The skin is known to be a highly immunogenic site for vaccination, but few vaccines in clinical use target skin largely because conventional intradermal injection is difficult and unreliable to perform. Now, a number of new or newly adapted delivery technologies have been shown to administer vaccine to the skin either by non-invasive or minimally invasive methods. Non-invasive methods include high-velocity powder and liquid jet injection, as well as diffusion-based patches in combination with skin abrasion, thermal ablation, ultrasound, electroporation, and chemical enhancers. Minimally invasive methods are generally based on small needles, including solid microneedle patches, hollow microneedle injections and tattoo guns. The introduction of these advanced delivery technologies can make the skin a site for simple, reliable vaccination that increases vaccine immunogenicity and offers logistical advantages to improve the speed and coverage of vaccination.

BackgroundSimple and effective vaccine administration is particularly important for annually recommended influenza vaccination. We hypothesized that vaccine delivery to the skin using a patch containing vaccine-coated microneedles could be an attractive approach to improve influenza vaccination compliance and efficacy.Methodology/Principal FindingsSolid microneedle arrays coated with inactivated influenza vaccine were prepared for simple vaccine delivery to the skin. However, the stability of the influenza vaccine, as measured by hemagglutination activity, was found to be significantly damaged during microneedle coating. The addition of trehalose to the microneedle coating formulation retained hemagglutination activity, indicating stabilization of the coated influenza vaccine. For both intramuscular and microneedle skin immunization, delivery of un-stabilized vaccine yielded weaker protective immune responses including viral neutralizing antibodies, protective efficacies, and recall immune responses to influenza virus. Immunization using un-stabilized vaccine also shifted the pattern of antibody isotypes compared to the stabilized vaccine. Importantly, a single microneedle-based vaccination using stabilized influenza vaccine was found to be superior to intramuscular immunization in controlling virus replication as well as in inducing rapid recall immune responses post challenge.Conclusions/SignificanceThe functional integrity of hemagglutinin is associated with inducing improved protective immunity against influenza. Simple microneedle influenza vaccination in the skin produced superior protection compared to conventional intramuscular immunization. This approach is likely to be applicable to other vaccines too.

Easy and effective vaccination methods could reduce mortality and morbidity due to vaccinepreventable influenza infections. In this study, we examined the use of microneedle patches to increase patient coverage through possible self administration and enhance vaccine immunogenicity by targeted delivery to skin. We carried out a detailed study of protective immune responses after a single influenza vaccination to the skin of mice with a novel microneedle patch designed to facilitate simple and reliable vaccine delivery. Skin vaccination with inactivated viruscoated microneedles provided superior protection against lethal challenge compared to intramuscular injection as evidenced by effective virus clearance in lungs. Detailed immunologic analysis suggests that induction of virus neutralizing antibodies as well as enhanced anamnestic humoral and cellular responses contributed to improved protection by microneedle vaccination to the skin. These findings suggest that vaccination in the skin using a microneedle patch can improve protective immunity, and simplify delivery of influenza and possibly other vaccines.

We have designed and fabricated a microneedle array with electrical functionality with the final goal of electroporating skin’s epidermal cells to increase their transfection by DNA vaccines. The microneedle array was made of polymethylmethacrylate (PMMA) by micromolding technology from a master PDMS mold, followed by metal deposition, patterning using laser ablation, and electrodeposition. This microneedle array possessed sufficient mechanical strength to penetrate human skin in vivo and was also able to electroporate both red blood cells and human prostate cancer cells as an in vitro model to demonstrate cell membrane permeabilization. A model to predict the effective volume for electroporation with respect to applied voltages was constructed from finite element simulation. This study demonstrates the mechanical and electrical functionalities of the first MEMS-fabricated microneedle array for electroporation, designed for DNA vaccine delivery.

In today's medical industry, the range of vaccines that exist for administration in humans represents an eclectic variety of forms and immunologic mechanisms. Namely, these are the live attenuated viruses, inactivated viruses, subunit proteins, and virus-like particles for treating virus-caused diseases, as well as the bacterial-based polysaccharide, protein, and conjugated vaccines. Currently, a new approach to vaccination is being investigated with the concept of DNA vaccines. As an alternative delivery route to enhance the vaccination efficacy, microneedles have been devised to target the rich network of immunologic antigen-presenting cells in the dermis and epidermis layers under the skin. Numerous studies have outlined the parameters of microneedle delivery of a wide range of vaccines, revealing comparable or higher immunogenicity to conventional intramuscular routes, overall level of stability, and dose-sparing advantages. Furthermore, recent mechanism studies have begun to successfully elucidate the biological mechanisms behind microneedle vaccination. This paper describes the current status of microneedle vaccine research.

Glucose-responsive glycol chitosan/sodium alginate-poly(l-glutmate-co-N-3-l-glutamylphenylboronic acid) double-layered nanogel is a promising platform for controlled insulin release systems, achieving glucose-triggered insulin release at diabetic glucose levels in vivo.

Perturbation of potassium homeostasis can affect various cell functions and lead to the onset of programmed cell death. Although ionophores have been intensively used as an ion homeostasis disturber, the mechanisms of cell death are unclear and the bioapplicability is limited. In this study, helical polypeptide‐based potassium ionophores are developed to induce endoplasmic reticulum (ER) stress‐mediated apoptosis. The polypeptide‐based potassium ionophores disturb ion homeostasis and then induce prolonged ER stress in the cells. The ER stress results in oxidative environments that accelerate the activation of mitochondria‐dependent apoptosis. Moreover, ER stress‐mediated apoptosis is triggered in a tumor‐bearing mouse model that suppresses tumor proliferation. This study provides the first evidence showing that helical polypeptide‐based potassium ionophores trigger ER stress‐mediated apoptosis by perturbation of potassium homeostasis.

The need for annual revaccination against influenza is a burden on the healthcare system, leads to low vaccination rates and makes timely vaccination difficult against pandemic strains, such as during the 2009 H1N1 influenza pandemic. In an effort toward achieving a broadly protective vaccine that provides cross-protection against multiple strains of influenza, this study developed a microneedle patch to co-immunize with A/PR8 influenza hemagglutinin DNA and A/PR8 inactivated virus vaccine. We hypothesize that this dual component vaccination strategy administered to the skin using microneedles will provide cross-protection against other strains of influenza. To test this hypothesis, we developed a novel coating formulation that did not require additional excipients to increase coating solution viscosity by using the DNA vaccine itself to increase viscosity and thereby enable thick coatings of DNA vaccine and inactivated virus vaccine on metal microneedles. Co-immunization in this way not only generated robust antibody responses against A/PR8 influenza but also generated robust heterologous antibody responses against pandemic 2009 H1N1 influenza in mice. Challenge studies showed complete cross-protection against lethal challenge with live pandemic 2009 H1N1 virus. Control experiments using A/PR8 inactivated influenza virus vaccine with placebo DNA coated onto microneedles produced lower antibody titers and provided incomplete protection against challenge. Overall, this is the first study showing DNA solution as a microneedle coating agent and demonstrating cross-protection by co-immunization with inactivated virus and DNA vaccine using coated microneedles.