An OspA-based DNA vaccine protects mice against infection with Borrelia burgdorferi

DNA lipid nanoparticle vaccine targeting outer surface protein C affords protection against homologous Borrelia burgdorferi needle challenge in mice

Introduction

The incidence of Lyme disease (LD) in Canada and the United States has risen over the last decade, nearing 480,000 cases each year. Borrelia burgdorferi sensu lato, the causative agent of LD, is transmitted to humans through the bite of an infected tick, resulting in flu-like symptoms and often a characteristic bull’s-eye rash. In more severe cases, disseminated bacterial infection can cause arthritis, carditis and neurological impairments. Currently, no vaccine is available for the prevention of LD in humans.

Methods

In this study, we developed a lipid nanoparticle (LNP)-encapsulated DNA vaccine encoding outer surface protein C type A (OspC-type A) of B. burgdorferi.

Results

Vaccination of C3H/HeN mice with two doses of the candidate vaccine induced significant OspC-type A-specific antibody titres and borreliacidal activity. Analysis of the bacterial burden following needle challenge with B. burgdorferi (OspC-type A) revealed that the candidate vaccine afforded effective protection against homologous infection across a range of susceptible tissues. Notably, vaccinated mice were protected against carditis and lymphadenopathy associated with Lyme borreliosis.

Discussion

Overall, the results of this study provide support for the use of a DNA-LNP platform for the development of LD vaccines.

Transmission Cycle of Tick-Borne Infections and Co-Infections, Animal Models and Diseases

Tick-borne pathogens such as species of Borrelia, Babesia, Anaplasma, Rickettsia, and Ehrlichia are widespread in the United States and Europe among wildlife, in passerines as well as in domestic and farm animals. Transmission of these pathogens occurs by infected ticks during their blood meal, carnivorism, and through animal bites in wildlife, whereas humans can become infected either by an infected tick bite, through blood transfusion and in some cases, congenitally. The reservoir hosts play an important role in maintaining pathogens in nature and facilitate transmission of individual pathogens or of multiple pathogens simultaneously to humans through ticks. Tick-borne co-infections were first reported in the 1980s in white-footed mice, the most prominent reservoir host for causative organisms in the United States, and they are becoming a major concern for public health now. Various animal infection models have been used extensively to better understand pathogenesis of tick-borne pathogens and to reveal the interaction among pathogens co-existing in the same host. In this review, we focus on the prevalence of these pathogens in different reservoir hosts, animal models used to investigate their pathogenesis and host responses they trigger to understand diseases in humans. We also documented the prevalence of these pathogens as correlating with the infected ticks’ surveillance studies. The association of tick-borne co-infections with other topics such as pathogens virulence factors, host immune responses as they relate to diseases severity, identification of vaccine candidates, and disease economic impact are also briefly addressed here.

Human and Veterinary Vaccines for Lyme Disease

Lyme disease (LD) is an emerging zoonotic infection that is increasing in incidence in North America, Europe, and Asia. With the development of safe and efficacious vaccines, LD can potentially be prevented. Vaccination offers a cost-effective and safe approach for decreasing the risk of infection. While LD vaccines have been widely used in veterinary medicine, they are not available as a preventive tool for humans. Central to the development of effective vaccines is an understanding of the enzootic cycle of LD, differential gene expression of Borrelia burgdorferi in response to environmental variables, and the genetic and antigenic diversity of the unique bacteria that cause this debilitating disease. Here we review these areas as they pertain to past and present efforts to develop human, veterinary, and reservoir targeting LD vaccines. In addition, we offer a brief overview of additional preventative measures that should employed in conjunction with vaccination.

Protection against Borreliella burgdorferi infection mediated by a synthetically engineered DNA vaccine

Lyme disease is the most common vector-borne disease in North America. The etiological agent is the spirochete Borreliella burgdorferi, transmitted to mammalian hosts by the Ixodes tick. In recent years there has been an increase in the number of cases of Lyme disease. Currently, there is no vaccine on the market for human use. We describe the development of a novel synthetically engineered DNA vaccine, pLD1 targeting the outer-surface protein A (OspA) of Borreliella burgdorferi. Immunization of C3 H/HeN mice with pLD1 elicits robust humoral and cellular immune responses that confer complete protection against a live Borreliella burgdorferi bacterial challenge. We also assessed intradermal (ID) delivery of pLD1 in Hartley guinea pigs, demonstrating the induction of robust and durable humoral immunity that lasts at least 1 year. We provide evidence of the potency of pLD1 by showing that antibodies targeting the OspA epitopes which have been associated with protection are prominently raised in the immunized guinea pigs. The described study provides the basis for the advancement of pDL1 as a potential vaccine for Lyme disease control.

Novel Plasmodium antigens identified via genome-based antibody screen induce protection associated with polyfunctional T cell responses

The development of vaccines against complex intracellular pathogens, such as Plasmodium spp., where protection is likely mediated by cellular immune responses, has proven elusive. The availability of whole genome, proteome and transcriptome data has the potential to advance rational vaccine development but yet there are no licensed vaccines against malaria based on antigens identified from genomic data. Here, we show that the Plasmodium yoelii orthologs of four Plasmodium falciparum proteins identified by an antibody-based genome-wide screening strategy induce a high degree of sterile infection-blocking protection against sporozoite challenge in a stringent rodent malaria model. Protection increased in multi-antigen formulations. Importantly, protection was highly correlated with the induction of multifunctional triple-positive T cells expressing high amounts of IFN-γ, IL-2 and TNF. These data demonstrate that antigens identified by serological screening are targets of multifunctional cellular immune responses that correlate with protection. Our results provide experimental validation for the concept of rational vaccine design from genomic sequence data.

Rapid outer-surface protein C DNA tattoo vaccination protects against Borrelia afzelii infection

Borrelia afzelii is the predominant Borrelia species causing Lyme borreliosis in Europe. Currently there is no human vaccine against Lyme borreliosis, and most research focuses on recombinant protein vaccines against Borrelia burgdorferi sensu stricto. DNA tattooing is a novel vaccination method that can be applied in a rapid vaccination schedule. We vaccinated C3H/HeN mice with B. afzelii strain PKo OspC (outer-surface protein C) using a codon-optimized DNA vaccine tattoo and compared this with recombinant protein vaccination in a 0-2-4 week vaccination schedule. We also assessed protection by DNA tattoo in a 0-3-6 day schedule. DNA tattoo and recombinant OspC vaccination induced comparable total IgG responses, with a lower IgG1/IgG2a ratio after DNA tattoo. Two weeks after syringe-challenge with 5 × 10(5) B. afzelii spirochetes most vaccinated mice had negative B. afzelii tissue DNA loads and all were culture negative. Furthermore, DNA tattoo vaccination in a 0-3-6 day regimen also resulted in negative Borrelia loads and cultures after challenge. To conclude, DNA vaccination by tattoo was fully protective against B. afzelii challenge in mice in a rapid vaccination protocol, and induces a favorable humoral immunity compared to recombinant protein vaccination. Rapid DNA tattoo is a promising vaccination strategy against spirochetes.

Fusion of antigen to a dendritic cell targeting chemokine combined with adjuvant yields a malaria DNA vaccine with enhanced protective capabilities

Although sterilizing immunity to malaria can be elicited by irradiated sporozoite vaccination, no clinically practical subunit vaccine has been shown to be capable of preventing the approximately 600,000 annual deaths attributed to this infection. DNA vaccines offer several potential advantages for a disease that primarily affects the developing world, but new approaches are needed to improve the immunogenicity of these vaccines. By using a novel, lipid-based adjuvant, Vaxfectin, to attract immune cells to the immunization site, in combination with an antigen-chemokine DNA construct designed to target antigen to immature dendritic cells, we elicited a humoral immune response that provided sterilizing immunity to malaria challenge in a mouse model system. The chemokine, MIP3αCCL20, did not significantly enhance the cellular infiltrate or levels of cytokine or chemokine expression at the immunization site but acted with Vaxfectin to reduce liver stage malaria infection by orders of magnitude compared to vaccine constructs lacking the chemokine component. The levels of protection achieved were equivalent to those observed with irradiated sporozoites, a candidate vaccine undergoing development for further large scale clinical trial. Only vaccination with the combined regimen of adjuvant and chemokine provided 80–100% protection against the development of bloodstream infection. Treating the immunization process as requiring the independent steps of 1) attracting antigen-presenting cells to the site of immunization and 2) specifically directing vaccine antigen to the immature dendritic cells that initiate the adaptive immune response may provide a rational strategy for the development of a clinically applicable malaria DNA vaccine.

Evaluation of approaches to identify the targets of cellular immunity on a proteome-wide scale

Background

Vaccine development against malaria and other complex diseases remains a challenge for the scientific community. The recent elucidation of the genome, proteome and transcriptome of many of these complex pathogens provides the basis for rational vaccine design by identifying, on a proteome-wide scale, novel target antigens that are recognized by T cells and antibodies from exposed individuals. However, there is currently no algorithm to effectively identify important target antigens from genome sequence data; this is especially challenging for T cell targets. Furthermore, for some of these pathogens, such as Plasmodium, protein expression using conventional platforms has been problematic but cell-free in vitro transcription translation (IVTT) strategies have recently proved successful. Herein, we report a novel approach for proteome-wide scale identification of the antigenic targets of T cell responses using IVTT products.

Principal Findings

We conducted a series of in vitro and in vivo experiments using IVTT proteins either unpurified, absorbed to carboxylated polybeads, or affinity purified through nickel resin or magnetic beads. In vitro studies in humans using CMV, EBV, and Influenza A virus proteins showed antigen-specific cytokine production in ELIspot and Cytometric Bead Array assays with cells stimulated with purified or unpurified IVTT antigens. In vitro and in vivo studies in mice immunized with the Plasmodium yoelii circumsporozoite DNA vaccine with or without IVTT protein boost showed antigen-specific cytokine production using purified IVTT antigens only. Overall, the nickel resin method of IVTT antigen purification proved optimal in both human and murine systems.

Conclusions

This work provides proof of concept for the potential of high-throughput approaches to identify T cell targets of complex parasitic, viral or bacterial pathogens from genomic sequence data, for rational vaccine development against emerging and re-emerging diseases that pose a threat to public health.

A host-restricted viral vector for antigen-specific immunization against Lyme disease pathogen

Newcastle disease virus (NDV) is an avian virus that is attenuated in primates and is a potential vaccine vector for human use. We evaluated NDV as a vector for expressing selected antigens of the Lyme disease pathogen Borrelia burgdorferi. A series of recombinant NDVs were generated that expressed intracellular or extracellular forms of two B. burgdorferi antigens: namely, the basic membrane protein A (BmpA) and the outer surface protein C (OspC). Expression of the intracellular and extracellular forms of these antigens was confirmed in cultured chicken cells. C3H or Balb/C mice that were immunized intranasally with the NDV vectors mounted vigorous serum antibody responses against the NDV vector, but failed to mount a robust response against either the intracellular or extracellular forms of BmpA or OspC. By contrast, a single immunization of hamsters with the NDV vectors via the intranasal, intramuscular, or intraperitoneal route resulted in rapid and rigorous antibody responses against the intracellular or extracellular forms of BmpA and OspC. When groups of hamsters were separately inoculated with various NDV vectors and challenged with B. burgdorferi (10⁸ cells/animal), immunization with vector expressing either intracellular or extracellular BmpA was associated with a significant reduction of the pathogen load in the joints. Taken together, our studies highlighted the importance of NDV as vaccine vector that can be used for simple yet effective immunization of hosts against bacterial infections including Lyme disease.

Evolution and distribution of the ospC Gene, a transferable serotype determinant of Borrelia burgdorferi

Borrelia burgdorferi, an emerging bacterial pathogen, is maintained in nature by transmission from one vertebrate host to another by ticks. One of the few antigens against which mammals develop protective immunity is the highly polymorphic OspC protein, encoded by the ospC gene on the cp26 plasmid. Intragenic recombination among ospC genes is known, but the extent to which recombination extended beyond the ospC locus itself is undefined. We accessed and supplemented collections of DNA sequences of ospC and other loci from ticks in three U.S. regions (the Northeast, the Midwest, and northern California); a total of 839 ospC sequences were analyzed. Three overlapping but distinct populations of B. burgdorferi corresponded to the geographic regions. In addition, we sequenced 99 ospC flanking sequences from different lineages and compared the complete cp26 sequences of 11 strains as well as the cp26 bbb02 loci of 56 samples. Besides recombinations with traces limited to the ospC gene itself, there was evidence of lateral gene transfers that involved (i) part of the ospC gene and one of the two flanks or (ii) the entire ospC gene and different lengths of both flanks. Lateral gene transfers resulted in different linkages between the ospC gene and loci of the chromosome or other plasmids. By acquisition of the complete part or a large part of a novel ospC gene, an otherwise adapted strain would assume a new serotypic identity, thereby being comparatively fitter in an area with a high prevalence of immunity to existing OspC types.

The tick-borne zoonosis Lyme borreliosis is increasing in incidence and spreading geospatially in North America. Further understanding of the evolution and genetics of its cause, Borrelia burgdorferi, in its environments fosters progress toward ecologically based control efforts. By means of DNA sequencing of a large sample collection of the pathogen from across the United States, we studied the gene for the bacterium’s highly diverse OspC protein, protective immunity against which develops in animals. We found that the distributions and frequencies of types of OspC genes differed between populations of B. burgdorferi in the Northeast, the Midwest, and California. Over time, OspC genes were transferred between strains through recombinations involving the whole or parts of the gene and one or both flanks. Acquisitions of OspC genes that are novel for the region confer to recipients unique identities to host immune systems and, presumably, selective advantage when immunity to existing types is widespread among hosts.

DNA vaccines for targeting bacterial infections

DNA vaccination has been of great interest since its discovery in the 1990s due to its ability to elicit both humoral and cellular immune responses. DNA vaccines consist of a DNA plasmid containing a transgene that encodes the sequence of a target protein from a pathogen under the control of a eukaryotic promoter. This revolutionary technology has proven to be effective in animal models and four DNA vaccine products have recently been approved for veterinary use. Although few DNA vaccines against bacterial infections have been tested, the results are encouraging. Because of their versatility, safety and simplicity a wider range of organisms can be targeted by these vaccines, which shows their potential advantages to public health. This article describes the mechanism of action of DNA vaccines and their potential use for targeting bacterial infections. In addition, it provides an updated summary of the methods used to enhance immunogenicity from codon optimization and adjuvants to delivery techniques including electroporation and use of nanoparticles.

From Plasmids to Protection: A Review of DNA Vaccines Against Infectious Diseases

The field of DNA vaccine development began over 16 years ago with the observation that plasmid DNA could be injected into and expressed in vivo and drive adaptive immune responses. Since then, there has been great interest in developing this technology to create a new generation of vaccines with the ability to elicit both humoral and cellular immune responses from an inherently innocuous injection. However, DNA vaccines have yet to proceed past phase I/II clinical trials in humans--primarily due to a desire to induce more potent immune responses. This review will examine how DNA vaccines function to induce an immune response and how this information might be useful in future vaccine design.

Transcriptionally active PCR for antigen identification and vaccine development: in vitro genome-wide screening and in vivo immunogenicity

We have evaluated a technology called transcriptionally active PCR (TAP) for high throughput identification and prioritization of novel target antigens from genomic sequence data using the Plasmodium parasite, the causative agent of malaria, as a model. First, we adapted the TAP technology for the highly AT-rich Plasmodium genome, using well-characterized P. falciparum and P. yoelii antigens and a small panel of uncharacterized open reading frames from the P. falciparum genome sequence database. We demonstrated that TAP fragments encoding six well-characterized P. falciparum antigens and five well-characterized P. yoelii antigens could be amplified in an equivalent manner from both plasmid DNA and genomic DNA templates, and that uncharacterized open reading frames could also be amplified from genomic DNA template. Second, we showed that the in vitro expression of the TAP fragments was equivalent or superior to that of supercoiled plasmid DNA encoding the same antigen. Third, we evaluated the in vivo immunogenicity of TAP fragments encoding a subset of the model P. falciparum and P. yoelii antigens. We found that antigen-specific antibody and cellular immune responses induced by the TAP fragments in mice were equivalent or superior to those induced by the corresponding plasmid DNA vaccines. Finally, we developed and demonstrated proof-of-principle for an in vitro humoral immunoscreening assay for down-selection of novel target antigens. These data support the potential of a TAP approach for rapid high throughput functional screening and identification of potential candidate vaccine antigens from genomic sequence data.

Induction of multi-antigen multi-stage immune responses against Plasmodium falciparum in rhesus monkeys, in the absence of antigen interference, with heterologous DNA prime/poxvirus boost immunization

The present study has evaluated the immunogenicity of single or multiple Plasmodium falciparum (Pf) antigens administered in a DNA prime/poxvirus boost regimen with or without the poloxamer CRL1005 in rhesus monkeys. Animals were primed with PfCSP plasmid DNA or a mixture of PfCSP, PfSSP2/TRAP, PfLSA1, PfAMA1 and PfMSP1-42 (CSLAM) DNA vaccines in PBS or formulated with CRL1005, and subsequently boosted with ALVAC-Pf7, a canarypox virus expressing the CSLAM antigens. Cell-mediated immune responses were evaluated by IFN-γ ELIspot and intracellular cytokine staining, using recombinant proteins and overlapping synthetic peptides. Antigen-specific and parasite-specific antibody responses were evaluated by ELISA and IFAT, respectively. Immune responses to all components of the multi-antigen mixture were demonstrated following immunization with either DNA/PBS or DNA/CRL1005, and no antigen interference was observed in animals receiving CSLAM as compared to PfCSP alone. These data support the down-selection of the CSLAM antigen combination. CRL1005 formulation had no apparent effect on vaccine-induced T cell or antibody responses, either before or after viral boost. In high responder monkeys, CD4+IL-2+ responses were more predominant than CD8+ T cell responses. Furthermore, CD8+ IFN-γ responses were detected only in the presence of detectable CD4+ T cell responses. Overall, this study demonstrates the potential for multivalent Pf vaccines based on rational antigen selection and combination, and suggests that further formulation development to increase the immunogenicity of DNA encoded antigens is warranted.

Enhancement of antibody and cellular immune responses to malaria DNA vaccines by in vivo electroporation

We evaluated the effectiveness of in vivo electroporation (EP) for the enhancement of immune responses induced by DNA plasmids encoding the pre-erythrocytic Plasmodium yoelii antigens PyCSP and PyHEP17 administered intramuscularly and intradermally to mice. EP resulted in a 16- and 2-fold enhancement of antibody responses to PyCSP and PyHEP17, respectively. Immunization with 5 microg of DNA via EP was equivalent to 50 microg of DNA via conventional needle, thus reducing by 10-fold the required dose to produce a given effect. Moreover, IFN-gamma responses were increased by approximately 2-fold. Data demonstrate the potential of EP to enhance immune responses to DNA vaccines against infectious agents.

Immune response in mice and swine to DNA vaccines derived from the Pasteurella multocida toxin gene

DNA vaccines were constructed with either a 5'-truncated or full-length, genetically detoxified toxin gene from Pasteurella multocida and two different DNA vaccine vectors, distinguished by the presence or absence of a secretion signal sequence. Optimal PMT-specific antibody responses and spleen cell secretion of interferon-gamma following immunization of mice were achieved with pMM4, the construct containing a signal sequence and encoding the entire toxin. Antibody responses were also induced in pigs immunized with pMM4 and levels increased significantly following booster injections and experimental infection with P. multocida. Significantly increased expression of interferon-gamma was detected in only a small subset of pMM4-immunized pigs. This report documents, for the first time, the ability of a DNA vaccine to elicit immune responses to the P. multocida toxin in both mice and swine.

Effect of plasmid backbone modification by different human CpG motifs on the immunogenicity of DNA vaccine vectors

DNA vaccines, in general, have been found to be poorly immunogenic in nonhuman primates and humans as compared with mice. As the immunogenicity of DNA plasmids relies, to a large extent, on the presence of CpG motifs as built in adjuvants, we addressed the issue of poor immunogenicity by inserting recently identified CpG oligonucleotides (ODN) optimal for human (K-type or D-type CpG ODN) into the backbone of plasmid VR1020. We found that plasmid DNA containing K-type CpG motifs or D-type CpG motifs significantly enhanced the up-regulation of surface molecules and production of interleukin-6 from human peripheral blood mononuclear cells (PBMC) and stimulated monocytes to develop into functionally mature dendritic cells (DC) compared with unmodified plasmid. Monocyte maturation into DC was through plasmacytoid DC present in the culture. It is interesting that the K-type CpG motif-modified plasmid stimulated significant levels of interferon (IFN)-gamma and IFN-alpha from human PBMC. Immunization of mice with D-type CpG motif-modified plasmid, encoding Plasmodium falciparum surface protein 25, yielded enhanced antigen-specific antibodies. Taken together, these results suggest that insertion of immunomodulatory human CpG motifs into plasmid DNA can improve immunogenicity of DNA vaccines.

Plasmid vaccines and therapeutics: from design to applications

In the late 1980s, Vical and collaborators discovered that the injection into tissues of unformulated plasmid encoding various proteins resulted in the uptake of the plasmid by cells and expression of the encoded proteins. After this discovery, a period of technological improvements in plasmid delivery and expression and in pharmaceutical and manufacturing development was quickly followed by a plethora of human clinical trials testing the ability of injected plasmid to provide therapeutic benefits. In this chapter, we summarize in detail the technologies used in the most recent company-sponsored clinical trials and discuss the potential for future improvements in plasmid design, manufacturing, delivery, formulation and administration. A generic path for the clinical development of plasmid-based products is outlined and then exemplified using a case study on the development of a plasmid vaccine from concept to clinical trial.

Bacteria as DNA vaccine carriers for genetic immunization

Genetic immunization with plasmid DNA vaccines has proven to be a promising tool in conferring protective immunity in various experimental animal models of infectious diseases or tumors. Recent research focuses on the use of bacteria, in particular enteroinvasive species, as effective carriers for DNA vaccines. Attenuated strains of Shigella flexneri, Salmonella spp., Yersinia enterocolitica or Listeria monocytogenes have shown to be attractive candidates to target DNA vaccines to immunological inductive sites at mucosal surfaces. This review summarizes recent progress in bacteria-mediated delivery of plasmid DNA vaccines in the field of infectious diseases and cancer.

High-throughput generation of P. falciparum functional molecules by recombinational cloning

Large-scale functional genomics studies for malaria vaccine and drug development will depend on the generation of molecular tools to study protein expression. We examined the feasibility of a high-throughput cloning approach using the Gateway system to create a large set of expression clones encoding Plasmodium falciparum single-exon genes. Master clones and their ORFs were transferred en masse to multiple expression vectors. Target genes (n = 303) were selected using specific sets of criteria, including stage expression and secondary structure. Upon screening four colonies per capture reaction, we achieved 84% cloning efficiency. The genes were subcloned in parallel into three expression vectors: a DNA vaccine vector and two protein expression vectors. These transfers yielded a 100% success rate without any observed recombination based on single colony screening. The functional expression of 95 genes was evaluated in mice with DNA vaccine constructs to generate antibody against various stages of the parasite. From these, 19 induced antibody titers against the erythrocytic stages and three against sporozoite stages. We have overcome the potential limitation of producing large P. falciparum clone sets in multiple expression vectors. This approach represents a powerful technique for the production of molecular reagents for genome-wide functional analysis of the P. falciparum genome and will provide for a resource for the malaria resource community distributed through public repositories.

Reduced immunogenicity of DNA vaccine plasmids in mixtures

We measured the ability of nine DNA vaccine plasmids encoding candidate malaria vaccine antigens to induce antibodies and interferon-gamma responses when delivered alone or in a mixture containing all nine plasmids. We further examined the possible immunosuppressive effect of individual plasmids, by assessing a series of mixtures in which each of the nine vaccine plasmids was replaced with a control plasmid. Given alone, each of the vaccine plasmids induced significant antibody titers and, in the four cases for which appropriate assays were available, IFN-gamma responses. Significant suppression or complete abrogation of responses were seen when the plasmids were pooled in a nine-plasmid cocktail and injected in a single site. Removal of single genes from the mixture frequently reduced the observed suppression. Boosting with recombinant poxvirus increased the antibody response in animals primed with either a single gene or the mixture, but, even after boosting, responses were higher in animals primed with single plasmids than in those primed with the nine-plasmid mixture. Boosting did not overcome the suppressive effect of mixing for IFN-gamma responses. Interactions between components in a multiplasmid DNA vaccine may limit the ability to use plasmid pools alone to induce responses against multiple targets simultaneously.

Safety, tolerability, and antibody responses in humans after sequential immunization with a PfCSP DNA vaccine followed by the recombinant protein vaccine RTS,S/AS02A

Optimal protection against malaria may require induction of high levels of protective antibody and CD8(+) and CD4(+) T cell responses. In humans, malaria DNA vaccines elicit CD8(+) cytotoxic T cells (CTL) and IFNgamma responses as measured by short-term (ex vivo) ELISPOT assays, and recombinant proteins elicit antibodies and excellent T cell responses, but no CD8(+) CTL or CD8(+) IFNgamma-producing cells as measured by ex vivo ELISPOT. Priming with DNA and boosting with recombinant pox virus elicits much better T cell responses than DNA alone, but not antibody responses. In an attempt to elicit antibodies and enhanced T cell responses, we administered RTS,S/AS02A, a partially protective Plasmodium falciparum recombinant circumsporozoite protein (CSP) vaccine in adjuvant, to volunteers previously immunized with a P. falciparum CSP DNA vaccine (VCL-2510) and to naïve volunteers. This vaccine regimen was well tolerated and safe. The volunteers who received RTS,S/AS02A alone had, as expected, antibody and CD4(+) T cell responses, but no CD8(+) T cell responses. Volunteers who received PfCSP DNA followed by RTS,S/AS02A had antibody and CD8(+) and CD4(+) T cell responses (Wang et al., submitted). Sequential immunization with DNA and recombinant protein, also called heterologous prime-boost, led to enhanced immune responses as compared to DNA or recombinant protein alone, suggesting that it might provide enhanced protective immunity.

Expression of the beta-adhesin part of HRgpA in Sprague Dawley rats induces a specific antibody response

The beta-adhesin part of the Porphyromonas gingivalis W50 (ATCC 53978) protease HRgpA was cloned in an eukaryotic expression vector and expressed in COS-7 cells. The monoclonal antibody MAb (61BG1.3), specific for the hemagglutinating domain of beta-adhesin, recognized the expressed beta-adhesin in the transfected cells both by immunoblot and immunofluorescence. Sprague Dawley rats were immunized intramuscularly with beta-adhesin encoding expression plasmid and expression plasmid without beta-adhesin insert. Skeletal muscle tissue at the site of immunization in the beta-adhesin immunized animals was shown to express this protein. The immunization induced a beta-adhesin-specific antibody response. Sera from the immunized animals were tested for hemagglutination inhibiting activity. Due to high natural inhibiting activity in all rat sera tested, no increased hemagglutination inhibition was detected in sera from the beta-adhesin immunized animals.

DNA prime–protein boost immunization in monkeys: efficacy of a novel construct containing functional domains ofPlasmodium cynomolgiCS and TRAP

We report the efficacy of a bimodal immunization regimen that involved priming with naked DNA (multiple doses) followed by a booster with recombinant protein in rhesus monkeys with a chimeric construct containing the N-terminus of thrombospondin-related adhesive protein and the C-terminus of circumsporozoite protein of Plasmodium cynomolgi. The vaccinated animals developed high titer antibodies against the chimeric antigen, the two components of the hybrid and the native proteins of sporozoites. The peripheral blood mononuclear cells isolated from the vaccinated animals had significant in vitro T cell proliferation activity when stimulated with the recombinant chimeric protein. Furthermore, following challenge with 1000 P. cynomolgi sporozoites, the peak and total parasitemia were significantly lower in vaccinated animals than in the control animals.

Evaluation of Venezuelan Equine Encephalitis (VEE) replicon-based Outer surface protein A (OspA) vaccines in a tick challenge mouse model of Lyme disease

Venezuelan Equine Encephalitis (VEE) virus replicon particles (VRPs) encoding Borrelia burgdorferi Outer surface protein A (OspA) were evaluated for their ability to induce an immune response and provide protection from tick-borne spirochetes. VRPs expressing ospA that accumulated intracellularly (VRP OspA) or that was secreted from host cells (VRP tPA-OspA) were tested. Both VRP OspA and VRP tPA-OspA expressed ospA in immunized mice. Mice vaccinated with VRPs expressing secreted OspA produced significant amounts of anti-OspA antibodies, whereas VRPs expressing intracellular OspA were less immunogenic. The VRP method of delivery induced a Th1 type immune response unlike the recombinant OspA protein in Freund's adjuvant, which induced a mixed (Th1 and Th2) immune response. The VRP tPA-OspA construct induced an immune response that reduced the bacterial load in feeding Ixodes scapularis and blocked transmission to the host. These results indicate that VRPs are capable of providing protection against tick-borne B. burgdorferi, and potentially can be used for developing improved vaccines against Lyme disease.

A DNA vaccine encoding the outer surface protein C from Borrelia burgdorferi is able to induce protective immune responses

The outer surface protein C (OspC) of Borrelia burgdorferi, the spirochete that causes Lyme disease, is a promising candidate for a vaccine against borreliosis. BALB/c and C3H/HeJ mice were immunized either with recombinant OspC protein or with plasmid DNA encoding OspC fused to the human tissue plasminogen activator leader sequence (pCMV-TPA/ZS7). The influence of the route of administering the DNA and the use of oligodeoxynucleotides containing CpG-motifs on the development of the immune response was investigated. In both mouse strains, protein as well as gene-gun immunization induced Th2 type responses, whereas needle injection of plasmid DNA resulted in Th1 type antibody production. Co-injection of CpG-motifs did not significantly modify the response type in any immunization group, as indicated by only marginal changes of antibody subclass distribution. The protection rate after challenge with 10(4) B. burgdorferi organisms per mouse was between 80% and 100% for all groups. These results demonstrate, for the first time, that a DNA vaccine encoding OspC of B. burgdorferi is suitable for inducing protection against Lyme borreliosis.

Immunization with the Chlamydia trachomatis major outer membrane protein, using the outer surface protein A of Borrelia burgdorferi as an adjuvant, can induce protection against a chlamydial genital challenge

Two strains of mice C3H/HeN (H-2(k)) and BALB/c (H-2(d)) were immunized with the Chlamydia trachomatis mouse pneumonitis (MoPn) major outer membrane protein (MOMP) using the Borrelia burgdorferi outer surface protein A (OspA) as an adjuvant. As a control, groups of mice were inoculated with ovalbumin instead of MOMP. Female mice were immunized using three different routes: intramuscular (i.m.) plus subcutaneous (s.c.), intranasal (i.n.) and perivaginal and perisacral (p.vag.+p.sac.). Significant humoral and cell mediated immune responses developed particularly in mice inoculated by the i.m.+s.c. routes as determined by the levels of chlamydial specific antibody in the serum and genital secretions and a T-cell proliferative assay. Following immunization the animals were challenged in the genital tract with C. trachomatis MoPn and the course of the infection followed by vaginal cultures. Significant protection against infection was achieved in the C3H/HeN mice inoculated i.m.+s.c. with MOMP+OspA, as shown by the intensity and duration of vaginal cultures, and by the number of mice with positive cultures. On the other hand in BALB/c mice there was only a decrease in the number of animals with positive vaginal cultures. Six weeks after the challenge the mice were mated and the outcome of the pregnancy evaluated. In both the C3H/HeN and the BALB/c mice immunized i.m.+s.c. with MOMP+OspA there was significant protection against infertility as shown by the number of animals with bilateral fertility and number of embryos per uterine horn. In conclusion, immunization using C. trachomatis MOMP, and B. burgdorferi OspA as an adjuvant, can induce significant protection against a chlamydial genital challenge.

Immunogenicity and protective efficacy of three DNA vaccines encoding pre-erythrocytic- and erythrocytic-stage antigens of Plasmodium cynomolgi in rhesus monkeys

Although several malaria vaccine candidate antigens have been identified, the most suitable methods for their delivery are still being investigated. In this regard, direct immunization with DNA encoding these vaccine target antigens is an attractive alternative. Here, we have investigated the immune responses to DNA immunization with three major vaccine target antigens: the apical membrane antigen-1 and the 19-kDa C-terminal fragment of merozoite surface protein-1 from the erythrocytic stage, and the thrombospondin-related adhesive protein from the pre-erythrocytic stage of Plasmodium cynomolgi in rhesus monkeys. Antigen-specific antibodies were developed in all the immunized monkeys and peripheral blood mononuclear cells from all immunized monkeys proliferated to different extents upon in vitro stimulation with the corresponding recombinant proteins. The immunized monkeys were challenged with P. cynomolgi sporozoites. All of the immunized animals developed infection but although there was no significant difference between the control and vaccinated animals in terms of pre-patent period, total duration of patency and primary peak parasitemia, the vaccinated animals had significantly lower secondary peak parasitemia than the control animals.

Safety, tolerability, and lack of antibody responses after administration of a PfCSP DNA malaria vaccine via needle or needle-free jet injection, and comparison of intramuscular and combination intramuscular/intradermal routes

Introduction of a new vaccine requires choosing a delivery system that provides safe administration and the desired level of immunogenicity. The safety, tolerability, and immunogenicity of three monthly 2.5-mg doses of a PfCSP DNA vaccine were evaluated in healthy volunteers as administered intramuscularly (IM) by needle, IM by jet injection (Biojector or IM/intradermally (ID) by jet injection. Vaccine administration was well-tolerated. Adverse events were primarily mild and limited to the site of injection (98%). Jet injections (either IM or ID) were associated with approximately twice as many adverse events per immunization as needle IM, but nevertheless were strongly and consistently preferred in opinion polls taken during the study. No volunteers had clinically significant biochemical or hematologic changes or detectable anti-dsDNA antibodies. In conclusion, the injection of Plasmodium falciparum circumsporozoite (PfCSP) DNA vaccine appeared to be safe and well-tolerated when administered by any of the three modes of delivery. However, despite improved antibody responses following both jet injection and ID delivery in animal models, no antibodies could be detected in volunteers by immunofluorescence antibody test (IFAT) or enzyme-linked immunosorbent assay (ELISA) after DNA vaccination.

A DNA vaccine encoding the 42 kDa C-terminus of merozoite surface protein 1 of Plasmodium falciparum induces antibody, interferon-gamma and cytotoxic T cell responses in rhesus monkeys: immuno-stimulatory effects of granulocyte macrophage-colony stimulating factor

We have constructed a DNA plasmid vaccine encoding the C-terminal 42-kDa region of the merozoite surface protein 1 (pMSP1(42)) from the 3D7 strain of Plasmodium falciparum (Pf3D7). This plasmid expressed recombinant MSP1(42) after in vitro transfection in mouse VM92 cells. Rhesus monkeys immunized with pMSP1(42) produced antibodies reactive with Pf3D7 infected erythrocytes by IFAT, and by ELISA against yeast produced MSP1(19) (yMSP1(19)). Immunization also induced antigen specific T cell responses as measured by interferon-gamma production, and by classical CTL chromium release assays. In addition, immunization with pMSP1(42) primed animals for an enhanced antibody response to a subsequent boost with the recombinant yMSP1(19). We also evaluated Granulocyte-Macrophage Colony-Stimulating Factor (GM-CSF) as an adjuvant for pMSP1(42.) We tested both rhesus GM-CSF expressed from a DNA plasmid, and E. coli produced recombinant human GM-CSF. Plasmids encoding rhesus GM-CSF (prhGM-CSF) and human GM-CSF (phuGM-CSF) were constructed; these plasmids expressed bio-active recombinant GMCSF. Co-immunization with a mixture of prhGM-CSF and pMSP1(42) induced higher specific antibody responses after the first dose of plasmid, but after three doses of DNA monkeys immunized with or without prhGM-CSF had the same final antibody titers and T cell responses. In comparison, rhuGM-CSF protein did not lead to accelerated antibody production after the first DNA dose. However, antibody titers were maintained at a slightly higher level in monkeys receiving GM-CSF protein, and they had a higher response to boosting with recombinant MSP1(19). The GM-CSF plasmid or protein appears to be less potent as an adjuvant in rhesus monkeys than each is in mice, and more work is needed to determine if GM-CSF can be a useful adjuvant in DNA vaccination of primates.

Absence of antigenic competition in Aotus monkeys immunized with Plasmodium falciparum DNA vaccines delivered as a mixture

Aotus lemurinus lemurinus monkeys were immunized four times with one of three DNA plasmids expressing important Plasmodium falciparum blood stage vaccine candidate proteins or with a mixture containing all three vaccines. The three vaccines encoded sequences from apical merozoite antigen-1 (AMA-1), erythrocyte binding protein-175 (EBA-175) and merozoite surface protein-1 (MSP-1). Antigen-specific enzyme-linked immunosorbant assays (ELISAs) showed no significant differences in antibody titer induced to the three antigens by a single vaccine compared with the titer induced to that same antigen by the trivalent preparation. Results of immunofluorescent antibody assays against erythrocytes infected with asexual blood stage P. falciparum indicated that each of the three monovalent vaccines induced significant antibody responses to whole parasites. The trivalent vaccine mixture induced, after four immunizations, an antibody titer to whole parasites that was 3--12-fold higher than those induced by any of the single vaccines. The fourth immunization with the trivalent vaccine increased the mean antibody in IFAT by more than five-fold.

A novel Plasmodium falciparum erythrocyte binding protein-2 (EBP2/BAEBL) involved in erythrocyte receptor binding

The 175-kDa erythrocyte binding protein (EBA-175) of Plasmodium falciparum and Duffy antigen binding proteins of P. vivax and P. knowlesi are members of a protein family. The features of this protein family include a cysteine-rich motif present in the erythrocyte receptor-binding domain. We identify here a novel 140-kDa P. falciparum erythrocyte binding protein (EBP2/BAEBL) containing the signature cysteine-rich motif by comparative analysis of gene sequence information. Polyclonal antibodies generated by immunization with an EBP2/BAEBL DNA vaccine immunoprecipitated a 140-kDa protein from P. falciparum schizont-infected erythrocyte lysates. Similar to EBA-175, the binding of EBP2/BAEBL to human erythrocytes was dependent on sialic acids because neuraminidase treatment of those erythrocytes rendered them incapable of binding, but differed from EBA-175 in that trypsin treatment decreased EBP2/BAEBL binding by only twofold compared to a 10-fold reduction in EBA-175 binding. Antibodies raised against the putative erythrocyte-binding domain of EBP2/BAEBL effectively blocked the binding of native EBP2/BAEBL to erythrocytes. These functional antibodies localize EBP2/BAEBL to the invasive apical end of the merozoite. We identify EBP2/BAEBL as a paralogue of EBA-175 and as a novel P. falciparum vaccine candidate.

The development of a bicistronic plasmid DNA vaccine for B-cell lymphoma

Tumor vaccines are a promising alternative to chemotherapy for the treatment of metastatic cancer. To be effective and safe, a therapeutic cancer vaccine should specifically target antigens expressed only on metastatic tumor cells. A vaccine directed against the unique surface immunoglobulin or idiotype expressed on non-Hodgkin's B-cell lymphoma fulfills these criteria, as both primary and metastatic tumor cells express tumor specific immunoglobulins. Using the murine 38C13 B-cell lymphoma tumor as a model system, a plasmid DNA vaccine was designed to express a bicistronic mRNA encoding both the light and heavy tumor immunoglobulin (idiotype) proteins expressed on the surface of the 38C13 tumor. To increase the immunogenicity of the plasmid DNA vaccine, each of the murine variable domains (light and heavy) were fused to their respective human immunoglobulin constant domains. In addition, a eukaryotic expression cassette was constructed to effect both high-level expression of the mouse/human chimeric immunoglobulin, and to elicit a protective immune response in vivo. Unique Sfi I restriction sites were used for the rapid cloning of any tumor specific immunoglobulin idiotype domains and a series of plasmid constructs were made to test changes to the J domain and/or the human C domain to insert the Sfi I restriction sites. Such changes were found to have significant effects on both expression and immunogenicity. Vaccination of mice with prototype idiotype vaccines was found to generate a protective immune response to the 38C13 tumor. This study indicates that a novel bicistronic plasmid DNA-based vaccine can be used to develop a tumor specific vaccine against B-cell lymphoma.

Codon optimization of gene fragments encoding Plasmodium falciparum merzoite proteins enhances DNA vaccine protein expression and immunogenicity in mice

In contrast to conventional vaccines, DNA and other subunit vaccines exclusively utilize host cell molecules for transcription and translation of proteins. The adenine plus thymine content of Plasmodium falciparum gene sequences (approximately 80%) is much greater than that of Homo sapiens (approximately 59%); consequently, codon usage is markedly different. We hypothesized that modifying codon usage of P. falciparum genes encoded by DNA vaccines from that used by the parasite to those resembling mammalian codon usage would lead to increased P. falciparum protein expression in vitro in mouse cells and increased antibody responses in DNA-vaccinated mice. We synthesized gene fragments encoding the receptor-binding domain of the 175-kDa P. falciparum erythrocyte-binding protein (EBA-175 region II) and the 42-kDa C-terminal processed fragment of the P. falciparum merozoite surface protein 1 (MSP-1(42)) using the most frequently occurring codon in mammals to code for each amino acid, and inserted the synthetic genes in DNA vaccine plasmids. In in vitro transient-expression assays, plasmids containing codon-optimized synthetic gene fragments (pS plasmids) showed greater than fourfold increased protein expression in mouse cells compared to those containing native gene fragments (pN plasmids). In mice immunized with 0.5, 5.0, or 50 microg of the DNA plasmids, the dose of DNA required to induce equivalent antibody titers was 10- to 100-fold lower for pS than for pN plasmids. These data demonstrate that optimizing codon usage in DNA vaccines can improve protein expression and consequently the immunogenicity of gene fragments in DNA vaccines for organisms whose codon usage differs substantially from that of mammals.

Disruption of disulfide linkages of the Plasmodium falciparum circumsporozoite protein: effects on cytotoxic and antibody responses in mice

The circumsporozoite protein is a predominant surface antigen present on Plasmodium sporozoites. In Plasmodium falciparum circumsporozoite protein (PfCSP), two cysteine residues (396 and 401) are present adjacent to two overlapping cytotoxic T-lymphocyte epitopes of the protein and are involved in the formation of disulfide bridges. We investigated the role of these cysteines on the cellular and antibody responses towards the CS protein because disruption of disulfide linkages and the presence of cysteine residues in the flanking region of an epitope has been shown to significantly alter the immune responses to various proteins. Mice were immunized with variant forms of PfCSP DNA vaccine plasmids where these cysteine residues were individually mutated to alanine. The plasmid vaccines induced antigen specific antibody and cytotoxic T lymphocyte responses. While no alterations of cysteine influenced the CTL responses to P. falciparum CS protein, vaccine pVRCS4, containing an altered cysteine at position 401, dramatically improved the antibody response to the carboxyl-terminal region of the protein. This work indicates that sequence alterations of genes in an anti-malarial vaccine could enhance the response towards the native protein. Given the fact that long term natural immunity to the pathogen has not been documented, it may be important to challenge the immune system with non-native proteins.

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.

Safety of a GM-CSF adjuvant-plasmid DNA malaria vaccine

MuStDO 5 is a multivalent plasmid DNA vaccine for malaria comprised of five plasmid DNAs encoding five proteins from Plasmodium falciparum and one plasmid DNA encoding human GM-CSF. To evaluate the safety of MuStDO 5, a series of pre-clinical studies were conducted in mice and rabbits. In pharmacology studies in mice, GM-CSF could not be detected in the serum following either intramuscular or a combined intramuscular/intradermal administration of the vaccine, but was readily detected in the muscle following intramuscular administration. In a tissue distribution study in mice, MuStDO 5 plasmid DNA was detected by PCR initially in highly vascularized tissues, while at later time-points the plasmid DNA was detected primarily at the site(s) of injection. In GLP safety studies in mice and rabbits, repeated intramuscular/intradermal administration of the MuStDO 5 vaccine was found to be safe and well tolerated without any evidence of autoimmune pathology.

In vivo transfection and/or cross-priming of dendritic cells following DNA and adenoviral immunizations for immunotherapy of cancer--changes in peripheral mononuclear subsets and intracellular IL-4 and IFN-gamma lymphokine profile

In order to provoke an immune response, a tumor vaccine should not only maximize antigen-specific signals, but should also provide the necessary "co-stimulatory" environment. One approach is to genetically manipulate tumor cells to either secrete lymphokines (GM-CSF, IL-12, IL-15) or express membrane bound molecules (CD80, CD86). Furthermore, patient dendritic cells can be loaded with tumor-associated antigens or peptides derived from them and used for immunotherapy. Genetic modification of dendritic cells can also lead to presentation of tumor-associated antigens. Transfection of dendritic cells with DNA encoding for such antigens can be done in vitro, but transfection efficiency has been uniformly low. Alternatively, dendritic cells can also be modulated directly in vivo either by "naked" DNA immunization or by injecting replication-deficient viral vectors that carry the tumor specific DNA. Naked DNA immunization offers several potential advantages over viral mediated transduction. Among these are the inexpensive production and the inherent safety of plasmid vectors, as well as the lack of immune responses against the carrier. The use of viral vectors enhances the immunogenicity of the vaccine due to the adjuvant properties of some of the viral products. Recent studies have suggested that the best strategy for achieving an intense immune response may be priming with naked DNA followed by boosting with a viral vector. We have successfully completed a phase I and phase II clinical trials on immunotherapy of prostate cancer using naked DNA and adenoviral immunizations against the prostate-specific membrane antigen (PSMA) and phase I clinical trial on colorectal cancer using naked DNA immunization against the carcinoembryonic antigen (CEA). The vaccination was tolerated well and no side effects have been observed so far. The therapy has proven to be effective in a number of patients treated solely by immunizations. The success of the treatment clearly depends on the stage of the disease proving to be most efficient in patients with minimal disease or no metastases. A panel of changes in the phenotype of peripheral blood lymphocytes and the expression of intra-T-cell lymphokines seems to correlate with clinical improvement.

Immunogenicity and protective efficacy of a Plasmodium yoelii Hsp60 DNA vaccine in BALB/c mice

The gene encoding the 60-kDa heat shock protein of Plasmodium yoelii (PyHsp60) was cloned into the VR1012 and VR1020 mammalian expression vectors. Groups of 10 BALB/c mice were immunized intramuscularly at 0, 3, and 9 weeks with 100 microg of PyHsp60 DNA vaccine alone or in combination with 30 microg of pmurGMCSF. Sera from immunized mice but not from vector control groups recognized P. yoelii sporozoites, liver stages, and infected erythrocytes in an indirect fluorescent antibody test. Two weeks after the last immunization, mice were challenged with 50 P. yoelii sporozoites. In one experiment the vaccine pPyHsp60-VR1012 used in combination with pmurGMCSF gave 40% protection (Fisher's exact test; P = 0.03, vaccinated versus control groups). In a second experiment this vaccine did not protect any of the immunized mice but induced a delay in the onset of parasitemia. In neither experiment was there any evidence of a protective effect against the asexual erythrocytic stage of the life cycle. In a third experiment mice were primed with PyHsp60 DNA, were boosted 2 weeks later with 2 x 10(3) irradiated P. yoelii sporozoites, and were challenged several weeks later. The presence of PyHsp60 in the immunization regimen did not lead to reduced blood-stage infection or development of parasites in hepatocytes. PyHsp60 DNA vaccines were immunogenic in BALB/c mice but did not consistently, completely protect against sporozoite challenge. The observation that in some of the PyHsp60 DNA vaccine-immunized mice there was protection against infection or a delay in the onset of parasitemia after sporozoite challenge deserves further evaluation.

Protection against Pseudomonas aeruginosa chronic lung infection in mice by genetic immunization against outer membrane protein F (OprF) of P. aeruginosa

The Pseudomonas aeruginosa major constitutive outer membrane porin protein OprF, which has previously been shown to be a protective antigen, was targeted as a DNA vaccine candidate. The oprF gene was cloned into plasmid vector pVR1020, and the plasmid vaccines were delivered to mice by biolistic (gene gun) intradermal inoculation. Antibody titers in antisera from immunized mice were determined by enzyme-linked immunosorbent assay, and the elicited antibodies were shown to be specifically reactive to OprF by immunoblotting. The immunoglobulin G (IgG) immune response was predominantly of the IgG1 isotype. Sera from DNA vaccine-immunized mice had significantly greater opsonic activity in opsonophagocytic assays than did sera from control mice. Following the initial immunization and two consecutive boosts, each at 2-week intervals, protection was demonstrated in a mouse model of chronic pulmonary infection by P. aeruginosa. Eight days postchallenge, both lungs were removed and examined. A significant reduction in the presence of severe macroscopic lesions, as well as in the number of bacteria present in the lungs, was seen. Based on these findings, genetic immunization with oprF has potential for development as a vaccine to protect humans against infection by P. aeruginosa.

DNA vaccines expressing a fusion product of outer surface proteins A and C from Borrelia burgdorferi induce protective antibodies suitable for prophylaxis but Not for resolution of Lyme disease

DNA vaccines encoding the outer surface protein A (OspA) of Borrelia burgdorferi have been shown to induce protective humoral responses capable of preventing but not curing infection in mice. Subsequent studies showed that an established infection or disease could be resolved by passive transfer of antibodies to OspC. In the present study, DNA vaccines encoding either the OspC antigen alone or fused to OspA and under the transcriptional control of the human elongation factor 1alpha promoter were evaluated for their protective and/or curative potential. In contrast to ospA-containing plasmids, none of the six constructs with ospC alone were immunogenic in vivo, independent of whether they contained promoter or leader sequences from ospA and/or ospC, or alternatively, the signal sequence of the human tissue plasminogen activator. Solely, a DNA vaccine encoding an OspA-OspC fusion product led to expression of the respective polypeptide chain in transfected cells in vitro and to the induction of OspA- and OspC-specific antibodies in vivo. Immune sera raised against the OspA-OspC fusion product conveyed full protection against subsequent infection, most probably via OspA-specific antibodies, but were unable to resolve infection.

Fasciola: kinetics and quality of humoral responses to fatty acid binding protein and cathepsin l following delivery as DNA vaccines in mice

The humoral response to DNA vaccination of mice with two important Fasciola antigens has been investigated. Both F. gigantica fatty acid binding protein (FABP) and F. hepatica cathepsin L5 (FhCatL5) were shown to be expressed in COS 7 cells and induced a humoral response when delivered as secretory constructs in mice. FABP induced an IgGl dominant response, with significant IgE, IgG2a, and IgG2b responses also present, indicating a mixed Th1/Th2 response. The total Ig response peaked at 1:24,500 and antibody titers were sustained for at least 32 weeks. In contrast, the delivery of FABP as a nonsecreted construct did not result in the induction of a measurable humoral response. FhCatL5 was delivered as a secretory construct, with secretion mediated by the native F. hepatica signal sequence, which was shown to operate in COS 7 cells. The humoral response peaked at 1:2000 at week 8 and was sustained for at least 20 weeks. Antibody isotype analysis demonstrated a Th2-like response, which was qualitatively different from that obtained for FABP with an IgE dominant response, and lower titers to IgG1 and IgG3. The results demonstrate that Fasciola antigens can be delivered as DNA vaccines, but that the quality of the response varies between antigens and is influenced by the method of vaccine delivery.

ELISPOT assay for detection of peptide specific interferon-gamma secreting cells in rhesus macaques

A reliable procedure to measure antigen specific T cell responses in rhesus macaques is required to determine the efficacy of vaccines and immunotherapies. The currently available T cell assays are poorly quantifiable or technically difficult to perform. Classical 51Cr-release cytotoxic T cell (CTL) assays are cumbersome and difficult to quantitate reproducibly. Detection of specific T-cell using MHC-peptide tetrameric complexes is highly sensitive, but requires knowledge of MHC type and prior identification of T cell epitopes. We therefore developed a rhesus interferon-gamma (IFN-gamma) ELISPOT assay capable of detecting IFN-gamma secretion in response to stimulation with pooled 20-mer peptides. Peripheral blood mononuclear cells (PBMCs) from rhesus monkeys immunized with a DNA vaccine and recombinant canary pox encoding the Plasmodium knowlesi circumsporozoite protein (PkCSP) were incubated with pools of peptides from PkCSP. Positive responses to peptide pools and individual peptides ranging from 100 to 450 spot forming cells (SFC)/10(6) PBMC were detected in four of four immunized monkeys and in zero of two control monkeys. In two monkeys studied in detail, the IFN-gamma response was focussed on a single 20-mer peptide, QGDGANAGQPQAQGDGANAG, and was dependent on CD4(+), but not CD8(+), T cells. Background responses in control monkeys and preimmunization PBMCs ranged from 10 to 50 SFC/10(6) PBMC. The average within assay and between assay coefficients of variation (CV) for this peptide ELISPOT were 21.9 and 24.7%, respectively. This peptide IFN-gamma assay will be a useful tool for evaluation of T cell responses in rhesus macaques.