Extracellular Enveloped Vaccinia Virus. In: Enjuanes L, Siddell SG, Spaan W, editors. Coronaviruses and Arteriviruses. Boston: Springer US; 1998. pp. 395-414. [DOI: 10.1007/978-1-4615-5331-1_51]

Cross-reactive immune responses to monkeypox virus induced by MVA vaccination in mice

Mpox (monkeypox) infection cases increased recently in non-Mpox outbreak areas, potentially causing an international threat. The desire to defend against a potential outbreak has led to renewed efforts to develop Mpox vaccines. In this report, mice were immunized with various doses of modified vaccinia virus Ankara (MVA) to evaluate the cross-reactive immune response of MVA immunization against protective antigens of the current monkeypox virus. We demonstrated that MVA induced specific antibodies against protective antigens (A29, A35, B6, M1, H3, and I1), mediating the neutralization abilities against the MVA and the monkeypox virus (MPXV). Moreover, recombinant protective antigens of the MPXV elicited cross-binding and cross-neutralizing activities for MVA. Hence, the MVA induced cross-reactive immune responses, which may guide future efforts to develop vaccines against the recent MPXV. Notably, compared to the other protective antigens, the predominant A29 and M1 antigens mediated higher cross-neutralizing immune responses against the MVA, which could serve as antigen targets for novel orthologous orthopoxvirus vaccine.

Evaluation of Virulence in Cynomolgus Macaques Using a Virus Preparation Enriched for the Extracellular Form of Monkeypox Virus

The 2022 global human monkeypox outbreak emphasizes the importance of maintaining poxvirus research, including enriching a basic understanding of animal models for developing and advancing therapeutics and vaccines. Intravenous administration of monkeypox virus in macaques is arguably one of the best animal models for evaluating the efficacy of medical countermeasures. Here we addressed one criticism of the model, a requirement for a high-titer administration of virus, as well as improving our understanding of monkeypox virus pathogenesis. To do so, we infected macaques with a challenge dose containing a characterized inoculum enriched for the extracellular form of monkeypox virus. Although there were some differences between diseases caused by the enriched preparation compared with a relatively similar unpurified preparation, we were unable to reduce the viral input with the enriched preparation and maintain severe disease. We found that inherent factors contained within the serum of nonhuman primate blood affect the stability of the monkeypox extracellular virions. As a first step to study a role of the extracellular form in transmission, we also showed the presence of this form in the oropharyngeal swabs from nonhuman primates exposed to monkeypox virus.

pH Sensitive Erythrocyte-Derived Membrane for Acute Systemic Retention and Increased Infectivity of Coated Oncolytic Vaccinia Virus

Oncolytic viruses have emerged as a promising modality in cancer treatment given their high synergy with highly efficient immune checkpoint inhibitors. However, their potency is limited by their rapid in vivo clearance. To overcome this, we coated oncolytic vaccinia viruses (oVV) with erythrocyte-derived membranes (EDMs), hypothesizing that they would not only remain in systemic circulation for longer as erythrocytes would when administered intravenously, but also respond to environmental pH cues due to their membrane surface sialic acid residues. For this, we developed a model based on DLVO theory to show that the acidic moieties on the surface of EDM confers it the ability to respond to pH-based stimuli. We corroborate our modeling results through in vitro cell culture models and show that EDM-coated oVV infects cancer cells faster under acidic conditions akin to the tumor microenvironment. When EDM-coated oVVs were intravenously injected into wild-type mice, they exhibited prolonged circulation at higher concentrations when compared to the unprocessed oVV. Furthermore, when EDM-coated oVV was directly injected into xenografted tumors, we observed that they were suppressed earlier than the tumors that received regular oVV, suggesting that the EDM coating does not hinder oVV infectivity. Overall, we found that EDM was able to serve as a multi-functional encapsulant that allowed the payload to remain in circulation at higher concentrations when administered intravenously while simultaneously exhibiting pH-responsive properties.

Characterization of an In Vivo Neutralizing Anti-Vaccinia Virus D8 Single-Chain Fragment Variable (scFv) from a Human Anti-Vaccinia Virus-Specific Recombinant Library

A panel of potent neutralizing antibodies are protective against orthopoxvirus (OPXV) infections. For the development of OPXV-specific recombinant human single-chain antibodies (scFvs), the IgG repertoire of four vaccinated donors was amplified from peripheral B-lymphocytes. The resulting library consisted of ≥4 × 10⁸ independent colonies. The immuno-screening against vaccinia virus (VACV) Elstree revealed a predominant selection of scFv clones specifically binding to the D8 protein. The scFv-1.2.2.H9 was engineered into larger human scFv-Fc-1.2.2.H9 and IgG1-1.2.2.H9 formats to improve the binding affinity and to add effector functions within the human immune response. Similar binding kinetics were calculated for scFv-1.2.2.H9 and scFv-Fc-1.2.2.H9 (1.61 nM and 7.685 nM, respectively), whereas, for IgG1-1.2.2.H9, the Michaelis-Menten kinetics revealed an increased affinity of 43.8 pM. None of the purified recombinant 1.2.2.H9 formats were able to neutralize VACV Elstree in vitro. After addition of 1% human complement, the neutralization of ≥50% of VACV Elstree was achieved with 0.0776 µM scFv-Fc-1.2.2.H9 and 0.01324 µM IgG1-1.2.2.H9, respectively. In an in vivo passive immunization NMRI mouse model, 100 µg purified scFv-1.2.2.H9 and the IgG1-1.2.2.H9 partially protected against the challenge with 4 LD₅₀ VACV Munich 1, as 3/6 mice survived. In contrast, in the scFv-Fc-1.2.2.H9 group, only one mouse survived the challenge.

A systemically deliverable Vaccinia virus with increased capacity for intertumoral and intratumoral spread effectively treats pancreatic cancer

BACKGROUND

Pancreatic cancer remains one of the most lethal cancers and is refractory to immunotherapeutic interventions. Oncolytic viruses are a promising new treatment option, but current platforms demonstrate limited efficacy, especially for inaccessible and metastatic cancers that require systemically deliverable therapies. We recently described an oncolytic vaccinia virus (VV), VVLΔTKΔN1L, which has potent antitumor activity, and a regime to enhance intravenous delivery of VV by pharmacological inhibition of pharmacological inhibition of PI3 Kinase δ (PI3Kδ) to prevent virus uptake by macrophages. While these platforms improve the clinical prospects of VV, antitumor efficacy must be improved.

METHODS

VVLΔTKΔN1L was modified to improve viral spread within and between tumors via viral B5R protein modification, which enhanced production of the extracellular enveloped virus form of VV. Antitumor immunity evoked by viral treatment was improved by arming the virus with interleukin-21, creating VVL-21. Efficacy, functional activity and synergy with α-programmed cell death protein 1 (α-PD1) were assessed after systemic delivery to murine and Syrian hamster models of pancreatic cancer.

RESULTS

VVL-21 could reach tumors after systemic delivery and demonstrated antitumor efficacy in subcutaneous, orthotopic and disseminated models of pancreatic cancer. The incorporation of modified B5R improved intratumoural accumulation of VV. VVL-21 treatment increased the numbers of effector CD8+ T cells within the tumor, increased circulating natural killer cells and was able to polarize macrophages to an M1 phenotype in vivo and in vitro. Importantly, treatment with VVL-21 sensitized tumors to the immune checkpoint inhibitor α-PD1.

CONCLUSIONS

Intravenously administered VVL-21 successfully remodeled the suppressive tumor-microenvironment to promote antitumor immune responses and improve long-term survival in animal models of pancreatic cancer. Importantly, treatment with VVL-21 sensitized tumors to the immune checkpoint inhibitor α-PD1. Combination of PI3Kδ inhibition, VVL-21 and α-PD1 creates an effective platform for treatment of pancreatic cancer.

Vaccinia virus-mediated cancer immunotherapy: cancer vaccines and oncolytics

Cancer vaccines and oncolytic immunotherapy are promising treatment strategies with potential to provide greater clinical benefit to patients with advanced-stage cancer. In particular, recombinant vaccinia viruses (VV) hold great promise as interventional agents. In this article, we first summarize the current understanding of virus biology and viral genes involved in host-virus interactions to further improve the utility of these agents in therapeutic applications. We then discuss recent findings from basic and clinical studies using VV as cancer vaccines and oncolytic immunotherapies. Despite encouraging results gleaned from translational studies in animal models, clinical trials implementing VV vectors alone as cancer vaccines have yielded largely disappointing results. However, the combination of VV vaccines with alternate forms of standard therapies has resulted in superior clinical efficacy. For instance, combination regimens using TG4010 (MVA-MUC1-IL2) with first-line chemotherapy in advanced-stage non-small cell lung cancer or combining PANVAC with docetaxel in the setting of metastatic breast cancer have clearly provided enhanced clinical benefits to patients. Another novel cancer vaccine approach is to stimulate anti-tumor immunity via STING activation in Batf3-dependent dendritic cells (DC) through the use of replication-attenuated VV vectors. Oncolytic VVs have now been engineered for improved safety and superior therapeutic efficacy by arming them with immune-stimulatory genes or pro-apoptotic molecules to facilitate tumor immunogenic cell death, leading to enhanced DC-mediated cross-priming of T cells recognizing tumor antigens, including neoantigens. Encouraging translational and early phase clinical results with Pexa-Vec have matured into an ongoing global phase III trial for patients with hepatocellular carcinoma. Combinatorial approaches, most notably those using immune checkpoint blockade, have produced exciting pre-clinical results and warrant the development of innovative clinical studies. Finally, we discuss major hurdles that remain in the field and offer some perspectives regarding the development of next generation VV vectors for use as cancer therapeutics.

Identification of 10 cowpox virus proteins that are necessary for induction of hemorrhagic lesions (red pocks) on chorioallantoic membranes

Cowpox viruses (CPXV) cause hemorrhagic lesions ("red pocks") on infected chorioallantoic membranes (CAM) of embryonated chicken eggs, while most other members of the genus Orthopoxvirus produce nonhemorrhagic lesions ("white pocks"). Cytokine response modifier A (CrmA) of CPXV strain Brighton Red (BR) is necessary but not sufficient for the induction of red pocks. To identify additional viral proteins involved in the induction of hemorrhagic lesions, a library of single-gene CPXV knockout mutants was screened. We identified 10 proteins that are required for the formation of hemorrhagic lesions, which are encoded by CPXV060, CPXV064, CPXV068, CPXV069, CPXV074, CPXV136, CPXV168, CPXV169, CPXV172, and CPXV199. The genes are the homologues of F12L, F15L, E2L, E3L, E8R, A4L, A33R, A34R, A36R, and B5R of vaccinia virus (VACV). Mutants with deletions in CPXV060, CPXV168, CPXV169, CPXV172, or CPXV199 induced white pocks with a comet-like shape on the CAM. The homologues of these five genes in VACV encode proteins that are involved in the production of extracellular enveloped viruses (EEV) and the repulsion of superinfecting virions by actin tails. The homologue of CPXV068 in VACV is also involved in EEV production but is not related to actin tail induction. The other genes encode immunomodulatory proteins (CPXV069 and crmA) and viral core proteins (CPXV074 and CPXV136), and the function of the product of CPXV064 is unknown.

IMPORTANCE

It has been known for a long time that cowpox virus induces hemorrhagic lesions on chicken CAM, while most of the other orthopoxviruses produce nonhemorrhagic lesions. Although cowpox virus CrmA has been proved to be responsible for the hemorrhagic phenotype, other proteins causing this phenotype remain unknown. Recently, we generated a complete single-gene knockout bacterial artificial chromosome (BAC) library of cowpox virus Brighton strain. Out of 183 knockout BAC clones, 109 knockout viruses were reconstituted. The knockout library makes possible high-throughput screening for studying poxvirus replication and pathogenesis. In this study, we screened all 109 single-gene knockout viruses and identified 10 proteins necessary for inducing hemorrhagic lesions. The identification of these genes gives a new perspective for studying the hemorrhagic phenotype and may give a better understanding of poxvirus virulence.

Myxoma virus oncolytic efficiency can be enhanced through chemical or genetic disruption of the actin cytoskeleton

Myxoma virus (MYXV) is one of many animal viruses that exhibit oncolytic properties in transformed human cells. Compared to orthopoxviruses like vaccinia (VACV), MYXV spreads inefficiently, which could compromise its use in treating tumors and their associated metastases. The VACV F11 protein promotes virus exit and rapid spread by inhibiting Rho signalling, which results in a disruption of cortical actin. We have previously shown that although MYXV lacks an F11 homolog, the F11L gene can be introduced into MYXV promoting the spread of this Leporipoxvirus in natural host cells. Here we show that the F11-encoding (F11L⁺) MYXV strain replicates to higher levels in a number of human cancer cells. We also show that F11L⁺ MYXV induces better tumor control and prolonged survival of mice bearing MDA-MB-231 cancer cells. Furthermore, we show that this virus also spreads more efficiently from the site of growth in one injected tumor, to a second untreated tumor.

While we focused mostly on the use of a modified MYXV we were able to show that the effects of F11 on MYXV growth in cancer cells could be mimicked through the use of pharmacological inhibition or siRNA-mediated silencing of key regulators of cortical actin (RhoA, RhoC, mDia1, or LIMK2). These data suggest that it may be possible to increase the oncolytic efficacy of wild-type MYXV using chemical inhibitors of RhoA/C or their downstream targets. Furthermore, since all viruses must overcome barriers to exit posed by structures like cortical actin, these findings suggest that the oncolytic activity of other viruses may be enhanced through similar strategies.

Inhibitors of C5 complement enhance vaccinia virus oncolysis

Genetically engineered tumor-selective vaccinia virus (VV) has been demonstrated to be a highly effective oncolytic agent, but immune clearance may limit its therapeutic potential. As previously demonstrated, immunosuppression can lead to significant enhancement of viral recovery and therapeutic effect, but the magnitude of complement-mediated viral inactivation has not been fully elucidated and warrants further investigation. Using fluorescent microscopy and quantitative plaque assays, we have determined complement's key role in viral clearance and its multi-faceted means to pathogen destruction. Complement can lead to direct viral destruction and inhibition of viral uptake into cells, even in the absence of anti-vaccinia antibodies. Our data demonstrate C5 to be integral to the clearance pathway, and its inhibition by Staphylococcal superantigen-like protein leads to a 90-fold and 150-fold enhancement of VV infectivity in both the presence and absence of anti-VV antibodies, respectively. This study suggests that complement inhibition may reduce vaccinia viral neutralization and may be critical to future in vivo work.

A rationally designed A34R mutant oncolytic poxvirus: improved efficacy in peritoneal carcinomatosis

Oncolytic poxviruses have demonstrated initial promising results in patients with cancer in clinical trials, yet further improvements are needed. It has been shown that a single point mutation in the A34R gene resulted in the production of more total progeny virus and more extracellular enveloped virus (EEV), a form that can be immune-evasive and with enhanced spread. We have genetically engineered a new oncolytic poxvirus (designated vA34R) by incorporating this mutated A34R gene into a viral backbone (vvDD) which was designed for tumor-selective replication. This rationally designed virus can evade neutralization from antipoxvirus antibodies and is highly cytotoxic to cancer cells. It demonstrates improved spread and increased replication within the peritoneal cavity resulting in improved antitumor effects in a peritoneal carcinomatosis (PC) model of MC38 colon cancer. Impressively, after carrier cell-mediated delivery in the preimmunized host, vA34R displayed high replication in tumor nodules yet low accumulation in normal tissues thus enhancing the therapeutic index leading to 70% long-term cures. These results demonstrate that vA34R gains an enhanced therapeutic index for PC via immune evasion, increased spread, and production of more progeny virus. Thus, vA34R may be a potent oncolytic virus (OV) for patients with PC, even after prior exposure to vaccinia virus (VV).

Epitope mapping by random peptide phage display reveals essential residues for vaccinia extracellular enveloped virion spread

BACKGROUND

A33 is a type II integral membrane protein expressed on the extracellular enveloped form of vaccinia virus (VACV). Passive transfer of A33-directed monoclonal antibodies or vaccination with an A33 subunit vaccine confers protection against lethal poxvirus challenge in animal models. Homologs of A33 are highly conserved among members of the Orthopoxvirus genus and are potential candidates for inclusion in vaccines or assays targeting extracellular enveloped virus activity. One monoclonal antibody directed against VACV A33, MAb-1G10, has been shown to target a conformation-dependent epitope. Interestingly, while it recognizes VACV A33 as well as the corresponding variola homolog, it does not bind to the monkeypox homolog. In this study, we utilized a random phage display library to investigate the epitope recognized by MAb-1G10 that is critical for facilitating cell-to-cell spread of the vaccinia virus.

RESULTS

By screening with linear or conformational random phage libraries, we found that phages binding to MAb-1G10 display the consensus motif CEPLC, with a disulfide bond formed between two cysteine residues required for MAb-1G10 binding. Although the phage motif contained no linear sequences homologous to VACV A33, structure modeling and analysis suggested that residue D115 is important to form the minimal epitope core. A panel of point mutants expressing the ectodomain of A33 protein was generated and analyzed by either binding assays such as ELISA and immunoprecipitation or a functional assessment by blocking MAb-1G10 mediated comet inhibition in cell culture.

CONCLUSIONS

These results confirm L118 as a component of the MAb-1G10 binding epitope, and further identify D115 as an essential residue. By defining the minimum conformational structure, as well as the conformational arrangement of a short peptide sequence recognized by MAb-1G10, these results introduce the possibility of designing small molecule mimetics that may interfere with the function of A33 in vivo. This information will also be useful for designing improved assays to evaluate the potency of monoclonal and polyclonal products that target A33 or A33-modulated EV dissemination.

The NYCBH vaccinia virus deleted for the innate immune evasion gene, E3L, protects rabbits against lethal challenge by rabbitpox virus

Vaccinia virus deleted for the innate immune evasion gene, E3L, has been shown to be highly attenuated and yet induces a protective immune response against challenge by homologous virus in a mouse model. In this manuscript the NYCBH vaccinia virus vaccine strain was compared to NYCBH vaccinia virus deleted for E3L (NYCBHΔE3L) in a rabbitpox virus (RPV) challenge model. Upon scarification, both vaccines produced a desired skin lesion, although the lesion produced by NYCBHΔE3L was smaller. Both vaccines fully protected rabbits against lethal challenge by escalating doses of RPV, from 10LD(50) to 1000LD(50). A single dose of NYCBHΔE3L protected rabbits from weight loss, fever, and clinical symptoms following the lowest dose challenge of 10LD(50), however it allowed a moderate level of RPV replication at the challenge site, some spread to external skin and mucosal surfaces, and increased numbers of secondary lesions as compared to vaccination with NYCBH. Alternately, two doses of NYCBHΔE3L fully protected rabbits from weight loss, fever, and clinical symptoms, following challenge with 100-1000LD(50) RPV, and it prevented development of secondary lesions similar to protection seen with NYCBH. Finally, vaccination with either one or two doses of NYCBHΔE3L resulted in similar neutralizing antibody titers following RPV challenge as compared to titers obtained by vaccination with NYCBH. These results support the efficacy of the attenuated NYCBHΔE3L in protection against an orthologous poxvirus challenge.

Temperature-sensitive mutant in the vaccinia virus E6 protein produce virions that are transcriptionally inactive

The vaccinia virus E6R gene encodes a late protein that is packaged into virion cores. A temperature-sensitive mutant was used to study the role of this protein in viral replicative cycle. Cts52 has a P226L missense mutation in the E6R gene, shows a two-log reduction in plaque formation, but displays normal patterns of gene expression, late protein processing and DNA replication during infection. Mutant virions produced at 40 degrees C were similar in their morphology to wt virions grown at 40 degrees C. The particle to infectivity ratio was 50 times higher in purified Cts52 grown at 40 degrees C when compared to the mutant grown at permissive temperature. In vitro characterization of Cts-52 particles grown at 40 degrees C revealed no differences in protein composition or in DNA content and the mutant virions could bind and enter cells. However, core particles prepared from Cts52 grown at 40 degrees C failed to transcribe in vitro. Our results show that E6 in the virion has either a direct or an indirect role in viral transcription.

F11-mediated inhibition of RhoA signalling enhances the spread of vaccinia virus in vitro and in vivo in an intranasal mouse model of infection

The cortical actin cytoskeleton beneath the plasma membrane represents a physical barrier that vaccinia virus has to overcome during its exit from an infected cell. Previous observations using overexpression and pharmacological approaches suggest that vaccinia enhances its release by modulating the cortical actin cytoskeleton by inhibiting RhoA signalling using the viral protein F11. We have now examined the role of F11 and its ability to interact with RhoA to inhibit its downstream signalling in the spread of vaccinia infection both in vitro and in vivo. Live cell imaging over 48 hours reveals that loss of F11 or its ability to bind RhoA dramatically reduces the rate of cell-to-cell spread of the virus in a cell monolayer. Cells infected with the DeltaF11L virus also maintained their cell-to-cell contacts, and did not undergo virus-induced motility as observed during wild-type infections. The DeltaF11L virus is also attenuated in intranasal mouse models of infection, as it is impaired in its ability to spread from the initial sites of infection to the lungs and spleen. Loss of the ability of F11 to bind RhoA also reduces viral spread in vivo. Our results clearly establish that viral-mediated inhibition of RhoA signalling can enhance the spread of infection not only in cell monolayers, but also in vivo.

Comparative evaluation of the immune responses and protection engendered by LC16m8 and Dryvax smallpox vaccines in a mouse model

The immune response elicited by LC16m8, a candidate smallpox vaccine that was developed in Japan by cold selection during serial passage of the Lister vaccine virus in primary rabbit kidney cells, was compared to Dryvax in a mouse model. LC16m8 carries a mutation resulting in the truncation of the B5 protein, an important neutralizing target of the extracellular envelope form of vaccinia virus (EV). LC16m8 elicited a broad-spectrum immunoglobulin G (IgG) response that neutralized both EV and the intracellular mature form of vaccinia virus and provoked cell-mediated immune responses, including the activation of CD4+ and CD8+ cells, similarly to Dryvax. Mice inoculated with LC16m8 had detectable but low levels of anti-B5 IgG compared to Dryvax, but both Dryvax and LC16m8 sera neutralized vaccinia virus EV in vitro. A truncated B5 protein (approximately 8 kDa) was expressed abundantly in LC16m8-infected cells, and both murine immune sera and human vaccinia virus immunoglobulin recognized the truncated recombinant B5 protein in antigen-specific enzyme-linked immunosorbent assays. At a high-dose intranasal challenge (100 or 250 50% lethal doses), LC16m8 and Dryvax conferred similar levels of protection against vaccinia virus strain WR postvaccination. Taken together, the results extend our current understanding of the protective immune responses elicited by LC16m8 and indicate that the relative efficacy in a mouse model rivals that of previously licensed smallpox vaccines.

Disulfide bond formation at the C termini of vaccinia virus A26 and A27 proteins does not require viral redox enzymes and suppresses glycosaminoglycan-mediated cell fusion

Vaccinia virus A26 protein is an envelope protein of the intracellular mature virus (IMV) of vaccinia virus. A mutant A26 protein with a truncation of the 74 C-terminal amino acids was expressed in infected cells but failed to be incorporated into IMV (W. L. Chiu, C. L. Lin, M. H. Yang, D. L. Tzou, and W. Chang, J. Virol 81:2149-2157, 2007). Here, we demonstrate that A27 protein formed a protein complex with the full-length form but not with the truncated form of A26 protein in infected cells as well as in IMV. The formation of the A26-A27 protein complex occurred prior to virion assembly and did not require another A27-binding protein, A17 protein, in the infected cells. A26 protein contains six cysteine residues, and in vitro mutagenesis showed that Cys441 and Cys442 mediated intermolecular disulfide bonds with Cys71 and Cys72 of viral A27 protein, whereas Cys43 and Cys342 mediated intramolecular disulfide bonds. A26 and A27 proteins formed disulfide-linked complexes in transfected 293T cells, showing that the intermolecular disulfide bond formation did not depend on viral redox pathways. Finally, using cell fusion from within and fusion from without, we demonstrate that cell surface glycosaminoglycan is important for virus-cell fusion and that A26 protein, by forming complexes with A27 protein, partially suppresses fusion.

Functional characterization of the vaccinia virus I5 protein

The I5L gene is one of ~90 genes that are conserved throughout the chordopoxvirus family, and hence are presumed to play vital roles in the poxvirus life cycle. Previous work had indicated that the VP13 protein, a component of the virion membrane, was encoded by the I5L gene, but no additional studies had been reported. Using a recombinant virus that encodes an I5 protein fused to a V5 epitope tag at the endogenous locus (vI5V5), we show here that the I5 protein is expressed as a post-replicative gene and that the ~9 kDa protein does not appear to be phosphorylated in vivo. I5 does not appear to traffic to any cellular organelle, but ultrastructural and biochemical analyses indicate that I5 is associated with the membranous components of assembling and mature virions. Intact virions can be labeled with anti-V5 antibody as assessed by immunoelectron microscopy, indicating that the C' terminus of the protein is exposed on the virion surface. Using a recombinant virus which encodes only a TET-regulated copy of the I5V5 gene (vΔindI5V5), or one in which the I5 locus has been deleted (vΔI5), we also show that I5 is dispensable for replication in tissue culture. Neither plaque size nor the viral yield produced in BSC40 cells or primary human fibroblasts are affected by the absence of I5 expression.

Comparison of multiple vaccine vectors in a single heterologous prime-boost trial

The prevention of infectious disease via prophylactic immunization is a mainstay of global public health efforts. Vaccine design would be facilitated by a better understanding of the type and durability of immune responses generated by different vaccine vectors. We report here the results of a comparative immunogenicity trial of six different vaccine vectors expressing the same insert antigen, cowpox virus B5 (CPXV-B5). Of those vectors tested, recombinant adenovirus (rAd5) was the most immunogenic, inducing the highest titer anti-B5 antibodies and conferring protection from sublethal vaccinia virus challenge in mice after a single immunization. We tested select heterologous prime-boost combinations and identified recombinant vesicular stomatitis virus (rVSV) and recombinant Venezuelan equine encephalitis virus replicons (VRP) as the most synergistic regimen. Comparative data such as those presented here are critical to efforts to generate protective vaccines for emerging infectious diseases as well as for biothreat agents.

Heterogeneity in the A33 protein impacts the cross-protective efficacy of a candidate smallpox DNA vaccine

We previously developed a gene-based vaccine, termed 4pox, which targets four orthopoxvirus proteins (A33, L1, B5, and A27). Because any subunit orthopoxvirus vaccine must protect against multiple species of orthopoxviruses, we are interested in understanding the cross-protective potential of our 4pox vaccine target immunogens. In our current studies, we focused on the A33 immunogen. We found one monoclonal antibody against A33, MAb-1G10, which could not bind the monkeypox virus A33 ortholog, A35. MAb-1G10 binding could be rescued if A35 amino acids 118 and 120 were substituted with those from A33. MAb-1G10 has been shown to protect mice from VACV challenge, thus our findings indicated a protective epitope differs among orthopoxviruses. Accordingly, we tested the cross-protective efficacy of a DNA vaccine consisting of A35R against VACV challenge and compared it to vaccination with A33R DNA. Mice vaccinated with A35R had greater mortality and more weight loss compared to those vaccinated with A33R. These findings demonstrate that despite high homology between A33R orthologs, amino acid differences can impact cross-protection. Furthermore, our results caution that adequate cross-protection by any pan-orthopoxvirus subunit vaccine will require not only careful evaluation of cross-protective immunity, but also of targeting of multiple orthopoxvirus immunogens.

Vaccination of BALB/c mice with Escherichia coli-expressed vaccinia virus proteins A27L, B5R, and D8L protects mice from lethal vaccinia virus challenge

The potential threat of smallpox use in a bioterrorist attack has heightened the need to develop an effective smallpox vaccine for immunization of the general public. Vaccination with the current smallpox vaccine, Dryvax, produces protective immunity but may result in adverse reactions for some vaccinees. A subunit vaccine composed of protective vaccinia virus proteins should avoid the complications arising from live-virus vaccination and thus provide a safer alternative smallpox vaccine. In this study, we assessed the protective efficacy and immunogenicity of a multisubunit vaccine composed of the A27L and D8L proteins from the intracellular mature virus (IMV) form and the B5R protein from the extracellular enveloped virus (EEV) form of vaccinia virus. BALB/c mice were immunized with Escherichia coli-produced A27L, D8L, and B5R proteins in an adjuvant consisting of monophosphoryl lipid A and trehalose dicorynomycolate or in TiterMax Gold adjuvant. Following immunization, mice were either sacrificed for analysis of immune responses or lethally challenged by intranasal inoculation with vaccinia virus strain Western Reserve. We observed that three immunizations either with A27L, D8L, and B5R or with the A27L and B5R proteins alone induced potent neutralizing antibody responses and provided complete protection against lethal vaccinia virus challenge. Several linear B-cell epitopes within the three proteins were recognized by sera from the immunized mice. In addition, protein-specific cellular responses were detected in spleens of immunized mice by a gamma interferon enzyme-linked immunospot assay using peptides derived from each protein. Our data suggest that a subunit vaccine incorporating bacterially expressed IMV- and EEV-specific proteins can be effective in stimulating anti-vaccinia virus immune responses and providing protection against lethal virus challenge.

Membrane cell fusion activity of the vaccinia virus A17-A27 protein complex

Vaccinia virus enters cells by endocytosis and via a membrane fusion mechanism mediated by viral envelope protein complexes. While several proteins have been implicated in the entry/fusion event, there is no direct proof for fusogenic activity of any viral protein in heterologous systems. Transient coexpression of A17 and A27 in mammalian cells led to syncytia formation in a pH-dependent manner, as ascertained by confocal fluorescent immunomicroscopy. The pH-dependent fusion activity was identified to reside in A17 amino-terminal ectodomain after overexpression in insect cells using recombinant baculoviruses. Through the use of A17 ectodomain deletion mutants, it was found that the domain important for fusion spanned between residues 18 and 34. To further characterize A17-A27 fusion activity in mammalian cells, 293T cell lines stably expressing A17, A27 or coexpressing both proteins were generated using lentivectors. A27 was exposed on the cell surface only when A17 was coexpressed. In addition, pH-dependent fusion activity was functionally demonstrated in mammalian cells by cytoplasmic transfer of fluorescent proteins, only when A17 and A27 were coexpressed. Bioinformatic tools were used to compare the putative A17-A27 protein complex with well-characterized fusion proteins. Finally, all experimental evidence was integrated into a working model for A17-A27-induced pH-dependent cell-to-cell fusion.

Vaccinia virus A34 glycoprotein determines the protein composition of the extracellular virus envelope

The outer envelope of the extracellular form of vaccinia virus contains five virus-encoded proteins, F13, A33, A34, A56, and B5, that, with the exception of A56, are implicated in virus egress or infectivity. A34, a type II transmembrane glycoprotein, is involved in the induction of actin tails, the release of enveloped virus from the surfaces of infected cells, and the disruption of the virus envelope after ligand binding prior to virus entry. To investigate interactions between A34 and other envelope proteins, a recombinant vaccinia virus (vA34R(HA)) expressing an epitope-tagged version of A34 (A34(HA)) was constructed by appending an epitope from influenza virus hemagglutinin to the C terminus of A34. Complexes of A34(HA) with B5 and A36, but not with A33 or F13, were detected in vA34R(HA)-infected cells. A series of vaccinia viruses expressing mutated versions of the B5 protein was used to investigate the domain(s) of B5 required for interaction with A34. Both the cytoplasmic and the transmembrane domains of B5 were dispensable for binding to A34. Most of the extracellular domain of B5, which contains four short consensus repeats homologous to complement control proteins, was sufficient for A34 interaction, indicating that both proteins interact through their ectodomains. Immunofluorescence experiments on cells infected with A34-deficient virus indicated that A34 is required for efficient targeting of B5, A36, and A33 into wrapped virions. Consistent with this observation, the envelope of A34-deficient virus contained normal amounts of F13 but decreased amounts of A33 and B5 with respect to the parental WR virus. These results point to A34 as a major determinant in the protein composition of the vaccinia virus envelope.

Antibody profiling by proteome microarray reveals the immunogenicity of the attenuated smallpox vaccine modified vaccinia virus ankara is comparable to that of Dryvax

Modified vaccinia virus Ankara (MVA) is a highly attenuated vaccinia virus that is under consideration as an alternative to the conventional smallpox vaccine Dryvax. MVA was attenuated by extensive passage of vaccinia virus Ankara in chicken embryo fibroblasts. Several immunomodulatory genes and genes that influence host range are deleted or mutated, and replication is aborted in the late stage of infection in most nonavian cells. The effect of these mutations on immunogenicity is not well understood. Since the structural genes appear to be intact in MVA, it is hypothesized that critical targets for antibody neutralization have been retained. To test this, we probed microarrays of the Western Reserve (WR) proteome with sera from humans and macaques after MVA and Dryvax vaccination. As most protein sequences of MVA are 97 to 99% identical to those of other vaccinia virus strains, extensive binding cross-reactivity is expected, except for those deleted or truncated. Despite different hosts and immunization regimens, the MVA and Dryvax antibody profiles were broadly similar, with antibodies against membrane and core proteins being the best conserved. The responses to nonstructural proteins were less well conserved, although these are not expected to influence virus neutralization. The broadest antibody response was obtained for hyperimmune rabbits with WR, which is pathogenic in rabbits. These data indicate that, despite the mutations and deletions in MVA, its overall immunogenicity is broadly comparable to that of Dryvax, particularly at the level of antibodies to membrane proteins. The work supports other information suggesting that MVA may be a useful alternative to Dryvax.

Microarray assay for evaluation of the genetic stability of modified vaccinia virus Ankara B5R gene

Adverse events associated with the use of live smallpox vaccines have led to the development of a new generation of attenuated smallpox vaccines that are prepared in cultured cells as alternatives. The inability to conduct direct clinical evaluation of their efficacy in humans demands that licensure be based on animal studies and exhaustive evaluation of their in vitro properties. One of the most important characteristics of live viral vaccines is their genetic stability, including reversion of the vaccine strain to more virulent forms, recombination with other viral sequences to produce potentially pathogenic viruses, and genetic drift that can result in decrease of immunogenicity and efficacy. To study genetic stability of an immunoessential vaccinia virus gene in a new generation smallpox vaccine, an advanced oligonucleotide microchip was developed and used to assay for mutations that could emerge in B5R gene, a vaccinia virus gene encoding for a protein that contains very important neutralizing epitopes. This microarray contained overlapping oligonucleotides covering the B5R gene of modified vaccinia virus Ankara (MVA), a well-studied candidate smallpox vaccine. The microarray assay was shown to be able to detect even a single point mutation, and to differentiate between vaccinia strains. At the same time, it could detect newly emerged mutations in clones of vaccinia strains. In the work described here, it was shown that MVA B5R gene was stable after 34 passages in Vero and MRC-5 cells that were proposed for use as cell substrates for vaccine manufacture. Potentially, the proposed method could be used as an identity test and could be extended for the entire viral genome and used to monitor consistency of vaccine production.

Characterization of chimpanzee/human monoclonal antibodies to vaccinia virus A33 glycoprotein and its variola virus homolog in vitro and in a vaccinia virus mouse protection model

Three distinct chimpanzee Fabs against the A33 envelope glycoprotein of vaccinia virus were isolated and converted into complete monoclonal antibodies (MAbs) with human gamma 1 heavy-chain constant regions. The three MAbs (6C, 12C, and 12F) displayed high binding affinities to A33 (K(d) of 0.14 nM to 20 nM) and may recognize the same epitope, which was determined to be conformational and located within amino acid residues 99 to 185 at the C terminus of A33. One or more of the MAbs were shown to reduce the spread of vaccinia virus as well as variola virus (the causative agent of smallpox) in vitro and to more effectively protect mice when administered before or 2 days after intranasal challenge with virulent vaccinia virus than a previously isolated mouse anti-A33 MAb (1G10) or vaccinia virus immunoglobulin. The protective efficacy afforded by anti-A33 MAb was comparable to that of a previously isolated chimpanzee/human anti-B5 MAb. The combination of anti-A33 MAb and anti-B5 MAb did not synergize the protective efficacy. These chimpanzee/human anti-A33 MAbs may be useful in the prevention and treatment of vaccinia virus-induced complications of vaccination against smallpox and may also be effective in the immunoprophylaxis and immunotherapy of smallpox and other orthopoxvirus diseases.

Major neutralizing sites on vaccinia virus glycoprotein B5 are exposed differently on variola virus ortholog B6

Immunization against smallpox (variola virus) with Dryvax, a live vaccinia virus (VV), was effective, but now safety is a major concern. To overcome this issue, subunit vaccines composed of VV envelope proteins from both forms of infectious virions, including the extracellular enveloped virion (EV) protein B5, are being developed. However, since B5 has 23 amino acid differences compared with its B6 variola virus homologue, B6 might be a better choice for such a strategy. Therefore, we compared the properties of both proteins using a panel of monoclonal antibodies (MAbs) to B5 that we had previously characterized and grouped according to structural and functional properties. The B6 gene was obtained from the Centers for Disease Control and Prevention, and the ectodomain was cloned and expressed in baculovirus as previously done with B5, allowing us to compare the antigenic properties of the proteins. Polyclonal antibodies to B5 or B6 cross-reacted with the heterologous protein, and 16 of 26 anti-B5 MAbs cross-reacted with B6. Importantly, 10 anti-B5 MAbs did not cross-react with B6. Of these, three have important anti-VV biologic properties, including their ability to neutralize EV infectivity and block comet formation. Here, we found that one of these three MAbs protected mice from a lethal VV challenge by passive immunization. Thus, epitopes that are present on B5 but not on B6 would generate an antibody response that would not recognize B6. Assuming that B6 contains similar variola virus-specific epitopes, our data suggest that a subunit vaccine using the variola virus homologues might exhibit improved protective efficacy against smallpox.

Myxoma virus in the European rabbit: interactions between the virus and its susceptible host

Myxoma virus (MV) is a poxvirus that evolved in Sylvilagus lagomorphs, and is the causative agent of myxomatosis in European rabbits (Oryctolagus cuniculus). This virus is not a natural pathogen of O. cuniculus, yet is able to subvert the host rabbit immune system defenses and cause a highly lethal systemic infection. The interaction of MV proteins and the rabbit immune system has been an ideal model to help elucidate host/poxvirus interactions, and has led to a greater understanding of how other poxvirus pathogens are able to cause disease in their respective hosts. This review will examine how MV causes myxomatosis, by examining a selection of the identified immunomodulatory proteins that this virus expresses to subvert the immune and inflammatory pathways of infected rabbit hosts.

Vaccinia virus 4c (A26L) protein on intracellular mature virus binds to the extracellular cellular matrix laminin

Vaccinia virus intracellular mature virus (IMV) binds to glycosaminoglycans (GAGs) on cells via three virion proteins, H3L, A27L, and D8L. In this study, we demonstrated that binding of IMV to BSC40 cells was competitively inhibited by soluble laminin but not by fibronectin or collagen V, suggesting that this cell surface extracellular matrix (ECM) protein may play a role in vaccinia virus entry. Moreover, IMV infection of GAG(-) sog9 cells was also inhibited by laminin, demonstrating that virion binding to laminin does not involve a prior interaction with GAGs. Furthermore, comparative envelope protein analyses of wild-type vaccinia virus strain Western Reserve, which binds to laminin, and of a mutant virus, IA27L, which does not, showed that the A26L open reading frame (ORF), encoding an envelope protein, was mutated in IA27L, resulting in A26L being absent from the IMV. Expression of the wild-type A26L ORF in IA27L resulted in laminin binding activity. Moreover, recombinant A26L protein bound to laminin in vitro with a high affinity, providing direct evidence that A26L is the laminin binding protein on IMV. In summary, these results reveal a novel role for the vaccinia viral envelope protein A26L in binding to the ECM protein laminin, an association that is proposed to facilitate IMV entry.

Genus Parapoxvirus

Highly contagious pustular skin infections of sheep, goats and cattle that were unwittingly transmitted to humans from close contact with infected animals, have been the scourge of shepherds, herdsmen and dairy farmers for centuries. In more recent times we recognise that these proliferative pustular lesions are likely to be caused by a group of zoonotic viruses that are classified as parapoxviruses. In addition to infecting the above ungulates, parapoxviruses have more recently been isolated from seals, camels, red deer and reindeer and most have been shown to infect man. The parapoxviruses have one of the smallest genomes of the poxvirus family (140 kb) yet share over 70% of their genes with the most virulent members. Like other poxviruses, the central core of the genomes encode factors for virus transcription and replication, and structural proteins, whereas the terminal regions encode accessory factors that give the parapoxvirus group many of its unique features. Several genes of parapoxviruses are unique to this genus and encode factors that target inflammation, the innate immune responses and the development of acquired immunity. These factors include a homologue of mammalian interleukin (IL)-10, a chemokine binding protein and a granulocyte-macrophage colony stimulating factor /IL-2 binding protein. The ability of this group to reinfect their hosts, even though a cell-mediated memory response is induced during primary infection, may be related to their epitheliotropic niche and the immunomodulators they produce. In this highly localised environment, the secreted immunomodulators only interfere with the local immune response and thus do not compromise the host’s immune system. The discovery of a vascular endothelial growth factor-like gene may explain the highly vascular nature of parapoxvirus lesions. There are many genes of parapoxviruses which do not encode polypeptides with significant matches with protein sequences in public databases, separating this genus from most other mammalian poxviruses. These genes appear to be involved in inhibiting apoptosis, manipulating cell cycle progression and degradation of cellular proteins that may be involved in the stress response, thus allowing the virus to subvert intracellular antiviral mechanisms and enhance the availability of cellular molecules required for replication. Parapoxviruses in common with Molluscum contagiosum virus lack a number of genes that are highly conserved in other poxviruses, including factors for nucleotide metabolism, serine protease inhibitors and kelch-like proteins. It is apparent that parapoxviruses have evolved a unique repertoire of genes that have allowed adaptation to the highly specialised environment of the epidermis.

The envelope G3L protein is essential for entry of vaccinia virus into host cells

The vaccinia virus G3L/WR079 gene encodes a conserved protein with a predicted transmembrane domain. Our proteomic analyses of vaccinia virus revealed that G3L protein is incorporated into intracellular mature virus; however, the function of G3L protein in the vaccinia virus life cycle has not been investigated. In this study, a recombinant vaccinia virus, viG3L, expressing G3L protein under IPTG (isopropyl-beta-d-thiogalactopyranoside) regulation was constructed. Under permissive conditions when G3L protein was expressed, the vaccinia virus life cycle proceeded normally, resulting in plaque formation in BSC40 cells. In contrast, under nonpermissive conditions when G3L protein expression was repressed, no plaques were formed, showing that G3L protein is essential for vaccinia virus growth in cell cultures. In infected cells when G3L protein was not expressed, the formation of intracellular mature virus (IMV) and cell-associated enveloped virus occurred normally, showing that G3L protein is not required for virion morphogenesis. IMV particles containing (G3L(+)) or lacking (G3L(-)) G3L protein were purified and were found to be indistinguishable on microscopic examination. Both G3L(+) and G3L(-) IMV bound to HeLa cells; however, G3L(-) IMV failed to enter the cells, showing that G3L protein is required for IMV penetration into cells. Finally, G3L protein was required for fusion of the infected cells under low-pH treatment. Thus, our results provide direct evidence that G3L is an essential component of the vaccinia virus fusion complex, in addition to the previously reported A28, H2, L5, A21, and A16 proteins.

Interaction between vaccinia virus extracellular virus envelope A33 and B5 glycoproteins

The extracellular form of vaccinia virus acquires its outer envelope by wrapping with cytoplasmic membranes that contain at least seven virus-encoded proteins, of which four are glycoproteins. We searched for interactions between the vaccinia virus A33 glycoprotein and proteins A34, A36, B5, F12, and F13. First, when myc epitope-tagged A33 was expressed in combination with other envelope proteins, A33 colocalized with B5 and A36, suggesting that direct A33-B5 and A33-A36 interactions occur in the absence of infection. A recombinant vaccinia virus (vA33Rmyc) was constructed by introduction of the myc-tagged A33 version (A33myc) into A33-deficient vaccinia virus. A33myc partially restored plaque formation and colocalized with enveloped virions in infected cells. Coimmunoprecipitation experiments with extracts of vA33Rmyc-infected cells confirmed the existence of a physical association of A33 with A36 and B5. Of these, the A33-B5 interaction is a novel finding, whereas the interaction between A33 and A36 has been previously characterized. A collection of vaccinia viruses expressing mutated versions of the B5 protein was used to investigate the domain(s) of B5 required for interaction with A33. Both the cytoplasmic domain and most of the extracellular domain, but not the transmembrane domain, of the B5 protein were dispensable for binding to A33. Mutations in the extracellular portions of B5 and A33 that enhance extracellular virus release did not affect the interaction between the two. In contrast, substituting the B5 transmembrane domain with that of the vesicular stomatitis virus G glycoprotein prevented the association with A33. Immunofluorescence experiments on virus mutants indicated that B5 is required for efficient targeting of A33 into enveloped virions. These results point to the transmembrane domain of B5 as the major determinant of the A33-B5 interaction and demonstrate that protein-protein interactions are crucial in determining the composition of the virus envelope.

Chimpanzee/human mAbs to vaccinia virus B5 protein neutralize vaccinia and smallpox viruses and protect mice against vaccinia virus

Chimpanzee Fabs against the B5 envelope glycoprotein of vaccinia virus were isolated and converted into complete mAbs with human gamma 1 heavy chain constant regions. The two mAbs (8AH8AL and 8AH7AL) displayed high binding affinities to B5 (Kd of 0.2 and 0.7 nM). The mAb 8AH8AL inhibited the spread of vaccinia virus as well as variola virus (the causative agent of smallpox) in vitro, protected mice from subsequent intranasal challenge with virulent vaccinia virus, protected mice when administered 2 days after challenge, and provided significantly greater protection than that afforded by a previously isolated rat anti-B5 mAb (19C2) or by vaccinia immune globulin. The mAb bound to a conformational epitope between amino acids 20 and 130 of B5. These chimpanzee/human anti-B5 mAbs may be useful in the prevention and treatment of vaccinia virus-induced complications of vaccination against smallpox and may also be effective in the immunoprophylaxis and immunotherapy of smallpox.

Evasion of innate immunity by vaccinia virus

Vaccinia virus, a member of the Poxviridae, expresses many proteins involved in immune evasion. In this review, we present a brief characterisation of the virus and its effects on host cells and discuss representative secreted and intracellular proteins expressed by vaccinia virus that are involved in modulation of innate immunity. These proteins target different aspects of the innate response by binding cytokines and interferons, inhibiting cytokine synthesis, opposing apoptosis or interfering with different signalling pathways, including those triggered by interferons and toll-like receptors.

Characterization of the major capsid proteins of myxoma virus particles using MALDI-TOF mass spectrometry

The protein composition of poxvirus particles remains uncertain because of their large size and structural complexity. This has complicated the characterization of even well-studied Orthopoxviruses, like vaccinia virus, and little or nothing is known about the capsid composition of viruses belonging to other poxvirus genera. This paper describes methods that address this problem and have been used to identify 17 different Leporipoxvirus capsid proteins. Myxoma virus particles were purified using sucrose and Nicodenz gradient centrifugation and subfractionated into membrane and core fractions by thiol and detergent treatment. These materials were further fractionated using reverse-phase chromatography and SDS-PAGE and the resulting proteins identified by mass spectroscopy. Most of the myxoma proteins identified in this manner were homologs of either vaccinia virus structural proteins (F17R, L4R, J1R, H3L, A3L, A10L, A27L, and A45R) or virion-associated enzymes (I7L, H4L, D11L, A7L, and A22R). However, the myxoma homolog of the vaccinia P4a/A10L protein (M099L) differs from P4a protein in being proteolytically cleaved only once. M095L and M151R were also detected in core fractions. M095L and M151R are homologs of vaccinia A6L and B13R proteins, respectively, and poxvirus proteins not previously known to be capsid components. M093L, a protein of unknown function and having no certain Orthopoxvirus homolog associates with membrane fractions. These studies illustrate the conservation of Chordopoxvirion architecture and the methods that can be used to elucidate the proteins comprising these structures.

Epitope-mapping studies define two major neutralization sites on the vaccinia virus extracellular enveloped virus glycoprotein B5R

Vaccinia extracellular enveloped virus (EEV) is critical for cell-to-cell and long-range virus spread both in vitro and in vivo. The B5R gene encodes an EEV-specific type I membrane protein that is essential for efficient EEV formation. The majority of the B5R ectodomain consists of four domains with homology to short consensus repeat domains followed by a stalk. Previous studies have shown that polyclonal antibodies raised against the B5R ectodomain inhibit EEV infection. In this study, our goal was to elucidate the antigenic structure of B5R and relate this to its function. To do this, we produced multimilligram quantities of vaccinia virus B5R as a soluble protein [B5R(275t)] using a baculovirus expression system. We then selected and characterized a panel of 26 monoclonal antibodies (MAbs) that recognize B5R(275t). Five of these MAbs neutralized EEV and inhibited comet formation. Two other MAbs were able only to neutralize EEV, while five others were able only to inhibit comet formation. This suggests that the EEV neutralization and comet inhibition assays measure different viral functions and that at least two different antigenic sites on B5R are important for these activities. We further characterized the MAbs and the antigenic structure of B5R(275t) by peptide mapping and by reciprocal MAb blocking studies using biosensor analysis. The epitopes recognized by neutralizing MAbs were localized to SCR1-SCR2 and/or the stalk of B5R(275t). Furthermore, the peptide and blocking data support the concept that SCR1 and the stalk may be in juxtaposition and may be part of the same functional domain.

Commensal bacteria as a novel delivery system for subunit vaccines directed against agents of bioterrorism

Following the anthrax attacks of 2001 and the recent SARS outbreak, concerns about emerging and re-emerging infectious diseases have catalyzed a renewed interest in developing new vaccination strategies that provide rapid and flexible response options to future threats. Because the probability of encountering one of these exotic agents is unknown, it is essential that new vaccine formulations employ methods that provide effective protection and extremely good safety profiles if they are to be used by either military or civilian populations. One approach, which potentially satisfies these criteria, is the use of live recombinant Gram-positive commensal bacteria as expression vectors. This review provides an overview of the system, its advantages and limitations, and details an example of how Gram-positive commensal bacteria are being developed as a fifth generation vaccine against a Class A biowarfare pathogen, namely smallpox.

Vaccinia virus penetration requires cholesterol and results in specific viral envelope proteins associated with lipid rafts

Vaccinia virus infects a wide variety of mammalian cells from different hosts, but the mechanism of virus entry is not clearly defined. The mature intracellular vaccinia virus contains several envelope proteins mediating virion adsorption to cell surface glycosaminoglycans; however, it is not known how the bound virions initiate virion penetration into cells. For this study, we investigated the importance of plasma membrane lipid rafts in the mature intracellular vaccinia virus infection process by using biochemical and fluorescence imaging techniques. A raft-disrupting drug, methyl-beta-cyclodextrin, inhibited vaccinia virus uncoating without affecting virion attachment, indicating that cholesterol-containing lipid rafts are essential for virion penetration into mammalian cells. To provide direct evidence of a virus and lipid raft association, we isolated detergent-insoluble glycolipid-enriched membranes from cells immediately after virus infection and demonstrated that several viral envelope proteins, A14, A17L, and D8L, were present in the cell membrane lipid raft fractions, whereas the envelope H3L protein was not. Such an association did not occur after virions attached to cells at 4 degrees C and was only observed when virion penetration occurred at 37 degrees C. Immunofluorescence microscopy also revealed that cell surface staining of viral envelope proteins was colocalized with GM1, a lipid raft marker on the plasma membrane, consistent with biochemical analyses. Finally, mutant viruses lacking the H3L, D8L, or A27L protein remained associated with lipid rafts, indicating that the initial attachment of vaccinia virions through glycosaminoglycans is not required for lipid raft formation.

Antibodies against the extracellular enveloped virus B5R protein are mainly responsible for the EEV neutralizing capacity of vaccinia immune globulin

In the event of smallpox bioterrorism, widespread vaccination may be required. Vaccinia immune globulin (VIG) has been used to treat complications from the smallpox vaccine. While the potency of VIG was defined by its ability to neutralize intracellular mature virus, a second form of vaccinia called the extracellular enveloped virus (EEV) is critical for virus spread in the host. The B5R-protein is one of many EEV-specific proteins. Immunoprecipitation and ELISA revealed that VIG recognizes the B5R-protein. An EEV plaque-reduction assay using a recombinant vaccinia that lacks the majority of the extracellular domain of B5R showed that the ability of VIG to neutralize EEV is principally directed at B5R. In addition, absorbing out the anti-B5R antibody present in VIG through the addition of recombinant B5R protein abrogated VIG's ability to significantly neutralize wild-type EEV. This work demonstrates the prominent role of B5R as a target of EEV-neutralizing activity of human antibodies.

Investigation of structural and functional motifs within the vaccinia virus A14 phosphoprotein, an essential component of the virion membrane

We have previously reported the construction and characterization of an inducible recombinant virus in which expression of the vaccinia virus membrane protein A14 is experimentally regulated using the tetracycline operator-repressor system. Repression of A14, which results in a 1,000-fold reduction in viral yield, leads to an early block in viral morphogenesis characterized by the accumulation of large virosomes, empty "crescents" that fail to contact these virosomes, and, most strikingly, large numbers of aberrant 25-nm vesicles. Here we report the establishment of a transient-complementation system for the structure-function analysis of A14. We have constructed numerous mutant alleles of A14 designed to identify and test the importance of key structural and sequence motifs within A14, including sites of posttranslational modification, such as glycosylation, phosphorylation, and dimerization. From these studies we have determined that robust complementation ability requires an intact N terminus and two regions flanking the first membrane-spanning domain of A14. We show that A14 is modified by N-linked glycosylation both in vitro and in vivo. However, only a minority of A14 molecules are glycosylated in vivo and these are not encapsidated. In this report we also identify the sole phosphorylated serine residue of A14 as lying within the NHS(85) motif that undergoes glycosylation. Additionally, we show that the Cys(71) residue is required for intermolecular disulfide bond formation and describe the properties of a virus expressing an allele of A14 that cannot form disulfide-linked dimers.

Plasma membrane localization and fusion inhibitory activity of the cowpox virus serpin SPI-3 require a functional signal sequence and the virus encoded hemagglutinin

The cowpox virus (CPV) glycoprotein serpin SPI-3, a functional protease inhibitor, and the viral hemagglutinin (HA) are required to prevent fusion of wt CPV infected cells. SPI-3 and HA from CPV infected cells co-localize to the plasma membrane and are found in extracellular enveloped virus (EEV). We also show that an N-terminal SPI-3 signal sequence, but not glycosylation, is required for membrane localization and fusion inhibition. In the absence of HA (CPVDeltaHA), no SPI-3 is found on the membrane and infected cells fuse. Conversely, HA from both wt CPV and CPVDeltaSPI-3 infections is on the membrane, indicating a requirement of HA for SPI-3 plasma membrane localization. In the absence of HA, secretion of SPI-3 or SPI-3 N-glyc(-) was markedly enhanced, suggesting HA serves to retain SPI-3 on the plasma membrane,thereby preventing cell fusion.

The oncolytic virotherapy treatment platform for cancer: unique biological and biosafety points to consider

The field of replication-selective oncolytic viruses (virotherapy) has exploded over the last 10 years. As with many novel therapeutic approaches, initial overexuberance has been tempered by clinical trial results with first-generation agents. Although a number of significant hurdles to this approach have now been identified, novel solutions have been proposed and improvements are being made at a furious rate. This article seeks to initiate a discussion of these hurdles, approaches to overcome them, and unique safety and regulatory issues to consider.

The formation and function of extracellular enveloped vaccinia virus

Vaccinia virus produces four different types of virion from each infected cell called intracellular mature virus (IMV), intracellular enveloped virus (IEV), cell-associated enveloped virus (CEV) and extracellular enveloped virus (EEV). These virions have different abundance, structure, location and roles in the virus life-cycle. Here, the formation and function of these virions are considered with emphasis on the EEV form and its precursors, IEV and CEV. IMV is the most abundant form of virus and is retained in cells until lysis; it is a robust, stable virion and is well suited to transmit infection between hosts. IEV is formed by wrapping of IMV with intracellular membranes, and is an intermediate between IMV and CEV/EEV that enables efficient virus dissemination to the cell surface on microtubules. CEV induces the formation of actin tails that drive CEV particles away from the cell and is important for cell-to-cell spread. Lastly, EEV mediates the long-range dissemination of virus in cell culture and, probably, in vivo. Seven virus-encoded proteins have been identified that are components of IEV, and five of them are present in CEV or EEV. The roles of these proteins in virus morphogenesis and dissemination, and as targets for neutralizing antibody are reviewed. The production of several different virus particles in the VV replication cycle represents a coordinated strategy to exploit cell biology to promote virus spread and to aid virus evasion of antibody and complement.

Identification of the orthopoxvirus p4c gene, which encodes a structural protein that directs intracellular mature virus particles into A-type inclusions

The orthopoxvirus gene p4c has been identified in the genome of the vaccinia virus strain Western Reserve. This gene encodes the 58-kDa structural protein P4c present on the surfaces of the intracellular mature virus (IMV) particles. The gene is disrupted in the genome of cowpox virus Brighton Red (BR), demonstrating that although the P4c protein may be advantageous for virus replication in vivo, it is not essential for virus replication in vitro. Complementation and recombination analyses with the p4c gene have shown that the P4c protein is required to direct the IMV into the A-type inclusions (ATIs) produced by cowpox virus BR. The p4c gene is highly conserved among most members of the orthopoxvirus genus, including viruses that produce ATIs, such as cowpox, ectromelia, and raccoonpox viruses, as well as those such as variola, monkeypox, vaccinia, and camelpox viruses, which do not. The conservation of the p4c gene among the orthopoxviruses, irrespective of their capacities to produce ATIs, suggests that the P4c protein provides functions in addition to that of directing IMV into ATIs. These findings, and the presence of the P4c protein in IMV but not extracellular enveloped virus (D. Ulaeto, D. Grosenbach, and D. E. Hruby, J. Virol. 70:3372-3377, 1996), suggest a model in which the P4c protein may play a role in the retrograde movement of IMV particles, thereby contributing to the retention of IMV particles within the cytoplasm and within ATIs when they are present. In this way, the P4c protein may affect both viral morphogenesis and processes of virus dissemination.

An investigation of incorporation of cellular antigens into vaccinia virus particles

Vaccinia virus (VV) infection produces several types of virus particle called intracellular mature virus (IMV), intracellular enveloped virus (IEV), cell-associated enveloped virus (CEV) and extracellular enveloped virus (EEV). Some cellular antigens are associated with EEV and these vary with the cell type used to grow the virus. To investigate if specific cell antigens are associated with VV particles, and to address the origin of membranes used to envelope IMV and IEV/CEV/EEV, we have studied whether cell antigens and foreign antigens expressed by recombinant VVs are incorporated into VV particles. Membrane proteins that are incorporated into the endoplasmic reticulum (ER), intermediate compartment (IC), cis/medial-Golgi, trans-Golgi network (TGN) or plasma membrane were not detected in purified IMV particles. In contrast, proteins present in the TGN or membrane compartments further downstream in the exocytic pathway co-purify with EEV particles when analysed by immunoblotting. Immunoelectron microscopy found only low levels of these proteins in IEV, CEV/EEV. The incorporation of foreign antigens into VV particles was not affected by loss of individual IEV or EEV-specific proteins or by redirection of B5R to the ER. These data suggest that (i) host cell antigens are excluded from the lipid envelope surrounding the IMV particle and (ii) membranes of the ER, IC and cis/medial-Golgi are not used to wrap IMV particles to form IEV. Lastly, the VV haemagglutinin was absent from one-third of IEV and CEV/EEV particles, whereas other EEV antigens were present in all these virions.

Administration to mice of a monoclonal antibody that neutralizes the intracellular mature virus form of vaccinia virus limits virus replication efficiently under prophylactic and therapeutic conditions

The WHO smallpox eradication program was concluded 21 years ago and the non-vaccinated population is now at risk of poxvirus infections, either by contact with monkeypox or through bioterrorism. Since drugs specific against poxvirus infections are limited, neutralizing monoclonal antibodies (mAbs) that are effective in vivo may be an important tool in controlling poxvirus infections. To this end, we studied the efficacy of the mAb C3, reactive against the trimeric 14-kDa protein of vaccinia virus (VV) localized in the membrane of the intracellular form of mature virus, for its ability to neutralize VV infection in mice. The results show that prophylactic as well as therapeutic administration of mAb C3 can be an effective means of control of VV replication within the host. The interval of antibody efficacy following a single administration, before and after VV inoculation, has been defined. This study reinforces the notion that neutralizing mAbs should be developed to control health-related human infections by poxviruses.

Cytokine signalling and disease

Cytokines mediate their response via cell surface receptors that in turn activate intracellular signalling pathways and lead to gene activation, cell proliferation and differentiation. Many recent studies have shown that cytokine and cytokine receptor pathways are frequently mutated in disease, thus shedding light on the generation of the inflammatory response, specific immunity and mechanisms of haematopoiesis. Many approaches are being used to translate this basic research into successful therapies and although host immune responses involve many different cells and crucial pathways, modulation of therapeutic responses can be induced or inhibited by, targeting a single cytokine. This review summarises current knowledge of cytokine pathways in disease and the use of cytokine- or receptor-directed therapy to exploit the immune response to disease.

Immunomodulatory proteins of myxoma virus

Poxviruses collectively encode an impressive collection of diverse immunomodulatory proteins. In this review we draw attention to some of the new open reading frames (ORFs) discovered during the sequencing of the myxoma virus DNA genome [Cameron C, Hota-Mitchell S, Chen L, Barrett J, Cao J-X, Macaulay C, Willer D, Evans D, McFadden G (1999) The complete DNA sequence of myxoma virus. Virology 264:298-318] that may function to subvert the host immune system. Most of these predicted functions are speculative but some of the deduced primary amino acid sequences contain intriguing similarities to known cellular and viral proteins in the public domain for which immunomodulatory functions have been assigned.

Use of chemokine receptors by poxviruses

Chemokine receptors serve as portals of entry for certain intracellular pathogens, most notably human immunodeficiency virus (HIV). Myxoma virus is a member of the poxvirus family that induces a lethal systemic disease in rabbits, but no poxvirus receptor has ever been defined. Rodent fibroblasts (3T3) that cannot be infected with myxoma virus could be made fully permissive for myxoma virus infection by expression of any one of several human chemokine receptors, including CCR1, CCR5, and CXCR4. Conversely, infection of 3T3-CCR5 cells can be inhibited by RANTES, anti-CCR5 polyclonal antibody, or herbimycin A but not by monoclonal antibodies that block HIV-1 infection or by pertussis toxin. These findings suggest that poxviruses, like HIV, are able to use chemokine receptors to infect specific cell subtypes, notably migratory leukocytes, but that their mechanisms of receptor interactions are distinct.

Mouse hepatitis virus strain JHM infects a human hepatocellular carcinoma cell line

Mouse hepatitis virus (MHV) strain JHM is a coronavirus that causes encephalitis and demyelination in susceptible rodents. The known receptors for MHV are all members of the carcinoembryonic antigen family. Although human forms of the MHV receptor can function as MHV receptors in some assays, no human cell line has been identified that can support wild-type MHV infection. Here we describe the infection of a human hepatocellular carcinoma cell line, HuH-7, with MHV. HuH-7 cells were susceptible to strains JHM-DL and JHM-DS, yielding virus titers nearly identical to those seen in mouse DBT cells. In contrast, HuH-7 cells were only marginally susceptible or completely resistant to infection by other MHV strains, including A59. JHM produced a strong cytopathic effect in HuH-7 cells with the formation of round plaques. Studies of various recombinant viruses between JHM and A59 strains suggested that the ability of JHM to infect HuH-7 cells was determined by multiple viral genetic elements. Blocking the viral spike (S) protein with a neutralizing antibody or a soluble form of the MHV receptor inhibited infection of HuH-7 cells, suggesting that infection is mediated through the S protein. Transfection with the prototype mouse receptor, biliary glycoprotein, rendered HuH-7 cells susceptible to infection by other MHV strains as well, suggesting that JHM uses a receptor distinct from the classical MHV receptor to infect HuH-7 cells. Possible implications for human disease are discussed.