Cationic microparticles: A potent delivery system for DNA vaccines

Simultaneous release of multiple molecules from poly(lactide-co-glycolide) nanoparticles assembled onto medical devices

Cell and tissue responses to implanted biomaterials often limit their effectiveness and lifetime. This is particularly true for materials implanted into the brain. We present here a new approach for the modification of materials to enable release of multiple agents, which might be useful in modulating tissue responses, without changing the properties of the underlying material, in this case, a silicon probe. Poly(lactide-co-glycolide) nanoparticles (NPs) were assembled onto silicon probe surfaces by electrostatic interactions. Charged NPs were fabricated by altering the properties of the surfactant. NPs formed with poly(ethylene-alt-maleic anhydride) (PEMA) were strongly negatively charged; these NPs assembled onto probes best when suspended at nearly physiological conditions (surface density approximately 83,600+/-3000 particles/mm(2)). The percentage of surface area coverage by the NPs was estimated to be approximately 13% and was maintained over two weeks during constant exposure to PBS. Multiple fluorescent NP populations were attached to the same probe to allow visualization of simultaneous delivery of multiple agents by fluorescence microscopy. Release from NP coatings was reproducible and controllable. The distinct release profiles of each agent from the coatings were preserved upon attachment to the surfaces. The unique feature of this new system is that NPs encapsulating various molecules (i.e. drugs, proteins, or DNA) can be fabricated separately, in advance, and simply mixed prior to attachment. The versatility of this delivery system, therefore, makes it suitable for many applications.

Virus-like particle vaccines and adjuvants: the HPV paradigm

Complex antigen structures currently represent the most-studied approach for prophylactic as well as therapeutic vaccines. Different types of complex vaccines, including virus-like particles and virosomes, have been developed depending on the nature of the viral pathogen they are trying to replicate (enveloped vs naked) or the modality to express antigenic epitopes (i.e., the binding of envelope protein on liposomic structures). The complex structure of these vaccines provides them with some adjuvanted properties, not uniformly present for all virus-like particle types. The further inclusion of specific adjuvants in vaccine preparations can modify the presentation modality of such particles to the immune system with a specific Th1 versus Th2 polarization efficacy. A paradigm of the relevance of these new adjuvants are the immunological results obtained with the inclusion of monophosphoryl lipid A adjuvant in the formulation of L1-based human papillomavirus-naked virus-like particles to reduce a Th1 cellular immunity impairment, peculiar for alum-derived adjuvants, along with the induction of highly enhanced humoral and memory B-cellular immunity.

DNA as therapeutics; an update

Human gene therapy is the introduction of new genetic material into the cells of an individual with the intention of producing a therapeutic benefit for the patient. Deoxyribonucleic acid and ribonucleic acid are used in gene therapy. Over time and with proper oversight, human gene therapy might become an effective weapon in modern medicine's arsenal to help fight diseases such as cancer, acquired immunodeficiency syndrome, diabetes, high blood pressure, coronary heart disease, peripheral vascular disease, neurodegenerative diseases, cystic fibrosis, hemophilia and other genetic disorders. Gene therapy trials in humans are of two types, somatic and germ line gene therapy. There are many ethical, social, and commercial issues raised by the prospects of treating patients whose consent is impossible to obtain. This review summarizes deoxyribonucleic acid-based therapeutics and gene transfer technologies for the diseases that are known to be genetic in origin. Deoxyribonucleic acid-based therapeutics includes plasmids, oligonucleotides for antisense and antigene applications, deoxyribonucleic acid aptamers and deoxyribonucleic acidzymes. This review also includes current status of gene therapy and recent developments in gene therapy research.

Strong antibody responses induced by protein antigens conjugated onto the surface of lecithin-based nanoparticles

An accumulation of research over the years has demonstrated the utility of nanoparticles as antigen carriers with adjuvant activity. Herein we defined the adjuvanticity of a novel lecithin-based nanoparticle engineered from emulsions. The nanoparticles were spheres of around 200nm. Model protein antigens, bovine serum albumin (BSA) or Bacillus anthracis protective antigen (PA) protein, were covalently conjugated onto the nanoparticles. Mice immunized with the BSA-conjugated nanoparticles developed strong anti-BSA antibody responses comparable to that induced by BSA adjuvanted with incomplete Freund's adjuvant and 6.5-fold stronger than that induced by BSA adsorbed onto aluminum hydroxide. Immunization of mice with the PA-conjugated nanoparticles elicited a quick, strong, and durable anti-PA antibody response that afforded protection of the mice against a lethal dose of anthrax lethal toxin challenge. The potent adjuvanticity of the nanoparticles was likely due to their ability to move the antigens into local draining lymph nodes, to enhance the uptake of the antigens by antigen-presenting cells (APCs), and to activate APCs. This novel nanoparticle system has the potential to serve as a universal protein-based vaccine carrier capable of inducing strong immune responses.

Preparation and Characterization of Cationic PLA-PEG Nanoparticles for Delivery of Plasmid DNA

The purpose of the present work was to formulate and evaluate cationic poly(lactic acid)-poly(ethylene glycol) (PLA-PEG) nanoparticles as novel non-viral gene delivery nano-device. Cationic PLA-PEG nanoparticles were prepared by nanoprecipitation method. The gene loaded nanoparticles were obtained by incubating the report gene pEGFP with cationic PLA-PEG nanoparticles. The physicochemical properties (e.g., morphology, particle size, surface charge, DNA binding efficiency) and biological properties (e.g., integrity of the released DNA, protection from nuclease degradation, plasma stability, in vitro cytotoxicity, and in vitro transfection ability in Hela cells) of the gene loaded PLA-PEG nanoparticles were evaluated, respectively. The obtained cationic PLA-PEG nanoparticles and gene loaded nanoparticles were both spherical in shape with average particle size of 89.7 and 128.9 nm, polydispersity index of 0.185 and 0.161, zeta potentials of +28.9 and +16.8 mV, respectively. The obtained cationic PLA-PEG nanoparticles with high binding efficiency (>95%) could protect the loaded DNA from the degradation by nuclease and plasma. The nanoparticles displayed sustained-release properties in vitro and the released DNA maintained its structural and functional integrity. It also showed lower cytotoxicity than Lipofectamine 2000 and could successfully transfect gene into Hela cells even in presence of serum. It could be concluded that the established gene loaded cationic PLA-PEG nanoparticles with excellent properties were promising non-viral nano-device, which had potential to make cancer gene therapy achievable.

DNA/amphiphilic block copolymer nanospheres promote low-dose DNA vaccination

Intramuscular (i.m.) DNA vaccination induces strong cellular immune responses in the mouse, but only at DNA doses that cannot be achieved in humans. Because antigen expression is weak after naked DNA injection, we screened five nonionic block copolymers of poly(ethyleneoxide)-poly(propyleneoxide) (PEO-PPO) for their ability to enhance DNA vaccination using a beta-galactosidase (betaGal) encoding plasmid, pCMV-betaGal, as immunogen. At a high DNA dose, formulation with the tetrafunctional block copolymers 304 (molecular weight [MW] 1,650) and 704 (MW 5,500) and the triblock copolymer Lutrol (MW 8,600) increased betaGal-specific interferon-gamma enzyme-linked immunosorbent spot (ELISPOT) responses 2-2.5-fold. More importantly, 704 allowed significant reductions in the dose of antigen-encoding plasmid. A single injection of 2 microg pCMV-betaGal with 704 gave humoral and ELISPOT responses equivalent to those obtained with 100 microg naked DNA and conferred protection in tumor vaccination models. However, 704 had no adjuvant properties for betaGal protein, and immune responses were only elicited by low doses of pCMV-betaGal formulated with 704 if noncoding carrier DNA was added to maintain total DNA dose at 20 microg. Overall, these results show that formulation with 704 and carrier DNA can reduce the dose of antigen-encoding plasmid by at least 50-fold.

PMMA particle-mediated DNA vaccine for cervical cancer

DNA vaccination is a novel immunization strategy that possesses many potential advantages over other vaccine strategies. One of the major difficulties hindering the clinical application of DNA vaccination is the relative poor immunogenicity of DNA vaccines. Poly(methyl methacrylate) (PMMA) is a synthetic polymer approved by the Food and Drug Administration for certain human clinical applications such as the bone cement. In vivo, PMMA particles are phagocytosable and have the potential to initiate strong immune responses by stimulating the production of inflammatory cytokines. In this study, we synthesized a series of PMMA particles (PMMA 1-5) with different particle sizes and surface charges to test the feasibility of implementing such polymer particles for DNA vaccination. To our knowledge, this is the first report to show that the gene gun can deliver DNA vaccine by propelling PMMA particles mixed with plasmid DNA for cervical cancer. It was found that PMMA 4 particles (particle size: 460 +/- 160 nm, surface charge: +11.5 +/- 1.8 mV) stimulated the highest level of TNF-alpha production by macrophages in vitro and yielded the best result of antitumor protection in vivo. Therefore, our results possess the potential for translation and implementation of polymer particles in gene gun delivering DNA vaccination.

Induction of humoral and enhanced cellular immune responses by novel core-shell nanosphere- and microsphere-based vaccine formulations following systemic and mucosal administration

Anionic surfactant-free polymeric core-shell nanospheres and microspheres were previously described with an inner core constituted by poly(methylmethacrylate) (PMMA) and a highly hydrophilic outer shell composed of a hydrosoluble co-polymer (Eudragit L100-55). The outer shell is tightly linked to the core and bears carboxylic groups capable of adsorbing high amounts (antigen loading ability of up to 20%, w/w) of native basic proteins, mainly by electrostatic interactions, while preserving their activity. In the present study we have evaluated in mice the safety and immunogenicity of new vaccine formulations composed of these nano- and microspheres and the HIV-1 Tat protein. Vaccines were administered by different routes, including intramuscular, subcutaneous or intranasal and the results were compared to immunization with Tat alone or with Tat delivered with the alum adjuvant. The data demonstrate that the nano- and microspheres/Tat formulations are safe and induce robust and long-lasting cellular and humoral responses in mice after systemic and/or mucosal immunization. These delivery systems may have great potential for novel Tat protein-based vaccines against HIV-1 and hold promise for other protein-based vaccines.

Innovative strategies for co-delivering antigens and CpG oligonucleotides

Cytosine-phosphorothioate-guanine oligodeoxynucleotides (CpG ODN) is a recent class of immunostimulatory adjuvants that includes unmethylated CpG dinucleotide sequences similar to those commonly found in bacterial DNA. CpG ODN specifically triggers toll like receptor 9 (TLR9), which is found within phagoendosomes of antigen presenting cells (APCs) such as dendritic cells (DCs). CpG ODN triggers activation and maturation of DCs and helps to increase expression of antigens. CpG ODN can be used to induce polarized Th1 type immune responses. Several studies have shown that antigens and CpG ODN must be co-localized in the same APC to generate the most potent therapeutic antigen-specific immune responses. Delivery vehicles can be utilized to ensure co-delivery of antigens and CpG ODN to the same APCs and to significantly increase uptake by APCs. These strategies can result in antigen-specific immune responses that are 5 to 500-fold greater than administration of antigen alone. In this review, we discuss several recent and innovative strategies to co-delivering antigens and CpG ODN adjuvants to APCs. These approaches include the utilization of conjugate molecules, multi-component nanorods, liposomes, biodegradable microparticles, pulsatile release chips and cell-microparticle hybrids.

Assembly of erodible, DNA-containing thin films on the surfaces of polymer microparticles: toward a layer-by-layer approach to the delivery of DNA to antigen-presenting cells

We report a layer-by-layer approach to the assembly of ultrathin and erodible DNA-containing films on the surfaces of polymer microparticles. DNA-containing multilayered films were fabricated layer-by-layer on the surfaces of polystyrene microspheres (approximately 6 microm) by iterative and alternating cycles of particle suspension, centrifugation and resuspension in solutions of plasmid DNA and a hydrolytically degradable polyamine. Film growth occurred in a stepwise manner, as demonstrated by characterization of the zeta potentials and fluorescence intensities of film-coated particles during film assembly. Characterization of film-coated particles by confocal fluorescence microscopy and scanning electron microscopy revealed the multilayered particle coatings to be smooth, uniform and free of large-scale physical defects. Film-coated microparticles sustained the release of transcriptionally active DNA into solution for approximately three days when incubated in physiologically relevant media. Previous studies have demonstrated that the adsorption of DNA onto the surfaces of cationic microparticles can be used to target the delivery of DNA to antigen-presenting cells. As a first step toward the application of this layer-by-layer approach to the development of methods for the delivery of DNA to antigen-presenting cells, we demonstrated that film-coated microparticles could be used to transport DNA into macrophage cells in vitro using a model mouse macrophage cell line. Our results suggest the basis of a general approach that could, with further development, prove useful for the delivery of DNA-encoded antigens to macrophages, or other antigen-presenting cells, and provide new materials-based methods for the formulation and delivery of DNA vaccines.

Polymeric Materials for Gene Delivery and DNA Vaccination

Gene delivery holds great potential for the treatment of many different diseases. Vaccination with DNA holds particular promise, and may provide a solution to many technical challenges that hinder traditional vaccine systems including rapid development and production and induction of robust cell-mediated immune responses. However, few candidate DNA vaccines have progressed past preclinical development and none have been approved for human use. This Review focuses on the recent progress and challenges facing materials design for nonviral DNA vaccine drug delivery systems. In particular, we highlight work on new polymeric materials and their effects on protective immune activation, gene delivery, and current efforts to optimize polymeric delivery systems for DNA vaccination.

Poly (epsilon-caprolactone) microparticles containing Levobunolol HCl prepared by a multiple emulsion (W/O/W) solvent evaporation technique: effects of some formulation parameters on microparticle characteristics

The aim of this study was to prepare poly (epsilon-caprolactone) (PCL) microparticles of Levobunolol HC1 (L-HC1) for use as an anti-glaucomatous drug to the eye. The double emulsion (W/O/W) solvent evaporation technique was used for encapsulating L-HC1 as a hydrophilic drug. The study examined the impact of different factors including the pH and volume of the external aqueous phase, the concentration of polyvinylalcohol (PVA) and Pluronic F68 (PF68) used as stabilizers and drug/polymer ratios on the characteristics of the microparticles. Scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) were used to identify the physical state of the drug and polymer. The zeta potential of the particles was also identified. Entrapment efficiency was found to be highest with a 0.5% PVA concentration and 100 mL volume of external aqueous phase at pH 12. The high efficiency was due to a reduction in the degree of drug ionization. The microparticles were spherical and appropriately sized for ophthalmic application. Drug release from the microparticles appears to consist of two components, with an initial rapid release followed by a slower stage. Drug release was slower when the microparticle was incorporated into the thermally reversible gel (Pluronic F127) in comparison to drug release from the free drug incorporated into the gel and drug release from the free microparticle.

Targeted cationic poly(D,L-lactic-co-glycolic acid) nanoparticles for gene delivery to cultured cells

We developed a new targeted cationic nanoparticulate system composed of poly(D,L-lactic-co-glycolic acid) (PLGA), 1,2-dioleoyl-3-(trimethylammonium) propane (DOTAP) and asialofetuin (AF), and found it to be a highly effective formulation for gene delivery to liver tumor cells. The nanoparticles (NP) were prepared by a modified solvent evaporation process that used two protocols in order to encapsulate (NP1 particles) or adsorb (NP2 particles) plasmid DNA. The final particles are in the nanoscale range. pDNA loaded in PLGA/DOTAP/AF particles with high loading efficiency showed a positive surface charge. Targeted asialofetuin-nanoparticles (AF-NP) carrying genes encoding for luciferase and interleukin-12 (IL-12) resulted in increased transfection efficiencies compared to free DNA and to plain (non-targeted) systems, even in the presence of 60% fetal bovine serum (FBS). The results of transfections performed on HeLa cells, defective in asialoglycoprotein receptors (ASGPr-), confirmed the receptor-mediated endocytosis mechanism. In summary, this is the first time that asialoglycoprotein receptor targeting by PLGA/DOTAP/DNA nanoparticles carrying the therapeutic gene IL-12 has been shown to be efficient in gene delivery to liver cancer cells in the presence of a very high concentration of serum, and this could be a potential system for in vivo application.

Cationic gold microparticles for biolistic delivery of nucleic acids

Here we report preparation and properties of positively charged gold microparticles, and their use for biolistic DNA delivery. Micron-sized gold microparticles were modified by building self-assembling polyethylenimine monolayers on their surfaces, which enabled their electrostatic interaction with negatively charged molecules such as DNA. One milligram of the surface-modified microparticles was able to bind directly to up to 3.5 microg of DNA, exceeding the 1 microg/mg limit of the conventional protocols. The binding showed no apparent dependency on DNA purity, size, or conformation. The interaction occurred over a broad range of pH values and salt concentrations, and was stable throughout the standard protocol for biolistic cartridge preparation. At the standard 1 microg dose, biological activity of the DNA biolistically delivered on the charge-modified gold was 25% higher than that delivered on conventional microparticles. Loading the charge-modified gold with more DNA stimulated proportionally higher gene expression. The charge-modified gold can be also used for delivery of small biological molecules such as siRNA. Tissue culture cells biolistically transfected with a LUC+ specific siRNA showed 80% reduction of Luc expression relative to those cells transfected with an irrelevant siRNA. Along with its superior properties as a DNA delivery vehicle, charge-modified gold offers a unique opportunity to deliver various DNA formulations in addition to traditional naked DNA.

DNA immunization as an efficient strategy for vaccination

The field of vaccinology provides excellent promises to control different infectious and non-infectious diseases. Genetic immunization as a new tool in this area by using naked DNA has been shown to induce humoral as well as cellular immune responses with high efficiency. This demonstrates the enormous potential of this strategy for vaccination purposes. DNA vaccines have been widely used to develop vaccines against various pathogens as well as cancer, autoimmune diseases and allergy. However, despite their successful application in many pre-clinical disease models, their potency in human clinical trials has been insufficient to provide protective immunity. Several strategies have been applied to increase the potency of DNA vaccine. Among these strategies, the linkage of antigens to Heat Shock Proteins (HSPs) and the utilization of different delivery systems have been demonstrated as efficient approaches for increasing the potency of DNA vaccines. The uptake of DNA plasmids by cells upon injection is inefficient. Two basic delivery approaches including physical delivery to achieve higher levels of antigen production and formulation with microparticles to target Antigen-Presenting Cells (APCs) are effective in animal models. Alternatively, different regimens called prime-boost vaccination are also effective. In this regimen, naked DNA is utilized to prime the immune system and either recombinant viral vector or purified recombinant protein with proper adjuvant is used for boosting. In this review, we discuss recent advances in upgrading the efficiency of DNA vaccination in animal models.

Production of antibodies to Little cherry virus 1 coat protein by DNA prime and protein boost immunization

Little cherry, an economically important disease of cherry is caused by at least two different viruses. One of these is Little cherry virus 1 (LChV-1) for the detection of which no efficient serological tools are available, so that diagnosis is based on molecular methods. In this study, different immunization strategies for producing antibodies against the viral coat protein of LChV-1 were tried, using either purified virus preparations, or bacterially expressed protein, or a DNA vector that expressed the cloned coat protein (CP) gene in vivo. Effective induction of specific antibodies to LChV-1 CP was obtained using DNA intramuscular immunization followed by a single boost with the recombinant protein. The entire coat protein sequence was cloned in a mammalian expression vector and, after being coated by an amphiphilic non-toxic reagent was delivered into rabbit. A protein boost increased the specific immune response against the virus protein. The sensitivity of this antiserum is lower if compared with that of antisera raised conventionally against other viruses, thus it requires improvements for use for diagnostic purposes.

Formulating poly(lactide-co-glycolide) particles for plasmid DNA delivery

Biodegradable poly(lactide-co-glycolide) (PLGA) particles have shown significant potential for sustained and targeted delivery of several pharmaceutical agents, including plasmid DNA (pDNA). Here, we survey current approaches to PLGA particle preparation for pDNA delivery and discuss recent progress on optimizing formulation development.

Physical characterization and in vivo evaluation of poloxamer-based DNA vaccine formulations

BACKGROUND

Plasmid DNA (pDNA) vaccines have generated significant interest for the prevention or treatment of infectious diseases. Broader applications may benefit from the identification of safe and potent vaccine adjuvants. This report describes the development of a novel polymer-based formulation to enhance the immunogenicity of pDNA-based vaccines.

METHODS

Plasmid DNA was formulated with a nonionic block copolymer, poloxamer CRL1005, and the cationic surfactant benzalkonium chloride (BAK) to produce a thermodynamically stable, self-assembling system. The influence of parameters such as polymer concentration and BAK composition on the immune responses was evaluated in mice vaccinated with pDNA encoding influenza nucleoprotein.

RESULTS

At concentrations of 7.5 mg/ml CRL1005, 0.3 mM BAK and 5 mg/ml pDNA, CRL1005/BAK/pDNA particles had a mean diameter of 261 +/- 0.2 nm and a surface charge of - 11.6 +/- 0.9 mV. The negative surface charge and atomic force microscopy images suggested that pDNA binds to BAK adsorbed to the surface of poloxamer particles. The CRL1005/BAK/pDNA formulation significantly enhanced antigen-specific cellular and humoral immune responses, and increased transgene levels in muscle and serum. The complexity of the formulation was reduced by replacing the commercial BAK, which is a mixture of four alkyl chains, with a C14 BAK homolog. The substitution yielded an analytically preferable formulation with equivalent physical characteristics and immunogenicity.

CONCLUSIONS

The results suggest that the CRL1005/BAK/pDNA formulation may enhance immunogenicity by improving the delivery of pDNA-based vaccines. This formulation is currently being evaluated for the prevention of CMV-associated disease in a phase 2 clinical trial.

DNA vaccination

This unit details some of the key methods for setting up and testing DNA vaccines in animal models. The basic procedures are discussed, as well as alternative methods that have been developed over the past several years. The Basic Protocol gives step-by-step instructions for administering the DNA vaccine via intramuscular injection of the quadriceps muscle, while an alternate procedure details injection of the anterior tibialis.

Surface modification of microspheres with steric stabilizing and cationic polymers for gene delivery

In this paper, we describe surface modification of poly( D,L-lactide- co-glycolide) (PLG) microspheres, intended for DNA vaccine application, with two functionalities: a steric stabilizing component, provided by poly(vinyl alcohol) (PVA) and a cationic component, aimed at subsequent DNA surface loading. The cationic functionality arises from polycations, such as PEI, poly( L-lysine), trimethyl chitosan, and (dimethylamino)ethyl methacrylate, introduced into the water phase of classical oil-in-water (o/w) solvent evaporation method of PLG microsphere fabrication. By systematic evaluation of production variables, a system was produced with balanced properties in terms of microsphere size appropriate for uptake by antigen presenting (e.g., dendritic) cells, colloidal stability, and relatively high DNA loading. The polycation (PEI) molecular weight and preparation concentration were both found to increase the surface polycation content and DNA binding capacity; however, they lead to an increased tendency for aggregation, particularly when the microsphere size was decreased. DNA loading of almost 100% efficiency was achieved under optimized conditions in physiologically acceptable buffers, resulting in a surface DNA loading appropriate for vaccine purposes. A further increase in surface DNA loading was however associated with an increase in the particles negative potential, indicating the surface presence of DNA charges not neutralized by the polycation and hence potentially not protected from in vivo enzymatic degradation. The internalization of surface-loaded DNA into the target cells was confirmed by monitoring fluorescent DNA after the microspheres were endocytosed by the cells in culture.

High loading efficiency and tunable release of plasmid DNA encapsulated in submicron particles fabricated from PLGA conjugated with poly-L-lysine

Poly(lactic-co-glycolic acid) (PLGA) particles have been widely explored as vehicles for delivery of plasmid DNA to mammalian cells both in vitro and in vivo. Achieving high incorporation efficiencies and control over release kinetics are significant challenges in encapsulating hydrophilic molecules such as DNA within submicron particles fabricated from PLGA. This study explored two modifications in the preparation of submicron particles to specifically address these challenges. Firstly, we compared homogenization and sonication as energy sources for emulsification. It was demonstrated that particles prepared with homogenization resulted in higher encapsulation efficiency and a linear release profile of DNA as compared to particles prepared with sonication, which exhibited lower encapsulation efficiency and a burst release. Also investigated was conjugation of poly-L-lysine to PLGA (PLGA-PLL) to create an electrostatically favorable interaction between the carrier material and the DNA. Particles fabricated with high weight percentages of PLGA-PLL/PLGA resulted in remarkably increased loading (>90%). Additionally, the release profile could be dictated by the quantity of PLGA-PLL incorporated into the particles. Particles incubated in vitro on COS-7 cells were able to transfect cells. These results demonstrated that DNA encapsulation and release were modulated by the method of fabrication.

Multilayered polyelectrolyte assemblies as platforms for the delivery of DNA and other nucleic acid-based therapeutics

Materials that provide spatial and temporal control over the delivery of DNA and other nucleic acid-based agents from surfaces play important roles in the development of localized gene-based therapies. This review focuses on a relatively new approach to the immobilization and release of DNA from surfaces: methods based on the layer-by-layer assembly of thin multilayered films (or polyelectrolyte multilayers, PEMs). Layer-by-layer methods provide convenient, nanometer-scale control over the incorporation of DNA, RNA, and oligonucleotide constructs into thin polyelectrolyte films. Provided that these assemblies can be designed in ways that permit controlled film disassembly under physiological conditions, this approach can contribute new methods for spatial and/or temporal control over the delivery of nucleic acid-based therapeutics in vitro and in vivo. We describe applications of layer-by-layer assembly to the fabrication of DNA-containing films that can be used to provide control over the release of plasmid DNA from the surfaces of macroscopic objects and promote surface-mediated cell transfection. We also highlight the application of these methods to the coating of colloidal substrates and the fabrication of hollow micrometer-scale capsules that can be used to encapsulate and control the release or delivery of DNA and oligonucleotides. Current challenges, gaps in knowledge, and new opportunities for the development of these methods in the general area of gene delivery are discussed.

A comparison between polymeric microsphere and bacterial vectors for macrophage P388D1 gene delivery

PURPOSE

The purpose of this study was to compare bacterial and polymeric gene delivery devices for the ability to deliver plasmid DNA to a murine macrophage P388D1 cell line.

METHODS

An 85:15 ratio of poly(lactic-co-glycolic acid) (PLGA) and poly(beta-amino ester) polymers were formulated into microspheres that physically entrapped plasmid DNA encoding for the firefly luciferase reporter gene; whereas, the same plasmid was biologically transformed into a strain of Escherichia coli engineered to produce recombinant listeriolysin O. The two delivery devices were then tested for gene delivery and dosage effects using a macrophage cell line with both assays taking advantage of a 96-well high throughput format to quantify and compare each vector type.

RESULTS

Gene delivery was comparable for both vectors at higher vector dosages while lower dosages showed an improved delivery for the microsphere vectors. Delivery efficiency (defined as luciferase measurement/mg cellular protein/ng DNA delivered) was 881 luminescence mg(-1) ng(-1) for polymeric microspheres compared to 171 luminescence mg(-1) ng(-1) for the bacterial vectors.

CONCLUSION

A first head-to-head comparison between polymeric and bacterial gene delivery vectors shows a delivery advantage for polymeric microspheres that must also be evaluated in light of vector production, storage, and future potential.

Dose-dependent protection against or exacerbation of disease by a polylactide glycolide microparticle-adsorbed, alphavirus-based measles virus DNA vaccine in rhesus macaques

Measles remains an important cause of vaccine-preventable child mortality. Development of a low-cost, heat-stable vaccine for infants under the age of 6 months could improve measles control by facilitating delivery at the time of other vaccines and by closing a window of susceptibility prior to immunization at 9 months of age. DNA vaccines hold promise for development, but achieving protective levels of antibody has been difficult and there is an incomplete understanding of protective immunity. In the current study, we evaluated the use of a layered alphavirus DNA/RNA vector encoding measles virus H (SINCP-H) adsorbed onto polylactide glycolide (PLG) microparticles. In mice, antibody and T-cell responses to PLG-formulated DNA were substantially improved compared to those to naked DNA. Rhesus macaques received two doses of PLG/SINCP-H delivered either intramuscularly (0.5 mg) or intradermally (0.5 or 0.1 mg). Antibody and T-cell responses were induced but not sustained. On challenge, the intramuscularly vaccinated monkeys did not develop rashes and had lower viremias than vector-treated control monkeys. Monkeys vaccinated with the same dose intradermally developed rashes and viremia. Monkeys vaccinated intradermally with the low dose developed more severe rashes, with histopathologic evidence of syncytia and intense dermal and epidermal inflammation, eosinophilia, and higher viremia compared to vector-treated control monkeys. Protection after challenge correlated with gamma interferon-producing T cells and with early production of high-avidity antibody that bound wild-type H protein. We conclude that PLG/SINCP-H is most efficacious when delivered intramuscularly but does not provide an advantage over standard DNA vaccines for protection against measles.

Preparation of mannan modified anionic PCL-PEG-PCL nanoparticles at one-step for bFGF antigen delivery to improve humoral immunity

In this article, blank anionic poly(epsilon-caprolactone)-poly(ethylene glycol)-poly(epsilon-caprolactone) (PCEC) and anionic mannan modified PCEC (MPCEC) nanoparticles with nearly the same particle size and zeta potential were prepared by emulsion solvent evaporation method. Human basic fibroblast growth factor (bFGF) was absorbed onto anionic nanoparticles surface due to electrostatic interaction. The obtained bFGF-nanoparticles complexes were injected subcutaneously into C57BL/6 mice at 20 microg of bFGF/dose on week 0, 1, 2 and 3. The mice serum was collected on week 4, and bFGF-specific autoantibody total IgG, IgG1 and IgG2a titer in serum was determined by ELISA. The results indicated that the autoantibody IgG, IgG1 and IgG2a titer of the mice immunized by bFGF-MPCEC complexes were higher than that immunized by either bFGF-PCEC or bFGF-Alum. This phenomenon might be due to that mannan functionalized MPCEC nanoparticles could be targeted to dendritic cells (DCs) to improve humoral immunity. The prepared anionic mannan modified PCEC nanoparticles (MPCEC) might have great potential application in vaccine delivery systems.

Direct plasmid DNA encapsulation within PLGA nanospheres by single oil-in-water emulsion method

Plasmid DNA was encapsulated within poly(d,l-lactic-co-glycolic acid) (PLGA) nanospheres by using polyethylene glycol (PEG) assisted solubilization technique of plasmid DNA in organic solvents. Plasmid DNA was solubilized in an organic solvent mixture composed of 80% methylene chloride and 20% DMSO by producing PEG/DNA nano-complexes having an average diameter less than 100 nm. DNA could be solubilized in the organic solvent mixture to a greater extent with increasing the weight ratio of PEG/DNA. PLGA nanospheres encapsulating DNA were successfully prepared by the single O/W emulsion method. They exhibited greater loading efficiency and better structural integrity, compared to those prepared by the W/O/W double emulsion method. Plasmid DNA could be successfully delivered to macrophage cells to express an exogenous gene. This new formulation enabled high loading of intact plasmid DNA within PLGA nanospheres useful for DNA vaccines.

Polylactide-co-glycolide (PLG) microparticles modify the immune response to DNA vaccination

Priming with the major surface glycoprotein G of respiratory syncytial virus (RSV) expressed by recombinant vaccinia leads to strong Th2 responses and lung eosinophilia during viral challenge. We now show that DNA vaccination in BALB/c mice with plasmids encoding G attenuated RSV replication but also enhanced disease with lung eosinophilia and increased IL-4/5 production. However, formulating the DNA with PLG microparticles reduced the severity of disease during RSV challenge without significantly lessening protection against viral replication. PLG formulation greatly reduced lung eosinophilia and prevented the induction of IL-4 and IL-5 during challenge, accompanied by a less marked CD4+ T cell response and a restoration of the CD8+ T cell recruitment seen during infection of non-vaccinated animals. After RSV challenge, lung eosinophilia was enhanced and prolonged in mice vaccinated with DNA encoding a secreted form of G; this effect was virtually prevented by PLG formulation. Therefore, PLG microparticulate formulation modifies the pattern of immune responses induced by DNA vaccination boosts CD8+ T cell priming and attenuates Th2 responses. We speculate that PLG microparticles affect antigen uptake and processing, thereby influencing the outcome of DNA vaccination.

CpG oligonucleotides accelerate and boost the immune response elicited by AVA, the licensed anthrax vaccine

Synthetic oligodeoxynucleotides (ODN) containing unmethylated CpG motifs act as immune adjuvants, improving the immune response elicited by coadministered vaccines. Combining CpG ODN with anthrax vaccine adsorbed (AVA), the licensed human vaccine, can increase the speed, magnitude and avidity of the resultant anti-anthrax response in mice, rhesus macaques and humans. Adsorbing the CpG ODN onto cationic poly(actide-coglycolides) microparticles further boosts immunity to coadministered AVA. The antibody response induced by CpG ODN plus AVA confers protection against systemic anthrax challenge in multiple animal models. These findings suggest that CpG ODN, alone or in combination with other adjuvants and delivery strategies, may support the development of prophylactic and therapeutic vaccines against biothreat pathogens.

A genetically engineered prime-boost vaccination strategy for oculonasal delivery with poly(D,L-lactic-co-glycolic acid) microparticles against infection of turkeys with avian Metapneumovirus

In this study we demonstrated the use of an oculonasally delivered poly(D,L-lactic-co-glycolic acid) microparticle (PLGA-MP)-based and genetically engineered vaccination strategy in the avian system. An avian Metapneumovirus (aMPV) fusion (F) protein-encoding plasmid vaccine and the corresponding recombinant protein vaccine were produced and bound to or encapsulated by PLGA-MP, respectively. The PLGA-MP as the controlled release system was shown in vitro to not induce any cytopathic effects and to efficiently deliver the F protein-based aMPV-vaccines to avian cells for further processing. Vaccination of turkeys was carried out by priming with an MP-bound F protein-encoding plasmid vaccine and a booster-vaccination with an MP-encapsulated recombinant F protein. Besides the prime-boost F-specific vaccinated birds, negative control birds inoculated with a mock-MP prime-boost regimen as well as non-vaccinated birds and live vaccinated positive control birds were included in the study. The MP-based immunization of turkeys via the oculonasal route induced systemic humoral immune reactions as well as local and systemic cellular immune reactions, and had no adverse effects on the upper respiratory tract. The F protein-specific prime-boost strategy induced partial protection. After challenge the F protein-specific MP-vaccinated birds showed less clinical signs and histopathological lesions than control birds of mock MP-vaccinated and non-vaccinated groups did. The vaccination improved viral clearance and induced accumulation of local and systemic CD4+ T cells when compared to the mock MP-vaccination. It also induced systemic aMPV-neutralizing antibodies. The comparison of mock- and F protein-specific MP-vaccinated birds to non-vaccinated control birds suggests that aMPV-specific effects as well as adjuvant effects mediated by MP may have contributed to the overall protective effect.

Conjugation of Polyamidoamine Dendrimers on Biodegradable Microparticles for Nonviral Gene Delivery

We report on the preparation and characterization of poly(D, L-lactide-co-glycolide) (PLGA) microparticles with surface-conjugated polyamidoamine (PAMAM) dendrimers of varying generations. The buffering capacity and zeta-potential of the PLGA PAMAM microparticles increased with increasing generation level of the PAMAM dendrimer conjugated. Conjugation of the PAMAM dendrimer to the surface of the PLGA microparticle removed generation-dependent cytotoxicity in HEK293 and COS7 cell lines. PLGA PAMAM pDNA microparticles displayed similar cytotoxicity profiles to unmodified PLGA pDNA microparticles in COS7 cells. A generation three PAMAM dendrimer conjugated to PLGA microparticles significantly increased transfection efficiencies in comparison to unmodified PLGA microparticles.

One-step surface modification of poly(lactide-co-glycolide) microparticles with heparin

PURPOSE

The aim of this study was to modify the surface of poly(lactide-co-glycolide) (PLGA) microparticles with heparin. The heparin-coated PLGA may enhance blood and tissue compatibility of PLGA devices and provide a novel approach to deliver growth factors.

MATERIALS AND METHODS

A one-step method using heparin to replace traditional emulsifiers (e.g., PVA) during emulsion-solvent evaporation process was employed to surface-entrap heparin in PLGA microspheres. The emulsifying activity of heparin was modified via varying counter ion form, including univalent (Na(+), K(+), Li(+), and [Formula: see text]) and divalent (Ca(2+), Mg(2+), Ba(2+), and Zn(2+)) cations, and complexation with amino acids (Arg, Lys, Leu, Val, Gly and Glu). Surface accessible and total heparin loading were determined by a modified toluidine blue assay and elemental analysis, respectively.

RESULTS

Heparin bound with univalent counter ions and amino acids exhibited emulsifying activity to varying degrees, whereas divalent heparin salts tended to cause complete aggregation of the PLGA o/w emulsion. Increasing pH (>or=7.4) of hardening medium enhanced heparin adsorption and significantly stabilized the PLGA o/w emulsion. The initial surface density of heparin on the PLGA microspheres prepared using univalent heparin salts was around 8-33 mg/m(2). Surface associated heparin desorbed quickly; potassium heparin showed the best retention, with approximately 0.2 and 0.1 mg/m(2) detected on PLGA microsphere surface following 1- and 14-day incubation in PBST at 37 degrees C, respectively.

CONCLUSIONS

PLGA microparticles were successfully surface-modified with heparin. Univalent salts and amino acid complexes of heparin, as effective emulsifiers, can become surface-immobilized in PLGA microspheres.

Enhance immune response to DNA vaccine based on a novel multicomponent supramolecular assembly

DNA vaccination has tremendous potential for treating or preventing numerous diseases for which traditional vaccines are ineffective but the technique can be limited by low immunogenicity. Current synthetic DNA delivery systems are versatile and safe, but substantially less efficient than viruses. Here, a novel multicomponent supramolecular system involving the preparation of mannose-bearing chitosan oligomers microspheres with entrapping complexes of DNA vaccine and polyethylenimine was developed to mimic many of the beneficial properties of the viruses. After delivery by intramuscular immunization in BALB/c mice, the microspheres induced an enhanced serum antibody responses two orders of magnitude greater than naked DNA vaccine. Additionally, in contrast to naked DNA, the microspheres induced potent cytotoxic T lymphocyte responses at a low dose. Consequently, formulation of DNA vaccines into multicomponent vectors is a powerful means of increasing vaccine potency.