization, we observed a novel compartmentalization of CTL avidity and proportion of functionally active Ag-specific CD8(+) T cells to tissues proximal to sites of immunization. Whereas both s.c. and intrarectal routes of immunization induced tetramer(+) cells in the spleen and gut, the mucosal vaccine induced a higher percentage of functioning IFN-gamma(+) Ag-specific CD8(+) T cells in the gut mucosa in mice. Translating to the CD8(+) CTL avidity distribution in rhesus macaques, intrarectal vaccination induced more high-avidity mucosal CTL than s.c. vaccination and protection of mucosal CD4(+) T cells from AIDS viral depletion, whereas systemic immunization induced higher avidity IFN-gamma-secreting cells in the draining lymph nodes but no protection of mucosal CD4(+) T cells, after mucosal challenge with pathogenic simian/human immunodeficiency virus. Mucosal CD4(+) T cell loss is an early critical step in AIDS pathogenesis. The preservation of CD4(+) T cells in colonic lamina propria and the reduction of virus in the intestine correlated better with high-avidity mucosal CTL induced by the mucosal AIDS vaccine. This preferential localization of high-avidity CTL may explain previous differences in vaccination results and may guide future vaccination strategy.

[Dr. Voronoff's curious glandular xeno-implants]

Dr. Serge Voronoff visited Brazil during the Jornadas Médicas of 1928, where he demonstrated his xenotransplantation technique to the local medical community. The present article uses newspaper clippings from that time to illustrate how this controversial surgery and Voronoff's alleged miraculous preservation of good health and longevity was viewed in the popular imagination. Voronoff's initiative paved the way for other health professionals to report on their surgical experiences with xenotransplantation and also popularized the topic, which became the subject of Carnival songs and sardonic jokes in the press. An analysis is offered, based on current scientific parameters, along with a suggestion concerning the possible involvement of xenotransplantation in HIV epidemiology.

SIV-specific CD8+ T cells express high levels of PD1 and cytokines but have impaired proliferative capacity in acute and chronic SIVmac251 infection

Programmed death-1 (PD-1) is a critical mediator of virus-specific CD8+ T-cell exhaustion. Here, we examined the expression of PD-1 on simian immunodeficiency virus (SIV)-specific CD8+ T cells and its possible involvement in regulation of cytokine production, proliferation, and survival of these cells. The majority of SIV-specific CD8+ T cells expressed a PD-1(high) phenotype, independent of their differentiation status, in all tissues tested. PD-1 expression gradually declined on CD8+ T cells specific for SIV-derived epitopes that had undergone mutational escape, indicating that antigen-specific TCR stimulation is the primary determinant of PD-1 expression. SIV-specific PD-1(high)CD8+ T cells produced IFN-gamma, TNF-alpha, and IL-2 under cognate peptide stimulation. While CD8+ T cells that proliferated in response to antigen had a PD-1(high) phenotype, it was determined that there was a reduced proliferative capacity of PD-1(high) compared with PD-1(low) SIV-specific CD8+ T cells. PD-1(high) SIV-specific CD8+ T cells were highly susceptible to cell death leading to loss of such cells after in vitro stimulation. Thus, PD-1 is a negative regulator of SIV-specific CD8+ T cells, operating predominantly through the induction of cell death. Manipulation of the interaction of PD-1 with its ligands could thus potentially restore the CD8+ T-cell responses in SIV infection.

Differential effects of IL-21 and IL-15 on perforin expression, lysosomal degranulation, and proliferation in CD8 T cells of patients with human immunodeficiency virus-1 (HIV)

An urgent need exists to devise strategies to augment antiviral immune responses in patients with HIV who are virologically well controlled and immunologically stable on highly active antiretroviral therapy (HAART). The objective of this study was to compare the immunomodulatory effects of the cytokines interleukin (IL)-21 with IL-15 on CD8 T cells in patients with HIV RNA of less than 50 copies/mL and CD4 counts greater than 200 cells/mm.(3) Patient CD8 T cells displayed skewed maturation and decreased perforin expression compared with healthy controls. Culture of freshly isolated patient peripheral-blood mononuclear cells (PBMCs) for 5 hours to 5 days with IL-21 resulted in up-regulation of perforin in CD8 T cells, including memory and effector subsets and virus-specific T cells. IL-21 did not induce T-cell activation or proliferation, nor did it augment T-cell receptor (TCR)-induced degranulation. Treatment of patient PBMCs with IL-15 resulted in induction of perforin in association with lymphocyte proliferation and augmentation of TCR-induced degranulation. Patient CD8 T cells were more responsive to cytokine effects than the cells of healthy volunteers. We conclude that CD8 T cells of patients with HIV can be modulated by IL-21 to increase perforin expression without undergoing overt cellular activation. IL-21 could potentially be useful for its perforin-enhancing properties in anti-HIV immunotherapy.

A DNA prime-oral Listeria boost vaccine in rhesus macaques induces a SIV-specific CD8 T cell mucosal response characterized by high levels of alpha4beta7 integrin and an effector memory phenotype

In this study in Rhesus macaques, we tested whether IL-12 or IL-15 in a DNA prime-oral Listeria boost amplifies the SIV-Gag-specific CD8 mucosal response. SIV-specific CD8 T cells were demonstrated in the peripheral blood (PB) in all test vaccine groups, but not the control group. SIV-Gag-specific CD8 T cells in the PB expressed alpha4beta7 integrin, the gut-homing receptor; a minor subset co-express alphaEbeta7 integrin. SIV-Gag-specific CD8 T cells were also detected in the gut tissue, intraepithelial (IEL) and lamina propria lymphocytes (LPL) of the duodenum and ileum. These cells were characterized by high levels of beta7 integrin expression and a predominance of the effector memory phenotype. Neither Il-12 nor IL-15 amplified the frequency of SIV-specific CD8 T cells in the gut. Thus, the DNA prime-oral Listeria boost strategy induced a mucosal SIV-Gag-specific CD8 T cell response characterized by expression of the alpha4beta7 integrin gut-homing receptor.

CTLA-4 blockade decreases TGF-beta, IDO, and viral RNA expression in tissues of SIVmac251-infected macaques

Regulatory T (T(reg)) cells are a subset of CD25(+)CD4(+) T cells that constitutively express high levels of cytotoxic T lymphocyte antigen-4 (CTLA-4) and suppress T-cell activation and effector functions. T(reg) cells are increased in tissues of individuals infected with HIV-1 and macaques infected with simian immunodeficiency virus (SIV(mac251)). In HIV-1 infection, T(reg) cells could exert contrasting effects: they may limit viral replication by decreasing immune activation, or they may increase viral replication by suppressing virusspecific immune response. Thus, the outcome of blocking T(reg) function in HIV/SIV should be empirically tested. Here, we demonstrate that CD25(+) T cells inhibit virus-specific T-cell responses in cultured T cells from blood and lymph nodes of SIV-infected macaques. We investigated the impact of CTLA-4 blockade using the anti-CTLA-4 human antibody MDX-010 in SIV-infected macaques treated with antiretroviral therapy (ART). CTLA-4 blockade decreased expression of the tryptophan-depleting enzyme IDO and the level of the suppressive cytokine transforming growth factor-beta (TGF-beta) in tissues. CTLA-4 blockade was associated with decreased viral RNA levels in lymph nodes and an increase in the effector function of both SIV-specific CD4(+) and CD8(+) T cells. Therefore, blunting T(reg) function in macaques infected with SIV did not have detrimental virologic effects and may provide a valuable approach to complement ART and therapeutic vaccination in the treatment of HIV-1 infection.

Evaluation of fowlpox–vaccinia virus prime-boost vaccine strategies for high-level mucosal and systemic immunity against HIV-1

We have tested the efficacy of recombinant fowl pox (rFPV) and recombinant vaccinia virus (rVV) encoding antigens of AE clade HIV-1 in a prime-boost strategy, using both systemic and mucosal delivery routes. Of the various vaccine routes tested, intranasal/intramuscular (i.n./i.m.) AE FPV/AE VV prime-boosting generated the highest mucosal and systemic T cell responses. Peak mucosal T cell responses occurred as early as 3 days post-boost vaccination. In contrast only low systemic responses were observed at this time with the peak response occurring at day 7. Current data also revealed that, due to better uptake of the rFPV, intranasal viral priming was much more effective than intranasal rDNA priming tested previously. The i.m./i.m. prime-boost delivery also generated strong systemic but poor mucosal responses to Gag peptides. Interestingly, the oral administration of AE FPV followed by i.m. AE VV delivery elicited strong systemic responses to sub-dominant Pol 1 peptides that were absent in mice that received vaccine by other routes. Moreover, priming with AE FPV co-expressing cytokine IL-12 significantly enhanced the T cell responses to target antigens, whilst co-expression of IFNgamma decreased these responses. The results also indicated that the route of inoculation and the vaccine vector combination could radically influence not only the magnitude but also the antigen specificity of the immune response generated. Further, in contrast to the generally protracted HIV rDNA/rFPV multiple delivery prime-boosting, this single rFPV prime and rVV boost approach was more flexible and generated excellent mucosal and systemic immune responses to HIV vaccine antigens.

HIV infection: first battle decides the war

The traditional view of HIV-1 infection characterized by the slow decline of CD4+ T cells has radically changed in light of recent observations in rhesus macaques and humans of rapid and extensive infection and removal of memory CD4+ T cells in mucosal tissues within the first three weeks of infection. This initial strike to the immune system seems to be the distinguishing feature of HIV-1 pathogenesis and its extent sets the overall course of the ensuing infection. Qualitatively different mechanisms of CD4+ T-cell depletion prevail during the acute, chronic and advanced phases of infection depending on the availability of the target-cell population and competence of the immune system. The elimination of CD4+ T cells in mucosal lymphoid tissues results in the absence of important regulatory and effector functions that these cells normally perform in controlling immune responses to environmental antigens and pathogens. Ablation of acute HIV-1 viremia limits the initial damage to the CD4+ T-cell compartment and helps to establish a state of equilibrium between the replicating virus, the availability of the target-cell population and the immune control characteristic of long-term non-progression.

SIV-specific T lymphocyte responses in PBMC and lymphoid tissues of SIV-infected pigtailed macaques during suppressive combination antiretroviral therapy

There is currently no SIV macaque model in which the effects of combination antiretroviral therapy on tissue immune responses and latent reservoirs have been measured. This study was performed to define the impact of combination therapy on the specificity and distribution of the T lymphocyte response in multiple tissue compartments. Pigtailed macaques (Macaca nemestrina) were infected with SIV/17E-Fr and treated with combination antiretroviral therapy consisting of 9-R-(2-phosphonomethoxypropyl)adenine (PMPA) and beta-2',3'-dideoxy-3'-thia-5-fluorocytidine (FTC). The SIV-specific T lymphocyte response was measured in peripheral blood, spleen and several lymph nodes at necropsy by IFN-gamma Elispot analysis. Two animals (one treated, one untreated) had high acute peak viremia, which was associated with lower SIV-specific T lymphocyte responses in the peripheral blood and lymphoid tissues. In the treated animal, viremia was controlled to low or undetectable for the study duration, and virus-specific responses remained low. The untreated animal remained viremic throughout the study and developed clinical symptoms of AIDS. In contrast, the two animals that had lower acute peak viremia (one treated, one untreated) had more robust T lymphocyte responses, and controlled viral replication. Virus-specific responses were detected in the treated animal despite 6 months of suppressive therapy. These data suggest that in this model, in the context of acute peak viremia and weak T cell responses, combination therapy may be essential to control virus replication and disease progression. Conversely, in the setting of low initial viremia and robust T lymphocyte responses, treatment does not have a detrimental effect on the immune response.

Correlation between viral RNA levels but not immune responses in plasma and tissues of macaques with long-standing SIVmac251 infection

Plasma virus in human immunodeficiency virus type 1/simian immunodeficiency virus (HIV-1/SIV) infection most likely results from the combination of viruses produced in different tissues. As immunological pressure may be higher in effector sites than secondary lymphoid tissues, we investigated quantitative and qualitative changes in viral RNA in blood and tissues of 10 Mamu-A*01-positive SIV-infected macaques in parallel with the frequency of CD8+ T cells recognizing the dominant Gag181-189 CM9 epitope. The plasma virus level in these macaques directly correlated with the viral RNA levels in lymph nodes, spleen, lungs, colon, and jejunum. In contrast, the frequency of the Gag181-189 CM9 tetramer did not correlate with SIV RNA levels in any compartment. We investigated the presence of viral immune escape in RNA from several tissues. The complete substitution of wild-type genotype with viral immune-escape variant within the Gag181-189 CM9 epitope was associated with low tetramer response in all tissues and blood of two macaques. In one macaque, the replacement of wild type with an immune-escape mutant was asynchronous. While the mutant virus was prevalent in blood and effector tissues (lungs, jejunum, and colon), secondary lymphoid organs such as spleen and lymph nodes still retained 80% and 40%, respectively, of the wild-type virus. These results may imply that there are differences in the immunological pressure exerted by cytotoxic T lymphocytes (CTLs) in tissue compartments of SIVmac251-infected macaques.

Characterization of the peptide-binding specificity of Mamu-A*11 results in the identification of SIV-derived epitopes and interspecies cross-reactivity

The SIV-infected Indian rhesus macaque is the most established model of HIV infection, providing insight into pathogenesis and a system for testing novel vaccines. However, only a limited amount of information is available regarding the peptide-binding motifs and epitopes bound by their class I and class II MHC molecules. In this study, we utilized a library of over 1,000 different peptides and a high throughput MHC-peptide binding assay to detail the binding specificity of the rhesus macaque class I molecule Mamu-A*11. These studies defined the fine specificity of primary anchor positions, and dissected the role of secondary anchors, for peptides of 8-11 residues in length. This detailed information was utilized to develop size-specific polynomial algorithms to predict Mamu-A*11 binding capacity. Testing SIVmac239-derived Mamu-A*11 binding peptides for recognition by peripheral blood mononuclear cells (PBMC) from Mamu-A*11-positive, SIV-infected macaques, identified five novel SIV-derived Mamu-A*11 epitopes. Finally, we detected extensive cross-reactivity at the binding level between Mamu-A*11 and the mouse H-2 class I molecule Kk. Further experiments revealed that three out of four Mamu-A*11 binding peptides which bound Kk and were immunogenic in Kk mice were also recognized in Mamu-A*11-infected macaques. This is the first detailed description of mouse-macaque interspecies cross-reactivity, potentially useful in testing novel vaccines in mice and macaques.

Not All Tetramer Binding CD8+ T Cells Can Produce Cytokines and Chemokines Involved in the Effector Functions of Virus-Specific CD8+ T Lymphocytes in HIV-1 Infected Children

In the pediatric human immunodeficiency virus type-1 (HIV-1) infection, the presence of cytotoxic T lymphocytes (CTL) is associated with a slow progression to AIDS. The secretion of cytokines by CTLs may be critical in the control of viral infection. We used the combination of cell surface and intracellular staining to study the functionality of tetramer binding CD8+ T cells recognizing two HIV-1 immunodominant epitopes, in peripheral blood mononuclear cells from HIV-1-infected children. A fraction of tetramer positive CD8+ T cells produce cytokines (IFN-gamma, TNF-alpha) or chemokines (CCL4, CCL5) after ex vivo stimulation with the cognate peptide. There was a negative correlation between the plasma viral load and the percentage of CD8+ Tetramer Gag+ T cells secreting IFN-gamma. This is the first report in the context of pediatric HIV-1 infection showing that only a fraction of HIV-1-specific CD8+ T cells have the capacity to produce cytokines and chemokines implicated in their antiviral functions.

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Functional simian immunodeficiency virus Gag-specific CD8+ intraepithelial lymphocytes in the mucosae of SIVmac251- or simian-human immunodeficiency virus KU2-infected macaques

The vaginal and rectal mucosae are the first line of cellular immune defense to sexually transmitted human immunodeficiency virus type 1 (HIV-1) entry. Thus, intraepithelial lymphocytes (IELs) may be important in the immune response to HIV infection. Here we investigated whether functional IELs in mucosal compartments could be visualized by direct staining with a tetrameric complex specific for the simian immunodeficiency virus (SIV) immunodominant Gag epitope in either separated IEL cells or tissues of macaques infected with SIVmac251. Of the 15 Mamu-A*01-positive macaques studied here, eight were chronically infected with either SIVmac251 or simian-human immunodeficiency virus (SHIV) KU2 and the remaining seven were exposed mucosally to SIVmac251 and sacrificed within 48 h to assess the local immune response. Gag-specific CD8+ T-cells were found in separated IELs from the rectum, colon, jejunum, and vagina of most infected animals. Direct staining of tetramers also revealed their presence in intact tissue. These Gag-specific IELs expressed the activation marker CD69 and produced IFN-gamma, suggesting an active immune response in this locale.

High frequency of virus-specific CD8+ T cells in the central nervous system of macaques chronically infected with simian immunodeficiency virus SIVmac251

Infection with human immunodeficiency virus or simian immunodeficiency virus (SIV) induces virus-specific CD8(+) T cells that traffic to lymphoid and nonlymphoid tissues. In this study, we used Gag-specific tetramer staining to investigate the frequency of CD8(+) T cells in peripheral blood and the central nervous system of Mamu-A*01-positive SIV-infected rhesus macaques. Most of these infected macaques were vaccinated prior to SIVmac251 exposure. The frequency of Gag(181-189) CM9 tetramer-positive cells was consistently higher in the cerebrospinal fluid and the brain than in the blood of all animals studied and did not correlate with either plasma viremia or CD4(+)-T-cell level. Little or no infection in the brain was documented for most animals by nucleic acid sequence-based amplification or in situ hybridization. These data suggest that this Gag-specific response may contribute to the containment of viral replication in this locale.

Improved protection of rhesus macaques against intrarectal simian immunodeficiency virus SIV(mac251) challenge by a replication-competent Ad5hr-SIVenv/rev and Ad5hr-SIVgag recombinant priming/gp120 boosting regimen

In this study we investigated the ability of a replication-competent Ad5hr-SIVenv/rev and Ad5hr-SIVgag recombinant priming/gp120 boosting regimen to induce protective immunity in rhesus macaques against pathogenic simian immunodeficiency virus(mac251). Immunization of macaques by two sequential administrations of the same recombinants by the same route resulted in boosting and persistence of SIV-specific cellular immune responses for 42 weeks past the initial immunization. Anti-SIV gp120 immunoglobulin G (IgG) and IgA antibodies were induced in secretory fluids, and all macaques exhibited serum neutralizing antibody activity. After intrarectal SIV(mac251) challenge, all of the macaques became infected. However, relative protection, as assessed by statistically significant lower SIV viral loads in plasma at both acute infection and set point, was observed in 8 out of 12 immunized non-Mamu-A(*)01 animals. Elevated mean cellular immune responses to Gag and Env, neutralizing antibody activity, and IgG and IgA binding antibody levels were observed in the eight protected macaques. Statistically significant correlations with protective outcome were observed for cellular immune responses to SIV Env and Gag and for SIV gp120-specific IgG antibodies in nasal and vaginal fluids. Two macaques that exhibited the greatest and most persistent viremia control also exhibited strong CD8(+) T-cell antiviral activity. The results suggest that a spectrum of immune responses may be necessary for adequate control of viral replication and disease progression and highlight a potential role for nonneutralizing antibodies at mucosal sites.

Prior DNA immunization enhances immune response to dominant and subdominant viral epitopes induced by a fowlpox-based SIVmac vaccine in long-term slow-progressor macaques infected with SIVmac251

A therapeutic vaccine for individuals infected with HIV-1 and treated with antiretroviral therapy (ART) should be able to replenish virus-specific CD4+ T-cells and broaden the virus-specific CD8+ T-cell response in order to maintain CD8+ T-cell function and minimize viral immune escape after ART cessation. Because a combination of DNA and recombinant poxvirus vaccine modalities induces high levels of virus-specific CD4+ T-cell response and broadens the cytolytic activity in naive macaques, we investigated whether the same results could be obtained in SIVmac251-infected macaques. The macaques studied here were long-term nonprogressors that naturally contained viremia but were nevertheless treated with a combination of antiviral drugs to assess more carefully the effect of vaccination in the context of ART. The combination of a DNA expressing the gag and pol genes (DNA-SIV-gp) of SIVmac239 followed by a recombinant fowlpox expressing the same SIVmac genes (FP-SIV-gp) was significantly more immunogenic than two immunizations of FP-SIV-gp in SIVmac251-infected macaques treated with ART. The DNA/FP combination significantly expanded and broadened Gag-specific T-cell responses measured by tetramer staining, ELISPOT, and intracellular cytokine staining and measurement of ex vivo cytolytic function. Importantly, the combination of these vaccine modalities also induced a sizeable expansion in most macaques of Gag-specific CD8-(CD4+) T-cells able to produce TNF-alpha. Hopefully, this modality of vaccine combination may be useful in the clinical management of HIV-1-infected individuals.

Heterogeneity of the simian immunodeficiency virus (SIV) specific CD8(+) T-cell response in mucosal tissues during SIV primary infection

Virus-specific CD8(+) T cells play an important role in controlling viral replication during acute primary infection. At this early stage, mucosal tissues represent a major site of viral replication. Therefore, the presence of functional virus-specific CD8(+) effector T cells in the mucosa during primary infection is a key issue in the pathogenesis of infection. In order to evaluate the extent of this response, six rhesus macaques were infected with simian immunodeficiency virus (SIV)mac251 and sacrificed on day 28 following infection. The functional activity of SIV-effector CD8(+) T cells was evaluated by means of a gamma-IFN ELISpot assay with autologous cells expressing SIV env, gag, pol and nef genes as antigen-presenting cells. This evaluation was performed on PBMCs, spleen, peripheral lymph node, gut-associated lymph node and lamina propria lymphocytes isolated from different mucosal sites. In parallel, the cell-associated viral load was quantified in all these tissues. Five macaques had gamma-IFN SIV-specific CD8(+) T cells in PBMCs and/or lymph nodes. However, in these macaques, these CD8(+) T cells were only present in seven mucosal sites out of 24 tested (the lamina propria lymphocytes of the duodenum, jejunum, ileum and colon were evaluated separately for each animal), whereas they were detected in all corresponding gut-associated lymph nodes. In addition, the mean frequency of SIV-specific gamma-IFN-secreting CD8(+) T cells was 117 +/- 228 per 10(6) cells in the lamina propria vs. 958 +/- 1184 in gut associated lymph nodes (P = 0.001). No overall correlation was observed between the CD8(+) T-cell activity and the viral load: among the 17 mucosal sites in which the virus was isolated, no specific activity was detected in 13 sites. In conclusion, these data indicate that the frequencies of SIV-specific gamma-IFN-secreting CD8(+) T cells are low in the mucosa during early primary infection. This may be of importance with regard to the intense viral replication observed in the mucosa at this stage.

Quantitative ex vivo analysis of functional virus-specific CD8 T lymphocytes in the blood and genital tract of HIV-infected women

BACKGROUND

CD8 T lymphocytes are important in HIV-1 control and mediate virus-specific immunity in the blood and genital tract. The induction and monitoring of mucosal CD8 cell responses will be an important component of HIV-1 vaccine trials, but information regarding the frequency, phenotype and function of genital tract CD8 cell responses is lacking.

METHODS

Simultaneous blood and cervical cytobrush samples were obtained from 16 HIV-1-infected Kenyan sex workers. Epitope-specific CD8 T lymphocyte frequencies in the blood and genital tract were analysed after short-term peptide incubation and intracellular cytokine staining for interferon-gamma (IFN gamma).

RESULTS

Cervical sampling resulted in adequate cell numbers for analysis in 10/16 women. Background IFN gamma production was higher in CD3+/CD8+ lymphocytes from the genital tract than from blood (0.48% versus 0.1%; P < 0.01). Responses to staphylococcal enterotoxin B were detected in cervical CD8 lymphocytes from 10/10 women, at a similar frequency to blood (16.7% in cervix and 13.3% in blood; P = 0.4). HIV-1-specific responses were detected the cervix of 8/10 women, with a trend to higher response frequencies in the genital tract than blood (2.1% versus 0.8%; P = 0.09). Co-expression of integrin CD103 (alpha E beta 7), a mucosal marker, was used to confirm the mucosal origin of cervical responses.

CONCLUSIONS

Cytobrush sampling and intracellular cytokine staining is well suited to the analysis of cervical CD8 cell responses. The frequency of functional virus-specific CD3+/CD8+ T cells is similar in the genital tract and blood of HIV-1-infected women. The role of genital tract CD8 cell responses in HIV-1 control warrants further investigation.

Trafficking of human immunodeficiency virus type 1-specific CD8+ T cells to gut-associated lymphoid tissue during chronic infection

Gut-associated lymphoid tissue (GALT) is a significant but understudied lymphoid organ, harboring a majority of the body's total lymphocyte population. GALT is also an important portal of entry for human immunodeficiency virus (HIV), a major site of viral replication and CD4(+) T-cell depletion, and a frequent site of AIDS-related opportunistic infections and neoplasms. However, little is known about HIV-specific cell-mediated immune responses in GALT. Using lymphocytes isolated from rectal biopsies, we have determined the frequency and phenotype of HIV-specific CD8(+) T cells in human GALT. GALT CD8(+) T cells were predominantly CD45RO(+) and expressed CXCR4 and CCR5. In 10 clinically stable, chronically infected individuals, the frequency of HIV Gag (SL9)-specific CD8(+) T cells was increased in GALT relative to peripheral blood mononuclear cells by up to 4.6-fold, while that of cytomegalovirus (CMV)-specific CD8(+) T cells was significantly reduced (P = 0.012). Both HIV- and CMV-specific CD8(+) T cells in GALT expressed CCR5, but only HIV-specific CD8(+) T cells expressed alpha E beta 7 integrin, suggesting that mucosal priming may account for their retention in GALT. Chronically infected individuals exhibited striking depletion of GALT CD4(+) T cells expressing CXCR4, CCR5, and alpha E beta 7 integrin, but CD4(+)/CD8(+) T-cell ratios in blood and GALT were similar. The percentage of GALT CD8(+) T cells expressing alpha E beta 7 was significantly decreased in infected individuals, suggesting that HIV infection may perturb lymphocyte retention in GALT. These studies demonstrate the feasibility of using tetramers to assess HIV-specific T cells in GALT and reveal that GALT is the site of an active CD8(+) T-cell response during chronic infection.

Emergence of cytotoxic T lymphocyte escape mutants following antiretroviral treatment suspension in rhesus macaques infected with SIVmac251

Structured treatment interruption (STI) of antiretroviral drugs has been proposed as an alternative approach for managing patients infected with HIV-1. While STI is thought to spare drug-related side effects and enhance the HIV-1-specific immune response, the long-lasting clinical benefit of this approach remains uncertain, particularly in patients with long-standing HIV-1 infection. Here, we investigated the basis of unabated virological replication following different STI regimens in rhesus macaques that expressed the MHC class I Mamu-A*01 molecule treated during acute and long-standing infection with SIVmac251. An amino acid change at the anchor residue within the immunodominant Mamu-A*01-restricted Gag(181-189) CM9 epitope (T --> A) in one of six macaques with acute SIVmac251 infection and in three of four macaques with long-standing SIVmac251 infection (T --> A; T --> S; S --> C) was found in the majority of plasma virus. These amino acid changes have been shown to severely decrease binding of the corresponding peptides to the Mamu-A*01 molecule and, in the case of the T --> A change, escape from CTL. In one macaque with long-standing SIVmac251 infection, a mutation emerged that conferred resistance to one of the antiretroviral drugs (PMPA) as well. These results provide insights into the mechanism underlying the limited capacity of repeated interruption of antiretroviral therapy as an approach to restrain viral replication. In addition, these data also suggest that interruption of therapy may be less effective in chronic infection because of preexisting immune escape and that immune escape is a risk of interruption of therapy.

Immunization of newborn rhesus macaques with simian immunodeficiency virus (SIV) vaccines prolongs survival after oral challenge with virulent SIVmac251

There is an urgent need for active immunization strategies that, if administered shortly after birth, could protect infants in developing countries from acquiring human immunodeficiency virus (HIV) infection through breast-feeding. Better knowledge of the immunogenic properties of vaccine candidates in infants and of the effect of maternal antibodies on vaccine efficacy will aid in the development of such a neonatal HIV vaccine. Simian immunodeficiency virus (SIV) infection of infant macaques is a useful animal model of pediatric HIV infection with which to address these questions. Groups of infant macaques were immunized at birth and 3 weeks of age with either modified vaccinia virus Ankara (MVA) expressing SIV Gag, Pol, and Env (MVA-SIVgpe) or live-attenuated SIVmac1A11. One MVA-SIVgpe-immunized group had maternally derived anti-SIV antibodies prior to immunization. Animals were challenged orally at 4 weeks of age with a genetically heterogeneous stock of virulent SIVmac251. Although all animals became infected, the immunized animals mounted better antiviral antibody responses, controlled virus levels more effectively, and had a longer disease-free survival than the unvaccinated infected monkeys. Maternal antibodies did not significantly reduce the efficacy of the MVA-SIVgpe vaccine. In conclusion, although the tested vaccines delayed the onset of AIDS, further studies are warranted to determine whether a vaccine that elicits stronger early immune responses at the time of virus exposure may be able to prevent viral infection or AIDS in infants.

Immune intervention strategies for HIV-1 infection of humans in the SIV macaque model

Studies in the SIVmac macaque model have demonstrated that the extent of virus-specific CD4+ and CD8+ T-cell responses induced by vaccination prior to virus-challenge exposure correlate with viremia containment following establishment of infection. These findings led to the hypothesis that active immunization with vaccines able to induce virus-specific T-cell responses following the establishment of infection could also ameliorate the virological outcome. Here, we will review the relative effect of ART and vaccination during primary SIVmac infection of macaques.

Frequencies of ex vivo-activated human immunodeficiency virus type 1-specific gamma-interferon-producing CD8+ T cells in infected children correlate positively with plasma viral load

HIV-specific CD8+ T cells are critical in controlling human immunodeficiency virus (HIV) replication. We present the evaluation of a gamma-interferon (IFN-gamma)-based enzyme linked immunospot (ELISPOT) assay for the quantification of HIV-specific CD8+ T cells from HIV-infected children. We studied 20 HLA-A*0201-positive HIV-infected children. The IFN-gamma production in response to stimulation with two HLA-A*0201-restricted immunodominant CD8 epitopes (SLYNTVATL [SL9] in Gag and ILKEPVHGV [IV9] in Pol) was tested using the ELISPOT assay. The results were compared to labeling with the corresponding tetramers. Among the 20 children, 18 had detectable responses against the SL9 and/or the IV9 epitope using the ELISPOT assay (medians, 351 and 134 spot-forming cells/10(6) peripheral blood mononuclear cells, respectively). Comparison of results from the tetramer and ELISPOT assays suggests that only a fraction of HIV-specific CD8+ T cells were able to produce IFN-gamma. Most importantly, we found that the frequencies of IFN-gamma-producing CD8+ T cells were positively correlated with the viral load whereas the frequencies of tetramer-binding CD8+ T cells were not. The high sensitivity of the ELISPOT assay and the fact that this functional assay provided information different from that of tetramer labeling support its use for measurement of HIV-specific CD8+ T cells. In conclusion, our results show that the ex vivo-activated IFN-gamma-producing HIV-specific CD8+ T-cell subset is dependent upon continuous antigenic stimulation.

Live, attenuated simian immunodeficiency virus SIVmac-M4, with point mutations in the Env transmembrane protein intracytoplasmic domain, provides partial protection from mucosal challenge with pathogenic SIVmac251

Attenuated molecular clones of simian immunodeficiency virus (SIVmac) are important tools for studying the correlates of protective immunity to lentivirus infection in nonhuman primates. The most highly attenuated SIVmac mutants fail to induce disease but also fail to induce immune responses capable of protecting macaques from challenge with pathogenic virus. We recently described a novel attenuated virus, SIVmac-M4, containing multiple mutations in the transmembrane protein (TM) intracytoplasmic domain. This domain has been implicated in viral assembly, infectivity, and cytopathogenicity. Whereas parental SIVmac239-Nef(+) induced persistent viremia and simian AIDS in rhesus macaques, SIVmac-M4 induced transient viremia in juvenile and neonatal macaques, with no disease for at least 1 year postinfection. In this vaccine study, 8 macaques that were infected as juveniles (n = 4) or neonates (n = 4) with SIVmac-M4 were challenged with pathogenic SIVmac251 administered through oral mucosa. At 1 year postchallenge, six of the eight macaques had low to undetectable plasma viremia levels. Assays of cell-mediated immune responses to SIVmac Gag, Pol, Env, and Nef revealed that all animals developed strong CD8(+) T-cell responses to Gag after challenge but not before. Unvaccinated control animals challenged with SIVmac251 developed persistent viremia, had significantly weaker SIV-specific T-cell responses, and developed AIDS-related symptoms. These findings demonstrate that SIVmac-M4, which contains a full-length Nef coding region and multiple point mutations in the TM, can provide substantial protection from mucosal challenge with pathogenic SIVmac251.

Both mucosal and systemic routes of immunization with the live, attenuated NYVAC/simian immunodeficiency virus SIV(gpe) recombinant vaccine result in gag-specific CD8(+) T-cell responses in mucosal tissues of macaques

As most human immunodeficiency virus (HIV) infection occurs via mucosal surfaces, an important goal of vaccination may be the induction of virus-specific immune responses at mucosal sites to contain viral infection early on. Here we designed a study in macaques carrying the major histocompatibility complex class I Mamu-A(*)01 molecule to assess the capacity of the highly attenuated poxvirus NYVAC/simian immunodeficiency virus (SIV) SIV(gpe) vaccine candidate administered by the intranasal, intramuscular, or intrarectal route to induce mucosal immunity. All macaques, including one naive macaque, were exposed to SIV(mac251) by the intrarectal route and sacrificed 48 h after infection. The kinetics of immune response at various time points following immunization with NYVAC/SIV(gpe) and the anamnestic response to SIV(mac251) at 48 h after challenge were assessed in blood, in serial rectal and vaginal biopsy samples, and in tissues at euthanasia with an SIV(mac) Gag-specific tetramer. In addition, at euthanasia, antigen-specific cells producing gamma interferon or tumor necrosis factor alpha from the jejunum lamina propria were quantified in all macaques. Surprisingly, antigen-specific CD8(+) T cells were found in the mucosal tissues of all immunized macaques regardless of whether the vaccine was administered by a mucosal route (intranasal or intrarectal) or systemically. In addition, following mucosal SIV(mac251) challenge, antigen-specific responses were mainly confined to mucosal tissues, again regardless of the route of immunization. We conclude that immunization with a live vector vaccine results in the appearance of CD8(+) T-cell responses at mucosal sites even when the vaccine is delivered by nonmucosal routes.