Enabling topical immunization via microporation: a novel method for pain-free and needle-free delivery of adenovirus-based vaccines

Micro-scale devices for transdermal drug delivery

Skin makes an excellent site for drug and vaccine delivery due to easy accessibility, immuno-surveillance functions, avoidance of macromolecular degradation in the gastrointestinal tract and possibility of self-administration. However, macromolecular drug delivery across the skin is primarily accomplished using hypodermic needles, which have several disadvantages including accidental needle-sticks, pain and needle phobia. These limitations have led to extensive research and development of alternative methods for drug and vaccine delivery across the skin. This review focuses on the recent trends and developments in this field of micro-scale devices for transdermal macromolecular delivery. These include liquid jet injectors, powder injectors, microneedles and thermal microablation. The historical perspective, mechanisms of action, important design parameters, applications and challenges are discussed for each method.

Delivery strategies of melanoma vaccines: an overview

For many years, various cancer vaccines have been widely evaluated, however clinical responses remain rare. In this review, we attempt to address the question of which delivery strategies and platforms are feasible to produce clinical response and define the characteristics of the strategy that will induce long-lasting antitumor response. We limit our analysis and discussion to microparticles/nanoparticles, liposomes, heat-shock proteins, viral vectors and different types of adjuvants. This review aims to provide an overview of the specific characteristics, strengths and limitations of these delivery systems, focusing on their impacts on the development of melanoma vaccine. To date, only adoptive T-cell transfer has shown promising clinical outcomes compared to other treatments.

The hairless mouse in skin research

The hairless (Hr) gene encodes a transcriptional co-repressor highly expressed in the mammalian skin. In the mouse, several null and hypomorphic Hr alleles have been identified resulting in hairlessness in homozygous animals, characterized by alopecia developing after a single cycle of relatively normal hair growth. Mutations in the human ortholog have also been associated with congenital alopecia. Although a variety of hairless strains have been developed, outbred SKH1 mice are the most widely used in dermatologic research. These unpigmented and immunocompetent mice allow for ready manipulation of the skin, application of topical agents, and exposure to UVR, as well as easy visualization of the cutaneous response. Wound healing, acute photobiologic responses, and skin carcinogenesis have been extensively studied in SKH1 mice and are well characterized. In addition, tumors induced in these mice resemble, both at the morphologic and molecular levels, UVR-induced skin malignancies in man. Two limitations of the SKH1 mouse in dermatologic research are the relatively uncharacterized genetic background and its outbred status, which precludes inter-individual transplantation studies.

Temperature-induced protein release from water-in-oil-in-water double emulsions

A model water-in-oil-in-water (W1/O/W2) double emulsion was prepared by a two-step emulsification procedure and subsequently subjected to temperature changes that caused the oil phase to freeze and thaw while the two aqueous phases remained liquid. Our previous work on individual double-emulsion globules1 demonstrated that crystallizing the oil phase (O) preserves stability, while subsequent thawing triggers coalescence of the droplets of the internal aqueous phase (W1) with the external aqueous phase (W2), termed external coalescence. Activation of this instability mechanism led to instant release of fluorescently tagged bovine serum albumin (fluorescein isothiocyanate (FITC)-BSA) from the W 1 droplets and into W2. These results motivated us to apply the proposed temperature-induced globule-breakage mechanism to bulk double emulsions. As expected, no phase separation of the emulsion occurred if stored at temperatures below 18 degrees C (freezing point of the model oil n-hexadecane), whereas oil thawing readily caused instability. Crucial variables were identified during experimentation, and found to greatly influence the behavior of bulk double emulsions following freeze-thaw cycling. Adjustment of these variables accounted for a more efficient release of the encapsulated protein.

Various carrier system(s)- mediated genetic vaccination strategies against malaria

The introduction of vaccine technology has facilitated an unprecedented multiantigen approach to develop an effective vaccine against complex pathogens, such as Plasmodium spp., that cause severe malaria. The capacity of multisubunit DNA vaccines encoding different stage Plasmodium antigens to induce CD8(+) cytotoxic T lymphocytes and IFN-gamma responses in mice, monkeys and humans has been observed. Moreover, genetic vaccination may be multi-immune (i.e., capable of eliciting more than one type of immune response, including cell-mediated and humoral). In the case of malaria parasites, a cytotoxic T-lymphocyte response is categorically needed against the intracellular hepatocyte stage while a humoral response, with antibodies targeted against antigens from all stages of the life cycle, is also needed. Therefore, the key to success for any DNA-based therapy is to design a vector able to serve as a safe and efficient delivery system. This has encouraged the development of nonviral DNA-mediated gene-transfer techniques, such as liposomes, virosomes, microspheres and nanoparticles. Efficient and relatively safe DNA transfection using lipoplexes makes them an appealing alternative to be explored for gene delivery. In addition, liposome-entrapped DNA has been shown to enhance the potency of DNA vaccines, possibly by facilitating uptake of the plasmid by antigen-presenting cells. Another recent technology using cationic lipids has been deployed and has generated substantial interest in this approach to gene transfer. This review comprises various aspects that could be decisive in the formulation of efficient and stable carrier system(s) for the development of malaria vaccines.

The effect of heat on skin permeability

Although the effects of long exposure (>>1s) to moderate temperatures (< or =100 degrees C) have been well characterized, recent studies suggest that shorter exposure (<1s) to higher temperatures (>100 degrees C) can dramatically increase skin permeability. Previous studies suggest that by keeping exposures short, thermal damage can be localized to the stratum corneum without damaging deeper tissue. Initial clinical trials have progressed to Phase II (see http://clinicaltrials.gov), which indicates the procedure can be safe. Because the effect of heating under these conditions has received little systematic or mechanistic study, we heated full-thickness skin, epidermis and stratum corneum samples from human and porcine cadavers to temperatures ranging from 100 to 315 degrees C for times ranging from 100ms to 5s. Tissue samples were analyzed using skin permeability measurements, differential scanning calorimetry, thermomechanical analysis, thermal gravimetric analysis, brightfield and confocal microscopy, and histology. Skin permeability was shown to be a very strong function of temperature and a less strong function of the duration of heating. At optimal conditions used in this study, transdermal delivery of calcein was increased up to 760-fold by rapidly heating the skin at high temperature. More specifically, skin permeability was increased (I) by a few fold after heating to approximately 100-150 degrees C, (II) by one to two orders of magnitude after heating to approximately 150-250 degrees C and (III) by three orders of magnitude after heating above 300 degrees C. These permeability changes were attributed to (I) disordering of stratum corneum lipid structure, (II) disruption of stratum corneum keratin network structure and (III) decomposition and vaporization of keratin to create micron-scale holes in the stratum corneum, respectively. We conclude that heating the skin with short, high temperature pulses can increase skin permeability by orders of magnitude due to structural disruption and removal of stratum corneum.

The magnitude of the CD8+ T cell response produced by recombinant virus vectors is a function of both the antigen and the vector

Virus-based recombinant vaccines have proven highly effective at generating protective CD8+ T cell responses. Multiple vector platforms are available, however, little is known about the relative influence of the different vectors on the transgene-specific CD8+ T cell population. To address this question, we compared several characteristics of the CD8+ T cell response elicited by recombinant adenovirus (rAd) and vaccinia virus (rVV). We found that following rAd immunization the transgene-specific CD8+ T cell response peaked around day 12 and was larger and more sustained than the response produced by rVV. In addition, the CD8+ T cell response generated by rAd was directed primarily against the transgene, whereas the CD8+ T cell response produced by rVV principally targeted the vector backbone. In addition, we also observed that transgene selection also impacted on the magnitude of the CD8+ T cell response elicited by both vectors. Despite differences in the magnitude of the anti-transgene CD8+ T cell response, both vectors elicited CD8+ T cell populations with similar cytokine production, functional avidity and cytolytic activity. In addition, plasmid priming prior to immunization with either rAd or rVV only impacted the magnitude of the transgene gene specific CD8+ T cell response. Our study demonstrates that both vector and transgene selection can influence the magnitude of the CD8+ T cell response, but they do not influence functionality.

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.

Analgesic properties of oral sucrose during routine immunizations at 2 and 4 months of age

OBJECTIVE

The purpose of this work was to evaluate the analgesic properties of oral sucrose during routine immunizations in infants at 2 and 4 months of age.

PATIENTS AND METHODS

A prospective, randomized, placebo-controlled clinical trial was conducted at a pediatric ambulatory care clinic. One-hundred healthy term infants scheduled to receive routine immunizations were recruited, randomly stratified into 2- or 4-month study groups, and further randomly assigned to receive 24% oral sucrose and pacifier or the sterile water control solution. The study preparations were administered 2 minutes before the combined diphtheria-tetanus-acellular pertussis, inactivated polio vaccine, and hepatitis B vaccine. Haemophilus influenzae type b vaccine was administered 3 minutes after the combined injection, followed by the pneumococcal conjugate vaccine, 2 minutes after the H. influenzae type b injection. The University of Wisconsin Children's Hospital Pain Scale measured serial acute pain responses for the treatment and control groups at baseline and 2, 5, 7, and 9 minutes after solution administration. Repeated-measures analysis of variance examined between-group differences and within-subject variability of treatment effect on overall pain scores.

RESULTS

Two- and 4-month-old infants receiving oral sucrose (n = 38) displayed reductions in pain scores 2 minutes after solution administration compared with 2- and 4-month-old infants in the placebo group (n = 45). Between-group comparisons for the oral sucrose and placebo groups showed lower pain responses at 5, 7, and 9 minutes after solution administration. The oral sucrose and placebo groups demonstrated their highest mean pain score at 7 minutes, with a mean pain score of 3.8 and 4.8, respectively. At 9 minutes, the placebo group had a mean pain score of 2.91 whereas the mean pain score for the oral sucrose group returned to near baseline, reflecting a 78.5% difference in mean pain score (oral sucrose - placebo) relative to the placebo mean.

CONCLUSIONS

Oral sucrose is an effective, easy-to-administer, short-acting analgesic for use during routine immunizations.

Overview of drug delivery and alternative methods to electroporation

This chapter provides an overview of the application of electroporation to areas other than gene delivery. These areas include the delivery of drugs and vaccines to tissues and tumors as well as into and through the skin. Achievements and limitations of electroporation in these areas are presented. Alternative physical methods for gene and drug delivery besides electroporation are described. The advantages and drawbacks of electroporation, compared with these methods, are also discussed.

Needle-free vaccine delivery

The need for minimally invasive delivery methods is urgent. As the number of registered vaccines increases, so does the number of injections. The use of sharps can be unsafe and needle immunisation is less suitable for mass immunisations during emergencies such as pandemics or bioterrorist attacks. The approach of combining vaccines has limitations due to high development costs, risk of pharmaceutical or immunological interference and economic risks. Advancements in the development of alternatives to injection with syringes and needles are discussed in this paper, and include: mucosal vaccination, injection without needles and vaccine delivery via the skin.

Elevated frequencies of self-reactive CD8+ T cells following immunization with a xenoantigen are due to the presence of a heteroclitic CD4+ T-cell helper epitope

Immunization of mice with human dopachrome tautomerase (hDCT) provides greater protection against melanoma than immunization with the murine homologue (mDCT). We mapped the CD8(+) and CD4(+) T-cell epitopes in both proteins to better understand the mechanisms of the enhanced protection. The dominant CD8(+) T-cell epitopes were fully conserved between both proteins, yet immunization with hDCT produced frequencies of CD8(+) T cells that were 5- to 10-fold higher than immunization with mDCT. This difference was not intrinsic to the two proteins because comparable frequencies of CD8(+) T cells were elicited by both antigens in DCT-deficient mice. Strikingly, only hDCT elicited a significant level of specific CD4(+) T cells in wild-type (WT) mice. The murine protein was not devoid of CD4(+) T-cell epitopes because immunization of DCT-deficient mice with mDCT resulted in robust CD4(+) T-cell immunity directed against two epitopes that were not identified in WT mice. These results suggested that the reduced immunogenicity of mDCT in WT mice may be a function of insufficient CD4(+) T-cell help. To address this possibility, the dominant CD4(+) T-cell epitope from hDCT was introduced into mDCT. Immunization with the mutated mDCT evoked CD8(+) T-cell frequencies and protective immunity comparable with hDCT. These results reveal a novel mechanism by which xenoantigens overcome tolerance. Our data also suggest that immunologic tolerance is more stringent for CD4(+) T cells than CD8(+) T cells, providing a mechanism of peripheral tolerance where autoreactive CD8(+) T cells fail to be activated due to a lack of autoreactive CD4(+) T cells specific for the same antigen.

Needle-free skin patch delivery of a vaccine for a potentially pandemic influenza virus provides protection against lethal challenge in mice

In the event of another influenza virus pandemic, strategies for effective mass vaccination will urgently be needed. We used a novel transdermal patch delivery technology, known as the PassPort system, to vaccinate mice with recombinant H5 hemagglutinin with or without immunomodulators. This needle-free form of vaccine delivery induced robust serum antibody responses that were augmented by different immunomodulators that stimulated the innate immune system and protected mice against lethal challenge with a highly pathogenic avian H5N1 influenza virus.

Transdermal delivery of interferon alpha-2B using microporation and iontophoresis in hairless rats

PURPOSE

To demonstrate transdermal delivery of interferon alpha-2b (IFNalpha2b) in hairless rats through aqueous microchannels (micropores) created in the skin and enhanced by iontophoresis.

MATERIALS AND METHODS

The Altea Therapeutics PassPort System was configured to form an array of micropores (2.0 cm(2); 72 micropores/cm(2)) on the rat abdomen. The transdermal patch (Iomed TransQ1-GS-hydrogel) was saturated with an IFNalpha2b solution (600 microg/ml) and applied for 4 h. Delivery was evaluated with and without cathodic iontophoresis (0.1 mA/cm(2)). Intravenous delivery (0.4 microg/100 g body weight) was performed to support pharmacokinetic calculations.

RESULTS

IFNalpha2b was not delivered through intact skin by itself (passive delivery) or during iontophoresis. However, passive delivery through micropores was achieved in vivo in rats. A dose of 397 +/- 67 ng was delivered over 6 h, with steady state serum concentrations reaching a plateau at 1 h post-patch application. These levels dropped rapidly after patch removal, and returned to baseline within 2 h of patch removal. Iontophoresis-enhanced delivery through micropores resulted in a two-fold increase in the dose delivered (722 +/- 169 ng) in the hairless rat.

CONCLUSIONS

In vivo delivery of IFNalpha2b was demonstrated through micropores created in the outer layer of the skin. Iontophoresis enhanced delivery through microporated skin in hairless rats.

Resealing of electroporation of porcine epidermis using phospholipids and poloxamers

The resealing of porcine epidermis after electroporation is investigated. Porcine epidermis was subjected to electroporation (30 pulses at 100 V, 1 ms and at 1 Hz) in a vertical diffusion apparatus, in the presence of 2 mg/ml dimyristoylphosphatidylserine, to produce a long lasting permeable state. Resealing treatments include incubation in 0.0625-0.25 mM poloxamer 188 (P188), or incorporation of phosphatidylcholines (PC) and/or cationic lipids with additional pulses. The recovery of electric resistance of the epidermis samples after electroporation with or without resealing treatments was monitored. The transports of carboxyfluorescein and glucose were measured during the recovery process. Both P188 and PC were effective in resealing in terms of electric conductance and transport, with P188 reacting more rapidly and completely. P188 mediated lipid exchange between stratum corneum lipid particles was measured by fluorescence resonance energy transfer (FRET). Lipid reorganization facilitated by P188 and PC is suggested to be a major resealing mechanism of electroporation damage.

Gene therapy progress and prospects: the skin – easily accessible, but still far away

Significant progress has been made in corrective gene therapy of inherited skin diseases. This includes advances in vector technology, targeted gene expression, gene replacement, and the availability of appropriate animal models for a variety of candidate diseases. In addition, an increased understanding of the uptake and trafficking mechanisms inside keratinocytes has evolved. Topical application facilitates DNA vaccination through the skin, albeit clinical benefits have not yet materialized. However, the translation into clinical trials has only been partially mastered. The latter and the control of immune responses represent challenges for the research community.

Topical application of Escherichia coli-vectored vaccine as a simple method for eliciting protective immunity

We report here that animals can be protected against lethal infection by Clostridium tetani cells and Bacillus anthracis spores following topical application of intact particles of live or gamma-irradiated Escherichia coli vectors overproducing tetanus and anthrax antigens, respectively. Cutaneous gammadeltaT cells were rapidly recruited to the administration site. Live E. coli cells were not found in nonskin tissues after topical application, although fragments of E. coli DNA were disseminated transiently. Evidence suggested that intact E. coli particles in the outer layer of skin may be disrupted by a gammadeltaT-cell-mediated innate defense mechanism, followed by the presentation of E. coli ligand-adjuvanted intravector antigens to the immune system and rapid degradation of E. coli components. The nonreplicating E. coli vector overproducing an exogenous immunogen may foster the development of a new generation of vaccines that can be manufactured rapidly and administered noninvasively in a wide variety of disease settings.

Recombinant Adenovirus Vaccines Can Successfully Elicit CD8+ T Cell Immunity under Conditions of Extreme Leukopenia

We have examined the efficacy of vaccination with recombinant adenovirus under conditions of extreme leukopenia in lethally irradiated mice reconstituted with autologous bone marrow. The expansion of antigen-specific CD8(+) T cells following immunization of lethally irradiated hosts paralleled the recovery of total CD8(+) T cells. Surprisingly, the numbers of antigen-specific CD8(+) T cells in lethally irradiated mice beyond 6 weeks postimmunization were comparable to the numbers found in nonirradiated controls. CD8(+) T cells elicited in the lethally irradiated hosts were functionally indistinguishable from those elicited in normal hosts. Antigen expression and presentation persisted for a longer period of time in the draining lymph nodes of irradiated mice compared to those of nonirradiated animals, suggesting that antigen presentation mechanisms were intact during the reconstitution period. Experiments employing allogeneic bone marrow demonstrated that radioresistant host antigen-presenting cells were responsible for antigen presentation during the process of immune reconstitution. These results demonstrate clear compatibility of adenovirus vaccines and cytotoxic therapy. Furthermore, these observations provide novel insights into the mechanisms of CD8(+) T cell activation following adenovirus immunization.

Immunization without needles

Most current immunization procedures make use of needles and syringes for vaccine administration. With the increase in the number of immunizations that children around the world routinely receive, health organizations are beginning to look for safer alternatives that reduce the risk of cross-contamination that arises from needle reuse. This article focuses on contemporary developments in needle-free methods of immunization, such as liquid-jet injectors, topical application to the skin, oral pills and nasal sprays.

The CD8+T Cell Population Elicited by Recombinant Adenovirus Displays a Novel Partially Exhausted Phenotype Associated with Prolonged Antigen Presentation That Nonetheless Provides Long-Term Immunity

We have previously reported that the CD8+ T cell response elicited by recombinant adenovirus vaccination displayed a delayed contraction in the spleen. In our current study, we demonstrate that this unusual kinetic is a general phenomenon observed in multiple tissues. Phenotypic analysis of transgene-specific CD8+ T cells present 30 days postimmunization with recombinant adenovirus revealed a population with evidence of partial exhaustion, suggesting that the cells had been chronically exposed to Ag. Although Ag expression could no longer be detected 3 wk after immunization, examination of Ag presentation within the draining lymph nodes demonstrated that APCs were loaded with Ag peptide for at least 40 days postimmunization, suggesting that Ag remains available to the system for a prolonged period, although the exact source of this Ag remains to be determined. At 60 days postimmunization, the CD8+ T cell population continued to exhibit a phenotype consistent with partially exhausted effector memory cells. Nonetheless, these CD8+ T cells conferred sterilizing immunity against virus challenge 7-12 wk postimmunization, suggesting that robust protective immunity can be provided by CD8+ T cells with an exhausted phenotype. These data demonstrate that prolonged exposure to Ag may not necessarily impair protective immunity and prompt a re-evaluation of the impact of persistent exposure to Ag on T cell function.

Gene therapy and the skin

Significant progress has been made during the past decade in corrective gene therapy of the skin. This includes advances in vector technology, targeted gene expression, gene replacement, gene correction, and the availability of appropriate animal models for a variety of candidate diseases. While non-viral integration of large genes such as essential basement membrane proteins has been mastered, new challenges such as the control of immune responses lie ahead of the research community. Among the first skin diseases, patients with junctional epidermolysis bullosa (JEB) and xeroderma pigmentosum (XP) will enter clinical trials.

Recombinant adeno-associated virus type 2-mediated gene transfer into human keratinocytes is influenced by both the ubiquitin/proteasome pathway and epidermal growth factor receptor tyrosine kinase

Efficient gene delivery into keratinocytes is a prerequisite for successful skin gene therapy. Vectors based on recombinant adeno-associated virus type 2 (rAAV-2) offer several promising features that make them attractive for cutaneous applications. However, highly efficient gene delivery may be hampered by different cellular factors, including lack of viral receptors, impairment of cytoplasmic trafficking or limitations in viral second-strand synthesis. This study was undertaken to find factors that influence rAAV-2-mediated in vitro gene transfer into human keratinocytes and, consequently, ways to optimize gene delivery. Transduction experiments using rAAV-2 vectors expressing green fluorescent protein (GFP) demonstrated that impaired cellular trafficking of vector particles and high levels of autophosphorylation at epidermal growth factor receptor tyrosine kinase (EGF-R TK) have a negative influence on gene transfer into keratinocytes. Treatment of keratinocytes with proteasome inhibitor MG132 resulted in a transient augmentation of GFP expression in up to 37% of cells. Treatment with EGF-R TK inhibitors (quinazoline type) enhanced transgene expression in 10-14.5% of the cells. Gene expression was stable for more than 10 weeks and persisted until proliferative senescence occurred. This stable gene expression allows speculation that keratinocyte stem cells have initially been transduced. These findings might have relevance for the use of rAAV-2 vectors in skin gene therapy: transient enhancement of rAAV-2 transduction with proteasome inhibitors might be useful for genetic promotion of wound healing or skin-directed vaccination. Treatment with quinazolines may increase rAAV-2 transduction of keratinocyte stem cells, which is important for gene therapy approaches to inherited diseases.

RETRACTED: Progress and prospects of skin gene therapy: a ten year history

Significant progress has been made in corrective gene therapy of the skin in the last decade. This includes advances in vector technology, targeted gene expression, gene replacement, gene correction, and the availability of appropriate animal models for a variety of candidate diseases. While non-viral integration of large genes such as essential basement membrane proteins has been mastered, new challenges such as the control of immune responses lie ahead of the research community until skin gene therapy will become clinical reality. Among the first skin diseases patients with junctional epidermolysis bullosa and xeroderma pigmentosum have entered clinical trials.

Safety and immunogenicity of adenovirus-vectored nasal and epicutaneous influenza vaccines in humans

The increasing number and density of the human population, the emergence of lethal influenza strains, and the potential use of designer influenza virus as a bioweapon, collectively highlight a critical need for more rapid production of influenza vaccines and less invasive means of delivery. We have developed a nonreplicative adenovirus-vectored influenza vaccine that can be produced without the prerequisite of growing influenza virus. This new class of vaccines can be administered as a nasal spray or skin patch by personnel without medical training. We report here that adenovirus-vectored nasal and epicutaneous influenza vaccines were well tolerated by human volunteers. The nasal vaccine was more potent than its epicutaneous counterpart under the adjuvant-free experimental condition. These results provide the foundation for further human testing of needleless vectored vaccines as promising alternatives to current vaccines.

The efficacy of electroporated plasmid vaccines correlates with long-term antigen production in vivo

We sought to determine whether in vivo electroporation might overcome the requirement for strong transcriptional promoters in plasmid vaccines. We tested plasmid vaccines containing viral promoters that exhibited a broad range of transcriptional activities by in vitro assay. In contrast to the in vitro observations, no difference in gene expression was measured in vivo 24h following injection when the plasmids were introduced via electroporation. Despite the similarities in gene expression in vivo, the cellular and humoral responses elicited by these plasmid vaccines were dramatically different and correlated more closely with the promoter activity measured in vitro. When antigen production in vivo was measured over a longer period following injection, significant differences in gene expression became apparent after 2-3 days and the differences in gene expression at day 7 correlated well with plasmid immunogenicity. These studies reconfirm the importance of antigen production for effective plasmid vaccination and demonstrate that the duration of gene expression should also be considered when designing plasmid vaccines.

Strategies for improved formulation and delivery of DNA vaccines to veterinary target species

Interest in DNA immunization of animals continues, despite the fact that immune responses induced by DNA vaccines are generally lower than those elicited by conventional vaccines. In attempts to enhance the immune response to DNA vaccines, individuals have tried a variety of immune modulators, cytokines, and costimulatory molecules, but these only boost immune responses marginally. These results clearly demonstrate that the major challenge to improving DNA-based vaccines is to improve the transfection efficiency. Gene gun and electroporation can increase transfection and improve immune responses significantly, but these technologies have not yet advanced to the stage of routine use in livestock. Hopefully, transfection efficiency can be increased further in a user-friendly manner to ensure that the benefits of using DNA vaccines become a reality.

Bacterial ghosts – biological particles as delivery systems for antigens, nucleic acids and drugs

Despite the exponential rate of discovery of new antigens and DNA vaccines resulting from modern molecular biology and proteomics, the lack of effective delivery technology is a major limiting factor in their application. The bacterial ghost system represents a platform technology for antigen, nucleic acid and drug delivery. Bacterial ghosts have significant advantages over other engineered biological delivery particles, owing to their intrinsic cellular and tissue tropic abilities, ease of production and the fact that they can be stored and processed without the need for refrigeration. These particles have found both veterinary and medical applications for the vaccination and treatment of tumors and various infectious diseases.

Current status and future potential of transdermal drug delivery

The past twenty five years have seen an explosion in the creation and discovery of new medicinal agents. Related innovations in drug delivery systems have not only enabled the successful implementation of many of these novel pharmaceuticals, but have also permitted the development of new medical treatments with existing drugs. The creation of transdermal delivery systems has been one of the most important of these innovations, offering a number of advantages over the oral route. In this article, we discuss the already significant impact this field has made on the administration of various pharmaceuticals; explore limitations of the current technology; and discuss methods under exploration for overcoming these limitations and the challenges ahead.

Vaccination-induced autoimmune vitiligo is a consequence of secondary trauma to the skin

A major concern for cancer vaccines targeting self-tumor antigens is the risk of autoimmune sequelae. Although antitumor immunity correlates with autoimmune disease in some preclinical models, the mechanism(s) linking antitumor immunity and subsequent autoimmune pathology remain(s) to be determined. In the current study, we demonstrated that intradermal (i.d.) immunization with a recombinant adenovirus (Ad) expressing the murine melanoma antigen tyrosinase-related protein 2 (AdmTrp-2) results in a moderate level of tumor protection against the B16F10 murine melanoma without any vitiligo. Similar immunization with an Ad encoding human Trp-2 (AdhTrp-2) resulted in 50-fold greater protective immunity and produced vitiligo in all of the mice, suggesting that the development of autoimmunity may reflect the potency of the vaccine. Interestingly, delivery of AdhTrp-2 by i.m. injection generated protective immunity comparable with that seen in mice that received the vaccine by the i.d. route, but none of the recipients in the i.m. group developed vitiligo. The cellular and humoral responses in the i.m. immunized mice were greater than in the i.d. group; therefore, the lack of vitiligo was not caused by reduced efficacy of the vaccine. These results led us to hypothesize that vaccine-induced vitiligo was associated with local inflammatory responses. Mice immunized i.m. with AdhTrp-2 did develop vitiligo when they subsequently were injected i.d. with either a control Ad vector or complete Freund's adjuvant, suggesting that vitiligo is initiated by some form of trauma within the skin. Our data demonstrated that autoimmune pathology is not an unavoidable outcome of effective cancer vaccines directed against self-tumor antigens.

Helper-Dependent Adenoviral Vectors Containing Modified Fiber for Improved Transduction of Developing and Mature Muscle Cells

Adenoviruses (Ads) have shown great utility as vectors for the delivery of genes to mammalian cells, partly because of their ability to infect a wide range of different cell types independent of the replicative state of the cell. However, Ads do not transduce mature muscle efficiently because of low levels of the natural viral primary receptor, the coxsackie virus and adenovirus receptor, on the surface of adult muscle cells. In this study, we have addressed whether incorporation of polylysine [p(K)] or arginine-glycine-aspartic acid (RGD) placed in the H-I loop of the adenoviral fiber protein can improve helper-dependent Ad vector (hdAd) transduction of mature muscle cells. We show that incorporation of the p(K) motif into the fiber of early region 1 (E1)-deleted Ad results in enhanced transduction of undifferentiated and differentiated C2C12 cells relative to a virus, containing a wild-type fiber (12- and 21-fold enhancement, respectively). Incorporation of the RGD motif resulted in only a 60-70% increase in transduction efficiency in these cells. The two fiber modifications were then incorporated into helper viruses for use in the Cre-lox system for generating hdAd, and the resulting retargeted Ad vectors, which encoded the beta-galactosidase reporter gene (beta-Gal), demonstrated enhanced transduction of C2C12 cells in culture. Although hdAdpK also showed enhanced infection of mature mouse muscle in vivo, hdAdRGD did not. All hdAd vectors elicited only minor anti-Ad immune responses, compared with an E1-deleted control vector, but each vector elicited strong anti-beta-Gal immunoreactivity. Our results demonstrate that hdAd with modified cell tropism can be generated efficiently and, in the case of polylysine-modified hdAd, can lead to improved transduction of adult muscle cells in vivo.

Electroporation Enables Plasmid Vaccines to Elicit CD8+T Cell Responses in the Absence of CD4+T Cells

In vivo electroporation dramatically enhances plasmid vaccine efficacy. This enhancement can be attributed to increased plasmid delivery and, possibly, to some undefined adjuvant properties. Previous reports have demonstrated CD8(+) T cell priming by plasmid vaccines is strongly dependent upon CD4(+) T cell help. Indeed, the efficacy of a plasmid vaccine expressing Escherichia coli beta-galactosidase was severely attenuated in MHC class II-deficient (C2D) mice. To determine whether electroporation could compensate for the absence of CD4(+) T cell help, C2D mice were immunized by a single administration of plasmid in combination with electroporation using two conditions which differed only by the duration of the pulse (20 or 50 msec). Both conditions elicited robust cellular and humoral responses in wild-type mice, as measured by IFN-gamma ELISPOT, anti-beta-galactosidase ELISA, and protection from virus challenge. In C2D mice, the cellular response produced by the vaccine combined with the 50-msec pulse, as measured by ELISPOT, was identical to the response in wild-type mice. The 20-msec pulse elicited a milder response that was approximately one-fifth that of the response elicited by the 50-msec pulse. By contrast, the 20-msec conditions provided comparable protection in both wild-type and C2D recipients whereas the protection elicited by the 50-msec conditions in C2D mice was weaker than in wild-type mice. Further investigation is required to understand the discordance between the ELISPOT results and outcome of virus challenge in the C2D mice. Nonetheless, using this technique to prime CD8(+) T cells using plasmid vaccines may prove extremely useful when immunizing hosts with limiting CD4(+) T cell function, such as AIDS patients.

DNA vaccines for non-infectious diseases: new treatments for tumour and allergy

The last decade of DNA vaccine research was characterised by a pioneer spirit and enormous enthusiasm, with a large number of publications demonstrating the usefulness of this approach. Unfortunately, DNA vaccines have not necessarily met the high clinical expectations and a number of complications need to be overcome. In the case of cancer and allergy, the requirements for achieving the objectives are very different. Vaccines against allergies need to suppress or alter an unwanted immune response, while a cancer DNA vaccine has to overcome tolerance and/or immune suppression and initiate a powerful immune response. This review addresses currently used general optimisation strategies for DNA vaccines such as modification of immunisation regimens, improving the delivery systems and using molecular adjuvants. In addition, cancer-specific approaches, such as the stimulation of innate and adaptive immunity with replicase-based DNA vaccines, and targeting non-tumour-associated antigens (TAAs) are discussed. Specifically for the optimisation of DNA vaccination against allergies, procedures such as allergen gene recoding, T helper (Th)1 modulation, and the creation of safe DNA vaccines by gene fragmentation, ubiquitination or using artificial hypoallergens are being analysed. These strategies, individually or in combination, hold the potential of making DNA vaccines useful for application in the clinic.