Pandemic 1918 Influenza Virus Does Not Cause Lethal Infection in Rhesus or Cynomolgus Macaques.

The 1918 H1N1 influenza pandemic was among the most severe in history, taking the lives of approximately 50 million people worldwide, and novel prophylactic vaccines are urgently needed to prevent another pandemic. Given that macaques are physiologically relevant preclinical models of human immunology that have advanced the clinical treatment of infectious diseases, a lethal pandemic influenza challenge model would provide a stringent platform for testing new influenza vaccine concepts. To this end, we infected rhesus macaques and Mauritian cynomolgus macaques with highly pathogenic 1918 H1N1 influenza virus and assessed pathogenesis and disease severity. Despite infection with a high dose of 1918 influenza delivered via multiple routes, rhesus macaques demonstrated minimal signs of disease, with only intermittent viral shedding. Cynomolgus macaques infected via intrabronchial instillation demonstrated mild symptoms, with disease severity depending on the infection dose. Cynomolgus macaques infected with a high dose of 1918 influenza delivered via multiple routes experienced moderate disease characterized by consistent viral shedding, pulmonary infiltrates, and elevated inflammatory cytokine levels. However, 1918 influenza was uniformly nonlethal in these two species, demonstrating that this isolate is insufficiently pathogenic in rhesus and Mauritian cynomolgus macaques to support testing novel prophylactic influenza approaches where protection from severe disease combined with a lethal outcome is desired as a highly stringent indication of vaccine efficacy. IMPORTANCE The world remains at risk of an influenza pandemic, and the development of new therapeutic and preventative modalities is critically important for minimizing human death and suffering during the next influenza pandemic. Animal models are central to the development of new therapies and vaccine approaches. In particular, nonhuman primates like rhesus and cynomolgus macaques are highly relevant preclinical models given their physiological and immunological similarities to humans. Unfortunately, there remains a scarcity of macaque models of pandemic influenza with which to test novel antiviral modalities. Here, we demonstrate that even at the highest doses tested, 1918 influenza was not lethal in these two macaque species, suggesting that they are not ideal for the development and testing of novel pandemic influenza-specific vaccines and therapies. Therefore, other physiologically relevant nonhuman primate models of pandemic influenza are needed.

Differential pathogenesis of closely related 2018 Nigerian outbreak clade III Lassa virus isolates.

Nigeria continues to experience ever increasing annual outbreaks of Lassa fever (LF). The World Health Organization has recently declared Lassa virus (LASV) as a priority pathogen for accelerated research leading to a renewed international effort to develop relevant animal models of disease and effective countermeasures to reduce LF morbidity and mortality in endemic West African countries. A limiting factor in evaluating medical countermeasures against LF is a lack of well characterized animal models outside of those based on infection with LASV strain Josiah originating form Sierra Leone, circa 1976. Here we genetically characterize five recent LASV isolates collected from the 2018 outbreak in Nigeria. Three isolates were further evaluated in vivo and despite being closely related and from the same spatial / geographic region of Nigeria, only one of the three isolates proved lethal in strain 13 guinea pigs and non-human primates (NHP). Additionally, this isolate exhibited atypical pathogenesis characteristics in the NHP model, most notably respiratory failure, not commonly described in hemorrhagic cases of LF. These results suggest that there is considerable phenotypic heterogeneity in LASV infections in Nigeria, which leads to a multitude of pathogenesis characteristics that could account for differences between subclinical and lethal LF infections. Most importantly, the development of disease models using currently circulating LASV strains in West Africa are critical for the evaluation of potential vaccines and medical countermeasures.

Differential pathogenesis between Andes virus strains CHI-7913 and Chile-9717869in Syrian Hamsters.

Hantavirus cardiopulmonary syndrome (HCPS) is a severe respiratory disease caused by orthohantaviruses in the Americas with a fatality rate as high as 35%. In South America, Andes orthohantavirus (Hantaviridae, Orthohantavirus, ANDV) is a major cause of HCPS, particularly in Chile and Argentina, where thousands of cases have been reported since the virus was discovered. Two strains of ANDV that are classically used for experimental studies of the virus are Chile-9717869, isolated from the natural reservoir, the long-tailed pygmy rice rat, and CHI-7913, an isolate from a lethal human case of HCPS. An important animal model for studying pathogenesis of HCPS is the lethal Syrian golden hamster model of ANDV infection. In this model, ANDV strain Chile-9717869 is uniformly lethal and has been used extensively for pathogenesis, vaccination, and therapeutic studies. Here we show that the CHI-7913 strain, despite having high sequence similarity with Chile-9717869, does not cause lethal disease in Syrian hamsters. CHI-7913, while being able to infect hamsters and replicate to moderate levels, showed a reduced ability to replicate within the tissues compared with Chile-9717869. Hamsters infected with CHI-7913 had reduced expression of cytokines IL-4, IL-6, and IFN-γ compared with Chile-9717869 infected animals, suggesting potentially limited immune-mediated pathology. These results demonstrate that certain ANDV strains may not be lethal in the classical Syrian hamster model of infection, and further exploration into the differences between lethal and non-lethal strains provide important insights into molecular determinants of pathogenic hantavirus infection.Importance:Andes orthohantavirus (ANDV) is a New World hantavirus that is a major cause of hantavirus cardiopulmonary syndrome (HCPS, also referred to as hantavirus pulmonary syndrome) in South America, particularly in Chile and Argentina. ANDV is one of the few hantaviruses for which there is a reliable animal model, the Syrian hamster model, which recapitulates important aspects of human disease. Here we infected hamsters with a human isolate of ANDV, CHI-7913, to assess its pathogenicity compared with the classical lethal Chile-9717869 strain. CHI-7913 had 22 amino acid differences compared with Chile-9717869, did not cause lethal disease in hamsters, and showed reduced ability to replicate in vivo Our data indicate potentially important molecular signatures for pathogenesis of ANDV infection in hamsters and may lead to insights into what drives pathogenesis of certain hantaviruses in humans.

Zika-Induced Male Infertility in Mice Is Potentially Reversible and Preventable by Deoxyribonucleic Acid Immunization.

Background: Zika virus (ZIKV) infection has been associated with prolonged viral excretion in human semen and causes testicular atrophy and infertility in 10-week-old immunodeficient mice. Methods: Male IFNAR-/- mice, knockout for type I interferon receptor, were immunized with GLS-5700, a deoxyribonucleic acid-based vaccine, before a subcutaneous ZIKV challenge with 6 × 105 plaque-forming units at 13 weeks of age. On day 28 postinfection, testes and epididymides were collected in some mice for histological and functional analyses, whereas others were mated with naive female wild-type C57BL/6J. Results: Although all mice challenged with ZIKV developed viremia, most of them were asymptomatic, showed no weight loss, and survived infection. On day 28 postinfection, none of the unvaccinated, infected mice (9 of 9) exhibited abnormal spermatozoa counts or motility. However, 33% (3 of 9) and 36% (4 of 11) of mated males from this group were infertile, from 2 independent studies. Contrarily, males from the noninfected and the vaccinated, infected groups were all fertile. On days 75 and 207 postinfection, partial recovery of fertility was observed in 66% (2 of 3) of the previously infertile males. Conclusions: This study reports the effects of ZIKV infection on male fertility in a sublethal, immunodeficient mouse model and the efficacy of GLS-5700 vaccination in preventing male infertility.

The Makona Variant of Ebola Virus Is Highly Lethal to Immunocompromised Mice and Immunocompetent Ferrets.

During 2013-2016, a novel isolate of Ebola virus (EBOV-Makona) caused an epidemic in West Africa. The virus was distinct from known EBOV strains (EBOV-Kikwit and EBOV-Mayinga), which were responsible for previous outbreaks in Central Africa. To investigate the pathogenicity of EBOV-Makona, we engineered and rescued an early isolate (H.sapiens-wt/GIN/2014/Makona-Gueckedou-C07, called rgEBOV-C07) using an updated reverse-genetics system. rgEBOV-C07 was found to be highly pathogenic in both the knockout mouse and ferret models, with median lethal dose values of 0.078 and 0.015 plaque-forming units, respectively. Therefore, these animals are appropriate for screening potential countermeasures against EBOV-Makona without the need for species adaptation.

Viral inhibition of the transporter associated with antigen processing (TAP): a striking example of functional convergent evolution.

Herpesviruses are large DNA viruses that are highly abundant within their host populations. Even in the presence of a healthy immune system, these viruses manage to cause lifelong infections. This persistence is partially mediated by the virus entering latency, a phase of infection characterized by limited viral protein expression. Moreover, herpesviruses have devoted a significant part of their coding capacity to immune evasion strategies. It is believed that the close coexistence of herpesviruses and their hosts has resulted in the evolution of viral proteins that specifically attack multiple arms of the host immune system. Cytotoxic T lymphocytes (CTLs) play an important role in antiviral immunity. CTLs recognize their target through viral peptides presented in the context of MHC molecules at the cell surface. Every herpesvirus studied to date encodes multiple immune evasion molecules that effectively interfere with specific steps of the MHC class I antigen presentation pathway. The transporter associated with antigen processing (TAP) plays a key role in the loading of viral peptides onto MHC class I molecules. This is reflected by the numerous ways herpesviruses have developed to block TAP function. In this review, we describe the characteristics and mechanisms of action of all known virus-encoded TAP inhibitors. Orthologs of these proteins encoded by related viruses are identified, and the conservation of TAP inhibition is discussed. A phylogenetic analysis of members of the family Herpesviridae is included to study the origin of these molecules. In addition, we discuss the characteristics of the first TAP inhibitor identified outside the herpesvirus family, namely, in cowpox virus. The strategies of TAP inhibition employed by viruses are very distinct and are likely to have been acquired independently during evolution. These findings and the recent discovery of a non-herpesvirus TAP inhibitor represent a striking example of functional convergent evolution.

Epstein-Barr virus large tegument protein BPLF1 contributes to innate immune evasion through interference with toll-like receptor signaling.

Viral infection triggers an early host response through activation of pattern recognition receptors, including Toll-like receptors (TLR). TLR signaling cascades induce production of type I interferons and proinflammatory cytokines involved in establishing an anti-viral state as well as in orchestrating ensuing adaptive immunity. To allow infection, replication, and persistence, (herpes)viruses employ ingenious strategies to evade host immunity. The human gamma-herpesvirus Epstein-Barr virus (EBV) is a large, enveloped DNA virus persistently carried by more than 90% of adults worldwide. It is the causative agent of infectious mononucleosis and is associated with several malignant tumors. EBV activates TLRs, including TLR2, TLR3, and TLR9. Interestingly, both the expression of and signaling by TLRs is attenuated during productive EBV infection. Ubiquitination plays an important role in regulating TLR signaling and is controlled by ubiquitin ligases and deubiquitinases (DUBs). The EBV genome encodes three proteins reported to exert in vitro deubiquitinase activity. Using active site-directed probes, we show that one of these putative DUBs, the conserved herpesvirus large tegument protein BPLF1, acts as a functional DUB in EBV-producing B cells. The BPLF1 enzyme is expressed during the late phase of lytic EBV infection and is incorporated into viral particles. The N-terminal part of the large BPLF1 protein contains the catalytic site for DUB activity and suppresses TLR-mediated activation of NF-κB at, or downstream of, the TRAF6 signaling intermediate. A catalytically inactive mutant of this EBV protein did not reduce NF-κB activation, indicating that DUB activity is essential for attenuating TLR signal transduction. Our combined results show that EBV employs deubiquitination of signaling intermediates in the TLR cascade as a mechanism to counteract innate anti-viral immunity of infected hosts.

EBV BILF1 evolved to downregulate cell surface display of a wide range of HLA class I molecules through their cytoplasmic tail.

Coevolution of herpesviruses and their hosts has driven the development of both host antiviral mechanisms to detect and eliminate infected cells and viral ploys to escape immune surveillance. Among the immune-evasion strategies used by the lymphocryptovirus (γ(1)-herpesvirus) EBV is the downregulation of surface HLA class I expression by the virally encoded G protein-coupled receptor BILF1, thereby impeding presentation of viral Ags and cytotoxic T cell recognition of the infected cell. In this study, we show EBV BILF1 to be expressed early in the viral lytic cycle. BILF1 targets a broad range of HLA class I molecules, including multiple HLA-A and -B types and HLA-E. In contrast, HLA-C was only marginally affected. We advance the mechanistic understanding of the process by showing that the cytoplasmic C-terminal tail of EBV BILF1 is required for reducing surface HLA class I expression. Susceptibility to BILF1-mediated downregulation, in turn, is conferred by specific residues in the intracellular tail of the HLA class I H chain. Finally, we explore the evolution of BILF1 within the lymphocryptovirus genus. Although the homolog of BILF1 encoded by the lymphocryptovirus infecting Old World rhesus primates shares the ability of EBV to downregulate cell surface HLA class I expression, this function is not possessed by New World marmoset lymphocryptovirus BILF1. Therefore, this study furthers our knowledge of the evolution of immunoevasive functions by the lymphocryptovirus genus of herpesviruses.

EBV lytic-phase protein BGLF5 contributes to TLR9 downregulation during productive infection.

Viruses use a wide range of strategies to modulate the host immune response. The human gammaherpesvirus EBV, causative agent of infectious mononucleosis and several malignant tumors, encodes proteins that subvert immune responses, notably those mediated by T cells. Less is known about EBV interference with innate immunity, more specifically at the level of TLR-mediated pathogen recognition. The viral dsDNA sensor TLR9 is expressed on B cells, a natural target of EBV infection. Here, we show that EBV particles trigger innate immune signaling pathways through TLR9. Furthermore, using an in vitro system for productive EBV infection, it has now been possible to compare the expression of TLRs by EBV(-) and EBV(+) human B cells during the latent and lytic phases of infection. Several TLRs were found to be differentially expressed either in latently EBV-infected cells or after induction of the lytic cycle. In particular, TLR9 expression was profoundly decreased at both the RNA and protein levels during productive EBV infection. We identified the EBV lytic-phase protein BGLF5 as a protein that contributes to downregulating TLR9 levels through RNA degradation. Reducing the levels of a pattern-recognition receptor capable of sensing the presence of EBV provides a mechanism by which the virus could obstruct host innate antiviral responses.

Adipose Tissues from Human and Bat-Derived Cell Lines Support Ebola Virus Infection.

Ebola virus is a zoonotic pathogen with a geographic range covering diverse ecosystems that are home to many potential reservoir species. Although researchers have detected Ebola virus RNA and serological evidence of previous infection in different rodents and bats, the infectious virus has not been isolated. The field is missing critical knowledge about where the virus is maintained between outbreaks, either because the virus is rarely encountered, overlooked during sampling, and/or requires specific unknown conditions that regulate viral expression. This study assessed adipose tissue as a previously overlooked tissue capable of supporting Ebola virus infection. Adipose tissue is a dynamic endocrine organ helping to regulate and coordinate homeostasis, energy metabolism, and neuroendocrine and immune functions. Through in vitro infection of human and bat (Eptesicus fuscus) brown adipose tissue cultures using wild-type Ebola virus, this study showed high levels of viral replication for 28 days with no qualitative indicators of cytopathic effects. In addition, alterations in adipocyte metabolism following long-term infection were qualitatively observed through an increase in lipid droplet number while decreasing in size, a harbinger of lipolysis or adipocyte browning. The finding that bat and human adipocytes are susceptible to Ebola virus infection has important implications for potential tissue tropisms that have not yet been investigated. Additionally, the findings suggest how the metabolism of this tissue may play a role in pathogenesis, viral transmission, and/or zoonotic spillover events.

Adenosine deaminase augments SARS-CoV-2 specific cellular and humoral responses in aged mouse models of immunization and challenge.

Despite numerous clinically available vaccines and therapeutics, aged patients remain at increased risk for COVID-19 morbidity. Furthermore, various patient populations, including the aged can have suboptimal responses to SARS-CoV-2 vaccine antigens. Here, we characterized vaccine-induced responses to SARS-CoV-2 synthetic DNA vaccine antigens in aged mice. Aged mice exhibited altered cellular responses, including decreased IFNγ secretion and increased TNFα and IL-4 secretion suggestive of TH2-skewed responses. Aged mice exhibited decreased total binding and neutralizing antibodies in their serum but significantly increased TH2-type antigen-specific IgG1 antibody compared to their young counterparts. Strategies to enhance vaccine-induced immune responses are important, especially in aged patient populations. We observed that co-immunization with plasmid-encoded adenosine deaminase (pADA)enhanced immune responses in young animals. Ageing is associated with decreases in ADA function and expression. Here, we report that co-immunization with pADA enhanced IFNγ secretion while decreasing TNFα and IL-4 secretion. pADA expanded the breadth and affinity SARS-CoV-2 spike-specific antibodies while supporting TH1-type humoral responses in aged mice. scRNAseq analysis of aged lymph nodes revealed that pADA co-immunization supported a TH1 gene profile and decreased FoxP3 gene expression. Upon challenge, pADA co-immunization decreased viral loads in aged mice. These data support the use of mice as a model for age-associated decreased vaccine immunogenicity and infection-mediated morbidity and mortality in the context of SARS-CoV-2 vaccines and provide support for the use of adenosine deaminase as a molecular adjuvant in immune-challenged populations.

Generation and Characterization of a SARS-CoV-2-Susceptible Mouse Model Using Adeno-Associated Virus (AAV6.2FF)-Mediated Respiratory Delivery of the Human ACE2 Gene.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the aetiological agent of coronavirus disease 2019 (COVID-19) that has caused a pandemic with millions of human infections. There continues to be a pressing need to develop potential therapies and vaccines to inhibit SARS-CoV-2 infection to mitigate the ongoing pandemic. Epidemiological data from the current pandemic indicates that there may be sex-dependent differences in disease outcomes. To investigate these differences, we proposed to use common small animal species that are frequently used to model disease with viruses. However, common laboratory strains of mice are not readily infected by SARS-CoV-2 because of differences in the angiotensin-converting enzyme 2 (ACE2), the cellular receptor for the virus. To overcome this limitation, we transduced common laboratory accessible strains of mice of different sexes and age groups with a novel a triple AAV6 mutant, termed AAV6.2FF, encoding either human ACE2 or luciferase via intranasal administration to promote expression in the lung and nasal turbinates. Infection of AAV-hACE2-transduced mice with SARS-CoV-2 resulted in high viral titers in the lungs and nasal turbinates, establishment of an IgM and IgG antibody response, and modulation of lung and nasal turbinate cytokine profiles. There were insignificant differences in infection characteristics between age groups and sex-related differences; however, there were significant strain-related differences between BALB/c vs. C57BL/6 mice. We show that AAV-hACE2-transduced mice are a useful for determining immune responses and for potential evaluation of SARS-CoV-2 vaccines and antiviral therapies, and this study serves as a model for the utility of this approach to rapidly develop small-animal models for emerging viruses.

Preclinical evaluation of a SARS-CoV-2 mRNA vaccine PTX-COVID19-B.

Safe and effective vaccines are needed to end the COVID-19 pandemic. Here, we report the preclinical development of a lipid nanoparticle­formulated SARS-CoV-2 mRNA vaccine, PTX-COVID19-B. PTX-COVID19-B was chosen among three candidates after the initial mouse vaccination results showed that it elicited the strongest neutralizing antibody response against SARS-CoV-2. Further tests in mice and hamsters indicated that PTX-COVID19-B induced robust humoral and cellular immune responses and completely protected the vaccinated animals from SARS-CoV-2 infection in the lung. Studies in hamsters also showed that PTX-COVID19-B protected the upper respiratory tract from SARS-CoV-2 infection. Mouse immune sera elicited by PTX-COVID19-B vaccination were able to neutralize SARS-CoV-2 variants of concern, including the Alpha, Beta, Gamma, and Delta lineages. No adverse effects were induced by PTX-COVID19-B in either mice or hamsters. Based on these results, PTX-COVID19-B was authorized by Health Canada to enter clinical trials in December 2020 with a phase 2 clinical trial ongoing.

Divergent SARS-CoV-2 variant emerges in white-tailed deer with deer-to-human transmission.

Wildlife reservoirs of broad-host-range viruses have the potential to enable evolution of viral variants that can emerge to infect humans. In North America, there is phylogenomic evidence of continual transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) from humans to white-tailed deer (Odocoileus virginianus) through unknown means, but no evidence of transmission from deer to humans. We carried out an observational surveillance study in Ontario, Canada during November and December 2021 (n = 300 deer) and identified a highly divergent lineage of SARS-CoV-2 in white-tailed deer (B.1.641). This lineage is one of the most divergent SARS-CoV-2 lineages identified so far, with 76 mutations (including 37 previously associated with non-human mammalian hosts). From a set of five complete and two partial deer-derived viral genomes we applied phylogenomic, recombination, selection and mutation spectrum analyses, which provided evidence for evolution and transmission in deer and a shared ancestry with mink-derived virus. Our analysis also revealed an epidemiologically linked human infection. Taken together, our findings provide evidence for sustained evolution of SARS-CoV-2 in white-tailed deer and of deer-to-human transmission.

Coding potential and transcript analysis of fowl adenovirus 4: insight into upstream ORFs as common sequence features in adenoviral transcripts.

Recombinant fowl adenoviruses (FAdVs) have been successfully used as veterinary vaccine vectors. However, insufficient definitions of the protein-coding and non-coding regions and an incomplete understanding of virus-host interactions limit the progress of next-generation vectors. FAdVs are known to cause several diseases of poultry. Certain isolates of species FAdV-C are the aetiological agent of inclusion body hepatitis/hydropericardium syndrome (IBH/HPS). In this study, we report the complete 45667 bp genome sequence of FAdV-4 of species FAdV-C. Assessment of the protein-coding potential of FAdV-4 was carried out with the Bio-Dictionary-based Gene Finder together with an evaluation of sequence conservation among species FAdV-A and FAdV-D. On this basis, 46 potentially protein-coding ORFs were identified. Of these, 33 and 13 ORFs were assigned high and low protein-coding potential, respectively. Homologues of the ancestral adenoviral genes were, with few exceptions, assigned high protein-coding potential. ORFs that were unique to the FAdVs were differentiated into high and low protein-coding potential groups. Notable putative genes with high protein-coding capacity included the previously unreported fiber 1, hypothetical 10.3K and hypothetical 10.5K genes. Transcript analysis revealed that several of the small ORFs less than 300 nt in length that were assigned low coding potential contributed to upstream ORFs (uORFs) in important mRNAs, including the ORF22 mRNA. Subsequent analysis of the previously reported transcripts of FAdV-1, FAdV-9, human adenovirus 2 and bovine adenovirus 3 identified widespread uORFs in AdV mRNAs that have the potential to act as important translational regulatory elements.

The Epstein-Barr virus G-protein-coupled receptor contributes to immune evasion by targeting MHC class I molecules for degradation.

Epstein-Barr virus (EBV) is a human herpesvirus that persists as a largely subclinical infection in the vast majority of adults worldwide. Recent evidence indicates that an important component of the persistence strategy involves active interference with the MHC class I antigen processing pathway during the lytic replication cycle. We have now identified a novel role for the lytic cycle gene, BILF1, which encodes a glycoprotein with the properties of a constitutive signaling G-protein-coupled receptor (GPCR). BILF1 reduced the levels of MHC class I at the cell surface and inhibited CD8(+) T cell recognition of endogenous target antigens. The underlying mechanism involves physical association of BILF1 with MHC class I molecules, an increased turnover from the cell surface, and enhanced degradation via lysosomal proteases. The BILF1 protein of the closely related CeHV15 gamma(1)-herpesvirus of the Rhesus Old World primate (80% amino acid sequence identity) downregulated surface MHC class I similarly to EBV BILF1. Amongst the human herpesviruses, the GPCR encoded by the ORF74 of the KSHV gamma(2)-herpesvirus is most closely related to EBV BILF1 (15% amino acid sequence identity) but did not affect levels of surface MHC class I. An engineered mutant of BILF1 that was unable to activate G protein signaling pathways retained the ability to downregulate MHC class I, indicating that the immune-modulating and GPCR-signaling properties are two distinct functions of BILF1. These findings extend our understanding of the normal biology of an important human pathogen. The discovery of a third EBV lytic cycle gene that cooperates to interfere with MHC class I antigen processing underscores the importance of the need for EBV to be able to evade CD8(+) T cell responses during the lytic replication cycle, at a time when such a large number of potential viral targets are expressed.

Downregulation of Cell Surface Major Histocompatibility Complex Class I Expression Is Mediated by the Left-End Transcription Unit of Fowl Adenovirus 9.

Major histocompatibility complex class I (MHC-I) molecules play a critical role in the host's antiviral response by presenting virus-derived antigenic peptides to cytotoxic T lymphocytes (CTLs), enabling the clearance of virus-infected cells. Human adenoviruses evade CTL-mediated cell lysis, in part, by interfering directly with the MHC-I antigen presentation pathway through the expression of E3-19K, which binds both MHC-I and the transporter associated with antigen processing protein and sequestering MHC-I within the endoplasmic reticulum. Fowl adenoviruses have no homologues of E3-19K. Here, we show that representative virus isolates of the species Fowl aviadenovirus C, Fowl aviadenovirus D, and Fowl aviadenovirus E downregulate the cell surface expression of MHC-I in chicken hepatoma cells, resulting in 71%, 11%, and 14% of the baseline expression level, respectively, at 12 h post-infection. Furthermore, this work reports that FAdV-9 downregulates cell surface MHC-I through a minimum of two separate mechanisms-a lysosomal-independent mechanism that requires the presence of the fowl adenovirus early 1 (FE1) transcription unit located within the left terminal genomic region between nts 1 and 6131 and a lysosomal-dependent mechanism that does not require the presence of FE1. These results establish a new functional role for the FE1 transcription unit in immune evasion. These studies provide important new information about the immune evasion of FAdVs and will enhance our understanding of the pathogenesis of inclusion body hepatitis and advance the progress made in next-generation FAdV-based vectors.

Simulated sunlight decreases the viability of SARS-CoV-2 in mucus.

The novel coronavirus, SARS-CoV-2, has spread into a pandemic since its emergence in Wuhan, China in December of 2019. This has been facilitated by its high transmissibility within the human population and its ability to remain viable on inanimate surfaces for an extended period. To address the latter, we examined the effect of simulated sunlight on the viability of SARS-CoV-2 spiked into tissue culture medium or mucus. The study revealed that inactivation took 37 minutes in medium and 107 minutes in mucus. These times-to-inactivation were unexpected since they are longer than have been observed in other studies. From this work, we demonstrate that sunlight represents an effective decontamination method but the speed of decontamination is variable based on the underlying matrix. This information has an important impact on the development of infection prevention and control protocols to reduce the spread of this deadly pathogen.

Host parameters and mode of infection influence outcome in SARS-CoV-2-infected hamsters.

The golden hamster model of SARS-CoV-2 infection recapitulates key characteristics of COVID-19. In this work we examined the influence of the route of exposure, sex, and age on SARS-CoV-2 pathogenesis in hamsters. We report that delivery of SARS-CoV-2 by a low- versus high-volume intranasal or intragastric route results in comparable viral titers in the lung and viral shedding. However, low-volume intranasal exposure results in milder weight loss, whereas intragastric exposure leads to a diminished capacity to regain body weight. Male hamsters, and particularly older male hamsters, display an impaired capacity to recover from illness and delayed viral clearance. These factors were found to influence the nature of the host inflammatory cytokine response but had a minimal effect on the quality and durability of the humoral immune response and susceptibility to re-infection. These data further elucidate key factors that impact pre-clinical challenge studies carried out in the hamster model of COVID-19.

A novel mouse AAV6 hACE2 transduction model of wild-type SARS-CoV-2 infection studied using synDNA immunogens.

More than 100 million people have been infected with severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Common laboratory mice are not susceptible to wild-type SARS-CoV-2 infection, challenging the development and testing of effective interventions. Here, we describe the development and testing of a mouse model for SARS-CoV-2 infection based on transduction of the respiratory tract of laboratory mice with an adeno-associated virus vector (AAV6) expressing human ACE-2 (AAV6.2FF-hACE2). We validated this model using a previously described synthetic DNA vaccine plasmid, INO-4800 (pS). Intranasal instillation of AAV6.2FF-hACE2 resulted in robust hACE2 expression in the respiratory tract. pS induced robust cellular and humoral responses. Vaccinated animals were challenged with 105 TCID50 SARS-CoV-2 (hCoV-19/Canada/ON-VIDO-01/2020) and euthanized four days post-challenge to assess viral load. One immunization resulted in 50% protection and two immunizations were completely protective. Overall, the AAV6.2FF-hACE2 mouse transduction model represents an easily accessible, genetically diverse mouse model for wild-type SARS-CoV-2 infection and preclinical evaluation of potential interventions.