Poxviruses as expression vectors

Defining antigen targets to dissect vaccinia virus and monkeypox virus-specific T cell responses in humans

The monkeypox virus (MPXV) outbreak confirmed in May 2022 in non-endemic countries is raising concern about the pandemic potential of novel orthopoxviruses. Little is known regarding MPXV immunity in the context of MPXV infection or vaccination with vaccinia-based vaccines (VACV). As with vaccinia, T cells are likely to provide an important contribution to overall immunity to MPXV. Here, we leveraged the epitope information available in the Immune Epitope Database (IEDB) on VACV to predict potential MPXV targets recognized by CD4⁺ and CD8⁺ T cell responses. We found a high degree of conservation between VACV epitopes and MPXV and defined T cell immunodominant targets. These analyses enabled the design of peptide pools able to experimentally detect VACV-specific T cell responses and MPXV cross-reactive T cells in a cohort of vaccinated individuals. Our findings will facilitate the monitoring of cellular immunity following MPXV infection and vaccination.

Working Safely with Vaccinia Virus: Laboratory Technique and Review of Published Cases of Accidental Laboratory Infections with Poxviruses

Vaccinia virus, the prototype Orthopoxvirus, is widely used in the laboratory as a model system to study various aspects of viral biology and virus-host interactions, as a protein expression system, as a vaccine vector, and as an oncolytic agent. The ubiquitous use of vaccinia viruses in laboratories around the world raises certain safety concerns because the virus can be a pathogen in individuals with immunological and dermatological abnormalities, and on occasion can cause serious problems in normal hosts. This chapter reviews standard operating procedures when working with vaccinia virus and reviews published cases of accidental laboratory infections with poxviruses.

Primary Human B Cells at Different Differentiation and Maturation Stages Exhibit Distinct Susceptibilities to Vaccinia Virus Binding and Infection

Vaccinia virus (VACV), the prototypical member of the poxvirus family, was used as a live-virus vaccine to eradicate smallpox worldwide and has recently received considerable attention because of its potential as a prominent vector for the development of vaccines against infectious diseases and as an oncolytic virus for cancer therapy. Studies have demonstrated that VACV exhibits an extremely strong bias for binding to and infection of primary human antigen-presenting cells (APCs), including monocytes, macrophages, and dendritic cells. However, very few studies have assessed the interactions of VACV with primary human B cells, a main type of professional APCs. In this study, we evaluated the susceptibility of primary human peripheral B cells at various differentiation and maturation stages to VACV binding, infection, and replication. We found that plasmablasts were resistant to VACV binding, while other B subsets, including transitional, mature naive, memory, and plasma cells, were highly susceptible to VACV binding. VACV binding preference was likely associated with differential expression of chemokine receptors, particularly CXCR5. Infection studies showed that plasmablast, plasma, transitional, and mature naive B cells were resistant to VACV infection, while memory B cells were preferentially infected. VACV infection in ex vivo B cells was abortive, which occurred at the stage of late viral gene expression. In contrast, activated B cells were permissive to productive VACV infection. Thus, primary human B cells at different differentiation stages exhibit distinct susceptibilities to VACV binding and infection, and the infections are abortive and productive in ex vivo and activated B cells, respectively.IMPORTANCE Our results provide critical information to the field of poxvirus binding and infection tropism. We demonstrate that VACV preferentially infects memory B cells that play an important role in a rapid and vigorous antibody-mediated immune response upon reinfection by a pathogen. Additionally, this work highlights the potential of B cells as natural cellular models to identify VACV receptors or dissect the molecular mechanisms underlying key steps of the VACV life cycle, such as binding, penetration, entry, and replication in primary human cells. The understanding of VACV biology in human primary cells is essential for the development of a safe and effective live-virus vector for oncolytic virus therapy and vaccines against smallpox, other pathogens, and cancer.

Assessing the Structure and Function of Vaccinia Virus Gene Products by Transient Complementation

Poxviruses are large, complex dsDNA viruses that are highly unusual in replicating solely within the cytoplasm of the infected cell. The most infamous poxvirus was variola virus, the etiological agent of smallpox; today, poxviruses remain of biomedical significance, both as pathogens and as recombinant vaccines and oncolytic therapies. Vaccinia virus is the prototypic poxvirus for experimental analysis. The 195 kb dsDNA genome contains >200 genes that encode proteins involved in such processes as viral entry, gene expression, genome replication and maturation, virion assembly, virion egress, and immune evasion.Molecular genetic analysis has been instrumental in the study of the structure and function of many viral gene products. Temperature-sensitive (ts) mutants have been especially useful in this endeavor; inducible recombinants and deletion mutants are now also important tools. Once a phenotype is observed following the repression, deletion, or inactivation of a particular gene product, the technique of transient complementation becomes central for further study.Simply put, transient complementation involves the transient expression of a variety of alleles of a given viral gene within infected cells, and the evaluation of which of these alleles can "complement" or "rescue" the phenotype caused by the loss of the endogenous allele. This analysis leads to the identification of key domains, motifs, and sites of posttranslational modification. Subcellular localization and protein:protein interactions can also be evaluated in these studies. The development of a reliable toolbox of vectors encoding viral promoters of different temporal classes, and the use of a variety of epitope tags, has greatly enhanced the utility of this experimental approach for poxvirus research.

Visualizing Poxvirus Replication and Recombination Using Live-Cell Imaging

A modernized version of an old saying goes that "If a picture is worth a thousand words, then a video is worth a million." Although made with reference to "YouTube", the quotation also has relevance for microbiologists when one considers how modern microscopes can be used to track biological fluorophores for hours without bleaching or phototoxicity. Confocal fluorescence microscopy provides a powerful tool for capturing dynamic processes within a cellular context that are better understood when viewed using time-lapse videos. In our laboratory we have long been interested in the links between poxvirus DNA replication and recombination and, since these are cytoplasmic viruses, such DNA-dependent processes are easily imaged throughout the virus life cycle without interference from signals coming from nuclear DNA. In this chapter we outline methods that can be used to follow the movement and replication of vaccinia virus DNA, and to also detect the products of poxvirus-catalyzed recombination reactions. We describe how to use the bacteriophage lambda DNA-binding protein, cro, as a way of labeling DNA within a cell when it is conjugated to fluorescent proteins. When used in conjunction with other fluorescent reagents, new labeling technologies, and tagged reporter constructs, these approaches can generate visually appealing and highly informative insights into diverse aspects of vaccinia virus biology.

ING4 expressing oncolytic vaccinia virus promotes anti-tumor efficiency and synergizes with gemcitabine in pancreatic cancer

With no effective treatments available for most pancreatic cancer patients, pancreatic cancer continues to be one of the most difficult malignancies to treat. Oncolytic virus mediated-gene therapy has exhibited ubiquitous antitumor potential. In this study, we constructed a novel oncolytic vaccinia virus harboring the inhibitor of growth family member 4 gene (VV-ING4) to investigate its therapeutic efficacy alone or in combination with gemcitabine against pancreatic cancer cells in vitro and in vivo. ING4 expression was determined via quantitative real-time polymerase chain reaction (qPCR) and western blot. The cytotoxicity of VV-ING4 was measured using a cell proliferation assay. Both flow cytometry and western blot were applied to analyze the cell cycle and apoptosis. Furthermore, the combination inhibitory effect of VV-ING4 and gemcitabine was assessed using Chou-Talalay analysis in vitro and a BLAB/c mice model in vivo. We found that VV-ING4 significantly increases ING4 expression, displayed greater cytotoxic efficiency, and induced pancreatic cancer cell apoptosis and G2/M phase arrest. Additionally, the combination of VV-ING4 and gemcitabine synergistically effect in vitro and in vivo. Taken together, our data implicate VV-ING4 as a conceivable pancreatic cancer therapeutic candidate alone or in combination with gemcitabine.

Facial synkinesia before and after surgical reanimation of the paralyzed face

BACKGROUND

Facial synkinesia is a common sequela of facial palsy, affecting 15 to 20 percent of patients. The rate of postoperative synkinesia after facial reanimation is not clearly established. The severity and type of synkinesia determine the degree of clinical relevance.

METHODS

One hundred sixty-seven patients with facial palsy were included in this retrospective cohort study. Three-dimensional video analysis of facial movements was performed preoperatively and 18 months after facial reanimation. The severity of synkinesia was rated subjectively on a four-degree severity scale. Objective three-dimensional analysis of synkinesia was performed on patients with 18-month follow-up times.

RESULTS

Preoperatively, 84.4 percent of patients were not affected by synkinesia, 9 percent presented with mild synkinesia, 4.2 percent presented with moderate synkinesia, and 2.4 percent presented with severe synkinesia. Postoperatively, 51 percent of all patients presented with facial synkinesia (41.8 percent mild, 17.3 percent moderate, and 1 percent severe synkinesia; some patients had more than one type). Patients treated with territorially differentiated gracilis muscle transplantation were most frequently affected (69.8 percent), followed by patients treated with gracilis muscle transplantation in combination with temporalis muscle transposition to the eye (51.8 percent). Oculo-oral synkinesia was the most frequent form of synkinesia.

CONCLUSIONS

After surgical reanimation of the paralyzed face, half of the patients presented with synkinesia. The majority of patients developed mild or moderate forms of synkinesia; therefore, the clinical relevance of synkinesia has to be seen in the context of total facial function. Because of the high prevalence of synkinesia, it should be documented and addressed in patients undergoing facial reanimation.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, IV.

Vaccination directed against the human endogenous retrovirus-K (HERV-K) gag protein slows HERV-K gag expressing cell growth in a murine model system

Background

Human endogenous retroviruses (HERVs) are remnants of ancestral infections and chromosomally integrated in all cells of an individual, are transmitted only vertically and are defective in viral replication. However enhanced expression of HERV-K accompanied by the emergence of anti-HERV-K-directed immune responses has been observed inter-alia in HIV-infected individuals and tumor patients. Therefore HERV-K might serve as a tumor-specific antigen or even as a constant target for the development of an HIV vaccine.

Results

To verify our hypothesis, we tested the immunogenicity of HERV-K Gag by using a recombinant vaccinia virus (MVA-HK_con) expressing the HERV-K Gag protein and established an animal model to test its vaccination efficacy. Murine renal carcinoma cells (Renca) were genetically altered to express E. coli beta-galactosidase (RLZ cells) and the HERV-K Gag protein (RLZ-HKGag cells). Subcutaneous application of RLZ-HKGag cells into syngenic BALB/c mice resulted in the formation of local tumors in MVA vaccinated mice. MVA-HK_con vaccination reduced the tumor growth. Furthermore, intravenous injection of RLZ-HKGag cells led to the formation of pulmonary metastases. Vaccination of tumor-bearing mice with MVA-HK_con drastically reduced the number of pulmonary RLZ-HKGag tumor nodules compared to vaccination with wild-type MVA.

Conclusion

The data demonstrate that HERV-K Gag is a useful target for vaccine development and might offer new treatment opportunities for cancer patients.

Recombinant vaccines against T. gondii: comparison between homologous and heterologous vaccination protocols using two viral vectors expressing SAG1

The use of recombinant viral vectors expressing T. gondii antigens is a safe and efficient approach to induce immune response against the parasite and a valuable tool for vaccine development. We have previously protected mice from toxoplasmosis by immunizing the animals with an adenovirus expressing the protein SAG1 (AdSAG1) of T. gondii. We are now looking for ways to improve the vaccination strategy and enhance protection. One limitation of homologous vaccinations (sequential doses of the same vector) is induction of anti-vector immune response that blocks cell transduction, restricts transgene expression and, consequently, compromises the overall outcome of vaccination. One way to avert the effects of anti-vector response is to use different viruses in prime and boost (heterologous vaccination). Bearing this in mind, we generated a modified Vaccinia Virus Ankara encoding SAG1 (MVASAG1), to be tested as boost agent after prime with AdSAG1. Although minor differences were observed in the magnitude of the anti-SAG1 immune response induced by each vaccination protocol, the heterologous immunization with AdSAG1 followed by MVASAG1 resulted in improved capacity to control brain cyst formation in a model of chronic toxoplasmosis in C57BL/6 mice.

CD4+ T cells provide intermolecular help to generate robust antibody responses in vaccinia virus-vaccinated humans

Immunization with vaccinia virus elicits a protective Ab response that is almost completely CD4(+) T cell dependent. A recent study in a rodent model observed a deterministic linkage between Ab and CD4(+) T cell responses to particular vaccinia virus proteins suggesting that CD4(+) T cell help is preferentially provided to B cells with the same protein specificity (Sette et al. 2008. Immunity 28: 847-858). However, a causal linkage between Ab and CD4(+) T cell responses to vaccinia or any other large pathogen in humans has yet to be done. In this study, we measured the Ab and CD4(+) T cell responses against four vaccinia viral proteins (A27L, A33R, B5R, and L1R) known to be strongly targeted by humoral and cellular responses induced by vaccinia virus vaccination in 90 recently vaccinated and 7 long-term vaccinia-immunized human donors. Our data indicate that there is no direct linkage between Ab and CD4(+) T cell responses against each individual protein in both short-term and long-term immunized donors. Together with the observation that the presence of immune responses to these four proteins is linked together within donors, our data suggest that in vaccinia-immunized humans, individual viral proteins are not the primary recognition unit of CD4(+) T cell help for B cells. Therefore, we have for the first time, to our knowledge, shown evidence that CD4(+) T cells provide intermolecular (also known as noncognate or heterotypic) help to generate robust Ab responses against four vaccinia viral proteins in humans.

Purification of recombinant vaccinia virus-expressed monomeric HIV-1 gp120 to apparent homogeneity

Vaccinia virus (VV) has been used to express a variety of heterologous proteins, including HIV envelope (Env) glycoproteins. The Env protein is synthesized as a precursor molecule, gp160, which is cleaved into the surface antigen gp120 and the transmembrane protein gp41. Even though production of gp160 by the VV expression system has been described, its use for gp120 production is not well documented. Here we report a new procedure for the purification of gp120 from serum-containing culture supernatant of VV-infected cells. The gp120 protein was enriched to a purity better than 60% on a snowdrop (Galanthus nivalis) lectin affinity column in the presence of 0.25% zwitterionic detergent Empigen BB. After additional DEAE anion exchange and Superdex size exclusion chromatography steps, the gp120 monomer was purified free of contamination as determined by SDS-PAGE. The retention of structural integrity was confirmed by determining the affinity constant of purified gp120s to soluble CD4 and a monoclonal antibody IgG1b12, using surface plasmon resonance analysis. The purification procedure is robust and reproducible, and may find general use for glycoprotein purifications from sources where the presence of serum is desirable.

Human immunodeficiency virus vaccine trials

More than 2 million AIDS-related deaths occurred globally in 2008, and more than 33 million people are living with HIV/AIDS. Despite promising advances in prevention, an estimated 2.7 million new HIV infections occurred in that year, so that for every two patients placed on combination antiretroviral treatment, five people became infected. The pandemic poses a formidable challenge to the development, progress, and stability of global society 30 years after it was recognized. Experimental preventive HIV-1 vaccines have been administered to more than 44,000 human volunteers in more than 187 separate trials since 1987. Only five candidate vaccine strategies have been advanced to efficacy testing. The recombinant glycoprotein (rgp)120 subunit vaccines, AIDSVAX B/B and AIDSVAX B/E, and the Merck Adenovirus serotype (Ad)5 viral-vector expressing HIV-1 Gag, Pol, and Nef failed to show a reduction in infection rate or lowering of postinfection viral set point. Most recently, a phase III trial that tested a heterologous prime-boost vaccine combination of ALVAC-HIV vCP1521 and bivalent rgp120 (AIDSVAX B/E) showed 31% efficacy in protection from infection among community-risk Thai participants. A fifth efficacy trial testing a DNA/recombinant(r) Ad5 prime-boost combination is currently under way. We review the clinical trials of HIV vaccines that have provided insight into human immunogenicity or efficacy in preventing HIV-1 infection.

The N-terminus of vaccinia virus host range protein C7L is essential for function

Vaccinia virus (VACV), a member of the Poxviridae family of large double-stranded DNA viruses, is being used as a smallpox vaccine as well as an expression vector for immunization against other infectious diseases and cancer. The host range of wild type VACV is very broad among mammalian cells. C7L is a host range gene identified in VACV and is well conserved in mammalian poxviruses except for parapoxviruses and molluscum contagiosum virus. The molecular mechanisms by which the C7L gene exerts host range function are not well understood. The C7L protein does not have any known conserved domains or show sequence similarity to cellular proteins or viral proteins other than the C7L homologs in mammalian poxviruses. We generated recombinant vaccinia viruses carrying deletion mutants of the C7L gene using NYVAC as a parental strain and found that the N-terminus is essential for host range function of C7L, which is consistent with a previous report that showed that homology among C7L homologs are greater near the N-terminus than the C-terminus.

Effects of route and coadministration of recombinant raccoon poxviruses on immune responses and protection against highly pathogenic avian influenza in mice

We previously demonstrated that recombinant raccoonpox (RCN) virus could serve as a vector for an influenza vaccine. RCN constructs expressing the hemagglutinin (HA) from H5N1 viruses were immunogenic in chickens. In the current study, we generated several recombinant RCN constructs expressing influenza (H5N1) antigens and a molecular adjuvant (Heat-Labile enterotoxin B from E. coli: RCN-LTB), demonstrated their expression in vitro, and evaluated their ability to protect mice against H5N1 virus challenge. RCN-HA provided strong protection when administered intradermally (ID), but not intranasally (IN). Conversely, the RCN-neuraminidase (NA) construct was highly efficacious by the IN route and elicited high titers of neutralizing antibodies in mice. Vaccination by combined ID (RCN-HA) and IN (RCN-NA) routes offered mice the best protection against an IN challenge with heterologous H5N1 virus. However, protection was reduced when the different RCN constructs were pre-mixed, perhaps due to reduced expression of antigen.

Innate immune recognition of poxviral vaccine vectors

The study of poxviruses pioneered the field of vaccinology after Jenner's remarkable discovery that 'vaccination' with the phylogenetically related cowpox virus conferred immunity to the devastating disease of smallpox. The study of poxviruses continues to enrich the field of virology because the global eradication of smallpox provides a unique example of the potency of effective immunization. Other poxviruses have since been developed as vaccine vectors for clinical and veterinary applications and include modified vaccinia virus strains such as modified vaccinia Ankara and NYVAC as well as the avipox viruses, fowlpox virus and canarypox virus. Despite the empirical development of poxvirus-based vectored vaccines, it is only now becoming apparent that we need to better understand how the innate arm of the immune system drives adaptive immunity to poxviruses, and how this information is relevant to vaccine design strategies, which are the topics addressed in this article.

Functional hyper-IL-6 from vaccinia virus-colonized tumors triggers platelet formation and helps to alleviate toxicity of mitomycin C enhanced virus therapy

Background

Combination of oncolytic vaccinia virus therapy with conventional chemotherapy has shown promise for tumor therapy. However, side effects of chemotherapy including thrombocytopenia, still remain problematic.

Methods

Here, we describe a novel approach to optimize combination therapy of oncolytic virus and chemotherapy utilizing virus-encoding hyper-IL-6, GLV-1h90, to reduce chemotherapy-associated side effects.

Results

We showed that the hyper-IL-6 cytokine was successfully produced by GLV-1h90 and was functional both in cell culture as well as in tumor-bearing animals, in which the cytokine-producing vaccinia virus strain was well tolerated. When combined with the chemotherapeutic mitomycin C, the anti-tumor effect of the oncolytic virotherapy was significantly enhanced. Moreover, hyper-IL-6 expression greatly reduced the time interval during which the mice suffered from chemotherapy-induced thrombocytopenia.

Conclusion

Therefore, future clinical application would benefit from careful investigation of additional cytokine treatment to reduce chemotherapy-induced side effects.

Working safely with vaccinia virus: laboratory technique and review of published cases of accidental laboratory infections

Vaccinia virus (VACV), the prototype orthopoxvirus, is widely used in the laboratory as a model system to study various aspects of viral biology and virus-host interactions, as a protein expression system, as a vaccine vector, and as an oncolytic agent. The ubiquitous use of VACVs in the laboratory raises certain safety concerns because the virus can be a pathogen in individuals with immunological and dermatological abnormalities, and on occasion can cause serious problems in normal hosts. This chapter reviews standard operating procedures when working with VACV and reviews published cases on accidental laboratory infections.

Vectors based on modified vaccinia Ankara expressing influenza H5N1 hemagglutinin induce substantial cross-clade protective immunity

BACKGROUND

New highly pathogenic H5N1 influenza viruses are continuing to evolve with a potential threat for an influenza pandemic. So far, the H5N1 influenza viruses have not widely circulated in humans and therefore constitute a high risk for the non immune population. The aim of this study was to evaluate the cross-protective potential of the hemagglutinins of five H5N1 strains of divergent clades using a live attenuated modified vaccinia Ankara (MVA) vector vaccine.

METHODOLOGY/PRINCIPAL FINDINGS

The replication-deficient MVA virus was used to express influenza hemagglutinin (HA) proteins. Specifically, recombinant MVA viruses expressing the HA genes of the clade 1 virus A/Vietnam/1203/2004 (VN/1203), the clade 2.1.3 virus A/Indonesia/5/2005 (IN5/05), the clade 2.2 viruses A/turkey/Turkey/1/2005 (TT01/05) and A/chicken/Egypt/3/2006 (CE/06), and the clade 2.3.4 virus A/Anhui/1/2005 (AH1/05) were constructed. These experimental live vaccines were assessed in a lethal mouse model. Mice vaccinated with the VN/1203 hemagglutinin-expressing MVA induced excellent protection against all the above mentioned clades. Also mice vaccinated with the IN5/05 HA expressing MVA induced substantial protection against homologous and heterologous AH1/05 challenge. After vaccination with the CE/06 HA expressing MVA, mice were fully protected against clade 2.2 challenge and partially protected against challenge of other clades. Mice vaccinated with AH1/05 HA expressing MVA vectors were only partially protected against homologous and heterologous challenge. The live vaccines induced substantial amounts of neutralizing antibodies, mainly directed against the homologous challenge virus, and high levels of HA-specific IFN-γ secreting CD4 and CD8 T-cells against epitopes conserved among the H5 clades and subclades.

CONCLUSIONS/SIGNIFICANCE

The highest level of cross-protection was induced by the HA derived from the VN/1203 strain, suggesting that pandemic H5 vaccines utilizing MVA vector technology, should be based on the VN/1203 hemagglutinin. Furthermore, the recombinant MVA-HA-VN, as characterized in the present study, would be a promising candidate for such a vaccine.

Phase III HIV vaccine trial in Thailand: a step toward a protective vaccine for HIV

The large human efficacy trail in Thailand, RV144, was concluded in the summer of 2009. This is the first Phase III trial to show limited, but significant, efficacy in preventing HIV acquisition. This trial represents the first sign that a preventive vaccine for HIV may be feasible. The vaccine regimen tested in Thailand consisted of priming with a Canarypox vector carrying three synthetic HIV genes. The priming was followed by booster inoculations with two recombinant envelope proteins from HIV, clade B and E. The need to understand the role in protection from HIV acquisition of the new responses, induced by this vaccine combination, has brought together many researchers with the common goal of improving the development of a safe and effective vaccine for HIV.

Uncovering the interplay between CD8, CD4 and antibody responses to complex pathogens

Vaccinia virus (VACV) was used as the vaccine strain to eradicate smallpox. VACV is still administered to healthcare workers or researchers who are at risk of contracting the virus, and to military personnel. Thus, VACV represents a weapon against outbreaks, both natural (e.g., monkeypox) or man-made (bioterror). This virus is also used as a vector for experimental vaccine development (cancer/infectious disease). As a prototypic poxvirus, VACV is a model system for studying host-pathogen interactions. Until recently, little was known about the targets of host immune responses, which was likely owing to VACVs large genome (>200 open reading frames). However, the last few years have witnessed an explosion of data, and VACV has quickly become a useful model to study adaptive immune responses. This review summarizes and highlights key findings based on identification of VACV antigens targeted by the immune system (CD4, CD8 and antibodies) and the complex interplay between responses.

Recombinant respiratory syncytial virus F protein expression is hindered by inefficient nuclear export and mRNA processing

Studies of the fusion activity of respiratory syncytial virus (RSV) F protein are significantly hindered by low recombinant expression levels. While infection produces F protein levels detectable by western blot, recombinant expression produces undetectable to low levels of F protein. Identifying the obstacles that hinder recombinant F protein expression may lead to improved expression and facilitate the study of F protein function. We hypothesized that nuclear localization and/or inefficient RNA polymerase II-mediated transcription contribute to poor recombinant F protein expression. This study shows a combination of stalled nuclear export, premature polyadenylation, and low mRNA abundance all contribute to low recombinant F protein expression levels. In addition, this study provides an expression optimization strategy that results in greater F protein expression levels than observed by codon-optimization of the F protein gene, which will be useful for future studies of F protein function.

Comparison of monkeypox viruses pathogenesis in mice by in vivo imaging

Monkeypox viruses (MPXV) cause human monkeypox, a zoonotic smallpox-like disease endemic to Africa, and are of worldwide public health and biodefense concern. Using viruses from the Congo (MPXV-2003-Congo-358) and West African (MPXV-2003-USA-044) clades, we constructed recombinant viruses that express the luciferase gene (MPXV-Congo/Luc+and MPXV-USA-Luc+) and compared their viral infection in mice by biophotonic imaging. BALB/c mice became infected by both MPXV clades, but they recovered and cleared the infection within 10 days post-infection (PI). However, infection in severe combined immune deficient (SCID) BALB/c mice resulted in 100% lethality. Intraperitoneal (IP) injection of both MPXV-Congo and MPXV-Congo/Luc+resulted in a systemic clinical disease and the same mean time-to-death at 9 (±0) days post-infection. Likewise, IP injection of SCID-BALB/c mice with MPXV-USA or the MPXV-USA-Luc+, resulted in similar disease but longer (P<0.05) mean time-to-death (11±0 days) for both viruses compared to the Congo strains. Imaging studies in SCID mice showed luminescence in the abdomen within 24 hours PI with subsequent spread elsewhere. Animals infected with the MPXV-USA/Luc+had less intense luminescence in tissues than those inoculated with MPXV-Congo/Luc+, and systemic spread of the MPXV-USA/Luc+virus occurred approximately two days later than the MPXV-Congo/Luc+. The ovary was an important target for viral replication as evidenced by the high viral titers and immunohistochemistry. These studies demonstrate the suitability of a mouse model and biophotonic imaging to compare the disease progression and tissue tropism of MPX viruses.

Vaccinia virus-specific CD8(+) T-cell responses target a group of epitopes without a strong immunodominance hierarchy in humans

Immunization with vaccinia virus (VACV) resulted in long-lasting protection against smallpox and successful global eradication of the disease. VACV elicits strong cellular and humoral immune responses. Although neutralizing antibody is essential for protection, cellular immunity seems to be more important for recovery from infection in humans. We analyzed the immunodominance hierarchy of 73 previously identified VACV human CD8(+) T-cell epitopes restricted by HLA-A1, -A2, -A3, -A24, -B7, or -B44 alleles or the alleles belonging to one of these supertypes in 56 donors after primary VACV immunization. With the exception of the responses to HLA-A24 supertype-restricted epitopes, there were no consistent patterns of epitope immunodominance among donors sharing the same HLA alleles or supertypes, which is in sharp contrast with the mouse studies. However, we identified 12 epitopes that were recognized by >or=20% of donors sharing the same HLA allele; 6 of these epitopes contributed >or=20% of the total VACV-specific T-cell response in at least one individual. VACV-specific CD8(+) T-cell responses targeted a group of epitopes, "relatively dominant" epitopes, without a strong immunodominance hierarchy in humans, which may be advantageous to humans to prevent the emergence of T-cell escape mutants.

Dendritic cells are preferentially targeted among hematolymphocytes by Modified Vaccinia Virus Ankara and play a key role in the induction of virus-specific T cell responses in vivo

Background

Modified Vaccinia Ankara (MVA) is a highly attenuated strain of vaccinia virus (VV) that has lost approximately 15% of the VV genome, along with the ability to replicate in most mammalian cells. It has demonstrated impressive safety and immunogenicity profile in both preclinical and clinical studies, and is being actively explored as a promising vaccine vector for a number of infectious diseases and malignancies. However, little is known about how MVA interacts with the host immune system constituents, especially dendritic cells (DCs), to induce strong immune responses despite its inability to replicate in vivo. Using in vitro and in vivo murine models, we systematically investigated the susceptibility of murine DCs to MVA infection, and the immunological consequences of the infection.

Results

Our data demonstrate that MVA preferentially infects professional antigen presenting cells, especially DCs, among all the subsets of hematolymphoid cells. In contrast to the reported blockage of DC maturation and function upon VV infection, DCs infected by MVA undergo phenotypic maturation and produce innate cytokine IFN-α within 18 h of infection. Substantial apoptosis of MVA-infected DCs occurs after 12 h following infection and the apoptotic DCs are readily phagocytosed by uninfected DCs. Using MHC class I – deficient mice, we showed that both direct and cross-presentation of viral Ags are likely to be involved in generating viral-specific CD8⁺ T cell responses. Finally, DC depletion abrogated the T cell activation in vivo.

Conclusion

We present the first in vivo evidence that among hematolymphoid cells, DCs are the most susceptible targets for MVA infection, and DC-mediated Ag presentation is required for the induction of MVA-specific immune responses. These results provide important information concerning the mechanisms by which strong immune responses are elicited to MVA-encoded antigens and may inform efforts to further improve the immunogenicity of this already promising vaccine vector.

The magnitude of the CD8+ T cell response produced by recombinant virus vectors is a function of both the antigen and the vector

Virus-based recombinant vaccines have proven highly effective at generating protective CD8+ T cell responses. Multiple vector platforms are available, however, little is known about the relative influence of the different vectors on the transgene-specific CD8+ T cell population. To address this question, we compared several characteristics of the CD8+ T cell response elicited by recombinant adenovirus (rAd) and vaccinia virus (rVV). We found that following rAd immunization the transgene-specific CD8+ T cell response peaked around day 12 and was larger and more sustained than the response produced by rVV. In addition, the CD8+ T cell response generated by rAd was directed primarily against the transgene, whereas the CD8+ T cell response produced by rVV principally targeted the vector backbone. In addition, we also observed that transgene selection also impacted on the magnitude of the CD8+ T cell response elicited by both vectors. Despite differences in the magnitude of the anti-transgene CD8+ T cell response, both vectors elicited CD8+ T cell populations with similar cytokine production, functional avidity and cytolytic activity. In addition, plasmid priming prior to immunization with either rAd or rVV only impacted the magnitude of the transgene gene specific CD8+ T cell response. Our study demonstrates that both vector and transgene selection can influence the magnitude of the CD8+ T cell response, but they do not influence functionality.

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

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

Vaccinia virus impairs directional migration and chemokine receptor switch of human dendritic cells

A crucial event for the induction of an anti-viral immune response is the coordinated, phenotype-dependent migration of dendritic cells (DC) to sites of infection and secondary lymphoid organs. Here we show that the vaccinia virus (VV) strains Western Reserve (WR) and modified virus Ankara (MVA) inhibit directional migration of mature DC toward the lymphoid chemokines CCL19 and CXCL12 without affecting surface expression of the respective chemokine receptors or impairing undirected cellular locomotion. Instead, infection with VV results in a deficiency of extracellular signal-regulated kinase-1 and a disturbance of intracellular calcium mobilization, indicating a viral interference with signaling events downstream of the surface chemokine receptors. In immature DC, apart from inhibiting chemokine-induced migration of infected DC, infection with both VV strains increases expression of the inflammatory chemokine receptors CCR1 and CXCR1 on non-infected bystander DC, which depends on the activity of IFN-alpha. Although functional, these chemokine receptors are resistant to lipopolysaccharide-induced down-regulation. In addition, VV-infected and non-infected bystander DC fail to up-regulate the lymphoid chemokine receptor CCR7 upon activation, together pointing to a disability to undergo the chemokine receptor switch. This study shows that VV targets directional migration of professional antigen-presenting cells at multiple functional levels, revealing a potent viral strategy of immune escape.

Immunity and immunological memory following smallpox vaccination

The smallpox vaccine consists of live vaccinia virus and is generally considered the gold standard of vaccines, since it is the only one that has led to the complete eradication of an infectious disease from the human population. Renewed fears that smallpox might be deliberately released in an act of bioterrorism have led to resurgence in the study of immunity and immunological memory to vaccinia virus and other poxviruses. Here we review our current understanding of memory T-cell, memory B-cell, and antibody responses to vaccinia and related poxviruses, both in animal models and human subjects. Of particular interest are recent advances in understanding protective immunity to poxviruses, quantifying immunological memory to the smallpox vaccine in humans, and identifying major vaccinia-specific T-cell and B-cell epitopes. In addition, potential mechanisms for maintenance of immunological memory are discussed.

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.

Development of the PANVAC-VF vaccine for pancreatic cancer

PANVAC-VF is a vaccine regimen composed of a priming dose of recombinant vaccinia virus and booster doses of recombinant fowlpox virus expressing carcinoembryonic antigen, mucin-1 and a triad of costimulatory molecules (TRICOM), which include B7.1, intercellular adhesion molecule-1 and leukocyte function-associated antigen-3. Vaccination is administered by subcutaneous injection followed by 4 days of local recombinant adjuvant granulocyte-macrophage colony-stimulating factor at the vaccination site. The vaccine has been developed for patients with advanced pancreatic cancer and has now entered a randomized Phase III clinical trial. This review will describe the background of recombinant poxvirus technology for tumor vaccine development, detail the key preclinical studies supporting the regimen, review the clinical trials supporting the current Phase III study, and highlight the key challenges and future obstacles to successful implementation of PANVAC-VF for pancreatic cancer.

Recombinant adenovirus vector vaccine induces stronger cytotoxic T-cell responses than recombinant vaccinia virus vector, plasmid DNA, or a combination of these

The efficiency of prime-boost vaccinations on the induction of T-cell responses to Sin Nombre virus nucleocapsid protein expressed by recombinant vaccinia virus, replication-deficient adenovirus, and plasmid DNA in mice was quantitated by the number of epitope-specific interferon-gamma-producing T cells and cytotoxic T-lymphocyte activity induced. In prime-boost immunizations, all combinations that included the recombinant adenovirus induced a much higher number of epitope-specific interferon-gamma-producing T cells than did other combinations. A single immunization of the recombinant adenovirus was able to induce similarly high levels of epitope-specific interferon-gamma-producing cells, despite the fact that the recombinant adenovirus produces less amount of the Sin Nombre virus nucleocapsid protein.

Identification of vaccinia CD8+ T-cell epitopes conserved among vaccinia and variola viruses restricted by common MHC class I molecules, HLA-A2 or HLA-B7

Immunization with vaccinia virus results in long-lasting protection against smallpox and is an approach that has been successfully used to eliminate natural smallpox infections worldwide. Today, vaccinia virus is very important not only as a vaccine virus to protect human against smallpox, but also as an expression vector for immunization against other infectious diseases, such as HIV and cancer. In this article, we identify three new vaccinia human CD8+ T-cell epitopes conserved among vaccinia and variola viruses restricted by HLA-A2, HLA-B7, or HLA-B*3502, which belongs to the HLA-B7 supertype. Identification of these CD8+ T-cell epitopes restricted by common HLA alleles will help to quantitate human CD8+ T-cell responses to licensed and experimental smallpox vaccines and to vaccinia virus vectors. CD8+ T-cell responses specific to these epitopes can also be used to quantitate cellular immune responses, especially with new smallpox vaccines that do not induce a "take," such as the modified vaccinia virus Ankara strain. Combined with previous reports by us and others, these results show that there are some vaccinia viral proteins containing multiple epitopes restricted by different MHC molecules of humans and mice.

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.

Identification of murine poxvirus-specific CD8+ CTL epitopes with distinct functional profiles

Murine T cell epitopes against vaccinia virus (VV) have not been characterized to date in part due to the large and complex genome of VV. We have identified and characterized two CD8+ T cell epitopes on the A47L (modified VV Ankara strain (MVA)-029) and J6R (MVA-043) proteins of VV that are Db and Kb restricted, respectively. Following i.p. immunization with VV New York City Board of Health (NYCBH) strain, MVA-029 peptide-stimulated splenocytes secreted IFN-gamma from 7 days to 7 mo postimmunization, and virus-stimulated effectors were also able to lyse MVA-029-pulsed target cells at the same time points. In contrast, MVA-043 peptide-stimulated splenocytes secreted very low levels of IFN-gamma only at day 7 but maintained the ability to lyse target cells up to 2 mo postimmunization. Both MVA-029 and MVA-043 peptide-stimulated lymph node cells degranulated similarly as assessed by Ag-induced CD107 expression. T cell responses to whole-virus stimulation remained robust and steady during the acute and memory T cell response to VV. Identification of T cell epitopes on VV will enable further studies to increase our understanding of the role of CD8+ T cells in VV infection and assist in the design of new protective strategies.

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.

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.

Raccoon poxvirus as a mucosal vaccine vector for domestic cats

In the present study, we evaluated both the immunogenicity and safety of recombinant raccoon poxvirus (RCN) as a mucosal vaccine vector for domestic cats. RCN is an orthopoxvirus that was isolated from healthy raccoons and has been used experimentally as a vaccine vector for rabies and other antigens in a variety of species, including raccoons, skunks, foxes, bobcats, rabbits, domestic cats, piglets, sheep and non-human primates. We evaluated the antibody response induced by a recombinant RCN vaccine expressing the rabies-G glycoprotein (RCN/rabies-G) administered to cats by the oral (PO), intranasal (IN), conjunctival (CO) or intranasal/conjunctival (IN/CO) route (dose: 10 plaque forming units or PFU). The IN route, either alone or combined with the CO route, induced the highest rabies virus neutralizing antibody (RVNA) titers. The RVNA titers remained high when measured at six months post-vaccination, demonstrating that the recombinant vaccine administered via these routes is very efficient at inducing long-lasting immunity. A dose-response was observed following IN vaccination in cats. Doses of 10 PFU induced strong antibody responses in 4 of 5 animals [geometric mean titer: 3.2 (log)]. None of the animals vaccinated with 10 PFU developed detectable RVNA titers. In this study, RCN/rabies-G viral shedding was below detectable levels. Nasal, oral and fecal swabs collected from these cats were negative for RCN by both virus isolation and by nested-PCR. In addition, no horizontal transmission of the virus could be detected. Gang-housed sentinel animals for each group did not develop detectable anti-RVNA or -RCN antibodies. To study tissue tropism of recombinant raccoon poxvirus vaccines, a RCN that can express the lacZ gene (RCN/lacZ) was constructed. Expression of beta-galactosidase (beta-gal) was validated in vitro and in mice in vivo. Cats were vaccinated IN with 10 PFU of RCN/lacZ. No histopathological lesions were detected in any of the tissues collected from these cats at 1, 4, 7 and 15 days post-vaccination. In addition, no virus or beta-gal expression was detected in any of these tissues. Controls demonstrated that virus could be reisolated from nasal swabs immediately after administration of 10 PFU to cats. These results suggest that recombinant RCN vaccines undergo limited replication after intranasal administration in cats that is sufficient to elicit strong, long-lasting systemic antibody responses.

Recombinant replication-restricted VSV as an expression vector for murine cytokines

Vesicular stomatitis virus (VSV) is a prototypic non-segmented, negative-strand RNA virus that rapidly and efficiently shuts down the production of host cell-encoded proteins and utilizes the cell's protein production machinery to express high levels of virally encoded proteins. In an effort to take advantage of this characteristic of VSV, we have employed a reverse genetics system to create recombinant forms of VSV encoding a variety of murine cytokines. Previous studies have revealed that cells infected with recombinant VSV that lack expression of the surface glycoprotein (G protein), designated deltaG-VSV, more efficiently express and secrete recombinant proteins than do recombinant "wild-type" VSV. Therefore, murine cytokine-expressing recombinants were produced as deltaG viruses. Propagation of these deltaG viruses in cells that transiently express G protein in vitro results in G-complemented virions that can infect cells, shut down host protein synthesis, and express at high levels each virally encoded protein (including the designated cytokine). We assessed the ability of each deltaG-VSV construct to express recombinant cytokine by infecting BHK cells and then monitoring/measuring the production of the desired cytokine. When possible, the bioactivity of the cytokine products was also measured. The results presented here reveal that large quantities of bioactive cytokines can be produced rapidly and inexpensively using deltaG-VSV as a protein expression system.

Enhanced intracellular availability and survival of hammerhead ribozymes increases target ablation in a cellular model of osteogenesis imperfecta

Antisense hammerhead ribozymes have the capability to cleave complementary RNA in a sequence-dependent manner. In osteogenesis imperfecta, a genetic disorder of connective tissue, mutant collagen type I has been shown to participate in but not sustain formation of the triple helix. Selective ablation of mutant collagen gene transcript could potentially remove the mutant gene product and reverse the dominant-negative effect exerted by the abnormal protein. In earlier studies we showed that the hammerhead ribozyme Col1A1Rz547 selectively cleaved a mutant Col1A1 gene transcript in a murine calvarial osteoblast cell line. In order to test the possible therapeutic efficacy of this approach, a dramatic downregulation of the mutant transcript must be achieved, a function directly related to high steady-state level of intracellular ribozyme. We report significantly enhanced expression of Col1A1Rz547 by vaccinia T7 polymerase following infection with an attenuated T7-pol vaccinia virus as shown both by the intracellular level of the ribozyme and the cleavage of the mutant Col1A1 gene transcript. We also describe the engineering of a multimeric ribozyme construct comprising eight subunits, which can self-cleave to monomers. These studies suggest the potential use of multimeric ribozymes expressed by a vaccinia-based system in the therapy of a variety of disorders.

Viral vectors for dendritic cell-based immunotherapy

Dendritic cells (DCs) constitute a specialised system of antigen-presenting cells with a high capacity to induce and to modulate the immune response against microbial, tumour and self-antigens. New techniques to generate large amounts of DCs together with the molecular identification of human tumour-associated antigens (TAA) have opened new ways for antigen-specific cancer immunotherapies. DCs loaded either with TAA-derived MHC class I-specific synthetic peptides or with whole tumour cell preparations have been used in numerous clinical trials evaluating the efficacy of DCs in patients with cancer. However, the disadvantages of DCs pulsed with synthetic peptides from TAA include the uncertainty regarding the longevity of antigen presentation, the restriction by the patient's haplotype and the relatively low number of known MHC class I and in particular of MHC class II helper cell-related epitopes. Whole tumour cell preparations are difficult to standardise, and they depend on the availability of tumour cells. Thus the utilisation of viral vectors genetically modified to express TAA for the ex vivo transduction of DCs is an attractive alternative to achieve a MHC I- and MHC II-restricted presentation of tumoural antigens. To induce protective anti-tumoural immune response an increasing number of modified viral vectors have been used to transduce DCs. Although high transduction efficacies were reported for several viruses, analysis of the interaction of viral vectors with DCs has revealed several viral mechanisms that interfere with main functions of DCs, dampening somewhat the initial optimism in the field of DC transduction. However, promising results with different vectors have been achieved. In this review we summarise available data and discuss advantages and drawbacks of currently available vectors.

Gene therapy: theoretical and bioethical concepts

Gene therapy holds great promise. Somatic gene therapy has the potential to treat a wide range of disorders, including inherited conditions, cancers, and infectious diseases. Early progress has already been made in the treatment of a range of disorders. Ethical issues surrounding somatic gene therapy are primarily those concerned with safety. Germline gene therapy is theoretically possible but raises serious ethical concerns concerning future generations.

Quantitation of CD8+ T cell responses to newly identified HLA-A*0201-restricted T cell epitopes conserved among vaccinia and variola (smallpox) viruses

Immunization with vaccinia virus resulted in long-lasting protection against smallpox and was the approach used to eliminate natural smallpox infections worldwide. Due to the concern about the potential use of smallpox virus as a bioweapon, smallpox vaccination is currently being reintroduced. Severe complications from vaccination were associated with congenital or acquired T cell deficiencies, but not with congenital agammaglobulinemia, suggesting the importance of T cell immunity in recovery from infection. In this report, we identified two CD8+ T cell epitopes restricted by the most common human major histocompatibility complex (MHC) class I allele, HLA-A*0201. Both epitopes are highly conserved in vaccinia and variola viruses. The frequency of vaccinia-specific CD8+ T cell responses to these epitopes measured by interferon (IFN)-gamma enzyme-linked immunospot (ELISPOT) assay and HLA/peptide tetramer staining peaked 2 wk after primary immunization and then declined, but were still detectable 1 to 3 yr after primary immunization. 2 wk after immunization, IFN-gamma-producing cells specific to these two epitopes were 14% of total vaccinia virus-specific IFN-gamma-producing cells in one donor, 35% in the second donor, and 6% in the third donor. This information will be useful for studies of human T cell memory and for the design and analyses of the immunogenicity of experimental vaccinia vaccines.

Construction of a novel set of transfer vectors to study vaccinia virus replication and foreign gene expression

Vaccinia virus (VV) is a useful expression vector for many laboratory applications. To date, approximately 60% ( approximately 120) of the VV genes remain uncharacterized. The thought of smallpox being used as a biological weapon has gained attention. In light of this, it is imperative that we continue to study the basic replication of VV, a poxvirus that is closely related to smallpox. A set of plasmid vectors were constructed to generate gene deletions (pZIPPY-NEO/GUS) in VV or for foreign gene expression (pBR-EXPRESS). The vectors contain the Escherichia coli neomycin resistance (neo) and beta-glucuronidase (gusA) genes as selectable markers to facilitate isolation of recombinant viruses. These are the first transfer vectors to use a neo/gusA selection system. We used these vectors to successfully generate a recombinant D9R deletion mutant of VV and to express E. coli lacZ gene. Results indicate that both vectors are highly suited for their designed purpose.

Molecular anatomy of Chilo iridescent virus genome and the evolution of viral genes

Chilo iridescent virus (CIV) or Insect iridescent virus 6 (IIV-6) is the type species of the genus iridovirus, a member of the Iridoviridae family. CIV is highly pathogenic for a variety of insect larvae and this implicates a possible use as a biological insecticide. CIV progeny and assembly occur in the cytoplasm of the infected cell and accumulate in the fatbody of the infected insects. Since the discovery of CIV in 1966, many attempts were made to elucidate the viral genome structure and the amino acid sequences of different viral gene products. The elucidation of the coding capacity and strategy of CIV was the first step towards understanding the underlying mechanisms of viral infection, replication and virus-host interaction. The virions contain a single linear ds DNA molecule that is circularly permuted and terminally redundant. The coding capacity of the CIV genome was determined by the analysis of the complete DNA nucleotide sequence consisting of 212,482 bp that represent 468 open reading frames encoding for polypeptides ranging from 40 to 2432 amino acid residues. The analysis of the coding capacity of the CIV genome revealed that 50% (234 ORFs) of all identified ORFs (468 ORFs) were non-overlapping. The identification of several putative viral gene products including a DNA ligase and a viral antibiotic peptide is a powerful tool for the investigation of the phylogenetic relatedness of this evolutionary and ecologically relevant eukaryotic virus.

Gene transfer in higher animals: theoretical considerations and key concepts

Gene transfer technology provides the ability to genetically manipulate the cells of higher animals. Gene transfer permits both germline and somatic alterations. Such genetic manipulation is the basis for animal transgenesis goals and gene therapy attempts. Improvements in gene transfer are required in terms of transgene design to permit gene targeting, and in terms of transfection approaches to allow improved transgene uptake efficiencies.

Large-scale preparation of biologically active measles virus haemagglutinin expressed by attenuated vaccinia virus vectors

A procedure described here allows the efficient and rapid purification of histidine-tagged measles virus haemagglutinin that is synthesized under the control of powerful promoters (PSFJ1-10 and PSFJ2-16) of the highly attenuated vaccinia virus (VV) strain LC16mO. A single affinity chromatography step purifies recombinant haemagglutinin proteins from the lysates of cells infected with the recombinant VVs. The recovery and purity are both very high (a yield of 0.5-2.8 mg/10(8) cells and purity of >94-98%), indicating that this procedure is approximately 400 times more efficient than the conventional methods used to prepare haemagglutinin. The haemagglutinins are correctly transported to the cell surface and have haemadsorption activity. Moreover, the recombinant haemagglutinin proteins cooperate with the measles virus fusion protein to elicit cell fusion activity. In addition, the antibody titres against measles virus, as measured by enzyme-linked immunosorbent assay using the purified haemagglutinin as the capture antigen, correlated closely with neutralization test titres (R(2) = 0.84, p < 0.05), indicating the preservation of immunologically relevant antigenicity. Such recombinant haemagglutinin preparations will be useful in diagnostic tests that measure functional anti-measles immunity and investigate the biological functions and structure of the haemagglutinin.

Recombinant vaccinia virus-induced T-cell immunity: quantitation of the response to the virus vector and the foreign epitope

Recombinant vaccinia viruses (rVV) have been extensively used as vaccines, but there is little information about the total magnitude of the VV-specific T-cell response and how this compares to the immune response to the foreign gene(s) expressed by the rVV. To address this issue, we quantitated the T-cell responses to both the viral vector and the insert following the infection of mice with VV expressing a cytotoxic T lymphocyte (CTL) epitope (NP118-126) from lymphocytic choriomeningitis virus (LCMV). The LCMV epitope-specific response was quantitated by intracellular cytokine staining after stimulation with the specific peptide. To analyze the total VV-specific response, we developed a simple intracellular cytokine staining assay using VV-infected major histocompatibility complex class I and II matched cells as stimulators. Using this approach, we made the following determinations. (i) VV-NP118 induced potent and long-lasting CD8 and CD4 T-cell responses to the vector; at the peak of the response (approximately 1 week), there were approximately 10(7) VV-specific CD8 T cells (25% of the CD8 T cells) and approximately 10(6) VV-specific CD4 T cells (approximately 5% of the CD4 T cells) in the spleen. These numbers decreased to approximately 5 x 10(5) CD8 T cells (approximately 5% frequency) and approximately 10(5) CD4 T cells (approximately 0.5% frequency), respectively, by day 30 and were then stably maintained at these levels for >300 days. The size of this VV-specific T-cell response was comparable to that of the T-cell response induced following an acute LCMV infection. (ii) VV-specific CD8 and CD4 T cells were capable of producing gamma interferon (IFN-gamma), tumor necrosis factor alpha (TNF-alpha), and interleukin-2; all cells were able to make IFN-gamma, a subset produced both IFN-gamma and TNF-alpha, and another subset produced all three cytokines. (iii) The CD8 T-cell response to the foreign gene (LCMV NP118-126 epitope) was coordinately regulated with the response to the vector during all three phases (expansion, contraction, and memory) of the T-cell response. The total number of CD8 T cells responding to NP118-126 were approximately 20- to 30-fold lower than the number responding to the VV vector (approximately 1% at the peak and 0.2% in memory). This study provides a better understanding of T-cell immunity induced by VV-based vaccines, and in addition, the technique described in the study can be readily extended to other viral vectors to determine the ratio of the T-cell response to the insert versus the vector. This information will be useful in optimizing prime-boost regimens for vaccination.