An epoch-making application of discharge plasma phenomenon to gene-transfer

Low-Temperature Plasma Techniques in Biomedical Applications and Therapeutics: An Overview

Plasma, the fourth fundamental state of matter, comprises charged species and electrons, and it is a fascinating medium that is spread over the entire visible universe. In addition to that, plasma can be generated artificially under appropriate laboratory techniques. Artificially generated thermal or hot plasma has applications in heavy and electronic industries; however, the non-thermal (cold atmospheric or low temperature) plasma finds its applications mainly in biomedicals and therapeutics. One of the important characteristics of LTP is that the constituent particles in the plasma stream can often maintain an overall temperature of nearly room temperature, even though the thermal parameters of the free electrons go up to 1 to 10 keV. The presence of reactive chemical species at ambient temperature and atmospheric pressure makes LTP a bio-tolerant tool in biomedical applications with many advantages over conventional techniques. This review presents some of the important biomedical applications of cold-atmospheric plasma (CAP) or low-temperature plasma (LTP) in modern medicine, showcasing its effect in antimicrobial therapy, cancer treatment, drug/gene delivery, tissue engineering, implant modifications, interaction with biomolecules, etc., and overviews some present challenges in the field of plasma medicine.

Combined effect of heat and corona charge on molecular delivery to a T cell line in vitro

With the rapid increase of gene and immunotherapies for treating cancer, there is a need to efficiently transfect cells. Previous studies suggest that electrotransfer can provide a non-viral method for gene delivery. Electrotransfer traditionally relies upon the application of direct current pulses to the cells of interest. Corona charge was investigated in this study as an alternative to traditional methods as a means of creating the electric field necessary to deliver materials via electrotransfer. The goal was to determine if there was an increase in molecular delivery across the membrane of a human T cell line used as a model system. In a novel dish created for the study, the effects of elevated temperatures (37, 40, 43, and 45°C) during the treatment process were also examined in combination with corona charge application. Results showed that treating cells with corona charge at room temperature (~23°C) caused a statistically significant increase in molecular delivery while maintaining viability. Heat alone did not cause a statistically significant effect on molecular delivery. Combined corona charge treatment and heating resulted in a statistically significant increase on molecular delivery compared to controls that were only heated. Combined corona charge treatment and heating to all temperatures when compared to controls treated at room temperature, showed a statistically significant increase in molecular delivery.

Cold atmospheric plasma mediated cell membrane permeation and gene delivery-empirical interventions and pertinence

Delivery of genetic material to cells is an integral tool to analyze and reveal the genetic interventions in normal cellular processes and differentiation, disease development and for gene therapy. It has profound applications in pharmaceutical, agricultural, environmental and biotechnological sectors. The major methods relied for gene delivery or transfection requires either viral vectors or xenogenic carrier molecules, which renders probabilistic carcinogenic, immunogenic and toxic effects. A newly evolved physical method, Cold atmospheric plasma induced transfection neither needs vector nor carriers. The 4th state of matter 'Plasma' is a quasineutral ionized gas-containing ions, neutral atoms, electrons and reactive radical molecules; and possess electric and magnetic field, along with emanating photons and UV radiations. Plasma produced at atmospheric pressure conditions, and having room temperature is conferred as Low temperature plasma or Cold atmospheric plasma. Selective and controlled application of cold atmospheric plasma on tissues creates temporary, restorable pores on cell membranes that could be diligently manipulated for gene delivery. Research in this regard attained pace since 2016. Cold atmospheric plasma induces transfection by lipid peroxidation, electroporation, and clathrin dependent endocytosis in cell membranes, by virtue of its reactive radicals and electric field. Plasma formed reactive radicals, especially 'OH' penetrates to the cell membrane and cleaves the phosphate head group of membrane lipids, peroxidize and detaches fatty acid tails. This decreases membrane thickness, increases membrane fluidity and permeability. Simultaneously plasma formed ions, electrons and reactive radicals accumulate over cells, generating local electric field and neutralize the negative charge of cell membrane. This induces stress on cell membrane and disrupts its structural integrity, by infringing the dynamic equilibrium between surface tension, spatial repulsion and linear tension between the head groups of phospholipids, generating minute pores. Neutralization of membrane charge promote foreign, external plasmid and gene movement towards cells and its enhanced binding with ligands and receptors on cell membrane, instigating clathrin dependent endocytosis. In vitro and in vivo studies have successfully delivered plasmids, linear DNA, siRNA and miRNA to several established cell lines like, HeLa, PC12, CHL, HUVEC, Jurkat, MCF, SH-SY5Y, HT, B16F10, HaCaT, LP-1, etc., and live C57BL/6 and BALB/c mice, using cold atmospheric plasma. This review delineates the cell surface mechanism of plasma-induced transfection, critically summarizes the research progress in this context, plasma devices used, and the inimitable features of this method. Metabolic activity, cell function, and viability are not adversely affected by this process; moreover, the cell permeating plasma-formed reactive radicals are effectively defended by cellular antioxidant mechanisms like superoxide dismutase, glutathione reductase and cytokines, alleviating its toxicity. A deeper understanding on mechanism of plasma action on cells, its aftermath, and the research status in this field would provide a better insight on future avenues of research.

Understanding the Role of Plasma Bullet Currents in Heating Skin to Mitigate Risks of Thermal Damage Caused by Low-Temperature Atmospheric-Pressure Plasma Jets

Low-temperature atmospheric-pressure plasma jets are generally considered a safe medical technology with no significant long-term side effects in clinical studies reported to date. However, there are studies emerging that show plasma jets can cause significant side effects in the form of skin burns under certain conditions. Therefore, with a view of developing safer plasma treatment approaches, in this study we have set out to provide new insights into the cause of these skin burns and how to tailor plasma treatments to mitigate these effects. We discovered that joule heating by the plasma bullet currents is responsible for creating skin burns during helium plasma jet treatment of live mice. These burns can be mitigated by treating the mice at a further distance so that the visible plasma plume does not contact the skin. Under these treatment conditions we also show that the plasma jet treatment still retains its medically beneficial property of producing reactive oxygen species in vivo. Therefore, treatment distance is an important parameter for consideration when assessing the safety of medical plasma treatments.

Delivery and expression of plasmid DNA into cells by a novel non-thermal plasma source

Medical applications such as plasma assisted gene transfer is a minimally invasive approach that can substantially reduce potential discomfort of treated area. Atmospheric pressure plasma discharge is an effective approach to deliver plasmid DNA for in vitro and in vivo applications. We investigated plasma assisted delivery in vitro in mouse melanoma cells (B16F10) using a novel surface plasma device, which is operated in air. We evaluated the influence of applied voltage and distance between the surface device and cell monolayer. We found no significant effect on the viability of cells. Highest expression following delivery of a plasmid encoding green fluorescent protein was achieved with an applied voltage of 11.25 kV at a 2 mm distance and 5 s exposure time. To better understand the influence of oxidative damages and stress on cells after plasma delivery, a mRNA expression study was performed. Our results indicated that TNFα mRNA was significantly upregulated. The mRNA response may be attributed to the RONS generated by plasma; however, this mRNA upregulation was not adequate to be reflected in a coordinate protein upregulation. From the results reported here, it is clear that this novel plasma device could be used for plasmid delivery.

Clarification of electrical current importance in plasma gene transfection by equivalent circuit analysis

We have been developing a method of plasma gene transfection that uses microdischarge plasma (MDP) and is highly efficient, minimally invasive, and safe. Using this technique, electrical factors (such as the electrical current and electric field created through processing discharge plasma) and the chemical factors of active species and other substances focusing on radicals are supplied to the cells and then collectively work to introduce nucleic acids in the cell. In this paper, we focus on the electrical factors to identify whether the electric field or electrical current is the major factor acting on the cells. More specifically, we built a spatial distribution model that uses an electrical network to represent the buffer solution and cells separately, as a substitute for the previously reported uniform medium model (based on the finite element method), calculated the voltage and electrical current acting on cells, and examined their intensity. Although equivalent circuit models of single cells are widely used, this study was a novel attempt to build a model wherein adherent cells distributed in two dimensions were represented as a group of equivalent cell circuits and analyzed as an electrical network that included a buffer solution and a 96-well plate. Using this model, we could demonstrate the feasibility of applying equivalent circuit network analysis to calculate electrical factors using fewer components than those required for the finite element method, with regard to electrical processing systems targeting organisms. The results obtained through this equivalent circuit network analysis revealed for the first time that the distribution of voltage and current applied to a cellular membrane matched the spatial distribution of experimentally determined gene transfection efficiency and that the electrical current is the major factor contributing to introduction.

New insights on molecular internalization and drug delivery following plasma jet exposures

In this study, we evaluated cold atmospheric plasmas as a physical drug delivery tool for human cervical cancer HeLa cells and murine breast carcinoma 4T1 cells. Different cell exposure protocols - plasma jet, plasma treated medium, and combinations of plasma-induced electric field and plasma treated medium- have been proposed and assessed to provide new insight on plasma-induced uptake mechanism. Cell culture medium composition and volume are key parameters to achieve an efficient molecular uptake. The plasma device enabled the delivery of molecules having 150 kDa-size into 4T1cells. For the first time to our knowledge, substance uptake kinetics after plasma treatment were investigated. The percentage of positive cells for propidium iodide and an anti-cancer agent, doxorubicin, was higher when the drugs were added a few minutes after treatment. The Plasma treated medium was not found to be as efficient as direct plasma treatment in 4T1 cells while allowing an efficient delivery in HeLa cells. Uptake levels as high as 39.3 ± 2.9% and 40.1 ± 9.5% for HeLa and 4 T1 cells respectively were achieved for optimized operating conditions, for which the viability of the cells was not severely affected. We also observed that plasma treatment induced the formation of actin stress fibers into cells revealing a mechanical stress.

Effects of low temperature plasmas and plasma activated waters on Arabidopsis thaliana germination and growth

Two plasma devices at atmospheric pressure (air dielectric barrier discharge and helium plasma jet) have been used to study the early germination of Arabidopsis thaliana seeds during the first days. Then, plasma activated waters are used during the later stage of plant development and growth until 42 days. The effects on both testa and endospserm ruptures during the germination stage are significant in the case of air plasma due to its higher energy and efficiency of producing reactive oxygen species than the case of helium plasma. The latter has shown distinct effects only for testa rupture. Analysis of germination stimulations are based on specific stainings for reactive oxygen species production, peroxidase activity and also membrane permeability tests. Furthermore, scanning electron microscopy (SEM) has shown a smoother seed surface for air plasma treated seeds that can explain the plasma induced-germination. During the growth stage, plants were watered using 4 kinds of water (tap and deionized waters activated or not by the low temperature plasma jet). With regards to other water kinds, the characterization of the tap water has shown a larger conductivity, acidity and concentration of reactive nitrogen and oxygen species. Only the tap water activated by the plasma jet has shown a significant effect on the plant growth. This effect could be correlated to reactive nitrogen species such as nitrite/nitrate species present in plasma activated tap water.

Tracking the Penetration of Plasma Reactive Species in Tissue Models

Electrically generated cold atmospheric plasma is being intensively researched for novel applications in biology and medicine. Significant attention is being given to reactive oxygen and nitrogen species (RONS), initially generated upon plasma-air interactions, and subsequently delivered to biological systems. Effects of plasma exposure are observed to millimeter depths within tissue. However, the exact nature of the initial plasma-tissue interactions remains unknown, including RONS speciation and delivery depth, or how plasma-derived RONS intervene in biological processes. Herein, we focus on current research using tissue and cell models to learn more about the plasma delivery of RONS into biological environments. We argue that this research is vital in underpinning the knowledge required to realize the full potential of plasma in biology and medicine.

Membrane Oxidation in Cell Delivery and Cell Killing Applications

Cell delivery or cell killing processes often involve the crossing or disruption of cellular membranes. We review how, by modifying the composition and properties of membranes, membrane oxidation can be exploited to enhance the delivery of macromolecular cargoes into live human cells. We also describe how membrane oxidation can be utilized to achieve efficient killing of bacteria by antimicrobial peptides. Finally, we present recent evidence highlighting how membrane oxidation is intimately engaged in natural biological processes such as antigen delivery in dendritic cells and in the killing of bacteria by antimicrobial peptides. Overall, the insights that have been recently gained in this area should facilitate the development of more effective delivery technologies and antimicrobial therapeutic approaches.

Direct Current Helium Plasma for In vivo Delivery of Plasmid DNA Encoding Erythropoietin to Murine Skin

The use of electric fields in vivo to deliver DNA, called electroporation, has the potential to broadly impact vaccination and disease treatment. The evidence for this has emerged from a large number of recently completed and ongoing clinical trials. The methods for applying electric fields to tissues traditionally involve contact between metal electrodes and the tissue. In this study, we investigated the use of helium plasma as a noncontact method for electrically treating tissue in a manner that results in the uptake and expression of foreign DNA in murine skin. More specifically, our goal was to demonstrate that DNA encoding a model-secreted protein could be delivered, detected in the blood, and remain functional to produce its known biological effect. Murine erythropoietin (EPO) was the model-secreted protein. Results clearly demonstrated that an intradermal DNA injection followed by plasma treatment for 2 min resulted in elevated levels of EPO in the blood and corresponding hemoglobin increases that were statistically significant relative to DNA injection alone.

Intracellular ROS mediates gas plasma-facilitated cellular transfection in 2D and 3D cultures

This study reports the potential of cold atmospheric plasma (CAP) as a versatile tool for delivering oligonucleotides into mammalian cells. Compared to lipofection and electroporation methods, plasma transfection showed a better uptake efficiency and less cell death in the transfection of oligonucleotides. We demonstrated that the level of extracellular aqueous reactive oxygen species (ROS) produced by gas plasma is correlated with the uptake efficiency and that this is achieved through an increase of intracellular ROS levels and the resulting increase in cell membrane permeability. This finding was supported by the use of ROS scavengers, which reduced CAP-based uptake efficiency. In addition, we found that cold atmospheric plasma could transfer oligonucleotides such as siRNA and miRNA into cells even in 3D cultures, thus suggesting the potential for unique applications of CAP beyond those provided by standard transfection techniques. Together, our results suggest that cold plasma might provide an efficient technique for the delivery of siRNA and miRNA in 2D and 3D culture models.

Nanopore formation process in artificial cell membrane induced by plasma-generated reactive oxygen species

We investigated morphological change of an artificial lipid bilayer membrane induced by oxygen radicals which were generated by non-equilibrium atmospheric pressure plasma. Neutral oxygen species, O((3)Pj) and O2((1)Δg), were irradiated of a supported lipid bilayer existing under a buffer solution at various conditions of dose time and distances, at which the dose amounts of the oxygen species were calculated quantitatively. Observation using an atomic force microscope and a fluorescence microscope revealed that dose of the neutral oxygen species generated nanopores with the diameter of 10-50 nm in a phospholipid bilayer, and finally destructed the bilayer structure. We found that protrusions appeared on the lipid bilayer surface prior to the formation of nanopores, and we attributed the protrusions to the precursor of the nanopores. We propose a mechanism of the pore formation induced by lipid oxidation on the basis of previous experimental and theoretical studies.

Investigation of plasma induced electrical and chemical factors and their contribution processes to plasma gene transfection

This study has been done to know what kind of factors in plasmas and processes on cells induce plasma gene transfection. We evaluated the contribution weight of three groups of the effects and processes, i.e. electrical, chemical and biochemical ones, inducing gene transfection. First, the laser produced plasma (LPP) was employed to estimate the contribution of the chemical factors. Second, liposomes were fabricated and employed to evaluate the effects of plasma irradiation on membrane under the condition without biochemical reaction. Third, the clathrin-dependent endocytosis, one of the biochemical processes was suppressed. It becomes clear that chemical factors (radicals and reactive oxygen/nitrogen species) do not work by itself alone and electrical factors (electrical current, charge and field) are essential to plasma gene transfection. It turned out the clathrin-dependent endocytosis is the process of the transfection against the 60% in all the transfected cells. The endocytosis and electrical poration are dominant in plasma gene transfection, and neither permeation through ion channels nor chemical poration is dominant processes. The simultaneous achievement of high transfection efficiency and high cell survivability is attributed to the optimization of the contribution weight among three groups of processes by controlling the weight of electrical and chemical factors.

The effects of cold atmospheric plasma on cell adhesion, differentiation, migration, apoptosis and drug sensitivity of multiple myeloma

Cold atmospheric plasma was shown to induce cell apoptosis in numerous tumor cells. Recently, some other biological effects, such as induction of membrane permeation and suppression of migration, were discovered by plasma treatment in some types of tumor cells. In this study, we investigated the biological effects of plasma treatment on multiple myeloma cells. We detected the detachment of adherent myeloma cells by plasma, and the detachment area was correlated with higher density of hydroxyl radical in the gas phase of the plasma. Meanwhile, plasma could promote myeloma differentiation by up-regulating Blimp-1 and XBP-1 expression. The migration ability was suppressed by plasma treatment through decreasing of MMP-2 and MMP-9 secretion. In addition, plasma could increase bortezomib sensitivity and induce myeloma cell apoptosis. Taking together, combination with plasma treatment may enhance current chemotherapy and probably improve the outcomes.

Short and long time effects of low temperature Plasma Activated Media on 3D multicellular tumor spheroids

This work investigates the regionalized antiproliferative effects of plasma-activated medium (PAM) on colon adenocarcinoma multicellular tumor spheroid (MCTS), a model that mimics 3D organization and regionalization of a microtumor region. PAM was generated by dielectric barrier plasma jet setup crossed by helium carrier gas. MCTS were transferred in PAM at various times after plasma exposure up to 48 hours and effect on MCTS growth and DNA damage were evaluated. We report the impact of plasma exposure duration and delay before transfer on MCTS growth and DNA damage. Local accumulation of DNA damage revealed by histone H2AX phosphorylation is observed on outermost layers and is dependent on plasma exposure. DNA damage is completely reverted by catalase addition indicating that H₂O₂ plays major role in observed genotoxic effect while growth inhibitory effect is maintained suggesting that it is due to others reactive species. SOD and D-mannitol scavengers also reduced DNA damage by 30% indicating that and OH^* are involved in H₂O₂ formation. Finally, PAM is able to retain its cytotoxic and genotoxic activity upon storage at +4 °C or −80 °C. These results suggest that plasma activated media may be a promising new antitumor strategy for colorectal cancer tumors.

Improvement of cell membrane permeability using a cell-solution electrode for generating atmospheric-pressure plasma

The cell membrane permeability, which is strongly related to gene transfection, is improved using a cell-solution electrode for generating atmospheric-pressure plasma (APP) just above the solution. In the case of the floating cells, the cell membrane permeability is significantly improved by the cell-solution electrode APP compared with the conventional diffusion type APP, because the distance between the plasma generation area and the cell solution surface becomes short, which could reduce the radial diffusion loss of the plasma irradiated to the cell suspended solution. In the case of the adherent cells, cell membrane permeability is found to be enhanced by the shorter distance between the solution surface and the adherent cells as well as using the cell-solution electrode, which means that the short-lived reactive oxygen species generated at the solution surface are essential for the improvement of cell membrane permeability.

Area-specific cell stimulation via surface-mediated gene transfer using apatite-based composite layers

Surface-mediated gene transfer systems using biocompatible calcium phosphate (CaP)-based composite layers have attracted attention as a tool for controlling cell behaviors. In the present study we aimed to demonstrate the potential of CaP-based composite layers to mediate area-specific dual gene transfer and to stimulate cells on an area-by-area basis in the same well. For this purpose we prepared two pairs of DNA–fibronectin–apatite composite (DF-Ap) layers using a pair of reporter genes and pair of differentiation factor genes. The results of the area-specific dual gene transfer successfully demonstrated that the cells cultured on a pair of DF-Ap layers that were adjacently placed in the same well showed specific gene expression patterns depending on the gene that was immobilized in theunderlying layer. Moreover, preliminary real-time PCR results indicated that multipotential C3H10T1/2 cells may have a potential to change into different types of cells depending on the differentiation factor gene that was immobilized in the underlying layer, even in the same well. Because DF-Ap layers have a potential to mediate area-specific cell stimulation on their surfaces, they could be useful in tissue engineering applications.

Optimization of a plasma facilitated DNA delivery method

Plasma-based methods have recently emerged as a technique for augmenting plasmid DNA delivery to skin. This delivery modality relies on the deposition of ionized gas molecules on to targeted cells or tissue to establish an electric field. It is hypothesized that this electric field results in the dielectric breakdown of cell membranes, making cells permeable to exogenous molecules. This in vivo investigation sought to optimize the intradermal delivery of a luciferase expressing plasmid DNA by modulating the total exposure to the plasma source and the plasmid DNA dose. Varying the plasma exposure time from 2, 5, 10, and 20 min allowed the conditions resulting in the highest expression of luciferase to be found. These conditions correlated to the 10 minute exposure time for a plasma derived from either +8 kV or -8 kV, when the generator was operated 3 cm from the epidermal tissue surface with a helium flow rate of 15 L/min. Exposing the injected flank skin for 10 min resulted in a rise of 37.3-fold for a plasma created with +8 kV and 27.1-fold for a plasma created with -8 kV. When using this treatment time with 50, 100, or 200 μg of a luciferase expressing plasmid, it was found that 100 μg resulted in the highest peak luminescence.

Electrogenetherapy of B16.F10 murine melanoma tumors with an interleukin-28 expressing DNA plasmid

Augmented delivery of cytokine-expressing DNA plasmids to subcutaneous tumors has been demonstrated to result in a level of enhanced anti-tumor activity. One delivery enhancement method which has been evaluated is in vivo electroporation (EP), a contact-dependent delivery technique where electric pulses are hypothesized to augment the transfer of DNA into cells and tissues through the induction of temporary cell membrane pores. Previous work by members of our group, as well as others, has demonstrated the anti-tumor effects of DNA plasmids expressing the cytokines IL-12 and IL-15. In this report the potential anti-tumor activity of a relatively newly-described cytokine, IL-28, was measured when administered intratumorally as a DNA expression plasmid (designated pIL28) to established murine (B16.F10) melanoma tumors. The administration of the IL-28 expressing plasmid was performed through enhanced delivery methods. One method was EP and the other a non-contact dependent technique using a helium plasma stream. IL-28 is a member of the type III interferon family of cytokines that has been characterized as possessing potent anti-viral activity. This cytokine has been demonstrated to function as an adjuvant in small animal model vaccination protocols and stimulates CD8+ CTL responses. In addition, stimulation of anti-tumor activity has been demonstrated in several studies using IL-28. Based on these activities, it was hypothesized that this cytokine could, when delivered through a DNA expression plasmid, mediate anti-tumor activity. The results of this study indicated that enhanced delivery of pIL-28 resulted in attenuation of tumor growth, compared with non-enhanced delivery. Of note, this is the first proof-of-concept experiment, of our knowledge, documenting the ability of a non-contact dependent helium plasma-based delivery method to mediate the enhancement of an anti-tumor effect by a cytokine-expressing DNA plasmid. This suggests the use of the helium plasma delivery method as an alternative or adjunctive method to EP for the effective delivery of agents that possess potential anti-tumor activity.

Non-contact helium-based plasma for delivery of DNA vaccines. Enhancement of humoral and cellular immune responses

Non-viral in vivo administration of plasmid DNA for vaccines and immunotherapeutics has been hampered by inefficient delivery. Methods to enhance delivery such as in vivo electroporation (EP) have demonstrated effectiveness in circumventing this difficulty. However, the contact-dependent nature of EP has resulting side effects in animals and humans. Noncontact delivery methods should, in principle, overcome some of these obstacles. This report describes a helium plasma-based delivery system that enhanced humoral and cellular antigen-specific immune responses in mice against an intradermally administered HIV gp120-expressing plasmid vaccine (pJRFLgp120). The most efficient plasma delivery parameters investigated resulted in the generation of geometric mean antibody-binding titers that were 19-fold higher than plasmid delivery alone. Plasma mediated delivery of pJRFLgp120 also resulted in a 17-fold increase in the number of interferon-gamma spot-forming cells, a measure of CD8+ cytotoxic T cells, compared with non-facilitated plasmid delivery. This is the first report demonstrating the ability of this contact-independent delivery method to enhance antigen-specific immune responses against a protein generated by a DNA vaccine.

Enhancement of antigen specific humoral immune responses after delivery of a DNA plasmid based vaccine through a contact-independent helium plasma

Non-viral in vivo delivery of DNA, encoding for specific proteins, has traditionally relied on chemical or physical forces applied directly to tissues. Physical methods typically involve contact between an applicator/electrode and tissue and often results in transient subject discomfort. To overcome these limitations of contact-dependent delivery, a helium plasma source was utilized to deposit ionized gasses to treatment/vaccination sites without direct contact between the applicator and the tissues. The study reported here evaluated the efficacy of this strategy as an effective method to administer DNA vaccines. Balb/C mice were vaccinated with a DNA plasmid expressing an HIVgp120 envelope glycoprotein either with or without co-administration of helium plasma or electroporation. The results indicated, for the first time, the potential efficacy of helium plasma delivery for the induction and enhancement of antigen specific immune responses following DNA vaccination.

Characterization of plasma mediated molecular delivery to cells in vitro

Ion-based strategies have recently emerged as a method to facilitate molecular delivery. These methods are attractive as they separate the applicator from the treatment site avoiding some issues encountered with other electrically driven methods. Current literature on plasma delivery has shown utility in vitro and in vivo for both drugs and genes. To advance this technology more information must become available on the mechanism responsible for delivery and the effects of ion exposure on eukaryotic cells. This in vitro investigation found that molecular delivery facilitated by a DC-based plasma follows a dose-response behavior, with optimum uptake of Sytox Green occurring in two cell lines after 600 s of exposure. In both cell lines exposure to the discharge caused no adverse effects in viability for exposure times up to 600 s. It was also found that membranes treated with ions remained permeabilized for several minutes following plasma treatment and that membrane resealing exhibited first order kinetics.

Plasma facilitated delivery of DNA to skin

Non-viral delivery of cell-impermeant drugs and DNA in vivo has traditionally relied upon either chemical or physical stress applied directly to target tissues. Physical methods typically use contact between an applicator, or electrode, and the target tissue and may involve patient discomfort. To overcome contact-dependent limitations of such delivery methodologies, an atmospheric helium plasma source was developed to deposit plasma products onto localized treatment sites. Experiments performed in murine skin showed that samples injected with plasmid DNA encoding luciferase and treated with plasma demonstrated increased levels of expression relative to skin samples that received injections of DNA alone. Increased response relative to injection alone was observed when either positive or negative voltage was used to generate the helium plasma. Quantitative results over a 26-day follow-up period showed that luciferase levels as high as 19-fold greater than the levels obtained by DNA injection alone could be achieved. These findings indicate that plasmas may compete with other physical delivery methodologies when skin is the target tissue.

A novel transfection method for mammalian cells using gas plasma

Introduction of foreign genes into target cells is a crucial step for achievement of gene therapy. We have recently developed a novel transfection system for eukaryotic cells, namely the electric pulse-activated gas plasma generator. To measure the transfection efficiency and mortality by flow-cytometry, we employed enhanced green fluorescent protein and propidium iodide staining, respectively. One day after the 1-3s plasma exposures with DNA concentration at 0.5 microg/microl, favorable transfection efficiencies (17.8-21.6%) and mortalities (0.65-2.86%) were obtained for HeLa-S3, HT-1080 and MCF-7 cells. The recipient cells became transiently permeable for plasmid DNA during the plasma exposure, suggesting that plasma-mediated transfection may involve similar mechanisms that accounts for electroporation. The relatively low mortality rates are encouraging in our attempt to apply this system to the various cell lines including the primary cell cultures.