A human immunodeficiency virus 1 (HIV-1) clade A vaccine in clinical trials: stimulation of HIV-specific T-cell responses by DNA and recombinant modified vaccinia virus Ankara (MVA) vaccines in humans

Deep analysis of cellular transcriptomes - LongSAGE versus classic MPSS

BACKGROUND

Deep transcriptome analysis will underpin a large fraction of post-genomic biology. 'Closed' technologies, such as microarray analysis, only detect the set of transcripts chosen for analysis, whereas 'open' e.g. tag-based technologies are capable of identifying all possible transcripts, including those that were previously uncharacterized. Although new technologies are now emerging, at present the major resources for open-type analysis are the many publicly available SAGE (serial analysis of gene expression) and MPSS (massively parallel signature sequencing) libraries. These technologies have never been compared for their utility in the context of deep transcriptome mining.

RESULTS

We used a single LongSAGE library of 503,431 tags and a "classic" MPSS library of 1,744,173 tags, both prepared from the same T cell-derived RNA sample, to compare the ability of each method to probe, at considerable depth, a human cellular transcriptome. We show that even though LongSAGE is more error-prone than MPSS, our LongSAGE library nevertheless generated 6.3-fold more genome-matching (and therefore likely error-free) tags than the MPSS library. An analysis of a set of 8,132 known genes detectable by both methods, and for which there is no ambiguity about tag matching, shows that MPSS detects only half (54%) the number of transcripts identified by SAGE (3,617 versus 1,955). Analysis of two additional MPSS libraries shows that each library samples a different subset of transcripts, and that in combination the three MPSS libraries (4,274,992 tags in total) still only detect 73% of the genes identified in our test set using SAGE. The fraction of transcripts detected by MPSS is likely to be even lower for uncharacterized transcripts, which tend to be more weakly expressed. The source of the loss of complexity in MPSS libraries compared to SAGE is unclear, but its effects become more severe with each sequencing cycle (i.e. as MPSS tag length increases).

CONCLUSION

We show that MPSS libraries are significantly less complex than much smaller SAGE libraries, revealing a serious bias in the generation of MPSS data unlikely to have been circumvented by later technological improvements. Our results emphasize the need for the rigorous testing of new expression profiling technologies.

Induction of HIV-specific functional immune responses by a multiclade HIV-1 DNA vaccine candidate in healthy Ugandans

A phase I randomized, double blind, placebo-controlled trial to assess the immunogenicity of a multiclade HIV-1 DNA plasmid vaccine was conducted in 31 HIV-1-negative Ugandans. Following immunization with DNA at 0, 1, and 2 months, the frequency of HIV-specific immune responses was assessed up to 10 months using a standard chromium release assay (CRA), lymphoproliferative assay (LPA), and antibody dependent cell-mediated cytotoxicity assay (ADCC). Seven of 15 (47%) vaccinees demonstrated CTL activity using the CRA to HIV-1 Env B with responses observed 1 month following the second vaccination and as late as 7 months following complete immunization. Additionally, lymphoproliferative reponses were observed in 14/15 vaccinees against p24. No CTL or LPA responses were observed at baseline or in the placebo group. ADCC activity was minimally induced by DNA vaccination. This study demonstrates that immunization with DNA alone induces CTL and lymphoproliferative responses in a population that will participate in a phase IIb study evaluating HIV-1 DNA priming followed by boosting with a replication-defective recombinant adenovirus vector.

A New Multi-clade DNA Prime/Recombinant MVA Boost Vaccine Induces Broad and High Levels of HIV-1-specific CD8+ T-cell and Humoral Responses in Mice

The results presented here are from the preclinical evaluation in BALB/c mice of a DNA prime/modified vaccinia virus Ankara (MVA) boost multi-gene multi-subtype human immunodeficiency virus-1 (HIV-1) vaccine intended for use in humans. The plasmid DNA vaccine was delivered intradermally using a Biojector, and the MVA was delivered intramuscularly by needle. This combination of recombinant DNA and MVA proved to induce extraordinarily strong cellular responses, with more than 80% of the CD8(+) T cells specific for HIV-1 antigens. Furthermore, we show that the DNA priming increases the number of T-cell epitopes recognized after the MVA boost. In the prime/boost-immunized animals, a significant proportion of CD8(+) T cells were stained positive for both interferon-gamma (IFN-gamma) and interleukin-2 (IL-2), a feature that has been associated with control of HIV-1 infection in long-term non-progressors. The HIV-1-specific antibody levels were moderate after the plasmid DNA immunizations but increased dramatically after the MVA boost. Although the initial injection of MVA induced significant levels of vaccinia-neutralizing antibodies, the HIV-specific responses were still significantly boosted by the second MVA immunization. The results from this study demonstrate the potency of this combination of DNA plasmids and MVA construct to induce broad and high levels of immune responses against several HIV-1 proteins of different subtypes.

Safety and immunogenicity of tyrosinase DNA vaccines in patients with melanoma

Immunity to self antigens on cancer is constrained by tolerance/ignorance. DNA vaccines encoding xenogeneic differentiation antigens, such as tyrosinase (TYR), mediate tumor protection and regression in implantable mouse models, and dogs with spontaneous melanoma. We conducted a trial of mouse and human TYR DNA vaccines in stage III/IV melanoma patients. Eighteen human leukocyte antigen (HLA)-A*0201(+) melanoma patients were randomized as follows: one group received three mouse TYR DNA injections followed by three human TYR DNA injections; the other group received the same vaccines in opposite sequence. The study was conducted at three dose levels: 100, 500, and 1,500 microg DNA/injection, administered intramuscularly (IM) every 3 weeks. Most toxicities were grade 1 injection site reactions. Seven patients developed CD8(+) T-cell responses, defined by a >3 SD increase in baseline reactivity to TYR peptide in tetramer or intracellular cytokine staining (ICS) assays. There was found to be no relationship between dose, assigned schedule, and T-cell response. At a median of 42 months follow-up, median survival has not been reached. Mouse and human TYR DNA vaccines were found safe and induced CD8(+) T-cell responses in 7 of 18 patients. T cells recognizing a native TYR peptide had a phenotype consistent with that of effector memory cells.

Broad TCR usage in functional HIV-1-specific CD8+ T cell expansions driven by vaccination during highly active antiretroviral therapy

During chronic HIV-1 infection, continuing viral replication is associated with impaired proliferative capacity of virus-specific CD8+ T cells and with the expansion and persistence of oligoclonal T cell populations. TCR usage may significantly influence CD8+ T cell-mediated control of AIDS viruses; however, the potential to modulate the repertoire of functional virus-specific T cells by immunotherapy has not been explored. To investigate this, we analyzed the TCR Vbeta usage of CD8+ T cells populations which were expanded following vaccination with modified vaccinia virus Ankara expressing a HIV-1 gag/multiepitope immunogen (MVA.HIVA) in HIV-1-infected patients receiving highly active antiretroviral therapy. Vaccinations induced the re-expansion of HIV-1-specific CD8+ T cells and these showed broad TCR Vbeta usage which was maintained for at least 1 year in some individuals. By contrast, virus-specific CD8+ T cell populations in the same donors which failed to expand after vaccination and in unvaccinated controls were oligoclonal. Simultaneously, we observed that CD8+ T cells recognizing vaccine-derived HIV-1 epitopes displayed enhanced capacity to proliferate and to inhibit HIV-1 replication in vitro, following MVA.HIVA immunizations. Taken together, these data indicate that an attenuated viral-vectored vaccine can modulate adaptive CD8+ T cell responses to HIV-1 and improve their antiviral functional capacity. The potential therapeutic benefit of this vaccination approach warrants further investigation.

HIV-1(89.6) Gag expressed from a replication competent HSV-1 vector elicits persistent cellular immune responses in mice

We have constructed a replication competent, gamma(1)34.5-deleted herpes simplex virus type-1 (HSV-1) vector (J200) that expresses the gag gene from human immunodeficiency virus type-1, primary isolate 89.6 (HIV-1(89.6)), as a candidate vaccine for HIV-1. J200 replicates in vitro, resulting in abundant Gag protein production and accumulation in the extracellular media. Immunization of Balb/c mice with a single intraperitoneal injection of J200 elicited strong Gag-specific CD8 responses, as measured by intracellular IFN-gamma staining and flow cytometry analysis. Responses were highest between 6 weeks and 4 months, but persisted at 9 months post-immunization, the last time-point evaluated. These data highlight the potential utility of neuroattenuated, replication competent HSV-1 vectors for delivery of HIV-1 immunogens.

Immunization of mice with the nef gene from Human Immunodeficiency Virus type 1: study of immunological memory and long-term toxicology

Background

The human immunodeficiency virus type 1 (HIV-1) regulatory protein, Nef, is an attractive vaccine target because it is involved in viral pathogenesis, is expressed early in the viral life cycle and harbors many T and B cell epitopes. Several clinical trials include gene-based vaccines encoding this protein. However, Nef has been shown to transform certain cell types in vitro. Based on these findings we performed a long-term toxicity and immunogenicity study of Nef, encoded either by Modified Vaccinia virus Ankara or by plasmid DNA. BALB/c mice were primed twice with either DNA or MVA encoding Nef and received a homologous or heterologous boost ten months later. In the meantime, the Nef-specific immune responses were monitored and at the time of sacrifice an extensive toxicological evaluation was performed, where presence of tumors and other pathological changes were assessed.

Results

The toxicological evaluation showed that immunization with MVAnef is safe and does not cause cellular transformation or other toxicity in somatic organs.

Both DNAnef and MVAnef immunized animals developed potent Nef-specific cellular responses that declined to undetectable levels over time, and could readily be boosted after almost one year. This is of particular interest since it shows that plasmid DNA vaccine can also be used as a potent late booster of primed immune responses. We observed qualitative differences between the T cell responses induced by the two different vectors: DNA-encoded nef induced long-lasting CD8⁺ T cell memory responses, whereas MVA-encoded nef induced CD4⁺ T cell memory responses. In terms of the humoral immune responses, we show that two injections of MVAnef induce significant anti-Nef titers, while repeated injections of DNAnef do not. A single boost with MVAnef could enhance the antibody response following DNAnef prime to the same level as that observed in animals immunized repeatedly with MVAnef. We also demonstrate the possibility to boost HIV-1 Nef-specific immune responses using the MVAnef construct despite the presence of potent anti-vector immunity.

Conclusion

This study shows that the nef gene vectored by MVA does not induce malignancies or other adverse effects in mice. Further, we show that when the nef gene is delivered by plasmid or by a viral vector, it elicits potent and long-lasting immune responses and that these responses can be directed towards a CD4⁺ or a CD8⁺ T cell response depending on the choice of vector.

Production of clinical-grade plasmid DNA for human Phase I clinical trials and large animal clinical studies

The use of plasmid DNA as vaccines for the treatment of cancer and infectious diseases is on the rise. In order to facilitate the manufacture of clinical-grade plasmid DNA for Phase I clinical trials, we developed a process whereby >200 mg plasmid could be produced in a single production run under Good Manufacturing Practices. A dedicated cleanroom (Class 10,000 with Class 100 biosafety cabinet) is utilized for production of the bacterial cell bank, fermentation, harvest/lysis of the biomass, and downstream purification. Fermentation requires three 16-18 h runs (approximately 12 L each) in shaker-flasks, yielding approximately 60 g bacterial paste following batch centrifugation. The biomass is alkaline-lysed, pooled, and the resulting flocculent precipitate is separated by a novel vacuum step, followed by depth-filtration. Downstream processing includes anion-exchange chromatography, utilizing Qiagen silica-based resin, and precipitation with isopropanol. Following precipitation, the DNA is harvested by centrifugation, dried, formulated, and sterile-filtered using a Sartorius Sartobran 150 filter prior to Final-Filling. All processing steps utilize sterilized, single-use components. This process results in a product manufactured according to regulatory guidelines. The plasmid DNA is sterile with >or=95% supercoiled DNA, an A260/A280 ratio>or=1.9, undetectable or extremely low residual endotoxin, RNA, genomic DNA, protein, and antibiotic. Residual solvent levels are negligible. The product yields the predicted profile upon restriction-enzyme digestion, is biologically active upon transfection and remains stable for several years at -20 degrees C. We have therefore developed a reproducible and cost effective process to manufacture clinical-grade plasmid DNA. This process can be adapted by other academic centers for human or large animal clinical trials.

Recombinant murine gammaherpesvirus 68 (MHV-68) as challenge virus to test efficacy of vaccination against chronic virus infections in the mouse model

Efficient vaccines against AIDS, Hepatitis C and other persistent virus infections are urgently needed. Vaccine development has been especially hampered by the lack of suitable small animal models to reliably test the protective capacity of candidate vaccines against such chronic viral infections. A natural mouse pathogen such as MHV-68 that persists lifelong after infection, appears to be a particularly promising candidate for a more relevant model system. Here, we investigated infections with recombinant MHV-68 as novel mouse challenge model to test the efficacy of heterologous vaccines based on recombinant modified vaccinia virus Ankara (MVA). To apply ovalbumin (OVA) as a model antigen, we constructed the recombinant virus MHV-68-OVA by BAC technology and characterized genetic stability and replicative capacity of the virus in vitro and in vivo. We demonstrated the ability of MHV-68-OVA to produce ovalbumin upon tissue culture infection. Moreover, the use of MHV-68-OVA-infected target cells allowed for efficient ex vivo amplification of OVA-specific, MHC class I-restricted CD8 T cells derived from MVA-OVA-vaccinated C57BL/6 mice. Finally, we immunized C57BL/6 mice with MVA-OVA and challenged the animals with MHV-68-OVA testing different time points and routes of infection. Vaccinated mice were infected with MHV-68-OVA but showed reduced viral loads in the acute and latent phase of challenge infection. These data strongly suggest the usefulness of the MHV-68 challenge model for further evaluation of recombinant vaccines against persisting virus infections.

The attenuation of vaccinia Tian Tan strain by the removal of the viral M1L-K2L genes

To generate a safe vaccinia Tian Tan (VTT)-based vaccine vector, it is necessary to develop a method to attenuate the virus. A modified VTT (MVTT(2-GFP)) was constructed by replacing the viral M1L-K2L genes with a GFP gene. In comparison to the parental VTT, MVTT(2-GFP) lost its replication capacity in rabbit RK13 and human HeLa cell lines. The life cycle of viral replication was blocked at different stages in these two cell lines as determined by electron microscope examination. MVTT(2-GFP) was less virulent than VTT for 100-fold by measuring mouse body weight loss after intranasal viral inoculation and for 340-fold by determining the intracranial LD(50) value in mice. The foreign GFP gene was stable genetically after 10 rounds of passage in Vero cells. Importantly, MVTT(2-GFP) elicited both humoral and cell-mediated immune responses to the GFP gene in mice. With two intramuscular inoculations of 10(5)PFU virus, the anti-GFP antibody reciprocal endpoint titer reached over 700 as determined by an ELISA. The number of IFN-gamma secreting T cells reached over 350SFU per million splenocytes against a CD8+ T cell-specific epitope of GFP. Collectively, the removal of the M1L-K2L genes is a useful method to generate an attenuated vaccinia Tian Tan vaccine vector.

Combined single-clade candidate HIV-1 vaccines induce T cell responses limited by multiple forms of in vivo immune interference

We assessed in mice whether broad CD8+ T cell responses capable of efficient recognition of multiple HIV-1 clades could be induced using current single-clade vaccine constructs that were or will be used in clinical trials in Europe and Africa. We found that single-clade A, B and C vaccines applied alone induced only limited cross-clade reactivity and that the epitope hierarchy varied according to the immunizing clade. However, combining single-clade HIV-1 vaccines into multi-clade formulations resulted in multiple forms of in vivo immune interference such as original antigenic sin and antagonism, which dampened or even abrogated induction of responses to epitope variants and reduced the breadth of induced T cell responses. Simultaneous administration of individual clade-specific vaccines into anatomically separated sites on the body alleviated antagonism and increased the number of detectable epitope responses. Although cross-reactivity of murine CD8+ T cells does not directly translate to humans, the molecular interactions involved in triggering T cell responses are the same in mouse and man. Thus, these results have important ramifications for the design of both prophylactic and therapeutic vaccines against HIV-1 and other highly variable pathogens.

Establishing acceptance criteria for cell-mediated-immunity assays using frozen peripheral blood mononuclear cells stored under optimal and suboptimal conditions

The enzyme-linked immunospot (ELISPOT) assay is a powerful tool for measuring antigen-specific cellular immune responses. The ability to use frozen peripheral blood mononuclear cells (PBMC) facilitates testing samples in multicenter clinical trials; however, unreliable ELISPOT responses may result if samples are not handled properly. Exposure of frozen PBMC to suboptimal storage temperature (-20 degrees C) or repeated cycling between more optimal storage temperatures (less than -130 degrees C and -70 degrees C) reduced the quality of frozen PBMC, as assessed by cell viability and functional ELISPOT response measures. Cell viability as assessed by trypan blue dye exclusion was reduced, and the percentage of apoptotic cells, as determined by the Guava Nexin assay, was significantly increased after these events. The functional gamma interferon ELISPOT responses to phytohemagglutinin (PHA) mitogen, a CD4 T-cell-specific antigen (varicella-zoster virus), and a CD8 T-cell-specific antigen (pool containing known cytomegalovirus, Epstein-Barr virus, and influenza virus peptides) were all significantly reduced after suboptimal storage events. However, for a given suboptimal storage event, the magnitude of the reduction varied between individuals and even among aliquots within an individual bleed, indicating the need for sample-specific acceptance criteria (AC). The percent viable or percent apoptotic cells after thaw, as well as the functional ELISPOT response to PHA, were all effective when applied with limits as AC for separating samples damaged during storage from valid control samples. Although all three AC measures could be effectively applied, the apoptosis AC limit applied was best for separating samples that could respond to antigenic stimulation from samples that could not effectively respond.

Problems and emerging approaches in HIV/AIDS vaccine development

According to recent estimates, 39.5 million people have been infected with HIV and 2.9 million have already died. The effect of HIV infection on individuals and communities is socially and economically devastating. Although antiretroviral drugs have had a dramatically beneficial impact on HIV-infected individuals who have access to treatment, it has had a negligible impact on the global epidemic. Therefore, the need for an efficacious HIV/AIDS vaccine remains the highest priority of the world HIV/AIDS agenda. The generation of a vaccine against HIV/AIDS has turned out to be extremely challenging, as indicated by > 20 years of unsuccessful attempts. This review discusses the major challenges in the field and key experimental evidence providing a rationale for the use of non-structural HIV proteins, such as Rev, Tat and Nef, either in the native form or expressed by viral vectors such as a replicating adeno-vector. These non-structural proteins alone or in combination with modified structural HIV-1 Env proteins represent a novel strategy for both preventative and therapeutic HIV/AIDS vaccine development.

In vivo effects of vaccination with six-transmembrane epithelial antigen of the prostate: a candidate antigen for treating prostate cancer

Immunotherapy may provide an alternative treatment for cancer patients, especially when tumors overexpress antigens that can be recognized by immune cells. The identification of markers and therapeutic targets that are up-regulated in prostate cancer has been important to design new potential treatments for prostate cancer. Among them, the recently identified six-transmembrane epithelial antigen of the prostate (STEAP) is considered attractive due to its overexpression in human prostate cancer tissues. Our study constitutes the first assessment of the in vivo effectiveness of STEAP-based vaccination in prophylactic and therapeutic mouse models. Two delivery systems, cDNA delivered by gene gun and Venezuelan equine encephalitis virus-like replicon particles (VRP), both encoding mouse STEAP (mSTEAP) and three vaccination strategies were used. Our results show that mSTEAP-based vaccination was able to induce a specific CD8 T-cell response against a newly defined mSTEAP epitope that prolonged the overall survival rate in tumor-challenged mice very significantly. This was achieved without any development of autoimmunity. Surprisingly, CD4 T cells that produced IFNgamma, tumor necrosis factor-alpha (TNF-alpha), and interleukin-2 (IL-2) played the main role in tumor rejection in our model as shown by using CD4- and CD8-deficient mice. In addition, the presence of high IL-12 levels in the tumor environment was associated with a favorable antitumor response. Finally, the therapeutic effect of STEAP vaccination was also assessed and induced a modest but significant delay in growth of established, 31 day old tumors. Taken together, our data suggest that vaccination against mSTEAP is a viable option to delay tumor growth.

Clinical experience with plasmid DNA- and modified vaccinia virus Ankara-vectored human immunodeficiency virus type 1 clade A vaccine focusing on T-cell induction

Candidate human immunodeficiency virus type 1 (HIV-1) vaccines focusing on T-cell induction, constructed as pTHr.HIVA DNA and modified vaccinia virus Ankara (MVA).HIVA, were delivered in a heterologous prime-boost regimen. The vaccines were tested in several hundred healthy or HIV-1-infected volunteers in Europe and Africa. Whilst larger trials of hundreds of volunteers suggested induction of HIV-1-specific T-cell responses in <15 % of healthy vaccinees, a series of small, rapid trials in 12-24 volunteers at a time with a more in-depth analysis of vaccine-elicited T-cell responses proved to be highly informative and provided more encouraging results. These trials demonstrated that the pTHr.HIVA vaccine alone primed consistently weak and mainly CD4(+), but also CD8(+) T-cell responses, and the MVA.HIVA vaccine delivered a consistent boost to both CD4(+) and CD8(+) T cells, which was particularly strong in HIV-1-infected patients. Thus, whilst the search is on for ways to enhance T-cell priming, MVA is a useful boosting vector for human subunit genetic vaccines.

Mucosal HIV-1 Pox Virus Prime-Boost Immunization Induces High-Avidity CD8+ T Cells with Regime-Dependent Cytokine/Granzyme B Profiles

The quality of virus-specific CD8(+) CTL immune responses generated by mucosal and systemic poxvirus prime-boost vaccines were evaluated in terms of T cell avidity and single-cell analysis of effector gene expression. Intranasal (I.N.) immunization regimes generated higher avidity CTL responses specific for HIV K(d)Gag(197-205) (amino acid sequence AMQMLKETI; H-2K(d) binding) compared with i.m. immunization regime. Single-cell RT-PCR of K(d)Gag(197-205)-specific mucosal and systemic CTL revealed that the cytokine and granzyme B expression profiles were dependent on both the route and time after immunization. The I.N./i.m.-immunized group elicited elevated number of CTL-expressing granzyme B mRNA from the genitomucosal sites compared with the i.m./i.m. regime. Interestingly, CTL generated after both I.N. or i.m. immunization demonstrated expression of Th2 cytokine IL-4 mRNA that was constitutively expressed over time, although lower numbers were observed after I.N./I.N. immunization. Results suggest that after immunization, Ag-specific CTL expression of IL-4 may be an inherent property of the highly evolved poxvirus vectors. Current observations indicate that the quality of CTL immunity generated after immunization can be influenced by the inherent property of vaccine vectors and route of vaccine delivery. A greater understanding of these factors will be crucial for the development of effective vaccines in the future.

Virus-like particles: designing an effective AIDS vaccine

Viruses that infect eukaryotic organisms have the unique characteristic of self-assembling into particles. The mammalian immune system is highly attuned to recognizing and attacking these viral particles following infection. The use of particle-based immunogens, often delivered as live-attenuated viruses, has been an effective vaccination strategy for a variety of viruses. The development of an effective vaccine against the human immunodeficiency virus (HIV) has proven to be a challenge, since HIV infects cells of the immune system causing severe immunodeficiency resulting in the syndrome known as AIDS. In addition, the ability of the virus to adapt to immune pressure and reside in an integrated form in host cells presents hurdles for vaccinologists to overcome. A particle-based vaccine strategy has promise for eliciting high titer, long-lived, immune responses to a diverse number of viral epitopes against different HIV antigens. Live-attenuated viruses are effective at generating both cellular and humoral immune responses. However, while these vaccines stimulate immunity, challenged animals rarely clear the viral infection and the degree of attenuation directly correlates with protection from disease. Further, a live-attenuated vaccine has the potential to revert to a pathogenic form. Alternatively, virus-like particles (VLPs) mimic the viral particle without causing an immunodeficiency disease. VLPs are self-assembling, non-replicating, non-pathogenic particles that are similar in size and conformation to intact virions. A variety of VLPs for lentiviruses are currently in preclinical and clinical trials. This review focuses on our current status of VLP-based AIDS vaccines, regarding issues of purification and immune design for animal and clinical trials.

Dynamic binding capacity of plasmid DNA in histidine–agarose chromatography

The use of histidine-agarose chromatography in the purification of supercoiled (sc) plasmid DNA (pDNA) from Escherichia coli lysates has been reported recently. In the current work we describe a set of breakthrough experiments which were designed to study the effect of parameters such as flow-rate, temperature, concentration and conformation on the dynamic binding capacity of pDNA to the histidine support. One of the most striking results shows that the dynamic binding capacity for sc pDNA decreases linearly from 250.8 to 192.0 microg sc pDNA/mL when the temperature is varied from 5 to 24 degrees C. This behaviour was attributed to temperature-induced, pre-denaturation conformational changes which promote the removal of negative superhelical turns in sc pDNA molecules and decrease the interaction of DNA bases with the histidine ligands. The capacity for sc pDNA was highly improved when using feeds with higher pDNA concentrations, a phenomenon which was attributed to the fact that pDNA molecules in more concentrated solutions are significantly compressed. A maximum capacity of 530.0 microg pDNA/mL gel was obtained when using a 125 microg/mL pDNA feed at 1 mL/min and 5 degrees C, a figure which is comparable to the plasmid capacity values published for other chromatographic supports. Finally, a more than 2-fold increase in capacity was obtained when changing from open circular to sc pDNA solutions. Overall, the results obtained provide valuable information for the future development and implementation of histidine chromatography in the process scale purification of pDNA.

Vaccine-delivered HIV envelope inhibits CD4(+) T-cell activation, a mechanism for poor HIV vaccine responses

The human immunodeficiency virus (HIV) causes impairment of the immune system in part by targeting CD4(+) T cells for infection and dysfunction. HIV envelope (Env) present on free virions and infected cells causes dysfunction of uninfected bystander CD4(+) T cells via interaction with both CD4 and coreceptors. Env is commonly used as part of a cocktail of HIV antigens in current vaccines. In DNA and viral vector vaccine approaches, antigen-presenting cells (APCs) and non-APCs in the vicinity of the vaccine delivery site and draining lymph node express vaccine-derived antigens. The studies here demonstrate that cell-surface expression of Env on APCs and non-APCs as part of the vaccine action causes an inhibition of antigen-induced CD4(+) T-cell activation and proliferation mediated by CD4 binding and suggests a potential mechanism for reduced activity of Env-containing HIV vaccines. Similar studies using a functional Env lacking CD4 binding circumvented suppression, suggesting an alternative and potentially superior approach to HIV vaccine design.

Immunisation with recombinant modified vaccinia virus Ankara expressing HIV-1 gag in HIV-1-infected subjects stimulates broad functional CD4+ T cell responses

Virus-specific CD4+ T cells with IL-2-secreting and/or proliferative capacity are detected readily in HIV-1-infected long-term nonprogressors and rarely in persons with untreated progressive infection. The contribution of these cells to viraemia control is uncertain, but this question might be addressed in clinical therapeutic vaccination studies. However, the quality of T helper responses induced by currently available HIV-1 vaccine candidates has not been explored in depth. We determined the effect of vaccination with modified vaccinia virus Ankara (MVA) expressing HIV-1 gag p24/p17 (MVA.HIVA) on HIV-1-specific CD4+ T cell responses in 16 chronically infected, highly active antiretroviral therapy (HAART)-treated subjects using CD8-depleted IFN-gamma ELISPOT assays, intracellular cytokine staining assays for IL-2 and IFN-gamma, and a CFSE-based proliferation assay. Gag-specific CD4+ T cell responses were significantly increased in magnitude and breadth after vaccination and targeted both known and new epitopes, several of which were also recognised by healthy HIV-uninfected volunteers immunised with the same vaccines. The frequencies of CD4+ T cells expressing IL-2 or IFN-gamma, alone or simultaneously, were also augmented. These findings indicate that functional virus-specific T helper cells can be boosted by vaccination in chronic HIV-1 infection. Further evaluation of their role in viraemia control is warranted.

Studies of a prophylactic HIV-1 vaccine candidate based on modified vaccinia virus Ankara (MVA) with and without DNA priming: effects of dosage and route on safety and immunogenicity

BACKGROUND

Two parallel studies evaluated safety and immunogenicity of a prophylactic HIV-1 vaccine in 192 HIV-seronegative, low-risk volunteers. Modified vaccinia virus Ankara (MVA) and plasmid DNA (pTHr) expressed HIV-1 clade A gag p24 and p17 fused to a string of 25 overlapping CD8+ T cell epitopes (HIVA).

METHODS

These studies compared intramuscular, subcutaneous, and intradermal MVA at dosage levels ranging from 5x10(6)-2.5x10(8) pfu. In Study IAVI-010, DNA vaccine was given as a prime at months 0 and 1, followed by MVA as a boost at months 5 and 8. In Study IAVI-011, MVA alone was given at months 0 and 2. Regular safety monitoring was performed. Immunogenicity was measured by the interferon (IFN)-gamma ELISPOT assay on peripheral blood mononuclear cells (PBMC).

RESULTS

No serious adverse events were attributed to either vaccine; most adverse events were mild or moderate, although MVA resulted in some severe local reactions. Five vaccine recipients had at least one positive IFN-gamma ELISPOT response, but none were sustained.

CONCLUSION

This HIV-1 vaccine candidate was in general safe and well-tolerated. Local reactions were common, but tolerable. Detectable immune responses were infrequent.

Development of safer pertussis DNA vaccine expressing non-toxic C180 polypeptide of pertussis toxin S1 subunit

A toxic N-terminal 180-amino-acid fragment (C180) of pertussis toxin S1 subunit has the most potent ability to induce protective immunity against pertussis toxin (PT) following DNA-based immunization [Kamachi K, Arakawa Y. Infect Immun 2004;72:4293-6]. For the development of a safer pertussis DNA vaccine, three plasmids encoding mutant C180 (C180-R9K, C180-E129G and C180-R9K/E129G) were constructed and tested for their protective immunogenicity and cytotoxicity. All of the gene gun delivery of the plasmid, performed by inserting the mutant C180 gene into a mammalian expression vector pcDNA3.1, successfully induced anti-PT IgG antibody production without the loss of immunogenicity in mice. The immunizations of mice with the plasmids significantly inhibited leukocytosis-promoting activity by PT. Among stably transfected Chinese hamster ovary (CHO) cells expressing mutant C180, the expression of C180-R9K and C180-R9K/E129G was non-toxic to the transfectants, confirming that these mutant C180s have no cytotoxicity to mammalian cells. These results indicate that C180-R9K and C180-R9K/E129G genes, especially C180-R9K/E129G, are candidates for safe and effective antigen DNAs in the development of pertussis DNA vaccine.

Differences and similarities in viral life cycle progression and host cell physiology after infection of human dendritic cells with modified vaccinia virus Ankara and vaccinia virus

Modified vaccinia virus Ankara (MVA) is an attenuated strain of vaccinia virus (VV) that has attracted significant attention as a candidate viral vector vaccine for immunization against infectious diseases and treatment of malignancies. Although MVA is unable to replicate in most nonavian cells, vaccination with MVA elicits immune responses that approximate those seen after the administration of replication-competent strains of VV. However, the mechanisms by which these viruses elicit immune responses and the determinants of their relative immunogenicity are incompletely understood. Studying the interactions of VV and MVA with cells of the human immune system may elucidate these mechanisms, as well as provide a rational basis for the further enhancement of the immunogenicity of recombinant MVA vectors. Toward this end, we investigated the consequences of MVA or VV infection of human dendritic cells (DCs), key professional antigen-presenting cells essential for the generation of immune responses. We determined that a block to the formation of intracellular viral replication centers results in abortive infection of DCs with both VV and MVA. MVA inhibited cellular protein synthesis more rapidly than VV and displayed a distinct pattern of viral protein expression in infected DCs. MVA also induced apoptosis in DCs more rapidly than VV, and DC apoptosis after MVA infection was associated with an accelerated decline in the levels of intracellular Bcl-2 and Bcl-X(L). These findings suggest that antigen presentation pathways may contribute differentially to the immunogenicity of VV and MVA and that targeted modifications of virus-induced DC apoptosis may further increase the immunogenicity of MVA-vectored vaccines.

Expression of CCL20 and granulocyte-macrophage colony-stimulating factor, but not Flt3-L, from modified vaccinia virus ankara enhances antiviral cellular and humoral immune responses

While modified vaccinia virus Ankara (MVA) is currently in clinical development as a safe vaccine against smallpox and heterologous infectious diseases, its immunogenicity is likely limited due to the inability of the virus to replicate productively in mammalian hosts. In light of recent data demonstrating that vaccinia viruses, including MVA, preferentially infect antigen-presenting cells (APCs) that play crucial roles in generating antiviral immunity, we hypothesized that expression of specific cytokines and chemokines that mediate APC recruitment and activation from recombinant MVA (rMVA) vectors would enhance the immunogenicity of these vectors. To test this hypothesis, we generated rMVAs that express murine granulocyte-macrophage colony-stimulating factor (mGM-CSF), human CCL20/human macrophage inflammatory protein 3alpha (hCCL20/hMIP-3alpha), or human fms-like tyrosine kinase 3 ligand (hFlt3-L), factors predicted to increase levels of dendritic cells (DCs), to recruit DCs to sites of immunization, or to promote maturation of DCs in vivo, respectively. These rMVAs also coexpress the well-characterized, immunodominant lymphocytic choriomeningitis virus nucleoprotein (NP) antigen that enabled sensitive and quantitative assessment of antigen-specific CD8(+) T-cell responses following immunization of BALB/c mice. Our results demonstrate that immunization of mice with rMVAs expressing mGM-CSF or hCCL20, but not hFlt3-L, results in two- to fourfold increases of cellular immune responses directed against vector-encoded antigens and 6- to 17-fold enhancements of MVA-specific antibody titers, compared to those responses elicited by nonadjuvanted rMVA. Of note, cytokine augmentation of cellular immune responses occurs when rMVAs are given as primary immunizations but not when they are used as booster immunizations, suggesting that these APC-modulating proteins, when used as poxvirus-encoded adjuvants, are more effective at stimulating naïve T-cell responses than in promoting recall of preexisting memory T-cell responses. Our results demonstrate that a strategy to express specific genetic adjuvants from rMVA vectors can be successfully applied to enhance the immunogenicity of MVA-based vaccines.

Evaluation of fowlpox–vaccinia virus prime-boost vaccine strategies for high-level mucosal and systemic immunity against HIV-1

We have tested the efficacy of recombinant fowl pox (rFPV) and recombinant vaccinia virus (rVV) encoding antigens of AE clade HIV-1 in a prime-boost strategy, using both systemic and mucosal delivery routes. Of the various vaccine routes tested, intranasal/intramuscular (i.n./i.m.) AE FPV/AE VV prime-boosting generated the highest mucosal and systemic T cell responses. Peak mucosal T cell responses occurred as early as 3 days post-boost vaccination. In contrast only low systemic responses were observed at this time with the peak response occurring at day 7. Current data also revealed that, due to better uptake of the rFPV, intranasal viral priming was much more effective than intranasal rDNA priming tested previously. The i.m./i.m. prime-boost delivery also generated strong systemic but poor mucosal responses to Gag peptides. Interestingly, the oral administration of AE FPV followed by i.m. AE VV delivery elicited strong systemic responses to sub-dominant Pol 1 peptides that were absent in mice that received vaccine by other routes. Moreover, priming with AE FPV co-expressing cytokine IL-12 significantly enhanced the T cell responses to target antigens, whilst co-expression of IFNgamma decreased these responses. The results also indicated that the route of inoculation and the vaccine vector combination could radically influence not only the magnitude but also the antigen specificity of the immune response generated. Further, in contrast to the generally protracted HIV rDNA/rFPV multiple delivery prime-boosting, this single rFPV prime and rVV boost approach was more flexible and generated excellent mucosal and systemic immune responses to HIV vaccine antigens.

Induction of multifunctional human immunodeficiency virus type 1 (HIV-1)-specific T cells capable of proliferation in healthy subjects by using a prime-boost regimen of DNA- and modified vaccinia virus Ankara-vectored vaccines expressing HIV-1 Gag coupled to CD8+ T-cell epitopes

A double-blind randomized phase I trial was conducted in human immunodeficiency virus type 1 (HIV-1)-negative subjects receiving vaccines vectored by plasmid DNA and modified vaccinia virus Ankara (MVA) expressing HIV-1 p24/p17 gag linked to a string of CD8(+) T-cell epitopes. The trial had two groups. One group received either two doses of MVA.HIVA (2x MVA.HIVA) (n=8) or two doses of placebo (2x placebo) (n=4). The second group received 2x pTHr.HIVA followed by one dose of MVA.HIVA (n=8) or 3x placebo (n=4). In the pTHr.HIVA-MVA.HIVA group, HIV-1-specific T-cell responses peaked 1 week after MVA.HIVA vaccination in both ex vivo gamma interferon (IFN-gamma) ELISPOT (group mean, 210 spot-forming cells/10(6) cells) and proliferation (group mean stimulation index, 37), with assays detecting positive responses in four out of eight and five out of eight subjects, respectively. No HIV-1-specific T-cell responses were detected in either assay in the 2x MVA.HIVA group or subjects receiving placebo. Using a highly sensitive and reproducible cultured IFN-gamma ELISPOT assay, positive responses mainly mediated by CD4(+) T cells were detected in eight out of eight vaccinees in the pTHr.HIVA-MVA.HIVA group and four out of eight vaccinees in the 2x MVA.HIVA group. Importantly, no false-positive responses were detected in the eight subjects receiving placebo. Of the 12 responders, 11 developed responses to previously identified immunodominant CD4(+) T-cell epitopes, with 6 volunteers having responses to more than one epitope. Five out of 12 responders also developed CD8(+) T-cell responses to the epitope string. Induced T cells produced a variety of anti-viral cytokines, including tumor necrosis factor alpha and macrophage inflammatory protein 1 beta. These data demonstrate that prime-boost vaccination with recombinant DNA and MVA vectors can induce multifunctional HIV-1-specific T cells in the majority of vaccinees.

Expansion and diversification of virus-specific T cells following immunization of human immunodeficiency virus type 1 (HIV-1)-infected individuals with a recombinant modified vaccinia virus Ankara/HIV-1 Gag vaccine

Affordable therapeutic strategies that induce sustained control of human immunodeficiency virus type 1 (HIV-1) replication and are tailored to the developing world are urgently needed. Since CD8(+) and CD4(+) T cells are crucial to HIV-1 control, stimulation of potent cellular responses by therapeutic vaccination might be exploited to reduce antiretroviral drug exposure. However, therapeutic vaccines tested to date have shown modest immunogenicity. In this study, we performed a comprehensive analysis of the changes in virus-specific CD8(+) and CD4(+) T-cell responses occurring after vaccination of 16 HIV-1-infected individuals with a recombinant modified vaccinia virus Ankara-vectored vaccine expressing the consensus HIV-1 clade A Gag p24/p17 sequences and multiple CD8(+) T-cell epitopes during highly active antiretroviral therapy. We observed significant amplification and broadening of CD8(+) and CD4(+) gamma interferon responses to vaccine-derived epitopes in the vaccinees, without rebound viremia, but not in two unvaccinated controls followed simultaneously. Vaccine-driven CD8(+) T-cell expansions were also detected by tetramer reactivity, predominantly in the CD45RA(-) CCR7(+) or CD45RA(-) CCR7(-) compartments, and persisted for at least 1 year. Expansion was associated with a marked but transient up-regulation of CD38 and perforin within days of vaccination. Gag-specific CD8(+) and CD4(+) T-cell proliferation also increased postvaccination. These data suggest that immunization with MVA.HIVA is a feasible strategy to enhance potentially protective T-cell responses in individuals with chronic HIV-1 infection.

Therapeutic immunization strategies for the control of HIV-1

Highly active antiretroviral therapy (HAART) is currently the only means to halt or prevent progression to AIDS. However, lack of access to medications for the vast majority of HIV-1-infected individuals in immediate need, together with the requirement for lifelong adherence and potential for serious toxicity, are significant limitations which have yet to be overcome. Augmentation of HIV-specific immunity by therapeutic vaccination is being explored as a possible alternative to continuous HAART. A few candidate HIV-1 vaccines have entered clinical trials involving an assessment of viremia control during an analytic therapy interruption, but even the most promising of these achieve a short-lived suppression of HIV-1 without HAART. Nevertheless, these studies are guiding the development of better immune augmentation strategies, which could extend the time off therapy and will also contribute to a better understanding of the immune correlates of protection against AIDS. The status of therapeutic vaccines that are currently undergoing preclinical and clinical evaluation is reviewed.

Overlapping synthetic peptides as vaccines

Several vaccine strategies aim to generate cell-mediated immunity (CMI) against microorganisms or tumors. While epitope-based vaccines offer advantages, knowledge of specific epitopes and frequency of major histocompatibility complex (MHC) alleles is required. Here we show that using promiscuous overlapping synthetic peptides (OSP) as immunogens generated peptide-specific CMI in all vaccinated outbred mice and in different strains of inbred mice; CMI responses also recognized viral proteins. OSP immunogens also induced CMI ex vivo in dendritic cell/T-cell cocultures involving cells from individuals with different HLA haplotypes. Thus, broad CMI was induced by OSP in different experimental settings, using different immunogens, without identifying either epitopes or MHC backgrounds of the vaccinees.

Long-term persistence of hepatitis B surface antigen and antibody induced by DNA-mediated immunization results in liver and kidney lesions in mice

DNA-mediated immunization has been recognized as a new approach for prevention and treatment of hepatitis B virus (HBV) infection. However, the side effects of this approach have not been well described. Here we report that DNA-mediated immunization by intramuscular injection of plasmid DNA encoding HBV surface antigen (HBsAg) induced long-term persistence of HBsAg and HBsAg-specific antibody (anti-HBs) in the sera of the immunized BALB/c mice and resulted in liver and kidney lesions. The lesions persisted for 6 months after injection. Lesions were also found in normal mice injected with the sera from immunized mice, and in HBV-transgenic mice injected with anti-HBs antibody, or sera from immunized mice. Furthermore, lesions were accompanied by deposition of circulating immune complex (CIC) of HBsAg and anti-HBs antibody in the damaged organs. These results indicate that long-term persistence of HBsAg and anti-HBs in the immunized mice can result in deposited CIC in liver and kidney, and in development of lesions. The use of DNA containing mammalian replication origins, such as the plasmids used in this study, is not appropriate for human vaccines due to safety concerns relating to persistence of DNA; nevertheless, the safety of DNA-mediated immunization protocols still needs to be carefully evaluated before practical application.

Safety Profile of the Viral Vectors of Attenuated Fowlpox Strain FP9 and Modified Vaccinia Virus Ankara Recombinant for Either of 2 Preerythrocytic Malaria Antigens, ME-TRAP or the Circumsporozoite Protein, in Children and Adults in Kenya

BACKGROUND

We are developing a heterologous prime-boost vaccine strategy against malaria. This approach uses sequential immunization with different vectors to deliver a common preerythrocytic malaria antigen. Preliminary evidence of efficacy and safety has been previously documented in studies from an area where malaria is nonendemic. Additional safety data from an area where malaria is endemic are now required before larger-scale studies are undertaken to determine the efficacy of this vaccine strategy in the field. Other modified vaccinia virus Ankara (MVA) recombinants and prime-boost immunizations are being developed as vaccines against human immunodeficiency virus (HIV) infection, tuberculosis, and cancer, and MVA is a candidate attenuated smallpox vaccine.

METHODS

Candidate vaccines against malaria were intradermally administered to 73 adults (7 of whom were HIV positive) and 22 children in Kenya. These vaccines used the attenuated fowlpox strain FP9 and the MVA recombinant for either of 2 preerythrocytic malaria antigens, multiple preerythrocytic-stage epitopes joined with the preerythrocytic-stage antigen TRAP (ME-TRAP) and the circumsporozoite protein (CS). Adverse events were recorded.

RESULTS

Reactogenicity was mild. MVA caused less frequent and less severe cutaneous reaction if given after FP9 priming. Half doses reduced the frequency and the severity of systemic reactogenicity, and particular vaccine lots were associated with different reactogenicities. Unexpectedly, prior immunity to the ME-TRAP antigen appeared to be protective against local reactions after immunization.

CONCLUSIONS

Where the final intention is to use MVA after FP9 priming, previous testing of MVA alone overestimates reactogenicity. These recombinant vectors appear to be safe and suitable for use in larger-scale studies of children in Africa and of HIV-positive individuals.

Impaired IFN-gamma-secreting capacity in mycobacterial antigen-specific CD4 T cells during chronic HIV-1 infection despite long-term HAART

OBJECTIVE

To determine whether long-term HAART in chronic HIV-1 infection restores fully functional Mycobacterium tuberculosis (MTB)-specific CD4 T-cell responses.

DESIGN

A cross-sectional study of HIV-1-seropositive subjects on continuous HAART for over one year with CD4 cell counts greater than 300 cells/microl and undetectable viraemia, antiretroviral-naive individuals with primary HIV-1 infection (PHI), and healthy bacillus Calmette-Guérin-vaccinated low-risk controls.

METHODS

Purified protein derivative (PPD)-specific cytokine-secreting CD4 T cells were quantified ex vivo by enzyme-linked immunospot assay and intracellular cytokine staining. Lymphoproliferation was detected by [3H]-thymidine incorporation.

RESULTS

PPD-specific IFN-gamma-secreting CD4 T cells were markedly reduced in chronic HAART-treated HIV-1-positive and PHI subjects compared with healthy controls [medians 30, 155 and 582 spot-forming cells/million peripheral blood mononuclear cells (PBMC), respectively, P < 0.0001 and P < 0.002], but the frequency of these cells was, nonetheless, significantly greater in viraemic PHI subjects than in aviraemic chronic HIV-1-positive subjects (P < 0.01). In the latter, low frequencies of PPD-specific IL-2 and IL-4-secreting CD4 T cells were also observed. However, lymphoproliferation was evident after the in-vitro stimulation of PBMC with PPD, indicating that MTB-specific T cells were present. The defect in IFN-gamma secretion could be overcome by culture with IL-12.

CONCLUSION

Despite an improvement in CD4 T-cell counts after HAART, MTB-specific CD4 T cells from chronically infected patients have impaired IFN-gamma-secreting capacity. The early initiation of HAART might preserve functional CD4 T-cell responses to MTB, and warrants evaluation in populations with a high risk of dual infection.

Infection of human dendritic cells with recombinant vaccinia virus MVA reveals general persistence of viral early transcription but distinct maturation-dependent cytopathogenicity

Vector-infected dendritic cells (DC) are evaluated for antigen delivery in experimental therapy of cancer and infectious diseases. Here, we investigated infections of immature or mature, monocyte-derived human DC with recombinant vaccinia virus MVA producing human Her-2/neu, a candidate tumor-associated antigen. Assessment of the molecular virus life cycle in infected DC revealed a general arrest at the level of viral early gene expression. When monitoring the phenotype of MVA-infected DC, including expression of cell surface markers, we found immature cells readily undergoing apoptosis. Nevertheless, we detected significant populations of viable DC being characterized by high level Her-2/neu expression and unimpaired display of costimulatory molecules. While infected viable immature DC failed to undergo maturation despite cytokine treatment, both DC populations efficiently presented MVA-produced target antigen. These findings allow to better define the requirements for MVA-mediated antigen delivery to DC and help to derive optimized vectors for this advanced therapy option.

Design and preclinical evaluation of a multigene human immunodeficiency virus type 1 subtype C DNA vaccine for clinical trial

In this study, the design and preclinical development of a multigene human immunodeficiency virus type 1 (HIV-1) subtype C DNA vaccine are described, developed as part of the South African AIDS Vaccine Initiative (SAAVI). Genetic variation remains a major obstacle in the development of an HIV-1 vaccine and recent strategies have focused on constructing vaccines based on the subtypes dominant in the developing world, where the epidemic is most severe. The vaccine, SAAVI DNA-C, contains an equimolar mixture of two plasmids, pTHr.grttnC and pTHr.gp150CT, which express a polyprotein derived from Gag, reverse transcriptase (RT), Tat and Nef, and a truncated Env, respectively. Genes included in the vaccine were obtained from individuals within 3 months of infection and selection was based on closeness to a South African subtype C consensus sequence. All genes were codon-optimized for increased expression in humans. The genes have been modified for safety, stability and immunogenicity. Tat was inactivated through shuffling of gene fragments, whilst maintaining all potential epitopes; the active site of RT was mutated; 124 aa were removed from the cytoplasmic tail of gp160; and Nef and Gag myristylation sites were inactivated. Following vaccination of BALB/c mice, high levels of cytotoxic T lymphocytes were induced against multiple epitopes and the vaccine stimulated strong CD8+ gamma interferon responses. In addition, high titres of antibodies to gp120 were induced in guinea pigs. This vaccine is the first component of a prime-boost regimen that is scheduled for clinical trials in humans in the USA and South Africa.

Vaxfectin™ enhances immunogenicity and protective efficacy of P. yoelii circumsporozoite DNA vaccines

We evaluated the capacity of the cationic lipid based formulation, Vaxfectin, to enhance the immunogenicity and protective efficacy of DNA-based vaccine regimens in the Plasmodium yoelii murine malaria model. We immunized Balb/c mice with varying doses (0.4-50 microg) of plasmid DNA (pDNA) encoding the P. yoelii circumsporozoite protein (PyCSP), either in a homologous DNA/DNA regimen (D-D) or a heterologous prime-boost DNA-poxvirus regimen (D-V). At the lowest pDNA doses, Vaxfectin substantially enhanced IFA titers, ELISPOT frequencies, and protective efficacy. Clinical trials of pDNA vaccines have often used low pDNA doses based on a per kilogram weight basis. Formulation of pDNA vaccines in Vaxfectin may improve their potency in human clinical trials.

Bioprocess engineering issues that would be faced in producing a DNA vaccine at up to 100 m3 fermentation scale for an influenza pandemic

The risk of a pandemic with a virulent form of influenza is acknowledged by the World Health Organization (WHO) and other agencies. Current vaccine production facilities would be unable to meet the global requirement for vaccine. As a possible supplement a DNA vaccine may be appropriate, and bioprocess engineering factors bearing on the use of existing biopharmaceutical and antibiotics plants to produce it are described. This approach addresses the uncertainty of timing of a pandemic that precludes purpose-built facilities. The strengths and weaknesses of alternative downstream processing routes are analyzed, and several gaps in public domain information are addressed. The conclusion is that such processing would be challenging but feasible.

SIV DNA vaccine co-administered with IL-12 expression plasmid enhances CD8 SIV cellular immune responses in cynomolgus macaques

Current evidence suggests that a strong induced CD8 human immunodeficiency virus type 1 (HIV-1)-specific cell mediated immune response may be an important aspect of an HIV vaccine. The response rates and the magnitude of the CTL responses induced by current DNA vaccines in humans need to be improved and cellular immune responses to DNA vaccines can be enhanced in mice by co-delivering DNA plasmids expressing immune modulators. Two reported to work well in the mouse systems are interleukin (IL)-12 and CD40L. We sought to compare these molecular adjuvants in a primate model system. The cDNA for macaque IL-12 and CD40L were cloned into DNA vectors. Groups of cynomolgus macaques were immunized with 2 mg of plasmid expressing SIVgag alone or in combination with either IL-12 or CD40L. CD40L did not appear to enhance the cellular immune response to SIVgag antigen. However, more robust results were observed in animals co-injected with the IL-12 molecular adjuvant. The IL-12 expanded antigen-specific IFN-gamma positive effector cells as well as granzyme B production. The vaccine immune responses contained both a CD8 component as well a CD4 component. The adjuvanted DNA vaccines illustrate that IL-12 enhances a CD8 vaccine immune response, however, different cellular profiles.

Altered primary CD8+ T cell response to a modified virus Ankara(MVA)-vectored vaccine in the absence of CD4+ T cell help

T cell receptor-transgenic F5 mice were used to assess primary CD8+ T cell responses to a modified virus Ankara (MVA)-vectored vaccine in the absence of CD4+ T cell help. Naive, CD8-enriched, CFSE-labelled F5 cells were transferred into normal or CD4+ cell-depleted mice and the mice were vaccinated with MVA.HIVA-NP. At different time points during the primary response, F5 cells were re-isolated and analysed on divisional basis for a number of parameters. We demonstrated that the primary CD8+ T cell response in the absence of CD4+ T cell help differed from that in normal CD4+ cell-undepleted mice. While in the absence of CD4+ T cell help, the initial migratory progress from the local response to a systemic one was not grossly affected, the proportion of dying F5 cells during the expansion phase was markedly increased and resulted in an overall smaller expansion and significantly decreased frequency of CD8+ T cell memory after contraction. T cells primed without help displayed accelerated proliferation and activation, while expression of interferon-gamma remained similar. These phenomena were observed in the lymph nodes draining the MVA.HIVA-NP immunization site and were similar, but delayed by 2-3 days in spleen and non-draining lymph nodes.

Biodistribution and persistence of an MVA-vectored candidate HIV vaccine in SIV-infected rhesus macaques and SCID mice

Recombinant modified vaccinia virus Ankara (MVA) is together with a few other attenuated viral vectors on the forefront of human immunodeficiency virus type 1 (HIV-1) vaccine development. As such, MVA-vectored vaccines are likely to be administered into immunocompromized individuals. Here, we demonstrated in a good laboratory practice study safety and biological clearance of candidate HIV-1 vaccine MVA.HIVA in simian immunodeficiency virus (SIV)-infected rhesus macaques and mice with a severe combined immunodeficiency (SCID) following an intradermal vaccine administration. In SIV-infected macaques, MVA.HIVA DNA was undetectable by nested PCR 6 weeks after dosing. In SCID mice, the MVA.HIVA vaccine was well tolerated and a positive PCR signal was only observed at the site of injection 49 days after dosing in four out of six mice, but even these sites were negative by day 81 post-injection. Therefore, the MVA.HIVA vaccine is considered safe for application in phase I clinical trials in HIV-1-infected human subjects. These results also contribute to the confidence of using MVA as a smallpox vaccine.

DNA vaccines: progress and challenges

In the years following the publication of the initial in vivo demonstration of the ability of plasmid DNA to generate protective immune responses, DNA vaccines have entered into a variety of human clinical trials for vaccines against various infectious diseases and for therapies against cancer, and are in development for therapies against autoimmune diseases and allergy. They also have become a widely used laboratory tool for a variety of applications ranging from proteomics to understanding Ag presentation and cross-priming. Despite their rapid and widespread development and the commonplace usage of the term "DNA vaccines," however, the disappointing potency of the DNA vaccines in humans underscores the challenges encountered in the efforts to translate efficacy in preclinical models into clinical realities. This review will provide a brief background of DNA vaccines including the insights gained about the varied immunological mechanisms that play a role in their ability to generate immune responses.

Ensuring safety of DNA vaccines

In 1990 a new approach for vaccination was invented involving injection of plasmid DNA in vivo, which elicits an immune response to the encoded protein. DNA vaccination can overcome most disadvantages of conventional vaccine strategies and has potential for vaccines of the future. However, today 15 years on, a commercial product still has not reached the market. One possible explanation could be the technique's failure to induce an efficient immune response in humans, but safety may also be a fundamental issue. This review focuses on the safety of the genetic elements of DNA vaccines and on the safety of the microbial host for the production of plasmid DNA. We also propose candidates for the vaccine's genetic elements and for its microbial production host that can heighten the vaccine's safety and facilitate its entry to the market.

Vaccine route, dose and type of delivery vector determine patterns of primary CD8+ T cell responses

The dynamics of primary CD8+ T cell responses following administration of modified virus Ankara (MVA)- and DNA-vectored vaccines was investigated in a mouse model. To overcome the low frequency of naive antigen-specific precursors and follow the early expansion events, naive CFSE-labelled T cell receptor-transgenic F5 lymphocytes were transferred into syngeneic non-transgenic recipients prior to vaccination. Using the i.d., i.v. and i.m. routes and increasing recombinant MVA (rMVA) vaccine doses, the primary response was analysed on a divisional basis at local and distant lymphoid organs at various times after vaccination. The results indicated that F5 cell divisions were initiated in the local draining lymph nodes and cells only after five to six divisions appeared at more distant sites. The rMVA dose affected frequencies of cells entering division and at the peak response. When priming induced by rMVA and plasmid DNA was compared, dramatic differences in the cycling patterns were observed with plasmid DNA inducing a response slower and more sustained over the first 2 wk than rMVA. Both rMVA and DNA induced comparable IFN-gamma production, which increased with cell divisions. Taken together, the vaccine type, dose and route have a strong influence on the spatial and temporal patterns of initial T cell responses.

Comparative immunogenicity in rhesus monkeys of multi-protein HIV-1 (CRF02_AG) DNA/MVA vaccines expressing mature and immature VLPs

We developed an AIDS vaccine for Western and West-Central Africa founded on HIV-1 subtype CRF02_AG. Rhesus macaques were primed with Gag-Pol-Env-expressing plasmid DNA and boosted with a recombinant modified vaccinia virus Ankara (rMVA), expressing matched proteins. Two DNA vaccine constructs (IC1-90 and IC48) that differed by point mutations in gag and pol were compared. IC1-90 produces primarily immature (core comprises unprocessed Pr55Gag) HIV-like particles (VLPs) and IC48 produces mature VLP with processed Pr55Gag, immature VLP, and intracellular protein aggregates. Both vaccines raised significant cellular responses for Gag, Pol, and Env. Approximate twofold higher ELISPOT responses to Gag and Env epitopes were observed for IC48 animals than for IC1-90 animals at the peak post-MVA effector (P = 0.028) and late memory (P = 0.051) phases, respectively. Greater breadth for IC48-primed animals was observed than for IC1-90-primed animals at peak response (P = 0.03). Our results indicated that the vaccines elicited high frequency T cell responses and primed anti-Env antibody. They also suggest that expression of different forms of VLP has a significant effect on elicited cellular and humoral immunity.

Therapeutic immunization of highly active antiretroviral therapy-treated HIV-1-infected patients: safety and immunogenicity of an HIV-1 gag/poly-epitope DNA vaccine

In view of the global emergency posed by lack of access to highly active antiretroviral therapy (HAART) and the limitations of current drug regimens, alternative therapeutic strategies are urgently needed. Cellular immune responses elicited by HIV-1 exert some control over virus replication, therefore the enhancement of HIV-1-specific responses by therapeutic vaccination might lead to viral containment without HAART. We evaluated the safety and immunogenicity, in HIV-1-infected individuals under HAART suppression, of a DNA vaccine, pTHr.HIVA.

Efficient expansion of HIV-1-specific T cell responses by homologous immunization with recombinant Semliki Forest virus particles

Vaccines based on recombinant viruses represent a promising strategy for the development of a prophylactic vaccine against HIV-1. However, despite a proven capacity to stimulate potent HIV-1-specific immune responses, viral systems have limited utility in homologous prime-boost regimens due to the generation of anti-vector immune responses. It is therefore important to develop a diverse set of vaccine candidates that can be combined in different heterologous prime-boost regimens and/or to identify a vaccine candidate that is less sensitive to anti-vector mediated immunity. In this report, we describe the design and pre-clinical immunogenicity of a Semliki Forest virus-based vaccine, VREP-C, encoding Indian origin HIV-1 clade C antigens. We show that a single immunization with VREP-C stimulates HIV-1-specific IFNgamma ELISPOT responses, which were efficiently boosted by a second and a third homologous VREP-C immunization resulting in highly potent cytotoxic T cell responses. These results suggest that VREP-C may be a valuable component of a future prophylactic vaccine against HIV-1.

Prime-boost immunisation strategies for tuberculosis

Vaccines against intracellular pathogens such as Mycobacterium tuberculosis need to induce strong cellular immune responses. Heterologous prime-boost immunisation strategies induce higher levels of both CD4+ and CD8+ T cells than homologous boosting with the same vector. Recombinant pox-viruses are particularly good at boosting previously primed T cell responses. Using BCG as the priming immunisation in such a heterologous prime-boost strategy is a practical solution, which allows the beneficial effects of BCG in children to be maintained.

Modified vaccinia virus Ankara as antigen delivery system: how can we best use its potential?

Safety-tested modified vaccinia virus Ankara (MVA) has been established as a potent vector system for the development of candidate recombinant vaccines. The versatility of the vector system was recently demonstrated by the rapid production of experimental MVA vaccines for immunization against severe acute respiratory syndrome associated coronavirus. Promising results were also obtained in the delivery of Epstein-Barr virus or human cytomegalovirus antigens and from the clinical testing of MVA vectors for vaccination against immunodeficiency virus, papilloma virus, Plasmodium falciparum or melanoma. Moreover, MVA is considered to be a prime candidate vaccine for safer protection against orthopoxvirus infections. Thus, vector development to challenge dilemmas in vaccinology or immunization against poxvirus biothreat seems possible, yet the right choice should be made for a most beneficial use.