Low Levels Of Immune Activation Research Articles

In-depth virological and immunological characterization of HIV-1 cure after CCR5Δ32/Δ32 allogeneic hematopoietic stem cell transplantation

Despite scientific evidence originating from two patients published to date that CCR5Δ32/Δ32 hematopoietic stem cell transplantation (HSCT) can cure human immunodeficiency virus type 1 (HIV-1), the knowledge of immunological and virological correlates of cure is limited. Here we characterize a case of long-term HIV-1 remission of a 53-year-old male who was carefully monitored for more than 9 years after allogeneic CCR5Δ32/Δ32 HSCT performed for acute myeloid leukemia. Despite sporadic traces of HIV-1 DNA detected by droplet digital PCR and in situ hybridization assays in peripheral T cell subsets and tissue-derived samples, repeated ex vivo quantitative and in vivo outgrowth assays in humanized mice did not reveal replication-competent virus. Low levels of immune activation and waning HIV-1-specific humoral and cellular immune responses indicated a lack of ongoing antigen production. Four years after analytical treatment interruption, the absence of a viral rebound and the lack of immunological correlates of HIV-1 antigen persistence are strong evidence for HIV-1 cure after CCR5Δ32/Δ32 HSCT.

The effects of early-life immune activation on microglia-mediated neuronal remodeling and the associated ontogeny of hippocampal-dependent learning in juvenile rats

Many neurodevelopmental disorders and associated learning deficits have been linked to early-life immune activation or ongoing immune dysregulation (Laskaris et al., 2016; O’Connor et al., 2014; Frick et al., 2013). Neuroscientists have begun to understand how the maturation of neural circuits allows for the emergence of cognitive and learning behaviors; yet we know very little about how these developing neural circuits are perturbed by certain events, including risk-factors such as early-life immune activation and immune dysregulation. To answer these questions, we examined the impact of early-life immune activation on the emergence of hippocampal-dependent learning in juvenile male and female rats using a well-characterized hippocampal-dependent learning task and we investigated the corresponding, dynamic multicellular interactions in the hippocampus that may contribute to these learning deficits. We found that even low levels of immune activation can result in hippocampal-depedent learning deficits days later, but only when this activation occurs during a sensitive period of development. The initial immune response and associated cytokine production in the hippocampus resolved within 24 h, several days prior to the observed learning deficit, but notably the initial immune response was followed by altered microglial-neuronal communication and synapse remodeling that changed the structure of hippocampal neurons during this period of juvenile brain development. We conclude that immune activation or dysregulation during a sensitive period of hippocampal development can precipitate the emergence of learning deficits via a multi-cellular process that may be initiated by, but not the direct result of the initial cytokine response. Significance StatementMany neurodevelopmental disorders have been linked to early-life immune activation or immune dysregulation; however, very little is known about how dynamic changes in neuroimmune cells mediate the transition from normal brain function to the early stages of cognitive disorders, or how changes in immune signaling are subsequently integrated into developing neuronal networks. The current experiments examined the consequences of immune activation on the cellular and molecular changes that accompany the emergence of learning deficits during a sensitive period of hippocampal development. These findings have the potential to significantly advance our understanding of how early-life immune activation or dysregulation can result in the emergence of cognitive and learning deficits that are the largest source of years lived with disability in humans.

High dose-rate brachytherapy of localized prostate cancer converts tumors from cold to hot.

BackgroundProstate cancer (PCa) has a profoundly immunosuppressive microenvironment and is commonly immune excluded with few infiltrative lymphocytes and low levels of immune activation. High-dose radiation has been demonstrated to stimulate the immune system in various human solid tumors. We hypothesized that localized radiation therapy, in the form of high dose-rate brachytherapy (HDRBT), would overcome immune suppression in PCa.MethodsTo investigate whether HDRBT altered prostate immune context, we analyzed preradiation versus postradiation human tissue from a cohort of 24 patients with localized PCa that received HDRBT as primary treatment (RadBank cohort). We performed Nanostring immune gene expression profiling, digital spatial profiling, and high-throughput immune cell multiplex immunohistochemistry analysis. We also resolved tumor and nontumor zones in spatial and bioinformatic analyses to explore the immunological response.ResultsNanostring immune profiling revealed numerous immune checkpoint molecules (eg, B7-H3, CTLA4, PDL1, and PDL2) and TGFβ levels were increased in response to HDRBT. We used a published 16-gene tumor inflammation signature (TIS) to divide tumors into distinct immune activation states (high:hot, intermediate and low:cold) and showed that most localized PCa are cold tumors pre-HDRBT. Crucially, HDRBT converted 80% of these ‘cold’-phenotype tumors into an ‘intermediate’ or ‘hot’ class. We used digital spatial profiling to show these HDRBT-induced changes in prostate TIS scores were derived from the nontumor regions. Furthermore, these changes in TIS were also associated with pervasive changes in immune cell density and spatial relationships—in particular, between T cell subsets and antigen presenting cells. We identified an increased density of CD4+ FOXP3+ T cells, CD68+ macrophages and CD68+ CD11c+ dendritic cells in response to HDRBT. The only subset change specific to tumor zones was PDL1- macrophages. While these immune responses were heterogeneous, HDRBT induced significant changes in immune cell associations, including a gained T cell and HMWCK+ PDL1+ interaction in tumor zones.ConclusionIn conclusion, we showed HDRBT converted “cold” prostate tumors into more immunologically activated “hot” tissues, with accompanying spatially organized immune infiltrates and signaling changes. Understanding and potentially harnessing these changes will have widespread implications for the future treatment of localized PCa, including rational use of combination radio-immunotherapy.

SAMHD1 expression is associated with low immune activation but not correlated with HIV‑1 DNA levels in CD4+ T cells of patients with HIV‑1.

Sterile α motif and histidine/aspartic acid domain-containing protein 1 (SAMHD1) can inhibit reverse transcription of human immunodeficiency virus-1 (HIV-1) by hydrolyzing intracellular deoxy-ribonucleoside triphosphate. However, its role in HIV-1 disease progression has not been extensively studied. To study the impacts of SAMHD1 on HIV-1 disease progression, especially on DNA levels, we investigated SAMHD1 levels in the peripheral blood of HIV-1 elite controllers (ECs), antiretroviral therapy (ART) naive viremic progressors (VPs) and patients with HIV-1 receiving ART (HIV-ARTs) compared with healthy controls. In addition, the present study analyzed the relationship between SAMHD1 and interferon-α, immune activation and HIV-1 DNA levels. The results of the present study demonstrated elevated SAMHD1 expression in the peripheral blood mononuclear cells of all patients withHIV-1, but higher SAMHD1 expression in the CD4+ T cells of only ECs compared with healthy controls. Immune activation was increased in the VPs and decreased in the ECs compared with healthy controls. Substantially lower HIV-1 DNA levels were identified in ECs compared with those in VPs and HIV-ARTs. SAMHD1 expression was associated with low levels of immune activation. No significant correlation was observed between SAMHD1 and HIV-1 DNA levels. Overall, the findings of the present study indicated that SAMHD1 was highly expressed in ECs, which may be associated with low immune activation levels, but was not directly related to HIV-1 DNA levels.

MTOR Inhibitors Maintain Low Levels of Immune Activation, Immune Senescence and EBV Load in Kidney Transplant Patients

Introduction Post-transplant lymphoproliferative disorders (PTLD) represent a severe complication in transplant patients. Epstein-Barr Virus (EBV) is the main driver of PTLD, particularly of those occurring early after transplantation. Immune activation/inflammation, immune senescence, reactivation of EBV and expansion of EBV-positive B cells, which play a pivotal role in the onset of PTLD, may be modulated by immunosuppressive strategies. The aim of this study was to assess the impact of mTOR inhibitor (mTORi) on viral and host cofactors involved in the PTLD’s pathogenesis. Materials and Methods Sixty-two kidney transplant patients were enrolled in the study: 33 were treated with mycophenolic acid (MPA) and 29 with mTORi, both in combination with tacrolimus and steroids. Thymoglobulin was the induction in all cases. All patients were assessed at the time of transplant and after 1 year of follow-up. Markers of T-cell activation(CD3+CD8+CD38+), exhaustion(CD3+CD8+PD-1+), senescence (CD3+CD8+CD28-CD57+), and B-cell activation (CD19+CD10-CD21lowCD27+) were evaluated by flow cytometry. Plasma levels of PAMPs(microbial translocation marker 16s ribosomal(r)DNA) and DAMPs(mitochondrial(mt)DNA) were quantified by real-time PCR. Inflammatory cytokines (IL-6 and TNF-alpha) were quantified by Luminex platform. EBV was typed and quantified by multiplex real-time PCR, and telomere lengths in peripheral blood cells (PBMC) were estimated by telomere/single copy gene ratio (T/S), using multiplex real-time PCR. Results After 1 year of follow-up, plasma levels of 16s rDNA increased in MPA-treated patients (p=0.029), while remained stable in the mTORi group. Levels of mtDNA and pro- inflammatory cytokines tended to decrease in mTORi-treated patients (mtDNA, p=0.034; IL-6, p=0.08; TNF-alpha, p<0.001), while no significant changes were observed in the MPA group. Percentages of activated, exhausted and senescent T cells significantly increased in the MPA-treated patients (4.6[2.2-9.1] vs 17.8[12.1-23.3],p<0.001; 4.8[3.0-6.9] vs 11.6[8.7-16.8],p<0.001; and 7.9[4.4-14.5] vs 14.5[8.5-27.7],p=0.005), but remained stable in the mTORi group (2.4[1.8-6.1] vs 4.1[2.4-6.3], p=0.161; 6.4[4.9-12.1] vs 7.1[4.3-12.7],p=0.888; and 9.7[5.2-13.8]vs 10.8[5.6-16.2],p=0.460). The increase in immunosenescent cells in the MPA group was supported by telomere shortening, higher in MPA than in mTORi-treated patients (ΔT/S=-0.449 vs ΔT/S=-0.219). Percentages of activated B cells and levels of EBV-DNA significantly increased in the MPA group (10.3[6.4-16.9] vs 18.3[11.6-28.4],p=0.002, and 1[1-17] vs 27[1-118] EBV-DNA copies/105 PBMC, p=0.004), while remained stable in the mTORi group (12.8[6.8-18.8]vs 13.0[9.2-18.0], p=0.836, and 1[1-7]vs 6[1-26] EBV-DNA copies/105 PBMC, p=0.128). Conclusions mTORi maintained low levels of pro-inflammatory cytokines, immune activation and senescence, thus constraining EBV reactivation and expansion of EBV-positive B cells. Overall, these findings suggest that mTORi may reduce the risk of EBV-related malignancies in kidney transplant patients. AIRC grant IG2016 Id 19112.

Residual inflammation and viral reservoirs: alliance against an HIV cure.

HIV persists in cellular and anatomical reservoirs during antiretroviral therapy (ART). Viral persistence is ensured by a variety of mechanisms including ongoing viral replication and proliferation of latently infected cells. In this review, we summarize recent findings establishing a link between the unresolved levels of inflammation observed in virally suppressed individuals on ART and the mechanisms responsible for HIV persistence. Residual levels of viral replication during ART are associated with persistent low levels of immune activation, suggesting that unresolved inflammation can promote the replenishment of the HIV reservoir in tissues. In addition, the recent findings that the latent HIV reservoir is maintained by continuous proliferation of latently infected cells provide another mechanism by which residual inflammation could contribute to HIV persistence. Residual inflammation during ART is likely to be a critical parameter contributing to HIV persistence. Therefore, reducing inflammation may be an efficient way to interfere with the maintenance of the HIV reservoir in virally suppressed individuals on ART.

Immune Activation and HIV Pathogenesis: Implications for Therapy

HIV infection is associated with continued activation of immune system and this is known to be the driving force behind CD4+ T cell depletion and progression to AIDS. Nonpathogenic Simian Immunodeficiency Virus (SIV) infections of natural hosts are characterized by low levels of immune activation even in the chronic phase of infection. Effective Antiretroviral Therapy (ART) does not fully resolve immune activation and HIV infected patients continue to experience non-AIDS related events leading to premature immune senescence. In this review, we summarize the possible mechanisms driving HIV associated immune activation, and novel therapeutic interventions that show promise in treating the disease.

F-104 Non-human primate models for immunological studies of HIV eradication

The mechanisms by which pathogenic HIV and SIV infections cause immune deficiency involve factors related to both the virus and the host immune system. Over the past few years, emphasis has been placed on the role of the chronic immune activation that is apparent during the natural history of the infection and remains as “residual” immune activation in HIV-infected individuals treated with antiretroviral therapy (ART). Several key concepts and hypotheses regarding the pathogenic role of immune activation have been generated in studies involving SIV-infected non-human primates (NHP) such as the sooty mangabeys, in which a natural, non-pathogenic infection is characterized by robust virus replication but low levels of immune activation, and Asian macaques, in which experimental infection with SIV results a progressive infection characterized by CD4+ T cell depletion, high immune activation, and simian AIDS. More recently, the SIV/NHP model has been developed and validated for studies of the HIV-associated “residual” disease under fully suppressive ART, which is characterized by persistent immune dysfunction and presence of a reservoir of latently infected cells which makes it impossible to eradicate the virus. In this presentation, I will briefly review the opportunities presented by NHP models to conduct studies that will improve our understanding of AIDS virology, immunology, and pathogenesis, with specific focus the goal of reducing the residual disease that persists in ART-treated HIV-infected individuals despite suppression of virus replication. I will discuss (1) the key pathogenic aspects of the residual immune activation observed in ART-treated HIV-infected individuals and SIV-infected macaques, (2) the role of type I interferons as both antiviral and pro-inflammatory factors, and (3) the key role played by the pattern of infected CD4+ T cell subsets as a determinant of both residual immune activation and persistent virus reservoir in the setting of ART-mediated suppression of virus replication.

Immunity to HIV in Early Life.

The developing immune system is adapted to the exposure to a plethora of pathogenic and non-pathogenic antigens encountered in utero and after birth, requiring a fine balance between protective immunity and immune tolerance. In early stages of life, this tolerogenic state of the innate and adaptive immune system and the lack of immunological memory render the host more susceptible to infectious pathogens like HIV. HIV pathogenesis is different in children, compared to adults, with more rapid disease progression and a substantial lack of control of viremia compared to adults. Plasma viral load remains high during infancy and only declines gradually over several years in line with immune maturation, even in rare cases where children maintain normal CD4 T-lymphocyte counts for several years without antiretroviral therapy (ART). These pediatric slow progressors also typically show low levels of immune activation despite persistently high viremia, resembling the phenotype of natural hosts of SIV infection. The lack of immunological memory places the fetus and the newborn at higher risk of infections; however, it may also provide an opportunity for unique interventions. Frequencies of central memory CD4+ T-lymphocytes, one of the main cellular reservoirs of HIV, are very low in the newborn child, so immediate ART could prevent the establishment of persistent viral reservoirs and result in “functional cure.” However, as recently demonstrated in the case report of the “Mississippi child” who experienced viral rebound after more than 2 years off ART, additional immunomodulatory strategies might be required for sustained viral suppression after ART cessation. In this review, we discuss the interactions between HIV and the developing immune system in children and the potential implications for therapeutic and prophylactic interventions.

Viremic long-term nonprogressive HIV-1 infection is not associated with abnormalities in known Nef functions

BackgroundA small minority of HIV-1-infected individuals show low levels of immune activation and do not develop immunodeficiency despite high viral loads. Since the accessory viral Nef protein modulates T cell activation and plays a key role in the pathogenesis of AIDS, we investigated whether specific properties of Nef may be associated with this highly unusual clinical outcome of HIV-1 infection.FindingsComprehensive functional analyses of sequential HIV-1 strains from three viremic long-term non-progressors (VNP) showed that they encode full-length Nef proteins that are capable of modulating CD4, CD28, CD8ß, MHC-I and CD74 cell surface expression. Similar to Nef proteins from HIV-1-infected individuals with progressive infection (P-Nefs) and unlike Nefs from simian immunodeficiency viruses (SIVs) that do not cause chronic immune activation and disease in their natural simian hosts, VNP-Nefs were generally unable to down-modulate TCR-CD3 cell surface expression to block T cell activation and apoptosis. On average, VNP-Nefs suppressed NF-AT activation less effectively than P-Nefs and were slightly less active in enhancing NF-κB activity. Finally, we found that VNP-Nefs increased virion infectivity and enhanced HIV-1 replication and cytopathicity in primary human cells and in ex vivo infected lymphoid tissues.ConclusionsOur results show that nef alleles from VNPs and progressors of HIV-1 infection show only modest differences in established functions. Thus, the lack of chronic immune activation and disease progression in HIV-1-infected VNPs is apparently not associated with unusual functional properties of the accessory viral Nef protein.

Simian Immunodeficiency Virus-Induced Alterations in Monocyte Production of Tumor Necrosis Factor Alpha Contribute to Reduced Immune Activation in Sooty Mangabeys

Human immunodeficiency virus type 1 (HIV-1) infection is characterized by persistent viral replication in the context of CD4(+) T cell depletion and elevated immune activation associated with disease progression. In contrast, simian immunodeficiency virus (SIV) infection of African-origin sooty mangabeys (SM) generally does not result in simian AIDS despite high viral loads and therefore affords a unique model in which to study the immunologic contributions to a nonpathogenic lentiviral disease outcome. A key feature of these natural SIV infections is the maintenance of low levels of immune activation during chronic infection. Our goal was to delineate the contribution of monocytes to maintaining low levels of immune activation in SIV-infected SM. Utilizing an ex vivo whole-blood assay, proinflammatory cytokine production was quantified in monocytes in response to multiple Toll-like receptor (TLR) ligands and a specific, significant reduction in the tumor necrosis factor alpha (TNF-α) response to lipopolysaccharide (LPS) was observed in SIV-infected SM. In contrast, monocytes from hosts of pathogenic infections (HIV-infected humans and SIV-infected Asian macaques) maintained a robust TNF-α response. In SIV-infected SM, monocyte TNF-α responses to low levels of LPS could be augmented by the presence of plasma from uninfected control animals. The impact of LPS-induced TNF-α production on immune activation was demonstrated in vitro, as TNF-α blocking antibodies inhibited downstream CD8(+) T cell activation in a dose-dependent manner. These data demonstrate an association between nonpathogenic SIV infection of SM and a reduced monocyte TNF-α response to LPS, and they identify a role for monocytes in contributing to the suppressed chronic immune activation observed in these natural hosts.

Absence of HIV-1 Evolution in the Gut-Associated Lymphoid Tissue from Patients on Combination Antiviral Therapy Initiated during Primary Infection

Mucosal mononuclear (MMC) CCR5+CD4+ T cells of the gastrointestinal (GI) tract are selectively infected and depleted during acute HIV-1 infection. Despite early initiation of combination antiretroviral therapy (cART), gut-associated lymphoid tissue (GALT) CD4+ T cell depletion and activation persist in the majority of HIV-1 positive individuals studied. This may result from ongoing HIV-1 replication and T-cell activation despite effective cART. We hypothesized that ongoing viral replication in the GI tract during cART would result in measurable viral evolution, with divergent populations emerging over time. Subjects treated during early HIV-1 infection underwent phlebotomy and flexible sigmoidoscopy with biopsies prior to and 15–24 months post initiation of cART. At the 2nd biopsy, three GALT phenotypes were noted, characterized by high, intermediate and low levels of immune activation. A representative case from each phenotype was analyzed. Each subject had plasma HIV-1 RNA levels <50 copies/ml at 2nd GI biopsy and CD4+ T cell reconstitution in the peripheral blood. Single genome amplification of full-length HIV-1 envelope was performed for each subject pre- and post-initiation of cART in GALT and PBMC. A total of 280 confirmed single genome sequences (SGS) were analyzed for experimental cases. For each subject, maximum likelihood phylogenetic trees derived from molecular sequence data showed no evidence of evolved forms in the GALT over the study period. During treatment, HIV-1 envelope diversity in GALT-derived SGS did not increase and post-treatment GALT-derived SGS showed no substantial genetic divergence from pre-treatment sequences within transmitted groups. Similar results were obtained from PBMC-derived SGS. Our results reveal that initiation of cART during acute/early HIV-1 infection can result in the interruption of measurable viral evolution in the GALT, suggesting the absence of de-novo rounds of HIV-1 replication in this compartment during suppressive cART.

Immunovirological Analyses of Chronically Simian Immunodeficiency Virus SIVmnd-1- and SIVmnd-2-Infected Mandrills (Mandrillus sphinx)

Simian immunodeficiency virus (SIV) infection in African nonhuman primate (NHP) natural hosts is usually nonpathogenic, despite high levels of virus replication. We have previously shown that chronic SIV infection in sooty mangabeys (SMs) and African green monkeys (AGMs) is associated with low levels of immune activation and bystander T cell apoptosis. To compare these features with those observed in another natural host, the mandrill (MND), we conducted a cross-sectional survey of the 23 SIV-infected and 25 uninfected MNDs from the only semifree colony of mandrills available worldwide. Viral loads (VLs) were determined and phenotypic and functional analysis of peripheral blood- and lymph node-derived lymphocytes was performed. We found that mandrills chronically infected with SIVmnd-1 or SIVmnd-2 have similar levels of viral replication, and we observed a trend toward lower CD4+ T cell counts in chronically SIVmnd-2-infected MNDs than SIVmnd-1-infected MNDs. No correlation between CD4+ T cell counts and VLs in SIV-infected MNDs could be established. Of note, the levels of T cell activation, proliferation, and apoptosis were comparable between SIVmnd-1- and SIVmnd-2-infected MNDs and to those observed in uninfected animals, with the only exception being an increase in tumor necrosis factor alpha-producing CD8+ T cells in SIVmnd-2-infected MNDs. Overall, these findings recapitulate previous observations in SIV-infected SMs and AGMs and lend further evidence to the hypothesis that low levels of immune activation protect natural SIV hosts from disease progression.

Plasmacytoid dendritic cells are recruited to the colorectum and contribute to immune activation during pathogenic SIV infection in rhesus macaques

AbstractIn SIV/HIV infection, the gastrointestinal tissue dominates as an important site because of the impact of massive mucosal CD4 depletion and immune activation-induced tissue pathology. Unlike AIDS-susceptible rhesus macaques, natural hosts do not progress to AIDS and resolve immune activation earlier. Here, we examine the role of dendritic cells (DCs) in mediating immune activation and disease progression. We demonstrate that plasmacytoid DCs (pDCs) in the blood up-regulate β7-integrin and are rapidly recruited to the colorectum after a pathogenic SIV infection in rhesus macaques. These pDCs were capable of producing proinflammatory cytokines and primed a T cytotoxic 1 response in vitro. Consistent with the up-regulation of β7-integrin on pDCs, in vivo blockade of α4β7-integrin dampened pDC recruitment to the colorectum and resulted in reduced immune activation. The up-regulation of β7-integrin expression on pDCs in the blood also was observed in HIV-infected humans but not in chronically SIV-infected sooty mangabeys that show low levels of immune activation. Our results uncover a new mechanism by which pDCs influence immune activation in colorectal tissue after pathogenic immunodeficiency virus infections.

HIV-Associated Immune Activation: From Bench to Bedside

HIV infection is associated with a state of chronic, generalized immune activation that has been shown in many studies to be a key predictor of progression to AIDS. Consistent with this model, nonpathogenic SIV infections of natural hosts, such as the sooty mangabeys, are characterized by low levels of immune activation during the chronic phase of infection. The molecular, cellular, and pathophysiological mechanisms underlying the HIV-associated immune activation are complex and still poorly understood. There is, however, growing consensus that both viral and host factors contribute to this phenotype, with emphasis on the role played by the mucosal immune dysfunction (and consequent microbial translocation) as well as the pattern of in vivo-infected CD4(+) T cells. The observation that antiretroviral therapy (ART)-induced suppression of HIV replication does not fully resolve immune activation provided the rationale for a number of exploratory studies of potential immune modulatory treatments to be used in HIV-infected individuals in addition to standard ART. This review provides an update on the causes and consequences of the HIV-associated immune activation, and a summary of the immune modulatory approaches that are currently under clinical investigation.

Lack of clinical AIDS in SIV-infected sooty mangabeys with significant CD4+ T cell loss is associated with double-negative T cells

SIV infection of natural host species such as sooty mangabeys results in high viral replication without clinical signs of simian AIDS. Studying such infections is useful for identifying immunologic parameters that lead to AIDS in HIV-infected patients. Here we have demonstrated that acute, SIV-induced CD4(+) T cell depletion in sooty mangabeys does not result in immune dysfunction and progression to simian AIDS and that a population of CD3(+)CD4(-)CD8(-) T cells (double-negative T cells) partially compensates for CD4(+) T cell function in these animals. Passaging plasma from an SIV-infected sooty mangabey with very few CD4(+) T cells to SIV-negative animals resulted in rapid loss of CD4(+) T cells. Nonetheless, all sooty mangabeys generated SIV-specific antibody and T cell responses and maintained normal levels of plasma lipopolysaccharide. Moreover, all CD4-low sooty mangabeys elicited a de novo immune response following influenza vaccination. Such preserved immune responses as well as the low levels of immune activation observed in these animals were associated with the presence of double-negative T cells capable of producing Th1, Th2, and Th17 cytokines. These studies indicate that SIV-infected sooty mangabeys do not appear to rely entirely on CD4(+) T cells to maintain immunity and identify double-negative T cells as a potential subset of cells capable of performing CD4(+) T cell-like helper functions upon SIV-induced CD4(+) T cell depletion in this species.

Global genomic analysis reveals rapid control of a robust innate response in SIV-infected sooty mangabeys

Natural SIV infection of sooty mangabeys (SMs) is nonprogressive despite chronic virus replication. Strikingly, it is characterized by low levels of immune activation, while pathogenic SIV infection of rhesus macaques (RMs) is associated with chronic immune activation. To elucidate the mechanisms underlying this intriguing phenotype, we used high-density oligonucleotide microarrays to longitudinally assess host gene expression in SIV-infected SMs and RMs. We found that acute SIV infection of SMs was consistently associated with a robust innate immune response, including widespread upregulation of IFN-stimulated genes (ISGs) in blood and lymph nodes. While SMs exhibited a rapid resolution of ISG expression and immune activation, both responses were observed chronically in RMs. Systems biology analysis indicated that expression of the lymphocyte inhibitory receptor LAG3, a marker of T cell exhaustion, correlated with immune activation in SIV-infected RMs but not SMs. Our findings suggest that active immune regulatory mechanisms, rather than intrinsically attenuated innate immune responses, underlie the low levels of immune activation characteristic of SMs chronically infected with SIV.

Decreased Immune Activation in Resistance to HIV‐1 Infection Is Associated with an Elevated Frequency of CD4+CD25+FOXP3+Regulatory T Cells

Human immunodeficiency virus (HIV)-resistant commercial sex workers provide a unique opportunity to study correlates of protection associated with natural resistance to HIV infection. Emerging data from studies of these individuals and other uninfected individuals who have been exposed to HIV suggest that low levels of immune activation may contribute to protection against infection. In the present study, HIV-resistant individuals were shown to have reduced frequencies of T cells expressing the activation marker CD69. They were also found to have elevated frequencies of regulatory T (T(reg)) cells, compared with HIV-negative control individuals. By controlling levels of T cell activation, T(reg) cells may contribute to HIV resistance by minimizing the pool of cells susceptible to infection.

Correlates of Preserved CD4+ T Cell Homeostasis during Natural, Nonpathogenic Simian Immunodeficiency Virus Infection of Sooty Mangabeys: Implications for AIDS Pathogenesis

In contrast to HIV-infected humans, naturally SIV-infected sooty mangabeys (SMs) very rarely progress to AIDS. Although the mechanisms underlying this disease resistance are unknown, a consistent feature of natural SIV infection is the absence of the generalized immune activation associated with HIV infection. To define the correlates of preserved CD4(+) T cell counts in SMs, we conducted a cross-sectional immunological study of 110 naturally SIV-infected SMs. The nonpathogenic nature of the infection was confirmed by an average CD4(+) T cell count of 1,076 +/- 589/mm(3) despite chronic infection with a highly replicating virus. No correlation was found between CD4(+) T cell counts and either age (used as a surrogate marker for length of infection) or viremia. The strongest correlates of preserved CD4(+) T cell counts were a low percentage of circulating effector T cells (CD28(-)CD95(+) and/or IL-7R/CD127(-)) and a high percentage of CD4(+)CD25(+) T cells. These findings support the hypothesis that the level of immune activation is a key determinant of CD4(+) T cell counts in SIV-infected SMs. Interestingly, we identified 14 animals with CD4(+) T cell counts of <500/mm(3), of which two show severe and persistent CD4(+) T cell depletion (<50/mm(3)). Thus, significant CD4(+) T cell depletion does occasionally follow SIV infection of SMs even in the context of generally low levels of immune activation, lending support to the hypothesis of multifactorial control of CD4(+) T cell homeostasis in this model of infection. The absence of AIDS in these "CD4(low)" naturally SIV-infected SMs defines a protective role of the reduced immune activation even in the context of a significant CD4(+) T cell depletion.

Gravity Spun Polycaprolactone Fibers for Applications in Vascular Tissue Engineering: Proliferation and Function of Human Vascular Endothelial Cells

Poly(epsilon-caprolactone) (PCL) fibers produced by wet spinning from solutions in acetone under lowshear (gravity-flow) conditions resulted in fiber strength of 8 MPa and stiffness of 0.08 Gpa. Cold drawing to an extension of 500% resulted in an increase in fiber strength to 43 MPa and stiffness to 0.3 GPa. The growth rate of human umbilical vein endothelial cells (HUVECs) (seeded at a density of 5 x 10(4) cells/mL) on as-spun fibers was consistently lower than that measured on tissue culture plastic (TCP) beyond day 2. Cell proliferation was similar on gelatin-coated fibers and TCP over 7 days and higher by a factor of 1.9 on 500% cold-drawn PCL fibers relative to TCP up to 4 days. Cell growth on PCL fibers exceeded that on Dacron monofilament by at least a factor of 3.7 at 9 days. Scanning electron microscopy revealed formation of a cell layer on samples of cold-drawn and gelatin-coated fibers after 24 hours in culture. Similar levels of ICAM-1 expression by HUVECs attached to PCL fibers and TCP were measured using RT-PCR and flow cytometry, indicative of low levels of immune activation. Retention of a specific function of HUVECs attached to PCL fibers was demonstrated by measuring their immune response to lipopolysaccharide. Levels of ICAM-1 expression increased by approximately 11% in cells attached to PCL fibers and TCP. The high fiber compliance, favorable endothelial cell proliferation rates, and retention of an important immune response of attached HUVECS support the use of gravity spun PCL fibers for three-dimensional scaffold production in vascular tissue engineering.