Chiara Agrati

Lack of CD27-CD45RA-V gamma 9V delta 2+ T cell effectors in immunocompromised hosts and during active pulmonary tuberculosis.

In humans, the circulating pool of mycobacteria-reactive Vγ9Vδ2+ T cells is expanded with age and may contribute to Mycobacterium tuberculosis immunosurveillance. We observed that two subsets of Vγ9Vδ2+ T cells could be identified on the basis of CD27 expression in immunocompetent adults, showing that functionally differentiated γδ T cells have lost CD27 expression. In contrast, the CD27−CD45RA−Vγ9Vδ2+ T cell subset of effector cells was absent in cord blood cells from healthy newborns and lacking in the peripheral blood from HIV-infected patients. Moreover, circulating Vγ9Vδ2+ T cell effectors were significantly reduced in patients with acute pulmonary tuberculosis, resulting in a reduced frequency of IFN-γ-producing cells after stimulation with nonpeptidic mycobacterial ligands. These observations indicate that monitoring and boosting γδ T cell effectors could be clinically relevant both in immunocompromised hosts and during active tuberculosis disease.

Cross-subtype Immunity against Avian Influenza in Persons Recently Vaccinated for Influenza

Seasonal influenza vaccination may induce heterosubtypic immunity against avian influenza virus (H5N1).

Cutting Edge: TGF-β1 and IL-15 Induce FOXP3+ γδ Regulatory T Cells in the Presence of Antigen Stimulation

Several subsets of αβ regulatory T cells (Tregs) have been described and studied intensively, but the potential regulatory role of γδ T cells remains largely unclear. Lymphocytes expressing γδ TCR are involved in both innate and adaptive immune responses, and their major adult human peripheral blood subset (Vγ9Vδ2) displays a broad reactivity against microbial agents and tumors. In this study we report that γδ T lymphocytes with regulatory functions (Vδ2 Tregs) are induced in vitro in the presence of specific Ag stimulation and cytokines (TGF-β1 and IL-15). These cells express FOXP3 and, similarly as αβ Tregs, suppress the proliferation of anti-CD3/anti-CD28 stimulated-PBMC. Phenotypic and functional analyses of Vδ2 Tregs will very likely improve our understanding about the role of γδ T cells in the pathogenesis of autoimmune, infectious, and neoplastic diseases.

Antiviral reactivities of γδ T cells

Abstract The complex antiviral immune mechanisms involve both adaptive and innate reactions mediated by γδ T lymphocytes, whose unique immunosurveillance contributions are analyzed here in different clinical and experimental settings. It is beyond any doubt that the fast, potent, cytotoxic as well as non-cytolytic antiviral activities of γδ T cells are critical in protecting the host against diverse viral pathogens.

Association of Profoundly Impaired Immune Competence in H1N1v-Infected Patients with a Severe or Fatal Clinical Course

BACKGROUND Pandemic A/H1N1v influenza is characterized by a mild clinical course. However, a small subset of patients develops a rapidly progressive course caused by primary viral pneumonia or secondary bacterial infections that, in many cases, lead to death due to respiratory failure. The aim of the present study was to analyze the involvement of the immune response in the clinical presentation of H1N1v influenza. METHODS The differentiation and functional capability of T cells from H1N1v-infected patients presenting with either mild disease (n=22) or severe or fatal disease (n=6) were compared. Moreover, plasma cytokines and chemokines were quantified. RESULTS T cells from H1N1v-infected patients presenting with a severe clinical course resulted in impaired effector cell differentiation and failed to respond to mitogenic stimulation. T cell anergy was strictly associated with a severe acute phase of infection, but T cells could be restored in patients able to recover. Of interest, massive expression of CD95 marker was found on anergic T cells, suggesting an apoptosis-related mechanism. Finally, lower plasma levels of interferon-alpha and monocyte chemoattractant protein-1 were found in patients with a worse clinical course of influenza, suggesting impaired production of these cytokines. CONCLUSIONS Our results show a strict association between host immune competence and the severity of the clinical course of H1N1v infection. By monitoring host functional response, patients with an enhanced risk of developing influenza-associated severe complications could be identified in a timely manner.

Unique human immune signature of Ebola virus disease in Guinea

Despite the magnitude of the Ebola virus disease (EVD) outbreak in West Africa, there is still a fundamental lack of knowledge about the pathophysiology of EVD. In particular, very little is known about human immune responses to Ebola virus. Here we evaluate the physiology of the human T cell immune response in EVD patients at the time of admission to the Ebola Treatment Center in Guinea, and longitudinally until discharge or death. Through the use of multiparametric flow cytometry established by the European Mobile Laboratory in the field, we identify an immune signature that is unique in EVD fatalities. Fatal EVD was characterized by a high percentage of CD4+ and CD8+ T cells expressing the inhibitory molecules CTLA-4 and PD-1, which correlated with elevated inflammatory markers and high virus load. Conversely, surviving individuals showed significantly lower expression of CTLA-4 and PD-1 as well as lower inflammation, despite comparable overall T cell activation. Concomitant with virus clearance, survivors mounted a robust Ebola-virus-specific T cell response. Our findings suggest that dysregulation of the T cell response is a key component of EVD pathophysiology.

Acute human immunodeficiency virus replication causes a rapid and persistent impairment of Vγ9Vδ2 T cells in chronically infected patients undergoing structured treatment interruption

T cells expressing Vgamma9Vdelta2 display lytic and proliferative responses against human immunodeficiency virus (HIV)-infected cells and release antiviral soluble factors. Chronic HIV-positive patients have deep changes in the composition and function of the circulating gammadelta T cell pool that are restored by highly active antiretroviral therapy (HAART). gammadelta T cells were analyzed during the rapid plasma HIV RNA rebound in HIV-infected patients undergoing structured treatment interruption (STI). A loss in circulating Vgamma9Vdelta2 T cells was observed, indicating that acute HIV replication may influence Vgamma9Vdelta2 homeostasis. These cells were lost among CD45RA(-)CD27(-) Vgamma9Vdelta2 T cell effectors, and a significant unresponsiveness, measured as antigen-driven interferon-gamma production, was observed during STI. After HAART resumption and consequent inhibition of HIV replication, Vgamma9Vdelta2 T cell reactivity was restored both quantitatively and functionally. These observations indicate that Vgamma9Vdelta2 T cells are activated early after active HIV replication but are rapidly lost when viremia is not controlled.

Activation of Vγ9Vδ2 T cells by non-peptidic antigens induces the inhibition of subgenomic HCV replication

Abstract Hepatitis C virus (HCV) has evolved complex strategies to evade host immune responses and establish chronic infection. Since human Vγ9Vδ2 T lymphocytes play a critical role in the immune response against viruses, we analyzed their antiviral functions on Huh7 hepatoma cells carrying the subgenomic HCV replicon (Rep60 cells). In a transwell culture system, Rep60 cells were co-cultured with either PBMCs or highly purified γδ T cells stimulated by non-peptidic antigens. Vγ9Vδ2 T cell activation was associated with a dramatic reduction of HCV RNA levels. Neutralizing antibodies targeting IFN-γ revealed a critical role for this cytokine in the inhibition of HCV replication. Interestingly, drugs already in clinical use, such as Phosphostim and Zoledronate, known to activate γδ T cells, were shown to induce the inhibition of HCV replication mediated by Vγ9Vδ2 T cells of HCV patients. Our data suggest that the therapeutic activation of Vγ9Vδ2 T lymphocytes may represent an additional strategy to inhibit HCV replication and to restore a Th1-oriented immune response in HCV-infected patients.

Molecular mechanisms of Ebola virus pathogenesis: focus on cell death

Ebola virus (EBOV) belongs to the Filoviridae family and is responsible for a severe disease characterized by the sudden onset of fever and malaise accompanied by other non-specific signs and symptoms; in 30–50% of cases hemorrhagic symptoms are present. Multiorgan dysfunction occurs in severe forms with a mortality up to 90%. The EBOV first attacks macrophages and dendritic immune cells. The innate immune reaction is characterized by a cytokine storm, with secretion of numerous pro-inflammatory cytokines, which induces a huge number of contradictory signals and hurts the immune cells, as well as other tissues. Other highly pathogenic viruses also trigger cytokine storms, but Filoviruses are thought to be particularly lethal because they affect a wide array of tissues. In addition to the immune system, EBOV attacks the spleen and kidneys, where it kills cells that help the body to regulate its fluid and chemical balance and that make proteins that help the blood to clot. In addition, EBOV causes liver, lungs and kidneys to shut down their functions and the blood vessels to leak fluid into surrounding tissues. In this review, we analyze the molecular mechanisms at the basis of Ebola pathogenesis with a particular focus on the cell death pathways induced by the virus. We also discuss how the treatment of the infection can benefit from the recent experience of blocking/modulating cell death in human degenerative diseases.

Innate T-Cell Immunity in HIV Infections: The Role of Vg9Vd2 T Lymphocytes

There is growing interest in the use of innate immune reactions in the therapy and prophylaxis of various diseases. Natural T (NT) lymphocytes that recognize infected cells or microbial compounds without the classical genetic restriction by polymorphic MHC molecules are crucial components of innate immunity. NT cells bearing the Vgamma9Vdelta2 T-cell receptor (TCR) are broadly reactive against intracellular pathogens, can lyse human immunodeficiency virus (HIV) infected cells, and release cytokines capable of regulating HIV replication. The potent antiviral activities of Vgamma9Vdelta2 T cells may help to contain viral spread during acute HIV infection and/or to prevent the establishment of viral persistence. Substantial changes in the composition and function of circulating gammadelta T-cell pools occur in HIV-infected patients. These changes a) may contribute to the etiopathogenesis of opportunistic infections and neoplasms, and b) are partly reversed by highly active anti-retroviral therapy (HAART). In addition to direct antiviral activities, activated gammadelta T cells influence dendritic cell maturation and the adaptive alphabeta T-cell response. Vgamma9Vdelta2 T cells can be stimulated in vivo and in vitro by various nonpeptidic antigens (NpAgs) and recent animal experimental data suggest that activated Vgamma9Vdelta2 T cells may help to control SIV replication. Currently, NpAgs are being assessed as potential therapeutic agents in AIDS, tuberculosis and certain cancers susceptible to Vgamma9Vdelta2 T-cell effector mechanisms.