Induction of potent immune responses by cationic microparticles with adsorbed human immunodeficiency virus 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.

Protection of rhesus monkeys by a DNA prime/poxvirus boost malaria vaccine depends on optimal DNA priming and inclusion of blood stage antigens

Background

We have previously described a four antigen malaria vaccine consisting of DNA plasmids boosted by recombinant poxviruses which protects a high percentage of rhesus monkeys against Plasmodium knowlesi (Pk) malaria. This is a multi-stage vaccine that includes two pre-erythrocytic antigens, PkCSP and PkSSP2(TRAP), and two erythrocytic antigens, PkAMA-1 and PkMSP-1(42kD). The present study reports three further experiments where we investigate the effects of DNA dose, timing, and formulation. We also compare vaccines utilizing only the pre-erythrocytic antigens with the four antigen vaccine.

Methodology

In three experiments, rhesus monkeys were immunized with malaria vaccines using DNA plasmid injections followed by boosting with poxvirus vaccine. A variety of parameters were tested, including formulation of DNA on poly-lactic co-glycolide (PLG) particles, varying the number of DNA injections and the amount of DNA, varying the interval between the last DNA injection to the poxvirus boost from 7 to 21 weeks, and using vaccines with from one to four malaria antigens. Monkeys were challenged with Pk sporozoites given iv 2 to 4 weeks after the poxvirus injection, and parasitemia was measured by daily Giemsa stained blood films. Immune responses in venous blood samples taken after each vaccine injection were measured by ELIspot production of interferon-γ, and by ELISA.

Conclusions

1) the number of DNA injections, the formulation of the DNA plasmids, and the interval between the last DNA injection and the poxvirus injection are critical to vaccine efficacy. However, the total dose used for DNA priming is not as important; 2) the blood stage antigens PkAMA-1 and PkMSP-1 were able to protect against high parasitemias as part of a genetic vaccine where antigen folding is not well defined; 3) immunization with PkSSP2 DNA inhibited immune responses to PkCSP DNA even when vaccinations were given into separate legs; and 4) in a counter-intuitive result, higher interferon-γ ELIspot responses to the PkCSP antigen correlated with earlier appearance of parasites in the blood, despite the fact that PkCSP vaccines had a protective effect.

Effects of chronic heat stress on immune responses of the foot-and-mouth disease DNA vaccination

The main purpose of this study was to assess the effects of chronic heat stress (CHS) on humoral and cellular responses of DNA vaccination. Mice with the CHS were exposed to a temperature set at 38 +/- 1 degrees C, 2h per day, for 35 days, and mice with thermoneutral (TN) temperature were maintained at 24 +/- 1 degrees C for the same period of time. Both groups of mice were immunized with a DNA vaccine-expressed viruscapsid protein 1 (VP1) of foot-and-mouth disease virus (FMDV), and we tested their antigen-specific humoral and cellular responses during the treatments. Compared with the TN group, titers of total Imunoglobulin G (IgG) and IgG1 and expression of interleukin 4 (IL-4) in CD4(+) cells of CHS group were not affected significantly. In contrast, the levels of IgG2a, T cell proliferations, and expression of interferon-gama (IFN-gamma) in both CD4(+) and CD8(+) cells were suppressed significantly, and cytotoxic T-lymphocyte (CTL) responses in vivo were also weakened by the CHS condition. These results indicate that the CHS treatment has negatively affected the immune responses of DNA vaccination and particularly impaired to the cell-mediated responses. It suggests that vaccination in animals is affected by the changes of ambient temperature.

MIDGE/hNIS vaccination generates antigen-associated CD8+IFN-gamma+ T cells and enhances protective antitumor immunity

Human sodium iodide symporter (hNIS) is a transmembrane protein that actively transports iodide ions into thyroid cells. hNIS is over-expressed in some cases of the thyroid cancers compared with the surrounding normal tissues and has been considered to be an attractive target for immunotherapy. The aim of this study is to determine the feasibility of utilizing the hNIS antigenic protein in enhanced-antigen-associated immunotherapy using image analysis with a gamma counter. To accomplish this, minimalistic immunogenically defined gene expression (MIDGE), either plain or coupled to a nuclear localization signal (NLS) peptide, was used as a vector system. Vaccination with MIDGE/hNIS, MIDGE/hNIS-NLS and pcDNA3.1/hNIS produced a significant increase in the number of hNIS-associated IFN-gamma-secreting CD8(+) T cells, with MIDGE/hNIS having the strongest effect. In addition, immunization with the hNIS encoding vectors induced antigen-mediated antitumor activity against NIS-expressing CT26 tumors in vivo, with the highest tumor free rate (100%) and lowest tumor growth being observed up to 40 days after the CT26/NIS tumor challenge with MIDGE/hNIS than those resulting from other immunization groups. Tumor progression could be followed noninvasively and repetitively by monitoring levels of hNIS gene expression in the tumors using scintigraphic image analysis. Overall, hNIS has a potential use as an antigen for immunization approaches, and vaccination with MIDGE/hNIS vectors is an effective means of generating hNIS-associated immune responses in mice.

Chemical adjuvants for plasmid DNA vaccines

Plasmid DNA vaccines are a promising modality for immunization against a variety of human pathogens. Immunization via multiple routes with plasmid DNA can elicit potent cellular immune responses, and these immunogens can be administered repeatedly without inducing anti-vector immunity. Nonetheless, the immunogenicity of plasmid DNA vaccines has been limited by problems associated with delivery. A number of adjuvants have been designed to improve plasmid DNA immunogenicity, either by directly stimulating the immune system or by enhancing plasmid DNA expression. Chemical adjuvants for enhancing plasmid DNA expression include liposomes, polymers, and microparticles, all of which have shown promise for enhancing the expression and immunogenicity of plasmid DNA vaccines in animal models. Micro- and nanoparticles have not been shown to enhance immune responses to plasmid DNA vaccines. However, formulation of plasmid DNA with some non-particulate polymeric adjuvants has led to a statistically significant enhancement of immune responses. Further development of these technologies will significantly improve the utility of plasmid DNA vaccination.

Microparticle-based technologies for vaccines

Microparticles have been effectively used for many years as delivery systems for drugs and therapeutic proteins. Their application to the delivery of vaccines is not as extensive, but is growing. Utility has been demonstrated for the delivery of various types of vaccines (e.g., recombinant proteins, plasmid DNA, and peptides) and other vaccine components (e.g., immune potentiators). With respect to delivery of immune potentiators, synergistic effects are often observed whereby much more potent immune responses are induced with a combination than with either component alone. Hence, the prospects for broad application of microparticle-based delivery systems for vaccines are excellent.

A modified process for preparing cationic polylactide-co-glycolide microparticles with adsorbed DNA

We have previously shown that cationic polylactide-co-glycolide (PLG) microparticles can be effectively used to adsorb DNA and generate potent immune responses in vivo. We now describe a modified and easier process containing a single lyophilization step to prepare these cationic PLG microparticles with adsorbed DNA. Cationic PLG microparticle formulations with adsorbed DNA were prepared using a modified solvent evaporation technique. Formulations with a fixed CTAB content and DNA load were prepared. The loading efficiency and 24h DNA release was evaluated for each formulation and compared to the earlier method of preparation. Select formulations were tested in vivo. The modified cationic PLG microparticle preparation method with a single lyophilization step, showed comparable physico-chemical behaviour to the two lyophilization steps process and induced comparable immune. The modified process with a single lyophilization step is a more practical process and can be utlized to prepare cationic PLG microparticles with adsorbed DNA on a large scale.

Suppression of major histocompatibility complex class II-associated invariant chain enhances the potency of an HIV gp120 DNA vaccine

Summary One function of the major histocompatibility complex (MHC) class II-associated invariant chain (Ii) is to prevent MHC class II molecules from binding endogenously generated antigenic epitopes. Ii inhibition leads to MHC class II presentation of endogenous antigens by APC without interrupting MHC class I presentation. We present data that in vivo immunization of BALB/c mice with HIV gp120 cDNA plus an Ii suppressive construct significantly enhances the activation of both gp120-specific T helper (Th) cells and cytotoxic T lymphocytes (CTL). Our results support the concept that MHC class II-positive/Ii-negative (class II(+)/Ii(-)) antigen-presenting cells (APC) present endogenously synthesized vaccine antigens simultaneously by MHC class II and class I molecules, activating both CD4(+) and CD8(+) T cells. Activated CD4(+) T cells locally strengthen the response of CD8(+) CTL, thus enhancing the potency of a DNA vaccine.

Intrathecal polymer-based interleukin-10 gene delivery for neuropathic pain

Research on communication between glia and neurons has increased in the past decade. The onset of neuropathic pain, a major clinical problem that is not resolved by available therapeutics, involves activation of spinal cord glia through the release of proinflammatory cytokines in acute animal models of neuropathic pain. Here, we demonstrate for the first time that the spinal action of the proinflammatory cytokine, interleukin 1 (IL-1) is involved in maintaining persistent (2 months) allodynia induced by chronic-constriction injury (CCI). The anti-inflammatory cytokine IL-10 can suppress proinflammatory cytokines and spinal cord glial amplification of pain. Given that IL-1 is a key mediator of neuropathic pain, developing a clinically viable means of long-term delivery of IL-10 to the spinal cord is desirable. High doses of intrathecal IL-10-gene therapy using naked plasmid DNA (free pDNA-IL-10) is effective, but the dose required limits its potential clinical utility. Here we show that intrathecal gene therapy for neuropathic pain is improved sufficiently using two, distinct synthetic polymers, poly(lactic-co-glycolic) and polyethylenimine, that substantially lower doses of pDNA-IL-10 are effective. In conclusion, synthetic polymers used as i.t. gene-delivery systems are well-tolerated and improve the long-duration efficacy of pDNA-IL-10 gene therapy.

DNA vaccines against cancer

Significant progress made in the field of tumor immunology by the characterization of a large number of tumor antigens, and the better understanding of the mechanisms preventing immune responses to malignancies has led to the extensive study of cancer immunization approaches such as DNA vaccines encoding tumor antigens. This article reviews major aspects of DNA immunization in cancer. It gives a brief history and then discusses the proposed mechanism of action, preclinical and clinical studies, and methods of enhancing the immune responses induced by DNA vaccines.

Methods for nano-particle based vaccine formulation and evaluation of their immunogenicity

Nano- and microparticles have long been used for the delivery of drugs and are currently being evaluated as vaccine delivery systems. Particulates can elicit potent immune responses, either by direct immuno-stimulation of antigen presenting cells (APC) or/and by delivering antigen to specific cellular compartments and promoting antigen uptake by appropriate stimulatory cell types. Herein, we describe a detailed method for the preparation of a novel nanoparticle-based antigen delivery system which induces strong cellular and humoral immune responses in mice and sheep. This simple system is based on the use of 40 nanometer (nm) inert solid carrier beads to which antigen is covalently coupled before injection. Covalent conjugation of antigen to the nanobeads, assessment of conjugation efficiency, characterisation and measurement of in vivo immunogenicity by cytokine ELISPOT (to measure antigen-specific T-cell responses) and ELISA (to measure antibody titers), are described. Emphasis is placed on providing trouble-shooting advice to enable the reproducible production of soluble nano-size formulations that do not suffer from common problems such as aggregation, as well as understanding the causes and thus avoiding a range of prevalent technical problems that occur when using immune response detection assays, such as the cytokine ELISPOT assay and ELISA.

Coadsorption of HIV-1 p24 and gp120 proteins to surfactant-free anionic PLA nanoparticles preserves antigenicity and immunogenicity

Biodegradable micro- or nanoparticles with surface adsorbed antigens represent a promising method for in vivo delivery of vaccines. Most vaccines, licensed or under development, are based on combined delivery of multiple antigens. Thus, we investigated the feasibility of combining two vaccine antigens, HIV-1 p24 and gp120 proteins, on the surface of surfactant-free anionic PLA nanoparticles obtained by an improved solvent diffusion method. The analysis of adsorption isotherms has shown that both proteins had similar and high affinities for the nanoparticles. Coadsorption of p24 and gp120 onto the same PLA particle was evidenced by sandwich ELISA, using antibodies directed against one protein for particle capture and the other one for detection. To assess structural integrity, the antigenicity of free and PLA-adsorbed antigens was compared by competition ELISA, using a set of 6 anti-p24 and 7 anti-gp120 antibodies, as well as soluble CD4. The antigenicity of proteins on the nanoparticle surface was well preserved, adsorbed either individually or in combination. Furthermore, both antigens maintained their immunogenicity, since high antibody titres (10(6) for p24 and 10(5) for gp120) were elicited in mice with monovalent and divalent PLA formulations. Taken together our results show that development of multivalent vaccines based on anionic PLA nanoparticles is possible. Moreover, coadsorption of a ligand for cell-specific targeting or of an immunostimulatory molecule will further extend the field of application of delivery systems based on charged micro- and nanoparticles.

DNA fusion vaccines induce epitope-specific cytotoxic CD8(+) T cells against human leukemia-associated minor histocompatibility antigens

The graft-versus-leukemia effect of allogeneic stem-cell transplantation is believed to be mediated by T-cell recognition of minor histocompatibility antigens on recipient cells. For minor histocompatibility antigens HA-1 and HA-2, normal cell expression is restricted to hemopoietic cells, and boosting the immune response to these antigens may potentiate graft-versus-leukemia effect without accompanying graft-versus-host disease. To increase efficacy, expansion of HA-1- or HA-2-specific CTL before transplantation is desirable. However, primary HA-1- or HA-2-specific CTL expanded in vitro are often of low avidity. An alternative approach is to prime specific CTL responses in vivo by vaccination. Clearly, donor vaccination must be safe and specific. We have developed DNA fusion vaccines able to induce high levels of epitope-specific CTL using linked CD4(+) T-cell help. The vaccines incorporate a domain of tetanus toxin (DOM) fused to a sequence encoding a candidate MHC class I binding peptide. This design generates antitumor CD8(+) T-cell responses and protective immunity in preclinical models. For clinical application, we constructed vaccines encoding HLA-A*0201-restricted peptides from human HA-1 and HA-2, which were fused to DOM, and tested their performance in HLA-A*0201-transgenic mice. Priming induced epitope-specific, IFNgamma-producing CD8(+) T cells with cytotoxic function boosted to high levels with electroporation. Strikingly, these mouse T cells efficiently killed human lymphoblastoid cell lines expressing endogenous HA-1 or HA-2. High avidity is indicated by the independence of cytolysis from CD8/MHC class I interaction. These safe epitope-specific vaccines offer a potential strategy to prime HA-1- or HA-2-specific CTL in transplant donors before adoptive transfer.

DNA prime and protein boost immunization with innovative polymeric cationic core-shell nanoparticles elicits broad immune responses and strongly enhance cellular responses of HIV-1 tat DNA vaccination

Novel biocompatible core-shell cationic nanoparticles, composed of an inner hard core of poly(methylmethacrylate) (PMMA) and a hydrophilic tentacular shell bearing positively charged groups and poly(ethyleneglycol) chains covalently bound to the core, were prepared by emulsion polymerization and characterized in vitro and in vivo for DNA vaccine applications. The nanoparticles reversibly adsorbed large amounts of DNA, mainly through electrostatic interactions, preserved its functional structure, efficiently delivered it intracellularly, and were not toxic in vitro or in mice. Furthermore, two intramuscular (i.m.) immunizations (4 weeks apart) with a very low dose (1 microg) of the plasmid pCV-tat delivered by these nanoparticles followed by one or two protein boosts induced significant antigen-specific humoral and cellular responses and greatly increased Th1-type T cell responses and CTLs against HIV-1 Tat.

Nonviral delivery of cancer genetic vaccines

The potential use of genetic vaccines to address numerous diseases including cancer is promising, but currently unrealized. Here, we review advances in the nonviral delivery of antigen-encoded plasmid DNA for the purpose of treating cancer through the human immune system, as this disease has drawn the most attention in this field to date. Brief overviews of dendritic cell immunobiology and the mechanism of immune activation through genetic vaccines set the stage for the desirability of delivery technology. Several promising nonviral delivery techniques are discussed along with a mention of targeting strategies aimed at improving the potency of vaccine formulations. Implications for the future of genetic vaccines are also presented.

Surfactant-free anionic PLA nanoparticles coated with HIV-1 p24 protein induced enhanced cellular and humoral immune responses in various animal models

Microparticles and nanoparticles prepared with poly(D,L-lactide-co-glycolide) (PLGA) or poly(D,L-lactide) (PLA) polymers represent a promising method for in vivo delivery of encapsulated peptide, protein or DNA antigens. However, one major issue that limits the potential of these delivery systems is the instability or the degradation of the entrapped antigen. Charged microparticles carrying surface adsorbed antigen were developed to resolve this problem and appear more suitable for vaccine applications. We describe here new anionic PLA nanoparticles obtained by the dialysis method that are absolutely surfactant-free, which makes them more appropriate for use in humans. The potency of this delivery system as a vaccine carrier was tested in various animal models using HIV-1 p24 protein. p24-coated PLA nanoparticles (p24/PLA) induced high antibody titres (>10(6)) in mice, rabbits and macaques. Moreover, p24/PLA nanoparticles elicited strong CTL responses and a Th1-biased cytokine release (IFNgamma, IL-2) in mice. p24 protein seemed to generate a more Th1-oriented response when administered coated onto the surface of PLA nanoparticles than adjuvanted with Freund's adjuvant. Most importantly, the ability of p24/PLA particles to induce Th1 responses was also confirmed in the macaque model, since high levels of IFNgamma-producing CD4+ T cells and CD8+ T cells could be detected by the ELISPOT assay. This protein delivery system confirms the potential of charged nanoparticles in the field of vaccine development.

One-step preparation of polyelectrolyte-coated PLGA microparticles and their functionalization with model ligands

This work aimed at the development of a novel surfactant-free, one-step process for the concomitant formation of poly(lactide-co-glycolide) (PLGA) microparticles (MP) and surface coating with the polyelectrolyte chitosan, which is suitable for subsequent covalent conjugation of bioactive ligands. The technology is based on solvent extraction from an O/W-dispersion using a static micromixer. Surface coating occurred through interaction of the negatively charged, nascent PLGA MP with the polycationic chitosan, which was dissolved in the aqueous extraction fluid. Particles of 1-10 mum in diameter were produced with excellent reproducibility. The chitosan-coated PLGA MP were spherical and showed a smooth surface without pores, as demonstrated by scanning electron microscopy (SEM). The chitosan coatings were characterized by zeta potential measurements and X-ray photoelectron spectroscopy (XPS). The functional amino groups of chitosan were used to conjugate two model ligands to the coating, i.e. fluorescamine and NHS-PEG-biotin. The presence of the conjugated ligands was revealed by confocal laser scanning microscopy (CLSM) and fluorescence activated cell sorting (FACS). Evidence for biotinylation was demonstrated through binding of fluorescently labelled streptavidin. The developed platform technology is straightforward and flexible. Future studies will focus on the design of microparticulate carriers with bioactive surfaces, e.g. as antigen delivery systems.

Multimeric soluble CD40 ligand and GITR ligand as adjuvants for human immunodeficiency virus DNA vaccines

For use in humans, human immunodeficiency virus (HIV) DNA vaccines may need to include immunostimulatory adjuvant molecules. CD40 ligand (CD40L), a member of the tumor necrosis factor (TNF) superfamily (TNFSF), is one candidate adjuvant, but it has been difficult to use because it is normally expressed as a trimeric membrane molecule. Soluble trimeric forms of CD40L have been produced, but in vitro data indicate that multimeric, many-trimer forms of soluble CD40L are more active. This multimerization requirement was evaluated in mice using plasmids that encoded either 1-trimer, 2-trimer, or 4-trimer soluble forms of CD40L. Fusion with the body of Acrp30 was used to produce the 2-trimer form, and fusion with the body of surfactant protein D was used to produce the 4-trimer form. Using plasmids for secreted HIV-1 antigens Gag and Env, soluble CD40L was active as an adjuvant in direct proportion to the valence of the trimers (1 < 2 < 4). These CD40L-augmented DNA vaccines elicited strong CD8(+) T-cell responses but did not elicit significant CD4(+) T-cell or antibody responses. To test the applicability of the multimeric fusion protein approach to other TNFSFs, a 4-trimer construct for the ligand of glucocorticoid-induced TNF family-related receptor (GITR) was also prepared. Multimeric soluble GITR ligand (GITRL) augmented the CD8(+) T-cell, CD4(+) T-cell, and antibody responses to DNA vaccination. In summary, multimeric CD40L and GITRL are new adjuvants for DNA vaccines. Plasmids for expressing multimeric TNFSF fusion proteins permit the rapid testing of TNFSF molecules in vivo.

Enhancement of cellular immune response to a prostate cancer DNA vaccine by intradermal electroporation

Recently it has become clear that more potent methods for DNA vaccine delivery need to be developed to enhance the efficacy of DNA vaccines. In vivo electroporation has emerged as a potent method for DNA vaccine delivery. In a mouse model, we evaluated the CD8(+) T lymphocyte response to a prostate cancer DNA vaccine encoding prostate-specific antigen (PSA) after intradermal electroporation. A significantly increased gene expression (100- to 1000-fold) and higher levels of PSA-specific T cells, compared to DNA delivery without electroporation, was demonstrated. Interestingly, investigation of a panel of different electroporation conditions showed that only some conditions that induce high levels of gene expression additionally induced cellular immunity. This suggests that electroporation parameters should be carefully optimized, not only to enhance transfection efficiency, but also to enhance the immune response to the vaccine. This study demonstrates the applicability of intradermal electroporation as a delivery method for genetic cancer vaccines and other DNA vaccines relying on antigen-specific T cell induction.

Non-Methylated CpG Motif Packaged into Fusogenic Liposomes Enhance Antigen-Specific Immunity in Mice

DNA rich in non-methylated CG motifs (CpGs) enhances induction of immune responses against co-administered antigen encoding genes. CpGs are therefore among the promising adjuvants known to date. However, naked plasmid DNA, even which contains CpG motifs, are taken up by antigen presenting cells via the endocytosis pathway. Endocytosed DNAs are thus degraded and their gene expression levels are inefficient. In this context, an effective plasmid delivery carrier is required for DNA vaccine development. We show in the present study that packaging plasmids containing CpGs into fusogenic liposomes (FL) derived from conventional liposomes and Sendai virus-derived active accessory proteins is an attractive method for enhancing the efficacy of a DNA vaccine. These CpG-enhanced plasmids (possessing 16 CpG repeats) that were packaged into FL, enhanced ovalbumin (OVA)-specific T cell proliferation and cytotoxic T cell activity after immunization. In fact, vaccination with CpG enhanced plasmid-loaded FL induced effective prophylactic effects compared with 13 repeats CpG containing plasmid in a tumor challenge experiment. Thus, the development of a CpG-enhanced DNA-FL genetic immunization system represents a promising tool for developing candidate vaccines against some of the more difficult infectious, parasitic, and oncologic disease targets.

Enhanced potency of plasmid DNA microparticle human immunodeficiency virus vaccines in rhesus macaques by using a priming-boosting regimen with recombinant proteins

DNA vaccines have been used widely in experimental primate models of human immunodeficiency virus (HIV), but their effectiveness has been limited. In this study, we evaluated three technologies for increasing the potency of DNA vaccines in rhesus macaques. These included DNA encoding Sindbis virus RNA replicons (pSINCP), cationic poly(lactide-co-glycolide) (PLG) microparticles for DNA delivery, and recombinant protein boosting. The DNA-based pSINCP replicon vaccines encoding HIV Gag and Env were approximately equal in potency to human cytomegalovirus (CMV) promoter-driven conventional DNA vaccines (pCMV). The PLG microparticle DNA delivery system was particularly effective at enhancing antibody responses induced by both pCMV and pSINCP vaccines and had less effect on T cells. Recombinant Gag and Env protein boosting elicited rapid and strong recall responses, in some cases to levels exceeding those seen after DNA or DNA/PLG priming. Of note, Env protein boosting induced serum-neutralizing antibodies and increased frequencies of gamma interferon-producing CD4 T cells severalfold. Thus, PLG microparticles are an effective means of delivering DNA vaccines in nonhuman primates, as demonstrated for two different types of DNA vaccines encoding two different antigens, and are compatible for use with DNA prime-protein boost regimens.

Cationic PLA nanoparticles for DNA delivery: Comparison of three surface polycations for DNA binding, protection and transfection properties

Biodegradable cationic nanoparticles (cNP) made of poly(lactide) (PLA) have been shown to be promising carrier systems for in vivo DNA delivery and immunization. In previous work, we have described a versatile approach for the elaboration of cationic PLA cNP based on the use of pre-formed particles and subsequent adsorption of a model polycation, the poly(ethylenimine) (PEI). Here, we evaluated two more polycations, chitosan and poly(2-dimethyl-amino)ethyl methacrylate (pDMAEMA)) to determine the most suitable one for the development of PLA cNP as DNA carriers. Cationic PLA-PEI, PLA-chitosan and PLA-pDMAEMA nanoparticles were compared for interaction with plasmid DNA and, more importantly, with regards to the biological properties of bound DNA. pDMAEMA coating yielded the most positively charged nanoparticles with the highest DNA binding capacity (32 mg/g). Loaded with DNA, all three cNP were in the same size range ( approximately 500 nm) and had a negative zeta potential (-50 mV). PLA-chitosan was the only cNP that released DNA at pH 7; the two others required higher pH. Adsorption and release from cNP did not alter structural and functional integrity of plasmid DNA. Moreover, DNA coated onto cNP was partially protected from nuclease degradation, although this protection was less efficient for PLA-chitosan than others. The highest transfection efficiency in cell culture was obtained with PLA-pDMAEMA carriers. We have shown that at least three different cationic polymers (chitosan, PEI, pDMAEMA) can be used for the production of PLA-based particulate DNA carriers and most probably other cationic polymers can also be used in the same purpose. PLA-pDMAEMA cNP were the most promising system for DNA delivery in this in vitro study. Our future work will focus on the in vivo evaluation of these gene delivery systems.

DNA vaccines for biodefence

The advantages associated with DNA vaccines include the speed with which they may be constructed and produced at large-scale, the ability to produce a broad spectrum of immune responses, and the ability for delivery using non-invasive means. In addition, DNA vaccines may be manipulated to express multiple antigens and may be tailored for the induction of appropriate immune responses. These advantages make DNA vaccination a promising approach for the development of vaccines for biodefence. In this review, the potential of DNA vaccines for biodefence is discussed.

The miscibility of poly(D,L-lactide-co-glycolide) with amphiphilic molecules and the interaction of their mixtures with DNA at air/water interface

The miscibility of poly(D,L-lactide-co-glycolide) (PLG) with three amphiphilic molecules and the interaction of the PLG/surfactant mixtures with DNA at air/water interface are investigated by pi-A isotherms, Brewster angle microscopy (BAM) and atomic force microscopy (AFM) techniques. The pi-A isotherms of the PLG mixtures with cationic C(12)AzoC(6)PyBr, and C(12)AzoC(6)N(CH(3))(3)Br, are quite different from the pi-A isotherm of pure PLG on water subphase. In contrast to the case, the pi-A isotherm of PLG mixed with nonionic C(12)AzoC(6)OPy is almost identical to the pure PLG except some increasing of molecular area. Similar phenomena are observed on DNA subphase. The in situ BAM and ex situ AFM observations demonstrate that the dispersion of PLG at air/water interface becomes good when it mixes with the two cationic surfactants, whereas quite poor due to the phase separation when it mixes with the nonionic amphiphilic molecule. Based on these results we conclude that the cationic surfactants can affect the conformation change of PLG at air/water interface and figure a well miscibility with polymer whereas the nonionic amphiphilic molecule presents poor miscibility. In addition, the even mixing of the PLG and the cationic surfactants is favorable for the adsorption to DNA more effectively.

Cationic microparticles are a potent delivery system for a HCV DNA vaccine

We initially evaluated in mice the ability of naked DNA encoding intracellular forms of the E1E2 envelope proteins from HCV to induce antibody responses and compared the responses induced with the same plasmid adsorbed onto cationic poly (lactide co-glycolide) (PLG) microparticles. Although naked DNA was only able to induce detectable responses at the 100 microg dose level, making this approach impractical for evaluation in larger animals, PLG/DNA induced detectable responses at 10 microg. In addition, the PLG/DNA microparticles induced significantly enhanced responses to naked DNA when compared at the same dose level. Remarkably, PLG/DNA induced comparable responses to recombinant E1E2 protein adjuvanted with the emulsion MF59. Furthermore, PLG/DNA effectively primed for a booster response with protein immunization, while naked DNA did not. Therefore, PLG/DNA was selected for further evaluation in a non-human primate model. In a study in rhesus macaques, PLG/DNA induced seroconversion in 3/3 animals following three immunizations. Although the antibody responses appeared lower than those induced with recombinant protein adjuvanted with MF59, following a fourth dose, PLG/DNA and protein induced comparable responses. However, a single booster dose of recombinant protein administered to the animals previously immunized with PLG/DNA induced much higher responses. In addition, one of three animals immunized with PLG/DNA showed a cytotoxic T lymphocyte response in peripheral blood lymphocytes. In conclusion, cationic PLG microparticles with adsorbed HCV DNA generates potent immune responses.

DNA vaccination against respiratory syncytial virus in young calves

A DNA vaccine encoding the fusion (F) gene (DNA-F) of bovine respiratory syncytial virus (BRSV) induced significant protection against BRSV infection in young calves. However, serum antibody to RSV developed more slowly in animals vaccinated with DNA-F when compared with those previously infected with BRSV. Furthermore, protection against BRSV infection was not as great as that induced by prior BRSV infection. Although there was little difference in the level of protection induced in calves vaccinated with DNA-F by either the intramuscular (i.m.) or intradermal (i.d.) routes, only the i.m. route primed for a rapid BRSV-specific IgA response after BRSV challenge. These results indicate that a DNA vaccination may be effective against RSV infection even in very young infants and calves.

Novel approaches to vaccine delivery

Although the currently available vaccines represent an outstanding success story in modern medicine and have had a dramatic effect on morbidity and mortality worldwide, it is clear that improvements are required in the current vaccine delivery technologies. Improvements are required to enable the successful development of vaccines against infectious diseases that have so far proven difficult to control with conventional approaches. Improvements may include the addition of novel injectable adjuvants or the use of novel routes of delivery, including mucosal immunization. Mucosal delivery may be required to provide protection against pathogens that infect at mucosal sites, including sexually transmitted diseases. Alternatively, novel approaches to delivery, including mucosal administration, may be used to improve compliance for existing vaccines. Of particular interest for safer mass immunization campaigns are needle-free delivery devices, which would avoid problems due to needle re-use in many parts of the world and would avoid needle-stick injuries.

Induction of Th1 type response by DNA vaccinations with N, M, and E genes against SARS-CoV in mice

Vaccination against the SARS-CoV infection is an attractive means to control the spread of viruses in public. In this study, we employed a DNA vaccine technology with the levamisole, our newly discovered chemical adjuvant, to generate Th1 type of response. To avoid the enhancement antibody issue, genes encoding the nucleocapsid, membrane, and envelope protein of SARS-CoV were cloned and their expressions in mammalian cells were determined. After the intramuscular introduction into animals, we observed that the constructs of the E, M, and N genes could induce high levels of specific antibodies, T cell proliferations, IFN-γ, DTH responses, and in vivo cytotoxic T cells activities specifically against SARS-CoV antigens. The highest immune responses were generated by the construct encoding the nucleocapsid protein. The results suggest that the N, M, and E genes could be used as the targets to prevent SARS-CoV infection in the DNA vaccine development.

Mucosal adjuvants and delivery systems for protein-, DNA- and RNA-based vaccines

Almost all vaccinations today are delivered through parenteral routes. Mucosal vaccination offers several benefits over parenteral routes of vaccination, including ease of administration, the possibility of self-administration, elimination of the chance of injection with infected needles, and induction of mucosal as well as systemic immunity. However, mucosal vaccines have to overcome several formidable barriers in the form of significant dilution and dispersion; competition with a myriad of various live replicating bacteria, viruses, inert food and dust particles; enzymatic degradation; and low pH before reaching the target immune cells. It has long been known that vaccination through mucosal membranes requires potent adjuvants to enhance immunogenicity, as well as delivery systems to decrease the rate of dilution and degradation and to target the vaccine to the site of immune function. This review is a summary of current approaches to mucosal vaccination, and it primarily focuses on adjuvants as immunopotentiators and vaccine delivery systems for mucosal vaccines based on protein, DNA or RNA. In this context, we define adjuvants as protein or oligonucleotides with immunopotentiating properties co-administered with pathogen-derived antigens, and vaccine delivery systems as chemical formulations that are more inert and have less immunomodulatory effects than adjuvants, and that protect and deliver the vaccine through the site of administration. Although vaccines can be quite diverse in their composition, including inactivated virus, virus-like particles and inactivated bacteria (which are inert), protein-like vaccines, and non-replicating viral vectors such as poxvirus and adenovirus (which can serve as DNA delivery systems), this review will focus primarily on recombinant protein antigens, plasmid DNA, and alphavirus-based replicon RNA vaccines and delivery systems. This review is not an exhaustive list of all available protein, DNA and RNA vaccines, with related adjuvants and delivery systems, but rather is an attempt to highlight many of the currently available approaches in immunopotentiation of mucosal vaccines.

CpG oligodeoxynucleotides adsorbed onto polylactide-co-glycolide microparticles improve the immunogenicity and protective activity of the licensed anthrax vaccine

To reduce the biothreat posed by anthrax, efforts are under way to improve the protection afforded by vaccination. This work examines the ability of immunostimulatory CpG oligodeoxynucleotides (ODN) adsorbed onto cationic polylactide-co-glycolide (PLG) microparticles (CpG ODN-PLG) to accelerate and boost the protective immunity elicited by Anthrax Vaccine Adsorbed (AVA, the licensed human anthrax vaccine). The results indicate that coadministering CpG ODN-PLG with AVA induces a stronger and faster immunoglobulin G response against the protective antigen of anthrax than AVA alone. Immunized mice were protected from lethal anthrax challenge within 1 week of vaccination with CpG ODN-PLG plus AVA, with the level of protection correlating with serum immunoglobulin G anti-protective antigen titers.

Strategies for enhancing the immunostimulatory effects of CpG oligodeoxynucleotides

Synthetic oligodeoxynucleotides (ODN) containing CpG sequences are recognized as a "danger" signal by the immune system of mammals. As a consequence, CpG ODN stimulate innate and adaptive immune responses in humans and a variety of animal species. Indeed, the potential of CpG ODN as therapeutic agents and vaccine adjuvants has been demonstrated in animal models of infectious diseases, allergy and cancer and are currently undergoing clinical trials in humans. While CpG ODN are potent activators of the immune system, their biologic activity is often transient, subsequently limiting their therapeutic application. Modifications in the CpG ODN backbone chemistry, various delivery methods including mixing or cross-linking of ODN to other carrier compounds have been shown to significantly enhance the biologic activity of ODN. However, the exact mechanisms that mediate this enhancement of activity are not well understood and may include local cell recruitment and activation, cytokine production, upregulation of receptor expression and increasing the half-life of ODN through creation of a depot. We will review the various approaches that have been used in enhancing the immunostimulatory effects of CpG ODN in vivo and also discuss the possible mechanisms that may be involved in this enhancement.

Characterization and biological evaluation of a microparticle adjuvant formulation for plasmid DNA vaccines

We describe the physiochemical characterization and immunological evaluation of plasmid DNA vaccine formulations containing a nonionic triblock copolymer adjuvant (CRL1005) in the presence and absence of a cationic surfactant, benzalkonium chloride (BAK). CRL1005 forms particles of 1-10 microns upon warming above its phase-transition temperature (approximately 6-8 degrees C) and the physical properties of the particles are altered by BAK. DNA/CRL1005 vaccines formulated with and without BAK were evaluated in rhesus macaques to determine the effect of CRL1005 and BAK on the ability of plasmid DNA to induce a cellular immune response. Immunogenicity results indicate that the addition of CRL1005 to human immunodeficiency virus-1 gag plasmid DNA formulated in phosphate-buffered saline leads to an enhancement in the gag-specific cellular immune response. Moreover, the addition of BAK to human immunodeficiency virus-1 gag plasmid DNA/CRL1005 formulations produces an additional enhancement in gag-specific cellular immunity. In vitro characterization studies of DNA/CRL1005 formulations indicate no detectable binding of DNA to CRL1005 particles in the absence of BAK, suggesting that the enhancement of cellular immunity induced by DNA/CRL1005 formulations is not due to enhanced DNA delivery. In the presence of BAK, however, results indicate that BAK binds to CRL1005 particles, producing cationic microparticles that bind DNA through electrostatic interactions. If BAK is present at the phase-transition temperature, it reduces the particle size from approximately 2 microns to approximately 300 nm, presumably by binding to hydrophobic surfaces during particle formation. Zeta potential measurements indicate that the surface charge of CRL1005-BAK particles changes from positive to negative upon DNA binding, and DNA bound to the surface of CRL1005-BAK particles was visualized by fluorescence microscopy. These results indicate that the addition of BAK to DNA/CRL1005 formulations leads to the formation of approximately 300 nm CRL1005-BAK-DNA particles that enhance the cellular immune response in rhesus monkeys.

Human Clinical Trials of Plasmid DNA Vaccines

This article gives an overview of DNA vaccines with specific emphasis on the development of DNA vaccines for clinical trials and an overview of those trials. It describes the preclinical research that demonstrated the efficacy of DNA vaccines as well as an explication of the immunologic mechanisms of action. These include the induction of cognate immune responses, such as the generation of cytolytic T lymphocytes (CTL) as well as the effect of the plasmid DNA upon the innate immune system. Specific issues related to the development of DNA as a product candidate are then discussed, including the manufacture of plasmid, the qualification of the plasmid DNA product, and the safety testing necessary for initiating clinical trials. Various human clinical trials for infectious diseases and cancer have been initiated or completed, and an overview of these trials is given. Finally, because the early clinical trials have shown less than optimal immunogenicity, methods to increase the potency of the vaccines are described.

Microparticles for the delivery of DNA vaccines

DNA vaccines have demonstrated a lack of adequate potency in humans, which has necessitated the exploration of various adjunct technologies. Inefficient delivery of DNA vaccines, particularly to antigen-presenting cells, may be contributing to this lack of potency. One effective means of facilitating delivery of DNA vaccines to APCs is through the use of microparticles. In this article, we review the background and rationale for microparticles as a vaccine delivery system, data demonstrating their utility and mode of action for DNA delivery, and the prospects for their development.

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

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

Adsorption of a Novel Recombinant Glycoprotein from HIV (Env gp120dV2 SF162) to Anionic PLG Microparticles Retains the Structural Integrity of the Protein, Whereas Encapsulation in PLG Microparticles Does Not

PURPOSE

To evaluate the delivery of a novel HIV-1 antigen (gp120dV2 SF162) by surface adsorption or encapsulation within polylactide-co-glycolide microparticles and to compare both the formulations for their ability to preserve functional activity as measured by binding to soluble CD4.

METHODS

Poly(lactide-co-glycolide) microparticles were synthesized by a water-in-oil-in-water (w/o/w) emulsification method in the presence of the anionic surfactant dioctylsulfosuccinate (DSS) or polyvinyl alcohol. The HIV envelope glyocoprotein was adsorbed and encapsulated in the PLG particles. Binding efficiency and burst release measured to determine adsorption characteristics. The ability to bind CD4 was assayed to measure the functional integrity of gp120dV2 following different formulation processes.

RESULTS

Protein (antigen) binding to PLG microparticles was influenced by both electrostatic interaction and other mechanisms such as hydrophobic attraction and structural accommodation of the polymer and biomolecule. The functional activity as measured by the ability of gp120dV2 to bind CD4 was maintained by adsorption onto anionic microparticles but drastically reduced by encapsulation.

CONCLUSIONS

The antigen on the adsorbed PLG formulation maintained its binding ability to soluble CD4 in comparison to encapsulation, demonstrating the feasibility of using these novel anionic microparticles as a potential vaccine delivery system.

Enhanced protective efficacy of a tuberculosis DNA vaccine by adsorption onto cationic PLG microparticles

Immunization with plasmid DNA vectors represents a promising new approach to vaccination. It has been shown to elicit humoral and cellular immunity and protection in various infection models. Here, we assessed the immunogenicity and protective efficacy of a DNA vaccine vector encoding the antigen 85A (Ag85A) of Mycobacterium tuberculosis. Since intramuscular (i.m.) immunization with naked DNA requires considerable amounts of DNA in order to be effective, we evaluated a strategy to reduce the amount of DNA needed. To this end, we used Ag85A DNA adsorbed onto cationic poly(DL-lactide-co-glycolide) (PLG) microparticles and observed similar levels of protection against aerosol challenge in mice using doses of PLG-DNA two orders of magnitude lower than with naked DNA itself.

Immunogenicity in mice of a cationic microparticle-adsorbed plasmid DNA encoding Japanese encephalitis virus envelope protein

Previously, we described a plasmid pMEa, synthesizing the anchored form of Japanese encephalitis virus (JEV) envelope protein that generated virus-neutralizing antibodies in mice upon intra-muscular injection. The immunized mice showed significant protection against lethal JEV challenge. In order to improve the efficacy of plasmid DNA immunization against JEV, methods need to be employed that would enhance neutralizing antibody titers. Plasmid DNA adsorbed to cationic microparticles has recently been shown to significantly improve its immunogenicity. In the present study, we have adsorbed the plasmid pMEa on cationic microparticles and have compared its immunogenicity with the naked plasmid DNA. As seen in ELISA, the microparticle-adsorbed DNA induced higher titers of anti-JEV antibodies when compared to those induced by the naked DNA. No difference, however, was seen in JEV neutralization titers. The microparticle-adsorbed DNA induced a mixed Th1-Th2 kind of immune responses as opposed to Th1 type of immune responses elicited by the naked DNA.

Approaches to enhance the efficacy of DNA vaccines

DNA vaccines consist of antigen-encoding bacterial plasmids that are capable of inducing antigen-specific immune responses upon inoculation into a host. This method of immunization is advantageous in terms of simplicity, adaptability, and cost of vaccine production. However, the entry of DNA vaccines and expression of antigen are subjected to physical and biochemical barriers imposed by the host. In small animals such as mice, the host-imposed impediments have not prevented DNA vaccines from inducing long-lasting, protective humoral, and cellular immune responses. In contrast, these barriers appear to be more difficult to overcome in large animals and humans. The focus of this article is to summarize the limitations of DNA vaccines and to provide a comprehensive review on the different strategies developed to enhance the efficacy of DNA vaccines. Several of these strategies, such as altering codon bias of the encoded gene, changing the cellular localization of the expressed antigen, and optimizing delivery and formulation of the plasmid, have led to improvements in DNA vaccine efficacy in large animals. However, solutions for increasing the amount of plasmid that eventually enters the nucleus and is available for transcription of the transgene still need to be found. The overall conclusions from these studies suggest that, provided these critical improvements are made, DNA vaccines may find important clinical and practical applications in the field of vaccination.

DNA vaccines to attack cancer

Delivery of antigens by injection of the encoding DNA allows access to multiple antigen-presenting pathways. Knowledge of immunological processes can therefore be used to modify construct design to induce selected effector functions. Expression can be directed to specific intracellular sites, and additional genes can be fused or codelivered to amplify responses. Therapeutic vaccination against cancer adds a requirement to overcome tolerance and to activate a weakened immune repertoire. Induction of CD4(+) T helper cells is critical for both antibody and T cell effector responses. To activate immunity against tumor antigens, we fused the tumor-derived sequences to genes encoding microbial proteins. This strategy engages T helper cells from the large antimicrobial repertoire for linked help for inducing antibody against cell-surface tumor antigens. The principle of linked T cell help also holds for induction of epitope-specific antitumor CD8(+) T cells, but the microbial sequence has to be minimized to avoid competition with tumor antigens. Epitope-specific DNA vaccination leads to powerful antitumor attack and can activate immunity from a profoundly tolerized repertoire. Vaccine designs validated in preclinical models are now in clinical trial with immune responses detected against both tumor antigens and fused microbial antigens. DNA priming is highly efficient, but boosting may benefit from increased antigen expression. Physical methods including electroporation provide increased expression without introducing additional competing antigens. A wide range of cancers can be targeted, and objective assays of response will determine efficacy.

Poly-beta amino ester-containing microparticles enhance the activity of nonviral genetic vaccines

Current nonviral genetic vaccine systems are less effective than viral vaccines, particularly in cancer systems where epitopes can be weakly immunogenic and antigen-presenting cell processing and presentation to T cells is down-regulated. A promising nonviral delivery method for genetic vaccines involves microencapsulation of antigen-encoding DNA, because such particles protect plasmid payloads and target them to phagocytic antigen-presenting cells. However, conventional microparticle formulations composed of poly lactic-co-glycolic acid take too long to release encapsulated payload and fail to induce high levels of target gene expression. Here, we describe a microparticle-based DNA delivery system composed of a degradable, pH-sensitive poly-beta amino ester and poly lactic-co-glycolic acid. These formulations generate an increase of 3-5 orders of magnitude in transfection efficiency and are potent activators of dendritic cells in vitro. When used as vaccines in vivo, these microparticle formulations, unlike conventional formulations, induce antigen-specific rejection of transplanted syngenic tumor cells.

An assessment of different DNA delivery systems for protection against respiratory syncytial virus infection in the murine model: gene-gun delivery induces IgG in the lung

Immunization with plasmid DNA (pDNA) has the potential to overcome the difficulties of neonatal vaccination that may be required for protection against infection with respiratory syncytial virus (RSV); however, little is known about optimal delivery modalities. In this pilot study we compared mucosal delivery of pDNA encoding RSV F protein encapsulated in poly(DL-lactide-co-glycolide) with delivery of pDNA by gene-gun for the induction of immunity in mice. Intra-gastric or intra-nasal immunization with various doses of microparticles induced weak low levels of RSV-specific serum antibodies in a proportion of mice; in contrast, gene-gun vaccination led to protective immunity associated with a humoral response. Interestingly, RSV-specific antibody was detected in lung fragment cultures following intradermal vaccination with the gene-gun.

Enhancement of DNA vaccine potency in rhesus macaques by electroporation

The potency of an HIV DNA vaccine was enhanced in rhesus macaques by in vivo electroporation, as judged by increased onset, magnitude and duration of antibody and cell-mediated immune responses against both components of a combination Gag and Env vaccine. These data demonstrate the utility of the electroporation technology for use in large animals.