Direct transfection and activation of human cutaneous dendritic cells

DNA Vaccines: History, Molecular Mechanisms and Future Perspectives

The history of DNA vaccine began as early as the 1960s with the discovery that naked DNA can transfect mammalian cells in vivo. In 1992, the evidence that such transfection could lead to the generation of antigen-specific antibody responses was obtained and supported the development of this technology as a novel vaccine platform. The technology then attracted immense interest and high hopes in vaccinology, as evidence of high immunogenicity and protection against virulent challenges accumulated from several animal models for several diseases. In particular, the capacity to induce T-cell responses was unprecedented in non-live vaccines. However, the technology suffered its major knock when the success in animals failed to translate to humans, where DNA vaccine candidates were shown to be safe but remained poorly immunogenic, or not associated with clinical benefit. Thanks to a thorough exploration of the molecular mechanisms of action of these vaccines, an impressive range of approaches have been and are currently being explored to overcome this major challenge. Despite limited success so far in humans as compared with later genetic vaccine technologies such as viral vectors and mRNA, DNA vaccines are not yet optimised for human use and may still realise their potential.

Microneedle-Mediated Vaccination: Innovation and Translation

Vaccine administration by subcutaneous or intramuscular injection is the most commonly prescribed route for inoculation, however, it is often associated with some deficiencies such as low compliance, high professionalism, and risk of infection. Therefore, the application of microneedles for vaccine delivery has gained widespread interests in the past few years due to its high compliance, minimal invasiveness, and convenience. This review focuses on recent advances in the development and application of microneedles for vaccination based on different delivery strategies, and introduces the current status of microneedle-mediated vaccination in clinical translation. The prospects for its application including opportunities and challenges are further discussed.

Nucleic Acid-Based Approaches for Tumor Therapy

Within the last decade, the introduction of checkpoint inhibitors proposed to boost the patients' anti-tumor immune response has proven the efficacy of immunotherapeutic approaches for tumor therapy. Furthermore, especially in the context of the development of biocompatible, cell type targeting nano-carriers, nucleic acid-based drugs aimed to initiate and to enhance anti-tumor responses have come of age. This review intends to provide a comprehensive overview of the current state of the therapeutic use of nucleic acids for cancer treatment on various levels, comprising (i) mRNA and DNA-based vaccines to be expressed by antigen presenting cells evoking sustained anti-tumor T cell responses, (ii) molecular adjuvants, (iii) strategies to inhibit/reprogram tumor-induced regulatory immune cells e.g., by RNA interference (RNAi), (iv) genetically tailored T cells and natural killer cells to directly recognize tumor antigens, and (v) killing of tumor cells, and reprograming of constituents of the tumor microenvironment by gene transfer and RNAi. Aside from further improvements of individual nucleic acid-based drugs, the major perspective for successful cancer therapy will be combination treatments employing conventional regimens as well as immunotherapeutics like checkpoint inhibitors and nucleic acid-based drugs, each acting on several levels to adequately counter-act tumor immune evasion.

Inhibition of antigen-specific immune responses by co-application of an indoleamine 2,3-dioxygenase (IDO)-encoding vector requires antigen transgene expression focused on dendritic cells

We have previously shown that particle-mediated epidermal delivery (PMED) of plasmids encoding β-galactosidase (βGal) under control of the fascin-1 promoter (pFascin-βGal) yielded selective production of the protein in skin dendritic cells (DCs), and suppressed Th2 responses in a mouse model of type I allergy by inducing Th1/Tc1 cells. However, intranasal challenge of mice immunized with pFascin-βGal induced airway hyperreactivity (AHR) and neutrophilic inflammation in the lung. The tryptophan-catabolizing enzyme indoleamine 2,3-dioxygenase (IDO) has been implicated in immune suppression and tolerance induction. Here we investigated the consequences of co-application of an IDO-encoding vector on the modulatory effect of DNA vaccination by PMED using pFascin-βGal in models of eosinophilic allergic and non-eosinophilic intrinsic airway inflammation. IDO-encoding plasmids and pFascin-βGal or pCMV-βGal were co-applied to abdominal skin of BALB/c mice without, before or after sensitization with βGal protein. Immune responses in the lung were analysed after intranasal provocation and airway reactivity was determined by whole body plethysmography. Co-application of pCMV-IDO with pFascin-βGal, but not pCMV-βGal inhibited the Th1/Tc1 immune response after PMED. Moreover, AHR in those mice was attenuated following intranasal challenge. Therapeutic vaccination of βGal-sensitized mice with pFascin-βGal plus pCMV-IDO slightly suppressed airway inflammation and AHR after provocation with βGal protein, while prophylactic vaccination was not effective. Altogether, our data suggest that only the combination of DC-restricted antigen and ubiquitous IDO expression attenuated asthma responses in mice, most probably by forming a tryptophan-depleted and kynurenine-enriched micromilieu known to affect neutrophils and T cells.

DNA Vaccines-How Far From Clinical Use?

Two decades ago successful transfection of antigen presenting cells (APC) in vivo was demonstrated which resulted in the induction of primary adaptive immune responses. Due to the good biocompatibility of plasmid DNA, their cost-efficient production and long shelf life, many researchers aimed to develop DNA vaccine-based immunotherapeutic strategies for treatment of infections and cancer, but also autoimmune diseases and allergies. This review aims to summarize our current knowledge on the course of action of DNA vaccines, and which factors are responsible for the poor immunogenicity in human so far. Important optimization steps that improve DNA transfection efficiency comprise the introduction of DNA-complexing nano-carriers aimed to prevent extracellular DNA degradation, enabling APC targeting, and enhanced endo/lysosomal escape of DNA. Attachment of virus-derived nuclear localization sequences facilitates nuclear entry of DNA. Improvements in DNA vaccine design include the use of APC-specific promotors for transcriptional targeting, the arrangement of multiple antigen sequences, the co-delivery of molecular adjuvants to prevent tolerance induction, and strategies to circumvent potential inhibitory effects of the vector backbone. Successful clinical use of DNA vaccines may require combined employment of all of these parameters, and combination treatment with additional drugs.

Functional therapies for cutaneous wound repair in epidermolysis bullosa

Chronic wounding as a result of recurrent skin blistering in the painful genetic skin disease epidermolysis bullosa, may lead to life-threatening infections, increased risk of tumor formation, and other serious medical complications. Therefore, epidermolysis bullosa patients have an urgent need for optimal wound care and tissue regeneration. Therapeutic strategies using gene-, protein-, and cell-therapies are being developed to improve clinical symptoms, and some of them have already been investigated in early clinical trials. The most favorable options of functional therapies include gene replacement, gene editing, RNA targeting, and harnessing natural gene therapy. This review describes the current progress of the different approaches targeting autologous skin cells, and will discuss the benefits and challenges of their application.

Biomaterials for polynucleotide delivery to anchorage-independent cells

Comparison of various chemical vectors used for polynucleotide delivery to mammalian anchorage-independent cells.

A Topical Mitochondria-Targeted Redox-Cycling Nitroxide Mitigates Oxidative Stress-Induced Skin Damage

Skin is the largest human organ, and it provides a first line of defense that includes physical, chemical, and immune mechanisms to combat environmental stress. Radiation is a prevalent environmental stressor. Radiation-induced skin damage ranges from photoaging and cutaneous carcinogenesis caused by UV exposure, to treatment-limiting radiation dermatitis associated with radiotherapy, to cutaneous radiation syndrome, a frequently fatal consequence of exposures from nuclear accidents. The major mechanism of skin injury common to these exposures is radiation-induced oxidative stress. Efforts to prevent or mitigate radiation damage have included development of antioxidants capable of reducing reactive oxygen species. Mitochondria are particularly susceptible to oxidative stress, and mitochondrial-dependent apoptosis plays a major role in radiation-induced tissue damage. We reasoned that targeting a redox cycling nitroxide to mitochondria could prevent reactive oxygen species accumulation, limiting downstream oxidative damage and preserving mitochondrial function. Here we show that in both mouse and human skin, topical application of a mitochondrially targeted antioxidant prevents and mitigates radiation-induced skin damage characterized by clinical dermatitis, loss of barrier function, inflammation, and fibrosis. Further, damage mitigation is associated with reduced apoptosis, preservation of the skin's antioxidant capacity, and reduction of irreversible DNA and protein oxidation associated with oxidative stress.

Delivery methods to increase cellular uptake and immunogenicity of DNA vaccines

DNA vaccines are ideal candidates for global vaccination purposes because they are inexpensive and easy to manufacture on a large scale such that even people living in low-income countries can benefit from vaccination. However, the potential of DNA vaccines has not been realized owing mainly to the poor cellular uptake of DNA in vivo resulting in the poor immunogenicity of DNA vaccines. In this review, we discuss the benefits and shortcomings of several promising and innovative non-biological methods of DNA delivery that can be used to increase cellular delivery and efficacy of DNA vaccines.

A Gene Gun-mediated Nonviral RNA trans-splicing Strategy for Col7a1 Repair

RNA trans-splicing represents an auspicious option for the correction of genetic mutations at RNA level. Mutations within COL7A1 causing strong reduction or absence of type VII collagen are associated with the severe skin blistering disease dystrophic epidermolysis bullosa. The human COL7A1 mRNA constitutes a suitable target for this RNA therapy approach, as only a portion of the almost 9 kb transcript has to be delivered into the target cells. Here, we have proven the feasibility of 5' trans-splicing into the Col7a1 mRNA in vitro and in vivo. We designed a 5' RNA trans-splicing molecule, capable of replacing Col7a1 exons 1-15 and verified it in a fluorescence-based trans-splicing model system. Specific and efficient Col7a1 trans-splicing was confirmed in murine keratinocytes. To analyze trans-splicing in vivo, we used gene gun delivery of a minicircle expressing a FLAG-tagged 5' RNA trans-splicing molecule into the skin of wild-type mice. Histological and immunofluorescence analysis of bombarded skin sections revealed vector delivery and expression within dermis and epidermis. Furthermore, we have detected trans-spliced type VII collagen protein using FLAG-tag antibodies. In conclusion, we describe a novel in vivo nonviral RNA therapy approach to restore type VII collagen expression for causative treatment of dystrophic epidermolysis bullosa.

Dendritic cell-derived interleukin-15 is crucial for therapeutic cancer vaccine potency

IL-15 supports improved antitumor immunity. How to best incorporate IL-15 into vaccine formulations for superior cancer immunotherapy remains a challenge. DC-derived IL-15 (DCIL-15) notably has the capacity to activate DC, to substitute for CD4⁺ Th and to potentiate vaccine efficacy making IL-15-based therapies attractive treatment options. We observed in transplantable melanoma, glioma and metastatic breast carcinoma models that DCIL-15-based DNA vaccines in which DC specifically express IL-15 and simultaneously produce tumor Aghsp70 were able to mediate potent therapeutic efficacy that required both host Batf3⁺ DC and CD8⁺ T cells. In an inducible Braf^V600E/Pten-driven murine melanoma model, DCIL-15 (not rIL-15)-based DNA vaccines elicited durable therapeutic CD8⁺ T cell-dependent antitumor immunity. DCIL-15 was found to be superior to rIL-15 in "licensing" both mouse and human DC, and for activating CD8⁺ T cells. Such activation occurred even in the presence of Treg, without a need for CD4⁺ Th, but was IL-15/IL-15Rα-dependent. A single low-dose of DCIL-15 (not rIL-15)-based DC vaccines induced therapeutic antitumor immunity. CD14⁺ DC emigrating from human skin explants genetically-immunized by IL-15 and Aghsp70 were more effective than similar DC emigrating from the explants genetically-immunized by Aghsp70 in the presence of rIL-15 in expressing membrane-bound IL-15/IL-15Rα and activating CD8⁺ T cells. These results support future clinical use of DCIL-15 as a therapeutic agent in battling cancer.

Micro- and nanotechnologies for intracellular delivery

The majority of drugs and biomolecules need to be delivered into cells to be effective. However, the cell membranes, a biological barrier, strictly resist drugs or biomolecules entering cells, resulting in significantly reduced intracellular delivery efficiency. To overcome this barrier, a variety of intracellular delivery approaches including chemical and physical ways have been developed in recent years. In this review, the focus is on summarizing the nanomaterial routes involved in making use of a collection of receptors for the targeted delivery of drugs and biomolecules and the physical ways of applying micro- and nanotechnologies for high-throughput intracellular delivery.

Dissolvable microneedle arrays for intradermal delivery of biologics: fabrication and application

PURPOSE

Design and evaluate a new micro-machining based approach for fabricating dissolvable microneedle arrays (MNAs) with diverse geometries and from different materials for dry delivery to skin microenvironments. The aims are to describe the new fabrication method, to evaluate geometric and material capability as well as reproducibility of the method, and to demonstrate the effectiveness of fabricated MNAs in delivering bioactive molecules.

METHODS

Precise master molds were created using micromilling. Micromolding was used to create elastomer production molds from master molds. The dissolvable MNAs were then fabricated using the spin-casting method. Fabricated MNAs with different geometries were evaluated for reproducibility. MNAs from different materials were fabricated to show material capability. MNAs with embedded bioactive components were tested for functionality on human and mice skin.

RESULTS

MNAs with different geometries and from carboxymethyl cellulose, polyvinyl pyrrolidone and maltodextrin were created reproducibly using our method. MNAs successfully pierce the skin, precisely deliver their bioactive cargo to skin and induce specific immunity in mice.

CONCLUSIONS

We demonstrated that the new fabrication approach enables creating dissolvable MNAs with diverse geometries and from different materials reproducibly. We also demonstrated the application of MNAs for precise and specific delivery of biomolecules to skin microenvironments in vitro and in vivo.

Biolistic DNA delivery to mice with the low pressure gene gun

Biolistic DNA delivery is an approach to deliver plasmid to culture cells, plants, or animals. Plasmid DNA is usually transferred through bombardment of DNA-coated particles by highly pressurized gas in various kinds of delivery vehicles. The low pressure gene gun can deliver plasmid at lower pressure. Here, we describe methods of biolistic DNA delivery to mice using the low pressure gene gun.

Application of a partial-thickness human ex vivo skin culture model in cutaneous wound healing study

A number of in vivo and ex vivo skin models have been applied to human wound healing studies. A reliable skin model, which recapitulates the features of human wound repair, is essential for the clinical and mechanical investigation of human cutaneous wound healing. Full-skin ex vivo culture systems have been used in wound healing studies. However, important structures of the skin, such as the differentiation of keratinocytes and epidermis-dermis junction, are poorly characterized in this model. This study aims to develop an optimized partial-thickness human ex vivo skin culture (HESC) model to maintain human skin characteristics in vitro. During our culture, the basal layer, suprabasal layer, and stratum granulosum layer of epidermis were preserved until day 8. Analyses of hemidesmosome proteins, bullous pemphigoid antigen 1 (BP180) and 2 (BP230), showed that the integrity of the basement membrane of the epidermis was well preserved in the HESC model. In contrast, an organotypic culture with human keratinocytes and fibroblasts failed to show an integrated basement membrane. Maintenance of skin structure by histological analysis and proliferation of epidermal keratinocytes by Ki67 staining were observed in our model for 12 days. Complete re-epithelialization of the wounding area was observed at day 6 post wounding when a superficial incisional wound was created. The expression of Ki-67 and keratin 6, indicators of activated keratinocytes in epidermis, was significantly upregulated and new collagen synthesis was found in the dermis during the wound healing process. As control, we also used organotypic culture in studying the differentiation of the keratinocyte layers and incisional wound repair. It turned out that our model has advantage in these study fields. The results suggest that our HESC model retains important elements of in vivo skin and has significant advantages for the wound healing studies in vitro.

Progress and outlook of inorganic nanoparticles for delivery of nucleic acid sequences related to orthopedic pathologies: a review

The anticipated growth in the aging population will drastically increase medical needs of society; of which, one of the largest components will undoubtedly be from orthopedic-related pathologies. There are several proposed solutions being investigated to cost-effectively prepare for the future--pharmaceuticals, implant devices, cell and gene therapies, or some combination thereof. Gene therapy is one of the more promising possibilities because it seeks to correct the root of the problem, thereby minimizing treatment duration and cost. Currently, viral vectors have shown the highest efficacies, but immunological concerns remain. Nonviral methods show reduced immune responses but are regarded as less efficient. The nonviral paradigms consist of mechanical and chemical approaches. While organic-based materials have been used more frequently in particle-based methods, inorganic materials capable of delivery have distinct advantages, especially advantageous in orthopedic applications. The inorganic gene therapy field is highly interdisciplinary in nature, and requires assimilation of knowledge across the broad fields of cell biology, biochemistry, molecular genetics, materials science, and clinical medicine. This review provides an overview of the role each area plays in orthopedic gene therapy as well as possible future directions for the field.

Evaluation of biolistic gene transfer methods in vivo using non-invasive bioluminescent imaging techniques

Background

Gene therapy continues to hold great potential for treating many different types of disease and dysfunction. Safe and efficient techniques for gene transfer and expression in vivo are needed to enable gene therapeutic strategies to be effective in patients. Currently, the most commonly used methods employ replication-defective viral vectors for gene transfer, while physical gene transfer methods such as biolistic-mediated ("gene-gun") delivery to target tissues have not been as extensively explored. In the present study, we evaluated the efficacy of biolistic gene transfer techniques in vivo using non-invasive bioluminescent imaging (BLI) methods.

Results

Plasmid DNA carrying the firefly luciferase (LUC) reporter gene under the control of the human Cytomegalovirus (CMV) promoter/enhancer was transfected into mouse skin and liver using biolistic methods. The plasmids were coupled to gold microspheres (1 μm diameter) using different DNA Loading Ratios (DLRs), and "shot" into target tissues using a helium-driven gene gun. The optimal DLR was found to be in the range of 4-10. Bioluminescence was measured using an In Vivo Imaging System (IVIS-50) at various time-points following transfer. Biolistic gene transfer to mouse skin produced peak reporter gene expression one day after transfer. Expression remained detectable through four days, but declined to undetectable levels by six days following gene transfer. Maximum depth of tissue penetration following biolistic transfer to abdominal skin was 200-300 μm. Similarly, biolistic gene transfer to mouse liver in vivo also produced peak early expression followed by a decline over time. In contrast to skin, however, liver expression of the reporter gene was relatively stable 4-8 days post-biolistic gene transfer, and remained detectable for nearly two weeks.

Conclusions

The use of bioluminescence imaging techniques enabled efficient evaluation of reporter gene expression in vivo. Our results demonstrate that different tissues show different expression kinetics following gene transfer of the same reporter plasmid to different mouse tissues in vivo. We evaluated superficial (skin) and abdominal organ (liver) targets, and found that reporter gene expression peaked within the first two days post-transfer in each case, but declined most rapidly in the skin (3-4 days) compared to liver (10-14 days). This information is essential for designing effective gene therapy strategies in different target tissues.

Development of an ex vivo human skin model for intradermal vaccination: tissue viability and Langerhans cell behaviour

The presence of resident Langerhans cells (LCs) in the epidermis makes the skin an attractive target for DNA vaccination. However, reliable animal models for cutaneous vaccination studies are limited. We demonstrate an ex vivo human skin model for cutaneous DNA vaccination which can potentially bridge the gap between pre-clinical in vivo animal models and clinical studies. Cutaneous transgene expression was utilised to demonstrate epidermal tissue viability in culture. LC response to the culture environment was monitored by immunohistochemistry. Full-thickness and split-thickness skin remained genetically viable in culture for at least 72 h in both phosphate-buffered saline (PBS) and full organ culture medium (OCM). The epidermis of explants cultured in OCM remained morphologically intact throughout the culture duration. LCs in full-thickness skin exhibited a delayed response (reduction in cell number and increase in cell size) to the culture conditions compared with split-thickness skin, whose response was immediate. In conclusion, excised human skin can be cultured for a minimum of 72 h for analysis of gene expression and immune cell activation. However, the use of split-thickness skin for vaccine formulation studies may not be appropriate because of the nature of the activation. Full-thickness skin explants are a more suitable model to assess cutaneous vaccination ex vivo.

Physical methods of nucleic acid transfer: general concepts and applications

Physical methods of gene (and/or drug) transfer need to combine two effects to deliver the therapeutic material into cells. The physical methods must induce reversible alterations in the plasma membrane to allow the direct passage of the molecules of interest into the cell cytosol. They must also bring the nucleic acids in contact with the permeabilized plasma membrane or facilitate access to the inside of the cell. These two effects can be achieved in one or more steps, depending upon the methods employed. In this review, we describe and compare several physical methods: biolistics, jet injection, hydrodynamic injection, ultrasound, magnetic field and electric pulse mediated gene transfer. We describe the physical mechanisms underlying these approaches and discuss the advantages and limitations of each approach as well as its potential application in research or in preclinical and clinical trials. We also provide conclusions, comparisons, and projections for future developments. While some of these methods are already in use in man, some are still under development or are used only within clinical trials for gene transfer. The possibilities offered by these methods are, however, not restricted to the transfer of genes and the complementary uses of these technologies are also discussed. As these methods of gene transfer may bypass some of the side effects linked to viral or biochemical approaches, they may find their place in specific clinical applications in the future.

Human skin culture as an ex vivo model for assessing the fibrotic effects of insulin-like growth factor binding proteins

Systemic sclerosis (SSc) is a connective tissue disease of unknown etiology. A hallmark of SSc is fibrosis of the skin and internal organs. We recently demonstrated increased expression of IGFBP-3 and IGFBP-5 in primary cultures of fibroblasts from the skin of patients with SSc. In vitro, IGFBP-3 and IGFBP-5 induced a fibrotic phenotype and IGFBP-5 triggered dermal fibrosis in mice. To assess the ability of IGFBPs to trigger fibrosis, we used an ex vivo human skin organ culture model. Our findings demonstrate that IGFBP-3 and IGFBP-5, but not IGFBP-4, increase dermal and collagen bundle thickness in human skin explants, resulting in substantial dermal fibrosis and thickening. These fibrotic effects were sustained for at least two weeks. Our findings demonstrate that human skin ex vivo is an appropriate model to assess the effects of fibrosis-inducing factors such as IGFBPs, and for evaluating the efficacy of inhibitors/therapies to halt the progression of fibrosis and potentially reverse it.

Particle-based vaccines for transcutaneous vaccination

Immunization concepts evolve with increasing knowledge of how the immune system works and the development of new vaccination methods. Traditional vaccines are made of live, attenuated, killed or fragmented pathogens. New vaccine strategies can take advantage of particulate compounds--microspheres or nanoparticles--to target antigen-presenting cells better, which must subsequently reach the secondary lymphoid organs, which are the sites of the immune response. The use of the skin as a target organ for vaccine delivery stems from the fact that immature dendritic cells (DCs), which are professional antigen-presenting cells can be found at high density in the epidermis and dermis of human or animal skin. This has led to design various methods of dermal or transcutaneous vaccination. The quality and duration of the humoral and cellular responses to vaccination depend on the appropriate targeting of antigen-presenting cells, of the vaccine dose, route of administration and use of adjuvant. In this review, we will focus on the use of micro- and nano-particles to target the skin antigen-presenting cells and will discuss recent advances in the field of transcutaneous vaccination in animal models and humans.

Comparative evaluation of CD8+CTL responses following gene gun immunization targeting the skin with intracutaneous injection of antigen-transduced dendritic cells

The skin is an attractive target for antigen-specific vaccination. Particle bombardment of the epidermis with plasmid DNA using the gene gun results in antigen expression in keratinocytes of the epidermis leading to antigen presentation in the draining lymph nodes by migratory dendritic cells (DC). In order to better understand the role of the skin in stimulating antigen-specific CD8+cytotoxic T cells (CTL), we compared gene gun immunization with intracutaneous injections of antigen-transduced DC. A single intracutaneous injection of antigen-transduced DC was able to induce in vivo expansion of CD8+CTL specific for the model antigen chicken ovalbumin while four simultaneous shots with the gene gun were not effective. Antigen-transduced DC were much more efficient than particle bombardment of the epidermis in stimulating adoptively transferred TCR-transgenic CD8+CTL in the draining lymph nodes. Employing the novel technique of in vivo bioluminescence imaging, we demonstrated efficient gene transfer to the skin following gene gun bombardment and confirmed that a similar amount of antigen reached the lymph node when compared with injection of antigen-transduced DC. Our results suggest that direct transfection of the skin does not optimally reach and activate appropriate antigen-presenting DC. We believe that this reflects the immunological function of the epidermis which must balance immunity and tolerance to foreign antigens. Further investigations will have to address the role of Langerhans cells for the activation of cellular immunity in the skin.

The potential of topical DNA vaccines adjuvanted by cytokines

To improve the efficacy of DNA immunization epidermal Langerhans cells are attractive targets to deliver antigen-encoding plasmid DNA. Topical vaccination with naked plasmid DNA has been shown to induce immune responses, and their potency might be improved by chemical and physical methods aimed to enhance the efficiency of plasmid DNA delivery into the skin. Cytokines have also been evaluated as adjuvants for DNA vaccines because they influence the host immune response. This review focuses on the action of several cytokines tested as molecular adjuvants for DNA vaccines and the combination of them with the DermaVir Patch vaccine. DermaVir vaccine, topically administered under a patch, consists of a plasmid DNA that is chemically formulated into a nanoparticle to support vaccine delivery into epidermal Langerhans cells and to induce antigen-specific memory T cells.

Epidermal langerhans cells are dispensable for humoral and cell-mediated immunity elicited by gene gun immunization

Gene gun immunization, i.e., bombardment of skin with DNA-coated particles, is an efficient method for the administration of DNA vaccines. Direct transfection of APC or cross-presentation of exogenous Ag acquired from transfected nonimmune cells enables MHC-I-restricted activation of CD8(+) T cells. Additionally, MHC-II-restricted presentation of exogenous Ag activates CD4(+) Th cells. Being the principal APC in the epidermis, Langerhans cells (LC) seem ideal candidates to accomplish these functions. However, the dependence on LC of gene gun-induced immune reactions has not yet been demonstrated directly. This was primarily hampered by difficulties to discriminate the contributions of LC from those of other dermal dendritic cells. To address this problem, we have used Langerin-diphtheria toxin receptor knockin mice that allow for selective inducible ablation of LC. LC deficiency, even over the entire duration of experiments, did not affect any of the gene gun-induced immune functions examined, including proliferation of CD4(+) and CD8(+) T cells, IFN-gamma secretion by spleen cells, Ab production, CTL activity, and development of protective antitumor immunity. Together, our data show that gene gun immunization is capable of inducing humoral and cell-mediated immune reactions independently of LC.

In vivo signaling through the neurokinin 1 receptor favors transgene expression by Langerhans cells and promotes the generation of Th1- and Tc1-biased immune responses

The proinflammatory capacities of the skin and the presence of high numbers of resident dendritic cells (DCs) constitute an ideal microenvironment for successful immunizations. Regardless of the ability of DCs to respond to local inflammatory signals in an immunostimulatory fashion, the immune functions of skin-resident DCs remain controversial, and epidermal Langerhans cells (LCs) have been referred to recently as anti-inflammatory/protolerogenic APCs. Substance P (SP), released by skin nerve fibers, is a potent proinflammatory neuropeptide that favors development of skin-associated cellular immunity. SP exerts its proinflammatory functions by binding with high affinity to the neurokinin 1 receptor (NK1R). In this study, we tested whether signaling skin cells via the NK1R promotes humoral and cellular immunity during skin genetic immunizations. We used the gene gun to deliver transgenic (tg) Ag to the skin of C57BL/6 mice and the selective NK1R agonist [Sar(9)Met (O(2)) (11)]-SP as a potential proinflammatory Th1-biasing adjuvant. Our strategy expressed tg Ag exclusively in the epidermis and induced a preferential migration of activated LCs to skin-draining lymph nodes. Local administration of the NK1R agonist during skin genetic immunizations increased significantly the expression of tg Ag by a mechanism involving the translocation of NF-kappaB into the nuclei of cutaneous DCs homing to skin-draining lymph nodes. Importantly, our immunization approach resulted in Th1 and T cytotoxic (CTL)-1 bias of effector T cells that supported cellular and Ab-mediated immune responses. We demonstrate that signaling skin cells via the NK1R provides the adjuvant effect which favors the immunostimulatory functions of LCs.

Plasmid DNA and viral vector-based vaccines for the treatment of cancer

Plasmid DNA and viral vector-based cancer vaccines have many inherent features that make them promising cancer vaccine candidates. This review focuses on the use of plasmid DNA and viral vector vaccines to deliver tumour-specific antigens to induce a tumour-specific immune response. Examples of different antigen delivery systems that have been tested in recent clinical trials are summarised and advantages and disadvantages of a number of delivery systems and approaches are discussed. Finally, an outlook on how plasmid DNA and viral vectors might be developed further as cancer vaccines is provided.

Particle-Mediated Gene Delivery and Human Skin: Ultrastructural Observations on Stratum Corneum Barrier Structures

The particle-mediated delivery systems are becoming a clinically relevant tool in dermatology and immunology. We investigated the qualitative ultrastructural morphology of skin following pressure-driven delivery of gold particles to ex vivo human breast skin, at different pressures ranging from 350 to 1,000 psi. Pressures of 800 and 1,000 psi appear to be more effective, as indicated by distribution of particles in the viable epidermis and dermis. Particle bombardment of the skin with gold beads caused microwounds that spanned the stratum corneum (SC). The SC lipids did not reseal these wounds in the SC after 24 h in organ culture. The implications of particle-mediated delivery to permeability barrier functions of the SC are discussed.

DNA vaccines for HIV: challenges and opportunities

In December 2005, the UNAIDS and WHO reported that the global epidemic known as acquired immunodeficiency syndrome (AIDS) has claimed the lives of more than 25 million adults and children over the past 26 years. These figures included an estimated 3.1 million AIDS-related deaths in 2005. Despite enormous efforts to control the spread of human immunodeficiency virus (HIV) new infection rates are on the rise. An estimated 40.3 million people are now living with HIV, including 4.9 million new infections this past year. Nearly half of new HIV infections are in young people between the ages of 15 and 24. While drug therapies have helped sustain the lives of infected individuals in wealthy regions, they are relatively unavailable to the poorest global regions. This includes sub-Saharan Africa which has approximately 25.8 million infected individuals, more than triple the number of infections of any other region in the world. It is widely believed that the greatest hope for controlling this devastating pandemic is a vaccine. In this review, we will discuss the current state of DNA-based vaccines and how they compare to other vaccination methods currently under investigation. We will also discuss innovative ideas for enhancing DNA vaccine efficacy and the progress being made toward developing an effective vaccine.

Multiphoton high-resolution 3D imaging of Langerhans cells and keratinocytes in the mouse skin model adopted for epidermal powdered immunization

Langerhans cells (LCs) can be targeted with DNA-coated gold micro-projectiles ("Gene Gun") to induce potent cellular and humoral immune responses. It is likely that the relative volumetric distribution of LCs and keratinocytes within the epidermis impacts on the efficacy of Gene Gun immunization protocols. This study quantified the three-dimensional (3D) distribution of LCs and keratinocytes in the mouse skin model with a near-infrared multiphoton laser-scanning microscope (NIR-MPLSM). Stratum corneum (SC) and viable epidermal thickness measured with MPLSM was found in close agreement with conventional histology. LCs were located in the vertical plane at a mean depth of 14.9 microm, less than 3 mum above the dermo-epidermal boundary and with a normal histogram distribution. This likely corresponds to the fact that LCs reside in the suprabasal layer (stratum germinativum). The nuclear volume of keratinocytes was found to be approximately 1.4 times larger than that of resident LCs (88.6 microm3). Importantly, the ratio of LCs to keratinocytes in mouse ear skin (1:15) is more than three times higher than that reported for human breast skin (1:53). Accordingly, cross-presentation may be more significant in clinical Gene Gun applications than in pre-clinical mouse studies. These interspecies differences should be considered in pre-clinical trials using mouse models.

Gene therapy and uterine leiomyoma: a review

Leiomyomas (fibroids) are common estrogen-dependent uterine tumours that cause significant morbidity for women and a substantial economic impact on health delivery systems. Currently, there is no effective medical treatment option for this condition-hysterectomy is the mainstay of management. This is not an attractive choice for many women, especially patients desiring to preserve their fertility potential. Gene therapy is becoming a clinical reality, with more than 600 clinical trials worldwide. Researchers have recently attempted to develop a gene-therapy-based approach for the ablation of uterine fibroids. The localized nature of this condition and its accessibility using different imaging or endoscopic techniques make it an attractive target for direct delivery of gene-based vectors. Recent work from our laboratory suggests the potential use of a dominant-negative form of estrogen receptor (ER) to inactivate estrogen signalling in leiomyoma cells and induce apoptosis. Our in vivo data in a mouse model demonstrate the ability of an adenovirus-expressing dominant-negative ER to arrest leiomyoma growth. We and others also have described the utility of the herpes simplex virus-thymidine kinase (HSV-TK) plus ganciclovir (GCV) suicide gene-therapy system to effectively eradicate leiomyoma cells by utilizing the bystandard effect phenomena and the high expression of gap-junction protein in these tumours. Further work on rat models will pave the way for future leiomyoma gene-therapy clinical trials and allow the realization of gene therapy as a viable non-surgical option for this common problem in women's health.

A differential proteome in tumors suppressed by an adenovirus-based skin patch vaccine encoding human carcinoembryonic antigen

We created an anti-tumor vaccine by using adenovirus as a vector which contains a cytomegalovirus early promoter-directed human carcinoembryonic antigen gene (AdCMV-hCEA). In an attempt to develop the skin patch vaccine, we epicutaneously vaccinated Balb/c mice with AdCMV-hCEA. After nine weeks post-immunization, vaccinated mice evoked a robust antibody titer to CEA and demonstrated the capability of suppressing in vivo growth of implanted murine mammay adenocarioma cell line (JC-hCEA) tumor cells derived from a female Balb/c mouse. Proteomic analysis of the tumor masses in the non-vaccinated naive and vaccinated mice reveal that six proteins change their abundance in the tumor mass. The levels of adenylate kinase 1, beta-enolase, creatine kinase M chain, hemoglobin beta chain and prohibitin were statistically increased whereas the level of a creatine kinase fragment, which is undocumented, was decreased in the tumor of vaccinated mice. These proteins may provide a vital link between early-stage tumor suppression and immune response of skin patch vaccination.

The role of particle-mediated DNA vaccines in biodefense preparedness

Particle-mediated epidermal delivery (PMED) of DNA vaccines is based on the acceleration of DNA-coated gold directly into the cytoplasm and nuclei of living cells of the epidermis, facilitating DNA delivery and gene expression. Professional antigen-presenting cells and keratinocytes in the skin are both targeted, resulting in antigen presentation via direct transfection and cross-priming mechanisms. Only a small number of cells need to be transfected to elicit humoral, cellular and memory responses, requiring only a low DNA dose. In recent years, data have accumulated on the utility of PMED for delivery of DNA vaccines against a number of viral pathogens, including filoviruses, flaviviruses, poxviruses, togaviruses and bunyaviruses. PMED DNA immunization of rodents and nonhuman primates results in the generation of neutralizing antibody, cellular immunity, and protective efficacy against a broad range of viruses of public health concern.

Highly efficient expression of transgenic proteins by naked DNA-transfected dendritic cells through terminal differentiation

Dendritic cells (DCs) play a key role in the induction and control of immunity. Genetic engineering of DCs is a promising approach for the development of a broad range of immunomodulatory strategies, for purposes ranging from genetic immunization to tolerance induction. The development of DC-based immunotherapies is limited by the inability to efficiently transfect DCs using naked DNA. Here we demonstrate that after plasmid DNA delivery, the transgene expression level controlled by the human immediate-early cytomegalovirus promoter (hIE-CMVp) is higher in mature DCs than in immature DCs and is further increased after terminal differentiation of DCs by agonist anti-CD40 monoclonal antibody (mAb) or after DC interaction with CD4+ T cells. CD40 signaling of DCs resulted in nuclear translocation of the transcription factors nuclear factor-κB (NF-κB), activator of protein-1 (AP-1), and cyclic adenosine monophosphate (cAMP)–responsive element, necessary for the activation of hIE-CMVp. Transgene expression by DCs diminished after the inhibition of these transcription factors or the blockade of adhesion molecules involved in the DC–T-cell synapse. Importantly, CD40 signaling of DCs results in the highly efficient expression and presentation of transgenic antigens and the induction of “in vivo” cytotoxic T-cell (CTL) responses specific for transgenic antigen peptides, demonstrating the functional potential of genetically engineered DCs.

DNA immunisation: altering the cellular localisation of expressed protein and the immunisation route allows manipulation of the immune response

DNA immunisation by intramuscular (IM) injection induces Th1 responses, whereas gene gun (GG) immunisation into the skin stimulates Th2 responses. Three ovalbumin (OVA) cDNA constructs, in which OVA is cytoplasmic (CYT), secreted (SECR), or transmembrane (TM), were compared in immunisation studies using intramuscular injection or biolistic bombardment of the skin. Gene gun immunisation with OVA-CYT or OVA-TM led to strong OVA-specific CTL responses, but not following OVA-SECR immunisation. In contrast, intramuscular immunisation with OVA-SECR or OVA-TM led to potent CTL while immunisation with OVA-CYT was ineffective. OVA-specific antibodies were detected following gene gun immunisation with all three constructs, whereas only the OVA-SECR construct induced antibody production following intramuscular immunisation. These results demonstrate the capacity to manipulate the nature of the immune response by altering the cellular localization of expressed proteins and the route of DNA immunisation.

DNA vaccines and their application against parasites--promise, limitations and potential solutions

DNA or nucleic acid vaccines are being evaluated for efficacy against a range of parasitic diseases. Data from studies in rodent model systems have provided proof of principle that DNA vaccines are effective at inducing both humoral and T cell responses to a variety of candidate vaccine antigens. In particular, the induction of potent cellular responses often gives DNA vaccination an immunological advantage over subunit protein vaccination. Protection against parasite challenge has been demonstrated in a number of systems. However, application of parasite DNA vaccines in large animals including ruminants, primates and humans has been compromised by the relative lack of immune responsiveness to the vaccines, but the reasons for this hyporesponsiveness are not clear. Here, we review DNA vaccines against protozoan parasites, in particular vaccines for malaria, and the use of genomic approaches such as expression library immunization to generate novel vaccines. The application of DNA vaccines in ruminants is reviewed. We discuss some of the approaches being evaluated to improve responsiveness in large animals including the use of cytokines as adjuvants, targeting molecules as delivery ligands, electroporation and CpG oligonucleotides.

Active, specific immunotherapy for lung cancer: hurdles and strategies using genetic modification

Active immunotherapy for lung cancer has been a challenge because of the poor antigenic characterization of these tumors and their ability to escape the immune response. However, knowledge of the mechanisms of anti-tumor immunity has expanded significantly over the past decade, leading to the development of more novel, specific strategies for augmenting the immune response. Genetic manipulation of tumor cells, immune cells, or both, may help overcome some of the previously encountered difficulties of immunotherapy. Laboratory and clinical investigations are currently ongoing to evaluate the feasibility and potential benefit of these novel approaches.

Optimization of DNA-based vaccination in cows using green fluorescent protein and protein A as a prelude to immunization against staphylococcal mastitis

Staphylococcus aureus is a contagious pathogen that often results in chronic intramammary infections in dairy cows. Current vaccine formulations are ineffective in preventing this infection. The objective of this study was to stimulate an immune response in dairy cows through injection of plasmid DNA designed to express staphylococcal Protein A in transfected cells. Intramuscular and intradermal vaccination sites were evaluated using a plasmid containing the human cytomegalovirus (CMV) promoter/enhancer directing expression of green fluorescent protein (pcDNA3/GFP). DNA was delivered by needle and syringe, or by high-, intermediate-, or low-pressure jet injections (Ped-o-Jet and LectraJet). Five cows per treatment were injected with 0.5 mg of plasmid DNA at 6, 4, and 2 wk prepartum. Serum antibody levels determined by ELISA indicated that intradermal high-pressure jet injection elicited a greater immune response compared to needle and syringe injection. Differences in antibody production among low-pressure and needle and syringe treatment groups were not significant. An expression plasmid containing the CMV promoter/enhancer driving expression of the Fc-binding domain of S. aureus Protein A was coinjected into cows by vulvamucosal vaccination using the high-pressure Ped-o-Jet. Beginning 6 wk prepartum, groups of cows (n = 5) were injected three times at 2-wk intervals with DNA in saline, DNA in aluminum phosphate adjuvant, or served as noninjected controls. A cellular immune response to Protein A was detected in 4 of 10 animals, while cellular responses to GFP were not detected. Humoral responses to Protein A were observed in 6 of 10 animals and to GFP in 2 of 10 animals. Aluminum phosphate adjuvant appeared to enhance antibody production in response to Protein A. In experiment 3, a protein boost injection of Protein A was given to six animals approximately 5 mo postpartum. Three animals were nonvaccinated controls, and three were among those stimulated to produce antibody in response to the DNA-based vaccine. These results showed that Protein A specific antibodies remained elevated as compared to nonvaccinated controls and were stimulated in response to the protein boost. However, the magnitude of the response in animals previously vaccinated with DNA was not different than that observed in the nonvaccinated controls. We have shown that a humoral and cellular immune response to abbreviated Protein A can be raised in dairy cows using intravulvamucosal jet injection of a DNA-based vaccine.

High-frequency interferon-gamma-secreting splenocytes specific for murine cytomegalovirus immediate-early-1 (IE-1) peptide 168YPHFMPTNL176 are insufficient to provide complete protection from viral challenge

Infection of Balb/c mice with murine cytomegalovirus (MCMV) has been used extensively as a model system with which to study host mechanisms of immunity to cytomegaloviruses. In this model, the cytotoxic T-lymphocyte (CTL) response crucial for clearing infected cells is dominated by CTLs specific for the MCMV nonapeptide 168YPHFMPTNL176 encoded by the immediate-early 1 (IE-1) gene. The intradermal injection of plasmid pcDNA89 encoding IE-1 has been shown to offer some protection from viral challenge. In the present studies, the protective efficacy of immunisation with pcDNA89 given by intradermal injection was compared with particle-mediated DNA delivery (PMDD) and contrasted with that induced by injection with the K181 MCMV strain and with temperature-sensitive mutants (tsm) derived from the K181 strain. Modest protection was afforded by pcDNA89 immunisation given by PMDD, but none was observed after intradermal injection. PMDD immunisation induced a frequency of 168YPHFMPTNL176-specific interferon-gamma (IFN-gamma)-secreting splenocytes, which was equivalent to that after K181 infection and significantly higher than tsm immunisation. Whereas tsm-immunised mice were completely protected from MCMV challenge, PMDD-immunised mice were only weakly protected. Tsm immunisation protected mice completely against challenge with natural isolates having sequence variation in the IE-1 nonapeptide, while PMDD-immunised mice were weakly protected from isolates encoding 168YPHFMPTNL176 and were not protected against isolates encoding 168YPHFMPPSL176 or 168YLDFMPPNL176. Thus, while IE-1-specific IFN-gamma-secreting splenocytes do contribute to immunity from MCMV challenge, their presence in isolation is insufficient to provide complete protection and they may not be involved in the protection observed against MCMV isolates having IE-1 sequence variation.

Advances in dendritic cell-based vaccine of cancer

Dendritic cells (DCs) are potent antigen presenting cells that exist in virtually every tissue, and from which they capture antigens and migrate to secondary lymphoid organs where they activate naïve T cells. Although DCs are normally present in extremely small numbers in the circulation, recent advances in DC biology have allowed the development of methods to generate large numbers of these cells in vitro. Because of their immunoregulatory capacity, vaccination with tumor antigen-presenting DCs has been proposed as a treatment modality for cancer. In animal models, vaccination with DCs pulsed with tumor peptides, lysates, or RNA or loaded with apoptotic/necrotic tumor cells could induce significant antitumor CTL responses and antitumor immunity. However, the results from early clinical trails pointed to a need for additional improvement of DC-based vaccines before they could be considered as practical alternatives to the existing cancer treatment strategies. In this regard, subsequent studies have shown that DCs that express transgenes encoding tumor antigens are more potent primers of antitumor immunity both in vitro and in vivo than DCs simply pulsed with tumor peptides. Furthermore, DCs that have been engineered to express certain cytokines or chemokines can display a substantially improved maturation status, capacity to migrate to secondary lymphoid organs in vivo, and abilities to stimulate tumor-specific T cell responses and induce tumor immunity in vivo. In this review we also discuss a number of factors that are important considerations in designing DC vaccine strategies, including (i) the type and concentrations of tumor peptides used for pulsing DCs; (ii) the timing and intervals for DC vaccination/boostable data on DC vaccination portends bright prospects for this approach to tumor immune therapy, either alone or in conjunction with other therapies.

Applications of gene transfer to cellular immunotherapy

Adoptive cellular therapy remains a potentially powerful method of eradicating established tumors. T-cells have been particularly potent effector cells, as demonstrated in animal models and clinical studies, and it is apparent that the stimulation of certain subpopulations of T-cells that are reactive to tumor antigens can lead to more therapeutic T-cells. The use of gene transfer techniques has resulted in more effective and specific methods to generate these tumor-specific T-cells. Another area of tremendous interest is in the adoptive transfer of DCs manipulated to present tumor antigen to resting, naive T-cells. Gene transfer techniques may offer more optimal ways to generate therapeutic DCs. Adoptive immunotherapy may ultimately [figure: see text] have its greatest use in patients undergoing cellular rescue after ablative chemotherapy; the infusion of immunocompetent T-cells, genetically modified stem cells, or programmed DCs may offer the opportunity to direct a patient's immune response to eliminate residual microscopic disease.

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

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

Disrupted homeostasis of Langerhans cells and interdigitating dendritic cells in monkeys with AIDS

Langerhans cells (LCs) are immature dendritic cells (DCs) that capture antigen in peripheral tissues and migrate to draining lymph nodes, where they reside in the paracortex as interdigitating dendritic cells (IDCs). We studied the effects of simian immunodeficiency virus (SIV) on LCs and IDCs during different stages of infection in monkeys. LCs isolated from monkeys with acute SIV infection or acquired immunodeficiency syndrome (AIDS) underwent normal maturation in vitro, including a switch in chemokine receptor expression from CCR5 to CXCR4 and CCR7. LCs migrated normally from skin in response to contact sensitization in monkeys with acute SIV infection. In contrast, LC migration from skin was markedly impaired during AIDS, associated with a reduction in antigen-bearing DCs in draining lymph nodes. Lymph node IDCs were increased in proportion during acute SIV infection and had an activated phenotype, whereas during AIDS IDCs had significantly lower expression of CD40 and the activation marker CD83. IDCs from monkeys with AIDS were refractory to stimulation with CD40L, demonstrating a functional consequence of decreased CD40 expression. SIV-infected DCs were not identified in lymph nodes or skin of monkeys with AIDS, suggesting an indirect effect of infection on DC populations in vivo. These data indicate that DCs are mobilized to lymph nodes during acute SIV infection, but that during AIDS this process is suppressed, with LC migration and IDC activation being impaired. We conclude that disruption of DC homeostasis may play a role in immunopathology induced by human immunodeficiency virus and suggest that therapeutic strategies targeting DCs may have limited efficacy during AIDS.