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Guido Silvestri

Publications and source records attributed to Guido Silvestri.

At least 19 recordsLinked to original sources
PubMed2006

Microbial translocation is a cause of systemic immune activation in chronic HIV infection.

Chronic activation of the immune system is a hallmark of progressive HIV infection and better predicts disease outcome than plasma viral load, yet its etiology remains obscure. Here we show that circulating microbial products, probably derived from the gastrointestinal tract, are a cause of HIV-related systemic immune activation. Circulating lipopolysaccharide, which we used as an indicator of microbial translocation, was significantly increased in chronically HIV-infected individuals and in simian immunodeficiency virus (SIV)-infected rhesus macaques (P <or= 0.002). We show that increased lipopolysaccharide is bioactive in vivo and correlates with measures of innate and adaptive immune activation. Effective antiretroviral therapy seemed to reduce microbial translocation partially. Furthermore, in nonpathogenic SIV infection of sooty mangabeys, microbial translocation did not seem to occur. These data establish a mechanism for chronic immune activation in the context of a compromised gastrointestinal mucosal surface and provide new directions for therapeutic interventions that modify the consequences of acute HIV infection.

Animals↗
PubMed2006

Paucity of CD4+CCR5+ T cells is a typical feature of natural SIV hosts.

In contrast to lentiviral infections of humans and macaques, simian immunodeficiency virus (SIV) infection of natural hosts is nonpathogenic despite high levels of viral replication. However, the mechanisms underlying this absence of disease are unknown. Here we report that natural hosts for SIV infection express remarkably low levels of CCR5 on CD4+ T cells isolated from blood, lymph nodes, and mucosal tissues. Given that this immunologic feature is found in 5 different species of natural SIV hosts (sooty mangabeys, African green monkeys, mandrills, sun-tailed monkeys, and chimpanzees) but is absent in 5 nonnatural/recent hosts (humans, rhesus, pigtail, cynomolgus macaques, and baboons), it may represent a key feature of the coevolution between the virus and its natural hosts that led to a nonpathogenic infection. Beneficial effects of low CCR5 expression on CD4+ T cells may include the reduction of target cells for viral replication and a decreased homing of activated CD4+ T cells to inflamed tissue.

Animals↗
PubMed2006

Impaired in-vitro growth of megakaryocytic colonies derived from CD34 cells of HIV-1-infected patients with active viral replication.

OBJECTIVE: To address the mechanisms of the thrombocytopoietic dysfunction that may follow HIV infection and to compare peripheral blood and bone marrow as sources of CD34 progenitor cells in HIV-infected patients. METHODS: The study used CD34 progenitor cells from 20 previously untreated HIV-infected individuals, 20 HIV-infected individuals treated with antiretroviral therapy and a control group of 20 HIV-uninfected healthy individuals to examine in-vitro megakaryocytopoiesis. There were no hematological abnormalities at baseline in the study groups. CD34 progenitor cells derived from peripheral blood and bone marrow were purified and cultured in medium containing thrombopoietin, interleukin-3, and interleukin-6. HIV-1 plasma viral load was determined by b-DNA technique. Expression of receptors for thrombopoietin, interleukin-3, and interleukin-6 was assessed on CD34 cells by flow cytometry, and numbers of receptors per single cell were calculated by Quanticalc software. RESULTS: Growth of megakaryocytopoietic colony-forming units (CFU-MK) were impaired in untreated HIV-infected individuals despite normal platelet counts. Viral load levels inversely correlate with CFU-MK growth and platelet counts. Antiretroviral drug-treated individuals showed normal megakaryocyte development. Similar results were obtained whether the CD34 progenitor cells derived from peripheral blood or bone marrow. CONCLUSIONS: These findings suggest that megakaryocyte differentiation is impaired before the onset of overt thrombocytopenia in HIV-infected patients and provide evidence for a direct link between viral replication and perturbed megakaryocytopoiesis, which appears to be prevented and/or restored by antiretroviral therapy. The results indicate that peripheral blood represents a suitable source of CD34 hematopoietic progenitors for studies of megakaryocytopoiesis in HIV disease.

Antigens, CD34↗
PubMed2006

Nef-mediated suppression of T cell activation was lost in a lentiviral lineage that gave rise to HIV-1.

High-level immune activation and T cell apoptosis represent a hallmark of HIV-1 infection that is absent from nonpathogenic SIV infections in natural primate hosts. The mechanisms causing these varying levels of immune activation are not understood. Here, we report that nef alleles from the great majority of primate lentiviruses, including HIV-2, downmodulate TCR-CD3 from infected T cells, thereby blocking their responsiveness to activation. In contrast, nef alleles from HIV-1 and a subset of closely related SIVs fail to downregulate TCR-CD3 and to inhibit cell death. Thus, Nef-mediated suppression of T cell activation is a fundamental property of primate lentiviruses that likely evolved to maintain viral persistence in the context of an intact host immune system. This function was lost during viral evolution in a lineage that gave rise to HIV-1 and may have predisposed the simian precursor of HIV-1 for greater pathogenicity in humans.

Animals↗
PubMed2006

The AIDS resistance of naturally SIV-infected sooty mangabeys is independent of cellular immunity to the virus.

In contrast to human immunodeficiency virus (HIV)-infected humans, natural hosts for simian immunodeficiency virus (SIV) very rarely progress to acquired immunodeficiency syndrome (AIDS). While the mechanisms underlying this disease resistance are still poorly understood, a consistent feature of natural SIV infection is the absence of the generalized immune activation associated with HIV infection. To investigate the immunologic mechanisms underlying the absence of AIDS in SIV-infected sooty mangabeys (SMs), a natural host species, we performed a detailed analysis of the SIV-specific cellular immune responses in 110 SIV-infected SMs. We found that while SIV-specific T-cell responses are detectable in the majority of animals, their magnitude and breadth are, in fact, lower than what has been described in HIV-infected humans, both in terms of cytokine production (ie, IFN-gamma, TNF-alpha, and IL-2) and degranulation (ie, CD107a expression). Of importance, SIV-specific T-cell responses were similarly low when either SIVmac239-derived peptides or autologous SIVsmm peptides were used as stimuli. No correlation was found between SIV-specific T-cell responses and either viral load or CD4+ T-cell count, or between these responses and markers of T-cell activation and proliferation. These findings indicate that the absence of AIDS in naturally SIV-infected sooty mangabeys is independent of a strong cellular immune response to the virus.

Acquired Immunodeficiency Syndrome↗
PubMed2006

Simian immunodeficiency viruses replication dynamics in African non-human primate hosts: common patterns and species-specific differences.

METHODS: To define potential common features of simian immunodeficiency virus (SIV) infections in different naturally infected host species, we compared the dynamics of viral replication in 31 African green monkeys (10 sabeus, 15 vervets and seven Caribbean AGMs), 14 mandrills and three sooty mangabeys (SMs) that were experimentally infected with their species-specific viruses. RESULTS: After infection, these SIVs replicated rapidly reaching viral loads (VLs) of 10(5)-10(9) copies/ml of plasma between days 9-14 post-infection (p.i). Set point viremia was established between days 42 and 60 p.i., with levels of approximately 10(5)-10(6) copies/ml in SM and mandrills, and lower levels (10(3)-10(5) copies/ml) in AGMs. VL during the chronic phase did not correlate with viral genome structure: SIVmnd-2 (a vpx-containing virus) and SIVmnd-1 (which does not contain vpu or vpx) replicated to similar levels in mandrills. VL was dependent on virus strain: vervets infected with three different viral strains showed different patterns of viral replication. The pattern of viral replication of SIVagm.sab, which uses both CCR5 and CXCR4 co-receptors was similar to those of the other viruses. CONCLUSIONS: Our results show a common pattern of SIV replication in naturally and experimentally infected hosts. This is similar overall to that observed in pathogenic SIV infection of macaques. This result indicates that differences in clinical outcome between pathogenic and non-pathogenic infections rely on host responses rather than the characteristics of the virus itself.

Animals↗
PubMed2005

Timely triggering of homeostatic mechanisms involved in the regulation of T-cell levels in SIVsm-infected sooty mangabeys.

Sooty mangabeys, the natural host of simian immunodeficiency virus (SIVsm), generally avoid progressive depletion of CD4+ T cells and opportunistic infections associated with infection of humans (HIV) and macaques (SIVmac). The means by which the SIVsm-infected mangabeys maintain CD4+ T-cell levels despite high rates of viral replication is unknown. One cytokine that has a key role in the regulation of T-cell levels is interleukin-7 (IL-7). Here, the longitudinal assessment of 6 SIVsm-infected mangabeys identified an early increase in plasma IL-7 levels at weeks 1 to 5 after infection. This IL-7 increase correlated with an early decline in CD4+ T-cell levels (decline of 492-1171 cells/microL) accompanying acute viremia. Elevated IL-7 levels were followed by increased T-cell proliferation (Ki67) and maintenance of lower but stable (more than 500 cells/microL) CD4+ T-cell levels in each mangabey through 37 weeks of infection. These data contrast with our earlier studies in SIVmac-infected macaques, in which the IL-7 increase was delayed until 20 to 40 weeks after infection, just before the onset of simian AIDS. Taken together, these data suggest that timely triggering of IL-7 is important for stabilizing healthy T-cell levels in mangabeys and that timely administration of exogenous IL-7 may show benefit during pathogenic SIVmac and HIV infection.

Animals↗
PubMed2005

Loss of CD127 expression defines an expansion of effector CD8+ T cells in HIV-infected individuals.

The immunodeficiency that follows HIV infection is related to the virus-mediated killing of infected CD4(+) T cells, the chronic activation of the immune system, and the impairment of T cell production. In this study we show that in HIV-infected individuals the loss of IL-7R (CD127) expression defines the expansion of a subset of CD8(+) T cells, specific for HIV as well as other Ags, that show phenotypic (i.e., loss of CCR7 and CD62 ligand expression with enrichment in activated and/or proliferating cells) as well as functional (i.e., production of IFN-gamma, but not IL-2, decreased ex vivo proliferative potential and increased susceptibility to apoptosis) features of effector T cells. Importantly, in HIV-infected individuals the levels of CD8(+)CD127(-) T cells are directly correlated with the main markers of disease progression (i.e., plasma viremia and CD4(+) T cell depletion) as well as with the indices of overall T cell activation. In all, these results identify the expansion of CD8(+)CD127(-) effector-like T cells as a novel feature of the HIV-associated immune perturbation. Further studies are thus warranted to determine whether measurements of CD127 expression on CD8(+) T cells may be useful in the clinical management of HIV-infected individuals.

Adult↗
PubMed2005

CD4+ T-cell depletion in HIV infection: killed by friendly fire?

Recent studies have emphasized the role of a chronic, generalized activation of the immune system as a prominent cause of CD4+ T-cell depletion in HIV-infected patients. The HIV-induced immune activation is a strong predictor of disease progression in humans, and lack of immune activation is a key feature of nonpathogenic simian immunodeficiency virus (SIV) infection of natural hosts. The mechanisms by which immune activation induces CD4+ T-cell depletion are still incompletely understood, but likely involve changes in the complex dynamics of the naive, memory, and effector subsets of T cells. A better understanding of how HIV-induced immune activation leads to CD4+ T-cell depletion may provide new targets for immune-based interventions that could be used, in addition to standard antiretroviral therapy, to slow disease progression in HIV-infected individuals.

Animals↗
PubMed2005

Viral and host factors in the pathogenesis of HIV infection.

Recent studies suggest that the pathogenesis of HIV infection and AIDS involves two distinct phases. During acute infection, massive depletion of CD4+CCR5+ memory T cells within the mucosal-associated lymphoid tissue leads to major and potentially irreversible damage to CD4+ T-cell-mediated immune functions. The emergence of potent, but ultimately ineffective, cell-mediated and humoral responses to HIV leads to the chronic phase of infection, which is characterized by partial control of viral replication, chronic immune activation, progressive decline of the naïve and memory T-cell pool, and systemic CD4+ T-cell depletion. The identification of these two pathogenic phases of HIV infection could have important implications in terms of HIV therapy and vaccine development.

AIDS Vaccines↗
PubMed2005

Naturally SIV-infected sooty mangabeys: are we closer to understanding why they do not develop AIDS?

Simian immunodeficiency viruses (SIV) infection of sooty mangabey (SM) monkeys (Cercocebus atys), a natural host species, does not induce CD4+ T cell depletion and acquired immunodeficiency syndrome (AIDS) despite chronic high levels of virus replication. In contrast, SIV infection of non-natural host species, such as rhesus macaques (RM), induces a disease that closely resembles AIDS in humans. The mechanisms underlying the lack of disease progression in SIV-infected SMs are incompletely understood, but certainly reflect a complex evolutionary adaptation whereby the host immune system is not significantly damaged by the highly replicating virus. It is now widely recognized that a better understanding of these mechanisms may provide clues to the pathogenesis of immunodeficiency in HIV-infected humans. In this article I discuss five different hypotheses that may account for the non-pathogenic course of infection in SIV-infected SMs and briefly review the available data supporting each of these hypotheses.

Animals↗
PubMed2005

Vaccinia virus tropism for primary hematolymphoid cells is determined by restricted expression of a unique virus receptor.

The presumed broad tropism of poxviruses has stymied attempts to identify both the cellular receptor(s) and the viral determinant(s) for binding. Detailed studies of poxvirus binding to and infection of primary human cells have not been conducted. In particular, the determinants of target cell infection and the consequences of infection for cells involved in the generation of antiviral immune responses are incompletely understood. In this report, we show that vaccinia virus (VV) exhibits a more restricted tropism for primary hematolymphoid human cells than has been previously recognized. We demonstrate that vaccinia virus preferentially infects antigen-presenting cells (dendritic cells, monocytes/macrophages, and B cells) and activated T cells, but not resting T cells. The infection of activated T cells is permissive, with active viral replication and production of infectious progeny. Susceptibility to infection is determined by restricted expression of a cellular receptor that is induced de novo upon T-cell activation and can be removed from the cell surface by either trypsin or pronase treatment. The VV receptor expressed on activated T cells displays unique characteristics that distinguish it from the receptor used to infect cell lines in culture. The observed restricted tropism of VV may have significant consequences for the understanding of natural poxvirus infection and immunity and for poxvirus-based vaccine development.

Animals↗
PubMed2005

Divergent host responses during primary simian immunodeficiency virus SIVsm infection of natural sooty mangabey and nonnatural rhesus macaque hosts.

To understand how natural sooty mangabey hosts avoid AIDS despite high levels of simian immunodeficiency virus (SIV) SIVsm replication, we inoculated mangabeys and nonnatural rhesus macaque hosts with an identical inoculum of uncloned SIVsm. The unpassaged virus established infection with high-level viral replication in both macaques and mangabeys. A species-specific, divergent immune response to SIV was evident from the first days of infection and maintained in the chronic phase, with macaques showing immediate and persistent T-cell proliferation, whereas mangabeys displayed little T-cell proliferation, suggesting subdued cellular immune responses to SIV. Importantly, only macaques developed (CD4+)-T-cell depletion and AIDS, thus indicating that in mangabeys limited immune activation is a key mechanism to avoid immunodeficiency despite high levels of SIVsm replication. These studies demonstrate that it is the host response to infection, rather than properties inherent to the virus itself, that causes immunodeficiency in SIV-infected nonhuman primates.

Animals↗
PubMed2004

Enhanced SIV replication and accelerated progression to AIDS in macaques primed to mount a CD4 T cell response to the SIV envelope protein.

Given the dual role of CD4 T cells as both immune effectors and targets for HIV infection, the balance of CD4 versus CD8 T cell-mediated responses induced by candidate AIDS vaccines may be critical in determining postvaccination infection outcomes. An attenuated recombinant varicella-zoster virus vaccine expressing the simian immunodeficiency virus (SIV) envelope (Env) elicited nonneutralizing Env-binding antibodies and little if any cytotoxic T lymphocyte responses in rhesus macaques (Macaca mulatta). After challenge with SIV, Env vaccinees manifested increased levels of SIV replication, more rapid CD4 depletion, and accelerated progression to AIDS compared with controls. Enhanced SIV replication correlated with increased CD4 T cell proliferation soon after SIV challenge, apparently the result of an anamnestic response to SIV antigens. Thus activation of virus-specific CD4 T cells at the time of exposure to a CD4 T cell-tropic lentivirus, in the absence of an effective CD8 response, may enhance virus replication and disease. These data suggest suggest that candidate AIDS vaccines may not simply be either efficacious or neutral; they may also have the potential to be harmful.

Animals↗
PubMed2004

Early correction of cell cycle perturbations predicts the immunological response to therapy in HIV-infected patients.

OBJECTIVE: To determine whether changes in the indices of HIV-associated cell cycle dysregulation (i.e., increased expression of cyclin B1 and abnormal nucleolar structure) may predict the level of immunological reconstitution in HIV-infected patients treated with highly active antiretroviral therapy (HAART). METHODS: Cross-sectional and longitudinal analysis of viral load, CD4 T cell counts, cyclin B1 expression, and AgNOR number and area of distribution in 30 HIV-infected patients who were studied before and up to 6 months after initiation of HAART. RESULTS: In HIV-infected individuals, the level of cell cycle dysregulation correlated with the type of response to HAART. While low levels of dysregulation were present in patients with complete (both virological and immunological) response to HAART, high levels were present in HAART-treated patients with limited CD4 T cell increases despite persistent viral suppression (immunological non-responders). Importantly, the level of correction of cell cycle dysregulation after 60 days of therapy predicted the level of immune reconstitution after 6 months. CONCLUSION: These observations suggest that correction of cell cycle dysregulation predicts a good immunological response to HAART and that sequential analysis of cell cycle dysregulation might help to identify patients that could benefit from alternative, immune-based interventions in addition to standard HAART.

Antiretroviral Therapy, Highly Active↗
PubMed2004

Prospects for an AIDS vaccine: three big questions, no easy answers.

The unremitting devastation created by the AIDS pandemic will probably only be controlled when a vaccine is developed that is safe, effective, affordable, and simple enough to permit implementation in developing countries where the impact of AIDS is most severe. Although formidable practical, political, economic, social, and ethical challenges face the AIDS vaccine development effort, the most fundamental challenges now reside at the level of the basic biology of HIV-1 infection and pathogenesis. Of these biological considerations, three questions loom especially large: can we design immunogens that will elicit neutralising antibodies that are reactive against a wide variety of primary HIV isolates; will vaccine-elicited cytotoxic T cells be fundamentally better at controlling HIV-1 replication and ameliorating disease progression than those responses that arise during natural HIV infection; and to what extent will the tremendous global genetic diversity of HIV-1 compromise the breadth of vaccine-elicited protective immunity and the overall effectiveness of an AIDS vaccine? Although these are three exceptionally challenging questions, they are now being approached with clear hypotheses whose testing is being facilitated by an ever-improving array of technologies for vaccine design and immunological characterisation. The extent to which the field of AIDS vaccine research can now come together to answer these questions in the best coordinated, most efficient manner will probably be an important determinant of how and when an effective AIDS vaccine will be developed.

AIDS Vaccines↗
PubMed2004

Roles of target cells and virus-specific cellular immunity in primary simian immunodeficiency virus infection.

There is an ongoing debate on whether acute human immunodeficiency virus infection is controlled by target cell limitation or by virus-specific cellular immunity. To resolve this question, we developed a novel mathematical modeling scheme which allows us to incorporate measurements of virus load, target cells, and virus-specific immunity and applied it to a comprehensive data set generated in an experiment involving rhesus macaques infected with simian immunodeficiency virus. Half of the macaques studied were treated during the primary infection period with reagents which block T-cell costimulation and as a result displayed severely impaired virus-specific immune responses. Our results show that early viral replication in normal infection is controlled to a large extent by virus-specific CD8(+) T cells and not by target cell limitation.

Abatacept↗