Engineering of in vivo immune responses to DNA immunization via codelivery of costimulatory molecule genes

Recent advances on HIV DNA vaccines development: Stepwise improvements to clinical trials

According to WHO (World Health Organization) reports, more than 770,000 people died from HIV and almost 1.7 million people becoming newly infected in the worldwide in 2018. Therefore, many attempts should be done to produce a forceful vaccine to control the AIDS. DNA-based vaccines have been investigated for HIV vaccination by researches during the recent 20 years. The DNA vaccines are novel approach for induction of both type of immune responses (cellular and humoral) in the host cells and have many advantages including high stability, fast and easy of fabrication and absence of severe side effects when compared with other vaccination methods. Recent studies have been focused on vaccine design, immune responses and on the use of adjuvants as a promising strategy for increased level of responses, delivery approaches by viral and non-viral methods and vector design for different antigens of HIV virus. In this review, we outlined the aforementioned advances on HIV DNA vaccines. Then we described the future trends in clinical trials as a strong strategy even in healthy volunteers and the potential developments in control and prevention of HIV.

A poly-neoantigen DNA vaccine synergizes with PD-1 blockade to induce T cell-mediated tumor control

The combination of immune-stimulating strategies has the potency to improve immunotherapy of cancer. Vaccination against neoepitopes derived from patient tumor material can generate tumor-specific T cell immunity, which could reinforce the efficacy of checkpoint inhibitor therapies such as anti-PD-1 treatment. DNA vaccination is a versatile platform that allows the inclusion of multiple neoantigen-coding sequences in a single formulation and therefore represents an ideal platform for neoantigen vaccination. We developed an anti-tumor vaccine based on a synthetic DNA vector designed to contain multiple cancer-specific epitopes in tandem. The DNA vector encoded a fusion gene consisting of three neoepitopes derived from the mouse colorectal tumor MC38 and their natural flanking sequences as 40 amino acid stretches. In addition, we incorporated as reporter epitopes the helper and CTL epitope sequences of ovalbumin. The poly-neoantigen DNA vaccine elicited T cell responses to all three neoantigens and induced functional CD8 and CD4 T cell responses to the reporter antigen ovalbumin after intradermal injection in mice. The DNA vaccine was effective in preventing outgrowth of B16 melanoma expressing ovalbumin in a prophylactic setting. Moreover, the combination of therapeutic DNA vaccination and anti-PD-1 treatment was synergistic in controlling MC38 tumor growth whereas individual treatments did not succeed. These data demonstrate the potential of DNA vaccination to target multiple neoepitopes in a single formulation and highlight the cooperation between vaccine-based and checkpoint blockade immunotherapies for the successful eradication of established tumors.

One Group's Historical Reflections on DNA Vaccine Development

DNA vaccines were pioneered by several groups in the early 1990s. This article presents the reflections of one of these groups on their work with retroviral vectors in chickens that contributed to the discovery and early development of DNA vaccines. Although the findings were initially met with skepticism, the work presented here combined with that of others founded a new method of vaccination: the direct inoculation of purified DNA encoding the target antigen.

MyD88/CD40 Genetic Adjuvant Function in Cutaneous Atypical Antigen-Presenting Cells Contributes to DNA Vaccine Immunogenicity

Therapeutic DNA-based vaccines aim to prime an adaptive host immune response against tumor-associated antigens, eliminating cancer cells primarily through CD8+ cytotoxic T cell-mediated destruction. To be optimally effective, immunological adjuvants are required for the activation of tumor-specific CD8+ T cells responses by DNA vaccination. Here, we describe enhanced anti-tumor efficacy of an in vivo electroporation-delivered DNA vaccine by inclusion of a genetically encoded chimeric MyD88/CD40 (MC) adjuvant, which integrates both innate and adaptive immune signaling pathways. When incorporated into a DNA vaccine, signaling by the MC adjuvant increased antigen-specific CD8+ T cells and promoted elimination of pre-established tumors. Interestingly, MC-enhanced vaccine efficacy did not require direct-expression of either antigen or adjuvant by local antigen-presenting cells, but rather our data supports a key role for MC function in "atypical" antigen-presenting cells of skin. In particular, MC adjuvant-modified keratinocytes increased inflammatory cytokine secretion, upregulated surface MHC class I, and were able to increase in vitro and in vivo priming of antigen-specific CD8+ T cells. Furthermore, in the absence of critical CD8α+/CD103+ cross-priming dendritic cells, MC was still able to promote immune priming in vivo, albeit at a reduced level. Altogether, our data support a mechanism by which MC signaling activates an inflammatory phenotype in atypical antigen-presenting cells within the cutaneous vaccination site, leading to an enhanced CD8+ T cell response against DNA vaccine-encoded antigens, through both CD8α+/CD103+ dendritic cell-dependent and independent pathways.

For t 2 DNA vaccine prevents Forcipomyia taiwana (biting midge) allergy in a mouse model

BACKGROUND

Forcipomyia taiwana (biting midge) is the most prevalent allergenic biting insect in Taiwan, and 60% of the exposed subjects develop allergic reactions. Subjects with insect allergy frequently limit their outdoor activities to avoid the annoyingly intense itchy allergic reactions, leading to significant worsening of their quality of life. Allergen-specific immunotherapy is the only known therapy that provides long-term host immune tolerance to the allergen, but is time-consuming and cumbersome. This study tested whether the For t 2 DNA vaccine can prevent allergic symptoms in For t 2-sensitized mice.

MATERIALS AND METHODS

Two consecutive shots of For t 2 DNA vaccine were given to mice with a 7-day interval before sensitization with recombinant For t 2 proteins, using the two-step sensitization protocol reported previously.

RESULTS

The For t 2 DNA vaccine at 50 μg prevented the production of For t 2-specific IgE (P < 0.05), as well as midge allergen-challenge-induced scratch bouts, midge allergen-induced IL-13 and IL-4 production from splenocytes, and inflammatory cell infiltrations in the lesions 48 h after intradermal challenge.

CONCLUSIONS

This study is the first to demonstrate that DNA vaccine encoding midge allergen is effective in preventing allergic skin inflammation induced by biting midge. Immunotherapy using For t 2 DNA vaccine can protect mice from being sensitized by midge allergen and may be a promising treatment for biting midge allergy in the future.

Using Plasmids as DNA Vaccines for Infectious Diseases

DNA plasmids can be used to induce a protective (or therapeutic) immune response by delivering genes encoding vaccine antigens. That naked DNA (without the refinement of coat proteins or host evasion systems) can cross from outside the cell into the nucleus and be expressed is particularly remarkable given the sophistication of the immune system in preventing infection by pathogens. As a result of the ease, low cost, and speed of custom gene synthesis, DNA vaccines dangle a tantalizing prospect of the next wave of vaccine technology, promising individual designer vaccines for cancer or mass vaccines with a rapid response time to emerging pandemics. There is considerable enthusiasm for the use of DNA vaccination as an approach, but this enthusiasm should be tempered by the successive failures in clinical trials to induce a potent immune response. The technology is evolving with the development of improved delivery systems that increase expression levels, particularly electroporation and the incorporation of genetically encoded adjuvants. This review will introduce some key concepts in the use of DNA plasmids as vaccines, including how the DNA enters the cell and is expressed, how it induces an immune response, and a summary of clinical trials with DNA vaccines. The review also explores the advances being made in vector design, delivery, formulation, and adjuvants to try to realize the promise of this technology for new vaccines. If the immunogenicity and expression barriers can be cracked, then DNA vaccines may offer a step change in mass vaccination.

Biomaterials at the interface of nano- and micro-scale vector-cellular interactions in genetic vaccine design

The development of safe and effective vaccines for the prevention of elusive infectious diseases remains a public health priority. Immunization, characterized by adaptive immune responses to specific antigens, can be raised by an array of delivery vectors. However, current commercial vaccination strategies are predicated on the retooling of archaic technology. This review will discuss current and emerging strategies designed to elicit immune responses in the context of genetic vaccination. Selected strategies at the biomaterial-biological interface will be emphasized to illustrate the potential of coupling both fields towards a common goal.

Plasmid DNA vaccines against cancer: cytotoxic T-lymphocyte induction against tumor antigens

In recent years, a number of tumor vaccination strategies have been developed. Most of these rely on the identification of tumor antigens that can be recognized by the immune system. DNA vaccination represents one such approach for the induction of both humoral and cellular immune responses against tumor antigens. Studies in animal models have demonstrated the feasibility of utilizing DNA vaccination to elicit protective antitumor immune responses. However, most tumor antigens expressed by cancer cells in humans are weakly immunogenic, and therefore require the development of strategies to potentiate DNA vaccine efficacy in the clinical setting. This review focuses on recent advances in understanding of the immunology of DNA vaccines, as well as strategies used to increase DNA vaccine potency with respect to cytotoxic T-lymphocyte activity.

Approaches for the design and evaluation of HIV-1 DNA vaccines

Although it is not clear what arm of the immune response correlates with protection from HIV-1 infection or disease, a robust broad cellular and humoral immune response will likely be needed to control this infection. Accordingly, it is crucial to characterize which HIV-1 gene products are potential targets to elicit these responses. DNA vaccination has been shown to be effective for induction of both humoral and cellular immune responses in animal models. Most DNA vaccine strategies studied to date have been based on targeting structural HIV-1 proteins, but others have focused on the regulatory/accessory HIV-1 proteins as an approach to induce immune responses able to recognize early infected cells. It has also become clear that HIV-DNA vaccine efficacy in humans requires improvement. Combinations of HIV-1 genes, improvement of the DNA vector itself, or addition of genetic adjuvants (cytokines or costimulatory molecules) as part of the DNA vaccine itself, have been evaluated by several groups as approaches for enhancing DNA vaccine-induced immune responses. Encouraging results have been obtained in primate models, supporting that these strategies should be further evaluated in humans, for either prophylaxis or immune therapy of HIV-1.

Induction of antigen-positive cell death by the expression of perforin, but not DTa, from a DNA vaccine enhances the immune response

The failure of traditional protein-based vaccines to prevent infection by viruses such as HIV or hepatitis C highlights the need for novel vaccine strategies. DNA vaccines have shown promise in small animal models, and are effective at generating anti-viral T cell-mediated immune responses; however, they have proved to be poorly immunogenic in clinical trials. We propose that the induction of necrosis will enhance the immune response to vaccine antigens encoded by DNA vaccines, as necrotic cells are known to release a range of intracellular factors that lead to dendritic cell (DC) activation and enhanced cross-presentation of antigen. Here we provide evidence that induction of cell death in DNA vaccine-targeted cells provides an adjuvant effect following intradermal vaccination of mice; however, this enhancement of the immune response is dependent on both the mechanism and timing of cell death after antigen expression. We report that a DNA vaccine encoding the cytolytic protein, perforin, resulted in DC activation, enhanced broad and multifunctional CD8 T-cell responses to the HIV-1 antigen GAG and reduced viral load following challenge with a chimeric virus, EcoHIV, compared with the canonical GAG DNA vaccine. This effect was not observed for a DNA vaccine encoding an apoptosis-inducing toxin, DTa, or when the level of perforin expression was increased to induce cell death sooner after vaccination. Thus, inducing lytic cell death following a threshold level of expression of a viral antigen can improve the immunogenicity of DNA vaccines, whereas apoptotic cell death has an inhibitory effect on the immune response.

Synthetic DNA vaccines: improved vaccine potency by electroporation and co-delivered genetic adjuvants

In recent years, DNA vaccines have undergone a number of technological advancements that have incited renewed interest and heightened promise in the field. Two such improvements are the use of genetically engineered cytokine adjuvants and plasmid delivery via in vivo electroporation (EP), the latter of which has been shown to increase antigen delivery by nearly 1000-fold compared to naked DNA plasmid delivery alone. Both strategies, either separately or in combination, have been shown to augment cellular and humoral immune responses in not only mice, but also in large animal models. These promising results, coupled with recent clinical trials that have shown enhanced immune responses in humans, highlight the bright prospects for DNA vaccines to address many human diseases.

Technologies for enhanced efficacy of DNA vaccines

Despite many years of research, human DNA vaccines have yet to fulfill their early promise. Over the past 15 years, multiple generations of DNA vaccines have been developed and tested in preclinical models for prophylactic and therapeutic applications in the areas of infectious disease and cancer, but have failed in the clinic. Thus, while DNA vaccines have achieved successful licensure for veterinary applications, their poor immunogenicity in humans when compared with traditional protein-based vaccines has hindered their progress. Many strategies have been attempted to improve DNA vaccine potency including use of more efficient promoters and codon optimization, addition of traditional or genetic adjuvants, electroporation, intradermal delivery and various prime-boost strategies. This review summarizes these advances in DNA vaccine technologies and attempts to answer the question of when DNA vaccines might eventually be licensed for human use.

Mesenchymal stromal cells for tissue-engineered tissue and organ replacements

Mesenchymal stromal cells (MSCs), a rare heterogeneous subset of pluripotent stromal cells that can be easily isolated from different adult tissues, in vitro expanded and differentiated into multiple lineages, are immune privileged and, more important, display immunomodulatory capacities. Because of this, they are the preferred cell source in tissue-engineered replacements, not only in autogeneic conditions, where they do not evoke any immune response, but especially in the setting of allogeneic organ and tissue replacements. However, more preclinical and clinical studies are requested to completely understand MSC's immune biology and possible clinical applications. We herein review the immunogenicity and immunomodulatory properties of MSCs, their possible mechanisms and potential clinical use for tissue-engineered organ and tissue replacement.

Immunological aspects of allogeneic mesenchymal stem cell therapies

Allogeneic mesenchymal stem or stromal cells (MSCs) are proposed as cell therapies for degenerative, inflammatory, and autoimmune diseases. The feasibility of allogeneic MSC therapies rests heavily on the concept that these cells avoid or actively suppress the immunological responses that cause rejection of most allogeneic cells and tissues. In this article the validity of the immune privileged status of allogeneic MSCs is explored in the context of recent literature. Current data that provide the mechanistic basis for immune modulation by MSCs are reviewed with particular attention to how MSCs modify the triggering and effector functions of innate and adaptive immunity. The ability of MSCs to induce regulatory dendritic and T-cell populations is discussed with regard to cell therapy for autoimmune disease. Finally, we examine the evidence for and against the immune privileged status of allogeneic MSCs in vivo. Allogeneic MSCs emerge as cells that are responsive to local signals and exert wide-ranging, predominantly suppressive, effects on innate and adaptive immunity. Nonetheless, these cells also retain a degree of immunogenicity in some circumstances that may limit MSC longevity and attenuate their beneficial effects. Ultimately successful allogeneic cell therapies will rely on an improved understanding of the parameters of MSC-immune system interactions in vivo.

Molecular adjuvant HMGB1 enhances anti-influenza immunity during DNA vaccination

DNA-based vaccines, while highly immunogenic in mice, generate significantly weaker responses in primates. Therefore, current efforts are aimed at increasing their immunogenicity, which include optimizing the plasmid/gene, the vaccine formulation and method of delivery. For example, co-immunization with molecular adjuvants encoding an immunomodulatory protein has been shown to improve the antigen (Ag)-specific immune response. Thus, the incorporation of enhancing elements, such as these, may be particularly important in the influenza model in which high titered antibody (Ab) responses are critical for protection. In this regard, we compared the ability of plasmid-encoded high-mobility group box 1 protein (HMGB1), a novel cytokine in which we have previously mutated in order to increase DNA vaccine immunogenicity, with boost Ag-specific immune responses during DNA vaccination with influenza A/PR/8/34 nucleoprotein or the hemagglutinin of A novel H1N1/09. We show that the HMGB1 adjuvant is capable of enhancing adaptive effector and memory immune responses. Although Ag-specific antibodies were detected in all vaccinated animals, a greater neutralizing Ab response was associated with the HMGB1 adjuvant. Furthermore, these responses improved CD8 T+-cell effector and memory responses and provided protection against a lethal mucosal influenza A/PR/8/34 challenge. Thus, co-immunization with HMGB1 has strong in vivo adjuvant activity during the development of immunity against plasmid-encoded Ag.

From Plasmids to Protection: A Review of DNA Vaccines Against Infectious Diseases

The field of DNA vaccine development began over 16 years ago with the observation that plasmid DNA could be injected into and expressed in vivo and drive adaptive immune responses. Since then, there has been great interest in developing this technology to create a new generation of vaccines with the ability to elicit both humoral and cellular immune responses from an inherently innocuous injection. However, DNA vaccines have yet to proceed past phase I/II clinical trials in humans--primarily due to a desire to induce more potent immune responses. This review will examine how DNA vaccines function to induce an immune response and how this information might be useful in future vaccine design.

DR5 activation of caspase-8 induces DC maturation and immune enhancement in vivo

Non-homeostatic tissue apoptosis in vivo has been shown to induce inflammatory responses and facilitate the cross-presentation of proteins within apoptotic bodies. We hypothesize that in the presence of foreign antigens, the apoptotic-inflammatory process improves immune priming; further, molecules that trigger apoptosis may be adapted for use as immune adjuvants. One very attractive molecule in this context is the tumor necrosis factor receptor (TNFR) family molecule DR5/TRAIL-receptor 2. We show a significant improvement in CD8(+) T-cell mediated vaccine immunity with the use of death receptor-5 (DR5) as an immune adjuvant, a property that is correlated with the activation of caspases-8 (casp8) and dependent on its ability to induce apoptosis in vivo.

Protection against simian/human immunodeficiency virus (SHIV) 89.6P in macaques after coimmunization with SHIV antigen and IL-15 plasmid

The cell-mediated immune profile induced by a recombinant DNA vaccine was assessed in the simian/HIV (SHIV) and macaque model. The vaccine strategy included coimmunization of a DNA-based vaccine alone or in combination with an optimized plasmid encoding macaque IL-15 (pmacIL-15). We observed strong induction of vaccine-specific IFN-gamma-producing CD8(+) and CD4(+) effector T cells in the vaccination groups. Animals were subsequently challenged with 89.6p. The vaccine groups were protected from ongoing infection, and the IL-15 covaccinated group showed a more rapidly controlled infection than the group treated with DNA vaccine alone. Lymphocytes isolated from the group covaccinated with pmacIL-15 had higher cellular proliferative responses than lymphocytes isolated from the macaques that received SHIV DNA alone. Vaccine antigen activation of lymphocytes was also studied for a series of immunological molecules. Although mRNA for IFN-gamma was up-regulated after antigen stimulation, the inflammatory molecules IL-8 and MMP-9 were down-regulated. These observed immune profiles are potentially reflective of the ability of the different groups to control SHIV replication. This study demonstrates that an optimized IL-15 immune adjuvant delivered with a DNA vaccine can impact the cellular immune profile in nonhuman primates and lead to enhanced suppression of viral replication.

Macaques co-immunized with SIVgag/pol-HIVenv and IL-12 plasmid have increased cellular responses

BACKGROUND

The cell mediated immune profiles following immunization with a recombinant DNA vaccine was assessed in the simian-human immunodeficiency virus (SHIV) and Macaque model. Earlier work demonstrated increased numbers of antigen specific CD8 and CD4 effector cells able to secrete IFN-gamma.

METHOD

The vaccine strategy included co-immunization of a DNA based vaccine alone or in combination with a macaque IL-12 expressing plasmid (pmacIL12). Antigen activated lymphocytes were studied for activation of a set of immunological molecules.

RESULTS

The current study demonstrates lymphocytes isolated and activated from the group that was immunized with DNA and pmacIL12 had a higher level of IFN-gamma producing cells. We also observed a different immunological profile when comparing the cells isolated from macaques immunized with DNA as compared to those animals that also received pmacIL12.

CONCLUSION

The observed immune profiles are reflective of the co-delivery of pmacIL12 and demonstrates that IL-12 can increase the magnitude and polyfunctionality of the cellular immune response.

Co-immunisation with DNA encoding RANK/RANKL or 4-1BBL costimulatory molecules does not enhance effector or memory CTL responses afforded by immunisation with a tumour antigen-encoding DNA vaccine

T cell mediated immune responses are induced following interaction of MHC-presented epitope on professional antigen presenting cells such as dendritic cells (DCs) with cognate T cell receptor. Up-regulation of receptor-ligand pairs of costimulatory molecules linking DC to T cell enhances the resulting T cell responses. This 'second signalling' occurs through the B7 molecules CD80/86 expressed by DCs, and importantly through members of the TNF ligand/TNF receptor superfamilies. We have previously shown that co-expression of RANK/RANKL or 41BB-L in addition to tumour antigen in dendritic cells augmented cognate effector and memory tumour antigen-directed cytotoxic T cell responses when the DCs were used to immunise mice. Here, we examined whether co-immunisation with naked plasmid DNAs encoding antigen and these costimulatory molecule(s), would enhance antigen specific T cell responses. We demonstrate that co-immunisation with DNAs encoding tumour antigen and costimulatory molecules failed to enhance antigen-directed CTL responses, or tumour protection, afforded by immunisation with DNA encoding tumour antigen alone.

An ESAT-6:CFP10 DNA vaccine administered in conjunction with Mycobacterium bovis BCG confers protection to cattle challenged with virulent M. bovis

The potency of genetic immunization observed in the mouse has demonstrated the utility of DNA vaccines to induce cell-mediated and humoral immune responses. However, it has been relatively difficult to generate comparable responses in non-rodent species. The use of molecular adjuvants may increase the magnitude of these suboptimal responses. In this study, we demonstrate that the co-administration of plasmid-encoded GM-CSF and CD80/CD86 with a novel ESAT-6:CFP10 DNA vaccine against bovine tuberculosis enhances antigen-specific cell-mediated immune responses. ESAT-6:CFP10+GM-CSF+CD80/CD86 DNA vaccinated animals exhibited significant (p<0.01) antigen-specific proliferative responses compared to other DNA vaccinates. Increased expression (p< or =0.05) of CD25 on PBMC from ESAT-6:CFP10+GM-CSF+CD80/CD86 DNA vaccinates was associated with increased proliferation, as compared to control DNA vaccinates. Significant (p<0.05) numbers of ESAT-6:CFP10-specific IFN-gamma producing cells were evident from all ESAT-6:CFP10 DNA vaccinated animals compared to control DNA vaccinates. However, the greatest increase in IFN-gamma producing cells was from animals vaccinated with ESAT-6:CFP10+GM-CSF+CD80/CD86 DNA. In a low-dose aerosol challenge trial, calves vaccinated as neonates with Mycobacterium bovis BCG and ESAT-6:CFP10+GM-CSF+CD80/CD86 DNA exhibited decreased lesion severity in the lung and lung-associated lymph nodes following viruluent M. bovis challenge compared to other vaccinated animals or non-vaccinated controls. These data suggest that a combined vaccine regimen of M. bovis BCG and a candidate ESAT-6:CFP10 DNA vaccine may offer greater protection against tuberculosis in cattle than vaccination with BCG alone.

Cytokine-adjuvanted HIV-DNA vaccination strategies

This review highlights some of the most common cytokines currently being tested as adjuvants in HIV-1-DNA vaccine regimens. We discuss their use in both the prophylactic and therapeutic setting. Finally, we describe a novel dendritic cell-targeted vaccine candidate for HIV-1 treatment and prevention called DermaVir and explore the combination of the DermaVir technology with the cytokine adjuvants interleukin-7 and interleukin-15.

DNA vaccines against cancer

Significant progress made in the field of tumor immunology by the characterization of a large number of tumor antigens, and the better understanding of the mechanisms preventing immune responses to malignancies has led to the extensive study of cancer immunization approaches such as DNA vaccines encoding tumor antigens. This article reviews major aspects of DNA immunization in cancer. It gives a brief history and then discusses the proposed mechanism of action, preclinical and clinical studies, and methods of enhancing the immune responses induced by DNA vaccines.

Vaccination with mRNAs encoding tumor-associated antigens and granulocyte-macrophage colony-stimulating factor efficiently primes CTL responses, but is insufficient to overcome tolerance to a model tumor/self antigen

Immunization of mice with dendritic cells transfected ex vivo with tumor-associated antigen (TAA)-encoding mRNA primes cytotoxic T lymphocytes (CTL) that mediate tumor rejection. Here we investigated whether direct injection of TAA mRNA, encapsulated in cationic liposomes, could function similarly as cancer immunotherapy. Intradermal and intravenous injection of ovalbumin (OVA) mRNA generated specific CTL activity and inhibited the growth of OVA-expressing tumors. Vaccination studies with DNA have demonstrated that co-administration of antigen (Ag)- and cytokine-encoding plasmids potentiate the T cell response; in analogous fashion, the inclusion of granulocyte-macrophage colony-stimulating factor (GM-CSF) mRNA enhanced OVA-specific cytotoxicity. The ability of this GM-CSF-augmented mRNA vaccine to treat an established spontaneous tumor was evaluated in the Transgenic Adenocarcinoma of Mouse Prostate (TRAMP) mouse, using the SV40 large T Ag (TAg) as a model tumor/self Ag. Repeated vaccination elicited vigorous TAg-specific CTL activity in nontransgenic mice, but tumor-bearing TRAMP mice remained tolerant. Adoptive transfer of naïve splenocytes into TRAMP mice prior to the first vaccination restored TAg reactivity, and slowed tumor progression. The data from this study suggests that vaccination with TAA mRNA is a simple and effective means of priming antitumor CTL, and that immunogenicity of the vaccine can be augmented by co-delivery of GM-CSF mRNA. Nonetheless, limitations of such vaccines in overcoming tolerance to tumor/self Ag may mandate prior or simultaneous reconstitution of the autoreactive T cell repertoire for this form of immunization to be effective.

Rational design of gene-based vaccines

Vaccine development has traditionally been an empirical discipline. Classical vaccine strategies include the development of attenuated organisms, whole killed organisms, and protein subunits, followed by empirical optimization and iterative improvements. While these strategies have been remarkably successful for a wide variety of viruses and bacteria, these approaches have proven more limited for pathogens that require cellular immune responses for their control. In this review, current strategies to develop and optimize gene-based vaccines are described, with an emphasis on novel approaches to improve plasmid DNA vaccines and recombinant adenovirus vector-based vaccines.

Dissecting the components of the humoral immune response elicited by DNA vaccines

Although DNA vaccines appear to be efficient at inducing strong cellular immune responses, a number of questions remain regarding their ability to induce humoral immunity. The essential components for generating an antibody response include B and T cell recognition of antigen, subsequent activation, clonal expansion of each lymphocyte type and migration of T cells into B cell follicles to provide help, all leading to germinal centre formation and antibody production. We have employed a double adoptive transfer system based on ovalbumin (OVA)-specific CD4+ DO11.10 T cells and hen egg lysozyme (HEL)-specific MD4 B cells to assess all of these parameters in the context of DNA vaccination in vivo. We find that vaccination with DNA constructs expressing an OVA-HEL gene fusion (encoding contiguous T and B cell epitopes) can induce T cell activation, clonal expansion and migration into B cell follicles accompanied by B cell activation, blastogenesis, expansion and antibody production. These findings show that DNA vaccination can induce all of the components required for humoral immunity and also provide a system for in depth analysis of factors that influence the development of antibody responses. Such strategies may facilitate the rational design of vaccines capable of inducing effective humoral immunity.

Antitumor efficacy of DNA vaccination to the epigenetically acting tumor promoting transcription factor BORIS and CD80 molecular adjuvant

Cancer testis (CT) antigens are promising candidates for tumor vaccines due to their immunogenicity and tissue-restricted expression. Recently, we identified a novel cancer testis gene, BORIS, whose expression is restricted to male testis after puberty and is strictly absent in non-malignant female tissue. BORIS encodes a DNA-binding protein that shares 11 zing finger (ZF) with transcription factor CTCF and differs at the N- and C-termini. CTCF has been implicated in epigenetic regulation of imprinting, X chromosome inactivation, repression, and activation of cancer testis antigens. BORIS expression has been documented in cancers of diverse histological origin, including, but not limited to breast, prostate, ovary, gastric, liver, endometrial, glia, colon, and esophagus. Interestingly, BORIS induces demethylation and subsequent expression of many cancer-testis genes, including MAGE-A1 and NY-ESO-1, indicating that it is expressed very early in malignancy and might be an attractive candidate for immunotherapy. In this study we tested BORIS as a vaccine in a very aggressive, highly metastatic, and poorly immunogenic murine model of mammary carcinoma. Immunizations with a DNA encoding the mutant form of murine BORIS antigen (pmBORIS lacking DNA-binding function) significantly prolonged survival, and inhibited tumor growth in BALB/c mice inoculated with 4T1 cells. Priming with pmBORIS mixed with molecular adjuvant and boosting with adenoviral vector expressing mBORIS was generally more effective, suggesting that the vaccination protocol could be further optimized. This is the first report demonstrating the feasibility of vaccination with a cancer associated epigenetic regulator for the induction of tumor inhibition.

SIV DNA vaccine co-administered with IL-12 expression plasmid enhances CD8 SIV cellular immune responses in cynomolgus macaques

Current evidence suggests that a strong induced CD8 human immunodeficiency virus type 1 (HIV-1)-specific cell mediated immune response may be an important aspect of an HIV vaccine. The response rates and the magnitude of the CTL responses induced by current DNA vaccines in humans need to be improved and cellular immune responses to DNA vaccines can be enhanced in mice by co-delivering DNA plasmids expressing immune modulators. Two reported to work well in the mouse systems are interleukin (IL)-12 and CD40L. We sought to compare these molecular adjuvants in a primate model system. The cDNA for macaque IL-12 and CD40L were cloned into DNA vectors. Groups of cynomolgus macaques were immunized with 2 mg of plasmid expressing SIVgag alone or in combination with either IL-12 or CD40L. CD40L did not appear to enhance the cellular immune response to SIVgag antigen. However, more robust results were observed in animals co-injected with the IL-12 molecular adjuvant. The IL-12 expanded antigen-specific IFN-gamma positive effector cells as well as granzyme B production. The vaccine immune responses contained both a CD8 component as well a CD4 component. The adjuvanted DNA vaccines illustrate that IL-12 enhances a CD8 vaccine immune response, however, different cellular profiles.

Adjuvant Action of MurineIL-2/IgPlasmid After Intramuscular Immunization With Indian HIV-1 Subtype C Recombinantenv.gp120 Construct

The human immunodeficiency virus (HIV) epidemic is probably the greatest scourge to affect mankind in the 20th century. Containment of the acquired immunodeficiency syndrome (AIDS) epidemic will require an effective vaccine. Of various vaccine approaches, immunization with DNA plasmids containing HIV-1 structural genes is the most popular approach. However, an important limitation of DNA immunization is that these responses are relatively weak and are often only transient in their nature. The use of immunologic adjuvants together with DNA vaccines is a promising way to enhance and to optimize DNA-derived immunity. Cytokines have been widely used to enhance the immune responses of DNA vaccines. In the present investigation, we studied the in vivo immunomodulation of HIV-1 Indian subtype C plasmid construct (pJWSK3, encoding envgp120 gene) by plasmid-based murine IL-2/Ig construct. Subcloning of mIL-2/Ig gene from pVRCmIL-2/Ig construct into pJW4304 vector was done followed by its in vitro expression study on the COS-7 cell line. Co-immunization of the recombinant HIV-1 env-gp120 construct with the IL-2/Ig construct in the female Balb/c mice by the intramuscular route resulted in induction of significantly higher levels of both HIV-1-specific antibody response and cell mediated immune response than by DNA plasmid construct alone (p < 0.001 and p < 0.05, respectively). The induced HIV-1-specific murine IFN-gamma response was robust, broad based, and seen even at the end of 6 months after immunization. Taken together these results indicate that the strategy of using IL-2/Ig plasmid can be highly effective when used along with recombinant DNA constructs and serve as the potential tool for the development of more rationally designed vaccines against HIV-1.

The synthetic peptide Trp-Lys-Tyr-Met-Val-D-Met as a novel adjuvant for DNA vaccine

Trp-Lys-Tyr-Met-Val-D-Met (WKYMVm) is a synthetic peptide known to activate human neutrophils, monocytes and dendritic cells, resulting in the enhancement of superoxide generation, bactericidal activity, chemotactic migration and survival. In this study, we demonstrated that WKYMVm enhanced the surface expression of CD80, but not that of CD40, CD86 and MHC class II, on mouse bone marrow-derived dendritic cells which is one of the essential costimulatory signals for the induction of immune responses. Furthermore, when WKYMVm was codelivered with HIV, HBV and Influenza DNA vaccines, WKYMVm selectively enhanced the vaccine-induced CD8(+) T cell responses in a dose-dependent manner, in terms of IFN-gamma secretion and cytolytic activity. Our results indicate that a synthetic peptide, WKYMVm can function as a novel adjuvant for DNA vaccine.

Feline B7.1 and B7.2 proteins produced from swinepox virus vectors are natively processed and biologically active: potential for use as nonchemical adjuvants

Costimulatory ligands, B7.1 and B7.2, have been incorporated into viral and DNA vectors as potential nonchemical adjuvants to enhance CTL and humoral immune responses against viral pathogens. In addition, soluble B7 proteins, minus their transmembrane and cytoplasmic domains, have been shown to block the down regulation of T-cell activation through blockade of B7/CTLA-4 interactions in mouse tumor models. Recently, we developed swinepox virus (SPV) vectors for delivery of feline leukemia antigens for vaccine use in cats [Winslow, B.J., Cochran, M.D., Holzenburg, A., Sun, J., Junker, D.E., Collisson, E.W., 2003. Replication and expression of a swinepox virus vector delivering feline leukemia virus Gag and Env to cell lines of swine and feline origin. Virus Res. 98, 1-15]. To explore the use of feline B7.1 and B7.2 ligands as nonchemical adjuvants, SPV vectors containing full-length feline B7.1 and B7.2 ligands were constructed and analyzed. Full-length feline B7.1 and B7.2 produced from SPV vectors were natively processed and costimulated Jurkat cells to produce IL-2, in vitro. In addition, we explored the feasibility of utilizing SPV as a novel expression vector to produce soluble forms of feline B7.1 (sB7.1) and B7.2 (sB7.2) in tissue culture. The transmembrane and cytoplasmic regions of the B7.1 and B7.2 genes were replaced with a poly-histidine tag and purified via a two-step chromatography procedure. Receptor binding and costimulation activity was measured. Although feline sB7.1-his and sB7.2-his proteins bound to the human homolog receptors, CTLA-4 and CD28, both soluble ligands possessed greater affinity for CTLA-4, compared to CD28. However, both retained the ability to partially block CD28-mediated costimulation in vitro. Results from these studies establish the use of SPV as a mammalian expression vector and suggest that full-length-vectored and purified soluble feline B7 ligands may be valuable, nonchemical immune-modulators.

Augmentation of HIV-1 subtype C vaccine constructs induced immune response in mice by CpG motif 1826-ODN

The greatest biomedical challenge of this century is to develop a preventive vaccine against Human Immunodeficiency Virus (HIV-1). For an HIV vaccine to be effective, it appears logical to develop new strategies that enhance the level of the immune response as well as steer it towards the desirable cellular type. In view of this, there is a need for rational inclusion of biological adjuvants into the HIV-1 vaccination strategies that could potentiate the immune responses both qualitatively and quantitatively. The adjuvant may include the immunostimulatory oligonucleotides containing CpG motifs, whose immunomodulatory characters are well established and represent the basis for an effective vaccine adjuvant. In our study, we investigated the use of an immunostimulatory oligonucleotide (or CpG motif), 1826-ODN to augment the immune response elicited by plasmid DNA vaccine constructs containing Indian subtype C HIV-1 envelope gp120 and gag-protease genes in Balb/c mouse model system. A dose of 2-microg CpG motifs/mouse was found to be optimum when co-administered with the DNA vaccine constructs with the peak level of humoral and cell mediated immune responses at 6 weeks post immunization. Murine IFN-gamma ELISpot assay demonstrated that the use of 1826-ODN led to a broad based and long term recognition of the subtype C envelope and gag peptides. The use of CpG motifs has been effective in augmenting the immune responses generated by the DNA constructs. Taken together, these results are an important advancement towards the design of future preclinical and clinical trials of these vaccine constructs.

Mechanisms of action of DNA vaccines

The field of DNA vaccines can trace its inception to two papers which demonstrated that administration of plasmid DNA vectors expressing proteins resulted in expression in situ. Thereafter, the possible application of this technique to vaccine development was demonstrated through the induction of antibody responses in mice against a foreign protein, cellular immune responses against a viral antigen and protective efficacy in an infectious disease challenge model. Subsequently, the general utility of DNA vaccines in animal models of infectious and non-infectious disease has been established (for review, see [5]). Initially, most efforts were directed toward demonstration of effectiveness in particular disease models. Recently, however, more attention has been paid to gaining a better understanding of some of the underlying mechanisms of DNA vaccines. This review will focus on this new information and discuss it in the context of how it could benefit the development of more effective DNA vaccines.

The role of cytokine DNAs as vaccine adjuvants for optimizing cellular immune responses

Cytokines represent a diverse group of immunologic effector and regulatory proteins that are critical components of the host response to invading pathogens. They have also been utilized as adjuvants to enhance immune responses to vaccines. In particular, plasmid cytokines have been studied extensively as candidate adjuvants for DNA vaccines in preclinical models and are now entering early-phase clinical trials. Here, we review recent advances in our understanding of cytokine biology, T-lymphocyte differentiation, and potential applications of plasmid cytokines in the rational design of improved vaccines.

Transcriptional regulation of dectin-2 promoter in transgenic mouse

Despite a preeminent role of epidermal Langerhans cells (LC) in inducing primary immunity, application of gene-based modification to LC function is limited by lack of well-defined transcription regulatory units that can direct LC-specific gene expression. Previously we reported that the promoter activity of a 5'-flanking region of the dectin-2 gene (Dec2FR) is highly targeted to epidermal LC of transgenic mice bearing a Dec2FR-driven Luc gene. Using the mice, in which transcription activity of Dec2FR is measured by Luc assays, presently we characterized regulation of Dec2FR activity in leukocyte subpopulations under resting and activation status. Luc activity was highly variable in LC isolated from different skin areas and detected in other DC subset (dermal DC) but the levels were much lower than in resting LC. Activation of leukocytes markedly up-regulated Luc activity in all four subpopulations (CD11c+ splenic DC, Mac-1high peritoneal macrophages, splenic B220+ B cells, and CD3+ T cells). However, these levels remained lower than those in the resting and activated LC. These findings indicate that dectin-2 promoter activity remains targeted to epidermal LC even after activation of leukocytes, suggesting a high potential of Dec2FR to engineer LC-targeted gene expression to heighten efficacy of genetic vaccination and to manipulate phenotypes of preexisting immunity (Th1 vs. Th2).

Novel approaches for the induction of T helper 1 (Th1)- or Th2-type mucosal and parenteral immune responses

Mucosal surfaces are constantly challenged by micro-organisms and are protected by an integrated component of the immune system called mucosa-associated lymphoreticular tissue (MALT). The immune responses elicited at the mucosal level are regulated by T-helper (Th) cells and involve secretory IgA (S-IgA) antibodies (Abs) and cytotoxic T-lymphocytes (CTLs). Mucosal immunisation has the advantage over parenteral immunisation, of inducing S-IgA Abs and of conferring protection at both the mucosal and parenteral levels; however, administration of soluble antigens through a mucosal route very seldom results in significant mucosal and systemic immune responses. Therefore, appropriate mucosal adjuvants, recombinant bacterial and viral vectors and delivery systems have been developed to increase the immunogenicity of vaccine antigens and to preferentially induce antigen-specific T-helper (Th)1- or Th2-type responses, which in turn result in polarised effector immune responses. Understanding the mechanisms underlying Th1- and Th2-type developmental pathways and the ability of novel mucosal adjuvants and delivery systems to target the desired Th1- or Th2-type immune response would help to design effective mucosal vaccines, inducing predominant cell-mediated or humoral responses.

Rabies DNA vaccines for protection and therapeutic treatment

Rabies is a successful zoonotic disease that has persisted over time, achieving worldwide distribution in a variety of species. Annually, in developing countries with limited access to high-quality antirabies biologics, approximately 50,000 individuals and millions of animals die of rabies. Many of these countries continue to use vaccines produced in sheep, goat or suckling mouse brain, with ultraviolet light or phenol inactivation of the virus. Although there are several efficacious rabies vaccines derived from cultured cells, such as the human diploid cell vaccine, they are costly to produce and prohibitively expensive for developing countries. DNA vaccines offer a new and powerful approach for the generation of needed vaccines. They are stable, inexpensive to produce, easy to construct and induce a full spectrum of long-lasting humoral and cellular immune responses. This review concerns the present state of rabies DNA vaccines, and addresses the technology that may enhance their therapeutic efficacy.

APC-targeted immunization for the treatment of HIV-1

Therapeutic immunization may be thought of as an adjunct to highly active antiretroviral therapy to prime the immune system and possibly correct for immunological defects. Most therapeutic vaccine strategies currently under investigation aim to increase HIV-specific cellular responses. This may be most successfully accomplished by utilizing professional antigen-presenting cells. Autologous dendritic cells may be isolated, cultured, loaded with antigen and re-injected into the subject (ex vivo) or antigen may be directly delivered in situ to Langerhans cells or dermal dendritic cells, which are located respectively at the epidermal and dermal layer of the skin. Once Langerhans cells or dermal dendritic cells have incorporated the antigen, they are expected to mature and migrate to the lymph node to present antigen and stimulate naive T-cells. Exciting results have been obtained in nonhuman primates with both ex vivo and topical antigen-presenting cell-based therapeutic immunization.

CD80 and CD86, but not CD154, augment DNA vaccine-induced protection in experimental bovine tuberculosis

DNA vaccination is known to elicit robust cellular and humoral responses to encoded antigen. The co-administration of costimulatory molecules CD80 (B7-1), CD86 (B7-2) and CD154 (CD40L) has been shown to enhance immune responses in several murine models. The role of specific costimulatory molecules in non-rodent species remains incompletely characterized. In these studies, we demonstrate that the co-administration of CD80 and CD86, but not CD154, to an existing candidate subunit DNA vaccine (ESAT-6) against bovine tuberculosis, enhances protection after aerosol challenge with virulent Mycobacterium bovis. Additionally, we have shown that vaccination with M. bovis BCG is protective against tuberculosis following aerosol challenge in cattle. Two independent trials were conducted in cattle to determine the adjuvant effect of encoded antigen + CD80/CD86 and directly compare the adjuvant activities of CD80/CD86 to those of CD154. Co-administration of either CD80/CD86 or CD154 enhanced ESAT-6-specific IFN-gamma responses as compared to animals vaccinated with ESAT-6 DNA alone. However, following aerosol challenge, only animals vaccinated with CD80/CD86 possessed decreased pathology of the lungs and associated lymph nodes, as measured by gross examination, radiographic lesion morphometry and bacterial recovery. Collectively, these results demonstrate that the co-administration of costimulatory molecules with a protective antigen target enhances bovine immune responses to DNA vaccination, and that CD80/CD86 is superior to CD154 in augmenting DNA vaccine-induced protection in experimental bovine tuberculosis.

IL-10 down-regulates costimulatory molecules on Mycobacterium tuberculosis-pulsed macrophages and impairs the lytic activity of CD4 and CD8 CTL in tuberculosis patients

Activation of T cells requires both TCR-specific ligation and costimulation through accessory molecules during T cell priming. IFNgamma is a key cytokine responsible for macrophage activation during Mycobacterium tuberculosis (Mtb) infection while IL-10 is associated with suppression of cell mediated immunity in intracellular infection. In this paper we evaluated the role of IFNgamma and IL-10 on the function of cytotoxic T cells (CTL) and on the modulation of costimulatory molecules in healthy controls and patients with active tuberculosis (TB). gamma-irradiated-Mtb (i-Mtb) induced IL-10 production from CD14(+) cells from TB patients. Moreover, CD3(+) T cells of patients with advanced disease also produced IL-10 after i-Mtb stimulation. In healthy donors, IL-10 decreased the lytic activity of CD4(+) and CD8(+) T cells whereas it increased gammadelta-mediated cytotoxicity. Furthermore, we found that the presence of IL-10 induced a loss of the alternative processing pathways of antigen presentation along with a down-regulation of the expression of costimulatory molecule expression on monocytes and macrophages from healthy individuals. Conversely, neutralization of endogenous IL-10 or addition of IFNgamma to either effector or target cells from TB patients induced a strong lytic activity mediated by CD8(+) CTL together with an up-regulation of CD54 and CD86 expression on target cells. Moreover, we observed that macrophages from TB patients could use alternative pathways for i-Mtb presentation. Taken together, our results demonstrate that the presence of IL-10 during Mtb infection might contribute to mycobacteria persistence inside host macrophages through a mechanism that involved inhibition of MHC-restricted cytotoxicity against infected macrophages.

Immunotherapeutic potential of B7-DC (PD-L2) cross-linking antibody in conferring antitumor immunity

A naturally occurring human antibody potentiates dendritic cell function on cross-linking B7-DC (PD-L2), supporting robust T-cell responses in vitro. Moreover, treatment of dendritic cells with B7-DC cross-linking antibody resulted in secretion of interleukin-12, suggesting a TH1 polarization of this response. Here we show an in vivo immunotherapeutic effect of this B7-DC cross-linking antibody using a poorly immunogenic B16 melanoma tumor model. Treatment of mice systemically with antibody at the time of tumor cell engraftment prevented tumor growth in a CD4 and CD8 T-cell-dependent manner. The protective effect of B7-DC cross-linking antibody treatment was independent of endogenous antibody responses. Tumor-specific CTL precursors could be isolated from lymph nodes draining the tumor site in animals treated with B7-DC cross-linking antibody, but not from those treated with isotype control antibodies. The elicited antitumor responses in vivo were specific and long-lasting. More strikingly, treatment of mice with B7-DC cross-linking antibody after the tumors were established in the lungs resulted in protection in a CD8-, perforin-, and granzyme B-dependent fashion. Depletion of natural killer cells did not block the effects of treatment with B7-DC cross-linking antibody. Together, these findings demonstrate that cross-linking B7-DC with the human IgM antibody sHIgM12 can induce a protective immune response against a weakly antigenic experimental tumor and therefore has potential as a novel immunotherapeutic approach for treating cancer.

Enhancement of antibody responses in DNA vaccination using a vector encoding a universal T-helper cell epitope

DNA vaccination appears as a very promising approach to raise protective antibodies against a variety of proteins from pathogens or tumor cells, but is often hindered by the low immunogenicity of the genetic vectors used for the immunizations. To enhance the humoral response through improvement of the antigenic presentation of newly synthesized proteins upon vaccination, we engineered a plasmid coding for a low immunogenic protein (an scFv, i.e. the single-chain Fragment variable of a well-characterized antibody) fused to a small-size universal T-helper cell epitope derived from tetanus toxin, whose efficiency in classical protein-based immunization protocols has already been demonstrated. We found that immunization of C57Bl/6 mice using this vector greatly enhanced the production not only of specific antibodies recognizing essentially conformational epitopes on the undenatured scFv protein but also of antibodies against linear epitopes on the denatured protein. Since this T-epitope is known to be accommodated by several haplotypes of H-2 molecules in mice, as well as by various class II MHC molecules in humans, the results reported here allow us to conclude that this method could be of general interest for future applications of genetic immunization, including DNA-based vaccinations in humans.

Enhancement of human immunodeficiency virus type 1-DNA vaccine potency through incorporation of T-helper 1 molecular adjuvants

It is clear that the development of a safe and effective vaccine for human immunodeficiency virus type 1 (HIV-1) remains a crucial goal for controlling the acquired immunodeficiency syndrome epidemic. At present, it is not clear what arm of the immune response correlates with protection from HIV-1 infection or disease. Therefore, a strong cellular and humoral immune response will likely be needed to control this infection. Among different vaccine alternatives, DNA vaccines appeared more than a decade ago, demonstrating important qualities of inducing both humoral and cellular immune responses in animal models. However, after several years and various clinical studies in humans, supporting the safety of the HIV-DNA vaccine strategies, it has become clear that their potency should be improved. One way to modulate and enhance the immune responses induced by a DNA vaccine is by including genetic adjuvants such as cytokines, chemokines, or T-cell costimulatory molecules as part of the vaccine itself. Particularly, vaccine immunogenicity can be modulated by factors that attract professional antigen-presenting cells, provide additional costimulation, or enhance the uptake of plasmid DNA. This review focuses on developments in the coadministration of molecular adjuvants for the enhancement of HIV-1 DNA-vaccine potency.