Biological and immunogenic properties of a canarypox-rabies recombinant, ALVAC-RG (vCP65) in non-avian species

A virus-like particle candidate vaccine based on CRISPR/Cas9 gene editing technology elicits broad-spectrum protection against SARS-CoV-2

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants with frequent mutations has seriously damaged the effectiveness of the 2019 coronavirus disease (COVID-19) vaccine. There is an urgent need to develop a broad-spectrum vaccine while elucidating the underlying immune mechanisms. Here, we developed a SARS-CoV-2 virus-like particles (VLPs) vaccine based on the Canarypox-virus vector (ALVAC-VLPs) using CRISPR/Cas9. Immunization with ALVAC-VLPs showed the effectively induce SARS-CoV-2 specific T and B cell responses to resist the lethal challenge of mouse adaptive strains. Notably, ALVAC-VLPs conferred protection in golden hamsters against SARS-CoV-2 Wuhan-Hu-1 (wild-type, WT) and variants (Beta, Delta, Omicron BA.1, and BA.2), as evidenced by the prevention of weight loss, reduction in lung and turbinate tissue damage, and decreased viral load. Further investigation into the mechanism of immune response induced by ALVAC-VLPs revealed that toll-like receptor 4 (TLR4) mediates the recruitment of dendritic cells (DCs) to secondary lymphoid organs, thereby initiating follicle assisted T (Tfh) cell differentiation, the proliferation of germinal center (GC) B cells and plasma cell production. These findings demonstrate the immunogenicity and efficacy of the safe ALVAC-VLPs vaccine against SARS-CoV-2 and provide valuable insight into the development of COVID-19 vaccine strategies.

Alterations of oral and gut viromes in hypertension and/or periodontitis

The microbiota plays an important role in both hypertension (HTN) and periodontitis (PD), and PD exacerbates the development of HTN by oral and gut microbiota. Previous studies have focused on exploring the importance of the bacteriome in HTN and PD but overlooked the impact of the virome, which is also a member of the microbiota. We collected 180 samples of subgingival plaques, saliva, and feces from a cohort of healthy subjects (nHTNnPD), subjects with HTN (HTNnPD) or PD (PDnHTN), and subjects with both HTN and PD (HTNPD). We performed metagenomic sequencing to assess the roles of the oral and gut viromes in HTN and PD. The HTNnPD, PDnHTN, and HTNPD groups all showed significantly distinct beta diversity from the nHTNnPD group in saliva. We analyzed alterations in oral and gut viral composition in HTN and/or PD and identified significantly changed viruses in each group. Many viruses across three sites were significantly associated with blood pressure and other clinical parameters. Combined with these clinical associations, we found that Gillianvirus in subgingival plaques was negatively associated with HTN and that Torbevirus in saliva was positively associated with HTN. We found that Pepyhexavirus from subgingival plaques was indicated to be transferred to the gut. We finally evaluated viral-bacterial transkingdom interactions and found that viruses and bacteria may cooperate to affect HTN and PD. Correspondingly, HTN and PD may synergize to improve communications between viruses and bacteria.IMPORTANCEPeriodontitis (PD) and hypertension (HTN) are both highly prevalent worldwide and cause serious adverse outcomes. Increasing studies have shown that PD exacerbates HTN by oral and gut microbiota. Previous studies have focused on exploring the importance of the bacteriome in HTN and PD but overlooked the impact of the virome, even though viruses are common inhabitants in humans. Alterations in oral and gut viral diversity and composition contribute to diseases. The present study, for the first time, profiled the oral and gut viromes in HTN and/or PD. We identified key indicator viruses and their clinical implications in HTN and/or PD. We also investigated interactions between viruses and bacteria. This work improved the overall understanding of the viromes in HTN and PD, providing vital insights into the role of the virome in the development of HTN and PD.

Why do poxviruses still matter?

Poxviruses comprise many members that infect both vertebrate and invertebrate animals, including humans. Despite the eradication of the historically notorious smallpox, poxviruses remain significant public health concerns and serious endemic diseases. This short review briefly summarizes the present, historical, and future threats posed by poxviruses to public health, wildlife and domestic animals, the role poxviruses have played in shaping modern medicine and biomedical sciences, the insight poxviruses have provided into complex life processes, and the utility of poxviruses in biotechniques and in fighting other infectious diseases and cancers. It is anticipated that readers will appreciate the great merit and need for continued strong support of poxvirus research; research which benefits not only the expansion of fundamental biological knowledge but also the battle against diverse diseases.

Novel Vaccine Technologies in Veterinary Medicine: A Herald to Human Medicine Vaccines

The success of inactivated and live-attenuated vaccines has enhanced livestock productivity, promoted food security, and attenuated the morbidity and mortality of several human, animal, and zoonotic diseases. However, these traditional vaccine technologies are not without fault. The efficacy of inactivated vaccines can be suboptimal with particular pathogens and safety concerns arise with live-attenuated vaccines. Additionally, the rate of emerging infectious diseases continues to increase and with that the need to quickly deploy new vaccines. Unfortunately, first generation vaccines are not conducive to such urgencies. Within the last three decades, veterinary medicine has spearheaded the advancement in novel vaccine development to circumvent several of the flaws associated with classical vaccines. These third generation vaccines, including DNA, RNA and recombinant viral-vector vaccines, induce both humoral and cellular immune response, are economically manufactured, safe to use, and can be utilized to differentiate infected from vaccinated animals. The present article offers a review of commercially available novel vaccine technologies currently utilized in companion animal, food animal, and wildlife disease control.

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.

Longevity of adenovirus vector immunity in mice and its implications for vaccine efficacy

There is a high incidence of adenovirus (AdV) infection in humans due to the presence of more than 60 types of human adenoviruses (HAdVs). The majority of individuals are exposed to one or more HAdV types early in their lives, leading to the development of AdV type-specific neutralizing antibodies. Similarly, immunization or gene therapy with AdV vectors leads to immune responses to the AdV vector. This 'vector immunity' is a concern for AdV vector-based applications for vaccines or gene therapy, especially when the repeated administration of a vector is required. The objective of this investigation was to establish whether AdV neutralizing antibody titers decline sufficiently in a year to permit annual vaccination with the same AdV vector. Naïve or human adenoviral vector group C, type 5 (HAdV-C5)-primed mice were mock-inoculated (with PBS) or inoculated i.m. with 10⁸ PFU of either HAd-GFP [HAdV-C5 vector expressing the green fluorescent protein (GFP)] to mimic the conditions for the first inoculation with an AdV vector-based vaccine. At 1, 3, 6, and 10 months post-HAd-GFP inoculation, naïve- or HAdV-primed animals were vaccinated i.m. with 10⁸ PFU of HAd-H5HA [HAdV-C5 vector expressing hemagglutinin (HA) of H5N1 influenza virus]. There was a significant continual decrease in vector immunity titers with time, thereby leading to significant continual increases in the levels of HA-specific humoral and cell-mediated immune responses. In addition, significant improvement in protection efficacy against challenge with an antigenically heterologous H5N1 virus was observed in HAdV-primed animals at 6 months and onwards. These results indicate that the annual immunization with the same AdV vector may be effective due to a significant decline in vector immunity.

Development of Recombinant Canarypox Viruses Expressing Immunogens

Canarypox viruses (CNPV) are excellent candidates to develop recombinant vector vaccines due to both their capability to induce protective immune responses and their incompetence to replicate in mammalian cells (safety profile). In addition, CNPV and the derived recombinants can be manipulated under biosafety level 1 conditions. There is no commercially available system to obtain recombinant CNPV; however, the methodology and tools required to develop recombinant vaccinia virus (VV), prototype of the Poxviridae family, can be easily adapted. This chapter provides protocols for the generation, plaque isolation, molecular characterization, amplification and purification of recombinant CNPV.

Protection from Hendra virus infection with Canarypox recombinant vaccine

Hendra virus (HeV) is an emerging zoonotic pathogen, which causes severe respiratory illness and encephalitis in humans and horses. Since its first appearance in 1994, spillovers of HeV from its natural reservoir fruit bats occur on almost an annual basis. The high mortality rate in both humans and horses and the wide-ranging reservoir distribution are making HeV a serious public health problem, especially for people exposed to sick horses. This study has aimed to develop an efficient low-cost HeV vaccine for horses based on Canarypox recombinant vector expressing HeV glycoproteins, attachment glycoprotein (G) and fusion protein (F). This vaccine was used to immunise hamsters and then challenged intraperitoneally with HeV 3 weeks later. The higher tested dose of the vaccine efficiently prevented oropharyngeal virus shedding and protected animals from clinical disease and virus-induced mortality. Vaccine induced generation of seroneutralising antibodies and prevented virus-induced histopathological changes and a production of viral RNA and antigens in animal tissues. Interestingly, some vaccinated animals, including those immunised at a lower dose, were protected in the absence of detectable specific antibodies, suggesting the induction of an efficient virus-specific cellular immunity. Finally, ponies immunised using the same vaccination protocol as hamsters developed strong seroneutralising titres against both HeV and closely related Nipah virus, indicating that this vaccine may have the ability to induce cross-protection against Henipavirus infection. These data suggest that Canarypox-based vectors encoding for HeV glycoproteins present very promising new vaccine candidate to prevent infection and shedding of the highly lethal HeV.

Six host-range restricted poxviruses from three genera induce distinct gene expression profiles in an in vivo mouse model

BACKGROUND

Host-range restricted poxviruses make promising vaccine vectors due to their safety profile and immunogenicity. An understanding of the host innate immune responses produced by different poxvirus vectors would aid in the assessment, selection and rational design of improved vaccines for human and veterinary applications. Novel avipoxviruses are being assessed to determine if they are different from other poxvirus vectors. Analysis of the transcriptome induced in a mouse model would aid in determining if there were significant differences between different poxvirus vectors which may reflect different adjuvant potential as well as establish if they should be further evaluated as vaccine vectors.

RESULTS

We compared host transcript abundance in the spleens of BALB/c mice twenty four hours after intravenous infection (10(5) pfu/mouse) with six host-restricted poxvirus species from three genera, namely Lumpy Skin Disease virus (LSDV), Canarypox virus (CNPV), Fowlpox virus (FWPV), modified vaccinia Ankara (MVA) and two novel South African avipoxviruses, Feral Pigeonpox virus (FeP2) and Penguinpox virus (PEPV). These six viruses produced qualitatively and quantitatively distinct host responses with LSDV, followed by MVA, inducing the greatest interferon (IFN) response. FeP2 and PEPV caused very little change to host transcript abundance compared to the other 4 viruses tested. CNPV and FWPV induced the up regulation of two immunoglobulin genes (Ighg and Ighg3 (IgG3)) with CNPV inducing a third, Ighm (IgM). HIV-1-specific IgG3 antibodies have been correlated with decreased risk of HIV-1 infection in the RV144 trial, which included a CNPV-based vector (Yates et al. (Sci Transl Med, 6(228) p228, 2014). Up regulation of IgG3 by CNPV and FWPV but not the other poxviruses tested in vivo, implies that these two avipoxvirus-vector backbones may be involved in stimulation of the clinically important IgG3 antibody subclass. Differential transcript abundance associated with the different poxviruses is further discussed with particular emphasis on responses related to immune responses.

CONCLUSION

Six, genetically diverse host-restricted poxviruses produce different responses in a mouse model early after infection. These differences may affect the immune response induced to vaccine antigen in vectors based on these viruses. The two novel avipoxviruses were clearly distinguishable from the other viruses.

The evolution of poxvirus vaccines

After Edward Jenner established human vaccination over 200 years ago, attenuated poxviruses became key players to contain the deadliest virus of its own family: Variola virus (VARV), the causative agent of smallpox. Cowpox virus (CPXV) and horsepox virus (HSPV) were extensively used to this end, passaged in cattle and humans until the appearance of vaccinia virus (VACV), which was used in the final campaigns aimed to eradicate the disease, an endeavor that was accomplished by the World Health Organization (WHO) in 1980. Ever since, naturally evolved strains used for vaccination were introduced into research laboratories where VACV and other poxviruses with improved safety profiles were generated. Recombinant DNA technology along with the DNA genome features of this virus family allowed the generation of vaccines against heterologous diseases, and the specific insertion and deletion of poxvirus genes generated an even broader spectrum of modified viruses with new properties that increase their immunogenicity and safety profile as vaccine vectors. In this review, we highlight the evolution of poxvirus vaccines, from first generation to the current status, pointing out how different vaccines have emerged and approaches that are being followed up in the development of more rational vaccines against a wide range of diseases.

Oral immunization of mice with recombinant rabies vaccine strain (ERAG3G) induces complete protection

PURPOSE

New rabies vaccine bait for both pets and raccoon dogs residing in Korea is needed to eradicate rabies infection among animals. In this study, we constructed a recombinant rabies virus (RABV), the ERAG3G strain, using a reverse genetics system. Then we investigated the efficacy of this strain in mice after oral administration and the safety of this strain in cats after intramuscular administration.

MATERIALS AND METHODS

The ERAG3G strain was rescued in BHK/T7-9 cells using the full-length genome mutated at the amino acid position 333 of the glycoprotein gene of RABV and helper plasmids. Four-week-old mice underwent one or two oral administrations of the ERAG3G strain and were challenged with the highly virulent RABV strain CVSN2c 14 days after the second administration. Clinical symptoms were observed and body weights were measured every day after the challenge.

RESULTS

All mice showed complete protection against virulent RABV. In addition, cats intramuscularly inoculated with the ERAG3G strain showed high antibody titers ranging from 2.62 to 23.9 IU/mL at 28-day postinoculation.

CONCLUSION

The oral immunization of the ERAG3G strain plays an important role in conferring complete protection in mice, and intramuscular inoculation of the ERAG3G strain induces the formation of anti-rabies neutralizing antibody in cats.

Comparison of antibody response to a non-adjuvanted, live canarypox-vectored recombinant rabies vaccine and a killed, adjuvanted rabies vaccine in Eld's deer (Rucervus eldi thamin)

Captive Eld's deer (Rucervus eldi thamin) were evaluated for the presence of rabies virus-neutralizing antibodies using a rapid fluorescent focus inhibition after vaccination with either a live canarypox-vectored recombinant rabies vaccine or a killed monovalent rabies vaccine. Twelve deer were vaccinated with 1.0 ml of killed, adjuvanted, monovalent rabies vaccine at 5-33 mo of age then annually thereafter, and 14 deer were vaccinated with 1.0 ml nonadjuvanted, live canarypox-vectored rabies vaccine at 3-15 mo of age then annually thereafter. Banked serum was available or collected prospectively from deer at 6 mo and 1 yr after initial vaccination, then collected annually. Rabies virus-neutralizing antibodies considered adequate (>0.5 IU/ml) were present in 20/34 samples vaccinated with canarypox-vectored rabies vaccine and in 12/14 samples vaccinated with killed adjuvanted rabies vaccine. Poor seroconversion was noted in deer less than 6 mo of age vaccinated with the canarypox-vectored rabies vaccine.

A single immunization with recombinant rabies virus (ERAG3G) confers complete protection against rabies in mice

Purpose

New alternative bait rabies vaccines applicable to pet dogs and wild animals are needed to eradicate rabies in Korea. In this study, recombinant rabies virus, ERAG3G strain was constructed using reverse genetic system and the safety, efficacy and immunogenicity of the ERAG3G strain was evaluated in mice and dogs.

Materials and Methods

Using the full-length genome mutated amino acid at position 333 of glycoprotein of rabies virus (RABV) and helper plasmids, the ERAG3G strain was rescued in BHK/T7-9 cells successfully. Mice were inoculated with the ERAG3G strain for safety and efficacy. Safety and immunogenicity of the dog inoculated with the ERAG3G strain (1 mL, 10^8.0 FAID₅₀/mL) via intramuscular route was evaluated for 28 days after inoculation.

Results

The ERAG3G strain rescued by reverse genetic system was propagated well in the mouse neuroblastoma cells revealing titer of 10^8.5 FAID₅₀/mL and was not pathogenic to 4- or 6-week-old mice that received by intramuscular or intracranical route. Immunization with the ERAG3G strain conferred complete protection from lethal RABV in mice. Dogs inoculated with the vaccine candidate via intramuscular route showed high neutralizing antibody titer ranging from 2.62 to 23.9 IU/mL at 28 days postinoculation.

Conclusion

Our findings suggest that the ERAG3G strain plays an important role in inducing protective efficacy in mice and causes to arise anti-rabies neutralizing antibody in dogs.

Immunity to bovine herpesvirus 1: II. Adaptive immunity and vaccinology

Bovine herpesvirus 1 (BHV-1) infection is widespread and causes a variety of diseases. Although similar in many respects to the human immune response to human herpesvirus 1, the differences in the bovine virus proteins, immune system components and strategies, physiology, and lifestyle mean the bovine immune response to BHV-1 is unique. The innate immune system initially responds to infection, and primes a balanced adaptive immune response. Cell-mediated immunity, including cytotoxic T lymphocyte killing of infected cells, is critical to recovery from infection. Humoral immunity, including neutralizing antibody and antibody-dependent cell-mediated cytotoxicity, is important to prevention or control of (re-)infection. BHV-1 immune evasion strategies include suppression of major histocompatibility complex presentation of viral antigen, helper T-cell killing, and latency. Immune suppression caused by the virus potentiates secondary infections and contributes to the costly bovine respiratory disease complex. Vaccination against BHV-1 is widely practiced. The many vaccines reported include replicating and non-replicating, conventional and genetically engineered, as well as marker and non-marker preparations. Current development focuses on delivery of major BHV-1 glycoproteins to elicit a balanced, protective immune response, while excluding serologic markers and virulence or other undesirable factors. In North America, vaccines are used to prevent or reduce clinical signs, whereas in some European Union countries marker vaccines have been employed in the eradication of BHV-1 disease.

Human exposure to rabid free-ranging cats: a continuing public health concern in Pennsylvania

Rabid free-ranging cats have been a public health concern in Pennsylvania since raccoon variant rabies first was recognized in the state in the early 1980s. Over the last decade, between 1.5 and 2.5% of cats submitted to Pennsylvania's state laboratories for rabies testing have been positive. In this report, we describe the extent of rabies in free-ranging cats in Pennsylvania. We also present two examples of human exposure to rabid free-ranging cats that occurred in Pennsylvania during 2010-2011 and the public health actions taken to address rabies exposure in the humans and animals. We then describe the concerns surrounding the unvaccinated and free-ranging cat population in Pennsylvania and possible options in managing this public and animal health problem.

Nonhuman primate models for HIV/AIDS vaccine development

The development of HIV vaccines has been hampered by the lack of an animal model that can accurately predict vaccine efficacy. Chimpanzees can be infected with HIV-1 but are not practical for research. However, several species of macaques are susceptible to the simian immunodeficiency viruses (SIVs) that cause disease in macaques, which also closely mimic HIV in humans. Thus, macaque-SIV models of HIV infection have become a critical foundation for AIDS vaccine development. Here we examine the multiple variables and considerations that must be taken into account in order to use this nonhuman primate (NHP) model effectively. These include the species and subspecies of macaques, virus strain, dose and route of administration, and macaque genetics, including the major histocompatibility complex molecules that affect immune responses, and other virus restriction factors. We illustrate how these NHP models can be used to carry out studies of immune responses in mucosal and other tissues that could not easily be performed on human volunteers. Furthermore, macaques are an ideal model system to optimize adjuvants, test vaccine platforms, and identify correlates of protection that can advance the HIV vaccine field. We also illustrate techniques used to identify different macaque lymphocyte populations and review some poxvirus vaccine candidates that are in various stages of clinical trials. Understanding how to effectively use this valuable model will greatly increase the likelihood of finding a successful vaccine for HIV.

Three-year duration of immunity in cats vaccinated with a canarypox-vectored recombinant rabies virus vaccine

Despite the availability of efficacious vaccines for animals and humans, rabies is still a major zoonosis. Prevention of rabies in dogs and cats is key for reducing the risk of transmission of this deadly disease to humans. Most veterinary vaccines are adjuvanted inactivated vaccines and have been shown to provide one to four-year duration of immunity. In response to debates about the safety of adjuvanted vaccines in cats, a non-adjuvanted feline rabies vaccine with one-year duration of immunity claim was specifically developed using the canarypoxvirus vector technology. The objective of this study was to validate a vaccination program based on primary vaccination, revaccination one year later and boosters every three years. Seronegative cats were vaccinated at 12 weeks of age and received a booster vaccination one year later. This vaccination regimen induced a strong and sustained antibody response, and all vaccinated animals were protected against virulent rabies challenge carried out 3 years after vaccination. These results validated 3-year duration of immunity after a complete basic vaccination program consisting in primary vaccination from 12 weeks of age followed by revaccination one year later with a non-adjuvanted canarypox-vectored vaccine.

ALVAC-HIV as a prophylactic and therapeutic vaccine: highlights from over a decade of clinical trials

ALVAC-HIV vaccines (vCP125, vCP205, vCP300, vCP1433, vCP1452 and vCP1521) are preparations of a modified recombinant canarypox virus designed to induce or augment CD8+ immune responses. As the focus of several Phase I–III trials, they have been the most extensively studied live vector-based HIV vaccines. Overall, ALVAC-HIV induces modest CD8+ T-cell responses in approximately 20–50% of recipients. The addition of IL-2, recombinant glycoprotein 120 or 160, Remune or LIPO-6T to ALVAC-HIV does not appear to enhance overall CD8+ T-cell immune responses. The ability of ALVAC-HIV to induce interclade immunity and immunogenicity in newborns with perinatal exposure to HIV has important implications for the control of HIV worldwide. Experience from clinical trials in over 10,000 HIV-infected and noninfected individuals has shown that ALVAC constructs are safe, with reactogenicity profiles similar to those reported for currently licensed vaccines. Despite seemingly modest immunogenicity at the present time, studies to date have set the stage for further exploration of the potential of ALVAC-HIV vaccines. This report highlights findings from clinical trials using ALVAC-HIV, alone and in combination with other agents, as both a prophylactic and a therapeutic vaccine.

Avipoxviruses: infection biology and their use as vaccine vectors

Avipoxviruses (APVs) belong to the Chordopoxvirinae subfamily of the Poxviridae family. APVs are distributed worldwide and cause disease in domestic, pet and wild birds of many species. APVs are transmitted by aerosols and biting insects, particularly mosquitoes and arthropods and are usually named after the bird species from which they were originally isolated. The virus species Fowlpox virus (FWPV) causes disease in poultry and associated mortality is usually low, but in flocks under stress (other diseases, high production) mortality can reach up to 50%. APVs are also major players in viral vaccine vector development for diseases in human and veterinary medicine. Abortive infection in mammalian cells (no production of progeny viruses) and their ability to accommodate multiple gene inserts are some of the characteristics that make APVs promising vaccine vectors. Although abortive infection in mammalian cells conceivably represents a major vaccine bio-safety advantage, molecular mechanisms restricting APVs to certain hosts are not yet fully understood. This review summarizes the current knowledge relating to APVs, including classification, morphogenesis, host-virus interactions, diagnostics and disease, and also highlights the use of APVs as recombinant vaccine vectors.

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.

Phylogenetic analysis of three genes of Penguinpox virus corresponding to Vaccinia virus G8R (VLTF-1), A3L (P4b) and H3L reveals that it is most closely related to Turkeypox virus, Ostrichpox virus and Pigeonpox virus

Phylogenetic analysis of three genes of Penguinpox virus, a novel Avipoxvirus isolated from African penguins, reveals its relationship to other poxviruses. The genes corresponding to Vaccinia virus G8R (VLTF-1), A3L (P4b) and H3L were sequenced and phylogenetic trees (Neighbour-Joining and UPGMA) constructed from MUSCLE nucleotide and amino acid alignments of the equivalent sequences from several different poxviruses. Based on this analysis, PEPV was confirmed to belong to the genus Avipoxvirus, specifically, clade A, subclade A2 and to be most closely related to Turkeypox virus (TKPV), Ostrichpox virus (OSPV)and Pigeonpox virus (PGPV).

Antigen delivery systems for veterinary vaccine development. Viral-vector based delivery systems

The recent advances in molecular genetics, pathogenesis and immunology have provided an optimal framework for developing novel approaches in the rational design of vaccines effective against viral epizootic diseases. This paper reviews most of the viral-vector based antigen delivery systems (ADSs) recently developed for vaccine testing in veterinary species, including attenuated virus and DNA and RNA viral vectors. Besides their usefulness in vaccinology, these ADSs constitute invaluable tools to researchers for understanding the nature of protective responses in different species, opening the possibility of modulating or potentiating relevant immune mechanisms involved in protection.

Role of cell signaling in poxvirus-mediated foreign gene expression in mammalian cells

Poxviruses have been extensively used as a promising vehicle to efficiently deliver a variety of antigens in mammalian hosts to induce immune responses against infectious diseases and cancer. Using recombinant vaccinia virus (VV) and canarypox virus (ALVAC) expressing enhanced green fluorescent protein (EGFP) or multiple HIV-1 gene products, we studied the role of four cellular signaling pathways, the phosphoinositide-3-OH kinase (PI3K), extracellular signal-regulated kinase (ERK), p38 mitogen-activated protein kinase (p38 MAPK), and c-Jun N-terminal kinase (JNK), in poxvirus-mediated foreign gene expression in mammalian cells. In nonpermissive infection (human monocytes), activation of PI3K, ERK, p38 MAPK, and JNK was observed in both VV and ALVAC and blocking PI3K, p38 MAKP, and JNK pathways with their specific inhibitors significantly reduced viral and vaccine antigen gene expression. Whereas, blocking the ERK pathway had no significant effect. Among these cellular signaling pathways studied, PI3K was the most critical pathway involved in gene expression by VV- or ALVAC-infected monocytes. The important role of PI3K in poxvirus-mediated gene expression was further confirmed in mouse epidermal cells stably transfected with dominant-negative PI3K mutant, as poxvirus-mediated targeted gene expression was significantly decreased in these cells when compared with their parental cells. Signaling pathway activation influenced gene expression at the mRNA level rather than virus binding. In permissive mammalian cells, however, VV DNA copies were also significantly decreased in the absence of normal function of the PI3K pathway. Poxvirus-triggered activation of PI3K pathway could be completely abolished by atazanavir, a new generation of antiretroviral protease inhibitors (PIs). As a consequence, ALVAC-mediated EGFP or HIV-1 gag gene expression in infected primary human monocytes was significantly reduced in the presence of atazanavir. These findings implicate that antiretroviral therapy (ART), also known as highly active antiretroviral therapy (HAART), may negatively impact the efficacy of live poxvirus vector-based vaccines and should be carefully considered when administering such live vaccines to individuals on ART.

Gene profiling analysis of ALVAC infected human monocyte derived dendritic cells

The recombinant canarypox virus ALVAC is being extensively studied as vaccine vector for the development of new vaccine strategies against chronic infectious diseases and cancer. However, the mechanisms by which ALVAC initiates the immune response have not been completely elucidated. In order to determine the type of innate immunity triggered by ALVAC, we characterized the gene expression profile of human monocyte derived dendritic cells (MDDCs) upon ALVAC infection. These cells are permissive to poxvirus infection and play a key role in the initiation of immune responses. The majority of the genes that were up-regulated by ALVAC belong to the type I interferon signaling pathway including IRF7, STAT1, RIG-1, and MDA-5. Genes involved in the NF-κB pathway were not up-regulated. The gene encoding for the chemokine CXCL10, a direct target of the transcription factor IRF3 was among those up-regulated and DC secretion of CXCL10 following exposure to ALVAC was confirmed by ELISA. Many downstream type I interferon activated genes with anti-viral activity (PKR, Mx, ISG15 and OAS among others) were also up-regulated in response to ALVAC. Among these, ISG15 expression in its unconjugated form by Western blot analysis was demonstrated. In view of these results we propose that ALVAC induces type I interferon anti-viral innate immunity via a cytosolic pattern-recognition-receptor (PRR) sensing double-stranded DNA, through activation of IRF3 and IRF7. These findings may aid in the design of more effective ALVAC-vectored vaccines.

Current status of veterinary vaccines

The major goals of veterinary vaccines are to improve the health and welfare of companion animals, increase production of livestock in a cost-effective manner, and prevent animal-to-human transmission from both domestic animals and wildlife. These diverse aims have led to different approaches to the development of veterinary vaccines from crude but effective whole-pathogen preparations to molecularly defined subunit vaccines, genetically engineered organisms or chimeras, vectored antigen formulations, and naked DNA injections. The final successful outcome of vaccine research and development is the generation of a product that will be available in the marketplace or that will be used in the field to achieve desired outcomes. As detailed in this review, successful veterinary vaccines have been produced against viral, bacterial, protozoal, and multicellular pathogens, which in many ways have led the field in the application and adaptation of novel technologies. These veterinary vaccines have had, and continue to have, a major impact not only on animal health and production but also on human health through increasing safe food supplies and preventing animal-to-human transmission of infectious diseases. The continued interaction between animals and human researchers and health professionals will be of major importance for adapting new technologies, providing animal models of disease, and confronting new and emerging infectious diseases.

Development and registration of recombinant veterinary vaccines

The canarypox vaccine vector (ALVAC) technology has been used to develop and license several vaccines for companion animals and horses in the European Union and USA. ALVAC is a ubiquitous vector with high biosafety since it is non-replicative in mammalians, is genetically and physically stable, and able to induce both humoral and cell-mediated immune responses against the expressed transgene product. Specific rules apply for the development and registration of recombinant vector vaccines. The biology of the vector as well as the recombinant virus must be thoroughly documented to allow the risk assessment of its use in the target species. In particular, its safety for the host and the environment must be extensively demonstrated before field trials can be authorized.

Pathobiology of henipavirus entry: insights into therapeutic strategies

The recently emerged paramyxoviruses, Nipah (NiV) and Hendra (HeV), designated as Biosafety Level 4 pathogens, can cause lethal respiratory and neurological disease in both animals and humans. NiV outbreaks have been associated with efficient transmission amongst livestock (pigs) and mortality rates exceeding 70%, with documented cases of human-to-human transmission. Without vaccines or effective therapeutics, NiV and HeV continue to present an impending threat to global health and economies. The current understanding of henipavirus pathobiology has led to the development of small animal models reflecting certain aspects of the human pathology. In this review, we discuss how these animal models have been critical in testing vaccination strategies and in eliciting neutralizing antibodies against the envelope glycoproteins. Additionally, the discovery of the viral receptor and development of pseudotyped-viral systems have allowed us to explore the multiple opportunities for therapeutic intervention existing within the individual steps of the henipavirus entry pathway. Current research shows promise for the future development of effective strategies to limit the impact of these biological threats.

Direct comparison of antigen production and induction of apoptosis by canarypox virus- and modified vaccinia virus ankara-human immunodeficiency virus vaccine vectors

Recombinant poxvirus vectors are undergoing intensive evaluation as vaccine candidates for a variety of infectious pathogens. Avipoxviruses, such as canarypox virus, are replication deficient in mammalian cells by virtue of a poorly understood species-specific restriction. Highly attenuated vaccinia virus strains such as modified vaccinia virus Ankara (MVA) are similarly unable to complete replication in most mammalian cells but have an abortive-late phenotype, in that the block to replication occurs post-virus-specific DNA replication. In this study, an identical expression cassette for human immunodeficiency virus gag, pro, and env coding sequences was placed in canarypox virus and MVA vector backbones in order to directly compare vector-borne expression and to analyze differences in vector-host cell interactions. Antigen production by recombinant MVA was shown to be greater than that from recombinant canarypox virus in the mammalian cell lines and in the primary human cells tested. This observation was primarily due to a longer duration of antigen production in recombinant MVA-infected cells. Apoptosis induction was found to be more profound with the empty canarypox virus vector than with MVA. Remarkably, however, the inclusion of a gag/pro/env expression cassette altered the kinetics of apoptosis induction in recombinant MVA-infected cells to levels equal to those found in canarypox virus-infected cells. Antigen production by MVA was noted to be greater in human dendritic cells and resulted in enhanced T-cell stimulation in an in vitro antigen presentation assay. These results reveal differences in poxvirus vector-host cell interactions that should be relevant to their use as immunization vehicles.

Animal Vaccines

Rabies in terrestrial animals, primarily carnivores, is caused by the classic genotype 1 rabies virus. Even though the widespread vaccination of domestic dogs has been the one most effective factor in the reduction of human rabies, the number of human deaths worldwide is greater than that of the combined deaths from polio, meningococcal meningitis, Japanese encephalitis, yellow fever, severe acute respiratory syndrome and avian influenze (bird flu).Tools are available in highly efficacious and safe animal and human vaccines. Multiple factors can, however, prevent their use effectively in many areas of the world. For several decades, virtually all rabies nerve tissue origin (NTO) vaccines were inactivated with phenol using the method described by Semple. The NTO vaccines currently in use for mass vaccination campaigns in Africa, Latin America, and the Caribbean are primarily produced from rabies virus-infected suckling mouse brains or lamb brains. These vaccines are shown to be effective in campaigns. However, NTO-killed vaccines for dogs and other animals have often, in the past, resulted in post-vaccinal nervous system reactions that could result in the death of the vaccinated animals.

Genus Avipoxvirus

Poxviruses identified in skin lesions of domestic, pet or wild birds are assigned largely by default to the Avipoxvirus genus within the subfamily Chordopoxvirinae of the family Poxviridae. Avipoxviruses have been identified as the causative agent of disease in at least 232 species in 23 orders of birds. Vaccines based upon attenuated avipoxvirus strains provide good disease control in production poultry, although with the large and intensive production systems there are suggestions and real risks of emergence of strains against which current vaccines might be ineffective. Sequence analysis of the whole genome has revealed overall genome structure and function resemblance to the Chordopoxvirinae; however, avipoxvirus genomes exhibit large-scale genomic rearrangements with more extensive gene families and novel host range gene in comparison with the other Chordopoxvirinae. Phylogenetic analysis places the avipoxviruses externally to the Chorodopoxvirinae to such an extent that in the future it might be appropriate to consider the Avipoxviruses as a separate subfamily within the Poxviridae. A unique relationship exists between Fowlpox virus (FWPV) and reticuloendothelosis viruses. All FWPV strains carry a remnant long terminal repeat, while field strains carry a near full-length provirus integrated at the same location in the FWPV genome. With the development of techniques to construct poxviruses expressing foreign vaccine antigens, the avipoxviruses have gone from neglected obscurity to important vaccine vectors in the past 20 years. The seminal observation of their utility for delivery of vaccine antigens to non-avian species has driven much of the interest in this group of viruses. In the veterinary area, several recombinant avipoxviruses are commercially licensed vaccines. The most successful have been those expressing glycoprotein antigens of enveloped viruses, e.g. avian influenza, Newcastle diseases and West Nile viruses. Several recombinants have undergone extensive human clinical trials as experimental vaccines against HIV/AIDS and malaria or as treatment regimens in cancer patients. The safety profile of avipoxvirus recombinants for use as veterinary and human vaccines or therapeutics is now well established.

Recombinant nipah virus vaccines protect pigs against challenge

Nipah virus (NiV), of the family Paramyxoviridae, was isolated in 1999 in Malaysia from a human fatality in an outbreak of severe human encephalitis, when human infections were linked to transmission of the virus from pigs. Consequently, a swine vaccine able to abolish virus shedding is of veterinary and human health interest. Canarypox virus-based vaccine vectors carrying the gene for NiV glycoprotein (ALVAC-G) or the fusion protein (ALVAC-F) were used to intramuscularly immunize four pigs per group, either with 10(8) PFU each or in combination. Pigs were boosted 14 days postvaccination and challenged with 2.5 x 10(5) PFU of NiV two weeks later. The combined ALVAC-F/G vaccine induced the highest levels of neutralization antibodies (2,560); despite the low neutralizing antibody levels in the F vaccinees (160), all vaccinated animals appeared to be protected against challenge. Virus was not isolated from the tissues of any of the vaccinated pigs postchallenge, and a real-time reverse transcription (RT)-PCR assay detected only small amounts of viral RNA in several samples. In challenge control pigs, virus was isolated from a number of tissues (10(4.4) PFU/g) or detected by real-time RT-PCR. Vaccination of the ALVAC-F/G vaccinees appeared to stimulate both type 1 and type 2 cytokine responses. Histopathological findings indicated that there was no enhancement of lesions in the vaccinees. No virus shedding was detected in vaccinated animals, in contrast to challenge control pigs, from which virus was isolated from the throat and nose (10(2.9) PFU/ml). Based on the data presented, the combined ALVAC-F/G vaccine appears to be a very promising vaccine candidate for swine.

Comparative analysis of tropism between canarypox (ALVAC) and vaccinia viruses reveals a more restricted and preferential tropism of ALVAC for human cells of the monocytic lineage

The poxviruses including canarypox (ALVAC) and vaccinia viruses are promising vaccine vectors in humans, but little is known about their biology in human cells. Using recombinant enhanced green fluorescence protein (EGFP)-expressing ALVAC and vaccinia viruses, we have focused here on a side-by-side comparison of ALVAC and vaccinia virus tropism for cells from human peripheral blood and bone marrow. Both ALVAC and vaccinia viruses showed a strong bias towards monocyte infection. ALVAC minimally infected CD19+ B cells and was unable to infect ex vivo NK cells and T lymphocytes, whereas vaccinia virus could infect B lymphocytes and NK cell populations. Vaccinia virus was also able to infect T lymphocytes at low, but detectable levels that could be enhanced upon their activation. The observed preferential infection of ALVAC or vaccinia virus to monocytes was the result of preferential binding to this population, rather than lineage-specific differences in the expression of viral genes. Moreover, the level of CD14 expression on monocytes correlated with their preference to be infected with ALVAC or vaccinia virus. Both ALVAC and vaccinia viruses could infect immature monocyte derived dendritic cells (MDDCs), but only ALVAC infection induced their subsequent maturation. Vaccinia virus, however, showed greater tropism for mature MDDCs compared to ALVAC. Infection in human bone marrow cultures showed that ALVAC infection was restricted to a myelomonocytoid cell-specific CD33(+) cell population, while vaccinia virus showed a strong, but not exclusive, preference for these cells. These findings have implications in terms of choosing optimal pox virus derived vectors as vaccines in terms of reducing clinical reactogenicity and inducing dendritic cell (DC) maturation.

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.

Immune characterization of clinical grade-dendritic cells generated from cancer patients and genetically modified by an ALVAC vector carrying MAGE minigenes

Gene delivery into dendritic cells (DC) is most efficiently achieved by viral vectors. Recombinant canarypox viruses (ALVAC) were validated safe and efficient in humans. We aimed firstly to evaluate DC transduction by ALVAC vectors, then to investigate if such infection induced or not the maturation of the DC, and finally to assess the efficiency of ALVAC-MAGE-transduced DC to activate specific CTL clones. Clinical grade DC from melanoma patients were generated from blood monocytes and infected with a recombinant ALVAC virus encoding either a marker gene (EGFP) or the MAGE-1-MAGE-3 minigenes. According to the patient-donor, 22+/-16% of immature DC were successfully transduced. Flow cytometry analysis of surface markers expressed on DC after ALVAC infection did not reveal a mature phenotype. Moreover, ALVAC transduction did not interfere with the capacity of the DC to further mature under poly:IC stimulation. But most importantly, our results demonstrated that DC from HLA-A1 patient-donors infected with the recombinant ALVAC MAGE-1-MAGE-3 minigenes virus were capable of activating a MAGE 3/A1 CTL clone more efficiently than same DC loaded with MAGE 3/A1 peptide, as shown by increased IFN-gamma secretion. These results could be the basis for the development of a new clinical strategy in melanoma patient's immunotherapy.

Molecular characterization of Jurkat cells persistently infected with vaccinia virus mutant vp811

Previous reports from this laboratory demonstrated that persistent infections could be established in Jurkat cells with wild-type vaccinia virus (Jvac). The infected cells elicit increased expression of IL-2, IL-2Ralpha and IL-6 but not of IL-1beta nor of interferon-gamma. The persistently infected cells are also capable to transactivate the LTR gene of HIV-1 virus (HIV-1LTR). In addition, NFkappabeta and NFAT are found activated in Jvac. To find out whether the gene(s) responsible for establishment, maintenance and molecular characteristics of persistently infected cells are located in the terminal ends of the molecule, Jurkat cells were infected with a deletion mutant Vp811 that lacks 32.7 and 14.9 kb at the left and right terminal, respectively. The results indicate that the deletion mutant is capable of establishing persistent infections. The persistently infected cells show a similar pattern of expression to that observed in Jvac cells. It is concluded that the viral gene(s) involved in persistence and molecular cellular changes is (are) present in the mutant.

Avipoxvirus multiplication in a mammalian cell line

Avipoxviruses have many advantages and are being increasingly employed as recombinant vaccine vectors. One attractive feature is that while inserted transgenes are expressed in immunologically favourable ways, avipoxvirus infections of mammalian cells are believed to be abortive. The experimental evidence supporting this belief is, however, based on a limited number of mammalian cell-types and a few avipoxvirus species. We evaluated two avian and eight mammalian cell lines for permissivity to three avipoxvirus strains, one reference fowlpoxvirus and two newly isolated strains from sparrow and pigeon, respectively. Both avian cell lines were, as expected, permissive for all three avipoxvirus strains. However, by multiplication assays, we found to our surprise that Syrian baby hamster kidney (BHK-21) cells were equally permissive to all virus strains. Results from electron microscopy of infected BHK-21 cells revealed viral morphogenesis proceeding to various forms of infectious viruses. These results were supported by the demonstration of avipoxvirus specific late gene expression and avipoxvirus specific DNA restriction pattern in BHK-21 infected cells.

Phase I study of sequential vaccinations with fowlpox-CEA(6D)-TRICOM alone and sequentially with vaccinia-CEA(6D)-TRICOM, with and without granulocyte-macrophage colony-stimulating factor, in patients with carcinoembryonic antigen-expressing carcinomas

PURPOSE

Our previous clinical experience with vaccinia and replication-defective avipox recombinant carcinoembryonic antigen (CEA) vaccines has demonstrated safety and clinical activity with a correlation between CEA-specific immune response and survival. Preclinical evidence demonstrated that the addition of the transgenes for three T-cell costimulatory molecules (B7-1, ICAM-1, LFA-3, designated TRICOM) results in a significant improvement in antigen-specific T-cell responses and antitumor activity. We describe here the first trial in humans of the CEA-TRICOM vaccines (also including an enhancer agonist epitope within the CEA gene).

PATIENTS AND METHODS

Fifty-eight patients with advanced CEA-expressing cancers were accrued to eight cohorts that involved vaccinations with the following: replication-defective fowlpox recombinant (rF)-CEA(6D)-TRICOM; primary vaccination with recombinant vaccinia (rV)-CEA(6D)-TRICOM plus rF-CEA(6D)-TRICOM booster vaccinations; and rV-CEA(6D)-TRICOM and then rF-CEA(6D)-TRICOM, plus granulocyte-macrophage colony-stimulating factor (GM-CSF) with vaccines, or with divided doses of vaccine with GM-CSF. Vaccines were administered every 28 days for six doses and then once every 3 months. Reverting to treatments every 28 days was allowed if patients progressed on the 3-month schedule.

RESULTS

In this phase I study, no significant toxicity was observed. Twenty-three patients (40%) had stable disease for at least 4 months, with 14 of these patients having prolonged stable disease (> 6 months). Eleven patients had decreasing or stable serum CEA, and one patient had a pathologic complete response. Enhanced CEA-specific T-cell responses were observed in the majority of patients tested.

CONCLUSION

We demonstrated that the CEA-TRICOM vaccines are safe and can generate significant CEA-specific immune responses, and they seem to have clinical benefit in some patients with advanced cancer.

Live vaccinia-rabies virus recombinants, but not an inactivated rabies virus cell culture vaccine, protect B-lymphocyte-deficient A/WySnJ mice against rabies: considerations of recombinant defective poxviruses for rabies immunization of immunocompromised individuals

Presently, commercially available cell culture rabies vaccines for humans and animals consist of the five inactivated rabies virus proteins. The vaccines elicit a CD4+ helper T-cell response and a humoral B-cell response against the viral glycoprotein (G) resulting in the production of virus neutralizing antibody. Antibody against the viral nucleoprotein (N) is also present, but the mechanism(s) of its protection is unclear. HIV-infected individuals with low CD4+ T-lymphocyte counts and individuals undergoing treatment with immunosuppressive drugs have an impaired neutralizing antibody response after pre- and post-exposure immunization with rabies cell culture vaccines. Here we show the efficacy of live vaccinia-rabies virus recombinants, but not a cell culture vaccine consisting of inactivated rabies virus, to elicit elevated levels of neutralizing antibody in B-lymphocyte deficient A/WySnJ mice. The cell culture vaccine also failed to protect the mice, whereas a single immunization of a vaccinia recombinant expressing the rabies virus G or co-expressing G and N equally protected the mice up to 18 months after vaccination. The data suggest that recombinant poxviruses expressing the rabies virus G, in particular replication defective poxviruses such as canarypox or MVA vaccinia virus that undergo abortive replication in non-avian cells, or the attenuated vaccinia virus NYVAC, should be evaluated as rabies vaccines in immunocompromised individuals.

Replication and expression of a swinepox virus vector delivering feline leukemia virus Gag and Env to cell lines of swine and feline origin

The host range of swinepox virus (SPV) is restricted to swine, although SPV has been shown to infect mammalian, non-swine cells, without recovery of infectious virus. SPV is a reasonable candidate for development as a non-productively replicating viral vector for use in non-swine, mammalian species, such as the cat. A novel SPV gene deletion (SPV 043) was created and found to be non-attenuating. This deletion was utilized to generate a stable recombinant virus expressing the Gag-Pro and Env proteins of feline leukemia virus (FeLV). Expression and replication of this vector was studied in embryonic swine kidney cells (ESK-4), and two feline cell lines, Crandell feline kidney cells (CRFK) and feline skin fibroblasts (FSF). Our results showed that feline cells were susceptible to infection by SPV and supported expression of foreign genes driven by synthetic poxvirus promoters, however, SPV viral DNA was not replicated in feline cells and infectious virus was not recovered. In addition, FeLV Gag virus-like particles were produced from both ESK-4 and CRFK cells and foreign antigens were incorporated into infectious SPV intracellular mature virions (IMV). These results suggest that SPV may have potential as a safe vaccine delivery vector for cats.

The genome of canarypox virus

Here we present the genomic sequence, with analysis, of a canarypox virus (CNPV). The 365-kbp CNPV genome contains 328 potential genes in a central region and in 6.5-kbp inverted terminal repeats. Comparison with the previously characterized fowlpox virus (FWPV) genome revealed avipoxvirus-specific genomic features, including large genomic rearrangements relative to other chordopoxviruses and novel cellular homologues and gene families. CNPV also contains many genomic differences with FWPV, including over 75 kbp of additional sequence, 39 genes lacking FWPV homologues, and an average of 47% amino acid divergence between homologues. Differences occur primarily in terminal and, notably, localized internal genomic regions and suggest significant genomic diversity among avipoxviruses. Divergent regions contain gene families, which overall comprise over 49% of the CNPV genome and include genes encoding 51 proteins containing ankyrin repeats, 26 N1R/p28-like proteins, and potential immunomodulatory proteins, including those similar to transforming growth factor beta and beta-nerve growth factor. CNPV genes lacking homologues in FWPV encode proteins similar to ubiquitin, interleukin-10-like proteins, tumor necrosis factor receptor, PIR1 RNA phosphatase, thioredoxin binding protein, MyD116 domain proteins, circovirus Rep proteins, and the nucleotide metabolism proteins thymidylate kinase and ribonucleotide reductase small subunit. These data reveal genomic differences likely affecting differences in avipoxvirus virulence and host range, and they will likely be useful for the design of improved vaccine vectors.

DNA immunization with hepatitis C virus (HCV) polycistronic genes or immunization by HCV DNA priming-recombinant canarypox virus boosting induces immune responses and protection from recombinant HCV-vaccinia virus infection in HLA-A2.1-transgenic mice

We studied immune responses to hepatitis C virus (HCV) genes delivered as DNA encoding the entire HCV protein coding genome in two polycistronic plasmids encoding HCV capsid-E1-E2-NS2-NS3 and HCV NS3-NS4-NS5 in HLA-A2.1-transgenic mice. Immune responses to HCV DNA prime and recombinant canarypox virus boost were also studied with the above constructs. At 8 weeks after a canarypox virus boost, the DNA prime/canarypox virus boosting regimen induced potent cellular immune responses to HCV structural and nonstructural proteins on target cells expressing the HLA-A2.1 allele. High frequencies of gamma interferon-secreting cells, as detected by enzyme-linked immunospot assay, were obtained in response to several endogenously expressed HCV proteins. We also observed cytotoxic-T-lymphocyte reactivity in response to endogenously expressed HCV proteins in fresh spleen cells without in vitro expansion. Upon challenge with a recombinant vaccinia virus expressing HCV proteins at 2 months postimmunization, the HCV DNA prime/canarypox virus-immunized mice showed a complete reduction in vaccinia virus titers compared to HCV DNA prime/boost- and mock-immunized controls. Immune responses were still detectable 4 months after canarypox virus boost in immunized mice. Interestingly, at 10 months postimmunization (8 months after canarypox virus boost), the protection in HCV DNA prime/boost-immunized mice against recombinant HCV-vaccinia virus challenge was higher than that observed in HCV DNA prime/canarypox virus boost-immunized mice.

Development of cytomegalovirus vaccines: prospects for prevention of congenital CMV infection

Congenital cytomegalovirus (CMV) infection is an important cause of hearing, cognitive, and motor impairments that cannot be effectively prevented or treated by any current medical or public health interventions. A review of priorities for vaccine development by The Institute of Medicine of the National Academy of Sciences concluded that a vaccine to prevent congenital CMV infection should be a top priority for the United States. Evidence from clinical studies indicates that immunity to CMV can reduce the frequency and severity of disease. Laboratory investigations have identified structural and nonstructural CMV proteins that play a key role in eliciting protective immunity. The rationale for development of a CMV vaccine has been strengthened further by studies in experimental animals demonstrating the ability of immunization with subunit vaccines to prevent disease and transplacental transmission of virus. At least 4 CMV vaccines are in clinical trials, and advances in biotechnology are paving the way for additional novel vaccines.

Safety and immunogenicity of ALVAC vCP1452 and recombinant gp160 in newly human immunodeficiency virus type 1-infected patients treated with prolonged highly active antiretroviral therapy

In order to boost immune responses in persons in whom highly active antiretroviral therapy (HAART) was initiated within 120 days of the onset of symptoms of newly acquired human immunodeficiency virus type 1 (HIV-1) infection, we administered vaccines containing a canarypox virus vector, vCP1452, with HIV-1 genes encoding multiple HIV-1 proteins, and recombinant gp160. Fifteen HIV-1-infected subjects who achieved sustained suppression of plasma viremia for at least 2 years were enrolled. While continuing antiretroviral therapy, each subject received at least four intramuscular injections of the vaccines on days 0, 30, 90, and 180. Adverse events were mild, with the most common being transient tenderness at the vCP1452 injection site. Of the 14 patients who completed vaccination, 13 had significant increases in anti-gp120 or anti-p24 antibody titers, and 9 had transient augmentation of their T-cell proliferation responses to gp160 and/or p24. HIV-1-specific CD8(+) T cells were quantified using an intracellular gamma interferon staining assay. Among 11 patients who had increased CD8(+) T-cell responses, seven had responses to more than one HIV-1 antigen. In summary, vaccination with vCP1452 and recombinant gp160 appears safe and immunogenic in newly HIV-1-infected patients on HAART.

Expression of vaccinia E3L and K3L genes by a novel recombinant canarypox HIV vaccine vector enhances HIV-1 pseudovirion production and inhibits apoptosis in human cells

Poxviruses that are attenuated for growth in human cells provide a safe means of HIV antigen expression and are capable of eliciting HIV-specific immune responses, including CD8+ cytotoxic T-lymphocyte (CTL) responses. HIV-1 antigen expression in human cells by attenuated poxvirus vectors may be limited by interferon-mediated host defense mechanisms. To enhance HIV antigen expression in human cells, the vaccinia virus E3L and K3L genes were inserted into a canarypox vector that expresses HIV-1 Gag, Env, and a Nef/Pol polyepitope string. E3L and K3L markedly reduced the activation of the double-stranded RNA-dependent protein kinase, PKR, and led to a significant reduction in apoptosis in HeLa cells. Production and release of HIV-1 antigen in the form of pseudovirions was enhanced in both duration and magnitude by this vector modification. The addition of immunomodulatory genes to attenuated poxviruses represents a novel strategy for enhancing antigen production by live vector HIV vaccine candidates.

Multistage multiantigen heterologous prime boost vaccine for Plasmodium knowlesi malaria provides partial protection in rhesus macaques

A nonhuman primate model for malaria vaccine development allowing reliable, stringent sporozoite challenge and evaluation of both cellular and antibody responses is needed. We therefore constructed a multicomponent, multistage DNA vaccine for the simian malaria species Plasmodium knowlesi including two preerythrocytic-stage antigens, the circumsporozoite protein (PkCSP) and sporozoite surface protein 2 (PkSSP2), and two blood stage antigens, apical merozoite antigen 1 (PkAMA1) and merozoite surface protein 1 (PkMSP1p42), as well as recombinant canarypox viruses encoding the four antigens (ALVAC-4). The DNA vaccine plasmids expressed the corresponding antigens in vitro and induced antiparasite antibodies in mice. Groups of four rhesus monkeys received three doses of a mixture of the four DNA vaccine plasmids and a plasmid encoding rhesus granulocyte-monocyte colony-stimulating factor, followed by boosting with a single dose of ALVAC-4. Three groups received the priming DNA doses by different routes, either by intramuscular needle injection, by intramuscular injection with a needleless injection device, the Biojector, or by a combination of intramuscular and intradermal routes by Biojector. Animals immunized by any route developed antibody responses against sporozoites and infected erythrocytes and against a recombinant PkCSP protein, as well as gamma interferon-secreting T-cell responses against peptides from PkCSP. Following challenge with 100 P. knowlesi sporozoites, 1 of 12 experimental monkeys was completely protected and the mean parasitemia in the remaining monkeys was significantly lower than that in 4 control monkeys. This model will be important in preclinical vaccine development.

Cross-presentation by dendritic cells of tumor antigen expressed in apoptotic recombinant canarypox virus-infected dendritic cells

We have investigated the possible usefulness of recombinant canarypox virus (ALVAC) encoding the melanoma-associated Ag, Melan-A/MART-1 (MART-1), in cancer immunotherapy, using a dendritic cell (DC)-based approach. ALVAC MART-1-infected DC express, and are able to process and present, the Ag coded by the viral vector. One consistent feature of infection by ALVAC is that these viruses induce apoptosis, and we show cross-presentation of Ag when uninfected DC are cocultured with ALVAC MART-1-infected DC. Uptake of apoptotic virally infected DC by uninfected DC and subsequent expression of tumor Ag in the latter were verified by flow cytometry analysis, image cytometry, and confocal microscopy. Functional activity was monitored in vitro by the stimulation of a MART-1-specific cytotoxic T cell clone. Heightened efficiency in Ag presentation is evidenced in the 2- to 3-fold increase in IFN-gamma production by the T cell clone, as compared with the ALVAC-infected DC alone. Cocultures of ALVAC MART-1-infected and uninfected DC are able to induce MART-1-specific T cell immune responses, as assessed by HLA class I/peptide tetramer binding, IFN-gamma ELISPOT assays, and cytotoxicity tests. Overall, our data indicate that DC infected with recombinant canarypox viruses may represent an efficient presentation platform for tumor Ags, which can be exploited in clinical studies.