La risposta immune all infezione da virus ebola. Chiara Agrati, PhD

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1 La risposta immune all infezione da virus ebola Chiara Agrati, PhD Pathogenetic mechanisms This virus infection is able to: - disable the immune system, preventing an effective protective immune response - disable the vascular system that leads to blood leakage (hemorrhage), hypotension, drop in blood pressure, followed by shock and death.

2 An effective immune response requires complex and well orchestrated cell-cell interplay The majority of information derived from studies in animal models About 150 papers were published on the immune response to Ebola infection. Since the difficulty to obtain human samples from Ebola-infected patients, the large majority of information on pathogenesis and immune response derived from studies in animal models. Thus, the picture of events during Ebola infection was obtained by integrating few results in humans with results obtained in animal models (MHP, mice)

3 Mechanisms of immune response failure during Ebola infection 1) Viral Escape mechanisms to Type I IFN 2) DC infection and APC function impairment 3) Macrophages infection and cytokines/chemokines storm induction 4) Dramatic loss and impairment of adaptive immune responses: B and T lymophocytes Mechanisms of immune response failure during Ebola infection 1) Viral Escape mechanisms to Type I IFN 2) DC infection and APC function impairment 3) Macrophages infection and cytokines/chemokines storm induction 4) Dramatic loss and impairment of adaptive immune responses: B and T lymophocytes

4 In vitro Ebola virus infection inhibits IFNα production In vitro IFN-α Poly-IC stimulation of uninfected-pbmc Poly-IC stimulation of Ebola-infected PBMC In vivo IFNα production is associated to survival Animal model Humans Nonsurvivors Survivors IFN-α IFN-α Mahanti S, Virology 2003 Hutchinson K, JID 2008 Ebola proteins are able to block type I IFN innate immune response

5 Mechanisms of immune response failure during Ebola infection 1) Viral Escape mechanisms to Type I IFN 2) DC infection and APC function impairment 3) Macrophages infection and cytokines/chemokines storm induction 4) Dramatic loss and impairment of adaptive immune responses: B and T lymophocytes DC are early and preferred replication site of replication and Dendritic cells (DC) are early and preferred replication site of Ebola virus and seem to have pivotal roles in dissemination of the virus as it spreads from the initial infection site to regional lymph nodes, probably through the lymphatic system, and to the liver and spleen through the blood. Martinez O, antiviral Research, 2012

6 Ebola infection impairs DC maturation DC maturation is an essential process to induce an effective adaptive immune response. DC activation and maturation result in an increase of expression of molecules necessary fro APC functions (CD80, CD83, CD86, HLA-DR). Impaired DC are unable to induce a T cell response In vitro Ebola infection of DC inhibited the expression of costimulatory molecules, essential for APC function Ebola-infected DC are unable to correctly stimulate T cell proliferation, thus impairing the adaptive immune response capability Martinez O, antiviral Research, 2012

7 Mechanisms of immune response failure during Ebola infection 1) Viral Escape mechanisms to Type I IFN 2) DC infection and APC function impairment 3) Macrophages infection and cytokines/chemokines storm induction 4) Dramatic loss and impairment of adaptive immune responses: B and T lymophocytes

8 In vitro infection induce inflammatory molecules production DEATH and HEMORRHAGE Were associated with elevated levels of chemokines and cytokines

9 DEATH and HEMORRHAGE Were associated with ferritin and thrombomodulin Associations between multiple pro-inflammatory cytokines and increased death rates have been showed, suggesting that systemic inflammation contributing to a fatal outcome. (Hensley LE, Immunol letter 2002; Hutchinson KL, JID 2009; Wauquier N, PLoS Negl Trop Dis 2010; Villinger F, JID 1999; Baize S, Clin Exp Immunol 2002) Mechanisms of immune response failure during Ebola infection 1) Viral Escape mechanisms to Type I IFN 2) DC infection and APC function impairment 3) Macrophages infection and cytokines/chemokines storm induction 4) Dramatic loss and impairment of adaptive immune responses: B and T lymophocytes

10 Depletion of lymphocyte count in blood during Ebola virus infection in mice. Mice model Non-human primates model Bradfute S B et al. J Infect Dis. 2007;196 A dramatic loss of NK, B and T lymphocytes was observed early after Ebola infection CD4 CD8

11 Massive Apoptosis of T cells in fatal cases Confirmed in vitro Aberrant antibody response in fatal cases of infections Antibody response Fatal cases Survivors cases Recovery of infected patients is associated with efficient EBOV-specific immunoglobulin G (IgG) responses, whereas fatal outcome is associated with defective humoral immunity The immunoreactivity was mainly directed against NP and GP

12 T-cell response Aberrant T cell response in fatal cases of infections SURVIVORS: The expression of markers of T cell response (IFN-γ, CD28 and perforin) is associated to recovery, suggesting an effective T cell-mediated immune response. FATALITIES: During the early phase of infection a massive apoptosis was observed, followed by T cell lost Thus, events very early in Ebola virus infection determine the control of viral replication and recovery or catastrophic illness and death. The ineffective activation of T cells Very few data are available on functional analysis of T cells during Ebola infection, due to the complexity of these assay in high biosafety level Inflammation Cytokine storm Ebola-DC CD4 + CD4 + CD4 + CD4 CD8 + + CD8 + CD8 + CD4 + DC B CD8 + CD8 + B Cytotoxic CD8 Collapse of adaptive immunity

13 Correlate of protective immunity to Ebola Vaccine ROLE OF ANTIBODIES Antibodies titer represents a good correlate of protection in NHP (Sullivan, Nature review, 2009) Nevertheless, the effectiveness of passive transfer of monoclonal antibodies in lethally infected NHPs gave controversial results (X. Qiu, Sci. Transl. Med. 4, 2012; Sullivan N, Nat Medicine, 2011). ROLE OF T CELLS Nevertheless, several evidences suggest a key role of T cells in mediating vaccine efficacy, mainly in long lasting vaccine effectiveness. Depletion of CD3+ T cells in vivo after vaccination and immediately before challenge eliminated immunity. It is not likely that long-lived immunity can be achieved without T-helper cells. Ebola Vaccines

14 Phase 1 NIH/GSK - ChAd3 Chimp Adenoviral Vector (ChAd3) carrying glicoprotein (GP) of one o two Ebola species (Zaire and Sudan). monovalent/bivalent NIH/GSK 100% protection on monkeys Phase I in USA e UK. The initial safety and immunogenicity data from the Phase 1 NIAID/GSK Ebola vaccine trials are expected by late Link Genetics corp. - VSV VSV (rvsv G) expressing GP 100% protection on monkeys 30-50% of post exposure prophylaxis in monkeys Phase I in USA (probably also in Gabon, Germania e Svizzera) In summary Fatal EBOV infections are characterized by a failure of immune system to clear the infection, excessive host inflammation, activation of coagulation cascades and massive lymphocyte apoptosis. Survivors and asymptomatic subjects develop an early and moderate inflammatory response together with an effective adaptive response Antibodies titer represents a good correlate of protection both in natural infection and after vaccination; nevertheless, T cells play a role in mediating protection mainly in long lasting immunity Thank you for your attention

15 These results demonstrate limited cross-reactivity of IgM antibodies to EBOV, and a stronger tendency for cross-reactive IgG antibody responses. This observation may assist in the development of antibody-mediated vaccines to EBOV All Ebola infection are highly pathogenic?

16 A large fraction of the human population living in forested areas of Gabon has both humoral and cellular immunity to ZEBOV. In the absence of identified risk factors, the high prevalence of immune persons suggests a common source of human exposure such as fruits contaminated by bat saliva. These findings provide significant new insights into ZEBOV circulation and human exposure, and raise important questions as to the human pathogenicity of ZEBOV and the existence of natural protective immunization.