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

Approaches to treating tuberculosis by encapsulating metal ions and anti-mycobacterial drugs utilizing nano- and microparticle technologies

Tuberculosis (TB) is caused by a bacterial infection that affects a number of human organs, primarily the lungs, but also the liver, spleen, and spine, causing key symptoms of fever, fatigue, and persistent cough, and if not treated properly, can be fatal. Every year, 10 million individuals become ill with active TB resulting with a mortality approximating 1.5 million. Current treatment guidelines recommend oral administration of a combination of first-line anti-TB drugs for at least 6 months. While efficacious under optimum conditions, 'Directly Observed Therapy Short-course' (DOTS) is not without problems. The long treatment time and poor pharmacokinetics, alongside drug side effects lead to poor patient compliance and has accelerated the emergence of multi-drug resistant (MDR) organisms. All this, combined with the limited number of newly discovered TB drugs to treat MDR-TB and shorten standard therapy time, has highlighted the need for new targeted drug delivery systems. In this respect, there has been recent focus on micro- and nano-particle technologies to prepare organic or/and metal particles loaded with TB drugs to enhance their efficacy by targeted delivery via the inhaled route. In this review, we provide a brief overview of the current epidemiology of TB, and risk factors for progression of latent stage tuberculosis (LTBI) to the active TB. We identify current TB treatment regimens, newly discovered TB drugs, and identify studies that have used micro- or nano-particles technologies to design a reliable inhalation drug delivery system to treat TB more effectively.

Recent progress in the design of DNA vaccines against tuberculosis

Current tuberculosis (TB) vaccines have some disadvantages and many efforts have been undertaken to produce effective TB vaccines. As a result of their advantages, DNA vaccines are promising future vaccine candidates. This review focuses on the design and delivery of novel DNA-based vaccines against TB.

Tuberculosis vaccine candidates based on mycobacterial cell envelope components

Even after decades searching for a new and more effective vaccine against tuberculosis, the scientific community is still pursuing this goal due to the complexity of its causative agent, Mycobacterium tuberculosis (Mtb). Mtb is a microorganism with a robust variety of survival mechanisms that allow it to remain in the host for years. The structure and nature of the Mtb envelope play a leading role in its resistance and survival. Mtb has a perfect machinery that allows it to modulate the immune response in its favor and to adapt to the host's environmental conditions in order to remain alive until the moment to reactivate its normal growing state. Mtb cell envelope protein, carbohydrate and lipid components have been the subject of interest for developing new vaccines because most of them are responsible for the pathogenicity and virulence of the bacteria. Many indirect evidences, mainly derived from the use of monoclonal antibodies, support the potential protective role of Mtb envelope components. Subunit and DNA vaccines, lipid extracts, liposomes and membrane vesicle formulations are some examples of technologies used, with encouraging results, to evaluate the potential of these antigens in the protective response against Mtb.

Advancements in DNA vaccine vectors, non-mechanical delivery methods, and molecular adjuvants to increase immunogenicity

A major advantage of DNA vaccination is the ability to induce both humoral and cellular immune responses. DNA vaccines are currently used in veterinary medicine, but have not achieved widespread acceptance for use in humans due to their low immunogenicity in early clinical studies. However, recent clinical data have re-established the value of DNA vaccines, particularly in priming high-level antigen-specific antibody responses. Several approaches have been investigated for improving DNA vaccine efficacy, including advancements in DNA vaccine vector design, the inclusion of genetically engineered cytokine adjuvants, and novel non-mechanical delivery methods. These strategies have shown promise, resulting in augmented adaptive immune responses in not only mice, but also in large animal models. Here, we review advancements in each of these areas that show promise for increasing the immunogenicity of DNA vaccines.

Advancements in DNA vaccine vectors, non-mechanical delivery methods, and molecular adjuvants to increase immunogenicity

A major advantage of DNA vaccination is the ability to induce both humoral and cellular immune responses. DNA vaccines are currently used in veterinary medicine, but have not achieved widespread acceptance for use in humans due to their low immunogenicity in early clinical studies. However, recent clinical data have re-established the value of DNA vaccines, particularly in priming high-level antigen-specific antibody responses. Several approaches have been investigated for improving DNA vaccine efficacy, including advancements in DNA vaccine vector design, the inclusion of genetically engineered cytokine adjuvants, and novel non-mechanical delivery methods. These strategies have shown promise, resulting in augmented adaptive immune responses in not only mice, but also in large animal models. Here, we review advancements in each of these areas that show promise for increasing the immunogenicity of DNA vaccines.

Plasmid Biopharmaceuticals

Plasmids are currently an indispensable molecular tool in life science research and a central asset for the modern biotechnology industry, supporting its mission to produce pharmaceutical proteins, antibodies, vaccines, industrial enzymes, and molecular diagnostics, to name a few key products. Furthermore, plasmids have gradually stepped up in the past 20 years as useful biopharmaceuticals in the context of gene therapy and DNA vaccination interventions. This review provides a concise coverage of the scientific progress that has been made since the emergence of what are called today plasmid biopharmaceuticals. The most relevant topics are discussed to provide researchers with an updated overview of the field. A brief outline of the initial breakthroughs and innovations is followed by a discussion of the motivation behind the medical uses of plasmids in the context of therapeutic and prophylactic interventions. The molecular characteristics and rationale underlying the design of plasmid vectors as gene transfer agents are described and a description of the most important methods used to deliver plasmid biopharmaceuticals in vivo (gene gun, electroporation, cationic lipids and polymers, and micro- and nanoparticles) is provided. The major safety issues (integration and autoimmunity) surrounding the use of plasmid biopharmaceuticals is discussed next. Aspects related to the large-scale manufacturing are also covered, and reference is made to the plasmid products that have received marketing authorization as of today.

Development of novel carrier(s) mediated tuberculosis vaccine: more than a tour de force

Despite worldwide availability of the vaccines against most of the infectious diseases, BCG and various programs such as Directly Observed Treatment Short course (DOTS) to prevent tuberculosis still remains one of the most deadly forms of the disease affecting millions of people globally. The evolution of multi drug resistant strains (MDR) has increased the complexity further. Although currently available marketed BCG vaccine has shown sufficient protection against childhood tuberculosis, it has failed to prevent the most common form of disease i.e., pulmonary tuberculosis in adults. However, various vaccine candidates have already entered phase I clinical trials and have shown promising outcomes. The most prominent amongst them is the heterologous prime-boost approach, which shows a great promise towards designing and development of a new efficacious tuberculosis vaccine. It has also been shown that the use of various viral and non-viral vectors as carriers for the potential vaccine candidates will further boost their effect on subsequent immunization. In this review, we briefly summarize the potential of a few novel nano-carriers for developing effective vaccination strategies against tuberculosis.

Engineering vaccines and niches for immune modulation

Controlled modulation of immune response, especially the balance between immunostimulatory and immunosuppressive responses, is critical for a variety of clinical applications, including immunotherapies against cancer and infectious diseases, treatment of autoimmune disorders, transplant surgeries, regenerative medicine, prosthetic implants, etc. Our ability to precisely modify both innate and adaptive immune responses could provide new therapeutic directions in a variety of diseases. In the context of vaccines and immunotherapies, the interplay between antigen-presenting cells (e.g. dendritic cells and macrophages), B cells, T helper and killer subtypes, and regulatory T- and B-cell responses is critical for generating effective immunity against cancer, infectious diseases and autoimmune diseases. In recent years, immunoengineering has emerged as a new field that uses quantitative engineering tools to understand molecular-, cellular- and system-level interactions of the immune system and to develop design-driven approaches to control and modulate immune responses. Biomaterials are an integral part of this engineering toolbox and can exploit the intrinsic biological and mechanical cues of the immune system to directly modulate and train immune cells and direct their response to a particular phenotype. A large body of literature exists on strategies to evade or suppress the immune response in implants, transplantation and regenerative medicine. This review specifically focuses on the use of biomaterials for immunostimulation and controlled modulation, especially in the context of vaccines and immunotherapies against cancer, infectious diseases and autoimmune disorders. Bioengineering smart systems that can simultaneously deliver multiple bioactive agents in a controlled manner or can work as a niche for in situ priming and modulation of the immune system could significantly enhance the efficacy of next-generation immunotherapeutics. In this review, we describe our perspective on the important design aspects for the development of biomaterials that can actively modulate immune responses by stimulating receptor complexes and cells, and delivering multiple immunomodulatory biomolecules.

Preparation and efficacy of Newcastle disease virus DNA vaccine encapsulated in PLGA nanoparticles

Background

Although the Newcastle disease virus (NDV) inactivated vaccines and attenuated live vaccines have been used to prevent and control Newcastle disease (ND) for years, there are some disadvantages. Recently, newly developed DNA vaccines have the potential to overcome these disadvantages. The low delivery efficiency, however, hindered the application of DNA vaccines for ND in practice.

Methodology/Principal Findings

The eukaryotic expression plasmid pVAX1-F (o) DNA that expressed the F gene of NDV encapsulated in PLGA nanoparticles (pFNDV-PLGA-NPs) were prepared by a double emulsion-solvent evaporation method and optimal preparation conditions of the pFNDV-PLGA-NPs were determined. Under the optimal conditions, the pFNDV-PLGA-NPs were produced in good morphology and had high stability with a mean diameter of 433.5±7.5 nm, with encapsulation efficiency of 91.8±0.3% and a Zeta potential of +2.7 mV. Release assay in vitro showed that the fusion gene plasmid DNA could be sustainably released from the pFNDV-PLGA-NPs up to 93.14% of the total amount. Cell transfection test indicated that the vaccine expressed and maintained its bioactivity. Immunization results showed that better immune responses of SPF chickens immunized with the pFNDV-PLGA-NPs were induced compared to the chickens immunized with the DNA vaccine alone. In addition, the safety of mucosal immunity delivery system of the pFNDV-PLGA-NPs was also tested in an in vitro cytotoxicity assay.

Conclusions/Significance

The pFNDV-PLGA-NPs could induce stronger cellular, humoral, and mucosal immune responses and reached the sustained release effect. These results laid a foundation for further development of vaccines and drugs in PLGA nanoparticles.

The long-term potential of biodegradable poly(lactide-co-glycolide) microparticles as the next-generation vaccine adjuvant

Biodegradable polymeric microparticles of poly(lactide-co-glycolide) (PLG) have been extensively evaluated for drug delivery and vaccine applications over the last three decades. Despite a wealth of studies on the use of PLG microparticles in vaccines through controlled release of antigens, there is no commercial PLG-based vaccine as yet. The key challenge that prevented the development of PLG microparticles as commercial vaccines was the instability of encapsulated antigen. Over the years, advancements were made towards maintaining antigen integrity during PLG microparticle preparation and sterilization. In parallel and independently, development of PLG microparticles as therapeutic commercial products established PLG with an excellent safety record in humans, and as a suitable candidate for next-generation vaccines. Through the combination of Toll-like receptor agonist encapsulation and surface adsorption of antigen, PLG microparticles can be used as a vaccine adjuvant to address unmet medical needs, such as vaccines against HIV, malaria and TB. With strategic development of PLG-based vaccines, PLG microparticles can offer advantages over the conventional vaccine adjuvants allowing commercial development of this adjuvant.

Effect of nanoparticle coating on the immunogenicity of plasmid DNA vaccine encoding P. yoelii MSP-1 C-terminal

In order to assess a new strategy for DNA vaccine formulation and delivery, plasmid encoding Plasmodium yoelii MSP-1 C-terminal was formulated with newly designed nanoparticle-an anionic ternary complex of polyethylenimine and γ-polyglutamic acid (pVAX-MSP-1/PEI/γ-PGA), and intravenously administered to C57BL/6 mice in four different doses, three times at 3-week interval. Antibody response as determined by ELISA, IFA and Western blot, was dose-dependent and subsequent challenge with 10(5)P. yoelii-infected red blood cells revealed 33-60% survival in repeated experiments at a dose of 80 μg pDNA/mouse. IgG subtypes and cytokine levels in the serum and culture supernatants of stimulated spleen cells were also measured. Antigen-specific IgG response provoked by the DNA vaccination was dominated by IgG1 and IgG2b. Although the elevation of IL-12p40 and IFN-γ was marginal (P≥0.354) in the coated group, interleukin-4 levels were significantly higher (P≥0.013) in the coated group than in the naked or control group, suggesting a predominant Th2-type CD4(+) T cell response. These results therefore, overall indicate the possibility of selection and optimization of DNA vaccine formulation for intravenous delivery and may be useful in designing a nanoparticle-coated DNA vaccine that could optimally elicit a desired antibody response for various disease conditions.

Mucosal vaccines: recent progress in understanding the natural barriers

It has long been known that protection against pathogens invading the organism via mucosal surfaces correlates better with the presence of specific antibodies in local secretions than with serum antibodies. The most effective way to induce mucosal immunity is to administer antigens directly to the mucosal surface. The development of vaccines for mucosal application requires antigen delivery systems and immunopotentiators that efficiently facilitate the presentation of the antigen to the mucosal immune system. This review provides an overview of the events within mucosal tissues that lead to protective mucosal immune responses. The understanding of those biological mechanisms, together with knowledge of the technology of vaccines and adjuvants, provides guidance on important technical aspects of mucosal vaccine design. Not being exhaustive, this review also provides information related to modern adjuvants, including polymeric delivery systems and immunopotentiators.

Administration of HPV DNA vaccine via electroporation elicits the strongest CD8+ T cell immune responses compared to intramuscular injection and intradermal gene gun delivery

DNA vaccines are an attractive approach to eliciting antigen-specific immunity. Intracellular targeting of tumor antigens through its linkage to immunostimulatory molecules such as calreticulin (CRT) can improve antigen processing and presentation through the MHC class I pathway and increase cytotoxic CD8+ T cell production. However, even with these enhancements, the efficacy of such immunotherapeutic strategies is dependent on the identification of an effective route and method of DNA administration. Electroporation and gene gun-mediated particle delivery are leading methods of DNA vaccine delivery that can generate protective and therapeutic levels of immune responses in experimental models. In this study, we perform a head-to-head comparison of three methods of vaccination--conventional intramuscular injection, electroporation-mediated intramuscular delivery, and epidermal gene gun-mediated particle delivery--in the ability to generate antigen-specific cytotoxic CD8+ T cell responses as well as anti-tumor immune responses against an HPV-16 E7 expressing tumor cell line using the pNGVL4a-CRT/E7(detox) DNA vaccine. Vaccination via electroporation generated the highest number of E7-specific cytotoxic CD8+ T cells, which correlated to improved outcomes in the treatment of growing tumors. In addition, we demonstrate that electroporation results in significantly higher levels of circulating protein compared to gene gun or intramuscular vaccination, which likely enhances calreticulin's role as a local tumor anti-angiogenesis agent. We conclude that electroporation is a promising method for delivery of HPV DNA vaccines and should be considered for DNA vaccine delivery in human clinical trials.

Pulmonary delivery of DNA encoding Mycobacterium tuberculosis latency antigen Rv1733c associated to PLGA-PEI nanoparticles enhances T cell responses in a DNA prime/protein boost vaccination regimen in mice

During persistent infection and hypoxic-stress, Mycobacterium tuberculosis (Mtb) expresses a series of Mtb latency antigens. The aim of this study was to evaluate the immunogenicity of a DNA vaccine encoding the Mtb latency antigen Rv1733c and to explore the effect of pulmonary delivery and co-formulation with poly (d,l-lactide-co-glycolide) (PLGA)-polyethyleneimine (PEI) nanoparticles (np) on host immunity. Characterization studies indicated that PLGA-PEI np kept their nanometer size after concentration and were positively charged. The np were able to mature human dendritic cells and stimulated them to secrete IL-12 and TNF-alpha comparable to levels observed after lipopolysaccharide (LPS) stimulation. Mtb latency antigen Rv1733c DNA prime combined with Rv1733c protein boost enhanced T cell proliferation and IFN-gamma secretion in mice in response to Rv1733c and Mtb hypoxic lysate. Rv1733c DNA adsorbed to PLGA-PEI np and applied to the lungs increased T cell proliferation and IFN-gamma production more potently compared to the same vaccinations given intramuscularly. The strongest immunogenicity was obtained by pulmonary priming with np-adsorbed Rv1733c DNA followed by boosting with Rv1733c protein. These results confirm that PLGA-PEI np are an efficient DNA vaccine delivery system to enhance T cell responses through pulmonary delivery in a DNA prime/protein boost vaccine regimen.

Measles: old vaccines, new vaccines

Isolation of measles virus in tissue culture by Enders and colleagues in the 1960s led to the development of the first measles vaccines. An inactivated vaccine provided only short-term protection and induced poor T cell responses and antibody that did not undergo affinity maturation. The response to this vaccine primed for atypical measles, a more severe form of measles, and was withdrawn. A live attenuated virus vaccine has been highly successful in protection from measles and in elimination of endemic measles virus transmission with the use of two doses. This vaccine is administered by injection between 9 and 15 months of age. Measles control would be facilitated if infants could be immunized at a younger age, if the vaccine were thermostable, and if delivery did not require a needle and syringe. To these ends, new vaccines are under development using macaques as an animal model and various combinations of the H, F, and N viral proteins. Promising studies have been reported using DNA vaccines, subunit vaccines, and virus-vectored vaccines.

Effects of menstrual cycle on gene transfection through mouse vagina for DNA vaccine

Human immunodeficiency virus (HIV) infections mainly occur through the vaginal and rectal mucosal membranes. In the present study, to develop a DNA vaginal vaccine against viral and bacterial infections, the effects of the menstrual cycle on DNA transfection through the vaginal mucosa in female mice and transfection enhancement by electroporation, a chelating agent, cell-penetrating peptides (CPP) and nuclear localizing signals (NLS) were investigated. The transfection efficiencies of a marker plasmid DNA (pDNA), pCMV-Luc, on the vaginal mucosal membrane in mice at the stages of metestrus and diestrus were significantly higher than those at the stages of proestrus and estrus. The gene expression was markedly enhanced by electroporation and by pretreatment with the chelating agent. The highest level of expression was obtained by 2h pretreatment with 5% citric acid solution combined with electroporation with 15 pulses at 250 V/cm for 5 milliseconds (ms). Furthermore, a synergistic promoting effect on pDNA transfection was obtained by co-administration of CPP, the Tat peptide analog, and NLS, the NF-kappaB analog. These results indicate that effective DNA vaccination administered through the vaginal tract is possible by selecting the menstrual stage and overcoming the mucosal barrier using a combination of methods that promotes uptake.

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.

Markedly enhanced immunogenicity of a Pfs25 DNA-based malaria transmission-blocking vaccine by in vivo electroporation

Pfs25 is a promising target antigen for the development of a malaria transmission-blocking vaccine and prior research has demonstrated induction of high and functionally effective antibodies in mice with IM injection of Pfs25 encoding DNA plasmid. Likewise, Pfs25 DNA vaccine was immunogenic in rhesus macaques but required a protein boost to elicit significant transmission-blocking antibodies. The translation of these encouraging findings to human clinical trials has been impeded largely by the relatively poor immunogenicity of DNA plasmids in larger animals. In vivo electroporation (EP) has revealed significant enhancement of the potency of DNA plasmids. The results reported here compared the immunogenicity and functional transmission-blocking effects of immunization with DNA plasmid (25 microg) by the traditional IM route compared to coupling the IM injection (0.25, 2.5 and 25 microg doses) with in vivo EP. Significantly, a 0.25 microg dose of DNA plasmid, when administered with EP, induced antibody titers (1:160,000) and functional transmission-blocking effects that were equivalent to those achieved by a one hundred fold higher (25 microg) dose of DNA plasmid given without EP. At a 25.0 microg DNA dose with or without EP there was sufficient antigenic stimulation to result in effective antibody titers; however EP method yielded antibody titer of 1:1,280,000 as compared to only 1:160,000 titer without EP. This observed two log reduction in the amount of DNA plasmid required to induce significant transmission-blocking effects makes a compelling argument in favor of further evaluation of DNA vaccines by in vivo EP method in larger animals. Further experiments in non-human primates and eventually in phase I human trials will determine if the use of EP will induce effective and sustained malaria transmission-blocking effects at acceptable doses of plasmid DNA.

Plasmid DNA and viral vector-based vaccines for the treatment of cancer

Plasmid DNA and viral vector-based cancer vaccines have many inherent features that make them promising cancer vaccine candidates. This review focuses on the use of plasmid DNA and viral vector vaccines to deliver tumour-specific antigens to induce a tumour-specific immune response. Examples of different antigen delivery systems that have been tested in recent clinical trials are summarised and advantages and disadvantages of a number of delivery systems and approaches are discussed. Finally, an outlook on how plasmid DNA and viral vectors might be developed further as cancer vaccines is provided.

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.

The effect of co-administration of DNA carrying chicken interferon-γ gene on protection of chickens against infectious bursal disease by DNA-mediated vaccination

The purpose of the present study was to determine whether DNA vaccination by co-administration of DNA coding for chicken interferon-gamma (IFN-gamma) gene and DNA encoding for the VP243 gene of IBDV could enhance immune response and protection efficacy of chickens against challenge by IBDV. Plasmids carrying VP243 gene of IBDV strain variant E (VE) (P/VP243/E) and chicken IFN-gamma gene (P/cIFN-gamma) were constructed, respectively. One-day-old chickens were intramuscularly injected with P/VP243/E, or P/cIFN-gamma, or both once, twice, or three times into the thigh muscle of one leg or the thigh muscles of two separate legs at weekly intervals. Chickens were orally challenged with IBDV strain VE at 3 weeks of age and observed for 10 days. Chickens receiving two plasmids in the same site two times had significantly higher (P<0.05) bursal lesion scores and significantly lower (P<0.05) bursa weight/body weight ratios than those that only received P/VP243/E two or three times. Chickens inoculated with two plasmids separately in the thigh muscles of different legs or P/VP243/E two times had 33-50% protection and those receiving two plasmids in the same sites did not have any protection against IBD. The enzyme-linked immunosorbent assay (ELISA) and virus neutralization (VN) titers to IBDV of chickens in the groups with three doses of P/VP243/E were significantly higher (P<0.05) than those in groups receiving two doses of P/VP243/E or P/VP243/E and P/cIFN-gamma. Chickens protected by DNA vaccination did not have detectable IBDV antigen in the bursae as determined by immunofluorescent antibody assay (IFA). The results indicated that co-administration of plasmid encoding chicken IFN-gamma gene with plasmid encoding a large segment gene of the IBDV did not enhance immune response and protection against challenge by IBDV.

Delivery systems and adjuvants for oral vaccines

The oral route is the ideal means of delivering prophylactic and therapeutic vaccines, offering significant advantages over systemic delivery. Most notably, oral delivery is associated with simple administration and improved safety. In addition, unlike systemic immunisation, oral delivery can induce mucosal immune responses. However, the oral route of vaccine delivery is the most difficult because of the numerous barriers posed by the gastrointestinal tract. To facilitate effective immunisation with peptide and protein vaccines, antigens must be protected, uptake enhanced and the innate immune response activated. Numerous delivery systems and adjuvants have been evaluated for oral vaccine delivery, including live vectors, inert particles and bacterial toxins. Although developments in oral vaccines have been disappointing so far, in terms of the generation of products, the availability of a range of novel delivery systems offers much greater hope for the future development of improved oral vaccines.

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.

Intramuscular delivery of DNA releasing microspheres: microsphere properties and transgene expression

Plasmid-loaded microspheres can provide localized and sustained release into the target tissue, and thus have the potential to enhance the efficiency of naked DNA at promoting transgene expression. In this report, microsphere design parameters are investigated by correlating the extent and duration of transgene expression intramuscularly to the polymer molecular weight and the mass of DNA delivered. Plasmid DNA was incorporated into poly (lactide-co-glycolide) microspheres using a cryogenic double emulsion process, and microspheres were injected intramuscularly. Bolus injection of naked plasmid was used for control, which exhibited transfection of muscle cells with transgene expression that gradually decreased over time. Microspheres fabricated from low molecular weight polymer had expression levels that increased from day 1 to day 92, which subsequently decreased through day 174. Decreasing the microsphere mass delivered resulted in steady expression during the same time. However, microspheres fabricated with high molecular weight polymer had expression for only 14 days. Intramuscular injection resulted in a foreign body response to the microspheres, and these infiltrating cells adjacent were primarily transfected. This understanding of microsphere properties that determine transgene expression and the distribution of transfected cells may facilitate their application to fields such as tissue engineering or DNA vaccines.

Preclinical testing of new vaccines for tuberculosis: A comprehensive review

The past decade has seen an explosive increase in the development of potential new tuberculosis vaccine candidates, as well as the establishment of at least two testing centers. Various animal models, but particularly the mouse and guinea pig models, have provided a lot information about how new vaccines can reduce disease progression and how this influences the pathology of the disease, but there is still much to learn at the immunological level, particularly in terms of the nature of the T cell response that is needed to confer long lived resistance. Several categories of vaccine candidates have been tried to date, and there are at least five individual vaccines moving towards clinical evaluation. There are still areas of the field that are poorly developed however. These include the fact that we have no models of post- exposure vaccination, or any models of latent disease. In addition, no standardized models of safety/toxicology exist as yet, which will be needed before extensive clinical development of the new vaccines.

Polymeric microspheres as stabilizing anchors for oligonucleotide delivery to dendritic cells

The aim of this study is to evaluate a novel microspheric vector for delivery of oligonucleotides (ODN) into dendritic cells (DC). A requirement of decoy-based modulation of transcriptional activities in DC is that the ODN would have to accumulate inside the cell. Using an ex vivo DC culture model, we demonstrate that anionic microspheres (MS) coated with an ornithine/histadine-based cationic peptide (O10H6) is an effective carrier of short ODN. This method does not disrupt the colloidal nature of the microspheric particles. The MS provide stabilizing effect on DNA and O10H6 complexation. Accumulation of ODN in DC is greatly enhanced with the surface modified MS. Taken together, these data demonstrate that the self assembly system of MS(O10H6) is an effective delivery vehicle for DNA-based modulation of DC functions.

Cationic cage-like complexes formed by DC-cholesterol, Quil-A, and phospholipid

This study describes the formation of cationic, cage-like complexes which have a structure similar to classic anionic ISCOMs. In order to prepare these complexes cholesterol, a major component of classic ISCOM formulations, was substituted with a cationic derivative, 3beta-[N-(N',N'-dimethylaminoethane)-carbamoyl]-cholesterol (DC-CHOL). Colloidal dispersions with varying compositions of DC-CHOL, phosphatidylcholine, and Quil-A, which is a mixture of anionic triterpene saponins, were prepared by the lipid-film hydration method and characterised by transmission electron microscopy and laser Doppler electrophoresis. The colloidal structures obtained are presented in pseudo-ternary phase diagrams with two buffer systems as the pseudo-component. It was found that the formation of cationic, cage-like particles is highly depending on the formulation buffer. With TRIS buffered saline (TBS) pH 7.4, cage-like particles formed at compositions with high proportions of DC-CHOL and had a strongly positive zeta-potential. These could be purified by differential centrifugation. With phosphate buffered saline pH 7.4, the formation of cage-like particles was much reduced. It was shown that the formation of cage-like particles with a positive charge depended on suitable concentrations of TRIS in the hydration buffer.

Combined DNA vaccine encapsulated in microspheres enhanced protection efficacy against Mycobacterium tuberculosis infection of mice

In a study to develop novel vaccination strategies against tuberculosis, we encapsulated DNA encoding Ag85B, MPT-64 and MPT-83 antigens mixed with dimethyldioctyldecyl ammonium bromide (DDA) into biodegradable poly(dl-lactide-co-glycolide, PLGA) microspheres. Scanning electron microscopy (SEM) analysis demonstrated a uniform microsphere population with a mean diameter of <5microm. Using RT-PCR we were able to demonstrate antigen gene expression in selected tissue. Moreover, in mice injected with PLGA encapsulated DNA, the levels of expression appeared to be higher comparing to those injected with non-encapsulated DNA. Also, C57BL/6 mice immunized with a single dose of PLGA encapsulated DNA produced increased levels of IFN-gamma in the supernatant of spleen cells when cultured in the presence of the recombinant antigens. High levels of specific IgG antibody against the three antigens were also observed. In vaccine/challenge experiments, mice receiving a single dose of PLGA encapsulated DNA were protected against Mycobacterium tuberculosis challenge at levels comparable to groups of mice immunized with three doses of non-encapsulated DNA vaccine or with Mycobacterium bovis BCG.

Cationic microparticles consisting of poly(lactide-co-glycolide) and polyethylenimine as carriers systems for parental DNA vaccination

Cationic microparticles for DNA adsorption were formulated by blending poly(lactide-co-glycolide) (PLGA) (50:50), with different cationic agents, either PEI 25 kDa (polyethylenimine) or CTAB (cetyl-trimethyl-ammonium-bromide). The aim was to create adjuvant delivery systems increasing the efficiency of DNA vaccines. Microparticles formulated with 10% PEI exhibited a highly positive zeta-potential, small particle sizes, in contrast to particles prepared with CTAB, which revealed highly aggregated structures in scanning electron micrographs. PEI 10% microparticles efficiently adsorbed DNA and protected DNA from enzymatic degradation. Microparticles with up to 10% PEI did not affect membrane integrity whereas CTAB particles showed higher LDH release. Transfection efficiencies were assessed using a luciferase reporter gene assay compared to naked DNA and PEI/DNA polyplexes. DNA adsorbed onto microspheres with 10% or 50% PEI generally had higher transfection efficiencies than CTAB but reached lower expression levels than PEI/DNA polyplexes alone. This documented the intact release of DNA. The mechanism of gene delivery to non-phagocytic cells was studied via covalent fluorescence labeling of both the DNA and PEI by confocal microscopy and suggested uptake of DNA. Immunization of mice was performed using plasmids encoding immunodominant antigens of Listeria monocytogenes adsorbed onto RG 502 H+PEI 10% microparticles. The efficiency was tested by intravenous challenge with an otherwise lethal dose of L. monocytogenes. PLGA+PEI microspheres can be used as adjuvant delivery systems for DNA but further optimization is necessary to exploit their full potential.