Rôles des protéines U54 et précoce immédiate 1 dans l'évasion immunitaire et l'immunothéraphie de l'herpèsvirus humain 6B

Le virus Herpès humain de type 6B (HHV-6B) est un virus qui infecte environ 95% de la population mondiale et qui est relativement bénin chez les personnes immunocompétentes mais dont les réactivations sont potentiellement graves chez les immunodéprimés. HHV-6B est l’agent étiologique de la roséole de l’enfant ou exanthème subit. Comme tout virus herpétique, HHV-6B a développé diverses stratégies lui permettant de moduler le système immunitaire à son avantage afin de persister au sein de son hôte. La caractérisation de nouveaux mécanismes d’évitement utilisés par HHV-6B ou l’identification de cibles immunodominantes permettraient de mettre en place de nouvelles stratégies afin de combattre l’infection. Au cours de nos recherches, nous avons identifié que la protéine de tégument U54 d’HHV-6B inhibe la synthèse d’interleukine-2 (IL-2). Nous avons déterminé la voie de signalisation de la calcineurine (CaN) / NFAT comme étant le facteur antagonisé par U54 et caractérisé le mécanisme aboutissant à cette inhibition. De plus, en nous basant sur ces résultats, nous avons testé l’impact d’une abrogation de la voie CaN/NFAT par U54 sur la progression de cellules de cancer du sein. Nous avons démontré que l’expression d’U54 provoque une baisse significative de la proliferation de cellules de cancer du sein MCF-7. Ces résultats ont fait germer l’idée du ciblage de cellules de cancer du sein exprimant la protéine U54 couplé à un protocole d’immunothérapie adoptive anti-cancéreuse. Enfin, l’immunothérapie adoptive antivirale est également un sujet d’étude qui a été abordé. Nous avons identifié des épitopes de la protéine IE1 d’HHV-6B présentés dans le contexte de trois des allèles les plus communs dans la population caucasienne : HLA-A*02, HLA-A*03 et HLA-B*07. Ceci nous a permit de perpétrer une expansion clonale de lymphocytes T cytotoxiques (CTL) capables de lyser des cellules infectées qui pourraient servir à contrôler d’éventuelles réactivations virales chez des patients immunodéprimés. De manière générale, nos travaux permettent d’étendre les connaissances sur les mécanismes utilisés par HHV-6B pour contourner le système immunitaire de l’hôte mais également d’identifier des cibles permettant de développer un éventuel protocole d’immunothérapie adoptive

La voie de signalisation cGAS/STING contrôle les infections par le virus de la rougeole et par le virus Nipah

International audienceNo abstract availabl

The Ebola Interferon Inhibiting Domains Attenuate and Dysregulate Cell-Mediated Immune Responses

<div><p>Ebola virus (EBOV) infections are characterized by deficient T-lymphocyte responses, T-lymphocyte apoptosis and lymphopenia. We previously showed that disabling of interferon-inhibiting domains (IIDs) in the VP24 and VP35 proteins effectively unblocks maturation of dendritic cells (DCs) and increases the secretion of cytokines and chemokines. Here, we investigated the role of IIDs in adaptive and innate cell-mediated responses using recombinant viruses carrying point mutations, which disabled IIDs in VP24 (EBOV/VP24m), VP35 (EBOV/VP35m) or both (EBOV/VP35m/VP24m). Peripheral blood mononuclear cells (PBMCs) from cytomegalovirus (CMV)-seropositive donors were inoculated with the panel of viruses and stimulated with CMV pp65 peptides. Disabling of the VP35 IID resulted in increased proliferation and higher percentages of CD4⁺ T cells secreting IFNγ and/or TNFα. To address the role of aberrant DC maturation in the IID-mediated suppression of T cell responses, CMV-stimulated DCs were infected with the panel of viruses and co-cultured with autologous T-lymphocytes. Infection with EBOV/VP35m infection resulted in a significant increase, as compared to wt EBOV, in proliferating CD4⁺ cells secreting IFNγ, TNFα and IL-2. Experiments with expanded CMV-specific T cells demonstrated their increased activation following co-cultivation with CMV-pulsed DCs pre-infected with EBOV/VP24m, EBOV/VP35m and EBOV/VP35m/VP24m, as compared to wt EBOV. Both IIDs were found to block phosphorylation of TCR complex-associated adaptors and downstream signaling molecules. Next, we examined the effects of IIDs on the function of B cells in infected PBMC. Infection with EBOV/VP35m and EBOV/VP35m/VP24m resulted in significant increases in the percentages of phenotypically distinct B-cell subsets and plasma cells, as compared to wt EBOV, suggesting inhibition of B cell function and differentiation by VP35 IID. Finally, infection with EBOV/VP35m increased activation of NK cells, as compared to wt EBOV. These results demonstrate a global suppression of cell-mediated responses by EBOV IIDs and identify the role of DCs in suppression of T-cell responses.</p></div

Measles Virus-Induced Host Immunity and Mechanisms of Viral Evasion

The immune system deploys a complex network of cells and signaling pathways to protect host integrity against exogenous threats, including measles virus (MeV). However, throughout its evolutionary path, MeV developed various mechanisms to disrupt and evade immune responses. Despite an available vaccine, MeV remains an important re-emerging pathogen with a continuous increase in prevalence worldwide during the last decade. Considerable knowledge has been accumulated regarding MeV interactions with the innate immune system through two antagonistic aspects: recognition of the virus by cellular sensors and viral ability to inhibit the induction of the interferon cascade. Indeed, while the host could use several innate adaptors to sense MeV infection, the virus is adapted to unsettle defenses by obstructing host cell signaling pathways. Recent works have highlighted a novel aspect of innate immune response directed against MeV unexpectedly involving DNA-related sensing through activation of the cGAS/STING axis, even in the absence of any viral DNA intermediate. In addition, while MeV infection most often causes a mild disease and triggers a lifelong immunity, its tropism for invariant T-cells and memory T and B-cells provokes the elimination of one primary shield and the pre-existing immunity against previously encountered pathogens, known as &ldquo;immune amnesia&rdquo;

Disabling of lymphocyte immune response by Ebola virus - Fig 1

<p>(A) Role of Evola virus (EBOV) glycoprotein (GP) steric shielding in impairment of T-cell response. Comparison between a typical viral infection and EBOV infection and the role of EBOV GP overexpression on cell surface membrane. (B) Role of EBOV VP35 interferon-inhibiting domain (IID) in suppression and dysregulation of cell-mediated response. Effects of wild-type (wt) EBOV (left) and the mutated virus with VP35 IID disabled by amino acid substitution R312A on dendritic cells (DCs), natural killer (NK) cells, B cells, and T cells. Summarized from references [<a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1006932#ppat.1006932.ref020" target="_blank">20</a>, <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1006932#ppat.1006932.ref023" target="_blank">23</a>, <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1006932#ppat.1006932.ref024" target="_blank">24</a>]. APC, antigen-presenting cells; CD-80, -86, cluster of differentiation; VP35, viral protein 35.</p

Involvement of Angiopoietin-like 4 in Matrix Remodeling during Chondrogenic Differentiation of Mesenchymal Stem Cells

International audienceBackground:Due to their ability to differentiate into chondrocytes, mesenchymal stem cells (MSCs) are candidates forcartilage repair.Results:During chondrogenic differentiation of MSCs, angiopoietin-like 4 (ANGPTL4) triggers degradation and reducedsynthesis of the cartilage matrix.Conclusion:ANGPTL4 promotes cartilage matrix remodeling.Significance:In the perspective of MSC-based cartilage engineering, inhibiting ANGPTL4 expression or action could help tostabilize cartilage formation.Mesenchymal stem cells (MSCs) are considered for cartilage engineering given their ability to differentiate into chondrocytes. Chondrogenic differentiation of MSCs is currently triggered by micromass culture in the presence of a member of the TGF-β superfamily. However, the main constituents of the cartilaginous matrix, aggrecan and type II collagen, are degraded at the end of the differentiation process through induction of matrix metallopeptidase (MMP)13. We hypothesized that MSCs undergoing chondrogenic differentiation produce an intermediate cytokine that triggers this matrix remodeling. Analysis of transcriptomic data identified angiopoietin-like 4 (ANGPTL4) as one of the most strongly up-regulated gene encoding a secreted factor during TGF-β-induced chondrogenesis. To gain insight into the role of ANGPTL4 during chondrogenesis, we used recombinant ANGPTL4 as well as a RNA interference approach. Addition of exogenous ANGPTL4 during the course of TGF-β-induced differentiation reduced the mRNA levels of aggrecan and type II collagen, although it increased those of MMP1 and MMP13. Accordingly, deposition of aggrecan and total collagens was diminished, whereas release of MMP1 and MMP13 was increased. Conversely, transfection of MSCs with an siRNA targeting ANGPTL4 prior to induction of chondrogenesis increased expression of type II collagen and aggrecan, whereas it repressed that of MMP1, MMP3, and MMP13. A neutralizing antibody against integrin αVβ5, a known receptor for ANGPTL4, mimicked some of the effects observed after siRNA-mediated ANGPTL4 silencing. Our data provide evidence that ANGPTL4 promotes cartilage matrix remodeling by inhibiting expression of its two key components and by up-regulating the level of certain MMPs

Early Permissiveness of Central Nervous System Cells to Measles Virus Infection Is Determined by Hyperfusogenicity and Interferon Pressure

The cessation of measles virus (MeV) vaccination in more than 40 countries as a consequence of the COVID-19 pandemic is expected to significantly increase deaths due to measles. MeV can infect the central nervous system (CNS) and lead to lethal encephalitis. Substantial part of virus sequences recovered from patients’ brain were mutated in the matrix and/or the fusion protein (F). Mutations of the heptad repeat domain located in the C terminal (HRC) part of the F protein were often observed and were associated to hyperfusogenicity. These mutations promote brain invasion as a hallmark of neuroadaptation. Wild-type F allows entry into the brain, followed by limited spreading compared with the massive invasion observed for hyperfusogenic MeV. Taking advantage of our ex vivo models of hamster organotypic brain cultures, we investigated how the hyperfusogenic mutations in the F HRC domain modulate virus distribution in CNS cells. In this study, we also identified the dependence of neural cells susceptibility on both their activation state and destabilization of the virus F protein. Type I interferon (IFN-I) impaired mainly astrocytes and microglial cells permissiveness contrarily to neurons, opening a new way of consideration on the development of treatments against viral encephalitis

Quercetin blocks Ebola Virus infection by counteracting the VP24 Interferon inhibitory function

Ebola Virus (EBOV) is among the most devastating pathogens causing fatal hemorrhagic fever in humans. The 2013–2016 epidemics resulted in over 11000 deaths, while another outbreak is currently ongoing. Since there is no FDA-approved drug so far to fight EBOV infection, there is an urgent need to focus on drug discovery. Considering the tight correlation between the high EBOV virulence and its ability to suppress the type-I Interferon (IFN-I) system, identifying molecules targeting viral protein VP24, one of the main virulence determinants blocking IFN response, is a promising novel anti-EBOV therapy approach. Hence, in the effort of finding novel EBOV inhibitors, a screening of a small set of flavonoids was performed, showing that Quercetin and Wogonin can suppress the VP24 effect on IFN-I signaling inhibition. The mechanism of action of the most active compound, Quercetin, showing an IC50 value of 7.4 μM, was characterized to significantly restore the IFN-I signaling cascade, blocked by VP24, by directly interfering with the VP24 binding to karyopherin-α and thus restoring P-STAT1 nuclear transport and IFN genes transcription. Quercetin significantly blocked viral infection, specifically targeting EBOV VP24 anti-IFN-I function. Overall, Quercetin is the first identified inhibitor of the EBOV VP24 anti-IFN function, representing a molecule interacting with a viral binding site that is very promising for further drug development aiming to block EBOV infection at the early steps