HIV-induced immunopathogenesis

Role of Apoptosis in HIV Pathogenesis

The apoptotic pathway is an important cell death pathway that contributes to the maintenance of homeostasis in living systems. However, variations in apoptosis have been linked to many diseases such as cancers and chronic infections. The HIV infection has contributed to increase mortality and morbidity worldwide, predominantly through the induction of gradual depletion of CD4+ T cells. The induction and mediation of both the intrinsic and extrinsic apoptotic pathways are crucial in HIV pathogenesis and intracellular survival. Consequently, a deep molecular understanding of how apoptosis is induced and modulated in HIV-mediated CD4+ T cell depletion is paramount, as this can lead to new portals of therapeutic intervention and control.

CD8+ T-Cell Mediated Control of HIV-1 in a Unique Cohort With Low Viral Loads

A unique population of HIV-1 infected individuals can control infection without antiretroviral therapy. These individuals fall into a myriad of categories based on the degree of control (low or undetectable viral load), the durability of control over time and the underlying mechanism (i.e., possession of protective HLA alleles or the absence of critical cell surface receptors). In this study, we examine a cohort of HIV-1 infected individuals with a documented history of sustained low viral loads in the absence of therapy. Through in vitro analyses of cells from these individuals, we have determined that infected individuals with naturally low viral loads are capable of controlling spreading infection in vitro in a CD8⁺ T-cell dependent manner. This control is lost when viral load is suppressed by antiretroviral therapy and correlates with a clinical CD4:CD8 ratio of <1. Our results support the conclusion that HIV-1 controllers with low, but detectable viral loads may be controlling the virus due to an effective CD8⁺ T-cell response. Understanding the mechanisms of control in these subjects may provide valuable understanding that could be applied to induce a functional cure in standard progressors.

New Insights Into Cryptococcus Spp. Biology and Cryptococcal Meningitis

PURPOSE OF REVIEW

Defective cell-mediated immunity is a major risk factor for cryptococcosis, a fatal disease if untreated. Cryptococcal meningitis (CM), the main presentation of disseminated disease, occurs through hematogenous spread to the brain from primary pulmonary foci, facilitated by yeast virulence factors. We revisit remarkable recent improvements in the prevention, diagnosis and management of CM.

RECENT FINDINGS

Cryptococcal antigen (CrAg), main capsular polysaccharide of Cryptococcus spp. is detectable in blood and cerebrospinal fluid of infected patients with point of care lateral flow assays. Recent World Health Organization guidelines recommend 7-day amphotericin B plus flucytosine, then 7-day high dose (1200 mg/day) fluconazole for induction treatment of HIV-associated CM. Management of raised intracranial pressure, a consequence of CM, should rely mainly on daily therapeutic lumbar punctures until normalisation. In HIV-associated CM, following introduction of antifungal therapy, (re)initiation of antiretroviral therapy should be delayed by 4-6 weeks to prevent immune reconstitution inflammatory syndrome, common in CM. CM is a fatal disease whose diagnosis has recently been simplified. Treatment should always include antifungal combination therapy and management of raised intracranial pressure. Screening for immune deficiency should be mandatory in all patients with cryptococcosis.

HIV-1 Nef physically associate with CAMKIIδ - ASK-1 complex to inhibit p38MAPK signalling and apoptosis in infected cells

Human immunodeficiency type 1 virus accessory protein Nef is a key modulator of AIDS pathogenesis. With no enzymatic activity, Nef regulated functions in host cells largely depends on its ability to form multi-protein complex with the cellular proteins. Here, we identified Calcium (Ca²⁺)/Calmodulin dependent protein kinase II subunit delta (CAMKIIδ) as novel Nef interacting host protein. Further, we confirmed that Nef mediated [Ca²⁺]_I promote formation of Nef-CAMKIIδ - apoptosis signal-regulating kinase (ASK-1) heterotrimeric complex. The assembly of Nef with CAMKIIδ - ASK-1 inhibits the downstream p38MAPK phosphorylation resulting in abrogation of apoptosis. Further, using competitive peptide inhibitors against Nef binding domains to CAMKIIδ, identified in the present study and ASK-1, individually blocked physical interaction of Nef with CAMKIIδ-ASK-1 complex and restored p38MAPK phosphorylation and apoptosis. Altogether, our study indicates that HIV-Nef modulates cytosolic [Ca²⁺]_I and blocks CAMKIIδ - ASK-1 kinase activity to inhibit apoptosis of infected cells.

Understanding Pathogenesis and Care Challenges of Immune Reconstitution Inflammatory Syndrome in Fungal Infections

Immune deficiency of diverse etiology, including human immunodeficiency virus (HIV), antineoplastic agents, immunosuppressive agents used in solid organ recipients, immunomodulatory therapy, and other biologics, all promote invasive fungal infections. Subsequent voluntary or unintended immune recovery may induce an exaggerated inflammatory response defining immune reconstitution inflammatory syndrome (IRIS), which causes significant mortality and morbidity. Fungal-associated IRIS raises several diagnostic and management issues. Mostly studied with Cryptococcus, it has also been described with other major fungi implicated in human invasive fungal infections, such as Pneumocystis, Aspergillus, Candida, and Histoplasma. Furthermore, the understanding of IRIS pathogenesis remains in its infancy. This review summarizes current knowledge regarding the clinical characteristics of IRIS depending on fungal species and existing strategies to predict, prevent, and treat IRIS in this patient population, and tries to propose a common immunological background to fungal IRIS.

HIV-1 Tat induces DNMT over-expression through microRNA dysregulation in HIV-related non Hodgkin lymphomas

BACKGROUND

A close association between HIV infection and the development of cancer exists. Although the advent of highly active antiretroviral therapy has changed the epidemiology of AIDS-associated malignancies, a better understanding on how HIV can induce malignant transformation will help the development of novel therapeutic agents.

METHODS

HIV has been reported to induce the expression of DNMT1 in vitro, but still no information is available about the mechanisms regulating DNMT expression in HIV-related B-cell lymphomas. In this paper, we investigated the expression of DNMT family members (DNMT1, DNMT3a/b) in primary cases of aggressive B-cell lymphomas of HIV-positive subjects.

RESULTS

Our results confirmed the activation of DNMT1 by HIV in vivo, and reported for the first time a marked up-regulation of DNMT3a and DNMT3b in HIV-positive aggressive B-cell lymphomas. DNMT up-regulation in HIV-positive tumors correlated with down-regulation of specific microRNAs, as the miR29 family, the miR148-152 cluster, known to regulate their expression. Literature reports the activation of DNMTs by the human polyomavirus BKV large T-antigen and adenovirus E1a, through the pRb/E2F pathway. We have previously demonstrated that the HIV Tat protein is able to bind to the pocket proteins and to inactivate their oncosuppressive properties, resulting in uncontrolled cell proliferation. Therefore, we focused on the role of Tat, due to its capability to be released from infected cells and to dysregulate uninfected ones, using an in vitro model in which Tat was ectopically expressed in B-cells.

CONCLUSIONS

Our findings demonstrated that the ectopic expression of Tat was per se sufficient to determine DNMT up-regulation, based on microRNA down-regulation, and that this results in aberrant hypermethylation of target genes and microRNAs. These results point at a direct role for Tat in participating in uninfected B-cell lymphomagenesis, through dysregulation of the epigenetical control of gene expression.

Study on Immunological Status of Chinese HIV-Infected Individuals

HIV-1 infection is characterized by a gradual decline of immune function, and the immune dysfunction is widely regarded as one of the most important determinants of disease progression. The present study was performed to analyze in more detail the immunological status of HIV-infected people in China. T cell counts, activation of T cells, HIV-1 specific CTL and plasma levels of cytokines were determined with flow cytometry, IFN-gamma Elispot or ELISA techniques. The HIV viral load was negatively correlated with CD4(+), CD8(+) T cell counts (r=-0.654, P<0.001; r=-0.228, P<0.05); the breadth and magnitude of HIV-1 specific CTL responses against HIV-1 Gag peptides was related to disease progression; the activation of CD8(+) T cells was significantly higher than that in HIV-negative controls; the level of plasma IL-12 was much lower and the plasma IFN-gamma, IL-10 and IL-6 were much higher in HIV-infected persons than in HIV-negative controls (P<0.05). Study on immunological status in HIV-infected Chinese is very important in predicting the disease progression and providing information for HAART therapy in China.

The determination of in vivo envelope-specific cell-mediated immune responses in equine infectious anemia virus-infected ponies

Distinct from human lentivirus infection, equine infectious anemia virus (EIAV)-infected horses will eventually enter an inapparent carrier state in which virus replication is apparently controlled by adaptive immune responses. Although recrudescence of disease can occur after immune suppression, the actual immune correlate associated with protection has yet to be determined. Therefore, EIAV provides a model for investigating immune-mediated protective mechanisms against lentivirus infection. Here, we have developed a method to monitor EIAV-envelope specific cellular immunity in vivo. An EIA carrier horse with no clinical signs infected 7 years ago and 4 related experimental ponies infected 6 months previously were used in this study. Forty-four 20-mer peptides, representing the entire surface unit protein (gp90) of EIAV, were combined into 14 peptide pools and intradermally injected into the neck of EIAV-infected horses. An identical volume of saline alone was injected into a fifteenth site as a negative control. After 48 h, those sites with palpable infiltrations were measured prior to the collection of 2mm and 4mm punch biopsies. Total RNA was extracted from each 2mm biopsy for determination of CD3 and interferon-γ (IFN-γ) mRNA expression by real-time PCR. The 4mm skin biopsies were formalin-fixed and paraffin-embedded for immunohistochemistry (IHC) staining for CD3, CD20, CD25 and MAC387 (macrophage marker). Peripheral blood mononuclear cells (PBMC) were obtained prior to the injection and tested for in vitro reactivity against the same peptides. Histological examination showed that some of the envelope peptides elicited a lymphocytic cellular infiltration at the injection site, as evidenced by positive staining for CD3. Gp90 peptide-specific increases in CD3 and IFN-γ gene expression were also detected in the injection sites. Furthermore, differences were found between in vivo and in vitro responses to gp90 specific peptides. These results demonstrate a novel method for detecting in vivo cell-mediated immune responses to EIAV-specific peptides that is readily applicable to other host/pathogen systems.

Influence of dendritic cells on B-cell responses during HIV infection

Dendritic cells (DCs) modulate B-cell differentiation, activation, and survival mainly through production of growth factors such as B lymphocyte stimulator (BLyS/BAFF). DC populations have been reported to be affected in number, phenotype and function during HIV infection and such alterations may contribute to the dysregulation of the B-cell compartment. Herein, we reflect on the potential impact of DC on the pathogenesis of HIV-related B cell disorders, and how DC status may modulate the outcome of mucosal B cell responses against HIV, which are pivotal to the control of disease. A concept that could be extrapolated to the overall outcome of HIV disease, whereby control versus progression may reside in the host's capacity to maintain DC homeostasis at mucosal sites, where DC populations present an inherent capacity of modulating the balance between tolerance and protection, and are amongst the earliest cell types to be exposed to the virus.

Beryllium-specific CD4+ T cells in blood as a biomarker of disease progression

BACKGROUND

CD4(+) T cells are responsible for the progressive lung damage seen in patients with chronic beryllium disease (CBD), a granulomatous lung disorder in which antigen-specific, T(H)1-type, cytokine-secreting T cells have been characterized. Compared with those seen in beryllium (Be)-sensitized subjects, increased numbers of Be-responsive T cells are present in the blood of patients with CBD.

OBJECTIVE

The aim of this study was to determine whether the number of Be-specific T cells in blood predicted the development of CBD in a cohort of Be-exposed subjects.

METHODS

Using IFN-γ ELISpot and proliferation-based assays, we determined the frequency and proliferative capacity of Be-responsive T cells in blood.

RESULTS

Compared with the Be lymphocyte proliferation test, which detected an abnormal Be-induced proliferative response in 11 (4.2%) of 260 workers from a Be-machining facility, the IFN-γ ELISpot detected a sensitization rate of 10% (χ(2) = 55.7, P < .0001). A significant positive correlation was also noted between the number of Be-responsive CD4(+) T cells in the blood and lung tissue of patients with CBD. Importantly, the transition from Be sensitization to CBD was associated with an increased number of antigen-specific T cells in blood.

CONCLUSION

These findings have important implications for Be-induced disease and potentially other immune-mediated disorders, suggesting that the frequency of antigen-specific T cells in blood can serve as a noninvasive biomarker to predict disease development and severity of the Be-specific CD4(+) T-cell alveolitis.

Infectious agents and lymphoma

In the past 25 years revelations on the genesis of human cancer have come at an increasing pace. Research on oncogenic infectious agents, especially viruses, has helped us to understand the process of malignant transformation of cells because the cellular events in viral-driven transformation mirror, often brilliantly, basic cellular processes that culminate in cancer, even those not associated with viruses. Infectious agents, especially viruses, account for several of the most common malignancies-up to 20% of all cancers. Some of these cancers are endemic, with a high incidence in certain geographic locations, but sporadic/lower incidence in other parts of the world. Lymphomas arise frequently in association with infectious agents such as Epstein-Barr virus, human immunodeficiency virus, human herpes virus 8, Helicobacter pylori, and hepatitis C virus. In this review, we will focus on the association between infectious agents and lymphomas, with a look at the molecular mechanisms they use to disturb cell regulation and eventually result in cancer.

HIV Nef is secreted in exosomes and triggers apoptosis in bystander CD4+ T cells

The HIV accessory protein negative factor (Nef) is one of the earliest and most abundantly expressed viral proteins. It is also found in the serum of infected individuals (Caby MP, Lankar D, Vincendeau-Scherrer C, Raposo G, Bonnerot C. Exosomal-like vesicles are present in human blood plasma. Int Immunol 2005;17:879-887). Extracellular Nef protein has deleterious effects on CD4(+) T cells (James CO, Huang MB, Khan M, Garcia-Barrio M, Powell MD, Bond VC. Extracellular Nef protein targets CD4(+) T cells for apoptosis by interacting with CXCR4 surface receptors. J Virol 2004;78:3099-3109), the primary targets of HIV, and can suppress immunoglobulin class switching in bystander B cells (Qiao X, He B, Chiu A, Knowles DM, Chadburn A, Cerutti A. Human immunodeficiency virus 1 Nef suppresses CD40-dependent immunoglobulin class switching in bystander B cells. Nat Immunol 2006;7:302-310). Nevertheless, the mode of exit of Nef from infected cells remains a conundrum. We found that Nef stimulates its own export via the release of exosomes from all cells examined. Depending on its intracellular location, these Nef exosomes form at the plasma membrane, late endosomes or both compartments in Jurkat, SupT1 and primary T cells, respectively. Nef release through exosomes is conserved also during HIV-1 infection of peripheral blood lymphocytes (PBLs). Released Nef exosomes cause activation-induced cell death of resting PBLs in vitro. Thus, HIV-infected cells export Nef in bioactive vesicles, which facilitate the depletion of CD4(+) T cells that is a hallmark of acquired immunodeficiency syndrome (AIDS).

Dynamics and consequences of IL-21 production in HIV-infected individuals: a longitudinal and cross-sectional study

IL-21 is a relatively newly discovered immune-enhancing cytokine that plays an essential role in controlling chronic viral infections. It is produced mainly by CD4(+) T cells, which are also the main targets of HIV-1 and are often depleted in HIV-infected individuals. Therefore, we sought to determine the dynamics of IL-21 production and its potential consequences for the survival of CD4(+) T cells and frequencies of HIV-specific CTL. For this purpose, we conducted a series of cross-sectional and longitudinal studies on different groups of HIV-infected patients and show in this study that the cytokine production is compromised early in the course of the infection. The serum cytokine concentrations correlate with CD4(+) T cell counts in the infected persons. Among different groups of HIV-infected individuals, only elite controllers maintain normal production of the cytokine. Highly active antiretroviral therapy only partially restores the production of this cytokine. Interestingly, HIV infection of human CD4(+) T cells inhibits cytokine production by decreasing the expression of c-Maf in virus-infected cells, not in uninfected bystander cells. We also show that the frequencies of IL-21-producing HIV-specific, but not human CMV-specific, Ag-experienced CD4(+) T cells are decreased in HIV-infected viremic patients. Furthermore, we demonstrate in this study that recombinant human IL-21 prevents enhanced spontaneous ex vivo death of CD4(+) T cells from HIV-infected patients. Together, our results suggest that serum IL-21 concentrations may serve as a useful biomarker for monitoring HIV disease progression and the cytokine may be considered for immunotherapy in HIV-infected patients.

HIV-1 Tat dysregulation of lipopolysaccharide-induced cytokine responses: microbial interactions in HIV infection

OBJECTIVE

To examine whether the HIV-1 Tat protein impairs the lipopolysaccharide (LPS)-induced cytokine responses.

DESIGN

Concurrent infections with pathogens including bacteria and viruses are common in AIDS patients. However, cytokine and interferon responses during infection with or translocation from the gut of these pathogens in HIV-infected patients are not well studied. As HIV-1 Tat contributes partly to the HIV-induced immune dysregulation, we investigated whether the protein may play a role in perturbing the LPS-induced cytokine responses.

METHODS

Expression levels of cytokines in human primary blood monocytes/macrophages were determined by quantitative polymerase chain reaction and enzyme-linked immunosorbent assay. Expression level of the cell surface Toll-like receptor 4 was examined by flow cytometry. Activations of signaling molecules were assayed by western blot and immunofluorescence.

RESULTS

We demonstrated that HIV-1 Tat downregulated the LPS-induction of IFN-beta and concomitantly upregulated IL-6 expression in primary blood monocytes/macrophages, whereas the viral protein had no significant effects on TNF-alpha expression. To delineate the underlying mechanism, we showed that Tat inhibited the LPS-activation of ERK1/2 but not the p38 mitogen-activated protein kinases. The viral protein suppressed the LPS-induced activation of NFkappaB p65 via its induction of IkappaBalpha expression, which resulted in retention of NFkappaB p65 in the cytosol.

CONCLUSION

These findings suggest that Tat may play a role in modulating the immune responses triggered by other coinfecting pathogens and thus providing a permissive environment for both HIV and other opportunistic microbes.

HIV-1 transactivator protein induction of suppressor of cytokine signaling-2 contributes to dysregulation of IFN{gamma} signaling

HIV infection remains a worldwide threat. HIV-1 transactivator protein Tat is one of the retroviral proteins identified as a key immunomodulator in AIDS pathogenesis. Although the primary function of Tat is to regulate HIV-1 replication in the infected cell, it also dysregulates cytokine production resulting in perturbation of the host immune response and enhancement of the retrovirus survival. Because interferon-gamma (IFNgamma) is a pleiotropic cytokine with potent antiviral and immunoregulatory effects, we investigated whether Tat interferes with the IFNgamma signal transduction in primary monocytes. We demonstrated that Tat impaired the IFNgamma-receptor signaling pathway at the level of STAT1 activation, possibly via Tat-dependent induction of suppressor of cytokine signaling-2 (SOCS-2) activity. We delineated the inhibitory role of SOCS-2 in IFNgamma signaling pathway by overexpression of exogenous SOCS-2 in HEK293 cell. The results showed that SOCS-2 suppressed the IFNgamma-activated STAT1 phosphorylation and consequent IFNgamma-regulated transcription of specific genes. To confirm the role of SOCS2 in the Tat-induced process, we demonstrated that SOCS-2 siRNA in human blood monocytes abrogated the Tat-dependent inhibition of IFNgamma signaling. Our data suggested a possible mechanism implicating the role of SOCS-2 in mediating HIV-1-induced immune evasion and dysregulation of IFNgamma signaling in primary human monocytes.

Enhanced levels of the CCR7 ligands CCL19 and CCL21 in HIV infection: correlation with viral load, disease progression and response to highly active antiretroviral therapy

The CCR7 ligands, CCL19 and CCL21, coordinate lymph node homing of naive and central memory T cells. In untreated HIV-infected patients, serum levels of CCL19 and CCL21 showed a biphasic pattern during progression; a marked increase was followed by a decline in patients with advanced immunodeficiency. During highly active antiretroviral therapy, a decrease in CCL19/CCL21 levels was restricted to virologic responders. We suggest that dysregulation of CCR7 ligands may play an important role in progression of HIV infection.

Immune dysregulation in human immunodeficiency virus infection: know it, fix it, prevent it?

Infection of humans by the human immunodeficiency virus (HIV) causes a progressive, multifactorial impairment of the immune system eventually leading to the acquired immunodeficiency syndrome (AIDS). No cure or vaccine exists yet against HIV infection. More worrisome is the fact that despite having identified HIV as the cause of the AIDS, we still do not understand what pathogenic mechanisms lead to the debacle of the immune system. In this review we consider the extent and the limits of our knowledge of HIV pathogenesis, and how this knowledge may be used to design preventive and therapeutic approaches.

Preserved central memory and activated effector memory CD4+ T-cell subsets in human immunodeficiency virus controllers: an ANRS EP36 study

Human immunodeficiency virus (HIV) controllers are rare individuals who spontaneously control HIV type 1 replication for 10 years or more in the absence of antiretroviral treatment. In the present study, HIV controllers (n = 11) maintained potent HIV-specific CD4 responses in spite of very low antigenic loads. Their CD4+ central memory T (T(CM)) cells were characterized by near-normal numbers and preserved interleukin-2 (IL-2) secretion in response to HIV antigens and uniformly high expression of the survival receptor IL-7 receptor alpha (IL-7Ralpha). Controllers expressed CCR7 at higher levels than uninfected controls, suggesting differences in T(CM)-cell homing patterns. CD4+ effector memory T (T(EM))-cell responses were polyfunctional in HIV controllers, while IL-2 secretion was lost in viremic patients. Cytokine production was three times higher in controllers than in treated patients with undetectable viral loads, suggesting an intrinsically more efficient response in the former group. The total CD4+ T(EM)-cell pool underwent immune activation in controllers, as indicated by increased HLA-DR expression, decreased IL-7Ralpha expression, a bias towards gamma interferon production upon polyclonal stimulation, and increased macrophage inflammatory protein 1beta secretion associated with chronic CCR5 down-regulation. Thus, HIV controllers showed a preserved CD4+ T(CM)-cell compartment and signs of potent functional activation in the CD4+ T(EM)-cell compartment. While controllers did not show the generalized immune activation pattern associated with disease progression, they had signs of immune activation restricted to the effector compartment. These findings suggest the induction of an efficient, nondetrimental type of immune activation in patients who spontaneously control HIV.

Progressive CD4+ central memory T cell decline results in CD4+ effector memory insufficiency and overt disease in chronic SIV infection

Primary simian immunodeficiency virus (SIV) infections of rhesus macaques result in the dramatic depletion of CD4⁺ CCR5⁺ effector–memory T (T_EM) cells from extra-lymphoid effector sites, but in most infections, an increased rate of CD4⁺ memory T cell proliferation appears to prevent collapse of effector site CD4⁺ T_EM cell populations and acute-phase AIDS. Eventually, persistent SIV replication results in chronic-phase AIDS, but the responsible mechanisms remain controversial. Here, we demonstrate that in the chronic phase of progressive SIV infection, effector site CD4⁺ T_EM cell populations manifest a slow, continuous decline, and that the degree of this depletion remains a highly significant correlate of late-onset AIDS. We further show that due to persistent immune activation, effector site CD4⁺ T_EM cells are predominantly short-lived, and that their homeostasis is strikingly dependent on the production of new CD4⁺ T_EM cells from central–memory T (T_CM) cell precursors. The instability of effector site CD4⁺ T_EM cell populations over time was not explained by increasing destruction of these cells, but rather was attributable to progressive reduction in their production, secondary to decreasing numbers of CCR5⁻ CD4⁺ T_CM cells. These data suggest that although CD4⁺ T_EM cell depletion is a proximate mechanism of immunodeficiency, the tempo of this depletion and the timing of disease onset are largely determined by destruction, failing production, and gradual decline of CD4⁺ T_CM cells.

A pre-HAART follow-up study of the hematologic manifestations in children with perinatal HIV-1 infection: suggestions for reclassification of clinical staging

Hematologic manifestations in perinatally human immunodeficiency virus-1-infected children have not been widely described in literature. Knowledge of the spontaneous evolution of this disease is essential for achieving optimum care of patients. We analyzed the main hematologic manifestations developed in the prehighly active antiretroviral therapy period of 1217 children, collected from the Italian Register for HIV infection. In 111 patients, the hematologic sign was the first clinical manifestation. Among anemic and neutropenic patients, the fraction of patients in clinical class C was significantly higher than the corresponding fraction in class B (76%, P<0.001 and 74%, P<0.01), and significantly lower in thrombocytopenic patients (42%, P<0.001). The overall progression from class B to C was overlapping to the control group; when separated, however, anemic patients progressed faster (P<0.0001), whereas thrombocytopenic patients had a slower progression, similar to the nonhematologic patients in class A. Anemic patients had a worse prognosis than the control group (P<0.0001), similar to the nonhematologic patients in class C. Finally, the negative prognostic value of anemia was independent from the immunologic condition. Anemia was associated with greater mortality risks. Thrombocytopenia appeared, paradoxically, to be a positive prognostic factor within class B. Centers for Disease Control and Prevention classification presently defines hematologic patients as a single entity; a finer distinction could improve its relevance for the rational design of prevention and therapy.

Persistent anti-gag, -Nef, and -Rev IgM levels as markers of the impaired functions of CD4+ T-helper lymphocytes during SIVmac251 infection of cynomolgus macaques

This study analyzed the antigen-specific (Gag, Nef, Rev, and Tat) IgM, IgG, and IgA humoral responses during the first 200 days of SIVmac251 infection in cynomolgus macaques. These responses were tested for correlation with the CD4(+) T-cell-related hematologic parameters and viral load throughout the course of the study (acute and chronic infection, during and after antiretroviral therapy). Strong inverse correlations were observed between the percentage of CD4(+) T cells at almost every timepoint of the study and the levels of IgM (but not IgG and IgA) against Gag, Nef, and Rev (but not Tat) measured after, but not during, the primary peak of IgM response. Significant levels of persistent antigen-specific IgMs may reflect the prevalence of mature plasma cells that have not undergone immunoglobulin class switching, possibly due to defects in helper T-cell function. Strong correlations were observed between the preinfection CD4(+) T-cell count or CD4/CD8 ratio and the same parameters measured throughout the study, suggesting the importance of preinfection immune status as a determinant of disease progression. The negative correlations between the post-acute-phase IgM levels and the percentage of CD4(+) T cells at later times during the study suggest the potential prognostic value of this measurement.

Viral strategies for evading antiviral cellular immune responses of the host

The host invariably responds to infecting viruses by activating its innate immune system and mounting virus-specific humoral and cellular immune responses. These responses are aimed at controlling viral replication and eliminating the infecting virus from the host. However, viruses have evolved numerous strategies to counter and evade host's antiviral responses. Providing specific examples from the published literature, we discuss in this review article various strategies that viruses have developed to evade antiviral cellular responses of the host. Unraveling these viral strategies allows a better understanding of the host-pathogen interactions and their coevolution. This knowledge is important for identifying novel molecular targets for developing antiviral reagents. Finally, it may also help devise new knowledge-based strategies for developing antiviral vaccines.

Ibogaine reduces organ colonization in murine systemic and gastrointestinal Candida albicans infections

In the present study the effect of the indole alkaloid ibogaine on the in vitro lipolytic activity and adherence to epithelial cells of Candida albicans was investigated. The substance was administered intraperitoneally at a dose of 5 mg kg(-1) day(-1) in mice with disseminated and gastrointestinal C. albicans infections. Ibogaine significantly decreased the rate of mortality and the number of C. albicans c.f.u. recovered from the kidney, liver and spleen. Ibogaine interfered with the early stages of both disseminated and gastrointestinal C. albicans infections but did not reduce the number of C. albicans c.f.u. in the organs at the late phase of infections. The development of a specific immune response was not influenced by ibogaine, since the delayed-type hypersensitivity reaction to C. albicans and the production of interferon (IFN)-gamma were similar in control and ibogaine-treated mice. The combined use of amphotericin B plus ibogaine in the treatment of mice with gastrointestinal infection reduced organ colonization more strongly than each substance alone.

The Nef-mediated AIDS-like disease of CD4C/human immunodeficiency virus transgenic mice is associated with increased Fas/FasL expression on T cells and T-cell death but is not prevented in Fas-, FasL-, tumor necrosis factor receptor 1-, or interleukin-1beta-converting enzyme-deficient or Bcl2-expressing transgenic mice

CD4(+)- and CD8(+)-T-cell death is a frequent immunological dysfunction associated with the development of human AIDS. We studied a murine model of AIDS, the CD4C/HIV transgenic (Tg) mouse model, to assess the importance of the apoptotic pathway in human immunodeficiency virus type 1 (HIV-1) pathogenesis. In these Tg mice, Nef is the major determinant of the disease and is expressed in immature and mature CD4(+) T cells and in cells of the macrophage/myeloid lineage. We report here a novel AIDS-like phenotype: enhanced death, most likely by apoptosis (as assessed by 7-aminoactinomycin D and annexin V/propidium iodide staining), of Tg thymic and peripheral CD4(+) and CD8(+) T cells. The Tg CD4(+) and CD8(+) T cells were also more susceptible to cell death after activation in vitro in mixed lymph node (LN) cultures. However, activation-induced cell death was not higher in Tg than in non-Tg-purified CD4(+) T cells. In addition, expression of Fas and FasL, assessed by flow cytometry, was increased in CD4(+) and CD8(+) T cells from Tg mice compared to that of non-Tg littermates. Despite the enhanced expression of Fas and FasL on Tg CD4(+) and CD8(+) T cells, Fas (lpr/lpr) and FasL (gld/gld) mutant CD4C/HIV Tg mice developed an AIDS-like disease indistinguishable from lpr/+ and gld/+ CD4C/HIV Tg mice, including loss of CD4(+) T cells. Similarly, CD4C/HIV Tg mice homozygous for mutations of two other genes implicated in cell death (interleukin-1beta-converting enzyme [ICE], tumor necrosis factor receptor 1 [TNFR-1]) developed similar AIDS-like disease as their respective heterozygous controls. Moreover, the double-Tg mice from a cross between the Bcl2/Wehi25 and CD4C/HIV Tg mice showed no major protection against disease. These results represent genetic evidence for the dispensable role of Fas, FasL, ICE, and TNFR-1 on the development of both T-cell loss and organ disease of these Tg mice. They also provide compelling evidence on the lack of protection by Bcl2 against Tg CD4(+)-T-cell death. In view of the high resemblance between numerous phenotypes observed in the CD4C/HIV Tg mice and in human AIDS, our findings are likely to be relevant for the human disease.

Allogeneic Corneal Tolerance in Rodents with Long-Term Graft Survival

BACKGROUND

Healthy C57BL/6 orthotopic corneal allografts in place for more than 8 weeks in BALB/c mice (acceptor8w+) can survive indefinitely due to active suppression of the donor-specific delayed-type hypersensitivity (DTH) response. This suggests a state of tolerance in the acceptor mice, however, the mechanism(s) underlying this acceptance remains to be demonstrated. We investigated the relationship between tolerance-induction and the DTH response using murine re-grafting models to explore the possibility of promoting allogeneic corneal regraft acceptance in high-risk graft beds.

METHODS

Acceptor8w+ BALB/c mice received C57BL/6- or C3H corneal regrafts onto the same eye. Re-grafting models were prepared by inducing corneal neovascularization in the graft beds of naive BALB/c mice 2 weeks before corneal allografting. These mice were intravenously (iv) injected with purified splenic T cells or T-cell-depleted splenocytes from acceptor8w+ mice at the time they received re-grafts of C57BL/6 corneas. We also iv injected acceptor8w+ splenocytes into mice bearing healthy primary corneal allografts for 4 weeks (acceptor4w) and assessed their DTH response to C57BL/6 alloantigen(s). In those experiments, acceptor4w mice received a C57BL/6 corneal regraft onto the same eye.

RESULTS

In all acceptor8w+ mice there was indefinite survival of C57BL/6-, but not of C3H regrafts. The iv injection of T cells, but not of T-cell-depleted populations, from acceptor8w+ splenocytes promoted allograft survival. Acceptor4w mice iv injected with acceptor8w+ splenocytes manifested a reduced C57BL/6-specific DTH response and the survival rate of C57BL/6 regrafts was increased from 0% to 87.5%.

CONCLUSION

As donor-specific T cells from acceptor8w+ mice induced prolonged regraft survival, we posit that the active suppression of DTH responses by T cells may have contributed to indefinite allogeneic regraft survival via the induction of corneal allograft tolerance.

Cell surface delivery of the measles virus nucleoprotein: a viral strategy to induce immunosuppression

Although only a few blood cells are infected during measles, this infectious disease is followed by acute immunosuppression, associated with high infant mortality. Measles virus nucleoprotein has been suggested to contribute to virus-induced inhibition of the immune response. However, it has been difficult to understand how this cytosolic viral protein could leave an infected cell and then perturb the immune response. Here we demonstrate that intracellularly synthesized nucleoprotein enters the late endocytic compartment, where it recruits its cellular ligand, the Fcgamma receptor. Nucleoprotein is then expressed at the surfaces of infected leukocytes associated with the Fcgamma receptor and is secreted into the extracellular compartment, allowing its interaction with uninfected cells. Finally, cell-derived nucleoprotein inhibits the secretion of interleukin-12 and the generation of the inflammatory reaction, both shown to be impaired during measles. These results reveal nucleoprotein egress from infected cells as a novel strategy in measles-induced immunosuppression.

Detection of the impairment of CD80 expression on circulating monocytes in HIV-infected Thai children

The mechanism of progressive anergic response in HIV-infected children has yet to be adequately described. One possibility is inappropriate delivery of an essential second signal for T-cell activation due to the inappropriate presentation of co-stimulatory molecules. To determine whether the ligand for the secondary signal is impaired in pediatric AIDS, we compared the level of CD80 expression by circulating monocytes in HIV-infected and-noninfected children (15 mild/asymptomatic, 13 symptomatic and 12 HIV seronegative children). By two-color flow cytometry analysis, there was no statistically significant difference in the percentage of monocytes expressing CD80 among the groups (i.e., 63.2 +/- 15.8, 60.9 +/- 12.7, 61.04 +/- 10.9 for uninfected children, mild-asymptomatic children and symptomatic children, respectively). However, both infected groups showed statistically significant lower levels of CD80 expression, with mean fluorescent intensities of 40.9 +/- 15.9 and 38.8 +/- 10.7 compared to 57.05 +/- 16.3 for the uninfected control group. Our data demonstrated a correlation between HIV infection and impairment of CD80 by circulating monocytes. Whether the impairment on CD80 expression contributes to destruction of the immunological network in HIV-infected children requires further investigation.

Establishment of an ELISA system for determining soluble LAIR-1 levels in sera of patients with HFRS and kidney transplant

LAIR-1, the leukocyte-associated Ig-like receptor-1, is a trans-membrane molecule that functions as an inhibitory receptor on natural killer cells, T lymphocytes and monocytes. It has been well known that many trans-membrane receptors can shed from the cell surface and be released into the circulation in soluble form when lymphocytes, endothelials and other immune cells are activated. In many cases, the levels of soluble receptors in the circulation can be used as markers of lymphocyte activation in transplant patients and virus infection patients. To investigate whether LAIR-1 is able to be released into the sera, we developed a sandwich enzyme-linked immunosorbent assay (ELISA) system based on two anti-LAIR-1 monoclonal antibodies (MAb) with different epitope specificities. Using this ELISA, we found that sLAIR-1 existed in the supernatants collected from PMA, PHA or CD3 MAb-stimulated lymphocytes cultures in vitro for the first time. Moreover, we found that LAIR-1 level in serum samples from healthy individuals was 6.2 +/- 3.3 ng/ml, whereas the levels in sera of patients with hemorrhagic fever with renal syndrome (HFRS) and patients 3-7 days after kidney transplant increased to 47.2 +/- 35.9 and 24.4 +/- 16.0 ng/ml, respectively. Furthermore, HFRS patients in oliguric phase showed higher serum sLAIR-1 levels than those in other phases, and transplant patients with rejection showed higher serum sLAIR-1 level than those without rejection. These findings demonstrated that LAIR-1 can be released when lymphocytes are activated, suggesting sLAIR-1 may be used as a predictor for monitoring immune reaction in some virus infections and organ transplants which may be useful in clinical treatment of these diseases.

A novel mechanism for HIV1-mediated bystander CD4+ T-cell death: neighboring dying cells drive the capacity of HIV1 to kill noncycling primary CD4+ T cells

CD4+ T-cell death is a crucial feature of AIDS pathogenesis, but the mechanisms involved remain unclear. Here, we present in vitro findings that identify a novel process of HIV1 mediated killing of bystander CD4+ T cells, which does not require productive infection of these cells but depends on the presence of neighboring dying cells. X4-tropic HIV1 strains, which use CD4 and CXCR4 as receptors for cell entry, caused death of unstimulated noncycling primary CD4+ T cells only if the viruses were produced by dying, productively infected T cells, but not by living, chronically infected T cells or by living HIV1-transfected HeLa cells. Inducing cell death in HIV1-transfected HeLa cells was sufficient to obtain viruses that caused CD4+ T-cell death. The addition of supernatants from dying control cells, including primary T cells, allowed viruses produced by living HIV1-transfected cells to cause CD4+ T-cell death. CD4+ T-cell killing required HIV1 fusion and/or entry into these cells, but neither HIV1 envelope-mediated CD4 or CXCR4 signaling nor the presence of the HIV1 Nef protein in the viral particles. Supernatants from dying control cells contained CD95 ligand (CD95L), and antibody-mediated neutralization of CD95L prevented these supernatants from complementing HIV1 in inducing CD4+ T-cell death. Our in vitro findings suggest that the very extent of cell death induced in vivo during HIV1 infection by either virus cytopathic effects or immune activation may by itself provide an amplification loop in AIDS pathogenesis. More generally, they provide a paradigm for pathogen-mediated killing processes in which the extent of cell death occurring in the microenvironment might drive the capacity of the pathogen to induce further cell death.

The AIDS-like disease of CD4C/human immunodeficiency virus transgenic mice is associated with accumulation of immature CD11bHi dendritic cells

CD4C/human immunodeficiency virus (HIV) transgenic mice develop an AIDS-like disease. We used this model to study the effects of HIV-1 on dendritic cells (DC). We found a progressive decrease in total DC numbers in the lymph nodes, with a significant accumulation of CD11b(Hi) DC. In the thymus, the recovery of transgenic CD8alpha(+) DC had a tendency to be lower. Spleen DC were augmented in the marginal zone. Transgenic DC showed a decreased capacity to present antigen in vitro, consistent with their reduced major histocompatibility complex class II expression and impaired maturation profile. The accumulation of immature DC may contribute to disease and may reflect an adaptive advantage for the virus by favoring its replication and preventing the generation of fully functional antiviral responses.

Virion-bound ICAM-1 and activated LFA-1: a combination of factors conferring resistance to neutralization by sera from human immunodeficiency virus type 1-infected individuals independently of the disease status and phase

The role of the supplementary interaction between virion-bound host ICAM-1 and LFA-1 on target cells in sensitivity to neutralization of human immunodeficiency virus type 1 (HIV-1) is poorly studied. Serum samples from four long-term nonprogressors (LTNPs) and sequential sera from one progressor were used to assess neutralization sensitivity of isogenic ICAM-1-negative and ICAM-1-bearing HIV-1(NL4-3), a prototype of T-cell-line-adapted viruses. We found that virus neutralization sensitivity to the studied sera is not modified by the additional interaction between virally embedded ICAM-1 and LFA-1 under an inactive state. However, expression on the target cell surface of an activated LFA-1 form renders ICAM-1-bearing virus particles, but not viruses devoid of ICAM-1, more refractory to neutralization by sera from three out of four LTNPs and all sequential sera from the person who has experienced a progression of the HIV-1-associated disease. Although no conclusive correlation could be drawn between virus susceptibility to neutralization and the disease status or stages of HIV-1 infection, these findings demonstrate that other nonspecific virus-cell interactions mediated by virion-anchored host proteins and their normal cognate ligands on target cells represent factors that can affect the mechanism of HIV-1 neutralization.

Expression and regulation of B7 family molecules on macrophages (MPhi) in preterm and term neonatal cord blood and peripheral blood of adults

BACKGROUND

Macrophage (MPhi) receptors of the B7 family (CD80, CD86) play a crucial role in T cell activation: the lack of costimulation leads to anergy or apoptosis of reactive T cells. MPhi may differentiate into different subsets, the balance of which defines MPhi-dependent T cell reactions. The aim of this study was to examine neonatal and adult T cell response with respect to the costimulatory MPhi-potential in order to identify molecular predictors for the neonatal immune defense.

METHODS

MPhi from peripheral blood (PBMPhi) or cord blood (CBMPhi) were stimulated with interferon-gamma (IFN-gamma), cyclic adenosine monophosphate (cAMP), CD40 ligand (CD40L), or alphaCD3.

RESULTS

As compared to PBMPhi, CBMPhi showed a significantly decreased upregulation of CD80 and/or CD86 after stimulation with IFN-gamma, cAMP, CD40L, and alphaCD3. Accordingly, the proliferative T cell response was impaired in the presence of CBMPhi. The fraction of T cells that underwent cell death was higher, and blast formation was significantly lower than that observed in the presence of PBMPhi.

CONCLUSIONS

CBMPhi, as compared to PBMPhi, delivered fewer costimulatory but more cytotoxic signals to T cells. These observations suggest that MPhi are one factor explaining the suboptimal immune defense of neonates and their increased susceptibility to infection. Using the costimulatory MPhi-potential as a predictor for immune responses requires a separate reference value system in neonatology.

Discordant effects of interleukin-2 on viral and immune parameters in human immunodeficiency virus-1-infected monocyte-derived mature dendritic cells

Use of interleukin-2 (IL-2) in the immunotherapy of human immunodeficiency virus (HIV) has frequently resulted in the restoration of CD4 lymphocyte counts but not of virus-specific responses. We reasoned that the absence of reconstituted functional immune parameters could be related to the inability of IL-2 to correct HIV-induced dysfunctions in antigen-presenting cells. In this study, we used in vitro-differentiated monocyte-derived macrophages (MDMs) and mature dendritic cells (MDDCs), acutely infected with primary HIV-1 isolates, to analyse the effects of IL-2 on virus replication, co-receptor expression, and cytokine or chemokine release. Stimulation of MDMs with IL-2 had no measurable effect on HIV-1 replication, on cytokine secretion, or on CD4 and CXCR4 gene expression. Moreover, although a significant down-regulation of CCR5 mRNA expression could be repeatedly detected in MDMs, this IL-2-mediated effect was not of substantial magnitude to affect virus replication. On the other hand, IL-2 stimulation of MDDCs dramatically increased HIV-1 replication and this effect was highly evident on low-replicating, CXCR4-dependent isolates. Nevertheless, the HIV-enhancing activity of IL-2 in MDDCs was not accompanied by any measurable change in cytokine or chemokine release, in virus receptor and co-receptor mRNA accumulation, or in the surface expression of a battery of receptors implicated in virus entry, cell activation or costimulatory function. Taken together, these findings point to a role for IL-2 in inducing virus purging from dendritic cell reservoirs but indicate no relevant potential of the cytokine in restoring defective elements of innate immunity in HIV infection.

Studies on the production of IL-15 in HIV-infected/AIDS patients

IL-15 is essential for the development and differentiation of NK cells. It selectively induces proliferation of CD8+ memory T lymphocytes. Despite its importance in both innate and adaptive immune responses, little is known about its production in HIV-infected persons. We report here that IL-15 levels are significantly decreased in the sera of HIV-infected/AIDS patients compared to control sera. We also show that PBMC from the infected patients are compromised in their ability to respond with enhanced production of IL-15 upon exposure to HSV-1. The decreased production of IL-15 occurs despite a comparable increase in IL-15 mRNA in the PBMC of HIV-infected and healthy HIV-seronegative donors when exposed to HSV-1. The HSV-stimulated patients' PBMC exhibited less NK activity compared to similarly treated normal PBMC. These results suggest that a compromised ability of PBMC from HIV-infected individuals to induce IL-15 production in response to a viral stimulus may be a reason of their compromised innate and adaptive immunity.

Elevated levels of circulating interleukin-18 in human immunodeficiency virus-infected individuals: role of peripheral blood mononuclear cells and implications for AIDS pathogenesis

Originally identified as the gamma interferon-inducing factor, interleukin-18 (IL-18) was rediscovered as a proinflammatory cytokine related to the IL-1 family of cytokines that plays an important role in both innate and adaptive immune responses against viruses and intracellular pathogens. Despite its importance in inducing and regulating immune responses, relatively little is known about its production in HIV infection. We report here significantly (P < 0.05) elevated levels of this cytokine in the sera of human immunodeficiency virus (HIV)-infected/AIDS patients compared to those of HIV-seronegative healthy persons. Surprisingly, the peripheral blood mononuclear cells (PBMC) from HIV-infected/AIDS patients were compromised in the ability to upregulate IL-18 gene expression and produce this cytokine with and without lipopolysaccharide (LPS) stimulation. A significant positive correlation (P < 0.05) existed between the concentration of IL-18 in serum and its production from PBMC of HIV-seronegative healthy individuals but not those of HIV-infected/AIDS patients. Furthermore, the patients' PBMC expressed relatively reduced levels of activated caspase-1 constitutively as well as in response to LPS stimulation. Our data suggest the involvement of transforming growth factor beta (TGF-beta) in suppressing IL-18 production from the patients' PBMC for the following reasons. (i) In in vitro studies it suppressed the production of IL-18 from PBMC. (ii) Its levels were significantly higher in the plasma of patients compared to that of control subjects. (iii) A significant negative correlation existed between the concentrations of TGF-beta in plasma and of IL-18 in serum of the patients. The elevated levels of IL-18 in the serum of HIV-infected individuals may contribute to AIDS pathogenesis, whereas its compromised production from their PBMC in response to stimuli may reduce their innate defense to opportunistic intracellular pathogens.

Potential roles of cellular proteins in HIV-1

Human immunodeficiency virus type-1 particles contain host proteins, both on their surface and interior. This review summarises the cellular proteins found in these virions and covers some of their potential roles in the viral life cycle and pathogenesis. For most proteins studied, their role and function are either unknown or in the hypothesis stage. This reflects the relatively recent emphasis given to these proteins by the HIV-1 field as well as the incomplete understanding of their function in the cell. The study of cellular proteins in HIV-1 promises to help us better understand the interaction of this virus with the cell, the immune system, and the whole human host as well as to shed light on the nature of AIDS and suggest more targets for therapeutic intervention. Finally, many of the cell systems themselves are still poorly understood. The extensive study of HIV-1 has already brought increased attention to the fields of immunology and vaccine science and, in the same way, might assist our understanding of the cellular pathways themselves.

Cytotoxic HIV-1 p55gag-specific CD4+ T cells produce HIV-inhibitory cytokines and chemokines

CD4+ T-helper cells appear to be essential in sustaining immune responses in chronic viral infections, as the maintenance of CD8+ cytotoxic T-lymphocyte responses and the control of viremia were demonstrated to depend on CD4+ T cell help. In order to investigate the function of HIV-specific CD4+ T cells in chronic HIV-1-infection, 49 chronically HIV-infected patients were analyzed before and 3 and 6 months after initiation of antiviral treatment. Ten patients showed a substantial, although weak, proliferative response to HIV-1-p55gag protein for which no improvement was observed upon initiation of HAART. From one individual, HIV-1-p55gag-specific CD4-positive T-cell clones were generated that were heterogeneous in their TCR Vbeta gene usage and HLA-DRB1*13 and DRB1*03 restricted, respectively. In addition, some CD4+ TCC produced substantial amounts of IFN-gamma and MIP-1alpha/beta were perforin-positive, and showed cytotoxic activity. These diverse functional features of HIV-specific CD4+ T cells suggest that they may exert direct antiviral activity.

Modulation of human immunodeficiency virus (HIV)-specific immune response by using efavirenz, nelfinavir, and stavudine in a rescue therapy regimen for HIV-infected, drug-experienced patients

Analysis of the virologic and immunomodulatory effects of an association of efavirenz (EFV), nelfinavir (NFV), and stavudine (d4T) was performed in 18 human immunodeficiency virus (HIV)-infected and highly active antiretroviral therapy (HAART)-experienced patients who failed multiple therapeutic protocols. Patients (<500 CD4(+) cells/ micro l; >10,000 HIV copies/ml) were nonnucleoside reverse transcriptase inhibitor (NNRTI)-naive and were treated for 10 months with EFV (600 mg/day) in association with NFV (750 mg three times daily) and d4T (30 or 40 mg twice daily). Measurement of HIV peptide- and mitogen-stimulated production of interleukin-2 (IL-2), gamma interferon (IFN-gamma), IL-4, and IL-10 as well as quantitation of mRNA for the same cytokines in unstimulated peripheral blood mononuclear cells were performed at baseline and 2 weeks (t1), 2 months (t2), and 10 months (t3) into therapy. The results showed that HIV-specific (but not mitogen-stimulated) IL-2 and IFN-gamma production was augmented and IL-10 production was reduced in patients who received EFV, NFV, and d4T. Therapy was also associated with a reduction in HIV RNA in plasma and an increase in CD4(+) cell count. These changes occurred in the first year of therapy (t2 and t3) and were confirmed by quantitation of cytokine-specific mRNA. Therapy with EFV, NFV, and d4T increases HIV-specific type 1 cytokine production as well as CD4 counts and reduces plasma viremia. This therapeutic regimen may be considered for use in cases of advanced HIV infection.

Clinical tolerance and immunologic effects after single or repeated administrations of the synthetic immunomodulator murabutide in HIV-1-infected patients

Correction of the virus-induced deficits in innate immunity of HIV-infected subjects could well contribute to enhanced immune recovery and efficacious control of viral replication. The safe synthetic immunomodulator Murabutide (ISTAC Biotechnology, Lille, France) has been found to regulate the function of antigen-presenting cells and to selectively activate CD4 lymphocytes leading to dramatic suppression of HIV replication, in vitro. Therefore, as a first step toward the evaluation of the immunotherapeutic potential of Murabutide in HIV disease, we have conducted two phase 1/2 clinical trials to address the safety and the immunologic effects of Murabutide administration into HIV-infected subjects receiving antiretroviral therapy. The first study revealed that single administration of 5, 7, or 9 mg of Murabutide, to 6 patients per dose, was well tolerated. This was accompanied by a selective induction of cytokines and chemokines detectable in the serum, and the levels appeared to plateau at the 7-mg dose. The second study then evaluated the safety and biological effects of repeated administrations of 7 mg Murabutide, on 5 consecutive days, in 12 HIV-1-infected patients. A good clinical tolerance was noted throughout the study. Moreover, changes in several immune parameters, including downregulation of coreceptor expression on lymphocytes and improved lymphoproliferative responses, were detected during or/and up to 3 weeks after Murabutide administration. These encouraging results warrant further evaluation of longer periods or cycles of immunotherapy with Murabutide in HIV-infected subjects.

Cytopathic killing of peripheral blood CD4(+) T lymphocytes by human immunodeficiency virus type 1 appears necrotic rather than apoptotic and does not require env

An important unresolved issue of AIDS pathogenesis is the mechanism of human immunodeficiency virus (HIV)-induced CD4(+) T-lymphocyte destruction. We show here that HIV type 1 (HIV-1) exerts a profound cytopathic effect upon peripheral blood CD4(+) T lymphocytes that resembles necrosis rather than apoptosis. Necrotic cytopathology was found with both laboratory-adapted strains and primary isolates of HIV-1. We carefully investigated the role of env, which has been previously implicated in HIV cytopathicity. HIV-1 stocks with equivalent infectivity were prepared from constructs with either an intact or mutated env coding region and pseudotyped with the glycoprotein of vesicular stomatitis virus (VSV-G) so that the HIV envelope was not rate-limiting for infection. Infected Jurkat T cells died whether or not env was intact; however, the expression of env accelerated death significantly. The accelerated death was blocked by protease inhibitors, indicating that it was due to reinfection by newly produced virus in env(+) cultures. Accordingly, we found no disparity in kinetics in CD4(lo) Jurkat cells. In highly infected peripheral blood T cells, profound necrosis occurred equivalently with both env(+) and env(-) stocks of HIV-1. We also found that HIV-1 cytopathicity was undiminished by the absence of nef. However, viral stocks made by complementation or packaging of HIV-1 genomes with the natural protein-coding sequences replaced by the green fluorescent protein were highly infectious but not cytopathic. Thus, env can accelerate cell death chiefly as an entry function, but one or more viral functions other than env or nef is essential for necrosis of CD4(+) T cells induced by HIV-1.

Disrupted homeostasis of Langerhans cells and interdigitating dendritic cells in monkeys with AIDS

Langerhans cells (LCs) are immature dendritic cells (DCs) that capture antigen in peripheral tissues and migrate to draining lymph nodes, where they reside in the paracortex as interdigitating dendritic cells (IDCs). We studied the effects of simian immunodeficiency virus (SIV) on LCs and IDCs during different stages of infection in monkeys. LCs isolated from monkeys with acute SIV infection or acquired immunodeficiency syndrome (AIDS) underwent normal maturation in vitro, including a switch in chemokine receptor expression from CCR5 to CXCR4 and CCR7. LCs migrated normally from skin in response to contact sensitization in monkeys with acute SIV infection. In contrast, LC migration from skin was markedly impaired during AIDS, associated with a reduction in antigen-bearing DCs in draining lymph nodes. Lymph node IDCs were increased in proportion during acute SIV infection and had an activated phenotype, whereas during AIDS IDCs had significantly lower expression of CD40 and the activation marker CD83. IDCs from monkeys with AIDS were refractory to stimulation with CD40L, demonstrating a functional consequence of decreased CD40 expression. SIV-infected DCs were not identified in lymph nodes or skin of monkeys with AIDS, suggesting an indirect effect of infection on DC populations in vivo. These data indicate that DCs are mobilized to lymph nodes during acute SIV infection, but that during AIDS this process is suppressed, with LC migration and IDC activation being impaired. We conclude that disruption of DC homeostasis may play a role in immunopathology induced by human immunodeficiency virus and suggest that therapeutic strategies targeting DCs may have limited efficacy during AIDS.

Presence of host ICAM-1 in laboratory and clinical strains of human immunodeficiency virus type 1 increases virus infectivity and CD4(+)-T-cell depletion in human lymphoid tissue, a major site of replication in vivo

Human immunodeficiency virus type 1 (HIV-1) incorporates several host proteins. Earlier studies have indicated that such foreign constituents can modulate the virus life cycle, although the potential roles that these proteins might play in the viral pathology in vivo remain unclear. In an attempt to shed light on this issue, we first exposed explants of human lymphoid tissue to isogenic viruses except for the presence or absence of host-derived ICAM-1. Incorporation of ICAM-1 alone increased HIV-1 infectivity for human tonsillar tissue cultured ex vivo. This observation was made for viruses bearing distinct coreceptor utilization profiles. Conversion of LFA-1 to a high-affinity-high-avidity state for ICAM-1 further augmented the susceptibility of human tonsillar histocultures to infection by ICAM-1-bearing virions. A more massive depletion of CD4(+) T lymphocytes was seen with X4 ICAM-1/POS viruses than with isogenic ICAM-1/NEG virions. Exposure of X4 and R5 primary isolates of HIV-1 to a blocking anti-ICAM-1 antibody resulted in a decrease of virus infection. Finally, X4 and R5 virions derived from a natural human lymphoid tissue microenvironment incorporated high levels of ICAM-1. Altogether, these results indicate that the incorporation of host ICAM-1 can significantly modulate the biology of HIV-1 in a cellular milieu recognized as the major site of replication in vivo and suggest that host proteins found in HIV-1 particles may participate in the pathogenesis of this disease.

Variable fate of virus-specific CD4(+) T cells during primary HIV-1 infection

Impairment of CD4(+) T lymphocyte responses to human immunodeficiency virus (HIV)-derived antigens is the classic immunological defect observed during the chronic phase of HIV-1 infection. Early intervention with potent antiretroviral therapy (ART) can preserve HIV-specific CD4(+) T lymphocyte reactivity, providing indirect evidence that such responses are mounted during primary infection and subsequently lost in the majority of infected individuals. Here, we demonstrate early and dramatic expansions of functional HIV-specific CD4(+) T lymphocyte frequencies directly ex vivo. These responses are initially of broad specificity, and can disappear rapidly during the natural course of primary infection. This process of loss is variable, such that the rapidity and extent of functional compromise differs between individuals. Institution of ART during these early phases of HIV-1 infection preserves patterns of functional reactivity within the HIV-specific CD4(+) T lymphocyte population. However, there was no evidence for the restoration of deleted responses. These findings indicate that, in some individuals at least, ART must be administered within a narrow window of opportunity during primary HIV-1 infection to effect substantial immune preservation.

Strategies for designing and optimizing new generation vaccines

Although the field of immunology developed in part from the early vaccine studies of Edward Jenner, Louis Pasteur and others, vaccine development had largely become the province of virologists and other microbiologists, because the model for classic vaccines was to isolate the pathogen and prepare a killed or attenuated pathogen vaccine. Only recently has vaccinology returned to the realm of immunology, because a new understanding of immune mechanisms has allowed translation of basic discoveries into vaccine strategies.

Overcoming original (antigenic) sin

Original antigenic sin describes a phenomenon in which the antibody response elicited in an individual after a secondary viral infection reacts more strongly to the viral variant that originally infected the individual. As T helper cells play critical roles in promoting antibody responses, a similar phenomenon may hold true for T helper cell responses. This concept is particularly relevant to the development of vaccines against viruses such as human immunodeficiency virus and hepatitis C virus, in which myriad viral variants are present throughout the human population. We have compared the effects of priming the immune system with a single peptide epitope or with a cocktail of related peptides based on the epitope. Our data demonstrate that immunization with multiple peptide variants expands a more broadly reactive and durable T helper cell response than does immunization with a single peptide. This vaccine strategy may circumvent original antigenic sin.

CCR5 and CXCR4 expression correlated with X4 and R5 HIV-1 infection yet not sustained replication in Th1 and Th2 cells

OBJECTIVE

To investigate the infectivity of T-helper (Th)1 and Th2 cells (derived from ccr5 wild-type and homozygous ccr5 Delta 32) to R5 and X4 HIV-1.

DESIGN

It remains unclear whether infection of Th1 and Th2 CD4 cells by R5 and X4 viruses mirrors their co-receptor expression profile as no direct quantitation of coreceptor levels and infection has been performed. In addition, it is unknown whether the lack of CCR5 expression affects the degree of Th1/Th2 polarization.

METHODS

Surface expression of CCR5 and CXCR4 was determined by quantitative fluorescence activated cell sorter analysis on in vitro differentiated Th1 and Th2 cells. R5 (Ba-L) and X4 (IIIB) HIV-1 isolates were used for infection studies and the efficiency of viral entry was determined by quantitative real time polymerase chain reaction detection of reverse transcribed proviral DNA.

RESULTS

Cell surface density of CCR5 molecules was eight-fold higher in Th1 versus Th2 subsets (P = 0.005) whereas CXCR4 surface density was four-fold higher in Th2 versus Th1 subsets (P = 0.006). Preferential infection and entry of Th1 cells by R5 HIV-1 was not associated with preferential replication, as eventually the R5-virus replicated to a higher level in Th2 cells in spite of lower initial viral infection/entry. By contrast, Th2 cells preferentially supported X4-virus infection and replication. High beta chemokine secretion by Th1 cells was associated with a lower R5 replication rate.

CONCLUSIONS

Th1 and Th2 cells differ in their infection efficiency for R5 and X4 HIV-1. ccr5 Delta 32-homozygous individuals maintain the ability for Th1/Th2 polarization, i.e., the expression of CCR5 is not required for Th1/Th2 polarization.

Dressed to kill? A review of why antiviral CD8 T lymphocytes fail to prevent progressive immunodeficiency in HIV-1 infection

CD8 T cells play an important role in protection and control of HIV-1 by direct cytolysis of infected cells and by suppression of viral replication by secreted factors. However, although HIV-1-infected individuals have a high frequency of HIV-1-specific CD8 T cells, viral reservoirs persist and progressive immunodeficiency generally ensues in the absence of continuous potent antiviral drugs. Freshly isolated HIV-specific CD8 T cells are often unable to lyse HIV-1-infected cells. Maturation into competent cytotoxic T lymphocytes may be blocked during the initial encounter with antigen because of defects in antigen presentation by interdigitating dendritic cells or HIV-infected macrophages. The molecular basis for impaired function is multifactorial, due to incomplete T-cell signaling and activation (in part related to CD3zeta and CD28 down-modulation), reduced perforin expression, and inefficient trafficking of HIV-specific CD8 T cells to lymphoid sites of infection. CD8 T-cell dysfunction can partially be corrected in vitro with short-term exposure to interleukin 2, suggesting that impaired HIV-specific CD4 T helper function may play a significant causal or exacerbating role. Functional defects are qualitatively different and more severe with advanced disease, when interferon gamma production also becomes compromised.

Evidence for a post-entry barrier to R5 HIV-1 infection of CD4 memory T cells

BACKGROUND

HIV-1 strains R5 and X4 can infect CD4 memory T cells in vivo. Anti-CD3/28 stimulation induces beta-chemokines and CCR5 down-regulation and renders these cells resistant to R5 HIV-1 infection. Here we describe an additional cellular mechanism that blocks productive R5 HIV-1 infection of CD4 memory T cells.

METHODS

Blood-derived CD4 memory T cells and CD4 T-cell clones were infected with primary R5 and X4 HIV-1 strains. Virus replication was correlated with CCR5 expression and beta-chemokine production. Virus entry and infectivity were measured by PCR for early and late products of HIV reverse transcription respectively.

RESULTS

R5 strains were up to 1000-fold less infectious than X4 viruses for CD4 memory T cells. This resistance was independent of CCR5 levels and of the Delta-32 mutation and the CCR2-V64I/CCR5-59653T linked mutations. Blocking endogenous beta-chemokines relieved minimally this restriction. At the single cell level, CD4 memory cells were either permissive or non-permissive for R5 HIV-1 infection. R5 HIV titre was up to 10-fold lower than X4 virus titre even in a permissive clone. However, R5 viruses replicated as efficiently as X4 viruses in the permissive clone when neutralizing anti-beta chemokine antibodies were added. Non-permissive cells blocked a post-entry step of the virus life-cycle and expressed early but not late HIV transcripts. Neutralizing anti-beta chemokine antibodies promoted R5 virus replication marginally in the non-permissive clone.

CONCLUSION

Some blood memory CD4 T cells retard R5 HIV-1 replication via endogenous beta-chemokines whereas others block productive R5 HIV-1 infection by an additional mechanism that interferes with a post-entry step of the virus life cycle. These natural barriers might contribute to lower pathogenicity of R5 HIV-1 strains for CD4 memory T cells than X4 viruses that emerge late in disease.