Mathieu Iampietro

Nipah virus (NiV) is a zoonotic highly pathogenic Paramyxovirus inducing lethal outbreaks of encephalitis and Acute Respiratory Distress Syndrome (ARDS) with an average case-fatality rate of 75%. Two viral strains, NiV-Malaysia (NiV-Mal) and NiV-Bangladesh (NiV-Ban), associated to distinct route of transmission, symptoms and lethality have been described. Due to the permanent threat of these emerging infections and the lack of approved therapeutics, it is crucial to improve our understanding regarding NiV-associated pathogenesis. Mice represent a small and accessible animal model, provided with numerous biological tools for the functional assessment of different genes related to antiviral response. Here, we explore the susceptibility of mice deficient for type I interferon receptor (IFNAR KO) to inoculation with either NiV-Mal or NiV-Ban through intraperitoneal or intranasal routes. Our results complement observations showing that IFNAR KO mice are susceptible to NiV-Ban infection via intraperitoneal route, although to a lesser extent than NiV-Mal, and develop encephalitis and a pulmonary syndrome with viral dissemination to various organs. Additionally, intranasal administration of both viral strains exhibited a subclinical infection with viral replication in the brain and the lungs along to the production of neutralizing antibodies in some animals. These results suggest that IFNAR KO mice may represent a reliable model permitting comparative studies of the immunopathogenesis induced by both NiV-Mal and NiV-Ban infections.

Nipah virus (NiV) is a zoonotic highly pathogenic Paramyxovirus inducing lethal outbreaks of encephalitis and severe acute respiratory syndrome (SARS) with an average case-fatality rate of 75%. Two viral strains, NiV-Malaysia (NiV-Mal) and NiV-Bangladesh (NiV-Ban), associated to distinct geographical distribution, route of transmission, symptoms and lethality have been described. Due to the permanent threat of these emerging infections and the lack of approved therapeutics, it is crucial to improve our understanding regarding NiV-associated pathogenesis. Mice represent a small and accessible animal model, provided with numerous biological tools for the functional assessment of different genes related to antiviral response. Here, we analyze the susceptibility of mice deficient for type I interferon receptor (IFNAR KO) to infection with either NiV-Mal or NiV-Ban through intraperitoneal or intranasal routes. Our results show that IFNAR KO mice are susceptible to NiV-Ban infection via intraperitoneal route, although to a lesser extent than NiV-Mal, and develop encephalitis and pulmonary syndrome with viral propagation to different organs and lethal outcome in 60% of infected animals. In addition, intranasal administration of both viral strains led to a subclinical infection with viral replication in brain and lungs and production of virus-specific neutralizing antibodies. These results indicate IFNAR KO mice as a small animal model permitting comparative studies of the immunopathogenesis perpetrated by both NiV-Mal and NiV-Ban infections. Author summary: Availability of small animal models represents a major issue to characterize virus-associated pathogenesis to further implement therapeutic strategies. Previous studies performed with NiV-Mal and NiV-Ban strains in wild-type (WT) mice did not indicate signs of NiV disease. However, when challenged with NiV-Mal, IFNAR KO mice suffered fatal outcomes, thus providing useful information on viral immunopathogenesis. Surprisingly, while being the more frequently re-emerging virus strain, no infection studies with NiV-Ban have been performed in IFNAR KO mice so far. Here, we sought comparing pathogenesis after NiV-Mal- and NiV-Ban-infection following IP and IN inoculations in IFNAR KO mice. Indeed, our results highlighted that contrary to fatal IP challenge, IN inoculation lead to a subclinical infection with both NiV strains. Moreover, we determined that NiV-Mal is more pathogenic than NiV-Ban following IP infection. Finally, distinct histopathological manifestations and tropism were associated with each viral strain and specific route of infection. Overall, our study implies that IFNAR KO mice represent a useful animal model to study strain-specific NiV pathophysiology.

Ebola virus (EBOV) causes a severe human disease with high lethality. Pathogenesis of EBOV disease is characterized by a paradoxical combination of hyperinflammation and immunosuppression. EBOV has a single envelope glycoprotein (GP), which is a type I transmembrane protein with strong immunomodulatory effects. GP contains a conserved immunosuppressive domain (ISD) with a high similarity to ISDs of envelope proteins retroviruses. To investigate the effects of ISD, a set of 17 EBOV viral-like particle (VLP) constructs containing the entire EBOV nucleoprotein, VP40, and GP with single alanine or glycine substitutions in each position of ISD was generated and tested in human peripheral blood mononuclear cells (PBMCs). Wild-type VLPs induced inflammatory responses; however, when added to pre-stimulated cells, they reduced inflammation, thus exerting immunosuppressive properties. Substitution of lysine at ISD position 5 (Lys-5) increased anti-inflammatory properties by reducing proliferative responses of VLPs and also reducing nuclear factor of activated T-cells 1 (NFAT1) and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) activation. In contrast, substitution of tryptophan at position 14 (Trp-14) increased both the pro-inflammatory and the proliferative responses and the adhesion of VLP-infected human monocytes to microvascular endothelial cells. Thus, the ISD N- and C-termini have pro- and anti-inflammatory properties, respectively, suggesting their unique implications in the EBOV pathogenesis. Furthermore, the immunomodulating effects of ISD were also mediated by shed GP, which is abundant in the medium. These data may be useful for the development of treatments for diseases caused by EBOV by targeting the ISD. IMPORTANCE: Our data suggest that the ISD N-terminus plays a role in activating immune cells and pro-inflammatory response. In contrast, the C-terminus of ISD downregulates the pro-inflammatory response through the reduction of NF-kB and NFAT activities. The data also show that EBOV GP increases the adhesion of monocytes to endothelial cells, and the effect is inhibited by the ISD C-terminus. Moreover, the data demonstrate that the immunomodulating effects of ISD are mediated not only by the virus-associated GP but also by the shed GP, which is abundant in the medium. Pathogenesis of the disease caused by EBOV is characterized by hyperinflammation and some features of immunosuppression, which could in part be affected by the complex effects of the ISD. These data indicate that targeting the ISD may be considered for the development of treatments for the disease caused by EBOV.

Activation of the DNA-sensing STING axis by RNA viruses plays a role in antiviral response through mechanisms that remain poorly understood. Here, we show that the STING pathway regulates Nipah virus (NiV) replication in vivo in mice. Moreover, we demonstrate that following both NiV and measles virus (MeV) infection, IFNγ-inducible protein 16 (IFI16), an alternative DNA sensor in addition to cGAS, induces the activation of STING, leading to the phosphorylation of NF-κB p65 and the production of IFNβ and interleukin 6. Finally, we found that paramyxovirus-induced syncytia formation is responsible for loss of mitochondrial membrane potential and leakage of mitochondrial DNA in the cytoplasm, the latter of which is further detected by both cGAS and IFI16. These results contribute to improve our understanding about NiV and MeV immunopathogenesis and provide potential paths for alternative therapeutic strategies.

Activation of the DNA-sensing STING axis by RNA viruses plays a role in antiviral response through mechanisms that remain poorly understood. Here, we show that the STING pathway regulates Nipah virus (NiV) replication in vivo in mice. Moreover, we demonstrate that following both NiV and measles virus (MeV) infection, IFNγ-inducible protein 16 (IFI16), an alternative DNA sensor in addition to cGAS, induces the activation of STING, leading to the phosphorylation of NF-κB p65 and the production of IFNβ and interleukin 6. Finally, we found that paramyxovirus-induced syncytia formation is responsible for loss of mitochondrial membrane potential and leakage of mitochondrial DNA in the cytoplasm, the latter of which is further detected by both cGAS and IFI16. These results contribute to improve our understanding about NiV and MeV immunopathogenesis and provide potential paths for alternative therapeutic strategies.

While the function of cGAS/STING signalling axis in the innate immune response to DNA viruses is well deciphered, increasing evidence demonstrates its significant contribution in the control of RNA virus infections. After the first evidence of cGAS/STING antagonism by flaviviruses, STING activation has been detected following infection by various enveloped RNA viruses. It has been discovered that numerous viral families have implemented advanced strategies to antagonize STING pathway through their evolutionary path. This review summarizes the characterized cGAS/STING escape strategies to date, together with the proposed mechanisms of STING signalling activation perpetrated by RNA viruses and discusses possible therapeutic approaches. Further studies regarding the interaction between RNA viruses and cGAS/STING-mediated immunity could lead to major discoveries important for the understanding of immunopathogenesis and for the treatment of RNA viral infections.

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.

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 “immune amnesia”.

Measles is the most contagious airborne viral infection and the leading cause of child death among vaccine-preventable diseases. We show here that aerosolized lipopeptide fusion inhibitor, derived from heptad-repeat regions of the measles virus (MeV) fusion protein, blocks respiratory MeV infection in a non-human primate model, the cynomolgus macaque. We use a custom-designed mesh nebulizer to ensure efficient aerosol delivery of peptide to the respiratory tract and demonstrate the absence of adverse effects and lung pathology in macaques. The nebulized peptide efficiently prevents MeV infection, resulting in the complete absence of MeV RNA, MeV-infected cells, and MeV-specific humoral responses in treated animals. This strategy provides an additional means to fight against respiratory infection in non-vaccinated people, that can be readily translated to human trials. It presents a proof-of-concept for the aerosol delivery of fusion inhibitory peptides to protect against measles and other airborne viruses, including SARS-CoV-2, in case of high-risk exposure.