Exosome-Mediated Antigen Delivery: Unveiling Novel Strategies in Viral Infection Control and Vaccine Design.

Exosomes are small subtypes of extracellular vesicles (EVs) naturally released by different types of cells into their environment. Their physiological roles appear to be multiple, yet many aspects of their biological activities remain to be understood. These vesicles can transport and deliver a variety of cargoes and may serve as unconventional secretory vesicles. Thus, they play a crucial role as important vectors for intercellular communication and the maintenance of homeostasis. Exosome production and content can vary under several stresses or modifications in the cell microenvironment, influencing cellular responses and stimulating immunity. During infectious processes, exosomes are described as double-edged swords, displaying both beneficial and detrimental effects. Owing to their tractability, the analysis of EVs from multiple biofluids has become a booming tool for monitoring various pathologies, from infectious to cancerous origins. In this review, we present an overview of exosome features and discuss their particular and ambiguous functions in infectious contexts. We then focus on their properties as diagnostic or therapeutic tools. In this regard, we explore the capacity of exosomes to vectorize immunogenic viral antigens and their function in mounting adaptive immune responses. As exosomes provide interesting platforms for antigen presentation, we further review the available data on exosome engineering, which enables peptides of interest to be exposed at their surface. In the light of all these data, exosomes are emerging as promising avenues for vaccine strategies.

Cell cycle and mitosis progression during ZIKA virus infection: The viral non-structural protein NS5 as a master regulator of the APC/cyclosome?

Alterations in cell cycle regulation contribute to Zika virus (ZIKV)-associated pathogenesis and may have implications for the development of therapeutic avenues. As a matter of fact, ZIKV alters cell cycle progression at multiple stages, including G1, S, G2, and M phases. During a cell cycle, the progression of mitosis is particularly controlled to avoid any abnormalities in cell division. In this regard, the critical metaphase-anaphase transition is triggered by the activation of anaphase-promoting complex/cyclosome (APC/C) by its E3 ubiquitin ligase subunit Cdc20. Cdc20 recognizes substrates by interacting with a destruction box motif (D-box). Recently, the ZIKV nonstructural protein 5 (NS5), one of the most highly conserved flavivirus proteins, has been shown to localize to the centrosome in each pole and to spindle fibers during mitosis. Inducible expression of NS5 reveals an interaction of this viral factor with centrosomal proteins leading to an increase in the time required to complete mitosis. By analyzing the NS5 sequence, we discovered the presence of a D-box. Taken together, these data support the idea that, in addition to its role in viral replication, NS5 plays a critical role in the control of the cell cycle of infected cells and, more specifically, in the regulation of the mitotic spindle. Here we propose that the NS5 protein may interfere with the metaphase-anaphase progression, and thus cause the observed delay in mitosis via the regulation of APC/C.

Zika virus restriction of host antioxidant response is mediated by intracellular NS1 and reveals its ability to upregulate Bach1 expression.

Zika virus (ZIKV), has gained global attention due to its association with severe disorders, including microcephaly and congenital Zika syndrome. We investigated the role of ZIKV nonstructural protein 1 (NS1) in altering the host's antioxidant response. Using a stable cell line expressing NS1, we found that NS1 significantly reduced the expression of antioxidant-related genes, including heme oxygenase 1 (HO-1), NAD(P)H quinone dehydrogenase 1 (NQO1), and sequestosome-1 (SQSTM1), which are regulated NRF2. Interestingly, this effect was attributed to increased expression of BACH1, a factor that competes with NRF2 for binding to certain antioxidant responsive elements (ARE). Thus, ZIKV NS1-mediated disruption of the antioxidant system is linked to BACH1 overexpression. These findings offer insights into ZIKV pathogenesis and suggest potential therapeutic strategies targeting the NRF2-BACH1 axis.

The Influence of Metabolism on Immune Response: A Journey to Understand Immunometabolism in the Context of Viral Infection.

In recent years, the emergence of the concept of immunometabolism has shed light on the pivotal role that cellular metabolism plays in both the activation of immune cells and the development of immune programs. The antiviral response, a widely distributed defense mechanism used by infected cells, serves to not only control infections but also to attenuate their deleterious effects. The exploration of the role of metabolism in orchestrating the antiviral response represents a burgeoning area of research, especially considering the escalating incidence of viral outbreaks coupled with the increasing prevalence of metabolic diseases. Here, we present a review of current knowledge regarding immunometabolism and the antiviral response during viral infections. Initially, we delve into the concept of immunometabolism by examining its application in the field of cancer-a domain that has long spearheaded inquiries into this fascinating intersection of disciplines. Subsequently, we explore examples of immune cells whose activation is intricately regulated by metabolic processes. Progressing with a systematic and cellular approach, our aim is to unravel the potential role of metabolism in antiviral defense, placing significant emphasis on the innate and canonical interferon response.

Extracellular Vesicles Are Conveyors of the NS1 Toxin during Dengue Virus and Zika Virus Infection.

Extracellular vesicles (EVs), produced during viral infections, are of emerging interest in understanding infectious processes and host-pathogen interactions. EVs and exosomes in particular have the natural ability to transport nucleic acids, proteins, and other components of cellular or viral origin. Thus, they participate in intercellular communication, immune responses, and infectious and pathophysiological processes. Some viruses are known to hijack the cell production and content of EVs for their benefit. Here, we investigate whether two pathogenic flaviviruses i.e., Zika Virus (ZIKV) and Dengue virus (DENV2) could have an impact on the features of EVs. The analysis of EVs produced by infected cells allowed us to identify that the non-structural protein 1 (NS1), described as a viral toxin, is associated with exosomes. This observation could be confirmed under conditions of overexpression of recombinant NS1 from each flavivirus. Using different isolation methods (i.e., exosome isolation kit, size exclusion chromatography, Polyethylene Glycol enrichment, and ELISA capture), we showed that NS1 was present as a dimer at the surface of excreted exosomes, and that this association could occur in the extracellular compartment. This finding could be of major importance in a physiological context. Indeed, this capacity of NS1 to address EVs and its implication in the pathophysiology during Dengue or Zika diseases should be explored. Furthermore, exosomes that have demonstrated a natural capacity to vectorize NS1 could serve as useful tools for vaccine development.

The Antiviral Potential of AdipoRon, an Adiponectin Receptor Agonist, Reveals the Ability of Zika Virus to Deregulate Adiponectin Receptor Expression.

Zika virus (ZIKV) is a pathogenic member of the flavivirus family, with several unique characteristics. Unlike any other arbovirus, ZIKV can be transmitted sexually and maternally, and thus produce congenital syndromes (CZS) due to its neurotropism. This challenges the search for safe active molecules that can protect pregnant women and their fetuses. In this context, and in the absence of any existing treatment, it seemed worthwhile to test whether the known cytoprotective properties of adiponectin and its pharmacological analog, AdipoRon, could influence the outcome of ZIKV infection. We showed that both AdipoRon and adiponectin could significantly reduce the in vitro infection of A549 epithelial cells, a well-known cell model for flavivirus infection studies. This effect was particularly observed when a pre-treatment was carried out. Conversely, ZIKV revealed an ability to downregulate adiponectin receptor expression and thereby limit adiponectin signaling.

The Efficient Antiviral Response of A549 Cells Is Enhanced When Mitochondrial Respiration Is Promoted.

When exposed to a viral infection, the attacked cells promptly set up defense mechanisms. As part of the antiviral responses, the innate immune interferon pathway and associated interferon-stimulated genes notably allow the production of proteins bearing antiviral activity. Numerous viruses are able to evade the interferon response, highlighting the importance of controlling this pathway to ensure their efficient replication. Several viruses are also known to manipulate the metabolism of infected cells to optimize the availability of amino acids, nucleotides, and lipids. They then benefit from a reprogramming of the metabolism that favors glycolysis instead of mitochondrial respiration. Given the increasingly discussed crosstalk between metabolism and innate immunity, we wondered whether this switch from glycolysis to mitochondrial respiration would be beneficial or deleterious for an efficient antiviral response. We used a cell-based model of metabolic reprogramming. Interestingly, we showed that increased mitochondrial respiration was associated with an enhanced interferon response following polyriboinosinic:polyribocytidylic acid (poly:IC) stimulation. This suggests that during viral infection, the metabolic reprogramming towards glycolysis is also part of the virus' strategies to inhibit the antiviral response.

Perivascular Mesenchymal Stem/Stromal Cells, an Immune Privileged Niche for Viruses?

Mesenchymal stem cells (MSCs) play a critical role in response to stress such as infection. They initiate the removal of cell debris, exert major immunoregulatory activities, control pathogens, and lead to a remodeling/scarring phase. Thus, host-derived 'danger' factors released from damaged/infected cells (called alarmins, e.g., HMGB1, ATP, DNA) as well as pathogen-associated molecular patterns (LPS, single strand RNA) can activate MSCs located in the parenchyma and around vessels to upregulate the expression of growth factors and chemoattractant molecules that influence immune cell recruitment and stem cell mobilization. MSC, in an ultimate contribution to tissue repair, may also directly trans- or de-differentiate into specific cellular phenotypes such as osteoblasts, chondrocytes, lipofibroblasts, myofibroblasts, Schwann cells, and they may somehow recapitulate their neural crest embryonic origin. Failure to terminate such repair processes induces pathological scarring, termed fibrosis, or vascular calcification. Interestingly, many viruses and particularly those associated to chronic infection and inflammation may hijack and polarize MSC's immune regulatory activities. Several reports argue that MSC may constitute immune privileged sanctuaries for viruses and contributing to long-lasting effects posing infectious challenges, such as viruses rebounding in immunocompromised patients or following regenerative medicine therapies using MSC. We will herein review the capacity of several viruses not only to infect but also to polarize directly or indirectly the functions of MSC (immunoregulation, differentiation potential, and tissue repair) in clinical settings.

Evidence of RedOX Imbalance during Zika Virus Infection Promoting the Formation of Disulfide-Bond-Dependent Oligomers of the Envelope Protein.

Flaviviruses replicate in membrane factories associated with the endoplasmic reticulum (ER). Significant levels of flavivirus viral protein accumulation contribute to ER stress. As a consequence, the host cell exhibits an Unfolded Protein Response (UPR), subsequently stimulating appropriate cellular responses such as adaptation, autophagy or apoptosis. The correct redox conditions of this compartment are essential to forming native disulfide bonds in proteins. Zika virus (ZIKV) has the ability to induce persistent ER stress leading to the activation of UPR pathways. In this study, we wondered whether ZIKV affects the redox balance and consequently the oxidative protein folding in the ER. We found that ZIKV replication influences the redox state, leading to the aggregation of the viral envelope protein as amyloid-like structures in the infected cells.

Apoptosis during ZIKA Virus Infection: Too Soon or Too Late?

Cell death by apoptosis is a major cellular response in the control of tissue homeostasis and as a defense mechanism in the case of cellular aggression such as an infection. Cell self-destruction is part of antiviral responses, aimed at limiting the spread of a virus. Although it may contribute to the deleterious effects in infectious pathology, apoptosis remains a key mechanism for viral clearance and the resolution of infection. The control mechanisms of cell death processes by viruses have been extensively studied. Apoptosis can be triggered by different viral determinants through different pathways as a result of virally induced cell stresses and innate immune responses. Zika virus (ZIKV) induces Zika disease in humans, which has caused severe neurological forms, birth defects, and microcephaly in newborns during the last epidemics. ZIKV also surprised by revealing an ability to persist in the genital tract and in semen, thus being sexually transmitted. Mechanisms of diverting antiviral responses such as the interferon response, the role of cytopathic effects and apoptosis in the etiology of the disease have been widely studied and debated. In this review, we examined the interplay between ZIKV infection of different cell types and apoptosis and how the virus deals with this cellular response. We illustrate a duality in the effects of ZIKV-controlled apoptosis, depending on whether it occurs too early or too late, respectively, in neuropathogenesis, or in long-term viral persistence. We further discuss a prospective role for apoptosis in ZIKV-related therapies, and the use of ZIKV as an oncolytic agent.

Viral Toxin NS1 Implication in Dengue Pathogenesis Making It a Pivotal Target in Development of Efficient Vaccine.

The mosquito-borne viral disease dengue is a global public health problem causing a wide spectrum of clinical manifestations ranging from mild dengue fever to severe dengue with plasma leakage and bleeding which are often fatal. To date, there are no specific medications to treat dengue and prevent the risk of hemorrhage. Dengue is caused by one of four genetically related but antigenically distinct serotypes DENV-1-DENV-4. The growing burden of the four DENV serotypes has intensified both basic and applied research to better understand dengue physiopathology. Research has shown that the secreted soluble hexameric form of DENV nonstructural protein-1 (sNS1) plays a significant role in the pathogenesis of severe dengue. Here, we provide an overview of the current knowledge about the role of sNS1 in the immunopathogenesis of dengue disease. We discuss the potential use of sNS1 in future vaccine development and its potential to improve dengue vaccine efficiency, particularly against severe dengue illness.

Robust and low-cost ELISA based on IgG-Fc tagged recombinant proteins to screen for anti-SARS-CoV-2 antibodies.

The development of new diagnostic assays become a priority for managing COVID-19. To this aim, we presented here an in-house ELISA based on the production of two major recombinant and high-quality antigens from SARS-CoV-2. Full-length N and S-RBD fragment proteins fused to mouse IgG2a-Fc were produced in the CHO cell line. Secreted recombinant proteins were easily purified with standard Protein A chromatography and were used in an in-house ELISA to detect anti-N and anti-RBD IgGs in the plasma of COVID-19 RTPCR-positive patients. High reactivity against recombinant antigens was readily detected in all positive plasma samples, whereas no recognition was observed with control healthy subject's plasmas. Remarkably, unpurified recombinant N protein obtained from cell culture supernatant was also suitable for the monitoring by ELISA of IgG levels in positive patients. This work provides an early prospection for low price but high-quality serological kit development.

Zika E Glycan Loop Region and Guillain-Barré Syndrome-Related Proteins: A Possible Molecular Mimicry to Be Taken in Account for Vaccine Development.

The neurological complications of infection by the mosquito-borne Zika virus (ZIKV) include Guillain-Barré syndrome (GBS), an acute inflammatory demyelinating polyneuritis. GBS was first associated with recent ZIKV epidemics caused by the emergence of the ZIKV Asian lineage in South Pacific. Here, we hypothesize that ZIKV-associated GBS relates to a molecular mimicry between viral envelope E (E) protein and neural proteins involved in GBS. The analysis of the ZIKV epidemic strains showed that the glycan loop (GL) region of the E protein includes an IVNDT motif which is conserved in voltage-dependent L-type calcium channel subunit alpha-1C (Cav1.2) and Heat Shock 70 kDa protein 12A (HSP70 12A). Both VSCC-alpha 1C and HSP70 12A belong to protein families which have been associated with neurological autoimmune diseases in central nervous system. The purpose of our in silico analysis is to point out that IVNDT motif of ZIKV E-GL region should be taken in consideration for the development of safe and effective anti-Zika vaccines by precluding the possibility of adverse neurologic events including autoimmune diseases such as GBS through a potent mimicry with Heat Shock 70 kDa protein 12A (HSP70 12A).

CHOP Pro-Apoptotic Transcriptional Program in Response to ER Stress Is Hacked by Zika Virus.

Zika virus (ZIKV) is an emerging mosquito-borne flavivirus considered as a threat to human health due to large epidemics and serious clinical outcomes such as microcephaly in new-borns. Like all flaviviruses, ZIKV relies on the cellular machinery to complete its viral cycle, with the endoplasmic reticulum (ER) being the critical site of viral replication factories. The sudden high protein load in the ER induces an ER stress to which the cell responds with an appropriate unfolded protein response (UPR) in an attempt to restore its disturbed homeostasis. When the restoration fails, the cell signalling leads to a programmed cell death by apoptosis with the upregulation of the UPR-induced C/EBP homologous protein (CHOP) which acts as the main trigger for this fatal outcome. Our previous studies have shown the ability of ZIKV to manipulate various cellular responses in order to optimize virus production. ZIKV is able to delay apoptosis to its benefit and although ER stress is induced, the UPR is not complete. Here we discovered that ZIKV impairs the expression of CHOP/DDIT3, the main factor responsible of ER-stress driven apoptosis. Surprisingly, the mechanism does not take place at the transcriptional level but at the translational level.

Serological Surveillance of COVID-19 Hospitalized Patients in Réunion Island (France) Revealed that Specific Immunoglobulin G Are Rapidly Vanishing in Severe Cases.

Humoral immunity is critically important to control COVID-19. Long-term antibody responses remain to be fully characterized in hospitalized patients who have a high risk of death. We compared specific Immunoglobulin responses against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) between two groups, intensive care unit (ICU) and non-ICU hospitalized patients over several weeks. Plasma specific IgG, IgM, and IgA levels were assessed using a commercial ELISA and compared to an in-house cell-based ELISA. Among the patients analyzed (mean (SD) of age, 64.4 (15.9) years, 19.2% female), 12 (46.2%) were hospitalized in ICU. IgG levels increased in non-ICU cases from the second to the eighth week after symptom onset. By contrast, IgG response was blunted in ICU patients over the same period. ICU patients with hematological malignancies had very weak or even undetectable IgG levels. While both groups had comparable levels of specific IgM antibodies, we found much lower levels of specific IgA in ICU versus non-ICU patients. In conclusion, COVID-19 ICU patients may be at risk of reinfection as their specific IgG response is declining in a matter of weeks. Antibody neutralizing assays and studies on specific cellular immunity will have to be performed.

Emerging Roles of Perivascular Mesenchymal Stem Cells in Synovial Joint Inflammation.

In contrast to the significant advances in our understanding of the mesenchymal stem cell (MSC) populations in bone marrow (BM), little is known about the MSCs that are resident in the synovial joint and their possible roles in the tissue homeostasis, chronic inflammation as well as in repair. Neural crest is a transient embryonic structure, generating multipotential MSC capable of migrating along peripheral nerves and blood vessels to colonize most tissue types. In adult, these MSC can provide functional stromal support as a stem cell niche for lymphocyte progenitors for instance in the BM and the thymus. Critically, MSC have major immunoregulatory activities to control adverse inflammation and infection. These MSC will remain associated to vessels (perivascular (p) MSC) and their unique expression of markers such as myelin P0 and transcription factors (e.g. Gli1 and FoxD1) has been instrumental to develop transgenic mice to trace the fate of these cells in health and disease conditions. Intriguingly, recent investigations of chronic inflammatory diseases argue for an emerging role of pMSC in several pathological processes. In response to tissue injuries and with the release of host cell debris (e.g. alarmins), pMSC can detach from vessels and proliferate to give rise to either lipofibroblasts, osteoblasts involved in the ossification of arteries and myofibroblasts contributing to fibrosis. This review will discuss currently available data that suggest a role of pMSC in tissue homeostasis and pathogenesis of the synovial tissue and joints. Graphical abstract.

Deciphering SARS-CoV-2 Virologic and Immunologic Features.

Severe acute respiratory syndrome coronavirus (SARS-CoV)-2 and its associated pathology, COVID-19, have been of particular concerns these last months due to the worldwide burden they represent. The number of cases requiring intensive care being the critical point in this epidemic, a better understanding of the pathophysiology leading to these severe cases is urgently needed. Tissue lesions can be caused by the pathogen or can be driven by an overwhelmed immune response. Focusing on SARS-CoV-2, we and others have observed that this virus can trigger indeed an immune response that can be dysregulated in severe patients and leading to further injury to multiple organs. The purpose of the review is to bring to light the current knowledge about SARS-CoV-2 virologic and immunologic features. Thus, we address virus biology, life cycle, tropism for many organs and how ultimately it will affect several host biological and physiological functions, notably the immune response. Given that therapeutic avenues are now highly warranted, we also discuss the immunotherapies available to manage the infection and the clinical outcomes.