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rVSV-ΔG-SARS-CoV-2-S is a clinical stage (Phase 2) replication competent recombinant vaccine against SARS-CoV-2. To evaluate the safety profile of the vaccine, a series of non-clinical safety, immunogenicity and efficacy studies were conducted in four animal species, using multiple doses (up to 108 Plaque Forming Units/animal) and dosing regimens. There were no treatment-related mortalities or any noticeable clinical signs in any of the studies. Compared to unvaccinated controls, hematology and biochemistry parameters were unremarkable and no adverse histopathological findings. There was no detectable viral shedding in urine, nor viral RNA detected in whole blood or serum samples seven days post vaccination. The rVSV-ΔG-SARS-CoV-2-S vaccination gave rise to neutralizing antibodies, cellular immune responses, and increased lymphocytic cellularity in the spleen germinal centers and regional lymph nodes. No evidence for neurovirulence was found in C57BL/6 immune competent mice or in highly sensitive type I interferon knock-out mice. Vaccine virus replication and distribution in K18-human Angiotensin-converting enzyme 2-transgenic mice showed a gradual clearance from the vaccination site with no vaccine virus recovered from the lungs. The nonclinical data suggest that the rVSV-ΔG-SARS-CoV-2-S vaccine is safe and immunogenic. These results supported the initiation of clinical trials, currently in Phase 2. Supplementary Information The online version contains supplementary material available at 10.1007/s00204-021-03214-w.

Both monogenic diseases and viral infections can manifest in a broad spectrum of clinical phenotypes that range from asymptomatic to lethal, suggesting that other factors modulate disease severity. Here, we examine the interplay between the genetic neuronopathic Gaucher’s disease (nGD), and neuroinvasive Sindbis virus (SVNI) infection. Infection of nGD mice with SVNI had no influence on nGD severity. However, nGD mice were more resistant to SVNI infection. Significantly different inflammatory responses were seen in nGD brains when compared with SVNI brains: the inflammatory response in the nGD brains consisted of reactive astrocytes and microglia with no infiltrating macrophages, but the inflammatory response in the brains of SVNI-infected mice was characterized by infiltration of macrophages and altered activation of microglia and astrocytes. We suggest that the innate immune response activated in nGD confers resistance against viral infection of the CNS. Electronic supplementary material The online version of this article (10.1186/s40478-020-01020-6) contains supplementary material, which is available to authorized users.

Significance Vaccines are required to control COVID-19 during the current pandemic and possibly afterward. Recombinant nucleic acids, proteins, and virus vectors that stimulate immune responses to the SARS-CoV-2 S protein have provided protection in experimental animal and human clinical trials, although questions remain regarding their ability to prevent spread and the duration of immunity. The present study focuses on replication-restricted modified vaccinia virus Ankara (MVA), which has been shown to be a safe, immunogenic, and stable smallpox vaccine and a promising vaccine vector for other infectious diseases and cancer. In a transgenic mouse model, one or two injections of recombinant MVAs that express modified forms of S inhibited SARS-CoV-2 replication in the upper and lower respiratory tracts and prevented severe disease., Modified vaccinia virus Ankara (MVA) is a replication-restricted smallpox vaccine, and numerous clinical studies of recombinant MVAs (rMVAs) as vectors for prevention of other infectious diseases, including COVID-19, are in progress. Here, we characterize rMVAs expressing the S protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Modifications of full-length S individually or in combination included two proline substitutions, mutations of the furin recognition site, and deletion of the endoplasmic retrieval signal. Another rMVA in which the receptor binding domain (RBD) is flanked by the signal peptide and transmembrane domains of S was also constructed. Each modified S protein was displayed on the surface of rMVA-infected cells and was recognized by anti-RBD antibody and soluble hACE2 receptor. Intramuscular injection of mice with the rMVAs induced antibodies, which neutralized a pseudovirus in vitro and, upon passive transfer, protected hACE2 transgenic mice from lethal infection with SARS-CoV-2, as well as S-specific CD3+CD8+IFNγ+ T cells. Antibody boosting occurred following a second rMVA or adjuvanted purified RBD protein. Immunity conferred by a single vaccination of hACE2 mice prevented morbidity and weight loss upon intranasal infection with SARS-CoV-2 3 wk or 7 wk later. One or two rMVA vaccinations also prevented detection of infectious SARS-CoV-2 and subgenomic viral mRNAs in the lungs and greatly reduced induction of cytokine and chemokine mRNAs. A low amount of virus was found in the nasal turbinates of only one of eight rMVA-vaccinated mice on day 2 and none later. Detection of low levels of subgenomic mRNAs in turbinates indicated that replication was aborted in immunized animals.

Liver resident macrophages Kupffer cells (KCs) and infiltrating Ly6C(hi) monocytes both contribute to liver tissue regeneration in various pathologies, but also to disease progression upon disruption of orderly consecutive regeneration cascades. Little is known about molecular pathways that regulate their differentiation, maintenance, or their inflammatory behavior during injury. Here we show that COMMD10-deficient KCs adopt liver-specific identity. Strikingly, COMMD10-deficiency in KCs and in other tissue resident macrophages impedes their homeostatic survival, leading to their continuous replacement by Ly6C(hi) monocytes. While COMMD10-deficiency in KCs mildly worsens acetaminophen-induced liver injury (AILI), its deficiency in Ly6C(hi) monocytes results in exacerbated and sustained hepatic damage. Monocytes display unleashed inflammasome activation and reduced type I interferon response and acquire ‘neutrophil-like’ and lipid associated macrophage differentiation fates. Collectively, COMMD10 appears indispensable for KC and other tissue resident macrophage survival and is an important regulator of Ly6C(hi) monocyte fate decisions and reparative behavior in the diseased liver.

SARS-CoV-2, a member of the coronavirus family, is the causative agent of the COVID-19 pandemic. Currently, there is still an urgent need in developing an efficient therapeutic intervention. In this study, we aimed at evaluating the therapeutic effect of a single intranasal treatment of the TLR3/MDA5 synthetic agonist Poly(I:C) against a lethal dose of SARS-CoV-2 in K18-hACE2 transgenic mice. We demonstrate here that early Poly(I:C) treatment acts synergistically with SARS-CoV-2 to induce an intense, immediate and transient upregulation of innate immunity-related genes in lungs. This effect is accompanied by viral load reduction, lung and brain cytokine storms prevention and increased levels of macrophages and NK cells, resulting in 83% mice survival, concomitantly with long-term immunization. Thus, priming the lung innate immunity by Poly(I:C) or alike may provide an immediate, efficient and safe protective measure against SARS-CoV-2 infection.

The liver’s extraordinary ability to regenerate has been known since the myth of Prometheus, but the mechanisms involved are still being discovered. Various small animal models have been used in this quest. Two of the most popular include partial hepatectomy (PHx), in which two-thirds of the liver mass is surgically removed to evoke a massive, immediate stimulus for regeneration, and prolonged exposure to toxins that kill liver cells more gradually, provoking chronic regenerative activity. In either case, multiple types of cells must interact effectively to repopulate the organ with functional mature hepatocytes and thus assure ultimate restoration of healthy liver structure and function. This complexity has confounded efforts to distinguish specific changes that occur in cells that repopulate the hepatocyte compartment from changes in other cell populations, including subpopulations of hepatocytes or hepatocyte precursors that do not become regenerative. In the current issue of the JCI, Wang et al. used translating ribosome affinity purification followed by high-throughput RNA sequencing (TRAP-seq) to isolate mRNAs from repopulating hepatocytes in order to profile gene expression specifically in the hepatocytes that regenerate the liver following toxic injury imposed by inherent byproducts of tyrosine metabolism. This innovative methodology can potentially be used to design therapeutic strategies for liver regeneration.

Diagnostic identification of pathogens is usually accomplished by isolation of the pathogen or its substances, and should correlate with the time and site of infection. Alternatively, immunoassays such as enzyme-linked immunosorbent assay (ELISA) tests for quantification of serum antibodies are expedient and are usually employed for retrospective diagnostic of a particular infective agent. Here, the potential of cell-based immunoassays for early pathogen detection was evaluated by quantification of specific, antigen-activated, low-frequency IFN&gamma, secreting cells in mouse spleens following infection with various pathogens. Using enzyme-linked immunospot (ELISPOT) assays, specific responses were observed within 3&ndash, 6 days following infection with F. tularensis, B. anthracis, Y. pestis, or Influenza virus. Blood samples collected from F. tularensis-infected mice revealed the presence of IFN&gamma, producing activated cells within one week post infection. When non-human primates were infected with B. anthracis, cellular response was observed in peripheral blood samples as early as five days post infection, 3&ndash, 5 days earlier than serum antibodies. Finally, the expression pattern of genes in splenocytes of F. tularensis-infected mice was inspected by a transcriptomic approach, enabling the identification of potential host targets for the future development of genetic-based cellular immunoassays. Altogether, the data demonstrate the potential of cell-based immunoassays for early pathogen detection.

Amiodarone is a commonly used antiarrhythmic drug and can cause liver steatosis. We investigated the role of endoplasmic reticulum (ER) stress/unfolded protein response in the pathogenesis of amiodarone-induced steatosis. Amiodarone-induced liver injury was obtained by 1 intraperitoneal injection to wild-type (WT) or C/EBP homologous protein knock-out mice (Ddit3-/-). Amiodarone directly reduced intracellular ATP and Ca2+ in hepatocytes invitro, inducing ER stress and lipid accumulation. In vivo, amiodarone-driven liver damage and lipid accumulation was accompanied by activation of ER stress/unfolded protein response, as demonstrated by up-regulation of genes encoding key ER stress mediators and by phosphorylation of eIF2α. In contrast to WT mice, Ddit3-/- mice were protected from amiodarone-induced ER stress and lipid accumulation. Importantly, amiodarone-induced lipid accumulation was not mediated by de novo hepatic lipogenesis, increased adipose tissue lipolysis or increased hepatic uptake of triglycerides or free fatty acids. Rather, amiodarone strongly increased hepatic mRNA expression of lipid droplet proteins, particularly Cidea and Cidec, in WT, but less so in Ddit3-/- mice, suggesting a link between ER stress and increased triglyceride storage. Moreover, while insulin attenuated amiodarone-induced phosphorylation of hormone sensitive lipase (HSL) in WT, it did not affect pHSL in Ddit3-/-, indicating increased lipolysis and therefore reduced lipid accumulation in these mice. Finally, ER stress attenuation using 2 different pharmacological chaperones reduced lipid accumulation, accompanied by reduced mRNA expression of Cidec. In conclusion, amiodarone-induced ER stress drives liver steatosis and may be considered for therapeutic targeting.

Congenital erythroderma is a rare and often life-threatening condition, which has been shown to result from mutations in several genes encoding important components of the epidermal differentiation program. Using whole exome sequencing, we identified in a child with congenital exfoliative erythroderma, hypotrichosis, severe nail dystrophy and failure to thrive, two heterozygous mutations in ABCA12 (c.2956C>T, p.R986W; c.5778+2T>C, p. G1900Mfs*16), a gene known to be associated with two forms of ichthyosis, autosomal recessive congenital ichthyosis, and harlequin ichthyosis. Because the patient displayed an atypical phenotype, including severe hair and nail manifestations, we scrutinized the exome sequencing data for additional potentially deleterious genetic variations in genes of relevance to the cornification process. Two mutations were identified in CAPN12, encoding a member of the calpain proteases: a paternal missense mutation (c.1511C>A; p.P504Q) and a maternal deletion due to activation of a cryptic splice site in exon 9 of the gene (c.1090_1129del; p.Val364Lysfs*11). The calpain 12 protein was found to be expressed in both the epidermis and hair follicle of normal skin, but its expression was dramatically reduced in the patient's skin. The downregulation of capn12 expression in zebrafish was associated with abnormal epidermal morphogenesis. Small interfering RNA knockdown of CAPN12 in three-dimensional human skin models was associated with acanthosis, disorganized epidermal architecture, and downregulation of several differentiation markers, including filaggrin. Accordingly, filaggrin expression was almost absent in the patient skin. Using ex vivo live imaging, small interfering RNA knockdown of calpain 12 in skin from K14-H2B GFP mice led to significant hair follicle catagen transformation compared with controls. In summary, our results indicate that calpain 12 plays an essential role during epidermal ontogenesis and normal hair follicle cycling and that its absence may aggravate the clinical manifestations of ABCA12 mutations.

Eczema vaccinatum is a severe and occasionally lethal complication of smallpox vaccine, characterized by systemic viral dissemination, distant from the initial inoculation site of the vaccine. A major risk factor for eczema vaccinatum is a background of atopic dermatitis, a chronic, common allergic, relapsing disorder, manifested by dry and inflamed skin, itchy rash, Th2 biased immune response and hypersensitivity to various antigens. Unlike the severe manifestations of eczema vaccinatum in humans, current models present only mild symptoms that limits examination of potential therapeutics for eczema vaccinatum. The atopic dermatitis and eczema vaccinatum models we present here, are the first to simulate the severity of the diseases in humans. Indeed, dermatitic mice display persistent severe dermatitis, characterized by dry and inflamed skin with barrier dysfunction, epidermal hyperplasia and significant elevation of serum IgE. By exposing atopic dermatitis mice to ectromelia virus, we generated eczema vaccinatum that mimic the human disease better than known eczema vaccinatum models. Similarly to humans, eczematous mice displayed enlarged and disseminated skin lesions, which correlated with elevated viral load. Cidofovir and antiviral antibodies conferred protection even when treatment started at a late eczematous stage. Moreover, we are the first to demonstrate that despite a severe background of atopic dermatitis, modified vaccinia Ankara virus (MVA) vaccination protects against lethal ectromelia virus exposure. We finally show that protection by MVA vaccination is dependent on CD4+ T cells and is associated with significant activation of CD8+ cytotoxic T cells and induction of humoral immunity.

In this study, we compared two lines of transgenic CD8+ T cells specific for the same KdM282-90 epitope of respiratory syncytial virus in the CB6F1 hybrid mouse model. Here we found that these two transgenic lines had similar in vivo abilities to control viral load after respiratory syncytial virus infection using adoptive transfer. Transfer of the TRBV13-2 line resulted in higher levels of IL-6 and MIP1-α in the lung than TRBV13-1 transfer. Interestingly, when large numbers of cells were co-transferred, the lines formed a hierarchy, with TRBV13-2 being immunodominant over TRBV13-1 in the mediastinal lymph node despite no identifiable difference in proliferation or apoptosis between the lines. This hierarchy was not established when lower cell numbers were transferred. The phenotype and frequency of proliferating cells were also cell transfer dose-dependent with higher percentages of CD127loCD62LloKLRG1lo and proliferating cells present when lower numbers of cells were transferred. These results illustrate the importance of cell number in adoptive transfer experiments and its influence on the phenotype and hierarchy of the subsequent T cell response.

Background. Decadesafterthecessationofsmallpoxvaccination,thepotentialofthedeliberatereleaseofpathogenic orthopoxviruses has forced a reconsideration of using these extremely efficient human vaccines. Scenarios of sudden biothreats have prompted demand for rapidly protective vaccination. However, the feasibility of short-term vaccination (i.e., vaccination shortly before exposure) with vaccinia virus (VACV) is uncertain. Methods. WetestedtherapidprotectivecapacityofvaccinesbasedonVACVstrainLister(VACV-Lister)andon modified VACV Ankara (MVA) in different mouse models, comparing lethal infections with VACV strain Western Reserve (VACV-WR) or ectromelia virus (ECTV). Results. In contrast to VACV-WR challenge, we found extended incubation periods after ECTV challenge, allowing successful therapeutic immunization with VACV-Lister and MVA when applied 2‐3 days after exposure. Rapid protection from respiratory tract ECTV infection was significantly affected by vaccine dose and was associated with occurrence of poxvirus-specific antibodies. Vaccinations in type I interferon receptor‐deficient mice were protective, whereas recombination activating gene 1‐deficient mice lacking mature T and B cells failed to mount immunity after short-term vaccination, confirming an essential role of adaptive immune responses. Conclusions. ECTV infection in mice models the course of human smallpox. Our data provide evidence to substantiate historical data on the usefulness of postexposure vaccination with conventional VACV and the new candidate MVA to protect against fatal orthopoxvirus infections.

Background & Aims Sortilin traffics newly synthesized molecules from the trans-Golgi apparatus along secretory pathways to endosomes, lysosomes or to the cell surface. Sortilin trafficking of acid sphingomyelinase (aSMase) may regulate ceramide levels, a major modulator of insulin signalling. We therefore tested whether sortilin deficiency reduces hepatic and adipose tissue aSMase activity, improving insulin sensitivity in diet-induced obesity (DIO). Methods DIO in C57BL/6 (WT) and sortilin −/− mice was induced by high-fat diet feeding for 10weeks. Results Sortilin −/− mice gained less body weight and less visceral fat, despite similar food intake compared to WT type mice and had enhanced glucose uptake in insulin tolerance tests, which was further corroborated by enhanced hepatic pAkt expression. Sortilin deficiency led to attenuated hepatic steatosis, reduced expression of genes involved in lipogenesis, ceramide synthesis and inflammatory cytokine production and reduced activity of ceramide synthase 5/6 (CerS5/6). Sortilin −/− mice had reduced hepatic aSMase activity under both steady-state and DIO. Likewise, sortilin −/− hepatocytes displayed hypersensitivity to insulin, due to enhanced insulin receptor downstream signalling. In adipose tissue, sortilin −/− mice exhibited lower expression of inflammatory cytokines and lower expression and activity of CerS5/6. As in liver, adipose tissue displayed increased insulin signalling, accompanied by attenuated aSMase activity. Conclusions Sortilin deficiency induces a beneficial metabolic phenotype in liver and adipose tissue upon DIO, mediated in part by reduced aSMase activity.

Our previous work has characterized the functional and clonotypic features of two respiratory syncytial virus (RSV) epitope-specific T cell responses in mice. Following single-cell sequencing, we selected T cell receptor sequences to represent both a public and a private clone specific for the dominant K(d)M2(82-90) epitope for the generation of T cell receptor transgenic (TCR Tg) mice. We evaluated cells from these TCR Tg strains for three major functions of CD8+ T cells: proliferation, cytokine production and cytolytic activity. In vitro comparisons of the functional characteristics of T cells from the newly-generated mice demonstrated many similarities in their responsiveness to cognate antigen stimulation. Cells from both TRBV13-1 (private) and TRBV13-2 (public) TCR Tg mice had similar affinity, and proliferated similarly in vitro in response to cognate antigen stimulation. When transferred to BALB/c mice, cells from both strains demonstrated extensive proliferation in mediastinal lymph nodes following RSV infection, with TRBV13-2 demonstrating better in vivo proliferation. Both strains similarly expressed cytokines and chemokines following stimulation, and had similar Granzyme B and perforin expression, however cells expressing TRBV13-1 demonstrated better cytolytic activity than TRBV13-2 cells. These new, well-characterized mouse strains provide new opportunities to study molecular mechanisms that control the phenotype and function of CD8+ T cell responses.

Eradication of smallpox and discontinuation of the vaccination campaign resulted in an increase in the percentage of unvaccinated individuals, highlighting the need for postexposure efficient countermeasures in case of accidental or deliberate viral release. Intranasal infection of mice with ectromelia virus (ECTV), a model for human smallpox, is curable by vaccination with a high vaccine dose given up to 3 days postexposure. To further extend this protective window and to reduce morbidity, mice were vaccinated postexposure with Vaccinia-Lister, the conventional smallpox vaccine or Modified Vaccinia Ankara, a highly attenuated vaccine in conjunction with TLR3 or TLR9 agonists. We show that co-administration of the TLR3 agonist poly(I:C) even 5 days postexposure conferred protection, avoiding the need to increase the vaccination dose. Efficacious treatments prevented death, ameliorated disease symptoms, reduced viral load and maintained tissue integrity of target organs. Protection was associated with significant elevation of serum IFNα and anti-vaccinia IgM antibodies, modulation of IFNγ response, and balanced activation of NK and T cells. TLR9 agonists (CpG ODNs) were less protective than the TLR3 agonist poly(I:C). We show that activation of type 1 IFN by poly(I:C) and protection is achievable even without co-vaccination, requiring sufficient amount of the viral antigens of the infective agent or the vaccine. This study demonstrated the therapeutic potential of postexposure immune modulation by TLR activation, allowing to alleviate the disease symptoms and to further extend the protective window of postexposure vaccination.

Background In an event of a smallpox outbreak in humans, the window for efficacious treatment by vaccination with vaccinia viruses (VACV) is believed to be limited to the first few days post-exposure (p.e.). We recently demonstrated in a mouse model for human smallpox, that active immunization 2–3 days p.e. with either VACV-Lister or modified VACV Ankara (MVA) vaccines, can rescue animals from lethal challenge of ectromelia virus (ECTV), the causative agent of mousepox. The present study was carried out in order to determine whether a single dose of the anti-viral cidofovir (CDV), administered at different times and doses p.e. either alone or in conjunction with active vaccination, can rescue ECTV infected mice. Methods Animals were infected intranasally with ECTV, treated on different days with various single CDV doses and monitored for morbidity, mortality and humoral response. In addition, in order to determine the influence of CDV on the immune response following vaccination, both the "clinical take”, IFN-gamma and IgG Ab levels in the serum were evaluated as well as the ability of the mice to withstand a lethal challenge of ECTV. Finally the efficacy of a combined treatment regime of CDV and vaccination p.e. was determined. Results A single p.e. CDV treatment is sufficient for protection depending on the initiation time and dose (2.5 – 100 mg/kg) of treatment. Solid protection was achieved by a low dose (5 mg/kg) CDV treatment even if given at day 6 p.e., approximately 4 days before death of the control infected untreated mice (mean time to death (MTTD) 10.2). At the same time point complete protection was achieved by single treatment with higher doses of CDV (25 or 100 mg/kg). Irrespective of treatment dose, all surviving animals developed a protective immune response even when the CDV treatment was initiated one day p.e.. After seven days post treatment with the highest dose (100 mg/kg), virus was still detected in some organs (e.g. lung and liver) yet all animals survived, suggesting that efficacious single CDV treatment requires a potent immune system. The combination of CDV and vaccination provided no additional protection over CDV alone. Yet, combining CDV and vaccination maintained vaccination efficacy. Conclusions Altogether, our data substantiate the feasibility of single post-exposure antiviral treatment to face orthopoxvirus infection.

The therapeutic potential of human vaccinia immunoglobulin (VIG) in orthopoxvirus infection was examined using two mouse models for human poxvirus, based on Ectromelia virus and Vaccinia Western Reserve (WR) respiratory infections. Despite the relatively fast clearance of human VIG from mice circulation, a single VIG injection protected immune-competent mice against both infections. Full protection against lethal Ectromelia virus infection was achieved by VIG injection up to one day post-exposure, and even injection of VIG two or three days post-infection conferred solid protection (60-80%). Nevertheless, VIG failed to protect VACV-WR challenged immune-deficient mice, even though repeated injections prolonged SCID mice survival. These results suggest the involvement of host immunity in protection. VIG provides the initial protective time-window allowing induction of the adaptive response required to achieve complete protection. Additionally, VIG can be administered in conjunction with active Vaccinia-Lister vaccination. Vaccine efficiency is not impaired, providing a non-prohibitive VIG dose is used. Thus, VIG can be used as a prophylactic measure against post-vaccinal complications but could also serve for post-exposure treatment against smallpox.

Rac GTPases are key regulators of leukocyte motility. In lymphocytes, chemokine-mediated Rac activation depends on the CDM adaptor DOCK2. The present studies addressed the role of DOCK2 in chemokine-triggered lymphocyte adhesion and motility. Rapid chemokine-triggered activation of both LFA-1 and VLA-4 integrins took place normally in DOCK2–/– T lymphocytes under various shear flow conditions. Consequently, DOCK2–/– T cells arrested normally on TNFα-activated endothelial cells in response to integrin stimulatory chemokine signals, and their resistance to detachment was similar to that of wild-type (wt) T lymphocytes. Nevertheless, DOCK2–/– T lymphocytes exhibited reduced microvillar collapse and lamellipodium extension in response to chemokine signals, ruling out a role for these events in integrin-mediated adhesion strengthening. Strikingly, arrested DOCK2–/– lymphocytes transmigrated through a CCL21-presenting endothelial barrier with similar efficiency and rate as wt lymphocytes but, unlike wt lymphocytes, could not locomote away from the transmigration site of the basal endothelial side. DOCK2–/– lymphocytes also failed to laterally migrate over multiple integrin ligands coimmobilized with chemokines. This is a first indication that T lymphocytes use 2 different chemokine-triggered actin remodeling programs: the first, DOCK2 dependent, to locomote laterally along apical and basal endothelial surfaces; the second, DOCK2 independent, to cross through a chemokine-bearing endothelial barrier.

Cadherins are a family of transmembrane glycoproteins mediating calcium-dependent, homophilic cell–cell adhesion. In addition, these molecules are involved in signaling events, regulating such processes as cell motility, proliferation, and apoptosis. Members of the cadherin subfamily, called either classical or type I cadherins, contain a highly conserved sequence at their homophilic binding site consisting of the three amino acids—histidine-alanine-valine (HAV). Previous studies have shown that peptides containing the HAV motif inhibit cadherin-dependent events such as cell aggregation, compaction, and neurite outgrowth. We report here that a cyclic peptide, N-Ac- CHAVC -NH 2 can perturb cadherin-mediated endothelial cell interactions, resulting in a progressive apoptotic cell death. This effect depends on cell density, as it is only observed when dense cultures are treated with the peptide. Adherens junction (AJ)-associated cadherin and catenins are differentially affected by the N-Ac- CHAVC -NH 2 treatment, as judged by double immunofluorescence labeling followed by immunofluorescence-ratio imaging. However, cell–cell adhesions are largely retained during the first few hours after addition of the peptide. It was also observed that following treatment, actin filaments partially lose their plasma membrane anchorage at AJs and translocate towards the cell center. Interestingly, addition of basic fibroblast growth factor to confluent, peptide-treated, endothelial cell cultures, completely blocks apoptosis and the inhibitory peptide reduce the phosphorylation of the FGF receptor target protein FRS2, suggesting that the peptide exerts its effect by inhibiting cadherin-mediated activation of fibroblast growth factor receptor signaling. We propose that cadherin-mediated signaling is essential for maintaining viability of confluent endothelial cells, and that its perturbation by N-Ac- CHAVC -NH 2 drives these cells to apoptosis.

Vaccinia virus protein A33 (A33VACV) plays an important role in protection against orthopoxviruses, and hence is included in experimental multi-subunit smallpox vaccines. In this study we show that single-dose vaccination with recombinant Sindbis virus expressing A33VACV, is sufficient to protect mice against lethal challenge with vaccinia virus WR (VACV-WR) and ectromelia virus (ECTV) but not against cowpox virus (CPXV), a closely related orthopoxvirus. Moreover, a subunit vaccine based on the cowpox virus A33 ortholog (A33CPXV) failed to protect against cowpox and only partially protected mice against VACV-WR challenge. We mapped regions of sequence variation between A33VACV and A33CPXVand analyzed the role of such variations in protection. We identified a single protective region located between residues 104–120 that harbors a putative H-2Kd T cell epitope as well as a B cell epitope - a target for the neutralizing antibody MAb-1G10 that blocks spreading of extracellular virions. Both epitopes in A33CPXV are mutated and predicted to be non-functional. Whereas vaccination with A33VACV did not induce in-vivo CTL activity to the predicted epitope, inhibition of virus spread in-vitro, and protection from lethal VACV challenge pointed to the B cell epitope highlighting the critical role of residue L118 and of adjacent compensatory residues in protection. This epitope’s critical role in protection, as well as its modifications within the orthopoxvirus genus should be taken in context with the failure of A33 to protect against CPXV as demonstrated here. These findings should be considered when developing new subunit vaccines and monoclonal antibody based therapeutics against orthopoxviruses, especially variola virus, the etiologic agent of smallpox.

Background Ectromelia virus, a member of the Orthopox genus, is the causative agent of the highly infectious mousepox disease. Previous studies have shown that different poxviruses induce cell-cell fusion which is manifested by the formation of multinucleated-giant cells (polykaryocytes). This phenomenon has been widely studied with vaccinia virus in conditions which require artificial acidification of the medium. Results We show that Ectromelia virus induces cell-cell fusion under neutral pH conditions and requires the presence of a sufficient amount of viral particles on the plasma membrane of infected cells. This could be achieved by infection with a replicating virus and its propagation in infected cells (fusion "from within") or by infection with a high amount of virus particles per cell (fusion "from without"). Inhibition of virus maturation or inhibition of virus transport on microtubules towards the plasma membrane resulted in a complete inhibition of syncytia formation. We show that in contrast to vaccinia virus, Ectromelia virus induces cell-cell fusion irrespectively of its hemagglutination properties and cell-surface expression of the orthologs of the fusion inhibitory complex, A56 and K2. Additionally, cell-cell fusion was also detected in mice lungs following lethal respiratory infection. Conclusion Ectromelia virus induces spontaneous cell-cell fusion in-vitro and in-vivo although expressing an A56/K2 fusion inhibitory complex. This syncytia formation property cannot be attributed to the 37 amino acid deletion in ECTV A56.