Smallpox vaccination in a mouse model

The monkeypox epidemic, which became unusually widespread among humans in 2022, has brought awareness about the necessity of smallpox vaccination of patients in the risk groups. The modern smallpox vaccine variants are introduced either intramuscularly or by skin scarification. Intramuscular vaccination cannot elicit an active immune response, since tissues at the vaccination site are immunologically poor. Skin has evolved into an immunologically important organ in mammals; therefore, intradermal delivery of a vaccine can ensure reliable protective immunity. Historically, vaccine inoculation into scarified skin (the s.s. route) was the first immunization method. However, it does not allow accurate vaccine dosing, and high-dose vaccines need to be used to successfully complete this procedure. Intradermal (i.d.) vaccine injection, especially low-dose one, can be an alternative to the s.s. route. This study aimed to compare the s.s. and i.d. smallpox immunization routes in a mouse model when using prototypic second- and fourth-generation low-dose vaccines (104 pfu). Experiments were conducted using BALB/c mice; the LIVP or LIVP-GFP strains of the vaccinia virus (VACV) were administered into the tail skin via the s.s. or i.d. routes. After vaccination (7, 14, 21, 28, 42, and 56 days post inoculation (dpi)), blood samples were collected from the retro-orbital venous sinus; titers of VACV-specific IgM and IgG in the resulting sera were determined by ELISA. Both VACV strains caused more profound antibody production when injected via the i.d. route compared to s.s. inoculation. In order to assess the level of the elicited protective immunity, mice were intranasally infected with a highly lethal dose of the cowpox virus on 62 dpi. The results demonstrated that i.d. injection ensures a stronger protective immunity in mice compared to s.s. inoculation for both VACV variants.

Correlated Target Search by Vaccinia Virus Uracil-DNA Glycosylase, a DNA Repair Enzyme and a Processivity Factor of Viral Replication Machinery

The protein encoded by the vaccinia virus D4R gene has base excision repair uracil-DNA N-glycosylase (vvUNG) activity and also acts as a processivity factor in the viral replication complex. The use of a protein unlike PolN/PCNA sliding clamps is a unique feature of orthopoxviral replication, providing an attractive target for drug design. However, the intrinsic processivity of vvUNG has never been estimated, leaving open the question whether it is sufficient to impart processivity to the viral polymerase. Here, we use the correlated cleavage assay to characterize the translocation of vvUNG along DNA between two uracil residues. The salt dependence of the correlated cleavage, together with the similar affinity of vvUNG for damaged and undamaged DNA, support the one-dimensional diffusion mechanism of lesion search. Unlike short gaps, covalent adducts partly block vvUNG translocation. Kinetic experiments show that once a lesion is found it is excised with a probability ~0.76. Varying the distance between two uracils, we use a random walk model to estimate the mean number of steps per association with DNA at ~4200, which is consistent with vvUNG playing a role as a processivity factor. Finally, we show that inhibitors carrying a tetrahydro-2,4,6-trioxopyrimidinylidene moiety can suppress the processivity of vvUNG.

Smallpox, Monkeypox and Other Human Orthopoxvirus Infections

Considering that vaccination against smallpox with live vaccinia virus led to serious adverse effects in some cases, the WHO, after declaration of the global eradication of smallpox in 1980, strongly recommended to discontinue the vaccination in all countries. This led to the loss of immunity against not only smallpox but also other zoonotic orthopoxvirus infections in humans over the past years. An increasing number of human infections with zoonotic orthopoxviruses and, first of all, monkeypox, force us to reconsider a possible re-emergence of smallpox or a similar disease as a result of natural evolution of these viruses. The review contains a brief analysis of the results of studies on genomic organization and evolution of human pathogenic orthopoxviruses, development of modern methods for diagnosis, vaccination, and chemotherapy of smallpox, monkeypox, and other zoonotic human orthopoxvirus infections.

Enhancing the Immunogenicity of Vaccinia Virus

The conventional live smallpox vaccine based on the vaccinia virus (VACV) cannot be widely used today because it is highly reactogenic. Therefore, there is a demand for designing VACV variants possessing enhanced immunogenicity, making it possible to reduce the vaccine dose and, therefore, significantly eliminate the pathogenic effect of the VACV on the body. In this study, we analyzed the development of the humoral and T cell-mediated immune responses elicited by immunizing mice with low-dose VACV variants carrying the mutant A34R gene (which increases production of extracellular virions) or the deleted A35R gene (whose protein product inhibits antigen presentation by the major histocompatibility complex class II). The VACV LIVP strain, which is used as a smallpox vaccine in Russia, and its recombinant variants LIVP-A34R*, LIVP-dA35R, and LIVP-A34R*-dA35R, were compared upon intradermal immunization of BALB/c mice at a dose of 10⁴ pfu/animal. The strongest T cell-mediated immunity was detected in mice infected with the LIVP-A34R*-dA35R virus. The parental LIVP strain induced a significantly lower antibody level compared to the strains carrying the modified A34R and A35R genes. Simultaneous modification of the A34R gene and deletion of the A35R gene in VACV LIVP synergistically enhanced the immunogenic properties of the LIVP-A34R*-dA35R virus.

[Mutations in the A34R gene increase the immunogenicity of vaccinia virus]

Самым простым и надежным способом защиты от вирусных инфекций является вакцинопрофилактика. При этом наибольшей протективной эффективностью обладают живые вакцины, в основе которых используют слабовирулентные для человека вирусы, близкородственные патогенным, или аттенуированные (ослабленные за счет мутаций/делеций в вирусном геноме) варианты патогенного для человека вируса. Вакцинация против оспы с использованием живого вируса осповакцины (vaccinia virus, VACV), близкородственного вирусу натуральной оспы, сыграла важнейшую роль в успехе программы глобальной ликвидации оспы, которая осуществлялась под эгидой Всемирной организации здравоохранения. Прекращение после 1980 г. противооспенной вакцинации привело к тому, что огромная часть населения Земли в настоящее время не имеет иммунитета не только к оспе, но и любым другим зоонозным ортопоксвирусным инфекциям. Это создает возможность циркуляции зоонозных ортопоксвирусов в человеческой популяции и, как следствие, приводит к изменению экологии и круга чувствительных хозяев для разных видов ортопоксвирусов. При этом использование классической живой вакцины на основе VACV для защиты от этих инфекций в настоящее время не приемлемо, так как она может обусловливать тяжелые побочные реакции. В связи с этим все более актуальной становится разработка новых безопасных вакцин против ортопоксвирусных инфекций человека и животных. Аттенуация (ослабление вирулентности) VACV достигается в результате направленной инактивации определенных генов вируса и обычно приводит к уменьшению эффективности размножения VACV in vivo. Следствием этого может быть снижение иммунного ответа при введении аттенуированного вируса пациентам в стандартных дозах. Часто используемым для встройки/инактивации в геноме VACV является ген тимидинкиназы, нарушение которого приводит к аттенуации вируса. В данной работе изучено, как введение двух точечных мутаций в ген A34R аттенуированного штамма LIVP-GFP (ТК-), увеличивающих выход внеклеточных оболочечных вирионов (EEV), влияет на свойства пато- и иммуногенности варианта VACV LIVP-GFP-A34R при интраназальном заражении лабораторных мышей. Показано, что увеличение продукции EEV рекомбинантным штаммом VACV LIVP-GFP-A34R не меняет аттенуированный фенотип, характерный для родительского штамма LIVP-GFP, но приводит к существенно большей продукции VACV-специфичных антител. Ключевые слова: вирус осповакцины; направленные мутации; аттенуация; иммуногенность.

[We should be prepared to smallpox re-emergence.]

The review contains a brief analysis of the results of investigations conducted during 40 years after smallpox eradication and directed to study genomic organization and evolution of variola virus (VARV) and development of modern diagnostics, vaccines and chemotherapies of smallpox and other zoonotic orthopoxviral infections of humans. Taking into account that smallpox vaccination in several cases had adverse side effects, WHO recommended ceasing this vaccination after 1980 in all countries of the world. The result of this decision is that the mankind lost the collective immunity not only to smallpox, but also to other zoonotic orthopoxvirus infections. The ever more frequently recorded human cases of zoonotic orthopoxvirus infections force to renew consideration of the problem of possible smallpox reemergence resulting from natural evolution of these viruses. Analysis of the available archive data on smallpox epidemics, the history of ancient civilizations, and the newest data on the evolutionary relationship of orthopoxviruses has allowed us to hypothesize that VARV could have repeatedly reemerged via evolutionary changes in a zoonotic ancestor virus and then disappeared because of insufficient population size of isolated ancient civilizations. Only the historically last smallpox pandemic continued for a long time and was contained and stopped in the 20th century thanks to the joint efforts of medics and scientists from many countries under the aegis of WHO. Thus, there is no fundamental prohibition on potential reemergence of smallpox or a similar human disease in future in the course of natural evolution of the currently existing zoonotic orthopoxviruses. Correspondingly, it is of the utmost importance to develop and widely adopt state-of-the-art methods for efficient and rapid species-specific diagnosis of all orthopoxvirus species pathogenic for humans, VARV included. It is also most important to develop new safe methods for prevention and therapy of human orthopoxvirus infections.

Effect of the Route of Administration of the Vaccinia Virus Strain LIVP to Mice on Its Virulence and Immunogenicity

The mass smallpox vaccination campaign has played a crucial role in smallpox eradication. Various strains of the vaccinia virus (VACV) were used as a live smallpox vaccine in different countries, their origin being unknown in most cases. The VACV strains differ in terms of pathogenicity exhibited upon inoculation of laboratory animals and reactogenicity exhibited upon vaccination of humans. Therefore, each generated strain or clonal variant of VACV needs to be thoroughly studied in in vivo systems. The clonal variant 14 of LIVP strain (LIVP-14) was the study object in this work. A comparative analysis of the virulence and immunogenicity of LIVP-14 inoculated intranasally (i.n.), intradermally (i.d.), or subcutaneously (s.c.) to BALB/c mice at doses of 108, 107, and 106 pfu was carried out. Adult mice exhibited the highest sensitivity to the i.n. administered LIVP-14 strain, although the infection was not lethal. The i.n. inoculated LIVP-14 replicated efficiently in the lungs. Furthermore, this virus was accumulated in the brain at relatively high concentrations. Significantly lower levels of LIVP-14 were detected in the liver, kidneys, and spleen of experimental animals. No clinical manifestations of the disease were observed after i.d. or s.c. injection of LIVP-14 to mice. After s.c. inoculation, the virus was detected only at the injection site, while it could disseminate to the liver and lungs when delivered via i.d. administration. A comparative analysis of the production of virus-specific antibodies by ELISA and PRNT revealed that the highest level of antibodies was induced in i.n. inoculated mice; a lower level of antibodies was observed after i.d. administration of the virus and the lowest level after s.c. injection. Even at the lowest studied dose (106 pfu), i.n. or i.d. administered LIVP-14 completely protected mice against infection with the cowpox virus at the lethal dose. Our findings imply that, according to the ratio between such characteristics as pathogenicity/immunogenicity/protectivity, i.d. injection is the optimal method of inoculation with the VACV LIVP-14 strain to ensure the safe formation of immune defense after vaccination against orthopoxviral infections.

Anti-inflammatory Effects of Variola Virus TNF Decoy Receptor in an Experimental Model of Contact Dermatitis

BACKGROUND

Large DNA poxviruses encode a diverse family of secreted proteins that modulate host inflammatory and antiviral responses, in particular by inhibiting one of the key players of the mammalian immune system, the tumor necrosis factor (TNF).

METHODS

We investigated the effects of a recombinant variola (smallpox) virus TNF-decoy receptor (VARV-CrmB) in a murine model of contact dermatitis. Our results demonstrate that the VARV-CrmB protein significantly reduces the 2,4-dinitrochlorbenzene (DNCB)-induced migration of skin leukocytes during the sensitization phase and suppresses ear oedema during the elicitation phase of the contact reaction.

RESULTS

Studies focusing on the bone marrow hematopoiesis in the contact dermatitis model revealed that the epicutaneous co-application of DNCB and VARV-CrmB protein normalized the DNCBinduced effects to control levels.

CONCLUSION

As an effective TNF antagonist, the VARV-CrmB protein might be conceived as a beneficial candidate for further research and development of therapeutic approaches in the field of the inflammatory skin diseases.

Virotherapy of the Malignant U87 Human Glioblastoma in the Orthotopic Xenotransplantation Mouse SCID Model

The possibility of glioblastoma virotherapy at intravenous injection of the LIVP-GFP recombinant virus was studied in experimental model of orthotopic xenotransplantation of human glioblastoma cell line U87 to SCID laboratory mice. The LIVP-GFP recombinant virus deficient for thymidine kinase exhibited a significantly greater oncolytic capacity than the original LIVP virus, and an intravenous injection of LIVP-GFP at the early stages of tumorigenesis in mouse brain in most cases resulted in the lysis of the tumor.

Are We Prepared in Case of a Possible Smallpox-Like Disease Emergence?

Smallpox was the first human disease to be eradicated, through a concerted vaccination campaign led by the World Health Organization. Since its eradication, routine vaccination against smallpox has ceased, leaving the world population susceptible to disease caused by orthopoxviruses. In recent decades, reports of human disease from zoonotic orthopoxviruses have increased. Furthermore, multiple reports of newly identified poxviruses capable of causing human disease have occurred. These facts raise concerns regarding both the opportunity for these zoonotic orthopoxviruses to evolve and become a more severe public health issue, as well as the risk of Variola virus (the causative agent of smallpox) to be utilized as a bioterrorist weapon. The eradication of smallpox occurred prior to the development of the majority of modern virological and molecular biological techniques. Therefore, there is a considerable amount that is not understood regarding how this solely human pathogen interacts with its host. This paper briefly recounts the history and current status of diagnostic tools, vaccines, and anti-viral therapeutics for treatment of smallpox disease. The authors discuss the importance of further research to prepare the global community should a smallpox-like virus emerge.

Species-specific differentiation of variola, monkeypox, and varicella-zoster viruses by multiplex real-time PCR assay

A method of one-stage rapid detection and differentiation of epidemiologically important variola virus (VARV), monkeypox virus (MPXV), and varicella-zoster virus (VZV) utilizing multiplex real-time TaqMan PCR assay was developed. Four hybridization probes with various fluorescent dyes and the corresponding fluorescence quenchers were simultaneously used for the assay. The hybridization probes specific for the VARV sequence contained FAM/BHQ1 as a dye/quencher pair; MPXV-specific, JOE/BHQ1; VZV-specific, TAMRA/BHQ2; and internal control-specific, Cy5/BHQ3. The specificity and sensitivity of the developed method were assessed by analyzing DNA of 32 strains belonging to orthopoxvirus and herpesvirus species.

The gene therapy of collagen-induced arthritis in rats by intramuscular administration of the plasmid encoding TNF-binding domain of variola virus CrmB protein

Wistar rats with collagen-induced arthritis were intramuscularly injected with the recombinant plasmid pcDNA/sTNF-BD encoding the sequence of the TNF-binding protein domain of variola virus CrmB protein (VARV sTNF-BD) or the pcDNA3.1 vector. Quantitative analysis showed that the histopathological changes in the hind-limb joints of rats were most severe in the animals injected with pcDNA3.1 and much less severe in the group of rats injected with pcDNA/sTNF-BD, which indicates that gene therapy of rheumatoid arthritis is promising in the case of local administration of plasmids governing the synthesis of VARV immunomodulatory proteins.

[Gene therapy of arthritis]

Gene therapy can offer a new approach to arthritis treatment which acts at an inflammation site. Numerous studies show high efficacy of gene therapy in different models of arthritis in humans. Even a single injection of a recombinant vector results in a stable prolonged expression of a therapeutic gene and a longterm therapeutic effect. In contrast to biologic therapy involving numerous systemic injections of recombinant anti-inflammatory proteins, gene therapy does not produce systemic side effects. Vectors based on retroviruses, adenoviruses, adeno-associated viruses, and recombinant plasmids could provide delivery of target genes. Of significant importance is the development of noninvasive methods of gene therapy: intranasal and peroral. The current state of research in arthritis gene therapy is discussed in this review.

Highly immunogenic variant of attenuated vaccinia virus

The LIVPΔ6 strain of vaccinia virus (VACV) was created by genetic engineering on the basis of previously obtained attenuated 1421ABJCN strain by target deletion of the A35R gene encoding an inhibitor of antigen presentation by the major histocompatibility complex class II. 1421ABJCN is the LIVP strain of VACV with five inactivated virulence genes encoding hemagglutinin (A56R), γ-interferon-binding protein (B8R), thymidine kinase (J2R), complement-binding protein (C3L), and Bcl2-like inhibitor of apoptosis (N1L). The highly immunogenic LIVPΔ6 strain could be an efficient fourth-generation attenuated vaccine against smallpox and other orthopoxvirus infections.

TNF binding protein of variola virus acts as a TNF antagonist at epicutaneous application

VARV-CrmB is a TNF binding protein of variola virus. VARV-CrmB protein was previously shown to be active as a TNF-antagonist in a number of in vivo and in vitro models. Here we investigated the epicutaneous effect of recombinant VARV-CrmB protein using an experimental model of muTNFinduced migration of skin leukocytes as well as colony forming activity of bone marrow cells (BMC). Epiсutaneous applications of muTNF enhanced the number of cells migrating from skin flaps of BALB/c mice, whereas subsequent applications of VARV-CrmB protein in 30 min after muTNF, abolished that effect. Epicutaneously applied muTNF influenced the activity of committed hematopoietic progenitors causing a reduction of erythroid (BFUe+CFUe) colonies and increase of granulocyte-macrophage (CFU-GM) colonies in the colony-forming tests. VARV-CrmB, applied in combination with muTNF, demonstrated an ability to reverse this effect, namely, to increase BFUe+CFUe and reduce CFU-GM back to the control levels. Taking together, these data demonstrate the TNF-blocking properties of VARV-CrmB in vivo at epicutaneous applications. As effective TNF antagonist VARV-CrmB protein might be conceded as a beneficial candidate for future research and development of therapeutic approaches in the field of inflammatory skin diseases.

Exploring interaction of TNF and orthopoxviral CrmB protein by surface plasmon resonance and free energy calculation

Inhibition of the activity of the tumor necrosis factor (TNF) has become the main strategy for treating inflammatory diseases. The orthopoxvirus TNF-binding proteins can bind and efficiently neutralize TNF. To analyze the mechanisms of the interaction between human (hTNF) or mouse (mTNF) TNF and the cowpox virus N-terminal binding domain (TNFBD-CPXV), also the variola virus N-terminal binding domain (TNFBD-VARV) and to define the amino acids most importantly involved in the formation of complexes, computer models, derived from the X-ray structure of a homologous hTNF/TNFRII complex, were used together with experiments. The hTNF/TNFBD-CPXV, hTNF/TNFBD-VARV, mTNF/TNFBD-CPXV, and mTNF/TNFBD-VARV complexes were used in the molecular dynamics (MD) simulations and MM/GBSA free energy calculations. The complexes were ordered as hTNF/TNFBD-CPXV, hTNF/TNFBD-VARV, mTNF/TNFBD-CPXV and mTNF/TNFBD-VARV according to increase in the binding affinity. The calculations were in agreement with surface plasmon resonance (SPR) measurements of the binding constants. Key residues involved in complex formation were identified.

Real-time PCR assay for specific detection of cowpox virus

The species cowpox virus (CPXV), genus Orthopoxvirus (OPV), consists of isolates highly variable in their biological properties and their genotypes. A TaqMan PCR assay for the specific detection of CPXV DNA based on sequences of the ORF D11L has been developed recently. (Gavrilova et al., 2010; Shchelkunov et al., 2011); however, a rather limited panel of CPXV stains has been used. When a much larger panel of 47 CPXV DNAs has been tested, three strains could not be amplified at all because of large deletions in their respective ORF D11L. In addition, a deletion of 23bp led to low-efficiency detection of five other CPXV strains. To solve this problem a new primer/probe combinations was selected based on sequences of ORF D8L, and a new real-time PCR method for (i) a genus-specific detection of OPVs and (ii) a simultaneous CPXV-specific differentiation is described in this study. The specificity and sensitivity were assessed by analyzing DNA of 67 strains belonging to human-pathogenic OPV species, including variola virus, as well as specimens of CPXV-infected mice.

Biological effects of individually synthesized TNF-binding domain of variola virus CrmB protein

The biological characteristics of a 17-kDa protein synthesized in bacterial cells, a TNF-binding domain (VARV-TNF-BP) of a 47-kDa variola virus CrmB protein (VARV-CrmB) consisting of TNF-binding and chemokine-binding domains, were studied. Removal of the C-terminal chemokine-binding domain from VARV-CrmB protein was inessential for the efficiency of its inhibition of TNF cytotoxicity towards L929 mouse fibroblast culture and for TNF-induced oxidative metabolic activity of mouse blood leukocytes. The results of this study could form the basis for further studies of VARV-TNF-BP mechanisms of activity for prospective use in practical medicine.

An increasing danger of zoonotic orthopoxvirus infections

On May 8, 1980, the World Health Assembly at its 33^rd session solemnly declared that the world and all its peoples had won freedom from smallpox and recommended ceasing the vaccination of the population against smallpox. Currently, a larger part of the world population has no immunity not only against smallpox but also against other zoonotic orthopoxvirus infections. Recently, recorded outbreaks of orthopoxvirus diseases not only of domestic animals but also of humans have become more frequent. All this indicates a new situation in the ecology and evolution of zoonotic orthopoxviruses. Analysis of state-of-the-art data on the phylogenetic relationships, ecology, and host range of orthopoxviruses—etiological agents of smallpox (variola virus, VARV), monkeypox (MPXV), cowpox (CPXV), vaccinia (VACV), and camelpox (CMLV)—as well as the patterns of their evolution suggests that a VARV-like virus could emerge in the course of natural evolution of modern zoonotic orthopoxviruses. Thus, there is an insistent need for organization of the international control over the outbreaks of zoonotic orthopoxvirus infections in various countries to provide a rapid response and prevent them from developing into epidemics.

Emergence and reemergence of smallpox: the need for development of a new generation smallpox vaccine

The review summarizes the archive data on smallpox, history of ancient civilizations, and the most recent data on the genome organization of orthopoxviruses, their evolutionary relationships, and the time points of smallpox emergence. The performed analysis provides the grounds for the hypothesis that smallpox could have emerged several times as a result of evolutionary changes in the zoonotic ancestor virus and disappeared due to insufficient population size of ancient civilizations. Smallpox reemerged in the Indian subcontinent approximately 2500-3000 years before present, which resulted in endemization of this anthroponotic infection, which had been preserved until the smallpox eradication in the 20th century AD. The conclusion suggests a potential possibility of future variola virus reemergence, presenting a great menace for mankind, as well as the need for development of new safe smallpox vaccines, design of anti-smallpox drugs, and activation of the control of zoonotic human orthopoxvirus infections.

[Development of current smallpox vaccines]

The review gives data on the history of smallpox vaccination and shows the high topicality of designing the current safe vaccines against orthopoxviruses. Four generations of live smallpox, protein subunit, and DNA vaccines are considered. Analysis of the data published leads to the conclusion that it is promising to use the up-to-date generations of safe smallpox subunit or DNA vaccines for mass primary immunization with possible further revaccination with classical live vaccine.

[Evasion of mammalian organism defense systems by orthopoxviruses]

Viruses during their evolution have mastered various molecular mechanisms to evade the defense reactions of the host organism. When understanding the mechanisms used by viruses to overcome manifold defense systems of the animal organism, represented by molecular factors and cells of the immune system, we would not only comprehend better, but also discover new patterns of organization and function of these most important reactions directed against infectious agents. Here, study of the orthopoxviruses pathogenic for humans, such as variola, monkeypox, cowpox, and vaccinia viruses, may be most important. Analysis of the experimental data, carried out in this review, allows to infer that variola virus and other orthopoxviruses possess an unexampled set of genes whose protein products efficiently modulate the manifold defense mechanisms of the host organisms compared with the viruses from other families.

[Comparison of protective properties of the smallpox DNA-vaccine based on the variola virus A30L gene and its variant with modified codon usage]

Efficacy of candidate DNA-vaccines based on the variola virus natural gene A30L and artificial gene A30Lopt with modified codon usage, optimized for expression in mammalian cells, was tested. The groups of mice were intracutaneously immunized three times with three-week intervals with candidate DNA-vaccines: pcDNA_A30L or pcDNA_A30Lopt, and in three weeks after the last immunization all mice in the groups were intraperitoneally infected by the ectromelia virus K1 strain in 10 LD50 dose for the estimation of protection. It was shown that the DNA-vaccines based on natural gene A30L and codon-optimized gene A30Lopt elicited virus, thereby neutralizing the antibody response and protected mice from lethal intraperitoneal challenge with the ectromelia virus with lack of statistically significant difference.

[Modeling spatial structures of variola and cowpox virus TNF-binding CrmB proteins bound to murine or human TNF]

Orthopoxviruses bear in their genomes several genes coding for homologous secreted proteins able to bind tumor necrosis factor. Different species of the genus possess different sets of these tumor necrosis factor-binding proteins. Viriola virus encodes the only one of them named CrmB. Despite sharing high sequence identity, CrmB proteins belonging to distinct orthopoxviral species were shown to significantly differ by their physico-chemical and biological properties. We modeled spatial structures of tumor necrosis factor receptor domains of variola and cowpox virus CrmB proteins bound to either murine, or human or mutated human tumor necrosis factor. In the sequence of last the arginine residue at position 31 is substituted with glutamine that is characteristic for murine tumor necrosis factor. Theoretical analysis of modeled ligand-receptor complexes revealed that the least stable should be the complex of cowpox virus CrmB with human tumor necrosis factor, and that arginine to glutamine substitution at position 31 should significantly stabilize binding of corresponding human tumor necrosis factor mutant to cowpox virus CrmB. Experimental evaluation of recombinant variola and cowpox virus CrmB efficiencies in inhibiting cytotoxic effect of all these tumor necrosis factors have approved our predictions.

SECRET domain of variola virus CrmB protein can be a member of poxviral type II chemokine-binding proteins family

BACKGROUND

Variola virus (VARV) the causative agent of smallpox, eradicated in 1980, have wide spectrum of immunomodulatory proteins to evade host immunity. Recently additional biological activity was discovered for VARV CrmB protein, known to bind and inhibit tumour necrosis factor (TNF) through its N-terminal domain homologous to cellular TNF receptors. Besides binding TNF, this protein was also shown to bind with high affinity several chemokines which recruit B- and T-lymphocytes and dendritic cells to sites of viral entry and replication. Ability to bind chemokines was shown to be associated with unique C-terminal domain of CrmB protein. This domain named SECRET (Smallpox virus-Encoded Chemokine Receptor) is unrelated to the host proteins and lacks significant homology with other known viral chemokine-binding proteins or any other known protein.

FINDINGS

De novo modelling of VARV-CrmB SECRET domain spatial structure revealed its apparent structural homology with cowpox virus CC-chemokine binding protein (vCCI) and vaccinia virus A41 protein, despite low sequence identity between these three proteins. Potential ligand-binding surface of modelled VARV-CrmB SECRET domain was also predicted to bear prominent electronegative charge which is characteristic to known orthopoxviral chemokine-binding proteins.

CONCLUSIONS

Our results suggest that SECRET should be included into the family of poxviral type II chemokine-binding proteins and that it might have been evolved from the vCCI-like predecessor protein.

Interaction of orthopoxviruses with the cellular ubiquitin-ligase system

Protein modification by ubiquitin or ubiquitin-like polypeptides is important for the fate and functions of the majority of proteins in the eukaryotic cell and can be involved in regulation of various biological processes, including protein metabolism (degradation), protein transport to several cellular compartments, rearrangement of cytoskeleton, and transcription of cytoprotective genes. The accumulated experimental data suggest that the ankyrin-F-box-like and BTB-kelch-like proteins of orthopoxviruses, represented by the largest viral multigene families, interact with the cellular Cullin-1- and Cullin-3-containing ubiquitin-protein ligases, respectively. In addition, orthopoxviruses code for their own RING-domain-containing ubiquitin ligase. In this review, this author discusses the differences between variola (smallpox), monkeypox, cowpox, vaccinia, and ectromelia (mousepox) viruses in the organization of ankyrin-F-box and BTB-kelch protein families and their likely functions.

Development of real-time PCR assay for specific detection of cowpox virus

Background

The number of recorded human cowpox cases are recently increasing. The symptoms caused by cowpox virus (CPXV) in a number of human cases are close to the symptoms characteristic of the orthopoxviral human infections caused by monkeypox or smallpox (variola) viruses. Any rapid and reliable real-time PCR method for distinguishing cowpox from smallpox and monkeypox is yet absent.

Objectives

The aim of this study was to develop a quick and reliable real-time TaqMan PCR assay for specific detection of cowpox virus and to determine the sensitivity and specificity of this method.

Study design

Based on aligned nucleotide sequences of orthopoxviruses, we found a virus-specific region in the CPXV genome and selected the oligonucleotide primers and hybridization probe within this region. The specificity of the developed method was tested using a panel of various orthopoxvirus (OPV) DNAs. The sensitivity was determined using the recombinant plasmid carrying a fragment of CPXV DNA and genomic DNA of the CPXV strain GRI-90.

Results

The analytical specificity of this method was determined using DNAs of 17 strains of four OPV species pathogenic for humans and amounted to 100%. The method allows 6 copies of plasmid DNA and 20 copies of CPXV DNA in the reaction mixture to be detected.

Conclusion

A quick and reliable TaqMan PCR assay providing for a highly sensitive and specific detection of CPXV DNA was developed.

Recombinant TNF-binding protein from variola virus as a novel potential TNF antagonist

Gel-filtration chromatographic separation of the lysate of Sf21 insect cells infected with recombinant baculovirus BVi67 containing the gene for TNF-binding protein (CrmB) of variola virus (VARV) revealed that hTNF-cytotoxicity neutralization activity is associated with a fraction corresponding mainly to high molecular weight proteins (above 500 kDa) and less with fractions corresponding to proteins of 270 or 90 kDa. The recombinant VARV-CrmB protein has been purified by affinity chromatography. Difference in the experimentally determined and estimated (according to amino acid composition) VARV-CrmB molecular weight is due to glycosylation of the recombinant protein expressed in the insect cells. VARV-CrmB neutralizes in vitro the cytotoxic effect of hTNF and hLTalpha, and its TNF-neutralizing activity is two to three orders of magnitude higher compared to the analogous effects of type I and II soluble TNF receptors, comparable with the activity of mAb MAK195, and somewhat lower than the effect of the commercial drug Remicade.

[Identification of human pathogenic variola and monkeypox viruses by real-time polymerase chain reaction]

A kit of specific oligonucleotide primers and hybridization probes has been proposed to detect orthopoxviruses (OPV) and to discriminate human pathogenic viruses, such as variola virus and monkey virus by real-time polymerase chain reaction (PCR). For real-time PCR, the following pairs of fluorophore and a fluorescence quencher were used: TAMRA-BHQ2 for genus-specific probes and FAM-BHQ1 for species-specific ones (variola virus, monkeypox virus, ectomelia virus). The specificity of this assay was tested on 38 strains of 6 OPV species and it was 100%.

[Orthopoxvirus genes for kelch-like proteins. III. Construction of mousepox (ectromelia) virus variants with targeted gene deletions]

Mousepox (ectromelia) virus genome contains four genes encoding for kelch-like proteins EVM018, EVM027, EVM150 and EVM167. A complete set of insertion plasmids was constructed to allow the production of recombinant ectromelia viruses with targeted deletions of one to four genes of kelch family both individually (single mutants) and in different combinations (double, triple and quadruple mutants). It was shown that deletion of any of the three genes EVMO18, EVM027 or EVM167 resulted in reduction of 50% lethal dose (LD50) by five and more orders in outbred white mice infected intraperitoneally. Deletion of mousepox kelch-gene EVM150 did not influence the virus virulence. Two or more kelch-genes deletion also resulted in high level of attenuation, which could evidently be due to the lack of three genes EVM167, EVM018 and/or EVM027 identified as virulence factors. The local inflammatory process on the model of intradermal injection of mouse ear pinnae (vasodilatation level, hyperemia, cutaneous edema, arterial thrombosis) was significantly more intensive for wild type virus and virulent mutant deltaEVM150 in comparison with avirulent mutant AEVM167.

[Investigation of the impact of cowpox virus BTB/kelch gene deletion on some characteristics of infection in vitro]

The biological properties of cowpox virus (CPXV) mutants with target deletion of 4 of the 6 BTB/kelch genes (D11L, C18L, G3L, and A56R) were examined in CV-1 cell cultures. There were changes in mutant temperature sensitivity and a reduction in a viral cytopathic effect. The mutant-infected culture yielded a smaller number of cells with actin-related long cellular protrusions (63 of 300 cells) as compared with wild CPXV (127 of 300). The length of the protrusions was 20-60 and 40-120 microm, respectively). Confocal microscopy revealed the formation of large globed structures containing both actin and CPXV antigens in the cells infected with quadruple mutants. These globed structures were recognized as incomplete protrusions. The findings show that the formation of long protrusions in the cells infected with wild type CPXV represents a type of specific viral potency related to the activity of BTB/kelch genes whose deletion results in cellular insufficiency to form full-fledged protrusions.

[Poxviral immunomodulatory proteins as new therapeutics for immunocorrection]

There are numerous viral proteins known to date to modulate protective responses of their hosts. Representatives of the Poxviridae family have the greatest number of genes coding for proteins, inhibiting inflammatory responses, activities of interferons, regulating immune reactions and other protective mechanisms of macroorganisms, among viruses. This review regards poxviral immunomodulatory proteins--namely, complement-binding proteins, inhibitors of serine proteases, chemokine- and TNF-binding proteins --that were shown to be efficient therapeutics in various animal models of inflammatory and autoimmune diseases. The prospects of their usage in clinical practice for treating human inflammatory and autoimmune disorders are discussed.

[Comparative analysis of variable regions in the genomes of variola virus]

Nucleotide sequences of two extended segments of the terminal variable regions in variola virus genome were determined. The size of the left segment was 13.5 kbp and of the right, 10.5 kbp. Totally, over 540 kbp were sequenced for 22 variola virus strains. The conducted phylogenetic analysis and the data published earlier allowed us to find the interrelations between 70 variola virus isolates, the character of their clustering, and the degree of intergroup and intragroup variations of the clusters of variola virus strains. The most polymorphic loci of the genome segments studied were determined. It was demonstrated that that these loci are localized to either noncoding genome regions or to the regions of destroyed open reading frames, characteristic of the ancestor virus. These loci are promising for development of the strategy for genotyping variola virus strains. Analysis of recombination using various methods demonstrated that, with the only exception, no statistically significant recombinational events in the genomes of variola virus strains studied were detectable.

[Construction of combinatorial immune library of single chain human antibodies to orthopoxviruses and selection from this library antibodies to recombinant protein prA30L of variola virus]

A combinatorial immune library of human single-chain antibody fragments (scFv) was constructed on the base of genes encoding variable domains of heavy and light chains of immunoglobulins cloned from the lymphocytes of four vaccinia virus (VACV) vaccinated donors. The size of the library was 3 x 10(7) independent clones. After the library was enriched with the clones producing scFv against recombinant analogue of variola virus surface protein prA30L, a panel of unique antibodies specific to both prA30L and VACV was selected from the library. A plaque reduction neutralization test was performed for all selected antibodies and two antibodies were shown to be able to neutralize plaque formation of VACV in Vero E6 cells monolayer. Binding specificities of these antibodies were confirmed using ELISA and Western blot analysis. To determine the amino acid sequences of neutralizing antibodies their genes were sequenced.

Comparative study of pathological changes in the mouse viscera in infection caused by two orthopoxviruses

The mechanisms of infection development in intraperitoneal inoculation of mice by ectromelia virus strain K-1 and cowpox strain EP-2 were studied. Ultrastructural parameters of virus assembly and maturation are described. Differences in the types of cells replicating the viruses and in the type of visceral injuries were detected. The studies showed a local type of strain EP-2 cowpox infection and dissemination of ectromelia strain K-1.

Properties of the recombinant TNF-binding proteins from variola, monkeypox, and cowpox viruses are different

Tumor necrosis factor (TNF), a potent proinflammatory and antiviral cytokine, is a critical extracellular immune regulator targeted by poxviruses through the activity of virus-encoded family of TNF-binding proteins (CrmB, CrmC, CrmD, and CrmE). The only TNF-binding protein from variola virus (VARV), the causative agent of smallpox, infecting exclusively humans, is CrmB. Here we have aligned the amino acid sequences of CrmB proteins from 10 VARV, 14 cowpox virus (CPXV), and 22 monkeypox virus (MPXV) strains. Sequence analyses demonstrated a high homology of these proteins. The regions homologous to cd00185 domain of the TNF receptor family, determining the specificity of ligand–receptor binding, were found in the sequences of CrmB proteins. In addition, a comparative analysis of the C-terminal SECRET domain sequences of CrmB proteins was performed. The differences in the amino acid sequences of these domains characteristic of each particular orthopoxvirus species were detected. It was assumed that the species-specific distinctions between the CrmB proteins might underlie the differences in these physicochemical and biological properties. The individual recombinant proteins VARV-CrmB, MPXV-CrmB, and CPXV-CrmB were synthesized in a baculovirus expression system in insect cells and isolated. Purified VARV-CrmB was detectable as a dimer with a molecular weight of 90 kDa, while MPXV- and CPXV-CrmBs, as monomers when fractioned by non-reducing SDS-PAGE. The CrmB proteins of VARV, MPXV, and CPXV differed in the efficiencies of inhibition of the cytotoxic effects of human, mouse, or rabbit TNFs in L929 mouse fibroblast cell line. Testing of CrmBs in the experimental model of LPS-induced shock using SPF BALB/c mice detected a pronounced protective effect of VARV-CrmB. Thus, our data demonstrated the difference in anti-TNF activities of VARV-, MPXV-, and CPXV-CrmBs and efficiency of VARV-CrmB rather than CPXV- or MPXV-CrmBs against LPS-induced mortality in mice.

Immunogenicity of a novel, bivalent, plant-based oral vaccine against hepatitis B and human immunodeficiency viruses

A synthetic chimeric gene, TBI-HBS, encoding the immunogenic ENV and GAG epitopes of human immunodeficiency virus (HIV-1) and the surface protein antigen (HBsAg) of hepatitis B virus (HBV), was expressed in tomato plants. Tomato fruits containing the TBI-HBS antigen were fed to experimental mice and, on days 14 and 28 post-feeding, high levels of HIV- and HBV-specific antibodies were present in the serum and feces of the test animals. Intraperitoneal injection of a DNA vaccine directing synthesis of the same TBI-HBsAg antigen boosted the antibody response to HIV in the blood serum; however, it had no effect on the high level of antibodies produced to HBV.

[Reproduction of cowpox virus strain EP-2 isolated from an elephant in primary fibroblast cultures and chorion-allantoic chick embryos]

Electron microscopy was used to study the reproduction of cowpox virus strain EP-2 in the cells of a primary fibroblast cultures (PFC) and chorion-allantoic membrane (CAM) of chick embryos (CE). The sequential stages of viral morphogenesis and the structure of A-type inclusions were described. The parameters of viral reproduction in PFC and CE CAM were compared. The formation of crystalloid tubular structures in PFC, unusual electron dense inclusions in the cells of CE CAN, and different variants of A-type inclusions in the cells of a pock was found. The histological and ultrastructural characteristics of pocks in CE CAM are described.

Microarray assay for detection and discrimination ofOrthopoxvirus species

A microarray method was developed for simultaneous detection and identification of six species of Orthopoxvirus (OPV) including Variola, Monkeypox, Cowpox, Camelpox, Vaccinia, and Ectromelia viruses. The method allowed us to discriminate OPV species from varicella-zoster virus (VZV), Herpes Simplex 1 virus (HSV-1), and Herpes Simplex 2 virus (HSV-2) that cause infections with clinical manifestations similar to OPV infections. The nucleotide sequences of the C23L/B29R and the B19R genes identified for 86 and 72 different OPV strains, respectively, were used to design species-specific microarray oligonucleotide probes (oligoprobes). The microarray also contained several oligoprobes selected from the ORF31, US4, and US5 genes of VZV, HSV-1, and HSV-2, respectively. The samples (from HSVs or OPVs) of ssDNAs for analyses were prepared by using asymmetric PCR followed by chemical labeling of ssDNA with Cy3 dye. DNA from 52 samples of various OPV species, two isolates of VZV, two of HSV-1, and three of HSV-2 were tested using the developed microarray assay; all tested viruses were accurately identified. To ensure the robustness of the microarray assay, three additional unrelated variola virus strains with unknown sequences of the C23L/B29R and the B19R genes were tested. In each instance the microarray unambiguously identified them as Variola virus species. The results obtained in this study demonstrated that this new microarray method is a valuable tool for the rapid and accurate detection and differentiation of these important viral pathogens.

Adequate system for studying translation initiation on the human retrotransposon L1 mRNA in vitro

Unlike vertebrates and RNA-containing viruses, the objective estimate of molecular clock for DNA-containing viruses was so far absent. An extended central conservative genomic region of orthopoxviruses (about 102 kbp) and the sequence of DNA polymerase gene (about 3 kbp) of the viruses belonging to various genera from the family Poxviridae were analyzed. During this analysis, the known dating of variola virus (VARV) transfer from West Africa to South America (XVI century) and our own data on close phylogenetic relations between the modem West African and South American VARV isolates were used. As a result of this work, it was calculated for the first time that the rate of mutation accumulation in these DNA-containing viruses amounted to 0.9-1.2 x 10(-6) substitutions per site per year. The poxviruses started separating from the ancestor virus to form the modem genera approximately 500 thousand years ago; the ancestor of the genus Orthopoxvirus separated about 300 thousand years ago; and its division into the modem studied species took place approximately 14 thousand years ago.

[An oligonucleotide microarray for detection and discrimination of orthopoxviruses based on oligonucleotide sequences of two viral genes]

An oligonucleotide microarray for detection and identification of orthopoxviruses was developed. Genus specific and orthopoxvirus species-specific regions of the genes encoding chemokine binding and alpha/beta-interferon binding proteins were used as a target. The developed microarray allows the variola, monkeypox, cowpox, vaccinia, camel-pox and ectromelia (mousepox) viruses to be distinguished with a high degree of reliability.

[Comparative study of variola virus and monkeypox virus interferon-gamma-binding]

DNA fragments containing genes for coding IFN-gamma-binding proteins (IFNgammaBPs) of variola virus (VARV) and monkeypox virus (MPXV) were obtained from viral genomes using PCR. Isolated genes coding desired proteins were expressed in the insect Sf21 cells using baculovirus expression system. Secreted recombinant IFNgammaBPs were isolated from culture medium of infected Sf21 cells through affinity chromatography procedure. SDS-PAAG and Western blot analysis of culture medium of infected insect cells and preparations of purified recombinant IFNgammaBPs indicated that recombinant viral proteins were dimerized even in the absence of ligand (hIFNgamma) unlike their cell (eucaryotic) analogs. Biological activity of the recombinant IFNgammaBPs were studied in the test of protective effect inhibition of hIFNgamma on L68 cells infected with murine encephalomyocarditis virus. It was shown that recombinant IFNgammaBPs had dose-dependent IFNgamma-inhibiting activity. A possibility of the elaboration of new therapeutics for anti-hIFNgamma therapy on the base of IFNgammaBPs is discussed.

[Fusion proteins encoded by orf 129L of ectromelia and orf A30L of smallpox viruses cross-react with neutralizing monoclonal antibodies]

Open reading frame (orf) 129L of ectromelia (EV) and orf A30L of smallpox viruses (SPV) encoding fusion proteins were cloned and expressed in E. coli cells. The recombinant polypeptides (prA30L H pr129L) were purified from cell lysates by Ni-NTA chromatography. Recombinant polypeptides were able to form trimers in buffered saline and they destroyed under treatment with SDS and 2-mercaptoethanol. Reactivity of prA30L, pr129L and orthopoxvirus proteins was analyzed by ELISA and Western blotting with panel of 22 monoclonal antibodies (MAbs) against orthopoxviruses (19 against EV, 2 MAbs against vaccinia virus and 1 Mabs against cowpox virus). This data allowed us to conclude that there are 12 EV-specific epitopes of pr129L and EV fusion proteins, ten orthopox-specific epitopes of EV, VV, CPV fusion proteins, from them 9 orthopox-specific epitopes of prA30L and SPV fusion proteins. Five Mabs, which cross-reacted with orthopox-specific epitopes, were able to neutralize the VV on Vero cells and from them two MAbs has neutralizing activity against smallpox virus. Our findings demonstrate that 129L fusion protein have EV-specific epitopes, that EV 129L and SPV A30L fusion proteins have a several orthopox-specific epitopes to induce a neutralizing antibodies against human pathogenic orthopoxviruses.

[Intranasal infection in mice inoculated with cowpox virus strain EP-2 isolated from the elephant]

The specific features of reproduction of EP-2 strain of cowpox virus (CPV) were studied in intranasally infected BALC/C mice by light and electron microscopy. Virus replication was found in the ciliated, intercalary, basal, and goblet cells (the nasal respiratory area), basal and supporting cells (the nasal olfactory area), ciliated, intercalary, goblet cells (the tracheal and bronchial epithelium), and collagen-producing, Schwann's, endothelial, smooth muscle, and adventitial cells. It has been shown that the CPV strain EP-2 locally replicates in the nasal cavity, trachea, and large bronchi and that there is no generalized infection.