Differential Response Following Infection of Mouse CNS with Virulent and Attenuated Vaccinia Virus Strains.

Viral infections of the central nervous system (CNS) lead to a broad range of pathologies. CNS infections with Orthopox viruses have been mainly documented as an adverse reaction to smallpox vaccination with vaccinia virus. To date, there is insufficient data regarding the mechanisms underlying pathological viral replication or viral clearance. Therefore, informed risk assessment of vaccine adverse reactions or outcome prediction is limited. This work applied a model of viral infection of the CNS, comparing neurovirulent with attenuated strains. We followed various parameters along the disease and correlated viral load, morbidity, and mortality with tissue integrity, innate and adaptive immune response and functionality of the blood⁻brain barrier. Combining these data with whole brain RNA-seq analysis performed at different time points indicated that neurovirulence is associated with host immune silencing followed by induction of tissue damage-specific pathways. In contrast, brain infection with attenuated strains resulted in rapid and robust induction of innate and adaptive protective immunity, followed by viral clearance and recovery. This study significantly improves our understanding of the mechanisms and processes determining the consequence of viral CNS infection and highlights potential biomarkers associated with such outcomes.

Induction, treatment and prevention of eczema vaccinatum in atopic dermatitis mouse models.

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.

TLR3 and TLR9 agonists improve postexposure vaccination efficacy of live smallpox vaccines.

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.

Active vaccination with vaccinia virus A33 protects mice against lethal vaccinia and ectromelia viruses but not against cowpoxvirus; elucidation of the specific adaptive immune response.

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.

A single cidofovir treatment rescues animals at progressive stages of lethal orthopoxvirus disease.

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.

Complement-bound human antibodies to vaccinia virus B5 antigen protect mice from virus challenge.

The mechanism of protection afforded by vaccinia virus (VACV) - the smallpox vaccine - is a key issue for the development of modern vaccines and countermeasures. Antibodies to VACV antigens of the extracellular virion (EV) form play a central role in protection against poxvirus diseases in animal models, and contribute to the protection of immunized humans against poxviruses. B5, a viral EV protein, is conserved among different orthopoxviruses and antibodies to B5 that protect mice against VACV challenge. Antibodies to B5 are primarily responsible for neutralization of vaccinia EVs, yet the mechanism of EV neutralization by antibodies to B5 is not fully understood. The paper under evaluation demonstrates that most of the neutralization in vitro and protection in vivo in a mouse model, by monoclonal human anti-B5 IgGs, is heavily dependent on the ability of the IgGs to bind complement (C3 and C1q). Similarly, IgGs capable of complement binding control complement-dependent cytotoxicity of VACV-infected cells. Human polyclonal antibodies induced by the smallpox vaccine were similarly dependent on complement for EV neutralization and the complement-dependent destruction of infected cells. These findings not only contribute to a better understanding of the mechanism of protection by antibodies, but might also help in the development and evaluation of newly-developed therapeutic and prophylactic antibody-based products against virulent orthopoxviruses, and for the prevention or treatment of smallpox vaccine-related post-vaccinal adverse effects.

Induction of cell-cell fusion by ectromelia virus is not inhibited by its fusion inhibitory complex.

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.

Effective post-exposure protection against lethal orthopoxviruses infection by vaccinia immune globulin involves induction of adaptive immune response.

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.

Postexposure immunization with modified vaccinia virus Ankara or conventional Lister vaccine provides solid protection in a murine model of human smallpox.

BACKGROUND: Decades after the cessation of smallpox vaccination, the potential of the deliberate release of pathogenic 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: We tested the rapid protective capacity of vaccines based on VACV strain Lister (VACV-Lister) and on 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.

Tail scarification with Vaccinia virus Lister as a model for evaluation of smallpox vaccine potency in mice.

Since smallpox eradication by the WHO during the 1980s, potency of new vaccines is compared to vaccines that were used during the eradication campaign. In this work we characterize the tail scarification technique in mice as a model for scarification in humans. Similar to humans, mice develop "clinical take" which is dependent on the vaccination dose. Appearance of anti-Vaccinia IgM is followed by IgG antibodies 10 days post scarification and lasting more then 1(1/2) years. Mice with "clinical take" are 100% protected against lethal respiratory challenge (100LD(50)) of Vaccinia WR indicating that the "clinical take" can serve as a correlate of protective immunity. Reducing the vaccination dose and using Cowpox virus as a more virulent strain, enabled us to draw the limit of the vaccine potency in mice. Similar to humans, in revaccinated mice the development of "clinical take" was inversely correlated to the level of pre-existing antibodies. These results indicate that tail scarification of mice can be used as a model for evaluation of smallpox vaccines. High correlation between "clinical take" and protective immunity allows the use of visual inspection to evaluate vaccine potency.

Adjuvant-enhanced antibody responses to recombinant proteins correlates with protection of mice and monkeys to orthopoxvirus challenges.

Recombinant proteins are being evaluated as smallpox and monkeypox vaccines because of their perceived safety compared to live vaccinia virus. Previously, we demonstrated that three or more injections of a Ribi-type adjuvant with a combination of three proteins from the outer membranes of intracellular (L1 protein) and extracellular (A33 and B5 proteins) forms of vaccinia virus protected mice against a lethal intranasal challenge with vaccinia virus. Here, we compared several adjuvants and found that QS-21 and to a lesser extent alum+CpG oligodeoxynucleotides accelerated and enhanced neutralizing antibody responses to a mixture of L1 and A33 proteins, provided the highest ratio of IgG2a to IgG1 isotype response, and protected mice against disease and death after only two immunizations 3 weeks apart. In addition, monkeys immunized with recombinant vaccinia virus proteins and QS-21 developed neutralizing antibody to monkeypox virus and had reduced virus load, skin lesions, and morbidity compared to the non-immunized group following monkeypox virus challenge.

Double labeling and simultaneous detection of B- and T cells using fluorescent nano-crystal (q-dots) in paraffin-embedded tissues.

A double immunohistochemical technique for the simultaneous detection of T- and B cells in paraffin-embedded mice tissues have been developed. This procedure is based on using fluorescent nano-crystals (q-dots). The benefit of using q-dots evolves from their unique fluorescence characteristics advantages: such as broad excitation spectrum, narrow emission band and high photo-bleaching threshold compare to organic fluorophores. T cells antigens (CD3) were stained using antibody-coated q-dots with max emission at 655 nm (GalphaRb-QD655). B cells antigens (CD45R/B220) were stained using streptavidin-coated q-dots with max emission at 585 nm (SA-QD585). The simultaneous detection of T- and B cells was demonstrated in paraffin-embedded lymph node using standard fluorescence microscope.

Combinations of polyclonal or monoclonal antibodies to proteins of the outer membranes of the two infectious forms of vaccinia virus protect mice against a lethal respiratory challenge.

Previous studies demonstrated that antibodies to live vaccinia virus infection are needed for optimal protection against orthopoxvirus infection. The present report is the first to compare the protective abilities of individual and combinations of specific polyclonal and monoclonal antibodies that target proteins of the intracellular (IMV) and extracellular (EV) forms of vaccinia virus. The antibodies were directed to one IMV membrane protein, L1, and to two outer EV membrane proteins, A33 and B5. In vitro studies showed that the antibodies to L1 neutralized IMV and that the antibodies to A33 and B5 prevented the spread of EV in liquid medium. Prophylactic administration of individual antibodies to BALB/c mice partially protected them against disease following intranasal challenge with lethal doses of vaccinia virus. Combinations of antibodies, particularly anti-L1 and -A33 or -L1 and -B5, provided enhanced protection when administered 1 day before or 2 days after challenge. Furthermore, the protection was superior to that achieved with pooled immune gamma globulin from human volunteers inoculated with live vaccinia virus. In addition, single injections of anti-L1 plus anti-A33 antibodies greatly delayed the deaths of severe combined immunodeficiency mice challenged with vaccinia virus. These studies suggest that antibodies to two or three viral membrane proteins optimally derived from the outer membranes of IMV and EV, may be beneficial for prophylaxis or therapy of orthopoxvirus infections.

Development of a tissue-culture-based enzyme-immunoassay method for the quantitation of anti-vaccinia-neutralizing antibodies in human sera.

Vaccination with vaccinia virus is carried out in order to induce protection against variola virus, the causative agent of smallpox. Serum titer of vaccinia virus-neutralizing antibodies is considered to be well-correlated with in vivo protection. Plaque reduction neutralization test (PRNT) is the gold standard for detecting and quantifying vaccinia virus-neutralizing antibodies in sera of vaccinees. However, PRNT is time and labor consuming, which does not allow large-scale screening needed for a population survey. A simplified, sensitive, standardized, reproducible and rapid method, neutralization tissue-culture enzyme immunoassay (NTC-EIA) was developed for quantitation of neutralizing antibodies against vaccinia virus. The assay consists of the following steps: neutralization of the virus with serially diluted sera, infection of cells in culture and measurement of residual virus replication using an enzyme immunoassay. The assay can be used for animal (rabbit) or human sera. Titer averages obtained using NTC-EIA were highly correlated (R2=0.9994) to those obtained using PRNT. The assay is carried out in 96-well plates and takes only 2 days to complete. With the appropriate setup, it can be automated fully to allow screening of a large number of sera.

Protective immunity to vaccinia virus induced by vaccination with multiple recombinant outer membrane proteins of intracellular and extracellular virions.

Infectious intracellular and extracellular forms of vaccinia virus have different outer membrane proteins, presenting multiple targets to the immune system. We investigated the immunogenicity of soluble forms of L1, an outer membrane protein of the intracellular mature virus, and of A33 and B5, outer membrane proteins of the extracellular enveloped virus. The recombinant proteins, in 10-microg amounts mixed with a Ribi- or saponin-type adjuvant, were administered subcutaneously to mice. Antibody titers to each protein rose sharply after the first and second boosts, reaching levels that surpassed those induced by percutaneous immunization with live vaccinia virus. Immunoglobulin G1 (IgG1) antibody predominated after the protein immunizations, indicative of a T-helper cell type 2 response, whereas live vaccinia virus induced mainly IgG2a, indicative of a T-helper cell type 1 response. Mice immunized with any one of the recombinant proteins survived an intranasal challenge with 5 times the 50% lethal dose of the pathogenic WR strain of vaccinia virus. Measurements of weight loss indicated that the A33 immunization most effectively prevented disease. The superiority of protein combinations was demonstrated when the challenge virus dose was increased 20-fold. The best protection was obtained with a vaccine made by combining recombinant proteins of the outer membranes of intracellular and extracellular virus. Indeed, mice immunized with A33 plus B5 plus L1 or with A33 plus L1 were better protected than mice immunized with live vaccinia virus. Three immunizations with the three-protein combination were necessary and sufficient for complete protection. These studies suggest the feasibility of a multiprotein smallpox vaccine.

Clinical and immune responses after revaccination of israeli adults with the Lister strain of vaccinia virus.

BACKGROUND: During the winter of 2002-2003, the Israeli health authorities launched a campaign to vaccinate first responders against smallpox. METHODS: In an open study, 159 healthy, preimmunized adults, 24-52 years old, who participated in the campaign were vaccinated with the Lister strain of vaccinia virus by the multipuncture technique. The safety, immunogenicity, and reactogenicity of the vaccine were assessed. RESULTS: Successful vaccination rates were 61% and 56%, on the basis of clinical take and seroconversion, respectively. Adverse events among the vaccinees were minor. Seventy-nine (88%) of the 90 vaccinees with clinical take also seroconverted ( kappa =0.779). The level of preexisting antibodies inversely correlated with the rates of clinical take and seroconversion (P

Synergistic neutralizing activities of antibodies to outer membrane proteins of the two infectious forms of vaccinia virus in the presence of complement.

The two forms of infectious vaccinia virus particles, known as intracellular mature virions and extracellular enveloped virions, are liberated by cell lysis and exocytosis, respectively. The extracellular enveloped form, which is highly resistant to antibody neutralization, contains an outer membrane surrounding an intracellular mature form. We provide evidence that complement mediates antibody-dependent lysis of the outer membrane of extracellular virus, exposing the inner infectious virus to neutralization by a second antibody. These results can help explain the disparity between the in vitro neutralizing and in vivo protective effects of antibodies to extracellular envelope proteins as well as the enhanced protection afforded by specific combinations of antibodies.

Prophylactic and therapeutic efficacy of human intravenous immunoglobulin in treating West Nile virus infection in mice.

West Nile virus (WNV) is a mosquito-borne disease found most commonly in Africa, West Asia, and the Middle East, where up to 40% of the human population possesses antibodies. It is an emerging disease in the United States. Humans infected with WNV develop a febrile illness that can progress to meningitis or encephalitis. In mice, WNV causes central nervous system infection, paralysis, encephalitis, and death. Currently, no specific therapy or vaccine has been approved for human use. We examined the prophylactic and therapeutic efficacy of pooled human plasma (PP) and intravenous immunoglobulin (IVIG) for treatment of WNV-infected mice. Full protection was achieved when the infected mice were treated with pooled plasma or IVIG obtained from healthy Israeli blood donors that contained WNV-specific antibodies. Similar treatments using PP or IVIG obtained from US blood donors had no protective effect. Recovery of the lethally infected mice was dependent on the dose and time of IVIG administration. These results indicate that antibodies play a major role in protection and recovery from WNV infection and that IVIG can be used as first-line therapy.

Inactivation of West-Nile virus during peptic cleavage of horse plasma IgG.

Peptic cleavage of horse plasma IgG is a common procedure for the preparation of F(ab)(2) products for human use, such as antivenin and antitoxin. The removal of the Fc fragment from the IgG molecule by enzymatic cleavage at low pH, ensures fewer side-effects of the F(ab)(2) product for passive immunotherapy compared with the whole IgG molecule. Since the starting material may be contaminated by zoonotic horse viruses, it is necessary to demonstrate the removal or inactivation of possible viral contaminants. Guidelines for performing such studies were published by the Commission for Plasma-Derived Medical Products (CPMP), and updated by the Committee for Proprietary Medical Products. It is recommended that viral clearance studies be performed on scaled down production processes that have been identified as possibly contributing to virus clearance and spiking of a model virus to the starting material. The model virus should be non-pathogenic but closely related to the potential infective virus. By quantifying the amount of virus in the product before and after the production process, the amount of virus cleared can be determined. Log(10) reductions of the order of 4 logs or more, and a biphasic inactivation curve (fast initial phase followed by a slower phase), are indicative of a clearance effect with a particular test virus under investigation.