A qualitative progression in HIV type 1 glycoprotein 120-specific cytotoxic cellular and humoral immune responses in mice receiving a DNA-based glycoprotein 120 vaccine

STING Is Required in Conventional Dendritic Cells for DNA Vaccine Induction of Type I T Helper Cell- Dependent Antibody Responses

DNA vaccines elicit antibody, T helper cell responses and CD8⁺ T cell responses. Currently, little is known about the mechanism that DNA vaccines employ to induce adaptive immune responses. Prior studies have demonstrated that stimulator of interferon genes (STING) and conventional dendritic cells (cDCs) play critical roles in DNA vaccine induced antibody and T cell responses. STING activation by double stranded (dsDNA) sensing proteins initiate the production of type I interferon (IFN),but the DC-intrinsic effect of STING signaling is still unclear. Here, we investigated the role of STING within cDCs on DNA vaccine induction of antibody and T cell responses. STING knockout (STING^-/- ) and conditional knockout mice that lack STING in cDCs (cDC STING cKO), were immunized intramuscularly with a DNA vaccine that expressed influenza A nucleoprotein (pNP). Both STING^-/- and cDC STING cKO mice had significantly lower type I T helper (Th1) type antibody (anti-NP IgG_2C) responses and lower frequencies of Th1 associated T cells (NP-specific IFN-γ⁺CD4⁺ T cells) post-immunization than wild type (WT) and cDC STING littermate control mice. In contrast, all mice had similar Th2-type NP-specific (IgG₁) antibody titers. STING^-/- mice developed significantly lower polyfunctional CD8⁺ T cells than WT, cDC STING cKO and cDC STING littermate control mice. These findings suggest that STING within cDCs mediates DNA vaccine induction of type I T helper responses including IFN-γ⁺CD4⁺ T cells, and Th1-type IgG_2C antibody responses. The induction of CD8⁺ effector cell responses also require STING, but not within cDCs. These findings are the first to show that STING is required within cDCs to mediate DNA vaccine induced Th1 immune responses and provide new insight into the mechanism whereby DNA vaccines induce Th1 responses.

A Guide to Nucleic Acid Vaccines in the Prevention and Treatment of Infectious Diseases and Cancers: From Basic Principles to Current Applications

Faced with the challenges posed by infectious diseases and cancer, nucleic acid vaccines present excellent prospects in clinical applications. Compared with traditional vaccines, nucleic acid vaccines have the characteristics of high efficiency and low cost. Therefore, nucleic acid vaccines have potential advantages in disease prevention and treatment. However, the low immunogenicity and instability of nucleic acid vaccines have limited their development. Therefore, a large number of studies have been conducted to improve their immunogenicity and stability by improving delivery methods, thereby supporting progress and development for clinical applications. This article mainly reviews the advantages, disadvantages, mechanisms, delivery methods, and clinical applications of nucleic acid vaccines.

Advancements in DNA vaccine vectors, non-mechanical delivery methods, and molecular adjuvants to increase immunogenicity

A major advantage of DNA vaccination is the ability to induce both humoral and cellular immune responses. DNA vaccines are currently used in veterinary medicine, but have not achieved widespread acceptance for use in humans due to their low immunogenicity in early clinical studies. However, recent clinical data have re-established the value of DNA vaccines, particularly in priming high-level antigen-specific antibody responses. Several approaches have been investigated for improving DNA vaccine efficacy, including advancements in DNA vaccine vector design, the inclusion of genetically engineered cytokine adjuvants, and novel non-mechanical delivery methods. These strategies have shown promise, resulting in augmented adaptive immune responses in not only mice, but also in large animal models. Here, we review advancements in each of these areas that show promise for increasing the immunogenicity of DNA vaccines.

A DNA inducing VLP vaccine designed for HIV and tested in mice

We developed a DNA vaccine that induces the formation of a VLP in vivo. This VLP was designed to elicit neutralizing antibodies, to induce better T-cell responses and to activate the innate immune system. Overall, 5 groups of 10 mice were electroporated with the following constructs: pVLP-LTR-GagPro [full], pVLP-GagPro [VLP wihout RNA], pVLP-LTR-Gag [VLP immature], pVLP-Gag and pVLP-EnvBG505 [regular DNA vaccine] and a mock group. We performed ICS on the mouse spleens and performed ELISA for ENV antibodies and a Luminex assay for inflammatory cytokines. The VLP showed good binding to the neutralizing antibodies. The percentage of CD4 cells producing cytokines was 0.1% [IFNg], 0.15%[IL-2] and 0.2% [TNFa] for the construct pVLP-LTR-GagPro. The percentage of CD8 cells producing cytokines was 0.3%[IFNg], 0.2%[IL-2] and 0.25%[TNFa]. All pVLP constructs induced more antibodies for EnvBG505 than the regular DNA vaccine Env. The pVLP-LTR-GagPro induced more IL-1B than the other constructs 24 hours post-vaccination.

Advancements in DNA vaccine vectors, non-mechanical delivery methods, and molecular adjuvants to increase immunogenicity

A major advantage of DNA vaccination is the ability to induce both humoral and cellular immune responses. DNA vaccines are currently used in veterinary medicine, but have not achieved widespread acceptance for use in humans due to their low immunogenicity in early clinical studies. However, recent clinical data have re-established the value of DNA vaccines, particularly in priming high-level antigen-specific antibody responses. Several approaches have been investigated for improving DNA vaccine efficacy, including advancements in DNA vaccine vector design, the inclusion of genetically engineered cytokine adjuvants, and novel non-mechanical delivery methods. These strategies have shown promise, resulting in augmented adaptive immune responses in not only mice, but also in large animal models. Here, we review advancements in each of these areas that show promise for increasing the immunogenicity of DNA vaccines.

A cGAS-Independent STING/IRF7 Pathway Mediates the Immunogenicity of DNA Vaccines

It has been known since the discovery of DNA vaccines >20 y ago that DNA vaccines can function as adjuvants. Our recent study reported the involvement of Aim2 as the sensor of DNA vaccines in eliciting Ag-specific Ab responses. Our findings indicated the presence of previously unrecognized innate immune response pathways in addition to the TLR9 pathway, which is mainly activated by the CpG motifs of DNA vaccines. Our data further demonstrated the requirement of type I IFN in DNA vaccine-induced immune responses via the Aim2 pathway, but the exact downstream molecular mechanism was not characterized. In the present study, we investigated the roles of the putative DNA sensor cyclic GMP-AMP synthase (cGas), as well as the downstream IFN regulatory factors (IRF) 3 and 7 in type I IFN induction and Ag-specific immune responses elicited by DNA vaccination. Our results showed that DNA vaccine-induced, Irf7-dependent signaling, as part of the Sting pathway, was critical for generation of both innate cytokine signaling and Ag-specific B and T cell responses. In contrast, Irf3 was not as critical as expected in this pathway and, more surprisingly, immune responses elicited by DNA vaccines were not cGas-dependent in vivo. Data from this study provide more details on the innate immune mechanisms involved in DNA vaccination and further enrich our understanding on the potential utility of DNA vaccines in generating Ag-specific immune responses.

Immunization with structural and non-structural proteins of Theiler's murine encephalomyelitis virus alters demyelinating disease

Theiler's murine encephalomyelitis virus (TMEV) causes a demyelinating disease similar to multiple sclerosis in the central nervous system (CNS) of susceptible SJL/J mice. Immune responses to TMEV contribute to viral clearance as well as to demyelination. We constructed recombinant vaccinia viruses (VV) that encode each or all of the capsid proteins (VV(VP1), VV(VP2), VV(VP3), VV(VP4), and VV(all)) or non-structural proteins (VV(P2), VV(P2P3), and VV(3'P3)) of the Daniels strain of TMEV. To determine the role of each of the coding regions of TMEV in vivo, we immunized SJL/J mice with each recombinant VV, with or without subsequent TMEV infection. The groups of mice were compared clinically, immunologically, and histologically. No mice immunized with any recombinant VV without subsequent TMEV infection developed demyelination. However, antibody responses to TMEV were detected in mice immunized with VV(all). In addition, in some mice, VV(P2) immunization induced mild meningitis. VV(VP3) or VV(VP4) immunization of mice prior to TMEV infection ameliorated TMEV-induced pathology or clinical signs of disease. The beneficial effect of VP4 immunization was also seen through DNA immunization with a plasmid encoding VP4 and leader prior to TMEV infection. Therefore, vaccination against not only surface capsid proteins (VV(VP3) and VV(all)) but also non-surface capsid protein (VV(VP4)), and non-structural proteins (VV(P2)) can elicit immune responses to virus or modulate subsequent viral-induced CNS disease.

Synergistic enhancement of immunogenicity and protection in mice against Schistosoma japonicum with codon optimization and electroporation delivery of SjTPI DNA vaccines

Schistosomiasis is an endemic, zoonotic parasitic disease caused by Schistosoma japonicum that remains a public health concern and an effective vaccine is needed. Triose-phosphate isomerase from S. japonicum is a promising schistosome vaccine antigen shown to be immunogenic when delivered as a DNA vaccine, however, the previous S. japonicum triose-phosphate isomerase (SjTPI) DNA vaccine needs to be further optimized to achieve higher protection. In the current study, codon optimization of SjTPI DNA insert, combined with electroporation but not with the addition of a tPA leader or heat-shock protein in-frame with the SjTPI gene insert, enhanced Th1-type antibody and cytokine production and most significantly, achieved great than 50% reduction of infection against challenge with S. japonicum cercariae, a major milestone in S. japonicum vaccine development. Our results suggest that the combination of a codon optimized vaccine design and an efficient vaccine delivery system can greatly improve the potential of a SjTPI DNA vaccine as a viable schistosome vaccine candidate.

Comparison of intramuscular and footpad subcutaneous immunization with DNA vaccine encoding HSV-gD2 in mice

Herpes simplex virus type 2 is the most common infectious agent in humans that causes genital herpes disease and vaccination is a desirable method to prevent herpes infections. An effective therapeutic vaccine will need to elicit virus-specific immune responses. The route of immunization has important role in immune responses. In this study, DNA vaccine encoding glycoprotein D of herpes simplex virus type 2 (HSV-gD2) was prepared and injected via intramuscular and footpad routes to determine the optimal method of delivery for immune stimulation. The control manipulation of immune response by concerning route of administration is highly appreciated issue by researches. Although DNA vaccine containing HSV-gD2 is effective in both intramuscular and footpad injection routes, the latter could induce significantly higher cellular responses against HSV-2.

Particle-mediated gene delivery in vivo and in vitro

Particle-mediated or "gene gun" technology has been developed as a nonviral method for gene transfer into various mammalian tissues. Gene delivery is achieved by physical force: a strong shock wave is generated that accelerates DNA-coated gold particles to high speeds, providing them with the momentum needed to penetrate the targeted cells. This unit describes general procedures for in vivo and in vitro DNA and RNA transfections by particle-mediated delivery. The Basic Protocol and an alternate protocol address in vivo delivery to mouse skin. In vitro delivery to cryopreserved and adherent cells is also described.

Immunogenicity of hybrid DNA vaccines expressing hepatitis B core particles carrying human and simian immunodeficiency virus epitopes in mice and rhesus macaques

An effective HIV vaccine will likely need to induce broad and potent CTL responses. Epitope-based vaccines offer significant potential for inducing multi-specific CTL, but often require conjugation to T helper epitopes or carrier moieties to induce significant responses. We tested hybrid DNA vaccines encoding one or more HIV or SIV CTL epitopes fused to a hepatitis B core antigen (HBcAg) carrier gene as a means to improve the immunogenicity of epitope-based DNA vaccines. Immunization of mice with a HBcAg-HIV epitope DNA vaccine induced CD8(+) T cell responses that significantly exceeded levels induced with DNA encoding either the whole HIV antigen or the epitope alone. In rhesus macaques, a multi-epitope hybrid HBcAg-SIV DNA vaccine induced CTL responses to 13 different epitopes, including 3 epitopes that were previously not detected in SIV-infected macaques. These data demonstrate that immunization with hybrid HBcAg-epitope DNA vaccines is an effective strategy to increase the magnitude and breadth of HIV-specific CTL responses.

Combination DNA plus protein HIV vaccines

A major challenge in developing an HIV vaccine is to identify immunogens and delivery methods that will elicit balanced humoral and cell mediate immunities against primary isolates of HIV with diverse sequence variations. Since the discovery of using protein coding nucleic acids (mainly DNA but also possible RNA) as a means of immunization in the early 1990s, there has been rapid progress in the creative use of this novel approach for the development of HIV vaccines. Although the initial impetus of using DNA immunization was for the induction of strong cell-mediated immunity, recent studies have greatly expanded our understanding on the potential role of DNA immunization to elicit improved quality of antibody responses. This function is particularly important to the development of HIV vaccines due to the inability of almost every previous attempt to develop broadly reactive neutralizing antibodies against primary HIV-1 isolates. Similar to the efforts of developing cell mediated immunity by using a DNA prime plus viral vector boost approach, the best antibody responses with DNA immunization were achieved when a protein boost component was included as part of the immunization schedule. Current experience has suggested that a combination DNA plus protein vaccination strategy is able to utilize the benefits of DNA and protein vaccines to effectively induce both cell-mediated immunity and antibody responses against invading organisms.

Combined immunization with fusion genes of mutated E7 gene of human papillomavirus type 16 did not enhance antitumor effect

BACKGROUND

The E7 oncoprotein of human papillomavirus type 16 (HPV16) is frequently used as a model tumor-associated antigen. Its immunogenicity has been substantially enhanced by fusion with several proteins of various origins and functions. Different mechanisms have been responsible for increased vaccination efficacy of fusion proteins.

METHODS AND RESULTS

We linked E7 and its mutated form (E7GGG) with the mouse heat-shock protein 70.1 (HSP70.1). Enhanced immunogenicity of both fusion genes administered via a gene gun was demonstrated by protection of C57BL/6 mice against oncogenic MHC class I positive TC-1 cells producing the HPV16 E7 oncoprotein but not against the MHC class I negative TC-1/A9 subline. To assess if the efficacy of E7-based DNA vaccines could be increased by combination of various fusion genes, we combined the HSP70.1 fusion genes (i.e. E7HSP or E7GGGHSP) with the fusion construct linking E7GGG with targeting signals of lysosome-associated membrane protein 1 (Sig/E7GGG/LAMP-1). Treatment of mice 4 days after TC-1 cell inoculation showed moderately higher immunization potency of HSP70.1 fusion genes in comparison with the Sig/E7GGG/LAMP-1 gene. Any combination of two fusion genes given in the same gene gun shot neither was more effective compared with single genes nor protected mice against TC-1/A9 cells. As fusion of E7GGG with E. coli glucuronidase (E7GGG.GUS) had been previously proven to provide partial protection from TC-1/A9-induced tumors, we also combined E7GGGHSP with E7GGG.GUS. The genes were inoculated either in mix in two gene gun shots or separately each gene in one shot into opposite sides of the abdomen. Neither mode of combined immunization induced higher protection than E7GGG.GUS alone. However, doubling the DNA dose considerably enhanced the antitumor efficacy of E7GGG.GUS.

CONCLUSIONS

We constructed highly immunogenic fusions of HPV16 E7 and E7GGG with mouse HSP70.1. Furthermore, we substantially enhanced protection against TC-1/A9 cells with downregulated MHC class I expression by doubling the pBSC/E7GGG.GUS dose, but we failed to demonstrate a beneficial effect of any combination of two fusion genes with different mechanisms causing enhancement of HPV16 E7 immunogenicity.

DNA vaccines against human immunodeficiency virus type 1 in the past decade

This article reviews advances in the field of human immunodeficiency virus type 1 (HIV-1) and AIDS vaccine development over the last decade, with an emphasis on the DNA vaccination approach. Despite the discovery of HIV-1 and AIDS in humans nearly 20 years ago, there is no vaccine yet that can prevent HIV-1 infection. The focus has shifted toward developing vaccines that can control virus replication and disease progression by eliciting broadly cross-reactive T-cell responses. Among several approaches evaluated, the DNA-based modality has shown considerable promise in terms of its ability to elicit cellular immune responses in primate studies. Of great importance are efforts aimed at improvement of the potency of this modality in the clinic. The review discusses principles of DNA vaccine design and the various mechanisms of plasmid-encoded antigen presentation. The review also outlines current DNA-based vaccine strategies and vectors that have successfully been shown to control virus replication and slow disease progression in animal models. Finally, it lists recent strategies that have been developed as well as novel approaches under consideration to enhance the immunogenicity of plasmid-encoded HIV-1 antigen in various animal models.

Intravascular naked DNA vaccine encoding glycoprotein B induces protective humoral and cellular immunity against herpes simplex virus type 1 infection in mice

Naked plasmid DNA (pDNA) vaccine expressing herpes simplex virus type 1 (HSV-1) glycoprotein B (gB) was tested for protective activity against acute HSV-1 infection in mice. The pDNA was intravenously injected into Balb/c mice via their tail vein under high pressure, and the vaccination was performed two times at an interval of 7 days. The gB gene vaccination significantly protected the mice from subsequent intraperitoneal challenge with a lethal dose of HSV-1, which killed all the animals given control plasmid or saline. The protective activity was correlated with the dose of the plasmid inoculated, the survival rate reaching 83% in mice vaccinated with 5 microg of pDNA. The vaccinated mice were also protected from latent HSV infection. The immunized mice showed significant elevation in neutralizing antibody against HSV-1 as well as serum levels of interleukin-12 (IL-12) and interferon-gamma (IFN-gamma). When mice were immunized with 5 microg of an Epstein-Barr virus (EBV)-based plasmid vector harboring the gB, the cytotoxic T lymphocytes (CTLs) activity and proliferative response for HSV-1 were also induced. The results strongly suggest that intravenous immunization of naked pDNA may induce humoral and cellular immune responses against the virus, leading to a significant prophylactic outcome against HSV-1 infection in mice.

DNA vaccination of macaques by a full-genome simian/human immunodeficiency virus type 1 plasmid chimera that produces non-infectious virus particles

A DNA vaccination regime was investigated previously in rhesus macaques using a full-genome human immunodeficiency virus type 1 (HIV-1) plasmid, which, due to mutations in the nucleocapsid (NC) proteins, produced only non-infectious HIV-1 particles (Akahata et al., Virology 275, 116-124, 2000). In that study, four monkeys were injected intramuscularly 14 times with the plasmid. All of them showed immunological responses against HIV-1 and partial protection from challenge with a simian immunodeficiency virus/HIV (SHIV) chimeric virus. To improve this DNA vaccination regime, the plasmid used for vaccination was changed. In the present study, four macaques were injected intramuscularly eight times with a full-genome SHIV plasmid that produces non-infectious SHIV particles. CTL activities were higher than those observed in monkeys vaccinated previously with the HIV-1 plasmid. In all macaques vaccinated, peak plasma virus loads after homologous challenge with SHIV were two to three orders of magnitude lower than those of the naive controls, and virus loads fell below the level of detection at 6 weeks post-challenge. This suggested that the vaccination regime in this study was partially effective and better than the previous regime.

Plasmid vectors encoding cholera toxin or the heat-labile enterotoxin from Escherichia coli are strong adjuvants for DNA vaccines

Two plasmid vectors encoding the A and B subunits of cholera toxin (CT) and two additional vectors encoding the A and B subunits of the Escherichia coli heat-labile enterotoxin (LT) were evaluated for their ability to serve as genetic adjuvants for particle-mediated DNA vaccines administered to the epidermis of laboratory animals. Both the CT and the LT vectors strongly augmented Th1 cytokine responses (gamma interferon [IFN-gamma]) to multiple viral antigens when codelivered with DNA vaccines. In addition, Th2 cytokine responses (interleukin 4 [IL-4]) were also augmented by both sets of vectors, with the effects of the LT vectors on IL-4 responses being more antigen dependent. The activities of both sets of vectors on antibody responses were antigen dependent and ranged from no effect to sharp reductions in the immunoglobulin G1 (IgG1)-to-IgG2a ratios. Overall, the LT vectors exhibited stronger adjuvant effects in terms of T-cell responses than did the CT vectors, and this was correlated with the induction of greater levels of cyclic AMP by the LT vectors following vector transfection into cultured cells. The adjuvant effects observed in vivo were due to the biological effects of the encoded proteins and not due to CpG motifs in the bacterial genes. Interestingly, the individual LT A and B subunit vectors exhibited partial adjuvant activity that was strongly influenced by the presence or absence of signal peptide coding sequences directing the encoded subunit to either intracellular or extracellular locations. Particle-mediated delivery of either the CT or LT adjuvant vectors in rodents and domestic pigs was well tolerated, suggesting that bacterial toxin-based genetic adjuvants may be a safe and effective strategy to enhance the potency of both prophylactic and therapeutic DNA vaccines for the induction of strong cellular immunity.

Induction of mucosal protection against primary, heterologous simian immunodeficiency virus by a DNA vaccine

An effective vaccine against human immunodeficiency virus (HIV) should protect against mucosal transmission of genetically divergent isolates. As a safe alternative to live attenuated vaccines, the immunogenicity and protective efficacy of a DNA vaccine containing simian immunodeficiency virus (SIV) strain 17E-Fr (SIV/17E-Fr) gag-pol-env was analyzed in rhesus macaques. Significant levels of cytotoxic T lymphocytes (CTL), but low to undetectable serum antibody responses, were observed following multiple immunizations. SIV-specific mucosal antibodies and CTL were also detected in rectal washes and gut-associated lymphoid tissues, respectively. Vaccinated and naive control monkeys were challenged intrarectally with SIV strain DeltaB670 (SIV/DeltaB670), a primary isolate whose env is 15% dissimilar to that of the vaccine strain. Four of seven vaccinees were protected from infection as determined by the inability to identify viral RNA or DNA sequences in the peripheral blood and the absence of anamnestic antibody responses postchallenge. This is the first report of mucosal protection against a primary pathogenic, heterologous isolate of SIV by using a commercially viable vaccine approach. These results support further development of a DNA vaccine for protection against HIV.

DNA vaccination with map1 gene followed by protein boost augments protection against challenge with Cowdria ruminantium, the agent of heartwater

A DNA vaccine encoding the immunodominant MAP1 protein of Cowdria ruminantium (Crystal Springs (CS) strain) was shown to partially protect DBA/2 mice against homologous lethal challenge. To enhance the protective capacity of this DNA vaccine, the effects of length of interval between vaccinations and of prime-boost regimes were investigated. Increasing the interval between vaccinations from 2 to 12 weeks did not result in better protection (P=0.900). However, boosting DNA vaccine-primed mice with recombinant MAP1 protein significantly augmented protection on homologous challenge in various trials from 13-27 to 53-67% (P<0.050). The augmented protection by the prime-boost regimen correlated with augmented T(H1) type immune responses that were induced by the DNA vaccine. These responses were characterized by production of IFN-gamma, IL-2 and anti-MAP1 antibodies of predominantly IgG2a isotype, and were critical for protection against C. ruminantium infection. Cytokine analyses were done at 48h after in vitro stimulation of splenocytes with C. ruminantium or control antigens. In contrast, splenocytes of DNA vector control mice produced no cytokines and these mice were fully susceptible to challenge. In addition, DBA/2 mice immunized with the recombinant MAP1 protein without DNA vaccine priming produced non-protective T(H2) type immune responses which were characterized by production of IL-4, IL-5, IL-10 and IgG1 anti-MAP1 antibodies. A second DNA vaccine containing map1 gene from the Mbizi strain of C. ruminantium also delivered by a prime-boost regime, conferred less protection against heterologous challenge. Hence, in developing DNA vaccines against heartwater that contain map1 gene, a prime-boost regimen should be adopted and gene sequence heterogeneity of field isolates should also be considered.

Cellular HIV-1 immune responses in natural infection and after genetic immunization

By eliminating infected cells, virus-specific cytotoxic T-lymphocytes (CTL) play a central role in host protection. Many studies to date seem to support the concept that human immunodeficiency virus (HIV)-specific CTL responses contribute to the control of viral replication, and thus delay the onset of disease. The feasibility of improving the virus-specific T-cell immunity by immunizing during the asymptomatic phase of infection has been studied in man. DNA vaccination is a novel strategy, involving direct inoculation of genetic material that is capable of producing antigen intracellularly for presentation to CTL. Such DNA-based immunization has been shown in animal models to be effective for the induction of both cellular and humoral immune responses as well as for protection from infectious challenge. This article reviews the cell-mediated immune responses in natural HIV-1 infection and the induction by DNA vaccination in humans.

Construction, biological activity, and immunogenicity of synthetic envelope DNA vaccines based on a primary, CCR5-tropic, early HIV type 1 isolate (BX08) with human codons

So far codon-optimized HIV-1 envelope genes have been investigated for the T cell line-adapted strain MN, which differs in several aspects from primary isolates. Envelopes of primary isolates may be more relevant for vaccine purposes. This article describes for the first time the engineering and characterization of four "humanized" genes encoding the secreted gp120/gp140, or the membrane-bound gp150/gp160, of a primary CCR5 tropic, clade B, clinical isolate HIV-1(BX08). The genes were built in fragments for easy cassette exchange of regions important for immunogenicity, function, and expression. The transcription and expression of the synthetic genes in mammalian cell lines were Rev independent and highly increased. Increased expression of membrane-bound gp160 induced a high cytopathic effect in U87.CD4.CCR5 cells. Gene gun and intramuscular DNA vaccination in mice induced a strong specific cytotoxic T lymphocyte response independent of the gene construct, expression level, or DNA immunization route. In contrast, the highest anti-gp120 antibody levels were induced by synthetic genes encoding the secreted glycoproteins followed by gp160/gp150. Unlike HIV-1(MN), HIV-1(BX08) V3 was not immune dominant. Despite the high antibody response only low and inconsistent neutralizing titers to the homologous HIV-1 isolate were measured. However, neutralization of SHIV89.6P could be obtained. Thus, the neutralizing epitopes on the cell line-adapted SHIV89.6P and HIV-1(MN) may be more antigenically available for the cross-neutralizing antibodies induced. In conclusion, complete "humanization" of the DNA vaccine genes failed to induce a consistent neutralizing antibody response, albeit expression and immunogenicity of the primary HIV-1 glycoproteins were greatly improved. Optimization in terms of improving neutralization may require further modifications of the DNA vaccine gene. The synthetic cassette construct described is a convenient tool developed to investigate this further.

Immunization of cats against feline immunodeficiency virus (FIV) infection by using minimalistic immunogenic defined gene expression vector vaccines expressing FIV gp140 alone or with feline interleukin-12 (IL-12), IL-16, or a CpG motif

Four groups of cats, each containing four animals, were immunized at 0, 3, and 6 weeks with minimalistic immunogenic defined gene expression vector (MIDGE) vaccines containing the gene(s) for feline immunodeficiency virus (FIV) gp140, FIV gp140 and feline interleukin-12 (IL-12), FIV gp140 and feline IL-16, or FIV gp140 and a CpG motif. MIDGEs were coated onto gold beads and injected intradermally with a gene gun. A fifth group of four cats were immunized in an identical manner but with blank gold beads. All cats were challenge exposed to virulent FIV 4 weeks following the final immunization, and the course of infection was monitored. The two groups of cats immunized with the FIV gp140 gene alone or with blank gold particles became highly viremic and seroconverted as early as 4 weeks after infection. In contrast, three of four cats immunized with FIV gp140 in combination with feline IL-12 failed to become viremic or seropositive, as has been shown elsewhere (F. S. Boretti, C. M. Leutenegger, C. Mislin, et al., AIDS 14:1749-1757, 2000). Here we show the effect of IL-12 when used as an adjuvant on the viral RNA and DNA load and on the cytokine profile. In addition, the two groups of cats immunized either with gp140 and IL-16 or with gp140 and the CpG had greatly reduced viremia. Protection correlated weakly with cytotoxic T-lymphocyte activity and increased cytokine transcription of IL-12, gamma interferon, and IL-10 by peripheral blood mononuclear cells in the postchallenge period. This study extends the data on IL-12 and provides new results on CpG motifs and IL-16 used as adjuvants in the FIV cat model.

Genetic vaccination against malaria infection by intradermal and epidermal injections of a plasmid containing the gene encoding the Plasmodium berghei circumsporozoite protein

The circumsporozoite protein (CSP) from the surface of sporozoite stage Plasmodium sp. malaria parasites is among the most important of the malaria vaccine candidates. Gene gun injection of genetic vaccines encoding Plasmodium berghei CSP induces a significant protective effect against sporozoite challenge; however, intramuscular injection does not. In the present study we compared the immune responses and protective effects induced by P. berghei CSP genetic vaccines delivered intradermally with a needle or epidermally with a gene gun. Mice were immunized three times at 4-week intervals and challenged by a single infectious mosquito bite. Although 50 times more DNA was administered by needle than by gene gun, the latter method induced significantly greater protection against infection. Intradermal injection of the CSP genetic vaccine induced a strong Th1-type immune response characterized by a dominant CSP-specific immunoglobulin G2a (IgG2a) humoral response and high levels of gamma interferon produced by splenic T cells. Gene gun injection induced a predominantly Th2-type immune response characterized by a high IgG1/IgG2a ratio and significant IgE production. Neither method generated measurable cytotoxic T lymphocyte activity. The results indicate that a gene gun-mediated CS-specific Th2-type response may be best for protecting against malarial sporozoite infection when the route of parasite entry is via mosquito bite.

DNA vaccination of macaques by a full genome HIV-1 plasmid which produces noninfectious virus particles

In this study, we tried a DNA vaccination regime in rhesus macaques using a full genome HIV-1 plasmid. The HIV-1 genome is under the control of its original LTR promoter, but has a mutated zinc finger motif gene in the nucleocapsid region. Due to the lack of genomic RNA packaging, the plasmid produces only noninfectious viral particles. We repeatedly injected four macaque monkeys intramuscularly with the naked DNA over a period of 40 weeks. To evaluate the humoral and cell-mediated immunity provided by this DNA vaccination, no other booster or other recombinant viral vectors were used. Immunological responses against HIV-1 were elicited in all of the vaccinated monkeys: stable anti-HIV-1 Env antibodies were raised in two monkeys and CTL activities were induced in the other monkeys. The macaques were intravenously challenged at 54 weeks with 100 TCID(50) of SHIV-NM-3rN, which possesses an envelope gene homologous to the one in the vaccinated plasmid. In all of the vaccinated macaques, the peak plasma viral loads induced by the challenge virus were two to three orders of magnitude lower than those of the naive controls. These results suggest that a DNA vaccination regime with a full genome plasmid alone is potentially efficacious and provides a new possibility for the development of an AIDS vaccine.

Interleukin-18 modulates immune responses induced by HIV-1 Nef DNA prime/protein boost vaccine

Many different HIV-1 vaccine strategies have been developed, but as yet none has been completely successful. Promising results from combined DNA prime/protein boost vaccines have been reported. Specific immune responses generated by DNA vaccines can be modulated by the co-delivery of genes coding for cytokines. In this study, we have used the intradermal route by needle injection of a plasmid coding for the HIV-1 Nef accessory protein. We show that DNA prime/protein boost vaccine combinations increase the humoral and cellular immune responses against HIV-1 Nef and that the co-injection of DNA encoding Interleukin-18 (IL-18) modulates the specific immune response towards a Th1 type.

DNA vaccines encoding viral glycoproteins induce nonspecific immunity and Mx protein synthesis in fish

Protective immunity by vaccination with plasmid DNA encoding a viral glycoprotein (G) has long been assumed to result from the induction of a specific immune response. We report here that the initial protection may be due to the induction of alpha/beta interferon, with long-term protection due to a specific response to the encoded viral G. DNA vaccines encoding the Gs of three serologically unrelated fish rhabdoviruses were used to vaccinate rainbow trout against a lethal challenge with infectious hematopoietic necrosis virus (IHNV). All three vaccines, each encoding the G gene of either IHNV (IHNV-G), snakehead rhabdovirus (SHRV) (SHRV-G), or spring viremia of carp virus (SVCV) (SVCV-G), elicited protective immunity against IHNV. Vaccinated fish were challenged at 30 or 70 days postvaccination with lethal doses of IHNV. At 30 days postvaccination, only 5% of fish that had received any of the G vaccines died, whereas more than 50% of the control fish succumbed to virus challenge. When fish were vaccinated and challenged at 70 days postvaccination, only 12% of the IHNV-G-vaccinated fish died compared to 68% for the SHRV-G- and 76% for the SVCV-G-vaccinated fish. Assays for trout Mx protein, an indicator of alpha/beta interferon induction, showed that only fish vaccinated with a G-containing plasmid produced high levels of Mx protein in the kidneys and liver. Interestingly, at day 7 after virus challenge, all of the fish vaccinated with the IHNV-G plasmid were negative for Mx, but the SHRV-G- and SVCV-G-vaccinated fish still showed detectable levels of Mx. These results suggest that DNA vaccines in fish induce an early, nonspecific antiviral protection mediated by an alpha/beta interferon and, later, a specific immune response.

DNA vaccines: immunology, application, and optimization*

The development and widespread use of vaccines against infectious agents have been a great triumph of medical science. One reason for the success of currently available vaccines is that they are capable of inducing long-lived antibody responses, which are the principal agents of immune protection against most viruses and bacteria. Despite these successes, vaccination against intracellular organisms that require cell-mediated immunity, such as the agents of tuberculosis, malaria, leishmaniasis, and human immunodeficiency virus infection, are either not available or not uniformly effective. Owing to the substantial morbidity and mortality associated with these diseases worldwide, an understanding of the mechanisms involved in generating long-lived cellular immune responses has tremendous practical importance. For these reasons, a new form of vaccination, using DNA that contains the gene for the antigen of interest, is under intensive investigation, because it can engender both humoral and cellular immune responses. This review focuses on the mechanisms by which DNA vaccines elicit immune responses. In addition, a list of potential applications in a variety of preclinical models is provided.

Effect of different promoters on immune responses elicited by HIV-1 gag/env multigenic DNA vaccine in Macaca mulatta and Macaca nemestrina

pCMV-NL(Deltapol) and pAKV-NL(Deltapol) expressed human immunodeficiency virus type 1 (HIV-1) gag and env under the regulation of the human cytomegalovirus (CMV) immediate-early (IE) promoter/enhancer and the endogenous AKV murine leukemia viral long terminal repeat (LTR), respectively. Analysis of the immune responses elicited by direct DNA injection of pCMV-NL(Deltapol) and pAKV-NL(Deltapol) in macaques indicated that generation of the humoral and T-cell proliferative responses correlated directly with the promoter strength of the vaccine DNAs. In Macaca mulatta, pCMV-NL(Deltapol) generated stronger humoral responses and T-cell proliferative responses to Gag and Env using less DNA and fewer number of injections than pAKV-NL(Deltapol). Similarly, in Macaca nemestrina pCMV-NL(Deltapol) elicited high humoral responses, which persisted long-term and were boostable. Injection of large amounts of pAKV-NL(Deltapol), in general, failed to produce antibody levels comparable to pCMV-NL(Deltapol). However, injection of a control animal with large amounts of vector DNA produced a generalized enzyme-linked immunosorbent assay (ELISA) reactivity to HIV-1. The results indicated that generation of high immune responses to HIV-1 cannot be achieved by increasing the vaccine DNA dose and may require high protein expression from the DNA by including a strong promoter or by the use of other boosting agents. Furthermore, safety concerns may arise with increasing the DNA dose that could need additional investigation.

Innovations and strategies for the development of anticancer vaccines

In 1893, William Coley reported the spontaneous regression of a soft tissue sarcoma in several patients suffering from acute bacterial infections. Although this observation occurred over a century ago, the concept of anticancer vaccines and the immunotherapy of cancer has only recently seemed plausible. A myriad of specific and non-specific immunostimulatory approaches have been tested throughout the years with only a modicum of success. Most of these approaches were doomed from the outset since they were based on false or inadequate knowledge of tumour immunology. Recent advances in our understanding, most notably the identification of genes encoding for cancer regression antigens, currently permit investigators to pursue a more cogent strategy to develop novel and specific anticancer vaccine approaches. Several of these approaches are currently being tested in clinical trials and have already yielded exciting results. However, a number of immunologic and host obstacles to the successful application of anticancer vaccines remain. This editorial will provide an update on the clinical status of anticancer vaccines and review areas of promising research initiatives.

Immunogenicity and protective efficacy of DNA vaccines encoding secreted and non-secreted forms of Mycobacterium tuberculosis Ag85A

OBJECTIVE

To determine the efficacy of Ag85A-DNA against challenge with a highly virulent human clinical isolate of Mycobacterium tuberculosis (CSU37) and to compare the potencies of two types of Ag85A-DNA vaccines; those expressing secreted and non-secreted forms of the protein.

DESIGN

Ag85A-DNA vaccinated mice were challenged with a highly virulent clinical isolate of M. tuberculosis (CSU37) in order to compare the efficacy of these vaccines. In vitro studies were also performed.

RESULTS

Enhanced humoral and cellular responses were induced in mice vaccinated with the secreted Ag85A-DNA compared to the non-secreted Ag85A-DNA. In addition, secreted Ag85A-DNA conferred protective immunity against infection with M. tuberculosis (CSU37).

CONCLUSIONS

DNA vaccines encoding M. tuberculosis Ag85A have been shown to induce potent humoral and cellular immune responses leading to protection from M. tuberculosis (Erdman) challenge in mouse models. In this study we demonstrate that Ag85A can confer protection in a rigorous challenge model using a highly virulent human clinical isolate of M. tuberculosis (CSU37). This challenge model appears able to discriminate between DNA vaccines of differing potencies, as the more immunogenic DNA construct encoding a secreted form of Ag85A was protective, whereas the less immunogenic DNA construct encoding a non-secreted form of Ag85A was not.

Immunogenicity of full length and truncated SIV envelope proteins

We have compared the immunogenicity of the full-length (FL) SIV envelope (Env) protein and a truncated (T) form of the Env protein which has a short cytoplasmic tail. The Env(T) protein was previously shown to be more fusogenic than Env(FL), has a higher level of incorporation into virus-like particles (VLPs) and membrane vesicles, and expands the viral host range. We have found that mice immunized with VLPs which contained an equal amount of Env(FL) or Env(T) produced similar titres of neutralizing antibody. Comparison of immune responses between animals that received DNA vaccines encoding Env(T) vs. Env (FL) by epidermal delivery demonstrated that a higher level of specific antibody was elicited by Env(T) than Env(FL). This result correlated with a higher level of expression of pCMVEnv(T) than pCMVEnv(FL) observed in vitro. DNA immunization combined with VLP boosting elicited a similar level of neutralizing antibody with both forms of Env proteins. These data indicate that the immunogenicity of Env(FL) and Env(T) is similar, and that either form of Env protein appears to be potentially suitable for use in further development of vaccine preparations.

Immune Responses in Asymptomatic HIV-1-Infected Patients After HIV-DNA Immunization Followed by Highly Active Antiretroviral Treatment

Intensive chemotherapy is capable of reducing the viral load in HIV-1-infected individuals while infected cells are still present. A special property of DNA immunization is to induce both new CTL and Ab responses. We evaluated the possibility of inducing new immune responses in already infected individuals by means of DNA constructs encoding the nef, rev, or tat regulatory HIV-1 genes. Significant changes in viral loads and CD4+ counts were observed in four patients who started highly active antiretroviral treatment (HAART) during the immunization study. The DNA immunization induced Ag-specific T cell proliferation, which persisted up to 9 mo after the last DNA injection, and cytolytic activities but did not, by itself, reduce viral load. Increased levels of CTL precursor cells were induced in all nine DNA-immunized patients. The profile of IFN-γ secretion observed when human PBMC were transfected with the nef, rev, and tat DNA resembled that found in the CTL activity (nef &gt; tat &gt; rev). Ab responses that occurred after immunizations were of a low magnitude. In accordance with the high IL-6 production induced by the nef DNA plasmid, IgG titers were highest in patients immunized with nef DNA. The initiation of HAART appears to contribute to the induction of new HIV-specific CTL responses, but by itself did not cause obvious re-induction of these activities.

Protective Immune Responses Induced by Vaccination with an Expression Genomic Library of Leishmania major

To develop an effective vaccine against the intracellular protozoan parasite Leishmania spp., we investigated the feasibility of expression library immunization (ELI) in the mouse. Genomic expression libraries of L. major were constructed and used to immunize mice. One of the three libraries (L1, with 105 clones) induced a significant protective immune response and delayed the onset of lesion development in highly susceptible BALB/c mice after i.m. immunization, compared with control mice immunized with the empty vector (EV). L1 was then divided into five sublibraries of ∼2 × 104 clones each. Mice immunized with one of the sublibraries (SL1A) developed an even stronger protective effect than that induced by L1. SL1A was further divided into 20 sublibraries (SL2) of ∼103 clones each. One of the SL2 libraries (SL2G) induced a strong protective effect against L. major infection. In direct comparative studies, the protective effect of the sublibraries was in the order of SL2G &gt; SL1A &gt; L1. Lymphoid cells from mice vaccinated with SL2G produced more IFN-γ and NO, compared with cells from control mice injected with EV. Serum from the vaccinated mice also contained more parasite-specific IgG2a Ab, compared with controls. Therefore, these data demonstrate that ELI is feasible against this complex intracellular parasitic infection, by preferentially inducing the development of Th1 responses. Furthermore, by sequential division of the libraries, this approach may be used to enrich and identify protective genes for effective gene vaccination against other parasitic infections.

Gene gun DNA vaccination with Rev-independent synthetic HIV-1 gp160 envelope gene using mammalian codons

DNA immunization with HIV envelope plasmids induce only moderate levels of specific antibodies which may in part be due to limitations in expression influenced by a species-specific and biased HIV codon usage. We compared antibody levels, Th1/Th2 type and CTL responses induced by synthetic genes encoding membrane bound gp160 versus secreted gp120 using optimized codons and the efficient gene gun immunization method. The in vitro expression of syn.gp160 as gp120 + gp41 was Rev independent and much higher than a classical wt.gp160 plasmid. Mice immunized with syn.gp160 and wt.gp160 generated low and inconsistent ELISA antibody titres whereas the secreted gp120 consistently induced faster seroconversion and higher antibody titres. Due to a higher C + G content the numbers of putative CpG immune (Th1) stimulatory motifs were highest in the synthetic gp160 gene. However, both synthetic genes induced an equally strong and more pronounced Th2 response with higher IgG1/IgG2a and IFNgamma/IL-4 ratios than the wt.gp160 gene. As for induction of CTL, synthetic genes induced a somewhat earlier response but did not offer any advantage over wild type genes at a later time point. Thus, optimizing codon usage has the advantage of rendering the structural HIV genes Rev independent. For induction of antibodies the level of expression, while important, seems less critical than optimal contact with antigen presenting cells at locations reached by the secreted gp120 protein. A proposed Th1 adjuvant effect of the higher numbers of CpG motifs in the synthetic genes was not seen using gene gun immunization which may be due to the low amount of DNA used.

Comparison of immunity generated by nucleic acid-, MF59-, and ISCOM-formulated human immunodeficiency virus type 1 vaccines in Rhesus macaques: evidence for viral clearance

The kinetics of T-helper immune responses generated in 16 mature outbred rhesus monkeys (Macaca mulatta) within a 10-month period by three different human immunodeficiency virus type 1 (HIV-1) vaccine strategies were compared. Immune responses to monomeric recombinant gp120SF2 (rgp120) when the protein was expressed in vivo by DNA immunization or when it was delivered as a subunit protein vaccine formulated either with the MF59 adjuvant or by incorporation into immune-stimulating complexes (ISCOMs) were compared. Virus-neutralizing antibodies (NA) against HIV-1SF2 reached similar titers in the two rgp120SF2 protein-immunized groups, but the responses showed different kinetics, while NA were delayed and their levels were low in the DNA-immunized animals. Antigen-specific gamma interferon (IFN-gamma) T-helper (type 1-like) responses were detected in the DNA-immunized group, but only after the fourth immunization, and the rgp120/MF59 group generated both IFN-gamma and interleukin-4 (IL-4) (type 2-like) responses that appeared after the third immunization. In contrast, rgp120/ISCOM-immunized animals rapidly developed marked IL-2, IFN-gamma (type 1-like), and IL-4 responses that peaked after the second immunization. To determine which type of immune responses correlated with protection from infection, all animals were challenged intravenously with 50 50% infective doses of a rhesus cell-propagated, in vivo-titrated stock of a chimeric simian immunodeficiency virus-HIVSF13 construct. Protection was observed in the two groups receiving the rgp120 subunit vaccines. Half of the animals in the ISCOM group were completely protected from infection. In other subunit vaccinees there was evidence by multiple assays that virus detected at 2 weeks postchallenge was effectively cleared. Early induction of potent type 1- as well as type 2-like T-helper responses induced the most-effective immunity.

Antibody response in mice immunized with a plasmid DNA encoding the colonization factor antigen I of enterotoxigenic Escherichia coli

The colonization factor antigen I (CFA/I) is one of the most epidemiologically relevant enterotoxigenic Escherichia coli (ETEC) fimbrial adhesins, which mediates the binding to human small intestine epithelium. A recombinant eukaryotic expression plasmid, pRECFA, encoding the CFA/I protein fused to the glycoprotein D of herpes simplex type 1 virus, was used to generate an antibody response in a murine model following intramuscular inoculation of purified DNA. Eukaryotic cells (BHK-21) transfected with pRECFA expressed the CFA/I protein in vitro, as revealed by Western blot and immunofluorescence microscopy. Administration of a single pRECFA 100-microg dose induced a long-term CFA/I-specific antibody response in BALB/c mice composed mainly of IgG and, to a lesser extent, IgA isotypes. The major CFA/I-specific IgG subclass was IgG2a, suggesting a Th-1-type immune response. A second dose with the same amount of purified DNA, given 2 weeks later, caused a booster effect on the immunoglobulin levels, but did not qualitatively alter the isotypes and subclasses of the induced antibody response. Immunization with different amounts of purified DNA and/or number of doses showed that maximal transient CFA/I-specific antibody levels could be obtained after two 100-microg doses of pRECFA given 2 weeks apart, but long-term antibody levels were similar.

Genetic vaccines

In a few short years, genetic vaccine technology has moved rapidly from a novel concept to an important strategy for the development of human and veterinary vaccines, for numerous indications. This article discusses current areas in which further refinements in technology will influence a variety of infectious disease treatments, including intramuscular and intradermal inoculation, gene gun inoculation, the mechanism of antigen presentation, and the use of genetic adjuvants.

DNA-plasmids of HIV-1 induce systemic and mucosal immune responses

DNA-based immunization has been shown to induce protective immunity against several microbial pathogens including HIV-1. Several routes of DNA vaccination have been exploited. However, the properties of the immune responses seem to differ with the different routes used for DNA delivery, ultimately affecting the outcome of experimental challenge. We measured the primary immune response following one vaccination. This report presents differences associated with three different DNA delivery routes: intramuscular injection, intranasal application, and gene-gun based immunization. Induction of systemic humoral immune responses was achieved most efficiently by either intranasal or gene-gun mediated immunization, followed by intramuscular injection. Mucosal IgA was reproducibly induced by intranasal instillation of the DNA, and found in lung washings, faeces, and vaginal washings. Cytotoxic T cells were not induced by a single immunization, but were observed after three immunizations using intramuscular injections.

Effective induction of HIV-specific CTL by multi-epitope using gene gun in a combined vaccination regime

Reliable and effective induction of cytotoxic T-lymphocytes (CTL) is one of the prime objectives of vaccine research. Previously, novel HIV vaccine candidates were constructed as a string of CTL epitopes (20 human, 3 macaque and 1 mouse) delivered using a DNA vector [Hanke T, Schneider J, Gilbert SG, Hill AVS, McMichael A. DNA multi-CTL epitope vaccines for HIV and Plasmodium falciparum: immunogenicity in mice. Vaccine 1998;16:426-435.] or modified vaccinia Ankara (MVA [Hanke T, Blanchard TJ, Schneider J, Ogg GS, Tan R, Becker MSC, Gilbert SG, Hill AVS, Smith GL, McMichael A. Immunogenicities of intravenous and intramuscular administrations of MVA-based multi-CTL epitope vaccine for HIV in mice. J Gen Virol 1998;79:83-90.]), i.e. vaccine vehicles acceptable for use in humans. In mice, a single intramuscular (i.m.) needle injection of either vaccine alone elicited good CTL responses. Here, it is demonstrated that the multi-epitope DNA also induced CTL when delivered intradermally using the Accell gene gun. The CTL responses increased after re-immunization and after three deliveries were comparable to those induced by a single i.m. injection. Recent evidence indicates that combining routes and vaccine vehicles enhances the immunogenicity of vaccine-delivered or -encoded antigens. Here, it is shown that administration of DNA by an i.m. priming/gene gun boosting more efficiently induced CTL than gene gun priming/i.m. boosting. A similar increment was obtained by sequential vaccinations using a gene gun-delivered DNA followed by recombinant MVA. Thus particular sequences of routes or vaccine vehicles rather than simple prime-boost delivery of a single vaccine is critical for an effective elicitation of CTL.

Immunological properties of gene vaccines delivered by different routes

Gene vaccines represent a new and promising approach to control infectious diseases, inducing a protective immune response in the appropriate host. Several routes and methods of genetic immunization have been shown to induce antibody production as well as T helper (Th) cell and cytotoxic T lymphocyte activation. However, few studies have compared the nature of the immune responses generated by different gene vaccination delivery systems. In the present study we reviewed some aspects of immunity induced by gene immunization and compared the immune responses produced by intramuscular (i.m.) DNA injection to gene gun-mediated DNA transfer into the skin of BALB/c mice. Using a reporter gene coding for beta-galactosidase, we have demonstrated that i.m. injection raised a predominantly Th1 response with mostly IgG2a anti-beta gal produced, while gene gun immunization induced a mixed Th1/Th2 profile with a balanced production of IgG2a and IgG1 subclasses. Distinct types of immune responses were generated by different methods of gene delivery. These findings have important implications for genetic vaccine design. Firstly, a combination between these two systems may create optimal conditions for the induction of a broad-based immune response. Alternatively, a particular gene vaccine delivery method might be used according to the immune response required for host protection. Here, we describe the characteristics of the immune response induced by gene vaccination and the properties of DNA involved in this process.

DNA vaccination against Theiler's murine encephalomyelitis virus leads to alterations in demyelinating disease

Although the etiology of multiple sclerosis (MS) is not known, several factors play a role in this disease: genetic contributions, immunologic elements, and environmental factors. Viruses and virus infections have been associated with the initiation and/or enhancement of exacerbations in MS. Theiler's murine encephalomyelitis virus (TMEV) infection of mice is one of the animal models used to mimic MS. In other animal model systems, DNA vaccination has been used to protect animals against a variety of virus infections. To explore the utility of DNA vaccination, we have constructed eukaryotic expression vectors encoding the TMEV capsid proteins VP1, VP2, and VP3. SJL/J mice were vaccinated intramuscularly once, twice, or three times with the different capsid protein cDNAs. This was followed by intracerebral TMEV infection to determine the effects of DNA vaccination on the course of TMEV-induced central nervous system (CNS) demyelinating disease. We found that vaccination of mice three times with cDNA encoding VP2 led to partial protection of mice from CNS demyelinating disease as determined by a decrease in clinical symptoms and histopathology. Vaccination of mice with cDNA encoding VP3 also led to a decrease in clinical symptoms. In contrast, mice vaccinated with cDNA encoding VP1 experienced a more severe disease with an earlier onset of clinical signs and enhanced histopathology compared with control mice. There was no correlation between anti-TMEV antibody titers and disease course. These results indicate that DNA immunization can modify chronic virus-induced demyelinating disease and may eventually lead to potential treatments for illnesses such as MS.

Cancer vaccines: novel approaches and new promise

Cancer vaccines are a promising tool in the hands of the clinical oncologist. We have summarized the most recent findings and achievements in this exciting field. Tumor-associated antigens, as a basis for the new cancer vaccines, are reviewed. We emphasize novel approaches for the design of safe and more effective vaccines for cancer. We also discuss the possible clinical applications and the future prospects for vaccine development.