Plenary speakers

VECTOR-BORNE VIRUSES: EMERGING THREATS AND GLOBAL CHALLENGES

Luisa Barzon, Department of Molecular Medicine, University of Padova, Padova, Italy

In the ever-evolving landscape of infectious diseases, the spread of arboviruses poses a significant challenge, particularly in European countires. Over the last decades, endemic arboviruses in Europe have expanded their geographical range, triggering a surge in human outbreaks. Notable among these is West Nile virus, exhibiting increased circulation in central and southern Europe where it had caused several large outbreaks of neuroinvasive disease in humans, Crimean-Congo hemorrhagic fever virus, which has recently emerged in Spain and France, tick-borne encephalitis virus, a significant cause of viral encepahlitis in Europe, which is also increasing in geographical range and encroaching upon higher altitudes due to climate warming. Moreover, the rise in global travel and trade intensifies the risk of introducing exotic arthropod vectors and arboviruses such as dengue and chikungunya viruses to Europe. This globalization of disease transmission underscores the urgent need for integrated One Health arbovirus surveillance programs to facilitate prompt identification of emerging outbreaks and implementation of control measures. However, detecting these outbreaks presents significant challenges, necessitating multidisciplinary approaches, heightened awareness and laboratory capacity, especially for neglected pathogens.

Cellular communication within a virus microenvironment

Dr. Ileana M. Cristea, Henry L. Hillman professor of Molecular Biology, Princeton University

Viral infections spread within complex and dynamic cellular microenvironments that shape the outcome of infection. As such, intra-cellular communication cascades, as well as communication between infected cells and cells in the surrounding tissue create a virus microenvironment. Here, we will describe some of our efforts to characterize communication at the intra- and inter-cellular levels. At the intra-cellular level, we will consider spatiotemporal alterations in organelle-organelle contacts that facilitate the rapid regulation of cellular metabolism and immune responses during infections with several DNA and RNA viruses. Upon infection with human cytomegalovirus (HCMV), we investigate the paradox of infection-induced mitochondria fragmentation concurrent with increased respiration. We integrated live, super-resolution microscopy, cryotomography, and molecular assays to show how HCMV infection selectively fragments mitochondria and circumvents host autophagy to promote increased mitochondrial bioenergetics. At the inter-cellular level, we describe our establishment of a cell-based system to characterize a virus microenvironment, distinguishing infected, proximal, and distal cells using differential fluorescent labeling. Fluorescence-activated cell sorting, microscopy, proteomics, virology, and cell cycle assays allow resolving cellular features and deciphering the functional consequences of proximity to the initial site of infection. We show that human cytomegalovirus (HCMV) infection primes proximal cells for secondary infection, as well as for infection with other viruses, such as herpes simplex virus 1 and influenza A. Characterization of involved mechanisms points to the contribution of alterations in cell cycle, organelle-organelle contacts, and mitochondrial functions in the increased susceptibility of uninfected, proximal cells to viral infections. Overall, these findings demonstrate how infection reshapes the surrounding microenvironment through intra- and inter-cellular signaling to facilitate viral spread and how spatial proximity to an infection guides cell fate.

Emerging viruses - when public health, diagnostics and translational research meets

Isabella Eckerle
Geneva Centre for Emerging Viral Diseases, University Hospitals of Geneva and University of Geneva, Switzerland

In the recent decades, a steep increase in the emergence of novel viruses was observed, with most of those spilling over from animal reservoirs. SARS-CoV, MERS-CoV, Zika virus, Ebola- and Marburg virus, SARS-CoV-2 and Mpox are just some examples of the recent decades. In addition, the Covid-19 pandemic has drastically highlighted gaps in pandemic response on national and global scale but also the detrimental effects of a pandemic on society.

In this talk, I want to give an overview on the work of our Centre of the recent years, that ranges from public health services to the development and validation of diagnostics to translational work on SARS-CoV-2 and other respiratory and emerging viruses. In addition, to perform an in vitro risk assessment of novel viruses, sophisticated cell culture models and clinical translational studies can help to explore the immuno-virological aspects of infection and vaccination. As climate change, biodiversity loss and other anthropogenic changes will most likely further increase the risk for new spillovers, there is a need for the development of better diagnostics and risk assessment tools for public health decision to rapidly respond to a new emerging infectious thread.

The Road Ahead: Metagenomics in Infectious Disease Diagnostics

Nicole Fischer

Metagenomic sequencing (mNGS) for the detection of pathogens in clinical samples has made its way into diagnostic applications as a method to identify pathogens in suspected infections due to decreasing costs and improving time-to-result. mNGS is one of several applications of high-throughput sequencing in diagnostics with mNGS as an unbiased approach to analyze the total nucleic acid content of patient samples for the detection and characterization of microbial DNA and/or RNA. This unbiased approach has the potential to identify more putative pathogens than any single conventional test, but poses significant challenges for interpretation and the involvement of microbiologists and virologists in the case history. Overall, this development is positive as it may lead to improved diagnostic options for patients, but there are new challenges in terms of implementation, evaluation and operational value.

It takes two to tango: protein interactions governing chronic and emerging virus infection

Lisa Lasswitz¹, Mara Duven¹, Eve Brown¹, Cora Stegmann¹, Belén Carriqui Madronal¹, Karsten Cirksena¹, Ju Eun Yoo¹, Miriam Becker¹, Anja de Bruin¹, Nele Villabruna¹, Tessy Hick^2,3, Gisa Gerold^1,2,3
1 Department of Biochemistry & Research Center for Emerging Infections and Zoonoses (RIZ), University of Veterinary Medicine Hannover, Hannover, Germany.
² Department of Clinical Microbiology, Umeå University, Sweden.
³ Wallenberg Centre for Molecular Medicine (WCMM), Umeå University, Sweden.

Virus emergence poses an increasing challenge to human health. Among the strategies for pandemic preparedness, the development of broadly acting antivirals assumes a central role. To devise such pan-virus strategies, it is imperative to uncover the molecular commonalities of viruses and their interactions with host cells. Here, we identify protein networks of plasma membrane proteins of the tetraspanin, scavenger receptor, and matrix metalloproteinase families to play critical roles in the infectious life cycle of hepaciviruses, coronaviruses, and mosquito-borne alphaviruses. For the latter, we observe human tissue-specific usage of protein family members. While CD81 is a critical replication factor for Chikungunya virus in hepatocytes and dermal fibroblasts, which play a role early after transmission, CD63 and CD9 support virus replication in synovial fibroblasts, which are important for pathophysiology. Viruses of the same genus that target the central nervous system, on the other hand, use the C8 tetraspanin Tspan10 to complete their life cycle. In contrast to the observed tissue specificity in tetraspanin use, we find that all tested viruses use matrix metalloproteinases as host factors independent of the infected cell type. Consequently, broad-spectrum metalloproteinase inhibitors efficiently block hepacivirus and alphavirus infection in cells of different tissue origins. Identification of central protein network hubs used by different virus families holds the promise of successful development of pandemic preparedness strategies.

Naturally skilled?! Natural killer cells and their adaptive instruction by virus

Hartmut Hengel
Albert-Ludwigs-University Freiburg, Institute of Virology, Hermann-Herder-Str. 11, D-79104 Freiburg, Germany

Natural killer (NK) cells represent a major subset of innate lymphocytes employed by the immune system that are designed for recognizing pathogenic cells. These include virus-infected cells, (virus-induced) tumor cells and target cells opsonized by antibodies. NK cells express a bewildering array of surface receptors, which generate stimulatory or inhibitory signals eventually unleashing immune effector responses. Initially, NK cells were characterized for their ability to recognize and rapidly kill harmful cells lacking major histocompatibility complex class I molecules (‘missing self’) resulting from virus infection or malignant transformation. Over the last years, the view on NK cells has broadened considerably by observations made in mice, humans and rhesus monkeys during infection with cytomegalovirus (CMV). The generation and expansion of ‘memory-like’ or ‘adaptive’ NK cells exclusively induced in CMV-infected individuals is driven by activating NK receptors (e.g. NKG2C/CD94, FcγRIIIA/CD16) in conjunction with epigenetic regulation, but at the same time counter-balanced by CMV-encoded inhibitors such as Fcγ-binding glycoproteins. While NK cells possess a multitude of features that could make them attractive cellular therapeutics, deeper insight into the intricate balance between viral manipulation and NK cell signals is vital to understand the ability of adaptive NK cells to ‘remember’.

Development of broadly protective influenza virus vaccines

Florian Krammer
Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, USA and
Ignaz Semmelweis Institute, Interuniversity Institute for Infection Research, Medical University of Vienna, Vienna, Austria

Seasonal influenza virus infections cause significant morbidity and mortality every year. In addition, influenza virus pandemics occur in irregular intervals and can claim millions of lives. Influenza virus vaccines are in use but have to be reformulated every year to be well matched to circulating viruses which is challenging due to constant antigenic drift. Antigenic drift is mostly mediated by changes in the immunodominant globular head domain of the viral hemagglutinin, which is the major influenza virus surface glycoprotein. We have developed vaccine strategies to target conserved parts of the virus, including the immunosubdominant stalk domain of the hemagglutinin and the viral neuraminidase, to induce broadly protective immunity to seasonal drifted, zoonotic and emerging pandemic influenza viruses.

Imnune control of human oncogenic γ-herpesviruses

Christian Münz
Viral Immunobiology, Institute of Experimental Immunology, University of Zürich, Switzerland, e-mail: christian.muenz@uzh.ch

The two human γ-herpesviruses Epstein Barr virus (EBV) and Kaposi sarcoma associated herpesvirus (KSHV) are WHO class I carcinogens and each of them is associated with 1-2% of human tumors. Fortunately, only a small subset of persistently infected virus carriers develops these malignancies. Therefore, it is important to understand how life-long protective immune control develops and protects the majority of EBV and KSHV positive individuals and how we might re-establish the respective immune responses in patients that suffer from γ-herpesvirus associated diseases.

For this purpose, we have established a small animal model with reconstituted human immune system components (humanized mice) that allows to investigate EBV and KSHV infection, associated lymphomagenesis, and protective cell-mediated immune responses. For EBV infection we have identified molecular requirements for T and natural killer (NK) cell responses to control viral titers and prevent diffuse large B cell lymphoma (DLBCL)-like malignancies.
 

KSHV persists in humanized mice and in vitro cultures of human B cells only during co-infection with EBV. It compromises NK cell mediated immune control of EBV but allows for the development of protective EBV and KSHV specific T cell responses. We have started to explore the specificities of KSHV specific CD8⁺ T cells for their protection against primary effusion lymphoma (PEL)-like tumors that we observe during co-infection with both viruses, in order to identify promising vaccine antigens.

Vaccines at last for RSV- what effect will they have?

Prof Peter JM Openshaw, Imperial College London

Respiratory syncytial virus (RSV) is well known to cause a surge in paediatric admissions each winter that fills hospital wards, putting great stress on healthcare and on families. What is less easy to define is the impact that RSV has on older adults, in whom it causes a more insidious disease which may or may not be recognised as being triggered by RSV.

The recent breakthrough in vaccine design that resulted from the recognition that viral antigen needs to be stabilised in a contracted pre-fusion form (rather than the extended post-fusion configuration) has now led to licencing of highly effective vaccines for RSV disease prevention in older adults. In the first season of use in the USA, many older adults have now been vaccinated, which will provide real-world data on the impact of these new vaccines.

In infants, there is a newly available long half-life antibody in widespread use in some parts of Spain, France and Luxembourg. Preliminary data from these settings show remarkable protection of babies against RSV disease and reduced healthcare burden.

We are now entering an era of RSV prevention in both children and adults, the impact of which will be discussed.

BoDV-1 Encephalitis: Past and Future

Borna disease virus 1 (BoDV-1) is known to cause a non-purulent, usually fatal encephalitis in horses, sheep, alpacas, and other domestic and wild animals. Since 2018, several groups have provided unequivocal evidence that humans are affected by an immunopathology similar to that of domestic mammals. Since then, around 50 cases of BoDV-1 encephalitis have been reported, which exceeds the number of deaths from rabies virus infections in Germany. Since March 2020, bornavirus encephalitis is a notifiable disease in Germany.

While domestic mammals and humans act as dead-end “spill-over” hosts for the virus, the bicoloured white-toothed shrew (Crocidura leucodon) is known to be the natural reservoir host. Surveys throughout the known endemic area, which is restricted to parts of Germany, Austria, Switzerland and Liechtenstein, have revealed infection rates of approximately 10-30% in local reservoir populations. The apparently healthy shrews shed BoDV-1 through skin, urine, faeces and saliva. Initial tenacity studies suggest that the virus remains infectious for at least a few days in a dried state.

Phylogenetic studies suggest that human BoDV-1 infections are due to single, independent spill-over events from the local reservoir, with the notable exception of iatrogenic BoDV-1 transmission from an unnoticedly infected solid organ transplant donor to three recipients. However, the precise route of natural transmission remains elusive. Several large seroepidemiological studies have shown very low seroprevalence even in highly endemic areas such as Bavaria. In a case-control study, living in a rural environment in a stand-alone location or on the edge of a settlement was identified as a significant risk factor for BoDV-1 infection.

After an incubation period of several weeks to a few months, signs of encephalitis such as aphasia, paresis, altered consciousness and seizures occur, leading to coma and death. In some cases, antiviral treatment with favipiravir and ribavirin in combination with immunosuppression has had a temporary beneficial effect on the disease. Diagnostics is not straightforward because the concentration of viral RNA in cerebrospinal fluid is usually very low or absent. Seroconversion, as determined by indirect immunofluorescence, immunoblotting, and ELISA, often occurs late in the course of disease, and cellular immune responses determined by the ELISPOT technique can be affected by immunosuppressive therapies.

Future work will focus on understanding the natural habitat and behaviour of shrews and the routes of transmission of the virus to humans. The aim should be to develop more targeted preventive and therapeutic measures, including the possibility of vaccination.

Impact of structural dynamics on flavivirus-antibody interactions

Flaviviruses include a number of mosquito- and tick-borne human pathogens of global public health importance. High-resolution structures of their structural proteins and virions, alone or in complex with antibodies, have provided insights into virus maturation and cell entry as well as interactions with antibodies. In addition to large-scale conformational changes of viral envelope proteins during the viral life cycle, there is increasing evidence that smaller-scale protein dynamics (referred to as virus “breathing”) provide additional flexibility for fine-tuning of interactions of flaviviruses with the immune system and host cell factors. In this talk, I will focus on how breathing affects flavivirus antigenic structure, with the potential to transiently expose otherwise inaccessible epitopes, which has consequences for virus neutralization and infection enhancement as well as implications for vaccine design and evaluation.

Broadly neutralizing HIV-1antibodies: Lone superstars or team players?

Broadly neutralizing antibodies (bnAbs) are considered a critical component of a preventative HIV vaccine. Despite continued progress in HIV-1 vaccine development, a recapitulation of bnAb responses observed in natural infection has not been achieved. While current vaccine approaches aim to create immunogens that induce bnAbs with a distinct specificity, there is increasing evidence that in natural infection multiple bnAb lineages with different specificities can develop.  In this lecture I will discuss recent findings from our group on the frequency of multi-specific bnAb activity and their relevance for future HIV vaccines.

Tunneling naontubes (TNTs), reshaping connectivity and spreading of viral infections

 Chiara Zurzolo, MD, PhD, Institut Pasteur, Paris France

Tunneling nanotubes (TNTs) are actin-based cellular connections that allow the transport of different cellular components between cells. Under homeostatic conditions, TNTs transport different vesicular cargoes and entire organelles like mitochondria and lysosomes. However, they can be hijacked by different pathogens and amyloid proteins involved in neurodegenerative diseases (NDs), such as Parkinson´s (PD) Alzheimer’s (AD). We have previously demonstrated that both alpha-synuclein and Tau aggregates, respectively the hallmark of PD and AD, can be spread from one cell to another via TNTs.  Overall, our data indicate that TNTs are more common in developing conditions. Our hypothesis is that in the brain TNTs precede synaptic connections and may be important for the establishment of mature neuronal networks while in the adult tissue they are induced by stressful and inflammatory stimuli like in NDs and infections. Specifically, in the case of severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) infection, neurological manifestations represent a major issue in long coronavirus disease. How SARS-CoV-2 gains access to the brain and how infection leads to neurological symptoms are not clear because the principal means of viral entry by endocytosis, the angiotensin-converting enzyme 2 receptor, are barely detectable in the brain. We report that SARS-CoV-2 induces the formation of tunneling nanotubes (TNTs) and exploits this route to spread to uninfected cells. In cellulo correlative fluorescence and cryo-electron tomography reveal that SARS-CoV-2 is also associated with TNTs between permissive cells. These data highlight a previously unknown mechanism of SARS-CoV-2 spreading, likely used as a route to invade nonpermissive cells and potentiate infection in permissive cells, and possibly promote immune evasion.