Genetically engineered poxviruses for recombinant gene expression, vaccination, and safety

Towards a unique and transmissible vaccine against myxomatosis and rabbit haemorrhagic disease for rabbit populations

Currently available vaccines against myxomatosis and rabbit hemorrhagic disease virus (RHDV) are not suited to immunise wild rabbit populations, as vaccines need to be delivered individually by conventional veterinary practices. As an alternative approach, research in Spain has focused on the development of a transmissible vaccine. A recombinant virus has been constructed based on a naturally attenuated myxoma virus (MV) field strain, expressing the RHDV capsid protein (VP60). Following inoculation of rabbits, the recombinant virus (MV-VP60) induced specific antibody responses against MV and RHDV, conferring protection against lethal challenges with both viruses. Furthermore, the recombinant MV-VP60 virus showed a limited horizontal transmission capacity, either by direct contact or in a flea-mediated process, promoting immunisation of contact uninoculated animals. Efficacy and safety of the vaccine have been extensively evaluated under laboratory conditions and in a limited field trial. The development of the transmissible vaccine strategy and the steps being taken to obtain the marketing authorisation for the vaccine in the European Union are presented in this review.

Expression and purification of viral glycoproteins using recombinant vaccinia viruses for functional and structural studies

Methods for generating recombinant vaccinia viruses for the expression of foreign viral glycoproteins in mammalian cell lines and the purification of expressed viral glycoproteins are described. These methods are based on many years of experience with the influenza hemagglutinin glycoprotein (HA). However, they are applicable for studies on other viral glycoproteins, and with slight modifications, could be useful for cellular proteins as well.

GeneChip resequencing of the smallpox virus genome can identify novel strains: a biodefense application

We developed a set of seven resequencing GeneChips, based on the complete genome sequences of 24 strains of smallpox virus (variola virus), for rapid characterization of this human-pathogenic virus. Each GeneChip was designed to analyze a divergent segment of approximately 30,000 bases of the smallpox virus genome. This study includes the hybridization results of 14 smallpox virus strains. Of the 14 smallpox virus strains hybridized, only 7 had sequence information included in the design of the smallpox virus resequencing GeneChips; similar information for the remaining strains was not tiled as a reference in these GeneChips. By use of variola virus-specific primers and long-range PCR, 22 overlapping amplicons were amplified to cover nearly the complete genome and hybridized with the smallpox virus resequencing GeneChip set. These GeneChips were successful in generating nucleotide sequences for all 14 of the smallpox virus strains hybridized. Analysis of the data indicated that the GeneChip resequencing by hybridization was fast and reproducible and that the smallpox virus resequencing GeneChips could differentiate the 14 smallpox virus strains characterized. This study also suggests that high-density resequencing GeneChips have potential biodefense applications and may be used as an alternate tool for rapid identification of smallpox virus in the future.

Suppression of hyperglycemia in NOD mice after inoculation with recombinant vaccinia viruses

In autoimmune (type 1) diabetes, autoreactive lymphocytes destroy pancreatic beta-cells responsible for insulin synthesis. To assess the feasibility of gene therapy for type 1 diabetes, recombinant vaccinia virus (rVV) vectors were constructed expressing pancreatic islet autoantigens proinsulin (INS) and a 55-kDa immunogenic peptide from glutamic acid decarboxylase (GAD), and the immunomodulatory cytokine interleukin (IL)-10. To augment the beneficial effects of recombinant virus therapy, the INS and GAD genes were fused to the C terminus of the cholera toxin B subunit (CTB). Five-week-old non-obese diabetic (NOD) mice were injected once with rVV. Humoral antibody immune responses and hyperglycemia in the infected mice were analyzed. Only 20% of the mice inoculated with rVV expressing the CTB::INS fusion protein developed hyperglycemia, in comparison to 70% of the mice in the uninoculated animal group. Islets from pancreatic tissues isolated from euglycemic mice from this animal group showed no sign of inflammatory lymphocyte invasion. Inoculation with rVV producing CTB::GAD or IL-10 was somewhat less effective in reducing diabetes. Humoral antibody isotypes of hyperglycemic and euglycemic mice from all treated groups possessed similar IgG1/IgG2c antibody titer ratios from 19 to 32 wk after virus inoculation. In comparison with uninoculated mice, 11-wk-old NOD mice injected with virus expressing CTB::INS were delayed in diabetes onset by more than 4 wk. The experimental results demonstrate the feasibility of using rVV expressing CTB::INS fusion protein to generate significant protection and therapy against type 1 diabetes onset and progression.

The potential role of fowlpox virus in rational vaccine design

The design of optimal vaccines requires detailed knowledge of how protective immune responses are generated in vivo under normal circumstances. This approach to vaccine development, where the immune correlates of protection are defined and vaccines are designed to elicit the same response, is called rational vaccine design. Poxviruses are attractive candidates for inclusion in such design strategies owing to their large genome, which allows for the inclusion of multiple heterologous genes, including those encoding antigens, co-stimulatory molecules and cytokines. Fowlpox virus, the prototypical member of the Avipoxvirus genus, is particularly suitable, as it is also incapable of replicating in mammalian cells. The potential of recombinant fowlpox virus as a safe vaccine vector is being evaluated currently in a number of clinical trials for diseases, including HIV, malaria and various types of cancer. Despite their promise, intricate details regarding how fowlpox virus interacts with the host immune system have not been resolved. In this review, the issues surrounding the use of fowlpox virus as a vaccine vector and possible strategies for enhancing its efficacy are discussed.

Cancer vaccines: preclinical studies and novel strategies

The development of cancer vaccines, aimed to enhance the immune response against a tumor, is a promising area of research. A better understanding of both the molecular mechanisms that govern the generation of an effective immune response and the biology of a tumor has contributed to substantial progress in the field. Areas of intense investigation in cancer immunotherapy will be discussed here, including: (1) the discovery and characterization of novel tumor antigens to be used as targets for vaccination; (2) the investigation of different vaccine-delivery modalities such as cellular-based vaccines, protein- and peptide-based vaccines, and vector-based vaccines; (3) the characterization of biological adjuvants to further improve the immunogenicity of a vaccine; and (4) the investigation of multimodal therapies where vaccines are being combined with other oncological treatments such as radiation and chemotherapy. A compilation of data from preclinical studies conducted in vitro as well as in animal models is presented here. The results from these studies would certainly support the development of new vaccination strategies toward cancer vaccines with enhanced clinical efficacy.

Evaluation of a needle-free delivery platform for prime-boost immunization with DNA and modified vaccinia virus ankara vectors expressing herpes simplex virus 2 glycoprotein D

A previous report described a prime-boost immunization strategy using plasmid and modified vaccinia virus Ankara (MVA) vectors expressing herpes simplex virus 2 glycoprotein D (gD). Enhanced humoral and cellular immune responses were elicited by the prime-boost combination compared to plasmid DNA immunization alone. Surprisingly, a more diverse antibody isotype response, and a greater antibody and cellular immune response, was obtained if the gD MVA vector was used as the priming immunization rather than the gD plasmid vector. The present report evaluates the use of a needle-free delivery platform (Biojector) for delivery of plasmid and MVA gD-expressing vectors in a prime-boost immunization strategy. Needle-free delivery of both plasmid and MVA gD expression vectors was efficient, reproducible, and elicited a strong immune response in immunized mice. Biojector delivery of plasmid DNA was able to evoke a broader isotype response and cellular immune response than that obtained by gene gun delivered plasmid DNA. Further, DNA priming by Biojector delivery as part of a prime-boost procedure with MVA-gD2 resulted in a diverse antibody isotype distribution and enhanced cellular immune responses, similar to the responses obtained when MVA-gD2 was used as the priming immunization. Thus, needle-free delivery of plasmid DNA may provide additional flexibility and options for effective prime-boost vaccination.

SARS-CoV spike protein-expressing recombinant vaccinia virus efficiently induces neutralizing antibodies in rabbits pre-immunized with vaccinia virus

A vaccine for severe acute respiratory syndrome (SARS) is being intensively pursued against its re-emergence. We generated a SARS coronavirus (SARS-CoV) spike protein-expressing recombinant vaccinia virus (RVV-S) using highly attenuated strain LC16m8. Intradermal administration of RVV-S into rabbits induced neutralizing (NT) antibodies against SARS-CoV 1 week after administration and the NT titer reached 1:1000 after boost immunization with RVV-S. Significantly, NT antibodies against SARS-CoV were induced by administration of RVV-S to rabbits that had been pre-immunized with LC16m8. RVV-S can induce NT antibodies against SARS-CoV despite the presence of NT antibodies against VV. These results suggest that RVV-S may be a powerful SARS vaccine, including in patients previously immunized with the smallpox vaccine.

Active treatment of murine tumors with a highly attenuated vaccinia virus expressing the tumor associated antigen 5T4 (TroVax) is CD4+ T cell dependent and antibody mediated

5T4 is a tumor associated antigen that is expressed on the surface of a wide spectrum of human adenocarcinomas. The highly attenuated virus, modified vaccinia Ankara, has been engineered to express human 5T4 (h5T4). In a pre-clinical murine model, the recombinant virus (TroVax) induces protection against challenge with CT26-h5T4 (a syngeneic tumor line expressing h5T4). Anti-tumor activity is long lived, with protection still evident 6 months after the final vaccination. In a therapeutic setting, injection of mice with TroVax results in a reduction in tumor burden of >90%. Depletion of CD8+ T cells has no effect upon therapy in the active treatment model, whereas depletion of CD4+ T cells completely abrogates anti-tumor activity. In a prophylactic setting, depletion of CD4+ and CD8+ T cells after the induction of a h5T4 immune response has no deleterious effect on protection following challenge with CT26-h5T4. In light of these studies, the role of antibodies in protection against tumor challenge was investigated. 5T4 specific polyclonal serum decreased tumor burden by approximately 70%. Thus, we conclude that CD4+ T cells are essential for the induction of a protective immune response and that antibodies are the likely effector moiety in this xenogeneic murine tumor model.

Cellular and biochemical differences between two attenuated poxvirus vaccine candidates (MVA and NYVAC) and role of the C7L gene

The poxvirus strains NYVAC and MVA are two candidate vectors for the development of vaccines against a broad spectrum of diseases. Although these attenuated virus strains have proven to be safe in animals and humans, little is known about their comparative behavior in vitro. In contrast with MVA, NYVAC infection triggers greater cytopathic effect in a range of permissive and nonpermissive cell lines. The yields of NYVAC cell-associated virus in permissive cells (BHK-21) were slightly reduced compared with those of MVA infection. During the course of infection in HeLa cells, there is a translational block induced by NYVAC late in infection, which correlated with a marked increase in phosphorylation levels of the initiation factor eIF-2alpha. In contrast to MVA, the synthesis of certain late viral proteins was only blocked in NYVAC-infected HeLa cells. Electron microscopy (EM) analysis revealed that morphogenesis of NYVAC in HeLa cells was blocked at the stage of formation of immature viral forms. Phase-contrast microscopy, EM, flow cytometry, and rRNA analyses demonstrated that contrary to MVA, NYVAC infection induces potent apoptosis, a phenomenon dependent on activation of caspases and RNase L. Apoptosis induced by NYVAC was prevented when the virus gene C7L was placed back into the NYVAC genome, recovering the ability of NYVAC to replicate in HeLa cells and maintaining the attenuated phenotype in mice. Overall, our findings demonstrate distinct behavior between NYVAC and MVA strains in cultured cells, as well as a new role for the C7L viral gene as an inhibitor of apoptosis in NYVAC infection.

Antibody and IFN-γ responses induced by a recombinant canarypox vaccine and challenge infection with equine influenza virus

In horses, equine influenza virus (EIV) is a leading cause of respiratory disease. Conventional inactivated vaccines induce a short-lived immune response. By comparison, natural infection confers a long-term immunity to re-infection. An aim of new equine influenza vaccines is to more closely mimic natural infection in order to achieve a better quality of immunity. A new live recombinant vaccine derived from the canarypox virus vector and expressing haemagglutinin genes of EIV (subtype H3N8) has been developed. Stimulation of the immune system was studied after immunisation with this canarypox-based vaccine and challenge infection by exposure to a nebulised aerosol of EIV. The humoral immune response was evaluated by measuring serum antibody levels using the single radial haemolysis (SRH) assay. The cellular immune response was assessed by the measurement of interferon gamma (IFN-gamma) synthesis in peripheral blood mononuclear cells (PBMC). Clinical signs of the disease (temperature, coughing, nasal discharge, dyspnoea, depression and anorexia) and virus excretion were monitored after challenge infection. Clinical signs and virus shedding were significantly reduced in vaccinates compared with unvaccinated controls. EIV-specific immunity was stimulated by vaccination with a recombinant vaccine as serological responses were detected after immunisation. This study also provided the first evidence for increased IFN-gamma protein synthesis in vaccinated ponies following challenge infection with EIV compared with control ponies.

Structure of complex viruses and virus-infected cells by electron cryo tomography

In microbiology, and in particular in virus research, electron microscopy (EM) is an important tool, offering a broad approach for investigating viral structure throughout their intracellular and extracellular life cycles. Currently, molecular tools and rapid developments in advanced light microscopy dominate the field and supply an enormous amount of information concerning virus biology. In recent years, numerous fascinating high-resolution EM structures obtained by single-particle electron cryo microscopy (cryo-EM) were revealed for viral particles that possess icosahedral symmetry. However, no comprehensive three-dimensional analysis of complex viruses or viruses within cells has yet been achieved using EM. Recent developments in electron cryo-tomography render this a proficient tool for the analysis of complex viruses and viruses within cells in greater detail.

Attenuation of a vaccine strain of vaccinia virus via inactivation of interferon viroceptor

BACKGROUND

Interferons (IFNs) play an important role in host antiviral responses, but viruses, including vaccinia viruses (VV), employ mechanisms to disrupt IFN activities, and these viral mechanisms are often associated with their virulence. Here, we explore an attenuation strategy with a vaccine strain of VV lacking a virus-encoded IFN-gamma receptor homolog (viroceptor).

METHODS

To facilitate the monitoring of virus properties, first we constructed a Lister vaccine strain derivative VV-RG expressing optical reporters. Further, we constructed a VV-RG derivative, VV-RG8, which lacks the IFN-gammaR viroceptor (B8R gene product). Replication, immunological and pathogenic properties of the constructed strains were compared.

RESULTS

Viruses did not show significant differences in humoral and cellular immune responses of immune-competent mice. Replication of constructed viruses was efficient both in vitro and in vivo, but showed marked difference in kinetics of propagation. In cultured CV-1 epithelial cells, the VV-RG8 strain retained the propagation potential of the parental virus, while, in the C6 glial cells, significant delay was observed in the kinetics of the VV-RG8 replication cycle compared to VV-RG. The pathogenesis of the viruses was tested by survival assay and biodistribution in nude mice. High dose inoculation of nude mice with VV-RG8 caused less pronounced virus dissemination, improved weight gain, and increased survival rate, as compared with the VV-RG strain.

CONCLUSIONS

The replication-competent virus VV-RG8 carrying a mutation at the B8R gene is less pathogenic for mice than the parental vaccine virus. We anticipate that step-wise inactivation of VV vaccine genes involved in evasion of host immune response may provide an alternative approach for generation of hyper-attenuated replication-competent vaccines.

Viral Vaccines for Cancer Immunotherapy

The understanding that tumor cells can be recognized and eliminated by the immune system has led to intense interest in the development of cancer vaccines. Viruses are naturally occurring agents that cause human disease but have the potential to prevent disease when attenuated forms or subunits are used as vaccines before exposure. A large number of viruses have been engineered as attenuated vaccines for the expression of tumor antigens, immunomodulatory molecules, and as vehicles for direct destruction of tumor cells or expression of highly specific gene products. This article focuses on the major viruses that are under development as cancer vaccines, including the poxviruses, adenoviruses, adeno-associated viruses, herpesviruses, retroviruses, and lentiviruses. The biology supporting these viruses as vaccines is reviewed and clinical progress is reported.

Evaluation of prime/boost regimens using recombinant poxvirus/tyrosinase vaccines for the treatment of patients with metastatic melanoma

PURPOSE

Two clinical trials were conducted to evaluate the clinical efficacy and immunologic impact of vaccination against the tyrosinase protein plus systemic interleukin 2 (IL-2) administration in patients with advanced metastatic melanoma.

EXPERIMENTAL DESIGN

Full-length tyrosinase was employed as an immunogen to induce diverse immunologic responses against a commonly expressed melanoma antigen. Heterologous prime/boost vaccination with recombinant vaccinia and fowlpox vectors encoding tyrosinase was first explored in a randomized three-arm phase II trial, in which vaccines were administered alone or concurrently with low-dose or high-dose IL-2. In a subsequent single cohort phase II trial, all patients received the same vaccines and high-dose IL-2 sequentially rather than concurrently.

RESULTS

Among a total of 64 patients treated on these trials, 8 objective partial responses (12.5%) were observed, all in patients receiving high-dose IL-2. Additional patients showed evidence of lesional regression (mixed tumor response) or overall regression that did not achieve partial response status (minor response). In vitro evidence of enhanced immunity against tyrosinase following protocol treatments was documented in 3 of 49 (6%) patients tested serologically, 3 of 23 (13%) patients tested for T-cell recognition of individual tyrosinase peptides, and 4 of 16 (25%) patients tested for T-cell recognition of full-length tyrosinase protein with real-time reverse transcription-PCR techniques.

CONCLUSIONS

Whereas prime/boost immunization with recombinant vaccinia and fowlpox viruses enhanced antityrosinase immunity in some patients with metastatic melanoma, it was ineffective alone in mediating clinical benefit, and in combination with IL-2 did not mediate clinical benefit significantly different from that expected from treatment with IL-2 alone.

Genetic modification of hematopoietic stem cells with nonviral systems: past progress and future prospects

Serious unwanted complications provoked by retroviral gene transfer into hematopoietic stem cells (HSCs) have recently raised the need for the development and assessment of alternative gene transfer vectors. Within this context, nonviral gene transfer systems are attracting increasing interest. Their main advantages include low cost, ease of handling and large-scale production, large packaging capacity and, most importantly, biosafety. While nonviral gene transfer into HSCs has been restricted in the past by poor transfection efficiency and transient maintenance, in recent years, biotechnological developments are converting nonviral transfer into a realistic approach for genetic modification of cells of hematopoietic origin. Herein we provide an overview of past accomplishments in the field of nonviral gene transfer into hematopoietic progenitor/stem cells and we point at future challenges. We argue that episomally maintained self-replicating vectors combined with physical methods of delivery show the greatest promise among nonviral gene transfer strategies for the treatment of disorders of the hematopoietic system.

Disruption of MHC class II-restricted antigen presentation by vaccinia virus

Vaccinia virus (VV), currently used in humans as a live vaccine for smallpox, can interfere with host immunity via several discrete mechanisms. In this study, the effect of VV on MHC class II-mediated Ag presentation was investigated. Following VV infection, the ability of professional and nonprofessional APC to present Ag and peptides to CD4+ T cells was impaired. Viral inhibition of class II Ag presentation could be detected within 1 h, with diminished T cell responses dependent upon the duration of APC infection and virus titer. Exposure of APC to replication-deficient virus also diminished class II Ag presentation. Virus infection of APC perturbed Ag presentation by newly synthesized and recycling class II molecules, with disruptions in both exogenous and cytoplasmic Ag presentation. Virus-driven expression of an endogenous Ag, failed to restore T cell responsiveness specific for this Ag in the context of MHC class II molecules. Yet, both class II protein steady-state and cell surface expression were not altered by VV. Biochemical and functional analysis revealed that VV infection directly interfered with ligand binding to class II molecules. Together, these observations suggest that disruption of MHC class II-mediated Ag presentation may be one of multiple strategies VV has evolved to escape host immune surveillance.

The enhanced tumor selectivity of an oncolytic vaccinia lacking the host range and antiapoptosis genes SPI-1 and SPI-2

The ability of cancer cells to evade apoptosis may permit survival of a recombinant vaccinia lacking antiapoptotic genes in cancer cells compared with normal cells. We have explored the deletion of two vaccinia virus host range/antiapoptosis genes, SPI-1 and SPI-2, for their effects on the viral replication and their ability to induce cell death in infected normal and transformed cells in vitro. Indeed, in three paired normal and transformed cell types, the SPI-1 and SPI-2 gene-deleted virus (vSP) preferentially replicates in transformed cells or p53-null cells when compared with their normal counterparts. This selectivity may be derived from the fact that vSP-infected normal cells died faster than infected cancer cells. A fraction of infected cells died with evidence of necrosis as shown by both flow cytometry and detection of high-mobility group B1 protein released from necrotic cells into the culture supernatant. When administered to animals, vSP retains full ability to replicate in tumor tissues, whereas replication in normal tissues is greatly diminished. In a model of viral pathogenesis, mice treated with vSP survived substantially longer when compared with mice treated with the wild-type virus. The mutant virus vSP displayed significant antitumoral effects in an MC38 s.c. tumor model in both nude (P < 0.001) and immunocompetent mice (P < 0.05). We conclude that this recombinant vaccinia vSP shows promise for oncolytic virus therapy. Given its enhanced tumor selectivity, improved safety profile, and substantial oncolytic effects following systemic delivery in murine models, it should also serve as a useful vector for tumor-directed gene therapy.

Protection of NOD mice from type 1 diabetes after oral inoculation with vaccinia viruses expressing adjuvanted islet autoantigens

Oral administration of autoantigens and allergens can delay or suppress clinical disease in experimental autoimmune and allergic disorders. However, repeated feeding of large amounts of the tolerogens is required over long periods and is only partially effective in animals systemically sensitized to the ingested antigen. Enhanced suppression of type 1 autoimmune diabetes insulitis and hyperglycemia was demonstrated in both naive and immune animals following oral inoculation with plant-based antigens coupled to the cholera toxin B subunit (CTB). Thus, plant-synthesized antigens linked to the CTB adjuvant, can enhance suppression of inflammatory TH1 lymphocyte-mediated autoreactivity in both naive and immune animals. To stimulate adjuvant-autoantigen fusion protein biosynthesis in the gut mucosae, the authors evaluated oral inoculation of juvenile non-obese diabetic (NOD) mice with recombinant vaccinia virus (rVV) expressing fusion genes encoding CTB linked to the pancreatic islet autoantigens proinsulin (INS) and a 55-kDa C-terminal peptide from glutamate decarboxylase (GAD55). Hyperglycemia in both rVV-CTB:: INS and rVV-CTB:: GAD inoculated mice was substantially reduced in comparison with the uninoculated mouse control. Oral inoculation with rVV carrying the CTB::INS fusion gene generated a significant reduction in insulitis. An increase in IgG1 in comparison with IgG2c antibody isotype titers in rVV-CTB::INS infected mice suggested possible activation of autoantigen specific Th2 lymphocytes. The experimental results demonstrate feasibility of using vaccinia virus oral delivery of adjuvanted autoantigens to the mucosae of prediabetic mice for suppression and therapy of type 1 autoimmune diabetes.

Pox Viral Vaccine Approaches

Recent advances in understanding tumor-specific immunity have introduced new excitement in the clinical development of vaccines for the treatment of cancer. A better understanding of basic immunologic principles has led to a variety of techniques for enhancing tumor-specific immunity through vaccination. Approaches to antigen-specific immunotherapy have included: (1) peptides, usually in combination with various immunological adjuvants; (2) soluble proteins; (3) dendritic cells pulsed with specific antigens; (4) monoclonal antibodies; (5) recombinant plasmid DNA; (6) autologous and allogeneic tumor cells; and (7) recombinant viral vectors. This review will focus on the use of viral vectors, which offer unique advantages as both gene delivery vectors and as agents supplying additional adjuvant activity for vaccination. Viral vectors are particularly attractive for immunotherapy since they mimic natural infection and can induce potent immune responses. Replicating and nonreplicating members of the poxvirus family have been widely studied for expression of tumor antigens and other immunomodulatory genes, such as cytokines and costimulatory molecules. Although a large number of TAAs are available for insertion into viral vectors, this review will discuss the preclinical and clinical development of prostate-specific antigen (PSA) and carcinoembryonic antigen (CEA) poxviral vaccines, as models of the pox viral vaccine approach.

Elicitation of neutralizing antibodies by intranasal administration of recombinant vesicular stomatitis virus expressing human immunodeficiency virus type 1 gp120

Recombinant viral vectors are useful tools for AIDS vaccine development. However, expression of HIV-1 envelope genes using viral vectors has not been successful in the induction of potent neutralizing antibodies in vivo. We took advantage of the strong immunogenicity of vesicular stomatitis virus (VSV)-based vector and expressed HIV-1 HXB2 gp120 gene in the recombinant VSV. Our results showed that HIV-1 gp120 protein expressed by the recombinant VSV retained the native conformation of the protein to some degree and was recognized by two well-characterized broad anti-HIV-1 neutralizing monoclonal antibodies b12, 2G12. We further showed that only one time intranasal immunization with the recombinant VSV led to production of anti-HIV-1 anti-sera in mice. In addition, we found that the anti-sera had the ability to neutralize not only HXB2 envelope-pseudotyped HIV-1 viruses but also HIV-1 pseudotyped viruses with JRFL envelopes. These results suggest that HIV-1 gp120 expressed by the recombinant VSV, in combination with the route of intranasal administration, is an effective strategy to evaluate the immunogenicity of HIV-1 envelope protein and its variants in mice.

Immunization with influenza A NP-expressing vaccinia virus recombinant protects mice against experimental infection with human and avian influenza viruses

Two-fold immunization of Balb/c mice with a vaccinia virus recombinant expressing the NP protein of influenza A/PR8/34 (H1N1) virus under the control of a strong synthetic promoter induced specific antibodies and protected animals against low-dose challenge by mouse-adapted heterosubtypic variants of human A/Aichi2/68 (H3N2) and avian A/Mallard/Pennsylvania/10218/84 (H5N2) influenza virus strains. The surviving immunized animals had lower anti-hemagglutinin antibody titers compared to non-immunized mice. There was no difference in viral titers in lungs of immunized and non-immunized animals that succumbed to the infection. In order to try to increase immune system presentation of NP-protein-derived peptides, and thereby increase their immunogenicity, we constructed another vaccinia-based NP-expressing recombinant containing a rapid proteolysis signal covalently bound to the NP protein. This sequence, derived from the mouse ornithine decarboxylase gene has been shown to increase degradation of various proteins. However, we found that when used as part of a recombinant NP, this signal neither increased its proteolytic degradation, nor was it more efficient in the induction of a protective response against influenza infection.

Recombinant poxviruses as mucosal vaccine vectors

The majority of infections initiate their departure from a mucosal surface, such as Human immunodeficiency virus (HIV), a sexually transmitted virus. Therefore, the induction of mucosal immunity is a high priority in the development of vaccines against mucosal pathogens. The selection of an appropriate antigen delivery system is necessary to induce an efficient mucosal immune response. Poxvirus vectors have been the most intensively studied live recombinant vector, and numerous studies have demonstrated their ability to induce mucosal immune responses against foreign expressed antigens. Previous studies have demonstrated that recombinants based on the attenuated modified vaccinia virus Ankara (MVA) vector were effective in inducing protective responses against different respiratory viruses, such as influenza and respiratory syncytial virus, following immunization via mucosal routes. Recent studies performed in the murine and macaque models have shown that recombinant MVA (rMVA) does not only stimulate HIV-specific immunity in the genital and rectal tracts following mucosal delivery, but can also control simian/human immunodeficiency viraemia and disease progression. In addition, a prime-boost vaccination approach against tuberculosis emphasized the importance of the intranasal rMVA antigen delivery to induce protective immunity against Mycobacterium tuberculosis. The aim of this review is to summarize the studies employing recombinant poxviruses, specifically rMVA as a mucosal delivery vector. The results demonstrate that rMVAs can activate specific immune responses at mucosal surfaces, and encourage further studies to characterize and improve the MVA mucosal immunogenicity of poxvirus vectors.

Use ofin vitrotransporter assays to understand hepatic and renal disposition of new drug candidates

Hepatic and renal transporters contribute to the uptake, secretion and reabsorption of endogenous compounds, xenobiotics and their metabolites and have been implicated in drug-drug interactions and toxicities. Characterising the renal and hepatic disposition of drug candidates early in development would lead to more rational drug design, as chemotypes with 'ideal' pharmacokinetic characteristics could be identified and further refined. Because transporters are often organ specific, 'custom' transporter panels need to be identified for each major organ and chemotype to be evaluated, and appropriate studies planned. This review outlines the major renal and hepatic transporters and some of the in vitro transporter reagents, assays and processes that can be used to evaluate the renal and hepatic disposition of new chemical entities during drug discovery and development.

Changes in Bcl-2 expression in vaccinia virus-infected human peripheral blood monocytes

In this study, we show that Bcl-2, one of the most important antiapoptotic agents, is expressed in a phase-dependent manner in the human adherent monocytes after vaccinia virus infection, reflecting the viral infection stages. Early viral infection induced Bcl-2 expression in a level higher than in control cells. At 14 h post-infection (p.i.), the Bcl-2 level measured in the whole cell extracts dramatically decreased, followed by the increase at 24 h p.i. The levels of active dephosphorylated Bcl- 2 protein present in the cells reflected the gene expression character, but were much lower than in case of a heat shock. The dramatic increase of Bcl-2 protein level in the nuclear fraction at 4 h p.i. was observed. Changes in Bcl-2 mRNA content in elutriated human blood monocytes isolated from the same donor showed different kinetics, increasing up to 12 h p.i. and diminishing to undetectable level at 24 h p.i. concomitantly with a severe increase in the number of dead cells. The results indicate that virally infected adherent monocytes remain resistant to apoptosis, while freshly isolated monocytes undergo apoptotic cell death. These results throw new light on the apoptotic mechanism in the monocyte-derived cells after vaccinia virus infection in vitro.

Solid tissues can be manipulated ex vivo and used as vehicles for gene therapy

BACKGROUND

Organ fragments can be cultured for weeks in vitro if they are prepared of microscopic thickness and if the basic organ structure is preserved. Such organ fragments, which we termed micro-organs (MOs), express in culture endogenous tissue-specific gene products. We have exploited this methodology to engineer MOs ex vivo by gene transfer.

METHODS

MOs prepared from spleen, lung, colon and skin were infected using: herpes simplex type-1, adeno virus, vaccinia virus and murine leukemia virus (MuLV), carrying the reporter gene beta-galactosidase.

RESULTS

All four viral vectors infected MOs in culture, with adeno infection giving significantly higher values. After optimization, high levels of expression (> 15% positive cells), comparable to those obtained with the adeno construct, were also obtained using the MuLV construct both in vitro and after implantation into syngeneic hosts. After implantation, the engineered tissue was found to remain localized, become vascularized, and to express the transduced gene for several months.

CONCLUSIONS

The system can be used to study interactions between viruses and tissues both ex vivo and in vivo. Furthermore, the approach proposes a novel platform for ex vivo gene therapy. Such engineered structures could be used as autologous biological pumps for continuous secretion in vivo of gene products of clinical importance.

Phase I study of the intratumoral administration of recombinant canarypox viruses expressing B7.1 and interleukin 12 in patients with metastatic melanoma

The objective of this study was to evaluate the safety and activity of the intratumoral administration of the immune costimulatory molecule, B7.1, encoded by a vector derived from the canarypox virus, ALVAC (ALVAC-B7.1), alone and with the intratumoral injection of ALVAC encoding the immune-stimulatory cytokine, interleukin 12 (ALVAC-IL-12). Fourteen patients with metastatic melanoma who had s.c. nodules received intratumoral injections on days 1, 4, 8, and 11. Nine patients were given escalating doses of up to 25 x 10(8) plaque-forming units of ALVAC-B7.1. Five patients were given 25 x 10(8) plaque-forming units of ALVAC-B7.1 combined with ALVAC-IL-12 50% tissue culture infective dose of 2 x 10(6). Toxicity was mild to moderate and consisted of inflammatory reactions at the injection site and fever, chills, myalgia, and fatigue. Higher levels of B7.1 mRNA were observed in ALVAC-B7.1-injected tumors compared with saline-injected control tumors. Higher levels of intratumoral vascular endothelial growth factor and IL-10, cytokines with immune suppressive activities, were also observed in ALVAC-B7.1- and ALVAC-IL-12-injected tumors compared with saline-injected controls. Serum levels of vascular endothelial growth factor increased at day 18 and returned to baseline at day 43. All patients developed antibody to ALVAC. Intratumoral IL-12 and IFN-gamma mRNA decreased. Changes in serum IL-12 and IFN-gamma levels were not observed. Tumor regressions were not observed. The intratumoral injections of ALVAC-B7.1 and ALVAC-IL-12 were well tolerated at these dose levels and at this schedule and resulted in measurable biological response. This response included the production of factors that may suppress the antitumor immunologic activity of these vectors.

Heterologous prime-boost vaccination with the LACK antigen protects against murine visceral leishmaniasis

This study reports the efficacy of a heterologous prime-boost vaccination using DNA and vaccinia viruses (Western Reserve [WR] virus and modified [attenuated] vaccinia virus Ankara [MVA]) expressing the LACK antigen (Leishmania homologue of receptors for activated C kinase) and an intradermal murine infection model employing Leishmania infantum. At 1 month postinfection, vaccinated mice showed high levels of protection in the draining lymph node (240-fold reduction in parasite burden) coupled with significant levels of gamma interferon (20 to 200 ng/ml) and tumor necrosis factor alpha/lymphotoxin (8 to 134 pg/ml). Significant but lower levels of protection (6- to 30-fold) were observed in the spleen and liver. Comparable levels of protection were found for mice boosted with either LACK-WR or LACK-MVA, supporting the use of an attenuated vaccinia virus-based vaccine against human visceral leishmaniasis.

Cancer vaccine development

A new era involving the evaluation of recombinant cancer vaccines has begun with the concurrent emergence of insights and technologies in the fields of molecular biology and immunology. These advances include: The identification and cloning of an array of genes associated with the neoplastic process, such as oncogenes, suppressor genes, genes encoding oncofoetal antigens and tissue-lineage determinants. The development of a variety of viral and bacterial vectors to deliver and present gene products. The identification of numerous T-cell costimulatory molecules and an understanding of their mode of action. The cloning and analysis of the modes of action of an array of cytokines and other immunomodulatory molecules. More sophisticated knowledge of the mode(s) of antigen presentation and T-cell activation. One current challenge in cancer therapy is the delineation of strategies toward the rational design and implementation of recombinant vaccines that will be of therapeutic benefit to cancer patients and/or members of groups at high risk for specific neoplasias. Numerous concepts are emerging in this regard. The study of immunologic intervention using laboratory animal models demonstrates that no one approach will prevail for all cancer types or, perhaps, for the various stages of the neoplastic process of a given tumour type. The immunological role(s) of CD8+, CD4+, natural killer and other cell types, as well as the roles of antibodies, must all be taken into consideration. This article reviews some of the strategies currently undergoing evaluation toward the development of recombinant vaccines for several carcinoma types.

Viruses in type 1 diabetes: brief review

Type 1 diabetes results from the progressive destruction of insulin-producing pancreatic beta cells. Although the etiology of type 1 diabetes is believed to have a major genetic component, studies on the risk of developing type 1 diabetes suggest that environmental factors, such as viruses, may be important etiological determinants. Among the viruses, the most clear and unequivocal evidence that a virus induces type 1 diabetes in animals comes from studies on the D variant of encephalomyocarditis (EMC-D) virus in mice and Kilham rat virus (KRV) in rats. A high titer of EMC-D viral infection results in the development of diabetes within 3 days, primarily due to the rapid destruction of beta cells by viral replication within the cells. A low titer of EMC-D viral infection results in the recruitment of macrophages to the islets. Soluble mediators produced by the activated macrophages such as interleukin-1Beta, tumor necrosis factor-alpha, and nitric oxide play a critical role in the destruction of residual beta cells. KRV causes autoimmune type 1 diabetes in diabetes resistant-BioBreeding rats by breakdown of immune balance, including the preferential activation of effector T cells, such as Th1-like CD45RC+CD4+ T cells and CD8+ T cells, and down-regulation of Th2-like CD45RC-CD4+ and CD4+CD25+ T cells, rather than by direct infection of pancreatic beta cells.

Vaccinia virus infection and gene transduction in cultured neurons

The study of neurons in culture would benefit from the development of a gene transduction system capable of delivering foreign genes at high efficiency, as transduction of primary neurons with existing systems is inefficient. The efficacy of lytic vaccinia virus (VV) infection of primary retinal cultures and PC12 cells (a model of neuronal differentiation) was examined in order to determine the efficiency of gene transduction using VV in neuronal primary culture. VV was able to infect retinal cells and PC12 cells and express transgenes of Escherichia coli beta-galactosidase (lacZ) and epithelial fatty acid binding protein (E-FABP) in a virus dose-dependent manner. Most (50-100%) of the retinal cells were positive for transgene protein at multiplicities of infection (MOI) between 10 and 100 plaque-forming units (PFU), while over 50% of VV-infected PC12 cells expressed the virus encoded gene at an MOI = 10. The production of foreign mRNA and protein by VV following infection was verified by PCR and Western blot. Because VV is a lytic virus, cytopathic effects were examined. Retinal cultures maintained for 0.5 days in vitro showed greater than 90% survival at 24 h post-infection, while 14-day cultures were equally viable for 48 h. Retinal ganglion cells and differentiated PC12 cells appear to be more protected against lytic VV infection than proliferating glial and undifferentiated PC12 cells. These data suggest that VV may be a useful vector for delivering foreign genes to neuronal cells with an efficient transient transgene expression.

Role of genes that modulate host immune responses in the immunogenicity and pathogenicity of vaccinia virus

Poxvirus vaccine vectors, although capable of eliciting potent immune responses, pose serious health risks in immunosuppressed individuals. We therefore constructed five novel recombinant vaccinia virus vectors which contained overlapping deletions of coding regions for the B5R, B8R, B12R, B13R, B14R, B16R, B18R, and B19R immunomodulatory gene products and assessed them for both immunogenicity and pathogenicity. All five of these novel vectors elicited both cellular and humoral immunity to the inserted HIV-BH10 env comparable to that induced by the parental Wyeth strain vaccinia virus. However, deletion of these immunomodulatory genes did not increase the immunogenicity of these vectors compared with the parental vaccinia virus. Furthermore, four of these vectors were slightly less virulent and one was slightly more virulent than the Wyeth strain virus in neonatal mice. Attenuated poxviruses have potential use as safer alternatives to current replication-competent vaccinia virus. Improved vaccinia virus vectors can be generated by deleting additional genes to achieve a more significant viral attenuation.

Viral vectors for use in the development of biodefense vaccines

The heightened concerns about bioterrorism and the use of biowarfare agents have prompted substantial increased efforts towards the development of vaccines against a wide range of organisms, toxins, and viruses. An increasing variety of platforms and strategies have been analyzed for their potential as vaccines against these agents. DNA vectors, live-attenuated viruses and bacteria, recombinant proteins combined with adjuvant, and viral- or bacterial-vectored vaccines have been developed as countermeasures against many potential agents of bioterrorism or biowarfare. The use of viruses, for example adenovirus, vaccinia virus, and Venezuelan equine encephalitis virus, as vaccine vectors has enabled researchers to develop effective means for countering the threat of bioterrorism and biowarfare. An overview of the different viral vectors and the threats they counter will be discussed.

Potential of equine herpesvirus 1 as a vector for immunization

Key problems using viral vectors for vaccination and gene therapy are antivector immunity, low transduction efficiencies, acute toxicity, and limited capacity to package foreign genetic information. It could be demonstrated that animal and human cells were efficiently transduced with equine herpesvirus 1 (EHV-1) reconstituted from viral DNA maintained and manipulated in Escherichia coli. Between 13 and 23% of primary human CD3+, CD4+, CD8+, CD11b+, and CD19+ cells and more than 70% of CD4+ MT4 cells or various human tumor cell lines (MeWo, Huh7, HeLa, 293T, or H1299) could be transduced with one infectious unit of EHV-1 per cell. After intranasal instillation of EHV-1 into mice, efficient transgene expression in lungs was detectable. Successful immunization using EHV-1 was shown after delivery of the human immunodeficiency virus type 1 Pr55gag precursor by the induction of a Gag-specific CD8+ immune response in mice. Because EHV-1 was not neutralized by human sera containing high titers of antibodies directed against human herpesviruses 1 to 5, it is concluded that this animal herpesvirus has enormous potential as a vaccine vector, because it is able to efficiently transduce a variety of animal and human cells, has high DNA packaging capacity, and can conveniently be maintained and manipulated in prokaryotic cells.

Targeting the local tumor microenvironment with vaccinia virus expressing B7.1 for the treatment of melanoma

Immunotherapy for the treatment of metastatic melanoma remains a major clinical challenge. The melanoma microenvironment may lead to local T cell tolerance in part through downregulation of costimulatory molecules, such as B7.1 (CD80). We report the results from the first clinical trial, to our knowledge, using a recombinant vaccinia virus expressing B7.1 (rV-B7.1) for monthly intralesional vaccination of accessible melanoma lesions. A standard 2-dose-escalation phase I clinical trial was conducted with 12 patients. The approach was well tolerated with only low-grade fever, myalgias, and fatigue reported and 2 patients experiencing vitiligo. An objective partial response was observed in 1 patient and disease stabilization in 2 patients, 1 of whom is alive without disease 59 months following vaccination. All patients demonstrated an increase in postvaccination antibody and T cell responses against vaccinia virus. Systemic immunity was tested in HLA-A*0201 patients who demonstrated an increased frequency of gp100 and T cells specific to melanoma antigen recognized by T cells 1 (MART-1), also known as Melan-A, by ELISPOT assay following local rV-B7.1 vaccination. Local immunity was evaluated by quantitative real-time RT-PCR, which suggested that tumor regression was associated with increased expression of CD8 and IFN-gamma. The local delivery of vaccinia virus expressing B7.1 was well tolerated and represents an innovative strategy for altering the local tumor microenvironment in patients with melanoma.

The ‘supervirus’? Lessons from IL-4-expressing poxviruses

Members of the Poxviridae family are particularly adept at avoiding the host immune system, encoding a plethora of immunomodulatory proteins that subvert host defense. With their large genome, poxviruses are also useful for studying the effect of exogenous genes on virus-host interactions and immune responses. The insertion of the Th2 cytokine interleukin-4 (IL-4) into several poxviruses significantly increases the efficiency of the recombinant virus as a pathogen by directly inhibiting the development of Th1 immunity, which is crucial for viral clearance. In an age in which the fear of genetically modified weaponized pathogens exists, the understanding of how to make viruses more pathogenic further blurs the distinction between fundamental academic research and bioweapons development. Here, the extent of immune evasion by IL-4-expressing poxviruses will be explored, as will the consequences of this increased pathogenicity on protective immune responses.

Engineering of a vaccinia virus bacterial artificial chromosome in Escherichia coli by bacteriophage lambda-based recombination

The large capacity of vaccinia virus (VAC) for added DNA, cytoplasmic expression and broad host range make it a popular choice for gene delivery, despite the burdensome need for multiple plaque purifications to isolate recombinants. Here we describe how a bacterial artificial chromosome (BAC) containing the entire VAC genome can be engineered in Escherichia coli by homologous recombination using bacteriophage lambda-encoded enzymes. The engineered VAC genomes can then be used to produce clonally pure recombinant viruses in mammalian cells without the need for plaque purification.

Host range, growth property, and virulence of the smallpox vaccine: Vaccinia virus Tian Tan strain

Vaccinia Tian Tan (VTT) was used as a vaccine against smallpox in China for millions of people before 1980, yet the biological characteristics of the virus remain unclear. We have characterized VTT with respect to its host cell range, growth properties in vitro, and virulence in vivo. We found that 11 of the 12 mammalian cell lines studied are permissive to VTT infection whereas one, CHO-K1, is non-permissive. Using electron microscopy and sequence analysis, we found that the restriction of VTT replication in CHO-K1 is at a step before viral maturation probably due to the loss of the V025 gene. Moreover, VTT is significantly less virulent than vaccinia WR but remains neurovirulent in mice and causes significant body weight loss after intranasal inoculation. Our data demonstrate the need for further attenuation of VTT to serve either as a safer smallpox vaccine or as a live vaccine vector for other pathogens.

Phase I study of immunization with dendritic cells modified with fowlpox encoding carcinoembryonic antigen and costimulatory molecules

PURPOSE

To determine the safety and immunologic and clinical efficacy of a dendritic cell vaccine modified to hyperexpress costimulatory molecules and tumor antigen.

EXPERIMENTAL DESIGN

In this phase I study, we administered one or two cycles of four triweekly s.c./intradermal injections of ex vivo generated dendritic cells modified with a recombinant fowlpox vector encoding carcinoembryonic antigen (CEA) and a triad of costimulatory molecules [rF-CEA(6D)-TRICOM]. Controls consisted of immature dendritic cells loaded with tetanus toxoid and a HLA A2-restricted peptide derived from cytomegalovirus pp65 protein.

RESULTS

Fourteen patients (11 with colorectal cancer and 3 with non-small cell lung cancer) were enrolled and 12 completed at least one cycle of immunization. There were no grade 3/4 toxicities directly referable to the immunizations. One patient had a decrease in the CEA level from 46 to 6.8 and a minor regression in adenopathy that occurred several months after completion of the immunizations. Five other patients were stable through at least one cycle of immunization (3 months). Direct analysis of peripheral blood mononuclear cells using the ELISpot assay showed an increase in the frequency of CEA-specific T cells in 10 patients (range, 10-541 CEA-specific cells/10(5) peripheral blood mononuclear cells). There was a trend for a greater peak frequency of CEA-specific T cells among those with either a minor response or a stable disease following at least one cycle of therapy. A second cycle was not associated with higher T-cell frequencies. Cytokine flow cytometry showed CEA-specific immune response among both CD4(+) and CD8(+) T cells in all immune responders.

CONCLUSION

This immunization strategy is safe and activates potent CEA-specific immune responses.

Vaccinia virus recombinants as a model system to analyze interferon-induced pathways

The interferons (IFNs) are a family of cytokines with broad antiviral activities that also control cell proliferation and modulate immune responses. IFNs exert their pleiotropic actions through the regulation of multiple pathways that have been subjected to extensive study using diverse approaches. The scope of this review is to show how we can take advantage of vaccinia virus (VV) to study IFN-related pathways. We summarize and present the different VV models available for studying IFN function and the possibilities that they offer to analyze IFN-induced pathways, IFN modulators, and the biologic effects at the molecular and cellular levels. Emphasis is given to studies of dsRNA-activated signaling with VV lacking E3L (VV DeltaE3L) and in RNA-activated protein kinase (PKR)-related pathways, through the use of VV recombinants (VVr) with inducible PKR (VV PKR). The latest system is versatile, as expression of PKR can be regulated and induced at different times; similarly, VVr can be generated expressing other PKR modulators. As an example of the utility of VVr, we describe how this model has been used to analyze the antiviral and proapoptotic functions of PKR, the impact of PKR on translation, and the PKR-induced activation of the nuclear factor-kappaB (NF-kappaB) pathway.

New considerations in infectious disease outbreaks: the threat of genetically modified microbes

Genetically altered microbes are used widely in the conduct of scientific study and have facilitated the development of new medical therapies, preventive strategies, and diagnostic tools. Unfortunately, such organisms may also cause infectious disease outbreaks as a result of accidental or intentional transmission to humans. The unique microbial properties of genetically altered pathogens and the clinical symptoms exhibited by persons infected with them may impede the usual diagnostic and clinical evaluations or preventive strategies. Practicing physicians and clinicians at microbiology laboratories, who would be the first to observe such infections, must consider the broad clinical possibilities of illnesses caused by deliberately altered microorganisms and the potential difficulty in confirming a diagnosis.

Vaccinia as a vector for gene delivery

Gene therapy is a promising approach, yet so far it has shown limited effectiveness in many clinical trials, mainly due to insufficient gene transduction. Recombinant vaccinia virus (rVV) has been well developed as a gene delivery vector, initially for protein expression in mammalian cells. rVV has been further developed to express antigens in vivo in generating immunity for protection against specific infectious diseases and cancer. rVVs, as non-replicating viral vectors, have been demonstrated for their great potential as vaccines, for their diminished cytopathic effects, high levels of protein expression and strong immunogenicity, and they are relatively safe in animals and in human patients. A number of clinical trials using rVVs as vaccines have shown promising results for treating infectious diseases and cancer. In the last few years, due to its exceptional ability to replicate in tumour cells, the Western Reserve strain vaccinia has been explored as a replicating oncolytic virus for cancer virotherapy. As more is learned about the functions of viral gene products in controlling the mammalian cell cycle and in disabling cellular defence mechanisms, specific viral functions can be augmented or eliminated to enhance antitumour efficacy and improve tumour cell targeting. General mechanisms by which this oncolytic virus achieves the antitumour efficacy and specificity are reviewed. Specifically, the deletion of the viral genes for thymidine kinase and vaccinia growth factor resulted in a vaccinia mutant with enhanced tumour targeting activity and fully retaining its efficiency of replication in cancer cells. Other potential strategies for improving this vector for gene delivery will also be discussed in this review.

Future directions for the field of oncolytic virotherapy: a perspective on the use of vaccinia virus

Oncolytic virotherapy is an emerging biotherapeutic platform based on genetic engineering of viruses capable of selectively infecting and replicating within cancer cells. Such viruses have been found to be both safe and to produce antitumour effects in a number of Phase I and II clinical trials. Early work in this field has been pioneered with strains of adenovirus which, although well suited to gene therapy approaches, have displayed certain limitations in their ability to directly destroy and spread through tumour tissues, particularly after systemic administration. Investigators have subsequently been examining the feasibility of using a variety of different viruses as oncolytic agents. Vaccinia virus is perhaps the most widely administered and successful medical product in history; it displays many of the qualities thought necessary for an effective antitumour agent and is particularly well characterised in people due to its role in the eradication of smallpox. Vaccinia has a short life cycle and rapid spread, strong lytic ability, inherent systemic tumour targeting, a large cloning capacity and well-defined molecular biology. In addition, the virus produces no known disease in humans, has been delivered safely to millions of people and has already demonstrated antitumoural efficacy in trials with vaccine strains. These qualities, along with strategies for further improving the safety and antitumour effectiveness of vaccinia, will be discussed in relation to the broad spectrum of clinical experience already achieved with this virus in cancer therapy.

Vaccinia viruses with a serpin gene deletion and expressing IFN-gamma induce potent immune responses without detectable replication in vivo

In a continuing effort to develop safe and efficacious vaccine and immunotherapeutic vectors, we constructed recombinant vaccinia virus (rVV) vaccines lacking either the B13R (SPI-2) or the B22R (SPI-1) immune-modulating gene and coexpressing IFN-gamma. B13R and B22R are nonessential VV immune-modulating genes that have antiapoptotic and antiinflammatory properties with sequence homology to serine protease inhibitors (serpins). IFN-gamma is a cytokine with potent immunoregulatory, antineoplastic, and antiviral properties. We observed that these rVVs with a deletion in a serpin gene and expressing IFN-gamma replicated to high titers in tissue culture yet were avirulent in both immunocompromised and immunocompetent mice with no detectable viral replication in these animals. A single immunization elicited potent humoral, T helper, and cytotoxic T cell immune responses in mice despite the absence of any detectable virus replication in vivo. IFN-gamma coexpression and the inactivation of one or more VV immune-modulating genes provide an optimized method for increasing the safety while maintaining the efficacy of rVV vaccines. This strategy provides a method for developing highly safe and efficacious vaccines for smallpox and other diseases and immunotherapeutic vectors.

A natural vaccinia virus promoter with exceptional capacity to direct protein synthesis

A survey of vaccinia virus promoters, through a reporter gene approach, has identified the viral I1L promoter as having exceptional activity. The I1L promoter exhibited over 10 times the activity of other vaccinia promoters and even rivaled the activity of the bacteriophage T7 promoter in the hybrid vaccinia/T7 expression system. The I1L promoter had high activity in both transient transfection experiments and in the context of recombinant viruses. The I1L promoter should be useful for high-level protein synthesis and poxvirus studies in general.

Cryo-electron tomography of vaccinia virus

The combination of cryo-microscopy and electron tomographic reconstruction has allowed us to determine the structure of one of the more complex viruses, intracellular mature vaccinia virus, at a resolution of 4-6 nm. The tomographic reconstruction allows us to dissect the different structural components of the viral particle, avoiding projection artifacts derived from previous microscopic observations. A surface-rendering representation revealed brick-shaped viral particles with slightly rounded edges and dimensions of approximately 360 x 270 x 250 nm. The outer layer was consistent with a lipid membrane (5-6 nm thick), below which usually two lateral bodies were found, built up by a heterogeneous material without apparent ordering or repetitive features. The internal core presented an inner cavity with electron dense coils of presumptive DNA-protein complexes, together with areas of very low density. The core was surrounded by two layers comprising an overall thickness of approximately 18-19 nm; the inner layer was consistent with a lipid membrane. The outer layer was discontinuous, formed by a periodic palisade built by the side interaction of T-shaped protein spikes that were anchored in the lower membrane and were arranged into small hexagonal crystallites. It was possible to detect a few pore-like structures that communicated the inner side of the core with the region outside the layer built by the T-shaped spike palisade.

Fighting Cancer with Vaccinia Virus: Teaching New Tricks to an Old Dog

Vaccinia virus has played a huge part in human beings' victory over smallpox. With smallpox being eradicated and large-scale vaccination stopped worldwide, vaccinia has assumed a new role in our fight against another serious threat to human health: cancer. Recent advances in molecular biology, virology, immunology, and cancer genetics have led to the design of novel cancer therapeutics based on vaccinia virus backbones. With the ability to infect efficiently a wide range of host cells, a genome that can accommodate large DNA inserts and express multiple genes, high immunogenicity, and cytoplasmic replication without the possibility of chromosomal integration, vaccinia virus has become the platform of many exploratory approaches to treat cancer. Vaccinia virus has been used as (1) a delivery vehicle for anti-cancer transgenes, (2) a vaccine carrier for tumor-associated antigens and immunoregulatory molecules in cancer immunotherapy, and (3) an oncolytic agent that selectively replicates in and lyses cancer cells.

VACCINIA VIRUS MEDIATED p53 GENE THERAPY FOR BLADDER CANCER IN AN ORTHOTOPIC MURINE MODEL

PURPOSE

We determined if vaccinia virus (VV) mediated delivery of human tumor suppressor p53 is safe and effective for bladder tumor therapy in an orthotopic murine model.

MATERIALS AND METHODS

We used recombinant VV (rVV) vectors to express transgenes in murine bladder cancer MB-49 cells in culture and those growing orthotopically in syngeneic mice. Cultured MB-49 cells were infected with rVV expressing reporter genes (rVV-L15) or p53 (rVV-TK-53) to measure virus infection and apoptosis induction. Orthotopic MB-49 tumors in C57/Bl6 mice were treated with intravesical instillation of rVV, and the tumor incidence, survival and transgene expression were determined.

RESULTS

Productive virus infection in vitro was observed in MB-49 cells, although at somewhat lower efficiency than in African Green Monkey kidney CV-1 cells (American Type Culture Collection, Manassas, Virginia). Expression of transgenes in vitro correlated with the virus dose. Cells infected with rVV underwent apoptosis with rVV-TK-53 inducing far greater cell death than rVV-L15. The rVV-L15 virus had no effect on tumor incidence but it increased mean survival compared with control. Instillation of rVV-TK-53 decreased the tumor incidence and 33% of mice survived treatment. At necropsy all nonsurviving mice had bladder tumor, whereas 2 survivors in the rVV-TK-53 treated group were tumor-free. Immunohistochemistry of tumors detected expression of the human p53 gene product in tumor cells.

CONCLUSIONS

To our knowledge we report for the first time that recombinant vaccinia virus expressing human p53 can induce the death of MB-49 tumor cells in vivo, not only through the lytic effect of the virus, but also through expression of the death inducing p53 transgene. Further studies are needed to shed light on the mechanisms of rVV-TK-53 mediated tumor apoptosis and the antitumor immune response.