Vaccinia Virus Defective Particles Lacking the F17 Protein Do Not Inhibit Protein Synthesis: F17, a Double-Edged Sword for Protein Synthesis?

Vaccinia virus (Orthopoxvirus) F17 protein is a major virion structural phosphoprotein having a molecular weight of 11 kDa. Recently, it was shown that F17 synthesised in infected cells interacts with mTOR subunits to evade cell immunity and stimulate late viral protein synthesis. Several years back, we purified an 11 kDa protein that inhibited protein synthesis in reticulocyte lysate from virions, and that possesses all physico-chemical properties of F17 protein. To investigate this discrepancy, we used defective vaccinia virus particles devoid of the F17 protein (designated iF17- particles) to assess their ability to inhibit protein synthesis. To this aim, we purified iF17- particles from cells infected with a vaccinia virus mutant which expresses F17 only in the presence of IPTG. The SDS-PAGE protein profiles of iF17- particles or derived particles, obtained by solubilisation of the viral membrane, were similar to that of infectious iF17 particles. As expected, the profiles of full iF17- particles and those lacking the viral membrane were missing the 11 kDa F17 band. The iF17- particles did attach to cells and injected their viral DNA into the cytoplasm. Co-infection of the non-permissive BSC40 cells with a modified vaccinia Ankara (MVA) virus, expressing an mCherry protein, and iF17- particles, induced a strong mCherry fluorescence. Altogether, these experiments confirmed that the iF17- particles can inject their content into cells. We measured the rate of protein synthesis as a function of the multiplicity of infection (MOI), in the presence of puromycin as a label. We showed that iF17- particles did not inhibit protein synthesis at high MOI, by contrast to the infectious iF17 mutant. Furthermore, the measured efficiency to inhibit protein synthesis by the iF17 mutant virus generated in the presence of IPTG, was threefold to eightfold lower than that of the wild-type WR virus. The iF17 mutant contained about threefold less F17 protein than wild-type WR. Altogether these results strongly suggest that virion-associated F17 protein is essential to mediate a stoichiometric inhibition of protein synthesis, in contrast to the late synthesised F17. It is possible that this discrepancy is due to different phosphorylation states of the free and virion-associated F17 protein.

Efficient production of protein complexes in mammalian cells using a poxvirus vector

The production of full length, biologically active proteins in mammalian cells is critical for a wide variety of purposes ranging from structural studies to preparation of subunit vaccines. Prior research has shown that Modified vaccinia virus Ankara encoding the bacteriophage T7 RNA polymerase (MVA-T7) is particularly suitable for high level expression of proteins upon infection of mammalian cells. The expression system is safe for users and 10-50 mg of full length, biologically active proteins may be obtained in their native state, from a few litres of infected cell cultures. Here we report further improvements which allow an increase in the ease and speed of recombinant virus isolation, the scale-up of protein production and the simultaneous synthesis of several polypeptides belonging to a protein complex using a single virus vector. Isolation of MVA-T7 viruses encoding foreign proteins was simplified by combining positive selection for virus recombinants and negative selection against parental virus, a process which eliminated the need for tedious plaque purification. Scale-up of protein production was achieved by infecting a BHK 21 suspension cell line and inducing protein expression with previously infected cells instead of virus, thus saving time and effort in handling virus stocks. Protein complexes were produced from infected cells by concatenating the Tobacco Etch Virus (TEV) N1A protease sequence with each of the genes of the complex into a single ORF, each gene being separated from the other by twin TEV protease cleavage sites. We report the application of these methods to the production of a complex formed on the one hand between the HIV-1 integrase and its cell partner LEDGF and on the other between the HIV-1 VIF protein and its cell partners APOBEC3G, CBFβ, Elo B and Elo C. The strategies developed in this study should be valuable for the overexpression and subsequent purification of numerous protein complexes.

The Production of Recombinant PDGF D Using the Second Generation Modified Vaccinia Ankara (MVA) Viral System

The vaccinia virus expression system is known for the efficient production of recombinant proteins with “appropriate” posttranslational modification using desired mammalian cell lines. However, being a replication competent virus, vaccinia virus poses a health threat to immunocompromised individuals and requires biosafety level 2 (BSL2) laboratory precautions, thereby restricting its use by the scientific community. Development of the host range restricted modified vaccinia Ankara (MVA) system has allowed researchers to work with a safer virus even at BSL1. Here, we report on the use of an improved second generation MVA viral system incorporating two selective markers and fluorescent proteins for easier recombinant virus identification. Notably, we demonstrate that this novel system is capable of producing secreted recombinant proteins, a finding not previously reported. Through purification and characterization of wild type and mutant platelet‐derived growth factor D (PDGF D) dimer species, we demonstrate this system is capable of producing the latent full‐length PDGF D dimer, partially processed intermediate dimer (hemidimer), as well as fully processed growth factor domain dimer that show chemical integrity and biological activity. Importantly, this system is amenable to scaling up for the mass production of recombinant PDGF D (rPDGF D) dimer species.

Structural basis for allosteric regulation of Human Topoisomerase IIα

The human type IIA topoisomerases (Top2) are essential enzymes that regulate DNA topology and chromosome organization. The Topo IIα isoform is a prime target for antineoplastic compounds used in cancer therapy that form ternary cleavage complexes with the DNA. Despite extensive studies, structural information on this large dimeric assembly is limited to the catalytic domains, hindering the exploration of allosteric mechanism governing the enzyme activities and the contribution of its non-conserved C-terminal domain (CTD). Herein we present cryo-EM structures of the entire human Topo IIα nucleoprotein complex in different conformations solved at subnanometer resolutions (3.6-7.4 Å). Our data unveils the molecular determinants that fine tune the allosteric connections between the ATPase domain and the DNA binding/cleavage domain. Strikingly, the reconstruction of the DNA-binding/cleavage domain uncovers a linker leading to the CTD, which plays a critical role in modulating the enzyme's activities and opens perspective for the analysis of post-translational modifications.

An innovative combined immunization platform for personalized cancer immunotherapy

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Background: Activity of immune checkpoint inhibitors relies mainly on the presence of an immune response directed against neoantigens resulting from tumor specific mutations. The induction and/or amplification of such an immune response is expected to increase the activity of these therapies. We describe here a novel immunization platform developed for the purpose of personalized cancer immunotherapy. This platform integrates a DNA vector coding for neoantigens, a live modified vaccinia of strain Ankara (MVA) used as a physiologic adjuvant and anti-CTLA-4 as a locally acting early immune checkpoint blocker. Methods: Immune potency was assessed in C57BL6 mice injected subcutaneously three times five days apart with an ovalbumine (OVA) expressing DNA vector (100 µg), either alone or in combination with increasing doses of MVA (up to 2.5x107 plaque forming units, pfu) and increasing doses of anti-CTLA-4 (up to 100 µg). OVA specific immune responses were measured by ELISpot. Anti-tumor efficacy was then investigated with a similar administration scheme in a therapeutic B16F10 mice melanoma model with a DNA vector coding for the B16F10-M30 tumor neoantigen. Results: At an optimal dose of 2.5x106 pfu, MVA significantly improved OVA specific immune response up to 10 times higher as compared to vector alone. Addition of CTLA-4 blockade further increased the magnitude of response, up to 30 times higher than with vector alone. Both MVA and CTLA-4 demonstrated a bell-shaped dose dependent effect. In tumor-bearing animals, 80% experienced durable tumor-free survival when treated with the combination therapy as compared to less than 20% in untreated animals or animals treated with each component independently. Treatment appeared feasible and well-tolerated. Conclusions: Neoantigen coding DNA vector, MVA and CTLA-4 immune checkpoint blockade, when co-administered in immunocompetent C57BL6 mice, acted synergistically to induce a cellular immune response. The same approach translated into a strong anti-tumoral response in an aggressive melanoma model. This combined immunization platform appears as a potential novel way to enhance clinical benefit from current immune checkpoint inhibitors.

Structural features of the salivary gland hypertrophy virus of the tsetse fly revealed by cryo-electron microscopy and tomography

Glossina palipides salivary gland hypertrophy virus (GpSGHV) infects tsetse flies, which are vectors for African trypanosomosis. This virus represents a major challenge in insect mass rearing and has hampered the implementation of the sterile insect technique programs in the Member States of the International Atomic Energy Agency. GpSGHV virions consist of long rod-shaped particles over 9000Å in length, but little is known about their detailed structural organization. We show by cryo electron microscopy and cryo electron tomography that the GpSGHV virion has a unique, non-icosahedral helical structure. Its envelope exhibits regularly spaced spikes that protrude from the lipid bilayer and are arranged on a four-start helix. This study provides a detailed insight into the 3D architecture of GpSGHV, which will help to understand the viral life cycle and possibly allow the design of antiviral strategies in the context of tsetse fly infections.

Expression of functional full-length hSRC-1 in eukaryotic cells using modified vaccinia virus Ankara and baculovirus

Purified protein expression level and quality are contingent upon specific host expression systems. This differential production is particularly observed for proteins of high molecular weight, hampering further structural studies. We developed an expression method aimed at producing proteins in Escherichia coli, insect, and mammalian systems. Our novel protocol was used to produce in large scale the full-length 160-kDa steroid receptor coactivator 1 (SRC-1), a coregulator of nuclear receptors. The results indicate that we can produce biologically active human SRC-1 in mammalian and insect cells in large scale.

Using Vaccinia's innate ability to introduce DNA into mammalian cells for production of recombinant proteins

Production of recombinant protein in mammalian cells is time-consuming, labor-intensive and costly. While seeking to overcome these limitations, we discovered that Vaccinia virus has the innate ability to transfer exogenous plasmid DNA into mammalian cells during the infection process. Parameters influencing the efficiency of this event were characterized and a quick, simple and inexpensive way to produce eukaryotic proteins was established.

Vectors for recombinational cloning and gene expression in mammalian cells using modified vaccinia virus Ankara

Modified vaccinia virus Ankara (MVA) is a safe vector for high-level expression of proteins in mammalian cells. To simplify the molecular cloning procedures for shuttling genes into the MVA genome, we constructed generic destination plasmids that allow in vitro recombinational cloning (Gateway) and quick isolation of expression plasmids for any gene to be incorporated into the virus. Downstream purification steps were simplified by including N-terminal peptide tags (His, Strep, and Flag) in the generic plasmids. We demonstrate the ability to produce 10mg of beta-glucuronidase from 10(8) hamster cells and to purify tagged proteins with affinity gels.

Extracellular vesicles containing virus-encoded membrane proteins are a byproduct of infection with modified vaccinia virus Ankara

Vaccinia virus is a structurally complex virus that multiplies in the cell cytoplasm. The assembly of Vaccinia virus particles and their egress from infected cells exploit cellular pathways. Most notably, intracellular mature viral particles are enwrapped by Golgi-derived or endosomal vesicles. These enveloped particles, enriched in virus-encoded proteins, migrate to the cell surface where they are released into the extracellular space through fusion of their outer envelope with the cell membrane. We report that baby hamster kidney cells productively infected with the modified vaccinia virus Ankara strain (MVA) also release extracellular vesicles containing virus-encoded envelope proteins but devoid of any virus cargo. Such vesicles were visualized on the cell surface by electron microscopy and immunogold labelling of the B5 envelope protein. A portion of the B5 protein was found to be associated with non-viral material in high speed ultracentrifugation pellets and displayed a buoyant density characteristic of exosomes released by some cell types. An unrelated transmembrane protein (CD40 ligand) encoded by the MVA genome was also incorporated into extracellular vesicles but not into the envelopes that surround extracellular enveloped virus. High speed pellets obtained by centrifugation of culture medium from cells infected with MVA encoding CD40 ligand displayed the ability to induce dendritic cell maturation suggesting that the ligand is on the outer surface of the extracellular vesicles. We propose that the formation of extracellular vesicles after vaccinia virus infection is a byproduct of the pathway leading to the formation of extracellular enveloped virus.

Short- and long-term immunogenicity and protection induced by non-replicating smallpox vaccine candidates in mice and comparison with the traditional 1st generation vaccine

This study assessed three non-replicating smallpox vaccine candidates (modified vaccinia Ankara (MVA), NYVAC and HR) for their immunogenicity and ability to protect mice against an intranasal cowpox virus challenge and compared them with the traditional replicating vaccine. A single immunisation with the non-replicating vaccines induced a complete protection from death at short-term, but was not fully protective when mice were challenged 150 days post-vaccination with protection correlated with the specific neutralizing antibodies and CD4(+) T-cells responses. Prime-boost vaccination enabled effective long-term protection from death for mice vaccinated with MVA, but protection from disease and CD4(+) T-cell level were lower than the ones induced by the traditional vaccine over the long-term period. Further investigations are necessary with MVA to determine the optimal conditions of immunisation to induce at long-term immunogenicity and protection observed with the 1st generation smallpox vaccine.

High level protein expression in mammalian cells using a safe viral vector: Modified vaccinia virus Ankara

Vaccinia virus vectors are attractive tools to direct high level protein synthesis in mammalian cells. In one of the most efficient strategies developed so far, the gene to be expressed is positioned downstream of a bacteriophage T7 promoter within the vaccinia genome and transcribed by the T7 RNA polymerase, also encoded by the vaccinia virus genome. Tight regulation of transcription and efficient translation are ensured by control elements of the Escherichia coli lactose operon and the encephalomyocarditis virus leader sequence, respectively. We have integrated such a stringently controlled expression system, previously used successfully in a standard vaccinia virus backbone, into the modified vaccinia virus Ankara strain (MVA). In this manner, proteins of interest can be produced in mammalian cells under standard laboratory conditions because of the inherent safety of the MVA strain. Using this system for expression of beta-galactosidase, about 15 mg protein could be produced from 10(8) BHK21 cells over a 24-h period, a value 4-fold higher than the amount produced from an identical expression system based on a standard vaccinia virus strain. In another application, we employed the MVA vector to produce human tubulin tyrosine ligase and demonstrate that this protein becomes a major cellular protein upon induction conditions and displays its characteristic enzymatic activity. The MVA vector should prove useful for many other applications in which mammalian cells are required for protein production.

Genomic sequence of a clonal isolate of the vaccinia virus Lister strain employed for smallpox vaccination in France and its comparison to other orthopoxviruses

Since 1980 there has been global eradication of smallpox due to the success of the vaccination programme using vaccinia virus (VACV). During the eradication period, distinct VACV strains circulated, the Lister strain being the most commonly employed in Europe. Analysis of the safety of smallpox vaccines has suggested that they display significant heterogeneity. To gain a more detailed understanding of the diversity of VACV strains it is important to determine their genomic sequences. Although the sequences of three isolates of the Japanese Lister original strain (VACV-LO) are available, no analysis of the relationship of any Lister sequence compared to other VACV genomes has been reported. Here, we describe the sequence of a representative clonal isolate of the Lister vaccine (VACV-List) used to inoculate the French population. The coding capacity of VACV-List was compared to other VACV strains. The 201 open reading frames (ORFs) were annotated in the VACV-List genome based on protein size, genomic localization and prior characterization of many ORFs. Eleven ORFs were recognized as pseudogenes as they were truncated or fragmented counterparts of larger ORFs in other orthopoxviruses (OPVs). The VACV-List genome also contains several ORFs that have not been annotated in other VACVs but were found in other OPVs. VACV-List and VACV-LO displayed a high level of nucleotide sequence similarity. Compared to the Copenhagen strain of VACV, the VACV-List sequence diverged in three main regions, one of them corresponding to a substitution in VACV-List with coxpox virus GRI-90 strain ORFs, suggestive of prior genetic exchanges. These studies highlight the heterogeneity between VACV strains and provide a basis to better understand differences in safety and efficacy of smallpox vaccines.

Intranasal cowpox virus infection of the mouse as a model for preclinical evaluation of smallpox vaccines

The intranasal infection of mice with cowpox virus (CPXV) has been evaluated as a model for smallpox infection in man. Administration of a lethal dose of CPXV allowed time for development of T-cell responses but antibodies could not be detected before death occurred. In contrast, infection with a sublethal dose was associated with an early T-cell response followed by neutralising antibodies which correlated with virus clearance. Comparison of two first generation smallpox vaccines revealed no significant differences in terms of immunogenicity, protection and post-challenge virus clearance. These studies show that the CPXV/mouse model is valuable for the initial assessment of smallpox vaccines.

[Update on smallpox vaccines]

Smallpox is among the most dangerous pathogens that could be used by bioterrorists. The former vaccines produced by scarification on the flanks of calves or sheep could be used to protect the whole French population when used with bifurcated needles. They should be replaced by a second-generation vaccine grown in cell culture and, eventually later by new and safer third-generation vaccines using non-replicative viral strains.

The cowpox virus host range gene, CP77, affects phosphorylation of eIF2 alpha and vaccinia viral translation in apoptotic HeLa cells

Host restriction of vaccinia virus has been previously described in CHO and RK13 cells in which a cowpox virus CP77 gene rescues vaccinia virus growth at the viral protein translation level. Here we investigate the restrictive stage of vaccinia virus in HeLa cells using a vaccinia mutant virus (VV-hr) that contains a deletion of 18-kb genome sequences resulting in no growth in HeLa cells. Insertion of CP77 gene into VV-hr generated a recombinant virus (VV-36hr) that multiplied well in HeLa cells. Both viruses could enter cells, initiate viral DNA replication and intermediate gene transcription. However, translation of viral intermediate gene was only detected in cells infected with VV-36hr, indicating that CP77 relieves host restriction at the intermediate gene translation stage in HeLa cells. Caspase-2 and -3 activation was observed in HeLa cells infected with VV-hr coupled with dramatic morphological alterations and cleavage of the translation initiation factor eIF4G. Caspase activation was reduced in HeLa cells infected with VV-36hr, indicating that CP77 acts upstream of caspase activation. Enhanced phosphorylation of PKR and eIF2alpha was also observed in cells infected with VV-hr and was suppressed by CP77. Suppression of eIF4G cleavage with the caspase inhibitor ZVAD did not rescue virus translation, whereas expression of a mutant eIF2alpha protein with an alanine substitution of serine at amino acid position 51 (eIF2alphaS51A) partially restored viral translation and moderately increased virus growth in HeLa cells.

Appearance of the bona fide spiral tubule of ORF virus is dependent on an intact 10-kilodalton viral protein

Parapoxviruses can be morphologically distinguished from other poxviruses in conventional negative staining electron microscopy (EM) by their ovoid appearance and the spiral tubule surrounding the virion's surface. However, this technique may introduce artifacts. We have examined Orf virus (ORFV; the prototype species of the Parapoxvirus genus) by cryoelectron microscopy (cryo-EM) and cryo-negative staining EM. From these studies we suggest that the shape and unique spiral tubule are authentic features of the parapoxviruses. We also constructed an ORFV mutant deleted of a gene encoding a 10-kDa protein, which is an orthologue of the vaccinia virus (VACV) 14-kDa fusion protein, and investigated its ultrastructure. This mutant virus multiplied slowly in permissive cells and produced infectious but morphologically aberrant particles. Mutant virions lacked the spiral tubule but displayed short disorganized tubules similar to those observed on the surface of VACV. In addition, thin extensions or loop-like structures were appended to the ORFV mutant particles. We suggest that these appended structures arise from a failure of the mutant virus particles to properly seal and that the sealing activity is dependent on the 10-kDa protein.

Modified vaccinia virus Ankara induces moderate activation of human dendritic cells

Modified vaccinia virus Ankara (MVA) is a highly attenuated strain known to be an effective vaccine vector. Here it is demonstrated that MVA, unlike standard vaccinia virus (VACV) strains, activates monocyte-derived human dendritic cells (DCs) as testified by an increase in surface co-stimulatory molecules and the secretion of pro-inflammatory cytokines. Inhibition of virus gene expression by subjecting MVA to UV light or heat treatment did not alter its ability to activate DCs. On the other hand, standard VACV strains activated DCs if virus gene expression was prevented by prior UV light or heat treatment. These results suggest that MVA or standard VACV particles are responsible for DC activation but, in the case of standard VACV strains, virus gene expression prevents activation. Additional experiments showed that DCs were activated by MVA-infected HeLa cells and, under these conditions, could induce secretion of gamma interferon from T lymphocytes more efficiently than if a replication-competent VACV strain was employed. These data provide one explanation for the remarkable immune-stimulating capacity of MVA in the absence of virus multiplication.

Characterisation of the substrate specificity of homogeneous vaccinia virus uracil-DNA glycosylase

The decision to stop smallpox vaccination and the loss of specific immunity in a large proportion of the population could jeopardise world health due to the possibility of a natural or provoked re-emergence of smallpox. Therefore, it is mandatory to improve the current capability to prevent or treat such infections. The DNA repair protein uracil-DNA glycosylase (UNG) is one of the viral enzymes important for poxvirus pathogenesis. Consequently, the inhibition of UNG could be a rational strategy for the treatment of infections with poxviruses. In order to develop inhibitor assays for UNG, as a first step, we have characterised the recombinant vaccinia virus UNG (vUNG) and compared it with the human nuclear form (hUNG2) and catalytic fragment (hUNG) UNG. In contrast to hUNG2, vUNG is strongly inhibited in the presence of 7.5 mM MgCl(2). We have shown that highly purified vUNG is not inhibited by a specific uracil-DNA glycosylase inhibitor. Interestingly, both viral and human enzymes preferentially excise uracil when it is opposite to cytosine. The present study provides the basis for the design of specific inhibitors for vUNG.

Embedding in Spurr's resin is a good choice for immunolabelling after freeze drying as shown with chemically unfixed dendritic cells

Immunocytochemical reactions on biological specimens depend on many factors, the most crucial one being the maintenance of antigenicity. Antigens are vulnerable at each stage during preparation for electron microscopy. One of the least traumatic methods of preparing biological tissues for post-embedding immunolabelling includes the following steps: (1) physical stabilization of the native biological material by rapid freezing (cryofixation) and keeping the immobilized biological sample at low temperature, thereby avoiding any movements of water, ions and macromolecules; (2) dehydrating the frozen biological material by freeze-drying at low temperature; (3) embedding of the dehydrated specimen. Here we show that embedding of chemically unfixed dendritic cells in Spurr's resin after cryofixation and freeze-drying enables the conservation of fine ultrastructure without cell distortion or shrinkage. Furthermore, we demonstrate the feasibility of protein localization in ultrathin sections by immunolabelling of the major histocompatibility class II molecules.

Heat shock proteins 70 and 60 share common receptors which are expressed on human monocyte-derived but not epidermal dendritic cells

Priming of CTL by means of heat shock proteins (hsp) is dependent on antigen-presenting cells (APC), which present the hsp-associated peptides, via their cell surface MHC class I molecules, toCD8(+) T cells. It has not yet been established how human (hu) hsp70 interacts with the major (hu)APC, the dendritic cells (DC). Here we show that (hu)hsp70 is specifically internalized intoCD14(-), Toll-like receptor 4(-) monocyte-derived (hu)DC by receptor-mediated endocytosis. We further demonstrate that (hu)hsp70 and (hu)hsp60 share the same receptors on (hu)monocyte-derived DC. Both molecules as well as MHC class I molecules are spontaneously internalized and reach the MHC class II-enriched compartments. Finally, freshly isolated (hu) epidermal Langerhans cells (LC), the DC of the skin, as well as CD34(+)-derived LC do not bind hsp60 or hsp70. Given the likely importance of the internalization of hsp70 by APC in the induction of the immune responses, the finding that hsp60 and hsp70 are internalized through the same receptor(s) may explain why microbial hsp60 represents a major T cell antigen. This may rationalize the use of microbial hsp60 to prime immune responses against microbes. The lack of hsp60/70 receptors on epidermal LC raises the crucial question as to whether absence of priming of the skin and mucosal immune systems by hsp-polypeptide complexes could account for some tissue-specific diseases. This work also points to a potential advantage of using monocyte-derived DC in human immunotherapeutic applications of hsp60/70.

Enveloped virus is the major virus form produced during productive infection with the modified vaccinia virus Ankara strain

Modified vaccinia virus Ankara (MVA) is a highly attenuated virus strain that may be useful as a vaccine vector. Ultrastructural examination of purified MVA showed that most of the viral particles are enveloped in contrast to the Copenhagen strain (COP). In CsCl gradients, the majority of the MVA particles displayed a light buoyant density characteristic of the enveloped form. Consistent with these results, MVA particles were poorly labeled with antibodies against the surface of intracellular mature virus but strongly labeled with antibodies against an envelope antigen. Furthermore, MVA was more resistant than the COP strain to neutralization by mouse anti-COP antibodies. These results suggest that the MVA strain may be particularly suitable for the engineering of envelope proteins and that MVA may be able to resist the humoral immunity displayed by previously vaccinated individuals.

Schnitzler syndrome: heterogeneous immunopathological findings involving IgM-skin interactions

The Schnitzler syndrome is the association of chronic urticaria, intermittent fever, osteosclerotic bone lesions and a monoclonal IgM gammopathy. It is not yet firmly established whether the monoclonal immunoglobulin component plays a part in the pathophysiology of the urticarial lesions. Immunoblotting on epidermal and dermal human skin extracts as well as immunoelectron microscopic (IEM) studies on Lowicryl K4M-embedded skin sections were performed in three patients with the Schnitzler syndrome. Western blotting on epidermal extracts showed the presence of IgM-kappa antiskin autoantibodies in two patients. These antibodies displayed the same isotype as the monoclonal components and recognized a 280-290-kDa antigen in one patient and a 200-kDa antigen in the other patient. IEM studies showed sparse IgM deposits in the epidermis, around the keratinocytes, near the desmosomes in one patient and dense deposits below the lamina densa, in the region of the anchoring fibrils, in another patient. Antiskin IgM autoantibodies of the same isotype as their monoclonal gammopathies can be present in the serum of some patients with the Schnitzler syndrome. These IgM antibodies seem to deposit in vivo in the epidermis and at the dermal-epidermal junction, in the region of the anchoring fibrils. These findings suggest that the monoclonal gammopathy plays a part in the pathophysiology of the skin rash. They also suggest patient heterogeneity both in the skin antigens that are recognized as well as in their localization.

Vaccinia virus-related events and phenotypic changes after infection of dendritic cells derived from human monocytes

The in vitro interactions between vaccinia virus (VV) and monocyte-derived human dendritic cells (DC) have been studied to gain a better understanding of the mechanisms involved in the induction of an immune response by VV. This work showed that VV binds to DC less efficiently than to HeLa cells (HeLa). Capping of viral antigens on the DC surface and electron microscopic examinations suggested that VV enters into DC mainly by endocytosis instead of fusion as for HeLa. Early viral-encoded proteins were expressed in DC but late viral proteins and viral DNA synthesis did not occur. Nevertheless, when successfully infected, DC expressed a similar amount of a foreign, viral-encoded protein, as HeLa, if the early component of the p7.5 promoter was used. VV infection did not lead to DC maturation as determined by following the level of several cell surface markers associated with maturation, but an inhibition of the expression of the costimulatory molecule CD80 was noticed. The proliferation of allogeneic peripheral blood lymphocytes (PBL) was stimulated by VV-infected DC or inhibited depending on the particular donor lymphocytes employed. PBL from VV-vaccinated individuals with good memory responses to VV antigens proliferated in the presence of infected autologous DC. PBL from individuals with poor memory responses to VV and one unvaccinated individual also proliferated, albeit to a lower level, in the presence of infected autologous DC. These results suggest that VV-infected DC could both stimulate memory cells and prime naive cells in vitro.

Inefficient measles virus budding in murine L.CD46 fibroblasts

Infection of mouse L.CD46 fibroblasts with measles virus resulted in a poor virus yield, although no defects in the steps of virus binding, entry or fusion, were detected. Two days post-infection, the level of expression of the viral F protein was found to be similar on the surface of infected L.CD46 and HeLa cells using a virus multiplicity enabling an equal number of cells to be infected. After immunofluorescence labelling and confocal microscopy, L.CD46 cells also displayed a significant increase in the co-localisation of the N protein with the cell surface H and F proteins. Immunogold labelling and transmission electron microscopy demonstrated the accumulation of numerous nucleocapsids near the plasma membrane of L. CD46 cells with little virus budding, in contrast to infected HeLa cells which displayed fewer cortical nucleocapsids and more enveloped viral particles. Purified virus particles from infected L. CD46 contained a reduced amount of H, F and M protein. Altogether, these data indicate that, in L.CD46 cells, the late stage of measles virus assembly is defective. This cellular model will be helpful for the identification of cellular factors controlling measles virus maturation.

A functional measles virus replication and transcription machinery encoded by the vaccinia virus genome

Measles virus encodes three proteins required for the encapsidation, transcription and replication of viral genomes. The genes for these proteins have been inserted into the vaccinia virus genome together with the gene for the bacteriophage T7 RNA polymerase. Cells infected with this recombinant virus were able to encapsidate, transcribe and replicate a CAT gene positioned in the negative polarity behind a T7 promoter and flanked by measles virus genomic termini. Inhibition of the accumulation of the nucleocapsid proteins by actinomycin D led to an increase in CAT expression. Thus the measles virus polymerase activity, encoded by the vaccinia genome, was regulated by the level of measles proteins just as the authentic polymerase. The recombinant vaccinia described in this study could be useful for the production of measles virus-like particles encoding foreign genes and employed in vaccination or gene therapy strategies.

A matrix-less measles virus is infectious and elicits extensive cell fusion: consequences for propagation in the brain

Measles viruses (MV) can be isolated from the brains of deceased subacute sclerosing panencephalitis patients only in a cell-associated form. These viruses are often defective in the matrix (M) protein and always seem to have an altered fusion protein cytoplasmic tail. We reconstituted a cell-free, infectious M-less MV (MV-DeltaM) from cDNA. In comparison with standard MV, MV-DeltaM was considerably more efficient at inducing cell-to-cell fusion but virus titres were reduced approximately 250-fold. In MV-DeltaM-induced syncytia the ribonucleocapsids and glycoproteins largely lost co-localization, confirming the role of M protein as the virus assembly organizer. Genetically modified mice were inoculated with MV-DeltaM or with another highly fusogenic virus bearing glycoproteins with shortened cytoplasmic tails (MV-Delta(tails)). MV-DeltaM and MV-Delta(tails) lost acute pathogenicity but penetrated more deeply into the brain parenchyma than standard MV. We suggest that enhanced cell fusion may also favour the propagation of mutated, assembly-defective MV in human brains.

The assembly of the measles virus nucleoprotein into nucleocapsid-like particles is modulated by the phosphoprotein

Measles virus nucleoprotein encoded from the vaccinia virus genome assembles into nucleocapsids similar in many respects to those observed during a natural measles virus infection. The influence of the measles virus phosphoprotein on nucleocapsid assembly has been studied using a vaccinia virus recombinant encoding both the nucleoprotein and the phosphoprotein. Infection of cells with the virus recombinant resulted in the formation of cytoplasmic inclusions in which the nucleoprotein and the phosphoprotein colocalized. Electron microscopic examination suggested that these inclusions contained characteristic nucleocapsid filaments. The buoyant density of nucleocapsids assembled in the presence of the phosphoprotein was found to be slightly higher than that of nucleocapsids assembled in its absence. Furthermore, the phosphoprotein partially inhibited the formation of nucleocapsids, a process which was extremely efficient when the nucleoprotein was expressed alone. Analysis of the nucleic acid content of nucleocapsids showed that they packaged heterologous RNA into a micrococcal nuclease-resistant form. These experiments demonstrate that the measles virus phosphoprotein regulates the efficiency with which the nucleoprotein assembles into nucleocapsids and the structural conformation they acquire.

Location, DNA sequence and transcriptional analysis of the DNA polymerase gene of orf virus

Degenerate oligonucleotides representing conserved regions of various DNA polymerases hybridized to a region located 26 kb from the left end of the orf virus (OV) strain NZ-2 genome. DNA sequence analysis of this region revealed a 3024 bp open reading frame able to encode a protein with 56 percent amino acid identity to the DNA polymerase of vaccinia virus (VAC) and with significant homology to other DNA polymerases. Early transcripts derived from the open reading frame were detected in RNA purified from OV-infected cells, and 5' ends were mapped to a region 8-19 nt downstream from an A/T-rich sequence that resembles VAC early promoters. Unlike the VAC gene, the OV DNA polymerase makes almost exclusive use of G/C coding options. Attempts to substitute the activity of the OV DNA polymerase for its VAC counterpart were unsuccessful. This may indicate that the OV DNA polymerase is incompatible with VAC accessory proteins.

A vaccinia virus transfer vector using a GUS reporter gene inserted into the I4L locus

A vaccinia virus (VV) transfer vector is described which enables integration of heterologous sequences into the I4L locus (ribonucleotide reductase-encoding gene) through co-insertion of a GUS selection marker. I4L- VV recombinants formed blue plaques when an agarose overlay containing XGluc (5-bromo-4-chloro-3-indolyl-beta-glucuronide) was added to the infected cell monolayer. Viruses already containing a lacZ reporter gene were also suitable recipients for the selection procedure since infection with a VV lacZ recombinant did not produce any blue plaques with XGluc. The addition of a synthetic early promoter downstream from the GUS cassette initiated the predicted-size transcript during an infection. Insertion of genes with VV p7.5-promoters into the I4L, J2R and K1L loci of the same virus produced viable virus recombinants even though recombination between these loci could be demonstrated. These techniques should be valuable for the further development of VV as a polyvalent vector.

Biological properties of recombinant HIV envelope synthesized in CHO glycosylation-mutant cell lines

N-glycosylation of the human immunodeficiency virus type-1 envelope (Env) glycoprotein precursor (gp160) occurs by transfer of Glc3Man9GlcNAc2 onto the nascent protein. Maturation then occurs via cleavage of the three Glc residues, which starts during translation. These events are considered necessary to create Env functional conformation: treatment with "alpha"-glucosidase inhibitors, but not alpha-mannosidase inhibitors (i) impairs gp160 cleavage into gp120 and gp41, (ii) diminishes the accessibility of gp120 V3 region, (iii) prevents gp120 binding to its CD4 receptor, and (iv) prevents gp41-mediated membrane fusion. These inhibitors are of therapeutic interest. Here, using a collection of parent and mutant CHO cells that possess mutations in different steps of glycosylation, we reassessed the role of glycans in both the processing and the properties of recombinant gp160 expressed from a vaccinia virus vector. Mutant cells were as follows: Lec23 (which lacks alpha-glucosidase I activity) produces a collection of triglucosylated structures (Glc3Man7-9GlcNAc2); LEC10 (which has increased GlcNAc transferase III activity) produces complex glycans with a bisected GlcNAc residue; Lec1 (which lacks GlcNAc transferase I) and Lec3.2.8.1 (which lacks GlcNAc transferase I and has decreased activity of CMP-NeuNAc and UDP-Gal translocases) produce Man5GlcNAc2 glycans at complex or hybrid sites. As expected, glycosylation of Env produced from mutants was affected but, irrespective of the glycosylation phenotype, (i) similar quantities of Env were synthesized, (ii) the immunoreactivity of V3 was similar, (iii) gp160 was efficiently cleaved into gp120 and gp41, (vi) Env was exposed at the cell membrane, (v) secreted gp120 bound CD4, and (vi) membrane gp41 was able to induce membrane fusion with CD4+ cells. Thus, the glycosylation alterations examined are dispensable for Env processing and biological activity in CHO cells. In particular, removal of the three outer Glc residues was not required per se for Env folding in this system because functional Env is obtained from Lec23 cells: it appears therefore that lack of modification is not equivalent to drug inhibition of modification. These data are discussed in the light of previous reports describing the use of glycosidase inhibitors to alter glycosylation.

The vaccinia virus J5L open reading frame encodes a polypeptide expressed late during infection and required for viral multiplication

A number of open reading frames (ORFs) are found in the vaccinia virus (VV) genome whose activities in the viral life cycle have not yet been determined. This report examines one such ORF, designated J5L, which was demonstrated to be essential for viral multiplication. Stable inactivation of the J5L ORF by insertion of a lacZ ORF was impossible unless another copy of the J5L ORF was present in the VV genome. Fusion genes between the J5L ORF and either the lacZ gene or the VV K1L gene were employed to study its temporal expression as well as its protein product. These experiments showed that J5L is transcribed late in infection and gives rise to a protein product which migrates by SDS-PAGE with the expected molecular weight (16 kDa). Numerous unsuccessful attempts to establish a stable cell line expressing J5L suggest that the J5L gene product could be cytotoxic.

The conserved N-terminal region of Sendai virus nucleocapsid protein NP is required for nucleocapsid assembly

Sendai virus nucleocapsid protein NP synthesized in the absence of other viral components assembled into nucleocapsid-like particles. They were identical in density and morphology to authentic nucleocapsids but were smaller in size. The reduction in size was probably due to the fact that they contained RNA only 0.5 to 2 kb in length. Nucleocapsid assembly requires NP-NP and NP-RNA interactions. To identify domains on NP protein involved in nucleocapsid formation, 29 NP protein mutants were tested for the ability to assemble. Any deletion between amino acid residues 1 and 399 abolished formation of nucleocapsid-like particles, but mutants within this region exhibited two different phenotypes. Deletions between positions 83 and 384 completely abolished all interactions. Deletions between residues 1 and 82 and between residues 385 and 399, at the N- and C-terminal ends of the region from 1 to 399, resulted in unstructured aggregates of NP protein, indicating only a partial loss of function. Deletions within the C-terminal 124 amino acids were the only ones that did not affect assembly. The results suggest that NP protein can be divided into at least two separate domains which function independently of each other. Domain I (residues 1 to 399) seems to contain all of the structural information necessary for assembly, while domain II (residues 400 to 524) is not involved in nucleocapsid formation.

In vitro and in vivo study of the ectromelia virus homolog of the vaccinia virus K1L host range gene

Ectromelia virus encodes a protein which is homologous to the product of the vaccinia virus host range gene, K1L, except for eight conservative and two non-conservative substitutions and an additional threonine residue at the carboxyl terminus. Unlike the vaccinia virus gene, the ectromelia virus homolog failed to support optimal virus replication in RK-13 cells and appeared to be expressed 20-fold less efficiently. This lower level of expression was not due to the genetic background of the virus, K1L RNA transcription, sequence of the K1L RNA leader, or stability of K1L RNA or protein. Infections of RK-13 cells with ectromelia or vaccinia virus mutants lacking an intact K1L gene resulted in transient expression of early genes followed by a rapid and irreversible cessation of both virus and host protein synthesis. Infections of the disease-susceptible ANCR or -resistant C57BL/6 mice with the K1L-lacking ectromelia virus yielded a pathogenesis pattern indistinguishable from wild-type, suggesting that the ectromelia virus homolog of vaccinia virus K1L is not important for ectromelia virus in vivo replication and spread.

Detection of a protein encoded by the vaccinia virus C7L open reading frame and study of its effect on virus multiplication in different cell lines

Vaccinia virus encodes several proteins, the activity of which is essential for multiplication in different cell types. Both the C7L and K1L open reading frames (ORFs) have been characterized as viral determinants for multiplication in human cells. To confirm and extend these findings we inserted the C7L ORF into the genome of a mutant virus unable to multiply in human cells and showed that this virus recovered its ability to replicate. Deletion of C7L from a wild-type viral genome did not adversely affect virus multiplication in human cells but it did reduce replication in hamster Dede cells. When both C7L and K1L were deleted from the vaccinia virus genome only poor or no viral yields were obtained from various human cell lines. Recombinant viruses were also constructed to facilitate the study of C7L protein synthesis during infection. One virus in which the lacZ ORF was fused downstream and in-frame with the C7L ORF enabled us to characterize the C7L protein as an early gene product. Another recombinant virus was constructed so that the carboxy terminus of the C7L ORF product contained an additional 28 amino acids from the carboxy terminus of K1L. Tagging of C7L in this way allowed us to detect the fusion protein by immunoprecipitation with antibodies against the K1L protein. Furthermore, the hybrid protein retained its biological properties. The recombinant viruses constructed in this work should be useful for studies of the molecular basis of the activity of viral host range proteins.

Vaccination of mice against canine distemper virus-induced encephalitis with vaccinia virus recombinants encoding measles or canine distemper virus antigens

Measles and canine distemper are caused by serologically related viruses. Although dogs immunized with measles virus (MV) do not elicit canine distemper virus (CDV) neutralizing antibodies, they are protected against the fatal disease. To investigate the potential role of the MV antigens in protection against CDV, we have immunized mice with vaccinia virus (VV) recombinants expressing the MV haemagglutinin (HA), fusion (F), nucleoprotein (NP) and matrix (M) antigens and challenged them with CDV. A partial protection was observed with the VV recombinants expressing the F, NP and M antigens, but not the HA. In contrast, immunization with a VV recombinant expressing the CDV F protein completely protected mice from CDV.

Restricted replication of ectromelia virus in cell culture correlates with mutations in virus-encoded host range gene

Ectromelia virus (strain Moscow) was shown to replicate poorly or not at all in cell lines derived from the rabbit or hamster. The failure of ectromelia virus to replicate in cell lines derived from the hamster suggested that the virus lacked a functional CHO host range (hr) gene required for multiplication in these cells. A DNA fragment which hybridized to the CHO hr gene was cloned from the ectromelia virus genome and shown by sequence analysis to be deleted of 506 bp within the ectromelia virus CHO hr homologue. Two additional ectromelia viruses (Hampstead and Mill Hill strains) were also shown to lack an intact CHO hr gene. Insertion of the CHO gene from cowpox virus into the ectromelia virus genome extended the host range of ectromelia virus in tissue culture. These results demonstrate that an intact CHO hr gene is not required for maintenance of ectromelia virus in nature and provide a partial explanation for ectromelia virus' narrow host range, as opposed to the broad host range of cowpox virus, which has a functional CHO hr gene.

Construction of vaccinia virus recombinants expressing several measles virus proteins and analysis of their efficacy in vaccination of mice

Measles virus genes encoding the haemagglutinin (HA), fusion protein (F) or nucleoprotein (NP) have been inserted into the vaccinia virus genome either alone or in various combinations. In each case the measles virus genes were expressed from the 7.5K promoter and were incorporated into the thymidine kinase (tk) or K1L loci of the Copenhagen strain of vaccinia virus. Cells infected by the recombinants synthesized measles virus proteins indistinguishable from those induced in measles virus-infected cells. However, in some instances the level of expression in cells infected by recombinants expressing more than one measles virus gene was reduced when compared to those encoding a single gene. The sera from mice immunized with recombinants containing either HA, HA.F, HA.NP or HA.F.NP had similar levels of measles virus neutralizing antibodies which remained constant throughout a 7 month period. Analysis of these sera by immunoprecipitation of radiolabelled measles virus confirmed the presence of specific antibody to each of the antigens where appropriate. The introduction of the measles virus genes into the K1L and the tk sites despite attenuating the virus for mice by 10-fold and 1000-fold respectively did not affect the vaccination efficiency, i.e. ability to induce measles virus antibody and protect mice. Vaccination of BALB/c (H2d) mice with HA and F, but not NP, recombinants completely protected the animals against a lethal measles virus challenge. In contrast, although the HA recombinant protected CBA (H2k) mice, the F recombinant did so poorly. However, by immunizing CBA mice with a recombinant expressing both F and NP, protection was increased to more than 75%. Our findings demonstrate the ability of three measles virus antigens expressed from the vaccinia virus genome alone or in combination to contribute to protective immunity against measles virus infection of mice. They also suggest that the association of measles virus antigens in a single recombinant DNA vaccine could be beneficial to overcome host-related restriction of the immune response to particular antigens.

Assembly of nucleocapsidlike structures in animal cells infected with a vaccinia virus recombinant encoding the measles virus nucleoprotein

A vaccinia virus recombinant containing the measles virus nucleoprotein gene was shown to induce the synthesis of a 60 kDa phosphorylated nucleoprotein similar to authentic measles virus nucleoprotein. Mammalian or avian cells infected with the recombinant virus displayed tubular structures reminiscent of viral nucleocapsids both in the cytoplasm and in the nucleus. Such structures could be labelled in situ by using an immunogold detection method specific for measles virus proteins. Electron microscopic examination of tubular structures purified from cells infected with the vaccinia virus recombinant indicated that they displayed most of the features of measles virus nucleocapsids, although their length was on the average shorter. These results demonstrate the spontaneous assembly of measles virus nucleocapsids in the absence of viral leader RNA and provide a means for a detailed molecular analysis of the requirements for nucleocapsid assembly. Furthermore, these findings raise the possibility of achieving complete assembly of measles virus particles, devoid of infectious RNA, by using a vaccinia virus vector.

Fowlpox virus recombinant encoding the measles virus fusion protein: protection of mice against fatal measles encephalitis

A recombinant Fowlpox virus engineered to encode the measles virus fusion protein was shown to protect mice against a challenge measles infection. A vaccine dose of about 10(6) p.f.u. was needed to protect nearly 100% of the animals. Mice failed to develop a significant level of antibodies directed against measles virus suggesting that other components of the immune system may be involved.

Construction of fowlpox virus vectors with intergenic insertions: expression of the beta-galactosidase gene and the measles virus fusion gene

A DNA fragment from fowlpox virus cloned on a plasmid vector was modified to contain foreign DNA inserts within an intergenic region. In a first step, a 32-base-pair intergenic region from the fowlpox virus genome corresponding to the position of the thymidine kinase locus in the vaccinia virus genome was enlarged to 55 base pairs by site-directed mutagenesis. A unique restriction endonuclease site introduced upstream of the intergenic region was then used to insert various foreign DNA fragments. The lacZ gene encoding beta-galactosidase and the measles virus gene encoding the fusion protein were positioned downstream of two vaccinia virus p7.5 promoter elements in either a direct repeat or inverted repeat orientation. Foreign DNA inserts contained within the fowlpox virus sequence were transferred to the viral genome by homologous recombination occurring in cells infected with a fowlpox virus temperature-sensitive mutant and transfected with both wild-type viral DNA and plasmid DNA. Recombinant viruses were selected for the expression of beta-galactosidase activity by screening for blue plaques in the presence of a chromogenic substrate. Stable recombinants expressing both the lacZ gene and the unselected measles gene were obtained when the p7.5 promoter was present as an inverted repeat. However, when the p7.5 promoter was in the direct repeat orientation, viral recombinants which initially expressed both gene inserts readily deleted the lacZ gene flanked by the promoter repeat. The methods described enable precise insertion and deletion of foreign genes in the fowlpox virus genome and could be applied to other intergenic regions of the same virus as well as other poxviruses.

Antibodies directed against a synthetic peptide enable detection of a protein encoded by a vaccinia virus host range gene that is conserved within the Orthopoxvirus genus

A vaccinia virus gene required for multiplication in some cell lines but not in others has been previously isolated and sequenced. A synthetic peptide predicted from the nucleotide sequence and corresponding to the carboxy-terminal 18 amino acids was used to raise antibodies in rabbits. The immune serum enabled detection of a 29-kilodalton (kDa) polypeptide by either immunoprecipitation or Western immunoblot assays. Synthesis of the 29-kDa polypeptide occurred immediately after infection and lasted for about 3 h. Shutoff of its synthesis was concomitant with the appearance of a delayed early polypeptide that may be antigenically related to the 29-kDa polypeptide. Analysis of cloned segments of the genomes of other orthopoxviruses by hybridization with the vaccinia virus host range gene demonstrates that it is well conserved within this genus.

A cowpox virus gene required for multiplication in Chinese hamster ovary cells

Cowpox virus, in contrast to vaccinia virus, can multiply in Chinese hamster ovary cells. To study the genetic basis for this difference in host range, recombinants between vaccinia and cowpox viruses were isolated and their DNA restriction patterns were examined. The ability to multiply in Chinese hamster ovary cells could be correlated with the conservation of cowpox virus sequences mapping at the left end of the genome. This was further demonstrated by marker rescue of the host range phenotype with restricted cowpox virus DNA. Marker rescue with cloned restriction fragments of decreasing size enabled the fine localization of the host range function to a 2.3-kilobase-pair fragment. Nucleotide sequencing revealed that the fragment encoded a single major polypeptide of approximately 77,000 daltons. It is suggested that the role of the host range gene from cowpox virus is to prevent the early and extensive shutoff of protein synthesis that normally occurs in Chinese hamster ovary cells infected by vaccinia virus.

Protection of mice from fatal measles encephalitis by vaccination with vaccinia virus recombinants encoding either the hemagglutinin or the fusion protein

Vaccinia virus recombinants encoding the hemagglutinin or fusion protein of measles virus have been constructed. Infection of cell cultures with the recombinants led to the synthesis of authentic measles proteins as judged by their electrophoretic mobility, recognition by antibodies, glycosylation, proteolytic cleavage, and presentation on the cell surface. Mice vaccinated with a single dose of the recombinant encoding the hemagglutinin protein developed antibodies capable of both inhibiting hemagglutination activity and neutralizing measles virus, whereas animals vaccinated with the recombinant encoding the fusion protein developed measles neutralizing antibodies. Mice vaccinated with either of the recombinants resisted a normally lethal intracerebral inoculation of a cell-associated measles virus subacute sclerosing panencephalitis strain.