Induction of active immune suppression by co-immunization with DNA- and protein-based vaccines

A First-in-Human Phase I Study of INVAC-1, an Optimized Human Telomerase DNA Vaccine in Patients with Advanced Solid Tumors

PURPOSE

Human telomerase reverse transcriptase (hTERT) is highly expressed in >85% of human tumors and is thus considered as a good tumor-associated antigen candidate for vaccine development. We conducted a phase I study to investigate the safety, tolerability, clinical response, and immunogenicity of INVAC-1, a DNA plasmid encoding a modified hTERT protein in patients with relapsed or refractory solid tumors.

PATIENTS AND METHODS

INVAC-1 was either administered by intradermal route followed by electroporation or by Tropis, a needle-free injection system. Safety and tolerability were monitored by clinical and laboratory assessments. Progression-free survival and overall survival were reported using Kaplan-Meier survival analysis. Immunogenicity was studied by ELISpot, Luminex, and Flow Cytometry.

RESULTS

Twenty-six patients were treated with INVAC-1 administered at three dose levels (100, 400, and 800 μg). Vaccination was well tolerated and no dose-limiting toxicity was reported. One treatment-related grade 3 SAE was reported. Fifty-eight percent of patients experienced disease stabilization. PFS was 2.7 months, median OS was 15 months, and 1-year survival was reached for 65% of patients. INVAC-1 vaccination stimulated specific anti-hTERT CD4 T-cell response as well as cytotoxic CD8 T-cell response. No evidence of peripheral vaccine-induced immunosuppression was observed.

CONCLUSIONS

INVAC-1 vaccination was safe, well tolerated, and immunogenic when administered intradermally at the three tested doses in patients with relapsed or refractory cancers. Disease stabilization was observed for the majority of patients (58%) during the treatment period and beyond.See related commentary by Slingluff Jr, p. 529.

Induced Regulatory T Cells Superimpose Their Suppressive Capacity with Effector T Cells in Lymph Nodes via Antigen-Specific S1p1-Dependent Egress Blockage

Regulatory T cells (Tregs) restrict overexuberant lymphocyte activation. While close proximity between Tregs and their suppression targets is important for optimal inhibition, and literature indicates that draining lymph nodes (LNs) may serve as a prime location for the suppression, signaling details orchestrating this event are not fully characterized. Using a protocol to enable peripheral generation of inducible antigen-specific Tregs (asTregs) to control allergen-induced asthma, we have identified an antigen-specific mechanism that locks asTregs within hilar LNs which in turn suppresses airway inflammation. The suppressive asTregs, upon antigen stimulation in the LN, downregulate sphingosine-1-phosphate receptor 1 egress receptor expression. These asTregs in turn mediate the downregulation of the same receptor on incoming effector T cells. Therefore, asTregs and effector T cells are locked in these draining LNs for prolonged interactions. Disruption of individual steps of this retention sequence abolishes the inflammation controlled by asTregs. Collectively, this study identifies a new requirement of spatial congregation with their suppression targets essential for asTreg functions and suggests therapeutic programs via Treg traffic control.

Diabetes tolerogenic vaccines targeting antigen-specific inflammation

Tolerance controls the magnitude of inflammation, and balance between beneficial and harmful effects of inflammation is crucial for organ function and survival. Inadequate tolerance leads to various inflammatory diseases. Antigen specific tolerance is ideal for inflammation control as alternative anti-inflammatory interventions are non-specific and consequently increase the risk of infection and tumorigenesis. With inherent antigen specificity, tolerogenic vaccines are potentially ideal for control of inflammation. Although the concept of tolerogenic vaccines is still in its infancy, tolerogenic mucosal vaccines and specific immuno-therapies have long been proven effective in pioneering examples. Now a body of evidence supporting the concept of tolerogenic vaccines has also accumulated. Here we comment on recent successes of the tolerogenic vaccine concept, present new evidence with a type 1 diabetes vaccine as an example and draw conclusions on the advantages and potential for inflammatory disease control at the bedside.

Plasmid DNA Vaccine Co-Immunisation Modulates Cellular and Humoral Immune Responses Induced by Intranasal Inoculation in Mice

Background

An effective HIV vaccine will likely require induction of both mucosal and systemic cellular and humoral immune responses. We investigated whether intramuscular (IM) delivery of electroporated plasmid DNA vaccine and simultaneous protein vaccinations by intranasal (IN) and IM routes could be combined to induce mucosal and systemic cellular and humoral immune responses to a model HIV-1 CN54 gp140 antigen in mice.

Results

Co-immunisation of DNA with intranasal protein successfully elicited both serum and vaginal IgG and IgA responses, whereas DNA and IM protein co-delivery did not induce systemic or mucosal IgA responses. Cellular IFNγ responses were preserved in co-immunisation protocols compared to protein-only vaccination groups. The addition of DNA to IN protein vaccination reduced the strong Th2 bias observed with IN protein vaccination alone. Luminex analysis also revealed that co-immunisation with DNA and IN protein induced expression of cytokines that promote B-cell function, generation of T_FH cells and CCR5 ligands that can reduce HIV infectivity.

Significance

These data suggest that while IN inoculation alone elicits both cellular and humoral responses, co-administration with homologous DNA vaccination can tailor these towards a more balanced Th1/Th2 phenotype modulating the cellular cytokine profile while eliciting high-levels of antigen-specific antibody. This work provides insights on how to generate differential immune responses within the same vaccination visit, and supports co-immunisation with DNA and protein by a mucosal route as a potential delivery strategy for HIV vaccines.

A coimmunization vaccine of Aβ42 ameliorates cognitive deficits without brain inflammation in an Alzheimer's disease model

INTRODUCTION

Vaccination against amyloid-β protein (Aβ42) induces high levels of antibody, making it a promising strategy for treating Alzheimer's disease (AD). One drawback in the past was that clinical trial approval was withheld because of speculation that the Aβ42 vaccine induces CD4(+) T cell infiltrations into the central nervous system. To reduce T-cell activation while concomitantly maintaining high anti-Aβ42 titers is a great challenge in immunology.

METHODS

We aimed to demonstrate that coimmunization with Aβ42 protein and expression plasmid can be beneficial in a mouse AD model and can prevent inflammation. We immunized the AD mice with the coimmunization vaccine and assessed behavior change and Aβ42 deposition. Furthermore, to determine the safety of the coimmunization vaccine, we used an induced Aβ42-EAE model to mimic the meningoencephalitis that happened in the AN-1792 vaccine clinical phase II trial and tested whether the coimmunization vaccine could ameliorate T-cell-mediated brain inflammation.

RESULTS

The coimmunization vaccination reduced Aβ plaques and significantly ameliorated cognitive deficit while inhibiting T-cell-mediated brain inflammation and infiltration. These studies demonstrate that the coimmunization strategy that we describe in this article can ameliorate AD pathology without notable adverse effects in mice.

CONCLUSIONS

A coimmunization strategy leading to the development of a safe immunotherapeutic/preventive protocol against AD in humans is warranted.

DNA and protein co-administration induces tolerogenic dendritic cells through DC-SIGN mediated negative signals

We previously demonstrated that DNA and protein co-administration induced differentiation of immature dendritic cells (iDCs) into CD11c⁺CD40^lowIL-10⁺ regulatory DCs (DCregs) via the caveolin-1 (Cav-1) -mediated signal pathway. Here, we demonstrate that production of IL-10 and the low expression of CD40 play a critical role in the subsequent induction of regulatory T cells (Tregs) by the DCregs. We observed that DNA and protein were co-localized with DC-SIGN in caveolae and early lysosomes in the treated DCs, as indicated by co-localization with Cav-1 and EEA-1 compartment markers. DNA and protein also co-localized with LAMP-2. Gene-array analysis of gene expression showed that more than a thousand genes were significantly changed by the DC co-treatment with DNA + protein compared with controls. Notably, the level of DC-SIGN expression was dramatically upregulated in pOVA + OVA co-treated DCs. The expression levels of Rho and Rho GNEF, the down-stream molecules of DC-SIGN mediated signal pathway, were also greatly upregulated. Further, the level of TLR9, the traditional DNA receptor, was significantly downregulated. These results suggest that DC-SIGN as the potential receptor for DNA and protein might trigger the negative pathway to contribute the induction of DCreg combining with Cav-1 mediated negative signal pathway.

HIV/SIV DNA vaccine combined with protein in a co-immunization protocol elicits highest humoral responses to envelope in mice and macaques

Vaccination with HIV/SIV DNAs elicits potent T-cell responses. To improve humoral immune responses, we combined DNA and protein in a co-immunization protocol using in vivo electroporation in mice and macaques. DNA&protein co-immunization induced higher antibody responses than DNA or protein alone, or DNA prime/protein boost in mice. DNA&protein co-immunization induced similar levels of cellular responses as those obtained by DNA only vaccination. The inclusion of SIV or HIV Env gp120 protein did not impair the development of cellular immune responses elicited by DNA present in the vaccine regimen. In macaques, the DNA&protein co-immunization regimen also elicited higher levels of humoral responses with broader cross-neutralizing activity. Despite the improved immunogenicity of DNA&protein co-immunization, the protein formulation with the EM-005 (GLA-SE) adjuvant further increased the anti-Env humoral responses. Dissecting the contribution of EM-005, we found that its administration upregulated the expression of co-stimulatory molecules and stimulated cytokine production, especially IL-6, by dendritic cells in vivo. These terminally differentiated, mature, dendritic cells possibly promote higher levels of humoral responses, supporting the inclusion of the EM-005 adjuvant with the vaccine. Thus, DNA&protein co-immunization is a promising strategy to improve the rapidity of development, magnitude and potency of the humoral immune responses.

Fel d 1-airway inflammation prevention and treatment by co-immunization vaccine via induction of CD4+CD25-Foxp3+ Treg cells

Pet allergens are major causes for asthma and allergic rhinitis. Fel d 1 protein, a key pet allergen from domestic cat, can sensitize host and trigger asthma attack. In this study, we report that co-immunization with recombinant Fel d 1 protein (rFel d 1) plus plasmid DNA that contains Fe1 d 1 gene was effective in preventing and treating the natural Fel d 1 (nFel d 1) induced allergic airway inflammation in mice. A population of T regulatory cells (iTreg) exhibiting a CD4+CD25-Foxp3+ phenotype and expressing IL-10 and TGF-β was induced by this co-immunization strategy. Furthermore, after adoptive transfers of the iTreg cells, mice that were pre-sensitized and challenged with nFel d 1 exhibited less signs of allergic inflammation, AHR and a reduced allergic immune response. These data indicate that co-immunization with DNA and protein mixture vaccine may be an effective treatment for cat allergy.

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.

Tolerogenic DNA vaccine for prevention of autoimmune ovarian disease

DNA vaccines have been widely used to induce immune responses against molecular targets. In this study, we explored the possibility of using DNA vaccine combined with the immunosuppressant FK506 (tacrolimus) to antigen-specifically suppress unwanted immune responses and prevent autoimmune ovarian disease. To that end, we immunized C57BL/6 mice with a DNA vaccine encoding mouse zona pellucida 3 (ZP3) together with FK506. The immunization induced ZP3-specific CD4(+)CD25(+)Foxp3(+) regulatory T cells (Treg), which suppressed the induction of ZP3-specific delayed-type hypersensitivity in the animals. Significantly, the immunization also protected the animals from experimentally induced autoimmune ovarian disease. These results suggest that DNA vaccination in the presence of FK506 may be used to induce Treg cells and prevent AOD.

Efficient induction of CD25- iTreg by co-immunization requires strongly antigenic epitopes for T cells

Background

We previously showed that co-immunization with a protein antigen and a DNA vaccine coding for the same antigen induces CD40^low IL-10^high tolerogenic DCs, which in turn stimulates the expansion of antigen-specific CD4⁺CD25^-Foxp3⁺ regulatory T cells (CD25^- iTreg). However, it was unclear how to choose the antigen sequence to maximize tolerogenic antigen presentation and, consequently, CD25^- iTreg induction.

Results

In the present study, we demonstrated the requirement of highly antigenic epitopes for CD25^- iTreg induction. Firstly, we showed that the induction of CD25^- iTreg by tolerogenic DC can be blocked by anti-MHC-II antibody. Next, both the number and the suppressive activity of CD25^- iTreg correlated positively with the overt antigenicity of an epitope to activate T cells. Finally, in a mouse model of dermatitis, highly antigenic epitopes derived from a flea allergen not only induced more CD25^- iTreg, but also more effectively prevented allergenic reaction to the allergen than did weakly antigenic epitopes.

Conclusions

Our data thus indicate that efficient induction of CD25^- iTreg requires highly antigenic peptide epitopes. This finding suggests that highly antigenic epitopes should be used for efficient induction of CD25^- iTreg for clinical applications such as flea allergic dermatitis.

Maltosylated polyethylenimine-based triple nanocomplexes of human papillomavirus 16L1 protein and DNA as a vaccine co-delivery system

To improve vaccine delivery, we herein designed a co-delivery system using a protein antigen and its encoding plasmid linked in nanocomplexes via maltosylated PEI (mPEI). Cationic mPEI was electrostatically complexed to a plasmid encoding the human papillomavirus (HPV) type 16L1 protein (pHPV16L1), and further complexed to a maltose binding protein (MBP)-fused human papillomavirus type 16L1 fusion protein (HPV16L1-MBP). The HPV16L1-MBP/mPEI/pHPV16L1 complexes were characterized by gel-retardation properties, zeta potentials and sizes. The intracellular co-delivery of protein and plasmid DNA vaccines was significantly higher for mPEI-based triple nanocomplexes than for a simple physical mixture of the proteins and DNA. Moreover, the cellular delivery of plasmid DNA using mPEI-based triple nanocomplexes resulted in higher expression levels comparable to those obtained using dual complexes of mPEI and the plasmid DNA. In vivo, co-immunization of mice with HPV16L1-MBP/mPEI/pHPV16L1 nanocomplexes triggered the highest levels of humoral immune responses among various vaccination groups. Moreover, the mPEI-based nanocomplexes significantly enhanced the number of interferon-γ producing CD8(+) T cells compared with the use of mixed proteins and plasmid DNA. These results suggest that the effective cellular co-delivery of MBP-fused antigen proteins and plasmid DNA using maltosylated PEI-based triple nanocomplexes could enhance the immunogenicity of HPV16L1 vaccines.

Current strategies for subunit and genetic viral veterinary vaccine development

Developing vaccines for livestock provides researchers with the opportunity to perform efficacy testing in the natural hosts. This enables the evaluation of different strategies, including definition of effective antigens or antigen combinations, and improvement in delivery systems for target antigens so that protective immune responses can be modulated or potentiated. An impressive amount of knowledge has been generated in recent years on vaccine strategies and consequently a wide variety of antigen delivery systems is now available for vaccine research. This paper reviews several antigen production and delivery strategies other than those based on the use of live viral vectors. Genetic and protein subunit vaccines as well as alternative production systems are considered in this review.

Protective response against type 1 diabetes in nonobese diabetic mice after coimmunization with insulin and DNA encoding proinsulin

Type 1 diabetes (T1D) in both humans and nonobese diabetic (NOD) mice is a T cell-mediated autoimmune disease characterized by lymphocytic infiltration of pancreatic islets with subsequent destruction of the insulin-producing cells. The T regulatory (Treg) cell has been suggested to play an important role in controlling T cell-mediated inflammatory T1D. We previously demonstrated that induction of antigen-specific Treg cells in vivo by co-immunization with a DNA vaccine and its encoded protein can effectively inhibit T cell-mediated inflammatory diseases. To further demonstrate the potential of this strategy, we show here that co-immunization of NOD mice twice with DNA encoding proinsulin plus insulin protein prevents the onset of T1D and induces the impairment of antigen-specific T cell responses in a dose-dependent manner. We further show that the inhibitory function is due to the induction of TGF-beta-producing CD4(+)CD25(-) islet-specific iTreg cells against the onset of T1D in NOD mice. Induced iTreg cells were observed only in the co-immunization group, but derived neither from the DNA vaccine nor the protein alone, suggesting that a biased helper T cell type 1 response plays no inhibitory role. A strategy based on co-immunization to induce a protective response against the onset of diabetes in NOD mice may lead to the development of an immunotherapeutic/preventive protocol against T1D in humans.

Protein/DNA vaccine-induced antigen-specific Treg confer protection against asthma

Asthma is a chronic inflammatory disorder caused by T-cell-mediated inflammation within airways. No antigen-specific treatment has been available. Using an OVA-induced murine asthma model, we find that co-immunization of an OVA epitope peptide with a DNA vaccine encoding the same epitope is able to prevent this experimental asthma as evidenced in the marked reduction of infiltrations of eosinophils and lymphocytes into the site of the allergen challenge. We demonstrate that the prevention of experimental asthma was directly related to the induction of a population of OVA-specific T-regulatory cells (Treg) exhibiting a CD4(+)CD25(-)FoxP3(+) phenotype and expressing IL-10, TGF-beta and IFN-gamma following the co-immunization. Blockade of IL-10 and TGF-beta of the Treg by anti-IL-10 and TGF-beta antibodies is partially able to reverse the suppression in vitro and in vivo, which caused the recurrence of the inflammation. Furthermore, adoptive transfer of the induced Treg is also able to suppress the OVA-induced asthma. To our knowledge, the combination of peptide with its cognate DNA vaccine protect experimental asthma via the induced epitope-specific Treg has not been previously reported and such strategy may lead to a novel immunotherapy against asthma in humans.

Treatment of autoimmune ovarian disease by co-administration with mouse zona pellucida protein 3 and DNA vaccine through induction of adaptive regulatory T cells

BACKGROUND

Autoimmune ovarian disease (AOD) caused by auto-reactive T cells is considered a major reason for human premature ovarian failure, which affects 5% of women worldwide.

METHODS AND RESULTS

To develop an effective treatment for AOD, we showed that the co-administration of mouse zona pellucida protein 3 (mZP3) protein and DNA vaccine encoding the mZP3 was able to meliorate AOD in an AOD murine model induced by the mZP3. We observed that established AOD in mice reverted to a normal ovarian morphology without notable T-cell infiltration in the co-administrated group; whereas mice in the control groups developed severe AOD. The amelioration appears to be antigen specific because other co-administration combinations failed to reverse AOD and correlates with significant reductions of pathogenic T-cell responses and productions of tumor necrosis factor-alpha and interferon-gamma. Furthermore, the melioration is apparently associated with the induction of mZP3 specific regulatory T cells that exhibit a phenotypic CD4(+)CD25(-)FoxP3(+)IL-10(+) in the co-administrated group, which can be transferred to reverse AOD in vivo.

CONCLUSIONS

Thus, co-administration of mZP3 DNA and protein vaccines can be used to treat established AOD, and may provide a novel immunotherapy strategy to treat other autoimmune diseases.

Induction of a protective immune response against swine Chlamydophila abortus infection in mice following co-vaccination of omp-1 DNA with recombinant MOMP

Chlamydophila abortus is the causative agent of abortion in pigs and pregnant women. Seroconversion rates were arranged from 11% to 80% in piglets and sows in China. These very high rates illustrate the scale of the problem in China and highlight the urgent need for the development of a C. abortus vaccine. An efficacious anti-chlamydial vaccine should induce not only strong mucosal and systemic T-helper type 1 (Th1) immune response but also give a humoral response that enhances Th1 activation following infection. In order to evaluate an active immune response of a combination of the major outer membrane protein (MOMP) DNA- and protein-based vaccines, 54 BALB/c mice were randomly assigned to six groups and inoculated intramuscularly with: (i) 100 microg pcDNA::MOMP, (ii) 10 microg r-MOMP, (iii) primed with 100 microg pcDNA::MOMP and boosted with 10 microg r-MOMP, (iv) primed-boosted with a combination of pcDNA::MOMP and r-MOMP simultaneously, (v) live-attenuated 1B vaccine, (vi) 100 microg pcDNA3.1 vector. All animals were vaccinated two times at 14 days intervals. Results showed that mice given DNA and r-MOMP induced higher antibody levels, higher T cells proliferation and an elevated level of chlamydial clearance in spleen, which was equivalent to the clearance of 1B vaccine. Mice administrated the DNA-primed/MOMP-boosted approach elicited moderate antibody levels, less T-lymphocyte proliferation and lower chlamydial clearance as compared with 1B vaccine. Co-immunization with DNA- and r-MOMP vaccine may provide novel ways for active immunization strategy against swine C. abortus.

Induction of adaptive T regulatory cells that suppress the allergic response by coimmunization of DNA and protein vaccines

Allergen-induced immediate hypersensitivity (AIH) is a health issue of significant concern. This robust inflammatory reaction is initiated by the allergen-specific T cell responsiveness. Severe lesion reactions on skin are consequential problem requiring medical treatment. Effective Ag-specific treatments or preventions are lacking. Using a rodent model of AIH induced by flea allergens, we first report that coimmunization of DNA and protein vaccines encoding the flea salivary specific Ag-1 ameliorated experimental AIH, including Ag-induced wheal formation, elevated T cell proliferation, and infiltration of lymphocytes and mast cells to the site of allergen challenge. The amelioration of AIH was directly related to the induction of a specific population of flea antigenic specific T cells exhibiting a CD4(+)CD25(-)FoxP3(+) phenotype, a characteristic of regulatory T (T(REG)) cells. These T(REG) cells expressing IL-10, IFN-gamma, and the transcriptional factor T-bet after Ag stimulation were driven by a tolerogenic MHC class II(+)/CD40(low) dendritic cell population that was induced by the coimmunization of DNA and protein vaccines. The tolerogenic dendritic cell could educate the naive T cells into CD4(+)CD25(-)FoxP3(+) T(REG) cells both in vitro and in vivo. The study identified phenomenon to induce an Ag-specific tolerance via a defined Ag vaccinations and lead to the control of AIH. Exploitation of these cellular regulators and understanding their induction provides a basis for the possible development of novel therapies against allergic and related disorders in humans and animals.

Enhanced contraceptive response by co-immunization of DNA and protein vaccines encoding the mouse zona pellucida 3 with minimal oophoritis in mouse ovary

Zona pellucida 3 (ZP3) acts as the primary sperm receptor, induces autoantibody that can prevent oocyte fertilization and has been proposed as a vaccine candidate for contraception in humans. Due to the elicited autoreactive T cell inflammation that causes ovarian destruction, ZP3-based vaccine with removed T epitopes from the ZP3 is considered as a preferred approach. We present here a new strategy to eliminate the T cell inflammation while retaining a high level of antibody by co-immunization of mZP3 DNA and protein vaccines, which resulted in a higher reduction rate of fertility in this group. Histological analysis showed that there were normal follicular developments of infertile mice in the co-immunized group; while other vaccine groups of the most infertile mice lacked mature follicles. There was a significant correlation between normal follicular development and the inhibition of T cell response in co-immunized mice. At the same time, co-immunization reduced the production of inflammatory cytokine, IFN-gamma, and increased the productions of IL-10 and FoxP3 in CD4 T cells, suggesting the anti-inflammation may be via a T regulatory function. The results indicate that co-immunization of mZP3 DNA- and protein-based vaccines can reduce fertility without interfering with the normal follicular development and present a novel strategy to develop a contraceptive vaccine in humans.

Combined DNA vaccination against three animal viruses elicits decreased immunogenicity of a single plasmid in mice

In order to investigate whether combined DNA vaccines are an ideal way to combine antigens in a single vaccine formulation, we immunized mice with three plasmids (pVSG, pVgD and pVE2), respectively, encoding the antigen of foot-and-mouth disease virus (FMDV), pseudorabies virus (PRV) and classic swine fever virus (CSFV), either alone or in a combined vaccine regimen. We also investigated the immune responses induced by a series of mixtures in which three plasmids were mixed in pairs. Then we further immunized mice with three different plasmids in separate sites and preformed an adoptive transfer experiment. While being given alone, each of the vaccine plasmids induced significant virus-specific antibody responses and splenocytes proliferative activity. But reduced immunogenicity of the pVSG plasmid was found in combined DNA vaccination, no matter whether it was injected in a single or a separate site. Removal single plasmid (pVgD or pVE2) from combined DNA vaccine led to significant increase in the immunogenicity of the pVSG plasmid (P<0.05). And the induction of immune suppression was not mediated by suppressor T cells, as demonstrated by an adoptive transfer experiment. Furthermore, by boosting with whole virus protein of FMDV, mice primed with either pVSG alone or combined DNA vaccine produced statistically significant increase in the FMDV-specific antibody titers (P<0.05). But after boosting, FMDV-specific splenocytes proliferative activity of mice primed with combined DNA vaccine was even lower than that of mice primed with pVSG alone (P<0.05). Taken together, this study reflected the immunogenicity of a single plasmid may be decreased in combined DNA immunization strategy, which still needs to be carefully evaluated before practical application.

Immune responses generated by Lactobacillus as a carrier in DNA immunization against foot-and-mouth disease virus

To exploit Lactobacillus acidophilus as a carrier in DNA immunization against foot-and-mouth disease virus (FMDV), a recombinant eukaryotic expression plasmid (pRc/CMV2-VP1-Rep. 8014) harboring pRc/CMV2 vector, the FMDV VP1 gene, and a replication origin from Lactobacillus plantarum ATCC 8014 strain was constructed. To detect the VP1 protein, pRc/CMV2-VP1-Rep. 8014 was expressed in PK 15 cells and transfected into a L. acidophilus SW1 strain (L. acidophilus SFMD-1). To evaluate the immunization effect of L. acidophilus SFMD-1, anti-FMDV VP1 antibody, T-cell proliferation, antigen-specific delayed-type hypersensitivity (DTH), and tissue distribution were investigated using intramuscular, intraperitoneal, intranasal, and oral administration delivery routes. The results showed that L. acidophilus SFMD-1 was able to elicit a detectable antibody level on day 21. The VP1 antibody levels induced by L. acidophilus SFMD-1 and commercial inactivated FMDV vaccine rose rapidly to 0.84 and 0.70, respectively, by day 42, then sustained a high level by day 49. The route of administration had an impact on the magnitude of the systemic antigen-specific IgG responses, with intramuscularly applied L. acidophilus SFMD-1 generating the greatest FMDV VP1 antibody response, followed by intraperitoneal, intranasal, and oral administration delivery routes. Using the T-cell proliferation assay, the stimulation index of a group immunized with L. acidophilus SFMD-1 reached 2.78 versus 5.08 in a group immunized with pRc/CMV2-VP1-Rep. 8014 plasmid. Mice immunized with L. acidophilus SFMD-1 were able to induce T-cell-mediated antigen-specific DTH. In addition, the VP1 gene was detected in the muscle, kidney, spleen, and heart, but not in the liver. The results demonstrate clearly that Lactobacillus as a carrier is a promising approach of DNA vaccination, and is a potentially guard against FMDV.

Co-inoculation of DNA and protein vaccines induces antigen-specific T cell suppression

Immunization can sometimes lead to antigen-specific immune suppression. In this study, we investigated this phenomenon by testing several combinations of DNA and protein vaccines directed against various viruses. We find that co-inoculation of mice with combined DNA and protein vaccines induces immune suppression if the two vaccines are "matched" by targeting the same antigen. Conversely, vaccine combinations never lead to immune suppression if they are derived from different viruses and, thus, mismatched antigenically. We have further identified CD4+CD25- T cells as the type of regulatory T cells induced by and are responsible for suppressing T cell activities in an antigen-specific manner in immunized animals. These regulatory T cells are phenotypically unique in their expression of Foxp3, IL-10, and IFN-gamma. Our study thus shows for the first time that co-administration of antigen-matched DNA and protein vaccines can generate this type of adaptive regulatory T cells.

Regulatory role of pro-Th1 and pro-Th2 cytokines in modulating the activity of Th1 and Th2 cells when B cell and macrophages are used as antigen presenting cells

BACKGROUND

Presence of antigen presenting cells, expression of costimulatory molecules, the strength of first signal and cytokine milieu are quite important in influencing the reactivation of differentiated Th1 and Th2 cells.

RESULTS

In the present study, we have analyzed the concerted action of pro-Th1 and pro-Th2 cytokines in the presence of B cells, peritoneal and splenic macrophages as antigen presenting cells and varied concentration of first (anti-CD3 Ab) and second (B7-1 transfectant) signals on the proliferation and cytokine secretion by Th1 and Th2 cells. Interesting observations were made that IFN-gamma significantly augmented the secretion of IL-4 by Th2 cells when either B cells or splenic or peritoneal macrophages were used as APC. Further, IFN-gamma significantly inhibited the proliferation of Th1 cells only in the presence of peritoneal macrophages. We have also observed that B cells could significantly respond to cytokines to further enhance the proliferation and cytokine release by Th1 and Th2 cells. But not much effect on addition of exogenous cytokines IL-1, IL-4, IL-5, IL-12 was observed on the proliferation of Th1 and Th2 cells in the presence of macrophages. In contrast, both IFN-gamma and IL-2 significantly enhanced the production of IL-4 and IL-5 respectively, by Th2 cells in presence of B cells, splenic and peritoneal macrophages. Another important observation was that the addition of B7-1 transfectants in the cultures, which were stimulated with low dose of anti-CD3 Ab significantly, enhanced the proliferation and cytokine secretion.

CONCLUSION

This study indicates involvement of different type of APCs, cytokine milieu, dose of first and second signals in a concerted manner in the outcome of the immune response. The significance of this study is that the immunization with antigen along with costimulatory molecules may significantly reduce the dose of antigen and can generate better immune response than antigen alone.

Enhanced immunogenicity of microencapsulated multiepitope DNA vaccine encoding T and B cell epitopes of foot-and-mouth disease virus in mice

The role of poly(D,L-lactic-co-glycolic acid, PLGA) microparticles on enhancing immune responses of multiepitope DNA vaccines was investigated in vitro and in vivo. pcDNA-SG encoding T and B cell epitopes of foot-and-mouth disease virus (FMDV) was encapsulated into PLGA microparticles. PLGA microparticles could protect themselves from nuclease degradation in vitro. PLGA-pcDNA-SG microparticles could be uptaken by cells and expressed His-tagged SG immunogen in vitro and in vivo. A prolonged expression and presentation of SG immunogen were observed by confocal laser scanning microscopy in the lymphocytes from the mice incubated with PLGA-pcDNA-SG microparticles, compared with the mice immunized with naked pcDNA-SG. PLGA-pcDNA-SG microparticles displayed a significant stronger immunogenicity than naked DNA vaccines with a higher titer of virus-specific antibody, elevated IFN-gamma production and enhanced lymphocyte proliferation. PLGA-DNA microparticle could elicit augmented humoral and cellular responses with reduced amounts and times of immunization.