Coimmunization with an optimized IL-15 plasmid results in enhanced function and longevity of CD8 T cells that are partially independent of CD4 T cell help

DNA vaccines are a promising technology for the induction of Ag-specific immune responses, and much recent attention has gone into improving their immune potency. In this study we test the feasibility of delivering a plasmid encoding IL-15 as a DNA vaccine adjuvant for the induction of improved Ag-specific CD8(+) T cellular immune responses. Because native IL-15 is poorly expressed, we used PCR-based strategies to develop an optimized construct that expresses 80-fold higher than the native IL-15 construct. Using a DNA vaccination model, we determined that immunization with optimized IL-15 in combination with HIV-1gag DNA constructs resulted in a significant enhancement of Ag-specific CD8(+) T cell proliferation and IFN-gamma secretion, and strong induction of long-lived CD8(+) T cell responses. In an influenza DNA vaccine model, coimmunization with plasmid expressing influenza A PR8/34 hemagglutinin with the optimized IL-15 plasmid generated improved long term CD8(+) T cellular immunity and protected the mice against a lethal mucosal challenge with influenza virus. Because we observed that IL-15 appeared to mostly adjuvant CD8(+) T cell function, we show that in the partial, but not total, absence of CD4(+) T cell help, plasmid-delivered IL-15 could restore CD8 secondary immune responses to an antigenic DNA plasmid, supporting the idea that the effects of IL-15 on CD8(+) T cell expansion require the presence of low levels of CD4 T cells. These data suggest a role for enhanced plasmid IL-15 as a candidate adjuvant for vaccine or immunotherapeutic studies.     

Plasmid vaccination with insulin B chain prevents autoimmune diabetes in nonobese diabetic mice

The insulin B (InsB) chain bears major type 1 diabetes-associated epitopes of significance for disease in humans and nonobese diabetic (NOD) mice. Somatic expression of InsB chain initiated early in life by plasmid inoculation resulted in substantial protection of female NOD mice against disease. This was associated with a T2 shift in spleen, expansion of IL-4-producing and, to a lesser extent, of IFN-gamma-secreting T cells in pancreatic lymph nodes, as well as intermolecular Th2 epitope spreading to glutamic acid decarboxylase determinants. A critical role of IL-4 for the Ag-specific protective effect triggered by plasmid administration was revealed in female IL-4(-/-) NOD mice that developed diabetes and higher Th1 responses. Coadministration of IL-4-expressing plasmid or extension of the vaccination schedule corrected the unfavorable response of male NOD mice to DNA vaccination with InsB chain. Thus, plasmid-mediated expression of the InsB chain early in diabetes-prone mice has the potential to prevent transition to full-blown disease depending on the presence of IL-4.     

Involvement of an ATP-dependent peptide chaperone in cross-presentation after DNA immunization

Immunization with plasmid DNA holds promise as a vaccination strategy perhaps useful in situations that currently lack vaccines, since the major means of immune induction may differ from more conventional approach. In the present study, we demonstrate that exposure of macrophages to plasmid DNA encoding viral proteins or OVA generates Ag-specific material that, when presented in vitro by dendritic cells to naive T cells, induces primary CTL response or elicits IL-2 production from an OVA peptide-specific T-T hybridoma. The immunogenic material released was proteinaceous in nature, free of apoptotic bodies, and had an apparent m.w. much larger than a 9-11-aa CTL-recognizable peptide. The macrophage-released factor(s) specifically required a hydrolyzable ATP substrate and was inhibited by procedures that removed or hydrolyzed ATP; in addition, anti-heat-shock protein 70 antiserum abrogated the activity to a large extent. These results indicate the possible involvement of a heat-shock protein 70-linked peptide chaperone in a cross-priming method of immune induction by DNA vaccination. Such a cross-priming process may represent a principal mechanism by which plasmid DNA delivered to cells such as myocytes effectively shuttle Ag to DC or other APC to achieve CTL induction in vivo.     

More stringent conditions of plasmid DNA vaccination are required to protect grafted versus endogenous islets in nonobese diabetic mice

Recurrent autoimmune destruction of the insulin-producing beta cells is a key factor limiting successful islet graft transplantation in type I diabetic patients. In this study, we investigated the feasibility of using an Ag-specific plasmid DNA (pDNA)-based strategy to protect pro-islets that had developed from a neonatal pancreas implanted under the kidney capsule of nonobese diabetic (NOD) mice. NOD recipient mice immunized with pDNA encoding a glutamic acid decarboxylase 65 (GAD65)-IgFc fusion protein (JwGAD65), IL-4 (JwIL4), and IL-10 (pIL10) exhibited an increased number of intact pro-islets expressing high levels of insulin 15 wk posttransplant, relative to NOD recipient mice immunized with pDNA encoding a hen egg lysozyme (HEL)-IgFc fusion protein (JwHEL)+JwIL4 and pIL10 or left untreated. Notably, the majority of grafted pro-islets detected in JwGAD65+JwIL4- plus pIL10-treated recipients was free of insulitis. In addition, administration of JwGAD65+JwIL4+pIL10 provided optimal protection for engrafted islets compared with recipient NOD mice treated with JwGAD65+JwIL4 or JwGAD65+pIL10, despite effective protection of endogenous islets mediated by the respective pDNA treatments. Efficient protection of pro-islet grafts correlated with a marked reduction in GAD65-specific IFN-gamma reactivity and an increase in IL-10-secreting T cells. These results demonstrate that pDNA vaccination can be an effective strategy to mediate long-term protection of pro-islet grafts in an Ag-specific manner and that conditions are more stringent to suppress autoimmune destruction of grafted vs endogenous islets.     

Caveolin-1-mediated negative signaling plays a critical role in the induction of regulatory dendritic cells by DNA and protein coimmunization

Induction of Ag-specific regulatory T cells (iTregs) by vaccination is a promising strategy for treating autoimmune diseases. We previously demonstrated that DNA and protein covaccination converted naive T cells to Ag-specific iTregs by inducing CD11c(+)CD40(low)IL-10(+) regulatory dendritic cells (DCregs). However, it is unclear how coimmunization induces the DCregs. In this paper, we report that the event is initiated by coentry of sequence-matched DNA and protein immunogens into the same DC via caveolae-mediated endocytosis, which leads to inhibition of phosphorylation of caveolin-1 (Cav-1), the main component of caveolae, and upregulation of Tollip. This triggers downstream signaling that upregulates suppressor of cytokine signaling 1 and downregulates NF-κB and STAT-1α. Silencing either Cav-1 or Tollip blocks the negative signaling, leading to upregulated expression of CD40, downregulated production of IL-10, and loss of iTreg-inducing function. We further show that DCregs can be induced in culture from primary DCs and JAWS II DC lines by feeding them sequence-matched DNA and protein immunogens. The in vitro-generated DCregs are effective in ameliorating autoimmune and inflammatory diseases in several mouse models. Our study thus suggests that DNA and protein coimmunization induces DCregs through Cav-1- and Tollip-mediated negative signaling. It also describes a novel method for generating therapeutic DCregs in vitro.     

Hydrodynamic vaccination with DNA encoding an immunologically privileged retinal antigen protects from autoimmunity through induction of regulatory T cells

The eye is an immunologically privileged organ whose Ags serve as targets for experimental autoimmune uveitis (EAU), a model for human uveitis. We used a hydrodynamic i.v. injection of naked DNA to express the uveitogenic retinal Ag interphotoreceptor retinoid-binding protein (IRBP) in the periphery, thus revoking its immune-privileged status. IRBP was expressed in the liver within hours of administration of as little as 10 microg of IRBP-DNA. Vaccinated mice were highly protected from EAU induced by immunization with IRBP for at least 10 wk after vaccination. Protection was partial in a reversal protocol. Mechanistic studies revealed specific hyporesponsiveness to IRBP without immune deviation, no evidence for apoptosis either by the Fas- or Bcl-2-regulated (mitochondrial) pathway and apparent lack of dependence on CD8(+) cells, IL-10, or TGF-beta. In contrast, depletion of CD25(+) cells after vaccination and before challenge markedly abrogated protection. IRBP-specific CD4(+)CD25(high) T cells could be cultured from vaccinated mice and transferred protection to unvaccinated, EAU-challenged recipients. In vitro characterization of these cells revealed that they are Ag specific, anergic, express FoxP3, CTLA-4, and glucocorticoid-induced TNFR, and suppress by contact. Thus, expression of IRBP in the periphery by DNA vaccination results in tolerance that acts at least in part through induction of IRBP-specific, FoxP3(+)CD4(+)CD25(+) regulatory T cells. DNA vaccination may offer a new approach to Ag-specific therapy of uveitis.     

IL-12 gene as a DNA vaccine adjuvant in a herpes mouse model: IL-12 enhances Th1-type CD4+ T cell-mediated protective immunity against herpes simplex virus-2 challenge

IL-12 has been shown to enhance cellular immunity in vitro and in vivo. Recent reports have suggested that combining DNA vaccine approach with immune stimulatory molecules delivered as genes may significantly enhance Ag-specific immune responses in vivo. In particular, IL-12 molecules could constitute an important addition to a herpes vaccine by amplifying specific immune responses. Here we investigate the utility of IL-12 cDNA as an adjuvant for a herpes simplex virus-2 (HSV-2) DNA vaccine in a mouse challenge model. Direct i.m. injection of IL-12 cDNA induced activation of resting immune cells in vivo. Furthermore, coinjection with IL-12 cDNA and gD DNA vaccine inhibited both systemic gD-specific Ab and local Ab levels compared with gD plasmid vaccination alone. In contrast, Th cell proliferative responses and secretion of cytokines (IL-2 and IFN-gamma) and chemokines (RANTES and macrophage inflammatory protein-1alpha) were significantly increased by IL-12 coinjection. However, the production of cytokines (IL-4 and IL-10) and chemokine (MCP-1) was inhibited by IL-12 coinjection. IL-12 coinjection with a gD DNA vaccine showed significantly better protection from lethal HSV-2 challenge compared with gD DNA vaccination alone in both inbred and outbred mice. This enhanced protection appears to be mediated by CD4+ T cells, as determined by in vivo CD4+ T cell deletion. Thus, IL-12 cDNA as a DNA vaccine adjuvant drives Ag-specific Th1 type CD4+ T cell responses that result in reduced HSV-2-derived morbidity as well as mortality.     

Factors associated with the development of neonatal tolerance after the administration of a plasmid DNA vaccine

A plasmid DNA vaccine encoding the circumsporozoite protein of malaria (pCSP) induces tolerance rather than immunity when administered to newborn mice. We find that this tolerance persists for >1 yr after neonatal pCSP administration and interferes with the induction of protective immunity in animals challenged with live sporozoites. Susceptibility to tolerance induction wanes rapidly with age, disappearing within 1 wk of birth. Higher doses of plasmid are more tolerogenic, and susceptibility to tolerance is not MHC-restricted. CD8+ T cells from tolerant mice suppress the in vitro Ag-specific immune response of cells from adult mice immunized with pCSP. Similarly, CD8+ T cells from tolerant mice transfer nonresponsiveness to naive syngeneic recipients. These findings clarify the cellular basis and factors contributing to the development of DNA vaccine-induced neonatal tolerance.     

Requirements for the maintenance of Th1 immunity in vivo following DNA vaccination: a potential immunoregulatory role for CD8+ T cells

Protective immunity against Leishmania major generated by DNA encoding the LACK (Leishmania homologue of receptor for activated C kinase) Ag has been shown to be more durable than vaccination with LACK protein plus IL-12. One mechanism to account for this may be the selective ability of DNA vaccination to induce CD8+ IFN-gamma-producing T cells. In this regard, we previously reported that depletion of CD8+ T cells in LACK DNA-vaccinated mice abrogated protection when infectious challenge was done 2 wk postvaccination. In this study, we extend these findings to study the mechanism by which CD8+ T cells induced by LACK DNA vaccination mediate both short- and long-term protective immunity against L. major. Mice vaccinated with LACK DNA and depleted of CD8+ T cells at the time of vaccination or infection were unable to control infection when challenge was done 2 or 12 wk postvaccination. Remarkably, it was noted that depletion of CD8+ T cells in LACK DNA-vaccinated mice was associated with a striking decrease in the frequency of LACK-specific CD4+ IFN-gamma-producing T cells both before and after infection. Moreover, data are presented to suggest a mechanism by which CD8+ T cells exert this regulatory role. Taken together, these data provide additional insight into how Th1 cells are generated and sustained in vivo and suggest a potentially novel immunoregulatory role for CD8+ T cells following DNA vaccination.     

Oral delivery of DNA vaccines using attenuated Salmonella typhimurium as carrier

The efficacious delivery of eukaryotic expression plasmids to inductive cells of the immune system constitutes a key prerequisite for the generation of effective DNA vaccines. Here, we have explored the use of bacteria as vehicles to orally deliver expression plasmids. Attenuated Salmonella typhimurium aroA harbouring eukaryotic expression plasmids that encoded virulence factors of Listeria monocytogenes were administered orally to BALB/c mice. Strong cytotoxic and helper T cell responses as well as antibody production were elicited even after a single administration. Mice immunised four times with Salmonella that carried a eukaryotic expression plasmid encoding the secretory listerial protein listeriolysin were protected against a subsequent lethal challenge with this pathogen. A single dose was already partially protective. The efficiency of this vaccination procedure was due to transfer of the expression plasmid from the bacterial carrier to the mammalian host. Evidence for such an event could be obtained in vivo and in vitro. Expression of the desired antigen in various lymphoid tissues was already detectable 1 day after administration of the DNA vaccine and persisted for at least 1 month in spleen and mesenteric lymph nodes. Induction of cytotoxic and helper T cell responses was observed in all mouse strains tested including outbred strains whereas antibodies were mainly detected in BALB/c. Furthermore, we could show that immunogenicity could be improved by increasing the invasiveness of the bacterial carrier.     

Therapeutic vaccination with simian immunodeficiency virus (SIV)-DNA + IL-12 or IL-15 induces distinct CD8 memory subsets in SIV-infected macaques

DNA vaccination is an invaluable approach for immune therapy in that it lacks vector interference and thus permits repeated vaccination boosts. However, by themselves, DNA-based vaccines are typically poor inducers of Ag-specific immunity in humans and non-human primates. Cytokines, such as IL-12 and IL-15, have been shown to be potent adjuvants for the induction and maintenance of cellular immune responses, in particular during HIV infection. In this study, we examined the ability of therapeutic vaccination with SIV-DNA+IL-12 or IL-15 as molecular adjuvants to improve DNA vaccine potency and to enhance memory immune responses in SIV-infected macaques. Our results demonstrate that incorporating IL-12 into the vaccine induces SIV-specific CD8 effector memory T cell (T(EM)) functional responses and enhances the capacity of IFN-gamma-producing CD8 T(EM) cells to produce TNF. Lower levels of PD-1 were expressed on T cells acquiring dual function upon vaccination as compared with mono-functional CD8 T(EM) cells. Finally, a boost with SIV-DNA+IL-15 triggered most T cell memory subsets in macaques primed with either DNA-SIV or placebo but only CD8 T(EM) in macaques primed with SIV-DNA+IL-12. These results indicate that plasmid IL-12 and IL-15 cytokines represent a significant addition to enhance the ability of therapeutic DNA vaccines to induce better immunity.     

The immunogenicity of dendritic cell-based vaccines is not hampered by doxorubicin and melphalan administration

Immunization of cancer patients is most effective in tumor-free conditions or in the presence of minimal residual disease. In the attempt to develop new strategies able to control tumor recurrence while allowing the development of protective immunity, we have investigated the immunogenic potential of two distinct vaccine formulations when provided alone or upon single and repeated treatment with chemotherapeutics drugs. Vaccine-induced T cell responses were first investigated by tracing Ag-specific T cell responses in mice bearing detectable frequencies of Ag-specific TCR transgenic CD4 and CD8 T cells. These studies indicated that immunization with peptide-pulsed dendritic cells and soluble Ag plus adjuvant elicited a comparable expansion and differentiation of CD4 and CD8 effector cells in the peripheral lymphoid tissues when provided alone or shortly after Doxorubicin or Melphalan administration. We also analyzed the potency of the combined vaccination in transgenic adenocarcinoma mouse prostate mice, which develop spontaneous prostate cancer. Dendritic cell-based vaccination elicited potent tumor-specific cytotoxic responses in mice bearing prostate intraepithelial neoplasia both in the absence and in the presence of Doxorubicin. Together our results indicate that Doxorubicin- or Melphalan-based chemotherapy and Ag-specific vaccination can be combined for adjuvant treatments of cancer patients.     

Effective genetic vaccination with a widely shared endogenous retroviral tumor antigen requires CD40 stimulation during tumor rejection phase

Endogenous retrovirus (ERV) products are recognized by T lymphocytes in mice and humans. As these Ags are preferentially expressed by neoplastic tissues, they might represent an ideal target for active immunization by genetic vaccination. However, i.m. inoculation of plasmid DNA encoding mouse gp70 or p15E, two products of the env gene of an endogenous murine leukemia virus, elicited a weak Ag-specific T lymphocyte response and resulted in partial protection from challenge with mouse tumors possessing these Ags. Depletion experiments showed that CD8(+), but not CD4(+), T lymphocytes were crucial for the antitumor activity of the vaccines. Systemic administration of agonistic anti-CD40 mAb increased the therapeutic potential of genetic vaccination, but only when given during the tumor rejection phase and not at the time of immunization. This effect correlated with a dramatic increase in the number of ERV-specific CD8(+) T lymphocytes. Adjuvant activity of CD40 agonists thus seems to be relevant to enhance the CD8(+) T cell-dependent response in tumor-bearing hosts, suggesting that sustaining tumor-specific T lymphocyte survival in subjects undergoing vaccination might be a key event in the successful vaccination with weak tumor Ags.     

Coadministration of plasmid DNA constructs encoding an encephalitogenic determinant and IL-10 elicits regulatory T cell-mediated protective immunity in the central nervous system

We have previously shown that Ag-specific IL-10-producing regulatory T cells (Tr1) participate in the regulation of experimental autoimmune encephalomyelitis and that their specificity undergoes determinant spread in a reciprocal manner to effector T cell specificity. The current study shows that coadministration of plasmid DNA vaccines encoding IL-10 together with a plasmid encoding a myelin basic protein (MBP) encephalitogenic determinant during an ongoing disease rapidly amplifies this Tr1-mediated response, in a disease-specific manner. Thus, coadministration of both plasmids, but not the plasmid DNA encoding MBP alone, rapidly suppresses an ongoing disease. Tolerance included elevation in Ag-specific T cells producing IL-10 and an increase in apoptosis of cells around high endothelial venules in the CNS after successful therapy. Tolerance could be transferred by MBP-specific primary T cells isolated from protected donors and reversed by neutralizing Abs to IL-10 but not to IL-4. Due to the nature of determinant spread in this model, we could bring about evidence implying that rapid and effective induction of Tr1-induced active tolerance is dependent on redirecting the Tr1 response to the epitope to which the effector function dominates the response at a given time. The consequences of these findings to multiple sclerosis, and possibly other inflammatory autoimmune diseases are discussed.     

Long-term protective and antigen-specific effect of heat-killed Mycobacterium vaccae in a murine model of allergic pulmonary inflammation

This report examines the effect of heat-killed Mycobacterium vaccae in a mouse model of allergic pulmonary inflammation. The s.c. administration of M. vaccae 3 wk before the immunization significantly reduced Ag-induced airway hyperreactivity and the increase in the numbers of eosinophils observed in the bronchoalveolar lavage fluid, blood, and bone marrow, even though no detectable changes in either cytokine (IL-4, IL-13, IL-5, and IFN-gamma) or total IgE levels were observed. Furthermore, transfer of splenocytes from OVA-immunized and M. vaccae-treated mice into recipient, OVA-immunized mice significantly reduced the allergen-induced eosinophilia by an IFN-gamma-independent mechanism, clearly indicating that the mechanism by which M. vaccae induces its inhibitory effect is not due to a redirection from a predominantly Th2 to a Th1-dominated immune response. The protective effect of M. vaccae on the allergen-induced eosinophilia lasted for at least 12 wk after its administration, and the treatment was also effective in presensitized mice. Moreover, the allergen specificity of the inhibitory effect could be demonstrated using a double-immunization protocol, where M. vaccae treatment before OVA immunization had no effect on the eosinophilic inflammation induced by later immunization and challenge with cockroach extract Ag. Taken together, these results clearly demonstrate that M. vaccae is effective in blocking allergic inflammation by a mechanism independent of IFN-gamma, induces long term and Ag-specific protection, and therefore has both prophylactic and therapeutic potential for the treatment of allergic diseases.     

Dual mechanisms of potentiation of murine antigen-specific IgE production by cyclosporin A in vitro.

Concomitant administration of cyclosporin A (CsA) with Ag has been shown to augment the production of Ag-specific IgE in vivo. We demonstrate that addition of CsA also markedly potentiated Ag-specific IgE in vitro. Low doses of CsA (3 and 10 ng/ml) added at the time of culture initiation selectively enhanced Ag-specific IgE but not IgA or IgG1 production, whereas higher doses (30 ng/ml) suppressed production of all the isotypes. Augmented IgE production was found to correlate with enhanced production of IL-4 and diminished production of IFN-gamma. Delayed addition (after 2 days) of low doses of CsA to Ag-stimulated cultures did not potentiate IgE production, even though CsA differentially affected levels of IL-4 and IFN-gamma. CsA enhanced Ag-mediated cognate T/B interaction was not affected by neutralizing doses of anti-IL-4, suggesting Ag-mediated lymphocytic "synapses" may be inaccessible to anti-IL-4. The effect of CsA on Ag presentation was determined by pulsing peritoneal exudate cells, spleen cells, or primed B cells with Ag and low doses of CsA before incubation with primed splenocytes. Enhanced Ag-specific IgE responses were detected with no effect on IL-4 or IFN-gamma levels. Thus, our study indicates that CsA potentiation of Ag-specific IgE response is due to cumulative action of CsA on two independent pathways: first, CsA differentially modulates IL-4 and IFN-gamma levels during the early phase of cognate Th2/B cell interaction; and second, CsA directly affects APC and IgE isotype-specific amplifying cellular components without apparently affecting the secretory levels of IL-4 and IFN-gamma. Dual mechanisms of CsA-potentiated IgE production are consistent with the hypothesis of two-tiered T cell regulation of Ag-specific IgE responses.     

Potential of transfected muscle cells to contribute to DNA vaccine immunogenicity

The mechanism(s) by which DNA vaccines trigger the activation of Ag-specific T cells is incompletely understood. A series of in vivo and in vitro experiments indicates plasmid transfection stimulates muscle cells to up-regulate expression of MHC class I and costimulatory molecules and to produce multiple cytokines and chemokines. Transfected muscle cells gain the ability to directly present Ag to CD8 T cells through an IFN-regulatory factor 3-dependent process. These findings suggest that transfected muscle cells at the site of DNA vaccination may contribute to the magnitude and/or duration of the immune response initiated by professional APCs.     

A suppressive oligodeoxynucleotide enhances the efficacy of myelin cocktail/IL-4-tolerizing DNA vaccination and treats autoimmune disease

Targeting pathogenic T cells with Ag-specific tolerizing DNA vaccines encoding autoantigens is a powerful and feasible therapeutic strategy for Th1-mediated autoimmune diseases. However, plasmid DNA contains abundant unmethylated CpG motifs, which induce a strong Th1 immune response. We describe here a novel approach to counteract this undesired side effect of plasmid DNA used for vaccination in Th1-mediated autoimmune diseases. In chronic relapsing experimental autoimmune encephalomyelitis (EAE), combining a myelin cocktail plus IL-4-tolerizing DNA vaccine with a suppressive GpG oligodeoxynucleotide (GpG-ODN) induced a shift of the autoreactive T cell response toward a protective Th2 cytokine pattern. Myelin microarrays demonstrate that tolerizing DNA vaccination plus GpG-ODN further decreased anti-myelin autoantibody epitope spreading and shifted the autoreactive B cell response to a protective IgG1 isotype. Moreover, the addition of GpG-ODN to tolerizing DNA vaccination therapy effectively reduced overall mean disease severity in both the chronic relapsing EAE and chronic progressive EAE mouse models. In conclusion, suppressive GpG-ODN effectively counteracted the undesired CpG-induced inflammatory effect of a tolerizing DNA vaccine in a Th1-mediated autoimmune disease by skewing both the autoaggressive T cell and B cell responses toward a protective Th2 phenotype. These results demonstrate that suppressive GpG-ODN is a simple and highly effective novel therapeutic adjuvant that will boost the efficacy of Ag-specific tolerizing DNA vaccines used for treating Th1-mediated autoimmune diseases.     

Modulatory effects of the human heat shock protein 70 on DNA vaccination

DNA vaccination with the plasmid expressing Japanese encephalitis virus (JEV) nonstructural protein 1 (pJNS1) has been shown to induce effective immunity against JEV infection. To further increase the efficacy of pJNS1 DNA vaccination, we coinjected pJNS1 with a plasmid that expresses heat shock protein 70.1 (pHSP70.1) into mice. We found that coinjection of pHSP70.1 enhanced both T cell proliferation and cytotoxic effects, but not the antibody response to JEV. Moreover, mice immunized with both pHSP70.1 and pJNS1 were resistant to lethal challenges of JEV, indicating that the protective immunity against JEV is not decreased, in spite of the low antibody titer via the immunization of pHSP70.1. Since DNA vaccination administered by pJNS1 did not elicit strong cellular immunity in our previous study, the administration of pHSP70.1 apparently could be used as an adjuvant to enhance cell-mediated immunity in this model system. Thus, coadministration of pHSP70.1 DNA with plasmid DNA encoding tumor- or virus-specific antigens might be very useful in the treatment of cancers and other infectious diseases.     

Antigen-specific mediated suppression of beta cell autoimmunity by plasmid DNA vaccination

In this study, we have investigated the use of plasmid DNA (pDNA) vaccination to elicit Th2 effector cell function in an Ag-specific manner and in turn prevent insulin-dependent diabetes mellitus (IDDM) in nonobese diabetic (NOD) mice. pDNA recombinants were engineered encoding a secreted fusion protein consisting of a fragment of glutamic acid decarboxylase 65 (GAD65) linked to IgGFc, and IL-4. Intramuscular injection of pDNA encoding GAD65-IgGFc and IL-4 effectively prevented diabetes in NOD mice treated at early or late preclinical stages of IDDM. This protection was GAD65-specific since NOD mice immunized with pDNA encoding hen egg lysozyme-IgGFc and IL-4 continued to develop diabetes. Furthermore, disease prevention correlated with suppression of insulitis and induction of GAD65-specific regulatory Th2 cells. Importantly, GAD65-specific immune deviation was dependent on pDNA-encoded IL-4. In fact, GAD65-specific Th1 cell reactivity was significantly enhanced in animals immunized with pDNA encoding only GAD65-IgGFc. Finally, NOD.IL4(null) mice treated with pDNA encoding GAD65-IgGFc and IL-4 continued to develop diabetes, indicating that endogenous IL-4 was also required for disease prevention. These results demonstrate that pDNA vaccination is an effective strategy to elicit beta cell-specific Th2 regulatory cell function for the purpose of preventing IDDM even at a late stage of disease development.