David Verhoeven

Simian immunodeficiency virus–induced mucosal interleukin-17 deficiency promotes Salmonella dissemination from the gut

Salmonella typhimurium causes a localized enteric infection in immunocompetent individuals, whereas HIV-infected individuals develop a life-threatening bacteremia. Here we show that simian immunodeficiency virus (SIV) infection results in depletion of T helper type 17 (TH17) cells in the ileal mucosa of rhesus macaques, thereby impairing mucosal barrier functions to S. typhimurium dissemination. In SIV-negative macaques, the gene expression profile induced by S. typhimurium in ligated ileal loops was dominated by TH17 responses, including the expression of interleukin-17 (IL-17) and IL-22. TH17 cells were markedly depleted in SIV-infected rhesus macaques, resulting in blunted TH17 responses to S. typhimurium infection and increased bacterial dissemination. IL-17 receptor–deficient mice showed increased systemic dissemination of S. typhimurium from the gut, suggesting that IL-17 deficiency causes defects in mucosal barrier function. We conclude that SIV infection impairs the IL-17 axis, an arm of the mucosal immune response preventing systemic microbial dissemination from the gastrointestinal tract.

Viral Suppression and Immune Restoration in the Gastrointestinal Mucosa of Human Immunodeficiency Virus Type 1-Infected Patients Initiating Therapy during Primary or Chronic Infection

ABSTRACT Although the gut-associated lymphoid tissue (GALT) is an important early site for human immunodeficiency virus (HIV) replication and severe CD4+ T-cell depletion, our understanding is limited about the restoration of the gut mucosal immune system during highly active antiretroviral therapy (HAART). We evaluated the kinetics of viral suppression, CD4+ T-cell restoration, gene expression, and HIV-specific CD8+ T-cell responses in longitudinal gastrointestinal biopsy and peripheral blood samples from patients initiating HAART during primary HIV infection (PHI) or chronic HIV infection (CHI) using flow cytometry, real-time PCR, and DNA microarray analysis. Viral suppression was more effective in GALT of PHI patients than CHI patients during HAART. Mucosal CD4+ T-cell restoration was delayed compared to peripheral blood and independent of the time of HAART initiation. Immunophenotypic analysis showed that repopulating mucosal CD4+ T cells were predominantly of a memory phenotype and expressed CD11α, αEβ7, CCR5, and CXCR4. Incomplete suppression of viral replication in GALT during HAART correlated with increased HIV-specific CD8+ T-cell responses. DNA microarray analysis revealed that genes involved in inflammation and cell activation were up regulated in patients who did not replenish mucosal CD4+ T cells efficiently, while expression of genes involved in growth and repair was increased in patients with efficient mucosal CD4+ T-cell restoration. Our findings suggest that the discordance in CD4+ T-cell restoration between GALT and peripheral blood during therapy can be attributed to the incomplete viral suppression and increased immune activation and inflammation that may prevent restoration of CD4+ T cells and the gut microenvironment.

Memory CD4 T Cells Direct Protective Responses to Influenza Virus in the Lungs through Helper-Independent Mechanisms

ABSTRACT Memory CD4 T cells specific for influenza virus are generated from natural infection and vaccination, persist long-term, and recognize determinants in seasonal and pandemic influenza virus strains. However, the protective potential of these long-lived influenza virus-specific memory CD4 T cells is not clear, including whether CD4 T-cell helper or effector functions are important in secondary antiviral responses. Here we demonstrate that memory CD4 T cells specific for H1N1 influenza virus directed protective responses to influenza virus challenge through intrinsic effector mechanisms, resulting in enhanced viral clearance, recovery from sublethal infection, and full protection from lethal challenge. Mice with influenza virus hemagglutinin (HA)-specific memory CD4 T cells or polyclonal influenza virus-specific memory CD4 T cells exhibited protection from influenza virus challenge that occurred in the presence of CD8-depleting antibodies in B-cell-deficient mice and when CD4 T cells were transferred into lymphocyte-deficient RAG2−/− mice. Moreover, the presence of memory CD4 T cells mobilized enhanced T-cell recruitment and immune responses in the lung. Neutralization of gamma interferon (IFN-γ) production in vivo abrogated memory CD4 T-cell-mediated protection from influenza virus challenge by HA-specific memory T cells and heterosubtypic protection by polyclonal memory CD4 T cells. Our results indicate that memory CD4 T cells can direct enhanced protection from influenza virus infection through mobilization of immune effectors in the lung, independent of their helper functions. These findings have important implications for the generation of universal influenza vaccines by promoting long-lived protective CD4 T-cell responses.

DNA vaccination of infants in the presence of maternal antibody: a measles model in the primate

To eradicate measles in developing nations a vaccine capable of being administered at birth may be necessary. We immunized newborn rhesus macaques with naked DNA encoding the measles virus hemagglutinin, fusion and nucleoprotein genes. Prior to vaccination we passively transferred measles immunoglobulin to mimic maternal antibody. In the presence or absence of measles immunoglobulin, 23 of 25 infant macaques had detectable cell mediated immunity and 16 had protective levels of neutralizing antibody. The co-administration of an IL-2/IgG plasmid augmented the vaccine, increasing cell mediated immunity in all infants and increasing the antibody response in infants vaccinated without immunoglobulin. We show for the first time that DNA vaccination can protect a newborn primate from the high-level viremia that correlates with severe measles, even in the presence of maternal antibody. Further, the addition of a molecular IL-2 adjuvant augments this DNA vaccine.

Antiviral Therapy during Primary Simian Immunodeficiency Virus Infection Fails To Prevent Acute Loss of CD4+ T Cells in Gut Mucosa but Enhances Their Rapid Restoration through Central Memory T Cells

ABSTRACT Gut-associated lymphoid tissue (GALT) is an early target of human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) and a site for severe CD4+ T-cell depletion. Although antiretroviral therapy (ART) is effective in suppressing HIV replication and restoring CD4+ T cells in peripheral blood, restoration in GALT is delayed. The role of restored CD4+ T-cell help in GALT during ART and its impact on antiviral CD8+ T-cell responses have not been investigated. Using the SIV model, we investigated gut CD4+ T-cell restoration in infected macaques, initiating ART during either the primary stage (1 week postinfection), prior to acute CD4+ cell loss (PSI), or during the chronic stage at 10 weeks postinfection (CSI). ART led to viral suppression in GALT and peripheral blood mononuclear cells of PSI and CSI animals at comparable levels. CSI animals had incomplete CD4+ T-cell restoration in GALT. In PSI animals, ART did not prevent acute CD4+ T-cell loss by 2 weeks postinfection in GALT but supported rapid and complete CD4+ T-cell restoration thereafter. This correlated with an accumulation of central memory CD4+ T cells and better suppression of inflammation. Restoration of CD4+ T cells in GALT correlated with qualitative changes in SIV gag-specific CD8+ T-cell responses, with a dominance of interleukin-2-producing responses in PSI animals, while both CSI macaques and untreated SIV-infected controls were dominated by gamma interferon responses. Thus, central memory CD4+ T-cell levels and qualitative antiviral CD8+ T-cell responses, independent of viral suppression, were the immune correlates of gut mucosal immune restoration during ART.

Costimulation Modulation Uncouples Protection from Immunopathology in Memory T Cell Responses to Influenza Virus

The rapid effector functions and tissue heterogeneity of memory T cells facilitate protective immunity, but they can also promote immunopathology in antiviral immunity, autoimmunity, and transplantation. Modulation of memory T cells is a promising but not yet achieved strategy for inhibiting these deleterious effects. Using an influenza infection model, we demonstrate that memory CD4 T cell-driven secondary responses to influenza challenge result in improved viral clearance yet do not prevent the morbidity associated with viral infection, and they exacerbate cellular recruitment into the lung, compared with primary responses. Inhibiting CD28 costimulation with the approved immunomodulator CTLA4Ig suppressed primary responses in naive mice infected with influenza, but was remarkably curative for memory CD4 T cell-mediated secondary responses to influenza, with reduced immunopathology and enhanced recovery. We demonstrate that CTLA4Ig differentially affects lymphoid and nonlymphoid responses to influenza challenge, inhibiting proliferation and egress of lymphoid naive and memory T cells, while leaving lung-resident memory CD4 T cell responses intact. Our findings reveal the dual nature of memory T cell-mediated secondary responses and suggest costimulation modulation as a novel strategy to optimize antiviral immunity by limiting the memory T cell response to its protective capacities.

Pulse-oximetry accurately predicts lung pathology and the immune response during influenza infection.

In animal models of influenza, systemic weight loss is the primary indicator of morbidity from infection, which does not assess local lung pathology or the immune response. Here, we used a mouse-adapted pulse-oximeter as a non-invasive clinical readout of lung function during influenza infection in mice, and found direct correlations between oxygen saturation levels and lung pathology, that reflected the morbidity and survival from influenza infection. We found blood oxygen levels to be a more accurate assessment than weight-loss morbidity in predicting lung pathology in hosts infected with different viral doses, and in assessing immune-mediated viral clearance in the lung.

TLR2 Engagement on Dendritic Cells Promotes High Frequency Effector and Memory CD4 T Cell Responses

Ligation of TLR by distinct pathogen components provides essential signals for T cell priming, although how individual TLR engagement affects primary and memory T cell responses is not well defined. In this study, we demonstrate distinct effects of TLR2 vs TLR4 engagement on primary and memory CD4 T cell responses due to differential effects on APC. Priming of influenza hemagglutinin (HA)-specific naive CD4 T cells with HA peptide and the TLR2 agonist Pam3CysK in vivo resulted in a high frequency of activated HA-specific CD4 T cells that predominantly produced IL-2 and IL-17, whereas priming with HA peptide and the TLR4 agonist LPS yielded a lower frequency of HA-specific CD4 T cells and predominant IFN-γ producers. TLR2 agonist priming depended on TLR2 expression by APC, as wild-type CD4 T cells did not expand in response to peptide and Pam3CysK in TLR2-deficient hosts. TLR2-mediated priming also led to an increased frequency of Ag-specific memory CD4 T cells compared with TLR4 priming and mediated enhanced secondary responses to influenza challenge. Our results show that TLR engagement on APC influences both primary and secondary CD4 T cell responses, and suggest that long-term functional capacities of T cells are set by innate signals during early phases of an infection.

Gene expression profiling of gut mucosa and mesenteric lymph nodes in simian immunodeficiency virus-infected macaques with divergent disease course.

Background  Although the majority of drug‐naïve HIV‐infected patients develop acquired immunodeficiency syndrome (AIDS), a small percentage remains asymptomatic without therapeutic intervention.

Vaccination with a Streptococcus pneumoniae trivalent recombinant PcpA, PhtD and PlyD1 protein vaccine candidate protects against lethal pneumonia in an infant murine model

Streptococcus pneumoniae infections continue to cause significant worldwide morbidity and mortality despite the availability of efficacious serotype-dependent vaccines. The need to incorporate emergent strains expressing additional serotypes into pneumococcal polysaccharide conjugate vaccines has led to an identified need for a pneumococcal protein-based vaccine effective against a broad scope of serotypes. A vaccine consisting of several conserved proteins with different functions during pathogenesis would be preferred. Here, we investigated the efficacy of a trivalent recombinant protein vaccine containing pneumococcal choline-binding protein A (PcpA), pneumococcal histidine triad D (PhtD), and genetically detoxified pneumolysin (PlyD1) in an infant mouse model. We found the trivalent vaccine conferred protection from lethal pneumonia challenges using serotypes 6A and 3. The observed protection with trivalent PcpA, PhtD, and PlyD1 vaccine in infant mice supports the ongoing study of this candidate vaccine in human infant clinical trials.