DNA vaccines: progress and challenges

Human major histocompatibility complex (MHC) class I molecules with disulfide traps secure disease-related antigenic peptides and exclude competitor peptides

The ongoing discovery of disease-associated epitopes detected by CD8 T cells greatly facilitates peptide-based vaccine approaches and the construction of multimeric soluble recombinant proteins (e.g. tetramers) for isolation and enumeration of antigen-specific CD8 T cells. Related to these outcomes of epitope discovery is the recent demonstration that MHC class I/peptide complexes can be expressed as single chain trimers (SCTs) with peptide, beta(2)m and heavy chain connected by linkers to form a single polypeptide chain. Studies using clinically relevant mouse models of human disease have shown that SCTs expressed by DNA vaccination are potent stimulators of cytotoxic T lymphocytes. Their vaccine efficacy has been attributed to the fact that SCTs contain a preprocessed and preloaded peptide that is stably displayed on the cell surface. Although SCTs of HLA class I/peptide complexes have been previously reported, they have not been characterized for biochemical stability or susceptibility to exogenous peptide binding. Here we demonstrate that human SCTs remain almost exclusively intact when expressed in cells and can incorporate a disulfide trap that dramatically excludes the binding of exogenous peptides. The mechanistic and practical applications of these findings for vaccine development and T cell isolation/enumeration are discussed.

Markedly enhanced immunogenicity of a Pfs25 DNA-based malaria transmission-blocking vaccine by in vivo electroporation

Pfs25 is a promising target antigen for the development of a malaria transmission-blocking vaccine and prior research has demonstrated induction of high and functionally effective antibodies in mice with IM injection of Pfs25 encoding DNA plasmid. Likewise, Pfs25 DNA vaccine was immunogenic in rhesus macaques but required a protein boost to elicit significant transmission-blocking antibodies. The translation of these encouraging findings to human clinical trials has been impeded largely by the relatively poor immunogenicity of DNA plasmids in larger animals. In vivo electroporation (EP) has revealed significant enhancement of the potency of DNA plasmids. The results reported here compared the immunogenicity and functional transmission-blocking effects of immunization with DNA plasmid (25 microg) by the traditional IM route compared to coupling the IM injection (0.25, 2.5 and 25 microg doses) with in vivo EP. Significantly, a 0.25 microg dose of DNA plasmid, when administered with EP, induced antibody titers (1:160,000) and functional transmission-blocking effects that were equivalent to those achieved by a one hundred fold higher (25 microg) dose of DNA plasmid given without EP. At a 25.0 microg DNA dose with or without EP there was sufficient antigenic stimulation to result in effective antibody titers; however EP method yielded antibody titer of 1:1,280,000 as compared to only 1:160,000 titer without EP. This observed two log reduction in the amount of DNA plasmid required to induce significant transmission-blocking effects makes a compelling argument in favor of further evaluation of DNA vaccines by in vivo EP method in larger animals. Further experiments in non-human primates and eventually in phase I human trials will determine if the use of EP will induce effective and sustained malaria transmission-blocking effects at acceptable doses of plasmid DNA.

Direct plasmid DNA encapsulation within PLGA nanospheres by single oil-in-water emulsion method

Plasmid DNA was encapsulated within poly(d,l-lactic-co-glycolic acid) (PLGA) nanospheres by using polyethylene glycol (PEG) assisted solubilization technique of plasmid DNA in organic solvents. Plasmid DNA was solubilized in an organic solvent mixture composed of 80% methylene chloride and 20% DMSO by producing PEG/DNA nano-complexes having an average diameter less than 100 nm. DNA could be solubilized in the organic solvent mixture to a greater extent with increasing the weight ratio of PEG/DNA. PLGA nanospheres encapsulating DNA were successfully prepared by the single O/W emulsion method. They exhibited greater loading efficiency and better structural integrity, compared to those prepared by the W/O/W double emulsion method. Plasmid DNA could be successfully delivered to macrophage cells to express an exogenous gene. This new formulation enabled high loading of intact plasmid DNA within PLGA nanospheres useful for DNA vaccines.

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.

In vivo antigen stability affects DNA vaccine immunogenicity

The factors that determine the immunogenicity of Ags encoded by viral vaccines or DNA vaccines in vivo are largely unknown. Depending on whether T cell induction occurs via direct presentation of vaccine-encoded epitopes or via one of the different proposed pathways for Ag cross-presentation, the effect of intracellular Ag stability on immunogenicity may possibly vary. However, the influence of Ag stability on CD8(+) T cell induction has not been addressed in clinically relevant vaccine models, nor has the accumulation of vaccine-encoded Ags been monitored in vivo. In this study, we describe the relationship between in vivo Ag stability and immunogenicity of DNA vaccine-encoded Ags. We show that in vivo accumulation of DNA vaccine-encoded Ags is required for the efficient induction of CD8(+) T cell responses. These data suggest that many of the currently used transgene designs in DNA vaccination trials may be suboptimal, and that one should either use pathogen-derived or tumor-associated Ags that are intrinsically stable, or should increase the stability of vaccine-encoded Ags by genetic engineering.

Epidermal langerhans cells are dispensable for humoral and cell-mediated immunity elicited by gene gun immunization

Gene gun immunization, i.e., bombardment of skin with DNA-coated particles, is an efficient method for the administration of DNA vaccines. Direct transfection of APC or cross-presentation of exogenous Ag acquired from transfected nonimmune cells enables MHC-I-restricted activation of CD8(+) T cells. Additionally, MHC-II-restricted presentation of exogenous Ag activates CD4(+) Th cells. Being the principal APC in the epidermis, Langerhans cells (LC) seem ideal candidates to accomplish these functions. However, the dependence on LC of gene gun-induced immune reactions has not yet been demonstrated directly. This was primarily hampered by difficulties to discriminate the contributions of LC from those of other dermal dendritic cells. To address this problem, we have used Langerin-diphtheria toxin receptor knockin mice that allow for selective inducible ablation of LC. LC deficiency, even over the entire duration of experiments, did not affect any of the gene gun-induced immune functions examined, including proliferation of CD4(+) and CD8(+) T cells, IFN-gamma secretion by spleen cells, Ab production, CTL activity, and development of protective antitumor immunity. Together, our data show that gene gun immunization is capable of inducing humoral and cell-mediated immune reactions independently of LC.

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.

Vaccination with plasmid DNA encoding KMPII, TRYP, LACK and GP63 does not protect dogs against Leishmania infantum experimental challenge

Vaccination of dogs, the domestic reservoir of Leishmania infantum, is the best method for controlling zoonotic visceral leishmaniasis. This strategy would reduce the incidence of disease in both the canine and, indirectly, the human population. Different vaccination approaches have been investigated against canine leishmaniasis (CaL) but to date there is only one licensed vaccine against this disease in dogs, in Brazil. DNA immunization is a promising method for inducing both humoral and cellular immune responses against this parasitic disease. Here, we report the results of a multiantigenic plasmid DNA vaccine encoding KMPII, TRYP, LACK and GP63 L. infantum antigens against experimentally induced CaL. Twelve dogs were randomly assigned to two groups receiving, at a 15 days interval, either four doses of plasmid DNA or similar injections of PBS. After vaccination, dogs were intravenously challenged with 5 x 10(7) promastigotes of L. infantum. The vaccine showed to be safe and well-tolerated. Neither cellular immune response nor antibodies directed against whole Leishmania antigen were detected after immunization in vaccinated dogs, although anti-LACK-specific antibodies were sporadically detected in two vaccinated dogs before challenge, thus suggesting that antigens were indeed expressed. A delay in the development of detectable specific immune response and parasite multiplication in vaccinated dogs was observed after challenge. Nevertheless, the multiantigenic Leishmania DNA vaccine was unable to induce protection against parasite dissemination or disease. This study emphasizes the need to strengthen DNA vaccines in order to obtain effective immune responses in models other than the murine.

Current status and future prospects for a vaccine against American trypanosomiasis

The clinically relevant pathognomonic consequences of human infection by Trypanosoma cruzi are dilation and hypertrophy of the left ventricle walls and thinning of the apex. The major complications and debilitating evolutionary outcomes of chronic infection include ventricular fibrillation, thromboembolism and congestive heart failure. American trypanosomiasis (Chagas disease) poses serious public healthcare and budgetary concerns. The currently available drugs, although effective against acute infection, are highly toxic and ineffective in arresting or attenuating clinical disease symptoms in chronic patients. The development of an efficacious prophylactic vaccine faces many challenges, and progress is slow, despite several years of effort. Studies in animal models and human patients have revealed the pathogenic mechanisms during disease progression, pathology of disease and features of protective immunity. Accordingly, several antigens, antigen-delivery vehicles and adjuvants have been tested in animal models, and some efforts have been successful in controlling infection and disease. This review will summarize the accumulated knowledge about the parasite and disease, as well as pathogenesis and protective immunity. The authors will discuss the efforts to date, and the challenges faced in achieving an efficient prophylactic vaccine against human American trypanosomiasis, and present the future perspectives.

Extended immunization intervals enhance the immunogenicity and protective efficacy of plasmid DNA vaccines

Effective vaccines against infectious diseases and biological warfare agents remain an urgent public health priority. Studies have characterized the differentiation of effector and memory T cells and identified a subset of T cells capable of conferring enhanced protective immunity against pathogen challenge. We hypothesized that the kinetics of T cell differentiation influences the immunogenicity and protective efficacy of plasmid DNA vaccines, and tested this hypothesis in the Plasmodium yoelii murine model of malaria. We found that increasing the interval between immunizations significantly enhanced the frequency and magnitude of CD8+ and CD4+ T cell responses as well as protective immunity against sporozoite challenge. Moreover, the interval between immunizations was more important than the total number of immunizations. Immunization interval had a significantly greater impact on T cell responses and protective immunity than on antibody responses. With prolonged immunization intervals, T cell responses induced by homologous DNA only regimens achieved levels similar to those induced by heterologous DNA prime/ virus boost immunization at standard intervals. Our studies establish that the dosing interval significantly impacts the immunogenicity and protective efficacy of plasmid DNA vaccines.

Trypanosoma cruzi infection from the view of CD8+ T cell immunity--an infection model for developing T cell vaccine

Chagas' disease is caused by Trypanosoma cruzi (T. cruzi) which was once prevalent in Central and South America. Although the recent success in Triatoma vector control has made the disease being possibly "extinct" in the near future, the development of effective preventive and therapeutic vaccines is still necessary to prevent the resurgence of the neglected infection. In addition to the importance for containing the disease, T. cruzi infection presents unique features for elucidating hosts' immune responses against intracellular infectious agents. Due to its biological capacity for invading into principally any types of cells and for causing systemic infection which damages particularly muscle and neural cells, T cell immunity is critical for resolving its infection. Although T cell-mediated immune responses have been, so far, extensively investigated in viral and bacterial infections, parasitic infection such as malaria has presented epoch-making discovery in T cell immunity. Recent advances in the analyses of T cell-mediated immune responses against T. cruzi infection now make this infectious disease potentially more suitable for detecting subtle immunological changes in hosts' immune defense upon modifying immune system. The current review focuses on the usefulness of T. cruzi infection as a model for developing effective CD8(+) T cell-mediated vaccine against intracellular infectious agents.

Targeting antigen to MHC Class I and Class II antigen presentation pathways for malaria DNA vaccines

An effective malaria vaccine which protects against all stages of Plasmodium infection may need to elicit robust CD8(+) and CD4(+) T cell and antibody responses. To achieve this, we have investigated strategies designed to improve the immunogenicity of DNA vaccines encoding the Plasmodium yoelii pre-erythrocytic stage antigens PyCSP and PyHEP17, by targeting the encoded proteins to the MHC Classes I and II processing and presentation pathways. For enhancement of CD8(+) T cell responses, we targeted the antigens for degradation by the ubiquitin (Ub)/proteosome pathway following the N-terminal rule. We constructed plasmids containing PyCSP or PyHEP17 genes fused to the Ub gene: plasmids where the N-terminal antigen residues were mutated from the stabilizing amino acid methionine to destabilizing arginine, plasmids where the C-terminal residues of Ub were mutated from glycine to alanine, and plasmids in which the potential hydrophobic leader sequences of the antigens were deleted. For enhancement of CD4(+) T cell and antibody responses, we targeted the antigens for degradation by the endosomal/lysosomal pathway by linking the antigen to the lysosome-associated membrane protein (LAMP). We found that immunization with DNA vaccine encoding PyHEP17 fused to Ub and bearing arginine induced higher IFN-gamma, cytotoxic and proliferative T cell responses than unmodified vaccines. However, no effect was seen for PyCSP using the same targeting strategies. Regarding Class II antigen targeting, fusion to LAMP did not enhance antibody responses to either PyHEP17 or PyCSP, and resulted in a marginal increase in lymphoproliferative CD4(+) T cell responses. Our data highlight the antigen dependence of immune enhancement strategies that target antigen to the MHC Class I and II pathways for vaccine development.

Polymeric nano- and microparticle technologies for oral gene delivery

Gene therapy refers to local or systemic administration of a nucleic acid construct that can prevent, treat and even cure diseases by changing the expression of genes that are responsible for the pathological condition. Oral gene therapy has significant promise for treatment of local diseases such as inflammatory bowel disease and for systemic absorption of the expressed protein therapeutics. In addition, efficient oral delivery of DNA vaccines can have significant impact in disease prevention. The use of polymeric gene delivery vectors promises the translation of this experimental medical concept into clinical reality. This review addresses the challenges and opportunities in the development of polymer-based nano- and microparticle technologies for oral gene therapy. Specifically, the discussion is focused on different synthetic and natural polymers used for formulating nano- and microparticle technologies and the use of these delivery systems for oral DNA administration for therapeutic and vaccination purposes.

Harnessing NKT cells for therapeutic applications

Activation of NKT cells leads to the maturation of dendritic cells and efficiently assists priming of antigen-specific immune responses. The lack of polymorphism of CDld molecules and the evolutionary conservation of NKT cell responses highlight the important role of these cells in bridging innate and adaptive immune responses and advocate the value of harnessing this system in clinical settings. Compounds capable of fine tuning NKT cell activation should be actively exploited as potent adjuvants in vaccination strategies or as immunomodulators of autoimmune diseases.

A combined DNA vaccine enhances protective immunity against Mycobacterium tuberculosis and Brucella abortus in the presence of an IL-12 expression vector

We examined the immunogenicity and protective efficacy of a combined DNA vaccine that included six genes encoding immunodominant antigens from Mycobacterium tuberculosis and Brucella abortus. The IL-12 adjuvant system was used for immunization in combination with the combined DNA vaccine (DNA-IL-12(+)). Mice immunized with DNA-IL-12(+) had significantly reduced CFU counts for M. tuberculosis and B. abortus in lung and spleen, respectively (P<0.001), and DNA-IL-12(+) elicited better protection than the combined DNA vaccine alone (DNA-IL-12(-)) or with the positive control groups after challenge with a virulent M. tuberculosis strain and B. abortus 2308 infection. The DNA-IL-12(+) group had stronger antigen-specific IFN-gamma ELISPOT activities and higher levels of antigen-specific CD4(+) and CD8(+) T cell responses than either the DNA-IL-12(-) or positive control groups. Likewise, antigen-specific IgG titers were also much higher than in other immunized groups. Moreover, DNA-IL-12(+) gave a stronger IgG2a-skewed response than did DNA-IL-12(-). In addition, its mean concentrations of IFN-gamma and IL-2 were about 2.5- to 4.5-fold higher than those observed in the DNA-IL-12(-)-treated mice, and were significantly higher than control groups (P<0.01 or P<0.001), whereas IL-4 and IL-10 secretion were lower. These results suggest that IL-12 acts as an adjuvant to enhance protective immunity against M. tuberculosis and B. abortus through the induction of stronger Th1-associated immune responses. This is the first report to show that a single combined DNA vaccine protects animals against two infectious diseases.

Natural history and surgical treatment of brown tumor lesions at various sites in refractory primary hyperparathyroidism

OBJECTIVE

Nowadays, the occurrence of brown tumor lesions or osteitis fibrosa cystica caused by long-lasting primary hyperparathyroidism are very rare, since measuring serum calcium became available routinely in the mid-1970s. It is a tumor-like lesion that may affect the entire skeleton, often presenting with diffuse focal bone pain or by pathological fracture.

METHODS

We describe our experience of brown tumor lesions at different skeletal sites that were treated at our trauma centre within the last two years. This included surgical therapy for the indications (i) pain at the pelvis, (ii) increased risk for pathological fracture at the tibia and (iii) acute radicular symptoms at the lumbar spine. The literature was reviewed for the current understanding of the pathophysiology as well as therapy of brown tumor lesions in primary hyperparathyroidism.

RESULTS

Curettage of a left-sided iliac crest brown tumor terminated focal pain. A less invasive stabilisation system and bone cement decreased both patient pain and the fracture risk of brown tumor lesion sites of the shinbone; and internal fixator including laminectomy at the lumbar spine ended radicular symptoms.

CONCLUSION

Patients with refractory primary hyperparathyroidism should be monitored closely by endocrinologists and the patient's serum calcium level should be adjusted as far as possible. Radiography is required only if focal bone pain or pathological fractures or radicular symptoms occur. Surgery should be considered if large bone defects with spontaneous fracture risk or increasing pain are present. Tumor curettage, Palacos plombage and less invasive stabilisation systems have proved to be acceptable surgical options.

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.

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.

mRNA-based cancer vaccine: prevention of B16 melanoma progression and metastasis by systemic injection of MART1 mRNA histidylated lipopolyplexes

Immunization with mRNA encoding tumor antigen is an emerging vaccine strategy for cancer. In this paper, we demonstrate that mice receiving systemic injections of MART1 mRNA histidylated lipopolyplexes were specifically and significantly protected against B16F10 melanoma tumor progression. The originality of this work concerns the use of a new tumor antigen mRNA formulation as vaccine, which allows an efficient protection against the growth of a highly aggressive tumor model after its delivery by intravenous route. Synthetic melanoma-associated antigen MART1 mRNA was formulated with a polyethylene glycol (PEG)ylated derivative of histidylated polylysine and L-histidine-(N,N-di-n-hexadecylamine)ethylamide liposomes (termed histidylated lipopolyplexes). Lipopolyplexes comprised mRNA/polymer complexes encapsulated by liposomes. The tumor protective effect was induced with MART1 mRNA carrying a poly(A) tail length of 100 adenosines at an optimal dose of 12.5 microg per mouse. MART1 mRNA lipopolyplexes elicited a cellular immune response characterized by the production of interferon-gamma and the induction of cytotoxic T lymphocytes. Finally, the anti-B16 response was enhanced using a formulation containing both MART1 mRNA and MART1-LAMP1 mRNA encoding the antigen targeted to the major histocompatibility complex class II compartments by the lysosomal sorting signal of LAMP1 protein. Our results provide a basis for the development of mRNA histidylated lipopolyplexes for cancer vaccine.

Enhancing the potency of HBV DNA vaccines using fusion genes of HBV-specific antigens and the N-terminal fragment of gp96

BACKGROUND

Many clinical trials show that DNA vaccine potency needs to be greatly enhanced. We have reported that the N-terminal fragment of glycoprotein 96 (gp96) is able to produce an adjuvant effect for production of cytotoxic T-lymphocytes (CTLs) with hepatitis B virus (HBV)-specific peptides. Here, we report a new strategy for HBV DNA vaccine design using a partial gp96 sequence.

MATERIALS AND METHODS

We linked the N-terminal 1-355aa (N355) of gp96 to HBV genes encoding for structural proteins, the major S and middle S2S envelope proteins and the truncated core HBcAg (1-149aa). ELISPOT, tetramer staining and intracellular IFN-gamma assay were performed to analyze the induced cellular immune responses of our DNA constructs in BALB/c mice and HLA-A2 transgenic mice. The relative humoral immune responses were analyzed in different IgG isotypes.

RESULTS

The fusion genes induced 2- to 6-fold higher HBV-specific CD8(+) T cells as compared to the antigens alone. There was an approximate 10-fold decrease in the humoral immune responses with fusion genes based on HBV envelope proteins. Interestingly, the decreased humoral immune responses were not observed when antigens and plasmid encoding N355 were co-delivered. However, an approximate 20-fold higher antibody level was induced when linking N355 to a truncated HBcAg. Immunization by intramuscular injection resulted in predominantly IgG2a antibodies, which indicated that these vaccines preferentially prime Th1 responses.

CONCLUSIONS

We constructed highly immunogenic fusions by linking the N-terminal fragment of gp96 to HBV antigens. Our results imply that the N-terminal fragment of gp96 may be used as a molecular adjuvant to enhance the potency of DNA vaccines.

The effects of gene gun delivered pIL-3 adjuvant on skin pathology and cytokine expression

The aim of this study was to investigate skin immunopathology following gene gun delivery of plasmid-encoding interleukin 3 (pIL-3) and hence explore the possible mechanisms of its adjuvant activity. Using the sheep as the experimental model, expressible pIL-3 was administered to the epidermis and the dermal/epidermal junction and its effects on the skin were assessed by histopathology, immunohistology and quantitative RT-PCR for a range of pro-inflammatory and immune response polarizing cytokines. Delivery of both functional and non-functional plasmids caused an acute inflammatory response with the infiltration of neutrophils and micro-abscess formation; however, the response to pIL-3 was more severe and was also associated with an early (24 h) infiltration of B cells and a later accumulation of CD172a-/CD45RA+ dendritic cells (DC). In terms of cytokine transcript expression, an early TNFalpha response was stimulated by gene gun delivery of plasmid-associated gold beads, which coincided with an immediate infiltration of neutrophils. However, only pIL-3 triggered the short-lived expression of IL-3 (peaking at 6 h) and significant long-term increases in both TNFalpha and IL-1beta. pIL-3 did not affect the expression of the immune response polarizing cytokines, IL-10 and IL-12.

A Combined DNA Vaccine Encoding BCSP31, SOD, and L7/L12 Confers High Protection Against Brucella abortus 2308 by Inducing Specific CTL Responses

We constructed a combined DNA vaccine comprising genes encoding the antigens BCSP31, superoxide dismutase (SOD), and L7/L12 and evaluated its immunogenicity and protective efficacy. Immunization of mice with the combined DNA vaccine offered high protection against Brucella abortus (B. abortus) infection. The vaccine induced a vigorous specific immunoglobulin G (IgG) response, with higher IgG2a than IgG1 titers. Cytokine profiling performed at the same time showed a biased Th1-type immune response with significantly increased interferon-gamma and tumor necrosis factor-alpha stimulation. CD8(+), but not CD4(+), T cells accumulated at significantly higher levels after administration of the vaccine. Granzyme B-producing CD8(+) T cells were significantly higher in number in samples prepared from combined DNA-vaccinated mice compared with S19-vaccinated mice, demonstrating that the cytotoxicity lysis pathway is involved in the response to Brucella infection. The success of our combined DNA vaccine in a mouse model suggests its potential efficacy against brucellosis infection in large animals.

Plasmid DNA Uptake and Subsequent Cellular Activation Characteristics in Human Monocyte-Derived Cells in Primary Culture

Plasmid DNA (pDNA) uptake and subsequent cellular activation characteristics were studied in three types of human monocyte-derived cells, that is, human monocytes, macrophages, and dendritic cells (DCs) in primary culture. Naked pDNA was bound to and taken up by the macrophages and DCs while only significant binding occurred in the monocytes. pDNA binding to these monocyte-derived cells was significantly inhibited by polyinosinic acid (poly[I]), dextran sulfate, maleylated bovine serum albumin (Mal-BSA) and to a lesser extent by polycytidylic acid (poly[C]), but not by dextran or galactosylated BSA (Gal-BSA), mannosylated BSA (Man-BSA), suggesting that a specific mechanism for polyanions is involved in the pDNA binding. In cellular activation studies, naked pDNA could not induce TNF-alpha production from any monocyte-derived cells, regardless of the abundant presence of CpG motifs in the pDNA. However, when complexed with cationic liposomes, pDNA produced a significant amount of TNF-alpha from the human macrophages. TNF-alpha induction was not observed in the monocytes or DCs. Moreover, calf thymus DNA (CT DNA) complexed with cationic liposomes also induced TNF-alpha production to a similar extent in the human macrophages. These results indicate that, among human monocyte-derived cells, macrophages are activated by DNA when complexed with cationic liposomes in a CpG motif-independent manner.

Immunomodulation as an option for the treatment of chronic hepatitis B virus infection: preclinical studies in the woodchuck model

New therapeutic approaches for chronic hepatitis B virus infection based on immunomodulation are now under investigation. The woodchuck model for hepatitis B virus infection has emerged as a useful animal model for the evaluation of such approaches, after developing necessary assays and reagents for immunologic studies in this model. Conventional and novel vaccines such as DNA vaccines were tested in woodchucks for their ability to induce protective immune responses against challenge infection with the woodchuck hepatitis virus (WHV). Furthermore, immunotherapeutic approaches for the control of chronic hepadnaviral infection were evaluated in woodchucks. Immunizations with WHV proteins and DNA vaccines led to the development of antibodies to the WHV surface antigen and to a significant decrease of viral load in chronically WHV-infected woodchucks. Viral vector-mediated gene transfer was explored for the delivery of antiviral cytokines IFN-alpha in woodchucks and resulted in the decrease of viral replication. It is now generally accepted that a combination of antiviral treatment and immunization will be necessary to achieve successful immunomodulation with a long-term control of chronic hepatitis B virus infection.

The effect of gene gun-delivered pGM-CSF on the immunopathology of the vaccinated skin

The aim of this study was to investigate the skin immunopathology of gene gun-delivered plasmid-encoded granulocyte-macrophage colony-stimulating factor (pGM-CSF) and hence explore the possible mechanisms of its adjuvant activity. Using sheep as the experimental model, expressible pGM-CSF was administered to the epidermis and the dermal/epidermal junction and its effects on the skin were assessed by histopathology, immunohistology and quantitative RT-PCR for a range of pro-inflammatory and immune response-polarizing cytokines. Both functional and non-functional plasmids caused an acute inflammatory response with the infiltration of neutrophils and micro-abscess formation; however, the response to pGM-CSF was more severe and was also associated with the accumulation of eosinophils, immature (CD1b(-)/CD172a(-)) dendritic cells and B cells. In terms of cytokine expression, an early TNF-alpha response was stimulated by gene gun delivery of plasmid-associated gold beads, which coincided with an immediate infiltration of neutrophils. However, only pGM-CSF triggered the short-lived expression of GM-CSF (peaking at 4 h) and significant long-term increases in both TNF-alpha and IL-1beta. pGM-CSF did not affect the expression of the immune response-polarizing cytokines, IL-10 and IL-12.

Clarification of how HIV-1 DNA and protein immunizations may be better used to obtain HIV-1-specific mucosal and systemic immunity

More focused research on a mucosal HIV-1 vaccine is needed urgently. An increasing amount of collected data, using heterologous multimodality prime-booster strategies, suggest that an efficient and protective HIV-1 vaccine must generate broad, long-lasting HIV-specific CD8(+) cytotoxic T-lymphocyte and neutralizing antibody responses. In the mucosa, these responses would be most effective if a preferential stimulus of HIV-1 neutralizing secretory immunoglobulin A and G were obtained. The attractive property of mucosal immunization is the obtained mucosal and systemic immunity, whereas systemic immunization induces a more limited immunity, predominantly in systemic sites. These objectives will require new vaccine regimens, such as multiclade HIV DNA and protein vaccines (nef, tat, gag and env expressed in DNA plasmids) delivered onto mucosal surfaces with needle-free delivery methods, such as nasal drop, as well as oral and rectal/vaginal delivery, and should merit clinical trials.

Protective role of DNA vaccination and passive immunization against the 1918 pandemic influenza virus

Evaluation of: Kong W-P, Hood C, Yang Z-Y et al.: Protective immunity to lethal challenge of the 1918 pandemic influenza virus by vaccination. Proc. Natl Acad. Sci. USA 103(43), 15987–15991 (2006). Lessons learnt from the 1918 Spanish influenza pandemic indicate that the world is vulnerable to pandemic viruses and that effective medical countermeasures are urgently needed to protect against future pandemics. The work, as published by Kong and colleagues, involved the use of genetically reconstructed 1918 pandemic virus and is of significant importance for a number of reasons. First, it highlights how advanced technology such as DNA vaccination could provide a modern solution for protection against a historic killer virus, such as the 1918 Spanish flu virus, and second, this paper describes the elucidation of the protective immunity that contributes to neutralization of virus infectivity, and therefore provides insights on the role of humoral and cellular responses in contributing to protective immunity against this virus. Third, it highlights the effectiveness of passive immunization using neutralizing antibody to protect against lethal virus challenge. The scientific information provided in this study is of significant importance in increasing our understanding of the infectivity and immunity of pandemic virus, and may better enhance our ability to prevent and treat future influenza infection caused by pandemic viruses.

Gastrointestinal distribution and in vivo gene transfection studies with nanoparticles-in-microsphere oral system (NiMOS)

The aim of this investigation was to develop and evaluate a novel nanoparticles-in-microsphere oral system (NiMOS) for gene delivery and transfection in specific regions of the gastrointestinal (GI) tract. Plasmid DNA, encoding either for beta-galactosidase (CMV-betagal) or enhanced green fluorescent protein (EFGP-N1), was encapsulated in type B gelatin nanoparticles. NiMOS were prepared by further protecting the DNA-loaded nanoparticles in a poly(epsilon-caprolactone) (PCL) matrix to form microspheres of less than 5.0 microm in diameter. In order to evaluate the biodistribution following oral administration, radiolabeled ((111)In-labeled) gelatin nanoparticles and NiMOS were administered orally to fasted Wistar rats. The results of biodistribution studies showed that, while gelatin nanoparticles traversed through the GI tract fairly quickly with more than 85% of the administered dose per gram localizing in the large intestine within the first hour, NiMOS resided in the stomach and small intestine for relatively longer duration. Following oral administration of CMV-betagal or EFGP-N1 plasmid DNA at 100 microg dose in the control and test formulations, the qualitative results presented in this study provide the proof-of-concept for the transfection capability of NiMOS upon oral administration. After 5 days post-administration, we observed transgene expression in the small and large intestine of rats. Based on these preliminary results, NiMOS show significant potential as novel gene delivery vehicle for therapeutic and vaccination purposes.

Fusion of antigen to Fas-ligand in a DNA vaccine enhances immunogenicity

DNA vaccines have considerable potential for the prophylaxis and therapy of a range of diseases, but their potential has not been realised largely due to poor immunogenicity. Fas ligand is a pro-apoptotic molecule, able to induce death of Fas expressing cells. We describe the construction of a DNA vaccine encoding a chimeric fusion between Fas ligand and a truncated version of HIV gp120 as a model antigen. The fusion DNA was used as a priming vaccine, along with boosting with recombinant gp120 protein. Priming with fusion protein DNA resulted in a powerful enhancement of immune responses to the protein boost, and, in the presence of aluminum phosphate, to a strong enhancement in T helper 2 type responses. Fas ligand delivered in a separate plasmid also had an adjuvant effect, although it was weaker than that delivered by the fusion protein.

Smallpox DNA vaccine delivered by novel skin electroporation device protects mice against intranasal poxvirus challenge

Previously, we demonstrated that an experimental smallpox DNA vaccine comprised of four vaccinia virus genes (4pox) administered by gene gun elicited protective immunity in mice challenged with vaccinia virus, and in nonhuman primates challenged with monkeypox virus (Hooper JW, et al. Smallpox DNA vaccine protects nonhuman primates against lethal monkeypox. J Virol 2004;78:4433-43). Here, we report that this 4pox DNA vaccine can be efficiently delivered by a novel method involving skin electroporation using plasmid DNA-coated microneedle arrays. Mice vaccinated with the 4pox DNA vaccine mounted robust antibody responses against the four immunogens-of-interest, including neutralizing antibody titers that were greater than those elicited by the traditional live virus vaccine administered by scarification. Moreover, vaccinated mice were completely protected against a lethal (>10LD(50)) intranasal challenge with vaccinia virus strain IHD-J. To our knowledge, this is the first demonstration of a protective immune response being elicited by microneedle-mediated skin electroporation.

DNA vaccines against dengue virus based on the ns1 gene: The influence of different signal sequences on the protein expression and its correlation to the immune response elicited in mice

We analyzed four DNA vaccines based on DENV-2 NS1: pcENS1, encoding the C-terminal from E protein plus the NS1 region; pcENS1ANC, similar to pcENS1 plus the N-terminal sequence from NS2a (ANC); pcTPANS1, coding the t-PA signal sequence fused to NS1; and pcTPANS1ANC, similar to pcTPANS1 plus the ANC sequence. The NS1 was detected in lysates and culture supernatants from pcTPANS1-, pcENS1- and pcENS1ANC-transfected cells and not in cells with pcTPANS1ANC. Only the pcENS1ANC leads the expression of NS1 in plasma membrane, confirming the importance of ANC sequence for targeting NS1 to cell surface. High levels of antibodies recognizing conformational epitopes of NS1 were induced in mice immunized with pcTPANS1 and pcENS1, while only few pcENS1ANC-inoculated animals presented detectable anti-NS1 IgG. Protection against DENV-2 was verified in pcTPANS1- and pcENS1-immunized mice, although the plasmid pcTPANS1 induced slight higher protective immunity. These plasmids seem to activate distinct patterns of the immune system.

Evaluation of the immune response induced by multiantigenic DNA vaccine encoding SAG1 and ROP2 of Toxoplasma gondii and the adjuvant properties of murine interleukin-12 plasmid in BALB/c mice

The heavy incidence and severe or lethal damages of toxoplasmosis clearly indicate the need for the development of a more effective vaccine. In the present study, we constructed a multiantigenic DNA vaccine, eukaryotic plasmid pcDNA3.1-SAG1-ROP2, expressing surface protein SAG1 and rhoptry protein ROP2 of Toxoplasma gondii, and examined the expression ability of the DNA vaccine in HeLa cells by Western blot. Afterwards, we investigated the efficacy of pcDNA3.1-SAG1-ROP2 with or without co-administration of a plasmid encoding murine interleukin-12 (pIL-12) as a genetic adjuvant to protect Bagg albino/c mice against toxoplasmosis. After T. gondii RH strain challenge, mice immunized with pcDNA3.1-SAG1-ROP2 displayed significant high survival rates. Moreover, the protection was markedly enhanced by pIL-12 co-administration. The results of lymphocyte proliferation assay, cytokine, and antibody determinations show that mice immunized with pcDNA3.1-SAG1-ROP2 elicited stronger humoral and Th1-type cellular immune responses than those immunized with single-gene plasmids, empty plasmid, or phosphate-buffered saline. Furthermore, co-immunization with IL-12 genes resulted in a dramatic enhancement of these responses. Our study indicates that the introduction of multiantigenic DNA vaccine is more powerful and efficient than single-gene vaccine, and the co-delivery of pIL-12 further enhanced the potency of multiantigenic DNA vaccine.

Therapeutic vaccination in chronic hepatitis B virus carriers

Despite effective prophylactic vaccines against hepatitis B virus existing for over 20 years, more than 2.5 billion people worldwide have been exposed to the disease and approximately 370 million people are chronically infected with it. Chronic infection in more than two thirds of infected patients results in chronic liver disease, which may lead to cirrhosis, exposure to noncarcinomatous complications and hepatocellular carcinoma. Currently available therapies fail to allow complete control of viral replication in most patients. Viral persistence has been associated with a defect in the development of hepatitis B virus-specific cellular immunity. Immunomodulatory strategies to boost or to broaden the weak virus-specific T-cell response have been proposed to bypass the chronic hepatitis B infection, including hepatitis B virus envelope- and nucleocapsid-based vaccines, and new formulations for recombinant and DNA-based vaccines, which are currently being evaluated in clinical trials.

DNA vaccine construct incorporating intercellular trafficking and intracellular targeting motifs effectively primes and induces memory B- and T-cell responses in outbred animals

We developed a vaccine construct in which a BVP22 domain and an invariant-chain major histocompatibility complex class II-targeting motif capable of enhancing dendritic cell antigen uptake and presentation were fused to a sequence encoding a B- and T-cell antigen from the Anaplasma marginale major surface protein 1a and tested whether this construct would prime and expand immune responses in outbred calves. A single inoculation with this construct effectively primed the immune responses, as demonstrated by a significant enhancement of CD4(+) T-cell proliferation compared to that in calves identically inoculated but inoculated with a DNA construct lacking the targeting domains and compared to that in calves inoculated with an empty vector. These proliferative responses were mirrored by priming and expansion of gamma interferon-positive CD4(+) T cells and immunoglobulin G responses against the linked B-cell epitope. Priming by the single immunization induced memory that underwent rapid recall following reexposure to the antigen. These results demonstrate that DNA vaccines targeting key intercellular and intracellular events significantly enhance priming and expansion and support the feasibility of single-dose DNA immunization in outbred populations.

Alum with Interleukin-12 Augments Immunity to a Melanoma Peptide Vaccine: Correlation with Time to Relapse in Patients with Resected High-Risk Disease

PURPOSE

We attempted to augment immunity to melanoma antigens using interleukin-12 (IL-12) with aluminum hydroxide (alum) for sustained release or granulocyte macrophage colony-stimulating factor (GM-CSF) added to a multipeptide vaccine.

EXPERIMENTAL DESIGN

Sixty patients with high-risk resected melanoma were randomized to receive melanoma peptides gp100(209-217) (210M), MART-1(26-35) (27L), and tyrosinase(368-376) (370D) with adjuvant Montanide ISA 51 and either IL-12 at 30 ng/kg with alum (group A), IL-12 at 100 ng/kg with alum (group B), or IL-12 at 30 ng/kg with 250 mug GM-CSF (group C).

RESULTS

Three patients had stage IIC (5%), 50 had stage III (83%), and 7 had stage IV (12%) melanoma. Most toxicities were grade 1/2 and resolved rapidly. Significant toxicity included grade 3 colitis and visual changes and grade 3 headache resolving after stopping IL-12 but continuing peptide vaccine. A higher rate of post-vaccine 6-month immune response to gp100 and MART-1 was observed in group A (15 of 19) or B (19 of 20) that received IL-12 plus alum versus group C with IL-12/GM-CSF (4 of 21; P < 0.001). Post-vaccine enzyme-linked immunospot response rates to peptide analogues in group B were higher than group A (P = 0.031 for gp100 and P = 0.010 for MART-1); both were higher than group C (P < 0.001 for gp100 and P < 0.026 for MART-1). With a median of 24 months of follow-up, 23 patients have relapsed. Post-vaccine immune response to MART-1 was associated with relapse-free survival (P = 0.012).

CONCLUSIONS

IL-12 with alum augmented an immune response to melanoma antigens compared with IL-12 with GM-CSF. Immune response was associated with time to relapse.

A recombinant non-pathogenic Leishmania vaccine expressing human immunodeficiency virus 1 (HIV-1) Gag elicits cell-mediated immunity in mice and decreases HIV-1 replication in human tonsillar tissue following exposure to HIV-1 infection

Live-vector human immunodeficiency virus (HIV) vaccines are an integral part of a number of HIV vaccine regimens currently under evaluation that have yielded promising results in pre-clinical testing. In this report, a non-pathogenic protozoan parasitic vector, Leishmania tarentolae, which shares common target cells with HIV-1, was used to express full-length HIV-1 Gag protein. Immunization of BALB/c mice with recombinant L. tarentolae led to the expansion of HIV-1 Gag-specific T cells and stimulated CD8+ T cells to produce gamma interferon in response to specific viral Gag epitopes. A booster immunization with recombinant L. tarentolae elicited effector memory HIV-1 Gag-specific CD4+ T lymphocytes and increased antibody titres against HIV-1 Gag. Most importantly, immunization of human tonsillar tissue cultured ex vivo with Gag-expressing L. tarentolae vaccine vector elicited a 75 % decrease in virus replication following exposure of the immunized tonsils to HIV-1 infection. These results demonstrated that recombinant L. tarentolae is capable of eliciting effective immune responses in mice and human systems, respectively, and suggest that this novel non-pathogenic recombinant vaccine vector shows excellent promise as a vaccination strategy against HIV-1.

Novel chitosan derivative nanoparticles enhance the immunogenicity of a DNA vaccine encoding hepatitis B virus core antigen in mice

BACKGROUND

Chitosan has been shown to possess useful properties such as non-toxicity, high biocompatibility and non-antigenicity that offer advantages for vaccine delivery systems. In this study, we prepared novel chitosan derivative nanoparticles as DNA vaccine carriers and the potential and mechanism of the DNA-nanoparticle complexes in inducing augmented immune responses were explored.

METHODS

The pVAX(HBc)DNA-nanoparticle complexes as vaccine delivery systems were studied in several aspects: the protection against DNase I degradation was measured by an in vitro inhibition assay; the sustained expression of the plasmid in vivo was determined by RT-PCR; the elevated uptake efficiency by phagocytes was observed with confocal microscopy; the biocompatibility was evaluated by cytotoxicity and histology assay; the complexes were administrated to C57BL/6 mice and the humoral and cellular immune responses were evaluated by ELISA, IFN-gamma production and cytolytic T lymphocyte (CTL)-specific lysis assay.

RESULTS

The remaining relative activity of DNase I after inhibition varied from 32.3% to 77.6%. The complexes were observed with higher uptake efficiency by phagocytes than naked DNA. Three types of nanoparticles did not induce significant cytotoxicity at concentrations<or=400 microg/ml. No specific histological alteration related to the injection of the complexes was observed. The formulations of DNA-nanoparticle complexes significantly enhanced the immunogenicity in several parameters: elevated antibody production, higher level of IFN-gamma secretion, and augmented specific cell lysis.

CONCLUSIONS

This study demonstrated the potential of the novel chitosan derivative nanoparticles for safe and effective DNA vaccine delivery.

Novel codon-optimized GM-CSF gene as an adjuvant to enhance the immunity of a DNA vaccine against HIV-1 Gag

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a potent immunomodulatory cytokine. Here we generated a novel codon-optimized murine GM-CSF gene as an adjuvant. The codon-optimized GM-CSF gene significantly increased protein expression levels in all cells tested. Although injection of the wild-type GM-CSF plasmids adjuvanted HIV-1 Gag DNA vaccine induced detectable immune responses, co-administration of plasmids encoding the codon-optimized GM-CSF sequence with the DNA vaccine resulted in a strong antibody and CTL responses and a protective immune response against infection with recombinant vaccinia virus expressing HIV-1 Gag. This novel codon-optimized GM-CSF gene offers a practical molecular strategy for potentiating immune responses to vaccines as well as other immunotherapeutic strategies.

Advances in combating fungal diseases: vaccines on the threshold

The dramatic increase in fungal diseases in recent years can be attributed to the increased aggressiveness of medical therapy and other human activities. Immunosuppressed patients are at risk of contracting fungal diseases in healthcare settings and from natural environments. Increased prescribing of antifungals has led to the emergence of resistant fungi, resulting in treatment challenges. These concerns, together with the elucidation of the mechanisms of protective immunity against fungal diseases, have renewed interest in the development of vaccines against the mycoses. Most research has used murine models of human disease and, as we review in this article, the knowledge gained from these studies has advanced to the point where the development of vaccines targeting human fungal pathogens is now a realistic and achievable goal.

Dengue tetravalent DNA vaccine increases its immunogenicity in mice when mixed with a dengue type 2 subunit vaccine or an inactivated Japanese encephalitis vaccine

We previously developed a dengue tetravalent DNA vaccine that can induce neutralizing antibodies against four dengue viruses in mice. Here, we demonstrated that immunogenicity of our tetravalent vaccine is synergistically increased in mice by co-immunization with dengue type 2 virus (DENV2) subviral extracellular particles (D2EPs) or inactivated Japanese encephalitis vaccine (JEVAX). A single immunization with a mixture of 100 microg of the tetravalent vaccine and 150 ng of D2EPs or a 1/10 dose of JEVAX induced moderate levels of neutralizing antibodies in a 90% plaque reduction assay. Immunized mice were protected from "artificial" viremia created by intravenous injection with DENV2.

Elicitation of strong immune responses by a DNA vaccine expressing a secreted form of hepatitis C virus envelope protein E2 in murine and porcine animal models

AIM: To characterize the immunogenicity of a hepatitis C virus (HCV) E2 DNA vaccine alone or with a protein vaccine boost in murine and porcine animal models.

METHODS: A DNA vaccine expressing a secreted form of HCV E2 protein was constructed and used to vaccinate mice and piglets with or without boosting with a recombinant E2 protein vaccine formulated with CpG ODN and 10% Emulsigen. The immunogenicity of HCV E2 vaccines was analyzed by ELISA for antibody responses, MTT assay for lymphocyte proliferation, ELISPOT for the number of interferon-γ secreting cells, and cytotoxic T lymphocyte assays.

RESULTS: Intradermal injection of E2 DNA vaccine induced strong Th1-like immune responses in mice. In piglets, E2 DNA vaccine elicited moderate and more balanced immune responses. A DNA vaccine prime and protein boost vaccination strategy induced significantly higher E2-specific antibody levels and shifted the immune response towards Th2-like ones in piglets.

CONCLUSION: A DNA vaccine expressing a secreted form of HCV E2 protein elicited E2-specific immune responses in mice and piglets. Recombinant E2 protein vaccination following DNA immunization significantly increased the antibody response in piglets. These HCV E2 vaccines may represent promising hepatitis C vaccine candidates for further investigations.

Immunogenicity and protective efficacy of DNA vaccines expressing rhesus cytomegalovirus glycoprotein B, phosphoprotein 65-2, and viral interleukin-10 in rhesus macaques

Rhesus cytomegalovirus (RhCMV) infection of macaques exhibits strong similarities to human CMV (HCMV) persistence and pathogenesis. The immunogenicity of DNA vaccines encoding three RhCMV proteins (a truncated version of glycoprotein B lacking the transmembrane region and endodomain [gBDeltaTM], phosphoprotein 65-2 [pp65-2], and viral interleukin-10 [vIL-10]) was evaluated in rhesus macaques. Two groups of monkeys (four per group) were genetically immunized four times with a mixture of either pp65-2 and gBDeltaTM or pp65-2, vIL-10, and gBDeltaTM. The vaccinees developed anti-gB and anti-pp65-2 antibodies in addition to pp65-2 cellular responses after the second booster immunization, with rapid responses observed with subsequent DNA injections. Weak vIL-10 immune responses were detected in two of the four immunized animals. Neutralizing antibodies were detected in seven monkeys, although titers were weak compared to those observed in naturally infected animals. The immunized monkeys and naïve controls were challenged intravenously with 10(5) PFU of RhCMV. Anamnestic binding and neutralizing antibody responses were observed 1 week postchallenge in the vaccinees. DNA vaccination-induced immune responses significantly decreased peak viral loads in the immunized animals compared to those in the controls. No difference in peak viral loads was observed between the pp65-2/gBDeltaTM DNA- and pp65-2/vIL-10/gBDeltaTM-vaccinated groups. Antibody responses to nonvaccine antigens were lower postchallenge in both vaccine groups than in the controls, suggesting long-term control of RhCMV protein expression. These data demonstrated that DNA vaccines targeting the RhCMV homologues of HCMV gB and pp65 altered the course of acute and persistent RhCMV infection in a primate host.

Evaluation of immunogenicity and efficacy of combined DNA and adjuvanted protein vaccination in a human immunodeficiency virus type 1/murine leukemia virus pseudotype challenge model

A DNA plasmid encoding human immunodeficiency virus type 1 (HIV-1) env, nef and tat genes was used in mice in a prime-boost immunization regimen with the corresponding recombinant proteins. The genetic immunogen was delivered with a gene gun and the proteins were injected intramuscularly together with the adjuvant AS02A. Immunizations were followed by experimental challenge with pseudotyped HIV-1 subtype A or B virus. In an initial experiment in which animals were challenged four weeks after the final immunization, all single modality and prime-boost vaccinations resulted in a significant level of protection as compared to control animals. There was a trend for DNA-alone immunization yielding the highest protection. In a subsequent study, a late challenge was performed 19 weeks after the final immunization. All groups having received the DNA vaccine, either alone or in combination with adjuvanted protein, exhibited strong protection against HIV replication. The subtype-specific protection against the experimental HIV challenge was significantly stronger than the cross-protection. Cellular and humoral immune responses were assessed during immunization and after challenge, but without clear correlation to protection against HIV replication. The data suggest that either DNA or protein antigens alone provide partial protection against an HIV-1/MuLV challenge and that DNA immunization is essential for achieving very high levels of efficacy in this murine HIV-1 challenge model. While prime-boost combinations were more immunogenic than DNA alone, they did not appear to provide any further enhancement over DNA vaccine mediated efficacy. The DNA immunogen might prime low levels of CD8+ T cells responsible for virus clearance or possibly a yet unidentified mechanism of protection.

Differential activities of alpha/beta IFN subtypes against influenza virus in vivo and enhancement of specific immune responses in DNA vaccinated mice expressing haemagglutinin and nucleoprotein

Vaccines are urgently needed to elicit immunity to different influenza virus strains. DNA vaccines can elicit partial protective immunity, however their efficacy requires improvement. We assessed the capacity of individual type I IFN multigene family members as subtype transgenes to abrogate influenza virus replication in a vaccination/challenge mouse model. Differences in antiviral efficacy were found among the subtypes with IFNA5 and IFNA6 being most effective, while IFNA1 was the least effective in reducing lung virus replication. Mice vaccinated with combinatorial HA/IFNA6 or NP/IFNA6 showed reduced lung viral titres, clinical score, body weight loss, and pulmonary tissue damage compared to IFNA6, HA, or NP viral vaccination alone. In addition, IFNA6 increased IgG2a titres with upregulation of IFN-gamma response in the respiratory tract. We conclude that IFN-alpha 6 has antiviral and immunomodulatory effects, which improve efficacy of DNA vaccines for enhanced control of influenza.

Distinct contributions of vaccine-induced immunoglobulin G1 (IgG1) and IgG2a antibodies to protective immunity against influenza

Vaccination represents the most effective form of protection against influenza infection. While neutralizing antibodies are typically measured as a correlate of vaccine-induced protective immunity against influenza, nonneutralizing antibodies may contribute to protection or amelioration of disease. The goal of this study was to dissect the individual contributions of the immunoglobulin G1 (IgG1) and IgG2a antibody isotypes to vaccine-induced immunity against influenza virus. To accomplish this, we utilized an influenza vaccine regimen that selectively enhanced IgG1 or IgG2a antibodies by using either DNA or viral replicon particle (VRP) vectors expressing influenza virus hemagglutinin (HA) (HA-DNA or HA-VRP, respectively). After HA-DNA vaccination, neutralizing antibodies were detected by both in vitro (microneutralization) and in vivo (lung viral titer) methods and were associated with increased IgG1 expression by enzyme-linked immunosorbent assay (ELISA). Vaccination with HA-VRP did not strongly stimulate either neutralizing or IgG1 antibodies but did induce IgG2a antibodies. Expression of IgG2a antibodies in this context correlated with clearance of virus and increased protection against lethal influenza challenge. Increased induction of both antibody isotypes as measured by ELISA was a better correlate for vaccine efficacy than neutralization alone. This study details separate but important roles for both IgG1 and IgG2a expression in vaccination against influenza and argues for the development of vaccine regimens that stimulate and measure expression of both antibody isotypes.

Bicistronic woodchuck hepatitis virus core and gamma interferon DNA vaccine can protect from hepatitis but does not elicit sterilizing antiviral immunity

The immunity elicited against nucleocapsid of hepatitis B virus (HBV) and closely related woodchuck hepatitis virus (WHV) has been shown to be important in resolution of hepatitis and protection from infection. Further, activity of gamma interferon (IFN-gamma), which may directly inhibit hepadnavirus replication, promotes antiviral defense and favors T helper cell type 1 (Th1) response, which is seemingly a prerequisite of HBV clearance. In this study, to enhance induction of protective immunity against hepadnavirus, healthy woodchucks were immunized with a bicistronic DNA vaccine carrying WHV core (WHc) and woodchuck IFN-gamma (wIFN-gamma) gene sequences. Three groups, each group containing three animals, were injected once or twice with 0.5 mg, 0.9 mg, or 1.5 mg per dose of this vaccine. In addition, four animals received two injections of 0.6 mg or 1 mg WHc DNA alone. All animals were challenged with WHV. The results showed that four of nine animals injected with the bicistronic vaccine and one of four immunized with WHc DNA became protected from serologically evident infection and hepatitis. This protection was not linked to induction of WHc antigen-specific antibodies or T-cell proliferative response and was not associated with enhanced transcription of Th1 cytokines or 2',5'-oligoadenylate synthetase. Strikingly, all animals protected from hepatitis became reactive for WHV DNA and carried low levels of replicating virus in hepatic and lymphoid tissues after challenge with WHV. This study shows that the bicistronic DNA vaccine encoding both hepadnavirus core antigen and IFN-gamma was more effective in preventing hepatitis than that encoding virus core alone, but neither of them could mount sterile immunity against the virus or prevent establishment of occult infection.

Delivery systems and adjuvants for oral vaccines

The oral route is the ideal means of delivering prophylactic and therapeutic vaccines, offering significant advantages over systemic delivery. Most notably, oral delivery is associated with simple administration and improved safety. In addition, unlike systemic immunisation, oral delivery can induce mucosal immune responses. However, the oral route of vaccine delivery is the most difficult because of the numerous barriers posed by the gastrointestinal tract. To facilitate effective immunisation with peptide and protein vaccines, antigens must be protected, uptake enhanced and the innate immune response activated. Numerous delivery systems and adjuvants have been evaluated for oral vaccine delivery, including live vectors, inert particles and bacterial toxins. Although developments in oral vaccines have been disappointing so far, in terms of the generation of products, the availability of a range of novel delivery systems offers much greater hope for the future development of improved oral vaccines.