Prevention of neonatal tolerance by a plasmid encoding granulocyte-macrophage colony stimulating factor

Genetic vaccination approaches against malaria based on the circumsporozoite protein

Malaria is the world's major parasitic disease, for which effective control measures are urgently needed. Despite considerable efforts, no successful vaccine against malaria has been developed so far. The method of DNA-based immunization offers the possibility to induce both antibody- and cell-mediated immune responses to a variety of antigens. The flexibility of the DNA vaccine technology permits the combination of several antigens from different developmental stages of the parasite's complicated life cycle. This review covers the development of DNA-based immunization against malaria from initial experiments in small animals to recently conducted clinical studies. Focusing on one of the best characterized malaria vaccine candidate antigens, the circumsporozoite protein, an overview of strategies to enhance vaccine efficacy is provided. Advanced application methods such as the gene gun technology or the needle-less jet injection device are described. As DNA vaccination represents a relatively new methodology, safety concerns associated with planned clinical applications are discussed. In summary, this novel type of vaccine has to be considered as a promising tool for future malaria vaccination strategies.

Cytokine GM-CSF genetic adjuvant facilitates prophylactic DNA vaccine against pseudorabies virus through enhanced immune responses

Granulocyte/macrophage colony-stimulatory factor (GM-CSF) is an attractive adjuvant for a DNA vaccine on account of its ability to recruit antigen-presenting cells (APCs) to the site of antigen synthesis as well as its ability to stimulate the maturation of dendritic cells (DCs). This study evaluated the utility of GM-CSF cDNA as a DNA vaccine adjuvant for glycoprotein B (gB) of pseudorabies virus (PrV) in a murine model. The co-injection of GM-CSF DNA enhanced the levels of serum PrV-specific IgG with a 1.5-to 2-fold increase. Moreover, GM-CSF co-injection inhibited the production of IgG2a isotype. However, it enhanced production of an IgG1 isotype resulting in humoral responses biased to the Th2-type against PrV antigen. In contrast, the co-administration of GM-CSF DNA enhanced the T cell-mediated immunity biased to the Th1-type, as judged by the significantly higher level of cytokine IL-2 and IFN-gamma production but not IL-4. When challenged with a lethal dose of PrV, the GM-CSF co-injection enhanced the resistance against a PrV infection. This suggests that co-inoculation with a vector expressing GM-CSF enhanced the protective immunity against a PrV infection. This immunity was caused by the induction of increased humoral and cellular immunity in response to PrV antigen.

A DNA vaccine encoding genetic fusions of carcinoembryonic antigen (CEA) and granulocyte/macrophage colony-stimulating factor (GM-CSF)

The anti-tumor immunologic effects of plasmid DNA vaccines encoding human carcinoembryonic antigen (CEA) fused to mouse granulocyte/macrophage colony-stimulating factor (GM-CSF) were examined. Immunization of C57BL/6 mice with the CEA-GMCSF fusion plasmids in a three injection, high-dose immunization schedule led to T cell and antibody responses specific for CEA. Mice injected with CEA-GMCSF fusion plasmids also developed IgG autoantibodies to GM-CSF. Tumor challenge with the CEA-expressing syngeneic mouse adenocarcinoma line, MC38-CEA-2, showed delayed tumor growth in mice immunized with the CEA-GMCSF fusion plasmids but complete protection in mice immunized with plasmid encoding CEA alone. In contrast, a single low-dose immunization with CEA-GMCSF fusion plasmids provided better tumor protection than low-dose CEA plasmid alone and resulted in lower titers of GM-CSF antibodies.

Use of CpG oligodeoxynucleotides as immune adjuvants

Synthetic oligodeoxynucleotides (ODNs) containing unmethylated CpG motifs directly stimulate human B cells and plasmacytoid dendritic cells (pDCs), thereby promoting the production of T helper 1 (Th1) and pro-inflammatory cytokines and the maturation/activation of professional antigen-presenting cells. These activities enable CpG ODNs to act as immune adjuvants, accelerating and boosting antigen-specific immune responses by 5-500-fold. These effects are optimized by maintaining close physical contact between the CpG DNA and the immunogen. Animal challenge models establish that protective immunity can be accelerated and magnified by coadministering CpG DNA with vaccines. Ongoing clinical studies indicate that CpG ODNs are safe and well tolerated when administered as adjuvants to humans, and in some cases, they increase vaccine-induced immune responses.

Mucosally delivered Salmonella live vector vaccines elicit potent immune responses against a foreign antigen in neonatal mice born to naive and immune mothers

The development of effective vaccines for neonates and very young infants has been impaired by their weak, short-lived, and Th-2 biased responses and by maternal antibodies that interfere with vaccine take. We investigated the ability of Salmonella enterica serovars Typhi and Typhimurium to mucosally deliver tetanus toxin fragment C (Frag C) as a model antigen in neonatal mice. We hypothesize that Salmonella, by stimulating innate immunity (contributing to adjuvant effects) and inducing Th-1 cytokines, can enhance neonatal dendritic cell maturation and T-cell activation and thereby prime humoral and cell-mediated immunity. We demonstrate for the first time that intranasal immunization of newborn mice with 10(9) CFU of S. enterica serovar Typhi CVD 908-htrA and S. enterica serovar Typhimurium SL3261 carrying plasmid pTETlpp on days 7 and 22 after birth elicits high titers of Frag C antibodies, previously found to protect against tetanus toxin challenge and similar to those observed in adult mice. Salmonella live vectors colonized and persisted primarily in nasal tissue. Mice vaccinated as neonates induced Frag C-specific mucosal and systemic immunoglobulin A (IgA)- and IgG-secreting cells, T-cell proliferative responses, and gamma interferon secretion. A mixed Th1- and Th2-type response to Frag C was established 1 week after the boost and was maintained thereafter. S. enterica serovar Typhi carrying pTETlpp induced Frag C-specific antibodies and cell-mediated immunity in the presence of high levels of maternal antibodies. This is the first report that demonstrates the effectiveness of Salmonella live vector vaccines in early life.

Immune response at birth, long-term immune memory and 2 years follow-up after in-utero anti-HBV DNA immunization

Infections occurring at the end of pregnancy, during birth or by breastfeeding are responsible for the high toll of death among first-week infants. In-utero DNA immunization has demonstrated the effectiveness in inducing specific immunity in newborns. A major contribution to infant immunization would be achieved if a vaccine proved able to be protective as early as at the birth, preventing the typical 'first-week infections'. To establish its potential for use in humans, in-utero DNA vaccination efficiency has to be evaluated for short- and long-term safety, protection at delivery, efficacy of boosts in adults and effective window/s for modulation of immune response during pregnancy, in an animal model suitable with human development. Here we show that a single intramuscular in-utero anti-HBV DNA immunization at two-thirds of pig gestation produces, at birth, antibody titers considered protective in humans. The boost of antibody titers in every animal following recall at 4 and 10 months demonstrates the establishment of immune memory. The safety of in-utero fetus manipulation is guaranteed by short-term (no fetus loss, lack of local alterations, at-term spontaneous delivery, breastfeeding) and long-term (2 years) monitoring. Treatment of fetuses closer to delivery results in immune ignorance without induction of tolerance. This result highlights the repercussion of selecting the appropriate time point when this approach is used to deliver therapeutic genes. All these findings illustrate the relevance of naked DNA-based vaccination technology in therapeutic efforts aimed to prevent the high toll of death among first-week infants.

Mucosally delivered E1-deleted adenoviral vaccine carriers induce transgene product-specific antibody responses in neonatal mice

E1-deleted adenoviral vectors of the human serotype 5 (AdHu5) and the chimpanzee serotype 68 (AdC68) expressing the rabies virus glycoprotein (rab.gp) were tested for induction of transgene product-specific Abs upon intranasal or oral immunization of newborn mice. Both vectors induced Abs to rabies virus that could be detected in serum and from mucosal secretions. Serum rabies virus neutralizing Ab titers sufficed to protect neonatally vaccinated mice against a subsequent challenge with rabies virus. The efficacy of the AdHu5rab.gp vector given orally to newborn mice born to AdHu5 virus-immune dams was not impaired by maternally transferred Abs to the vaccine carrier.

Antitumor activity of the intratumoral injection of fowlpox vectors expressing a triad of costimulatory molecules and granulocyte/macrophage colony stimulating factor in mesothelioma

Deficiency in costimulatory molecule expression has been implicated in the ability of tumors to escape immune effectors. The activity of the intratumoral administration of recombinant fowlpox vectors expressing a triad of costimulatory molecules (rF-TRICOM) was evaluated in the asbestos-induced AB12 and AC29 mouse models of mesothelioma. Mesothelioma cell infected with rF-TRICOM expressed high levels of the costimulatory molecules. Prolongation of survival was observed in mice receiving rF-TRICOM in AB12 and AC29 intraperitoneal models. Complete tumor regressions were observed in mice receiving intratumoral rF-TRICOM in the AB12 subcutaneous tumor model. Tumor regressions were associated with the development of serum IgG reactivities to mesothelioma-associated determinants and specific systemic cytolytic activity, and responding mice were capable of rejecting tumors upon re-challenge. Antitumor activity was also observed in mice with established AB12 tumor vaccinated with irradiated rF-TRICOM-infected AB12 cells. The antitumor activity of intratumoral rF-TRICOM was superior to that of the intratumoral injection of a fowlpox vector expressing granulocyte-macrophage colony stimulating factor (rF-GM-CSF). AB12 and AC29 tumors were found to produce GM-CSF and to have substantial macrophage infiltration. Production of GM-CSF decreased in vivo in tumors injected with rF-TRICOM. rF-TRICOM and wild-type fowlpox inhibited the growth of AB12 and AC29 cells in vitro; less inhibition was observed with rF-GM-CSF. These results indicate that the intratumoral injection of rF-TRICOM has significant activity in mouse models of mesothelioma and can elicit a systemic antitumor immune response. The results also suggest potential limitations to the intratumoral administration of cytokines, such as GM-CSF, in mesothelioma.

Development of DNA vaccines against hemolytic-uremic syndrome in a murine model

Shiga toxin type 2 (Stx2) produced by Escherichia coli O:157H7 can cause hemolytic-uremic syndrome in children, a disease for which there is neither a vaccine nor an effective treatment. This toxin consists of an enzymatically active A subunit and a pentameric B subunit responsible for the toxin binding to host cells, and also found to be immunogenic in rabbits. In this study we developed eukaryotic plasmids expressing the B subunit gene of Stx2 (pStx2B) and the B subunit plus the gene coding for the A subunit with an active-site deletion (pStx2 Delta A). Transfection of eukaryotic cells with these plasmids produced proteins of the expected molecular weight which reacted with specific monoclonal antibodies. Newborn and adult BALB/c mice immunized with two intramuscular injections of each plasmid, either alone or together with the same vector expressing the granulocyte and monocyte colony-stimulating factor (pGM-CSF), elicited a specific Th1-biased humoral response. The effect of pGM-CSF as an adjuvant plasmid was particularly notable in newborn mice and in pStx2B-vaccinated adult mice. Stx2-neutralizing activity, evaluated in vitro on VERO cell monolayers, correlated with in vivo protection. This is the first report using plasmids to induce a neutralizing humoral immune response against the Stx2.

The antibody response to HBs antigen is regulated by coordinated Th1 and Th2 cytokine production in healthy neonates

A proportion of healthy neonates fail to produce protective levels of anti-HBs antibody following vaccination with recombinant hepatitis B vaccine. This study was undertaken to investigate contribution of Th1 and Th2 responses to anti-HBs antibody production and to explore the mechanism(s) of unresponsiveness to HBsAg in human neonates. Peripheral blood manonuclear cells (PBMCs) were isolated form 28 nonresponder (anti-HBs antibody <10 IU/l) and 25 responder neonates. The cells were stimulated in vitro with recombinant HBsAg and PHA mitogen and concentrations of IL-4, IL-10 and IFN-gamma were quantified in culture supernatants by sandwich ELISA. Our results demonstrated significantly increased production of all cytokines, including IL-4 (P < 0.001), IL-10 (P < 0.002) and IFN-gamma (P < 0.01) in responder compared to nonresponder vaccinees. No significant differences, however, were observed between the two groups of neonates in the levels of cytokines induced by PHA or secreted in absence of antigen and mitogen. Our findings suggest that unresponsiveness to recombinant HBsAg in healthy neonates is linked to inadequate secretion of both Th1 and Th2 cytokines.

The antibody response to HBs antigen is regulated by coordinated Th1 and Th2 cytokine production in healthy neonates

A proportion of healthy neonates fail to produce protective levels of anti-HBs antibody following vaccination with recombinant hepatitis B vaccine. This study was undertaken to investigate contribution of Th1 and Th2 responses to anti-HBs antibody production and to explore the mechanism(s) of unresponsiveness to HBsAg in human neonates. Peripheral blood manonuclear cells (PBMCs) were isolated form 28 nonresponder (anti-HBs antibody <10 IU/l) and 25 responder neonates. The cells were stimulated in vitro with recombinant HBsAg and PHA mitogen and concentrations of IL-4, IL-10 and IFN-gamma were quantified in culture supernatants by sandwich ELISA. Our results demonstrated significantly increased production of all cytokines, including IL-4 (P < 0.001), IL-10 (P < 0.002) and IFN-gamma (P < 0.01) in responder compared to nonresponder vaccinees. No significant differences, however, were observed between the two groups of neonates in the levels of cytokines induced by PHA or secreted in absence of antigen and mitogen. Our findings suggest that unresponsiveness to recombinant HBsAg in healthy neonates is linked to inadequate secretion of both Th1 and Th2 cytokines.

Antigen-based immune modulation: DNA vectors and beyond

The ultimate goal for autoimmune immunotherapy is to achieve a specific downregulation or modification of autoaggressive immune responses while leaving in place the normal repertoire, capable of mediating antimicrobial responses. A multitude of preclinical studies, particularly during the last 15 years, raised hopes that self-antigens could be used to achieve the goal of specific immune modulation. Difficulties associated with the translation of this concept to the clinic revealed inherent limitations of antigen-based immune modulation. To increase the efficiency of antigen-dependent immune modulation, researchers started to investigate novel vectors for antigen delivery. Plasmid vectors, as opposed to protein antigens or peptides, have the ability to trigger prolonged production of limited amounts of antigen in the periphery. However, one complicating factor may be the inherent "danger" signal stimulated by the nature of the unmethylated CpG motifs on bacterial plasmid. Currently, various approaches are being explored to improve the efficacy of response while ameliorating the safety concerns of plasmids as immunotherapeutic tools. This manuscript offers a perspective on such efforts and outlines how the knowledge accumulated in the process will help scientists advance to the next generation of immunotherapeutics.

Genetic immunization of neonates

The vaccination of neonates is generally difficult due to immaturity of the immune system, higher susceptibility to tolerance and potential negative interference of maternal antibodies. Studies carried out in rodents and non-human primates showed that plasmid vaccines expressing microbial antigens, rather than inducing tolerance, triggered significant humoral and cellular immunity with a Th1 component. The ability of bacterial CpG motifs to activate immature antigen-presenting cells is critical for the neonatal immunogenicity of DNA vaccines. In addition, the endogenous production of antigen subsequent to transfection of antigen-presenting cells may explain the lack of inhibition by maternal antibodies of cellular responses. Together, these features make the plasmid vaccines an appealing strategy to prime immune responses against foreign pathogens, during early life. In combination with subsequent boosting using conventional vaccines, DNA vaccine-based regimens may provide a qualitatively superior immunity against microbes. Thorough understanding of immunomodulatory properties of plasmid-vectors may extend their use for early prophylaxis of inflammatory disorders.

A multilateral effort to develop DNA vaccines against falciparum malaria

Scientists from several organizations worldwide are working together to develop a multistage, multigene DNA-based vaccine against Plasmodium falciparum malaria. This collaborative vaccine development effort is named Multi-Stage DNA-based Malaria Vaccine Operation. An advisory board of international experts in vaccinology, malariology and field trials provides the scientific oversight to support the operation. This article discusses the rationale for the approach, underlying concepts and the pre-clinical development process, and provides a brief outline of the plans for the clinical testing of a multistage, multiantigen malaria vaccine based on DNA plasmid immunization technology.

Advances DNA vaccines

Extraordinary advances in biotechnology make DNA vaccines the most promising area of vaccinology. This article reviews the public health impact of vaccines in the 20th century, summarizes immunologic concepts, and updates the status of DNA vaccine development and its impact on clinical practice.

T cell immunity in neonates

Typically, neonates exhibit decreased or aberrant cellular immune responses when compared to adults, resulting in increased susceptibility to infection. However, it is clear that newborns are able to generate adult-like protective T cell responses under certain conditions. The focus of our research is to understand the deficiencies within the neonatal immune system that lead to improper cellular responses and how priming conditions can be altered to elicit the appropriate T cell response necessary to protect against development of pathogen-induced disease. With these goals in mind, we are exploring the attributes of neonatal T cells and their development, as well as the conditions during priming that influence the resulting response to immune challenge during the neonatal period.

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.

Genomic DNA released by dying cells induces the maturation of APCs

Mature APCs play a key role in the induction of Ag-specific immunity. This work examines whether genomic DNA released by dying cells provides a stimulus for APC maturation. Double-stranded but not single-stranded genomic DNA triggered APC to up-regulate expression of MHC class I/II and various costimulatory molecules. Functionally, dsDNA enhanced APC function in vitro and improved primary cellular and humoral immune responses in vivo. These effects were dependent on the length and concentration of the dsDNA but were independent of nucleotide sequence. The maturation of APC induced by dsDNA may promote host survival by improving immune surveillance at sites of tissue injury/infection.

Fetal immunization by a DNA vaccine delivered into the oral cavity

Infectious diseases are the main cause of neonatal morbidity and mortality in humans. The World Health Organization estimated that in 1995 approximately 8 million infants died within the first year of life from infectious diseases, including 5 million during the first week of life. Some of the salient pathogens involved include herpes simplex virus, human immunodeficiency virus, hepatitis B virus, human cytomegalovirus, group B streptococcus, hemophilus and chlamydia. Infection with these pathogens usually occurs at the end of pregnancy, during birth or by breastfeeding. To reduce the risk of disease transmission, caesarian sections, prophylactic treatment with antibiotics or maternal antiviral therapy during the last trimester are used where available, together with improved neonatal care. None of these approaches, however, completely eliminates the risk of neonatal infection. Therefore, active or passive immunization of the fetus might represent an effective approach to reduce the high risk of neonatal diseases. Here, we demonstrate that a single immunization with a DNA vaccine delivered into the amniotic fluid in the oral cavity induces high serum antibody titers and a cell-mediated immune response, combined with induction of local immunity in the oral cavities of fetal lambs.

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.