Targeting the skin for genetic immunization

Induction of food-specific IgG by Gene Gun-delivered DNA vaccines

Background

Shellfish and tree nut allergies are among the most prevalent food allergies, now affecting 2%–3% and 1% of the US population, respectively. Currently, there are no approved therapies for shellfish or tree nut allergies, with strict avoidance being the standard of care. However, oral immunotherapy for peanut allergy and subcutaneous immunotherapy for environmental allergens are efficacious and lead to the production of allergen-specific IgG, which causes suppression of allergen effector cell degranulation. Since allergen-specific IgG is a desired response to alleviate IgE-mediated allergies, we tested transcutaneously-delivered DNA vaccines targeting shellfish and tree nut allergens for their ability to induce antigen-specific IgG, which would have therapeutic potential for food allergies.

Methods

We assessed Gene Gun-delivered DNA vaccines targeting either crustacean shellfish or walnut/pecan allergens, with or without IL-12, in naïve mice. Three strains of mice, BALB/cJ, C3H/HeJ and CC027/GeniUnc, were evaluated for IgG production following vaccination. Vaccines were administered twice via Gene Gun, three weeks apart and then blood was collected three weeks following the final vaccination.

Results

Vaccination with shellfish allergen DNA led to increased shrimp-specific IgG in all three strains, with the highest production in C3H/HeJ from the vaccine alone, whereas the vaccine with IL-12 led to the highest IgG production in BALB/cJ and CC027/GeniUnc mice. Similar IgG production was also induced against lobster and crab allergens. For walnut/pecan vaccines, BALB/cJ and C3H/HeJ mice produced significantly higher walnut- and pecan-specific IgG with the vaccine alone compared to the vaccine with IL-12, while the CC027 mice made significantly higher IgG with the addition of IL-12. Notably, intramuscular administration of the vaccines did not lead to increased antigen-specific IgG production, indicating that Gene Gun administration is a superior delivery modality.

Conclusions

Overall, these data demonstrate the utility of DNA vaccines against two lifelong food allergies, shellfish and tree nuts, suggesting their potential as a food allergy therapy in the future.

Polyfunctional Tier 2-Neutralizing Antibodies Cloned following HIV-1 Env Macaque Immunization Mirror Native Antibodies in a Human Donor

Vaccine efforts to combat HIV are challenged by the global diversity of viral strains and shielding of neutralization epitopes on the viral envelope glycoprotein trimer. Even so, the isolation of broadly neutralizing Abs from infected individuals suggests the potential for eliciting protective Abs through vaccination. This study reports a panel of 58 mAbs cloned from a rhesus macaque (Macaca mulatta) immunized with envelope glycoprotein immunogens curated from an HIV-1 clade C-infected volunteer. Twenty mAbs showed neutralizing activity, and the strongest neutralizer displayed 92% breadth with a median IC50 of 1.35 μg/ml against a 13-virus panel. Neutralizing mAbs predominantly targeted linear epitopes in the V3 region in the cradle orientation (V3C) with others targeting the V3 ladle orientation (V3L), the CD4 binding site (CD4bs), C1, C4, or gp41. Nonneutralizing mAbs bound C1, C5, or undetermined conformational epitopes. Neutralization potency strongly correlated with the magnitude of binding to infected primary macaque splenocytes and to the level of Ab-dependent cellular cytotoxicity, but did not predict the degree of Ab-dependent cellular phagocytosis. Using an individualized germline gene database, mAbs were traced to 23 of 72 functional IgHV alleles. Neutralizing V3C Abs displayed minimal nucleotide somatic hypermutation in the H chain V region (3.77%), indicating that relatively little affinity maturation was needed to achieve in-clade neutralization breadth. Overall, this study underscores the polyfunctional nature of vaccine-elicited tier 2-neutralizing V3 Abs and demonstrates partial reproduction of the human donor's humoral immune response through nonhuman primate vaccination.

Cutaneous immunization: an evolving paradigm in influenza vaccines

INTRODUCTION

Most vaccines are administered by intramuscular injection using a hypodermic needle and syringe. Some limitations of this procedure include reluctance to be immunized because of fear of needlesticks, and concerns associated with the safe disposal of needles after their use. Skin delivery is an alternate route of vaccination that has potential to be painless and could even lead to dose reduction of vaccines. Recently, microneedles have emerged as a novel painless approach for delivery of influenza vaccines via the skin.

AREAS COVERED

In this review, we briefly summarize the approaches and devices used for skin vaccination, and then focus on studies of skin immunization with influenza vaccines using microneedles. We discuss both the functional immune response and the nature of this immune response following vaccination with microneedles.

EXPERT OPINION

The cutaneous administration of influenza vaccines using microneedles offers several advantages: it is painless, elicits stronger immune responses in preclinical studies and could improve responses in high-risk populations. These dry formulations of vaccines provide enhanced stability, a property of high importance in enabling their rapid global distribution in response to possible outbreaks of pandemic influenza and newly emerging infectious diseases.

Optimizing particle-mediated epidermal delivery of an influenza DNA vaccine in ferrets

Particle-mediated DNA delivery technologies ("gene guns") have been shown in both animal and clinical studies to be an effective means of increasing the immunogenicity and protective efficacy of DNA vaccines. The primary goal in optimizing particle-mediated epidermal delivery (PMED) vaccination in different animal models is to achieve delivery of DNA-coated gold beads into the viable epidermis. Two key para-meters that influence this outcome include the delivery pressure, which controls the penetrative force of the beads into the skin, and the anatomical site of DNA delivery. Although the ferret has been extensively used as an experimental model for influenza infection in humans, very few studies have investigated the capacity for PMED DNA vaccination to induce protective immune responses in ferrets. Here we describe methods to optimize DNA vaccine delivery using the PowderJect XR1 gene delivery in ferrets. We first assess the effects of firing pressure on both the delivery of DNA-coated gold beads into the desired epidermal layer and the degree of DNA vaccine reporter gene expression at the target site. Second, we evaluate the impact of vaccination site (skin or tongue) on DNA vaccine immunogenicity by measuring serum antibody responses to the model antigens influenza virus hemagglutinin and hepatitis B core antigen. Results from these studies support the use of the PowderJect XR1 device in ferrets for the study of prophylactic and therapeutic DNA vaccines against clinically important diseases such as influenza virus infection.

Increased immunogenicity of avian influenza DNA vaccine delivered to the skin using a microneedle patch

Effective public health responses to an influenza pandemic require an effective vaccine that can be manufactured and administered to large populations in the shortest possible time. In this study, we evaluated a method for vaccination against avian influenza virus that uses a DNA vaccine for rapid manufacturing and delivered by a microneedle skin patch for simplified administration and increased immunogenicity. We prepared patches containing 700-μm long microneedles coated with an avian H5 influenza hemagglutinin DNA vaccine from A/Viet Nam/1203/04 influenza virus. The coating DNA dose increased with DNA concentration in the coating solution and the number of dip-coating cycles. Coated DNA was released into the skin tissue by dissolution within minutes. Vaccination of mice using microneedles induced higher levels of antibody responses and hemagglutination inhibition titers, and improved protection against lethal infection with avian influenza as compared to conventional intramuscular delivery of the same dose of the DNA vaccine. Additional analysis showed that the microneedle coating solution containing carboxymethylcellulose and a surfactant may have negatively affected the immunogenicity of the DNA vaccine. Overall, this study shows that DNA vaccine delivery by microneedles can be a promising approach for improved vaccination to mitigate an influenza pandemic.

GM-CSF increases mucosal and systemic immunogenicity of an H1N1 influenza DNA vaccine administered into the epidermis of non-human primates

Background

The recent H5N1 avian and H1N1 swine-origin influenza virus outbreaks reaffirm that the threat of a world-wide influenza pandemic is both real and ever-present. Vaccination is still considered the best strategy for protection against influenza virus infection but a significant challenge is to identify new vaccine approaches that offer accelerated production, broader protection against drifted and shifted strains, and the capacity to elicit anti-viral immune responses in the respiratory tract at the site of viral entry. As a safe alternative to live attenuated vaccines, the mucosal and systemic immunogenicity of an H1N1 influenza (A/New Caledonia/20/99) HA DNA vaccine administered by particle-mediated epidermal delivery (PMED or gene gun) was analyzed in rhesus macaques.

Methodology/Principal Findings

Macaques were immunized at weeks 0, 8, and 16 using a disposable single-shot particle-mediated delivery device designed for clinical use that delivers plasmid DNA directly into cells of the epidermis. Significant levels of hemagglutination inhibiting (HI) antibodies and cytokine-secreting HA-specific T cells were observed in the periphery of macaques following 1–3 doses of the PMED HA DNA vaccine. In addition, HA DNA vaccination induced detectable levels of HA-specific mucosal antibodies and T cells in the lung and gut-associated lymphoid tissues of vaccinated macaques. Importantly, co-delivery of a DNA encoding the rhesus macaque GM-CSF gene was found to significantly enhance both the systemic and mucosal immunogenicity of the HA DNA vaccine.

Conclusions/Significance

These results provide strong support for the development of a particle-mediated epidermal DNA vaccine for protection against respiratory pathogens such as influenza and demonstrate, for the first time, the ability of skin-delivered GM-CSF to serve as an effective mucosal adjuvant for vaccine induction of immune responses in the gut and respiratory tract.

Enhancement of anti-DIII antibodies by the C3d derivative P28 results in lower viral titers and augments protection in mice

Antibodies generated against West Nile virus (WNV) during infection are essential for controlling dissemination. Recent studies have demonstrated that epitopes in all three domains of the flavivirus envelope protein (E) are targets for neutralizing antibodies, with determinants in domain III (DIII) eliciting antibodies with strong inhibitory properties. In order to increase the magnitude and quality of the antibody response against the WNV E protein, DNA vaccines with derivatives of the WNV E gene (full length E, truncated E, or DIII region, some in the context of the pre-membrane [prM] gene) were conjugated to the molecular adjuvant P28. The P28 region of the complement protein C3d is the minimum CR2-binding domain necessary for the adjuvant activity of C3d. Delivery of DNA-based vaccines by gene gun and intramuscular routes stimulated production of IgG antibodies against the WNV DIII region of the E protein. With the exception of the vaccine expressing prM/E given intramuscularly, only mice that received DNA vaccines by gene gun produced protective neutralizing antibody titers (FRNT80 titer >1/40). Correspondingly, mice vaccinated by the gene gun route were protected to a greater level from lethal WNV challenge. In general, mice vaccinated with P28-adjuvated vaccines produced higher IgG titers than mice vaccinated with non-adjuvanted vaccines.

Prospects for developing an effective particle-mediated DNA vaccine against influenza

Vaccine strategies capable of conferring broad protection against both seasonal and pandemic strains of influenza are urgently needed. DNA vaccines are an attractive choice owing to their capacity to induce robust humoral and cellular immune responses at low doses and because they can be developed and manufactured rapidly to more effectively meet the threat of an influenza epidemic or pandemic. Particle-mediated epidermal delivery (PMED), or the gene gun, is a DNA vaccine delivery technology shown to induce protective levels of antibody and T-cell responses in animals and humans against a wide variety of diseases, including influenza. This review focuses on current advances toward the development of an effective PMED DNA vaccine against influenza, including strategies to enhance vaccine immunogenicity, the potential for PMED-based DNA vaccines to improve protection in the vulnerable elderly population, and the prospects for a vaccine capable of providing cross-protection against both seasonal and pandemic strains of influenza.

Preclinical and clinical progress of particle-mediated DNA vaccines for infectious diseases

This review provides an overview of studies employing particle-mediated epidermal delivery (PMED) or the gene gun to administer DNA vaccines for infectious diseases in preclinical studies employing large animal models and in human clinical trials. It reviews the immunogenicity and protective efficacy of PMED DNA vaccines in nonhuman primates and swine and studies that have directly compared the effectiveness of PMED in these large animal models to existing licensed vaccines and intramuscular or intradermal delivery of DNA vaccines with a needle. Various clinical trials employing PMED have been completed and an overview of the immunogenicity, safety, and tolerability of this approach in humans is described. Finally, efforts currently in progress for commercial development of particle-mediated DNA vaccines are discussed.

Advanced Techniques in the Diagnosis and Management of Infectious Pulmonary Diseases in Horses

Techniques for novel approaches to the diagnosis and management of equine pulmonary disease continue to be developed and used in clinical practice. Diagnostic techniques involving immunoassays and nucleic acid-based tests not only decrease the time in which results become available but increase the sensitivity and specificity of test results. These assays do not substitute for careful clinical evaluation but can shorten the time to a confirmed accurate diagnosis, and thus allow for early initiation of therapeutic strategies and prevention protocols. With further understanding of the molecular biology and immunology of equine pulmonary disease, diagnostic and management techniques should become further refined.

Epidermal powder immunization against influenza

Epidermal powder immunization (EPI) can efficiently deliver powdered protein vaccines to the epidermis. A phase I clinical trial was conducted to evaluate powdered trivalent influenza vaccine delivered using the PowderJect ND5.2 delivery system. Subjects received either Fluvirin IM injection (15 microg of each influenza strain), a single EPI vaccination (15 microg of each influenza strain) or two adjacent EPI (total of 30 microg of each influenza strain). Systemic reactogenicity was similar between control and EPI vaccines. Site reactions following EPI were primarily mild and self-limiting. Seroconversions, titer increases and geometric mean titers to all strains were equivalent or higher in EPI-immunized groups than in controls. Powdered influenza vaccine delivered by EPI is safe and elicits humoral immune responses in humans.

A Library-Selected, Langerhans Cell-Targeting Peptide Enhances an Immune Response

The ability to deliver antigens and immunomodulators specifically to Langerhans cells (LCs) in the skin could impact vaccine development. However, cell-specific targeting of therapeutic molecules remains a challenge in biomedicine. Using phage display technologies, we have developed a protocol that identifies peptides that mediate uptake into target cell types. Employing this approach, we have isolated a 20-mer peptide that mediates specific uptake by immunopotent LCs. The peptide is functional outside the context of the phage and is able to deliver a nanoparticle to LCs in vitro. Although selected on cells in vitro, the peptide is able to direct antigens and genes to LCs in vivo. Liposomes bearing the LC targeting peptide are able to deliver a transcriptionally active gene to LCs in a mouse model. Furthermore, we demonstrate that a low-dose injection into mice of phage bearing the LC-targeting peptide yields faster and higher immune responses against phage-associated antigens than control-phage injections.

Enhancement of the effectiveness of electroporation-augmented cutaneous DNA vaccination by a particulate adjuvant

DNA vaccines are attracting increased attention due to multiple advantages over conventional vaccines. Attempts to improve these vaccines focus on enhancing DNA delivery and employing novel immunoadjuvants. Electroporation (EP) has emerged as an effective method for delivering DNA vaccines, significantly enhancing humoral and cellular responses. To further improve EP-augmented DNA vaccination, we used micron-size gold particles as a particulate adjuvant. DNA is not bound, or adsorbed, to the particles. Gold particles were coinjected intradermally with plasmid DNA encoding the hepatitis B virus surface antigen (HBsAg) into mice, both in the absence and presence of noninvasive EP. The particles enhanced the percentage of responding animals, and shortened the time for reaching maximal antibody titers by 2 weeks. Subtyping of the produced antibodies revealed a predominantly Th1-like response which did not change significantly with the absence or presence of particles. The particles likely function as an attractant for antigen-presenting cells (APCs), and probably do not affect EP or antigen expression to a significant extent. We conclude that micron-size gold particles injected intradermally together with DNA followed by EP give rise to an accelerated, potent immune response with a strong cellular component. This method may become important for the development of fast-acting therapeutic and prophylactic vaccines.

Gene transfer into human keloid tissue with adeno-associated virus vector

BACKGROUND Gene transfer is a new territory for clinicians. Intractable disorders might be approached in such a way. Adeno-associated virus (AAV) vector has been transfected successfully into a variety of tissues including skin. We evaluated the ability of this vector to transfer and cause expression of the reporter gene in human keloid tissue. METHODS Human keloid specimens were injected with an AAV vector encoding beta-galactosidase and incubated for 4 weeks after injection. The presence of mRNA and beta-galactosidase enzymatic activity were assayed by reverse-transcriptase polymerase chain reaction and the X-gal technique. RESULTS Gene expression shown by reverse-transcriptase polymerase chain reaction was observed in keloid tissue 4 weeks after injection, and so was the positive X-gal staining. CONCLUSION Our results showed that AAV vector could transduce human keloid tissue effectively. Replacement of the reporter gene with a functioning gene might be feasible for keloid treatment.

Enhanced delivery of naked DNA to the skin by non-invasive in vivo electroporation

DNA delivery to skin may be useful for the treatment of skin diseases, DNA vaccinations, and other gene therapy applications requiring local or systemic distribution of a transgene product. However, the effective, consistent and patient-friendly transfection of skin cells remains a challenge. In a mouse model, we evaluated the effectiveness of intradermal injection of plasmid DNA followed by noninvasive in vivo electroporation (EP) as a method to improve transfection in skin. We achieved a several hundred-fold stimulation of gene expression by EP, sufficient to produce clinically relevant amounts of transgene product. We studied the effect of DNA dose and time after treatment as well as various EP pulse parameters on the efficiency of gene expression. EP under conditions of constant charge transfer revealed that the applied voltage was the main determinant for transgene expression efficiency while other pulse parameters had lesser effects. Patient-friendly, noninvasive meander electrodes which we designed for clinical applications proved equally effective and safe as plate electrodes. We also showed for the first time that noninvasive EP is effective in stimulating transfection and gene expression in human skin, particularly in the epidermis. Our findings demonstrate the applicability of EP-enhanced DNA delivery to skin for gene therapy, DNA immunization and other areas.

Intra-epithelial vaccination with COPV L1 DNA by particle-mediated DNA delivery protects against mucosal challenge with infectious COPV in beagle dogs

Protection against viral challenge with canine oral papillomavirus (COPV) was achieved by immunisation via particle-mediated DNA delivery (PMDD) of a plasmid encoding the COPV L1 gene to cutaneous and oral mucosal sites in beagle dogs. The initial dose of approximately 9 microg of DNA was followed by two booster doses at 6 week intervals. A similar approach was used to vaccinate a control group of animals with plasmid DNA encoding the Hepatitis B virus S gene. Following challenge at the oral mucosa with COPV all animals vaccinated with the COPV L1 gene were protected against disease. However five of six animals in the control group developed COPV induced papillomas at the oral mucosa. Both cell-mediated lymphoproliferative and humoral antibody responses to the DNA vaccine were observed. Our data indicate that PMDD of plasmid DNA can protect against mucosal challenge with papillomavirus.

Direct transfection and activation of human cutaneous dendritic cells

Gene therapy techniques can be important tools for the induction and control of immune responses. Antigen delivery is a critical challenge in vaccine design, and DNA-based immunization offers an attractive method to deliver encoded transgenic protein antigens. In the present study, we used a gene gun to transfect human skin organ cultures with a particular goal of expressing transgenic antigens in resident cutaneous dendritic cells. Our studies demonstrate that when delivered to human skin, gold particles are observed primarily in the epidermis, even when high helium delivery pressures are used. We demonstrate that Langerhans cells resident in the basal epidermis can be transfected, and that biolistic gene delivery is sufficient to stimulate the activation and migration of skin dendritic cells. RT-PCR analysis of dendritic cells, which have migrated from transfected skin, demonstrates the presence of transgenic mRNA, indicating direct transfection of cutaneous dendritic cells. Importantly, transfected epidermal Langerhans cells can efficiently present a peptide derived from the transgenic melanoma antigen MART-1 to a MART-1-specific CTL. Taken together, our results demonstrate direct transfection, activation, and antigen-specific stimulatory function of in situ transduced human Langerhans cells.

Cutaneous transfection and immune responses to intradermal nucleic acid vaccination are significantly enhanced by in vivo electropermeabilization

Naked DNA injection with electropermeabilization (EP) is a promising method for nucleic acid vaccination (NAV) and in vivo gene therapy. Skin is an ideal target for NAV due to ease of administration and the accessibility of large numbers of antigen-presenting cells within the tissue. This study demonstrates that in vivo skin EP may be used to increase transgene expression up to an average of 83-fold relative to naked DNA injection (50 microg DNA per dose, P < 0.005). Transfected cells were principally located in dermis and included adipocytes, fibroblasts, endothelial cells, and numerous mononuclear cells with dendritic processes in a porcine model. Transfected cells were also observed in lymph nodes draining electropermeabilized sites. A HBV sAg-coding plasmid was used to test skin EP-mediated NAV in a murine model. Analysis of humoral immune responses including immunoglobulin subclass profiles revealed strong enhancement of EP-mediated NAV relative to naked DNA injection, with a Th1-dominant, mixed-response pattern compared to immunization with HBV sAg protein that was exclusively Th2 (P = 0.02). Applications for these findings include NAV-based modulation of immune responses to pathogens, allergens, and tumor-associated antigens and the modification of tolerance.

Virus-mediated gene transfer for cutaneous gene therapy

Cutaneous gene therapy offers unique opportunities and limitations in the use of viral vectors for corrective gene transfer. Skin presents a formidable barrier to microbial invasion and is nourished by small blood vessels, thus ruling out the possibility of directed virus delivery through cannulated blood vessels. However, skin is physically accessible and its resident keratinocyte stem cell population is susceptible to direct in vivo transduction with retroviral vectors. Furthermore, keratinocyte stem cells transduced in culture have been shown to persist and to express the encoded transgene when grafted to immunocompromised mice. Cutaneous gene therapy trials are likely to involve virus-mediated transduction as a principal means of gene transfer.

Nonviral skin gene therapy

Nonviral skin gene therapy is an effective method to directly deliver and transiently express genes in the skin. Several different nonviral delivery methods have been successfully used and are analyzed here for their efficiency and efficacy in achieving specific therapeutic applications. For one important and frequently used application of nonviral skin gene therapy, genetic immunization, the types of resulting immune responses (Th1 versus Th2) will depend on which delivery method is used. In addition, we discuss the contributions of DNA as an immunostimulatory adjuvant in genetic immunization and how activation of skin dendritic cells and induction of IL-12 expression are mechanistically important in this process. Nonviral skin gene therapy has also been successfully used to enhance tumor regression in animal models, frequently by inducing a specific immune response against the tumor. In the future, nonviral skin gene therapy may be successfully used for the treatment of additional skin diseases if genes can be selectively delivered and expressed in specific skin cells, and if increased level and duration of gene expression can be achieved.

Gene gun-mediated DNA immunization primes development of mucosal immunity against bovine herpesvirus 1 in cattle

Vaccination by a mucosal route is an excellent approach to the control of mucosally acquired infections. Several reports on rodents suggest that DNA vaccines can be used to achieve mucosal immunity when applied to mucosal tissues. However, with the exception of one study with pigs and another with horses, there is no information on mucosal DNA immunization of the natural host. In this study, the potential of inducing mucosal immunity in cattle by immunization with a DNA vaccine was demonstrated. Cattle were immunized with a plasmid encoding bovine herpesvirus 1 (BHV-1) glycoprotein B, which was delivered with a gene gun either intradermally or intravulvomucosally. Intravulvomucosal DNA immunization induced strong cellular immune responses and primed humoral immune responses. This was evident after BHV-1 challenge when high levels of both immunoglobulin G (IgG) and IgA were detected. Intradermal delivery resulted in lower levels of immunity than mucosal immunization. To determine whether the differences between the immune responses induced by intravulvomucosal and intradermal immunizations might be due to the efficacy of antigen presentation, the distributions of antigen and Langerhans cells in the skin and mucosa were compared. After intravulvomucosal delivery, antigen was expressed early and throughout the mucosa, but after intradermal administration, antigen expression occurred later and superficially in the skin. Furthermore, Langerhans cells were widely distributed in the mucosal epithelium but found primarily in the basal layers of the epidermis of the skin. Collectively, these observations may account for the stronger immune response induced by mucosal administration.

IL-12-Dependent enhancement of CTL response to weak class I-restricted peptide immunogens requires coimmunization with T helper cell immunogens

The effect of in vivo administration of rmIL-12 on the CTL response to immunization with a weakly immunogenic class I-restricted peptide emulsified in incomplete Freund's adjuvant was investigated. In the absence of IL-12, peptide-specific CTL responses were significantly greater following coimmunization with class I-restricted peptide and T helper cell antigens than following immunization with the class I-restricted peptide alone. IL-12-dependent enhancement of the CTL response to peptide immunization was demonstrated in the presence of, but not in the absence of, coimmunization with T helper cell antigen. These findings indicate that IL-12 enhancement of the CTL response to weak class I-restricted immunogens is T helper cell dependent. Treatment with rmIL-12 also enhanced the CTL response to immunization with cDNA encoding both CTL and T helper cell epitopes. These findings are relevant to the design of vaccines containing tumor-associated class I-restricted peptides currently being tested as an immunotherapy for cancer patients.

Cutaneous gene therapy. Principles and prospects

As investigators continue to close the gap between basic research and clinical science, gene therapy is becoming of increasing interest to the dermatologist. Most notably, recent advances in gene-based cancer therapy, DNA vaccination, and molecular pharmacology have opened new avenues for investigation beyond those of the traditional gene replacement applications. Different gene delivery systems are currently being tested, each with specific advantages and disadvantages. This article summarizes some of the principles of gene therapy and its applications to cutaneous diseases.