Induction of broad and potent anti-human immunodeficiency virus immune responses in rhesus macaques by priming with a DNA vaccine and boosting with protein-adsorbed polylactide coglycolide microparticles

MicroRNA replacement therapy in cancer

Despite the recent progress in cancer management approaches, the mortality rate of cancer is still growing and there are lots of challenges in the clinics in terms of novel therapeutics. MicroRNAs (miRNA) are regulatory small noncoding RNAs and are already confirmed to have a great role in regulating gene expression level by targeting multiple molecules that affect cell physiology and disease development. Recently, miRNAs have been introduced as promising therapeutic targets for cancer treatment. Regulatory potential of tumor suppressor miRNAs, which enables regulation of entire signaling networks within the cells, makes them an interesting option for developing cancer therapeutics. In this regard, over recent decades, scientists have aimed at developing powerful and safe targeting approaches to restore these suppressive miRNAs in cancerous cells. The present review summarizes the function of miRNAs in tumor development and presents recent findings on how miRNAs have served as therapeutic agents against cancer, with a special focus on tumor suppressor miRNAs (mimics). Moreover, the latest investigations on the therapeutic strategies of miRNA delivery have been presented.

Biodegradable polylactide microspheres enhance specific immune response induced by Hepatitis B surface antigen

Hepatitis B (HB) infection caused by Hepatitis B virus (HBV) is the most common liver disease in the world. HB vaccine, when administered in conjunction with alum adjuvants, induces Th2 immunity that confers protection against HBV. However, currently available vaccine formulations and adjuvants do not elicit adequate Th1 and CTL responses that are important for prevention of maternal transmission of the virus. Microspheres synthesized from poly (D, L-lactide-co-glycolide) (PLGA) or poly (D, L-lactide) (PLA) polymers have been considered as promising tools for in vivo delivery of antigens and drugs. Here we describe PLA microspheres synthesized by premix membrane emulsification method and their application in formulating a new microsphere based HB vaccine. To evaluate the immunogenicity of this microsphere vaccine, BALB/c mice were immunized with microsphere vaccine and a series of immunological assays were conducted. Results of Enzyme-linked ImmunoSpot (ELISPOT) assays revealed that the number of interferon-gamma (IFN-γ)-producing splenocytes and CD8(+) T cells increased significantly in the microsphere vaccine group. Microsphere vaccine group showed enhanced specific cell lysis when compared with HB surface antigen (HBsAg) only group in (51)Cr cytotoxicity assays. Moreover, microsphere vaccine elicited a comparable level of antibody production as that of HB vaccine administered with alum adjuvant. We show that phagocytosis of HBsAg by dendritic cells is more pronounced in microsphere vaccine group when compared with other control groups. These results clearly demonstrate the potential of using PLA microspheres as effective HB vaccine adjuvants for an enhanced Th1 immune response.

Recent progress in microRNA delivery for cancer therapy by non-viral synthetic vectors

MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression. Because of significant changes in their expression in cancer, miRNAs are believed to be key factors in cancer genetics and to have potential as anticancer drugs. However, the delivery of miRNAs is limited by many barriers, such as low cellular uptake, immunogenicity, renal clearance, degradation by nucleases, elimination by phagocytic immune cells, poor endosomal release, and untoward side effects. Nonviral delivery systems have been developed to overcome these obstacles. In this review, we provide insights into the development of non-viral synthetic miRNA vectors and the promise of miRNA-based anticancer therapies, including therapeutic applications of miRNAs, challenges of vector design to overcome the delivery obstacles, and the development of miRNA delivery systems for cancer therapy. Additionally, we highlight some representative examples that give a glimpse into the current trends into the design and application of efficient synthetic systems for miRNA delivery. Overall, a better understanding of the rational design of miRNA delivery systems will promote their translation into effective clinical treatments.

Engineering synthetic vaccines using cues from natural immunity

Vaccines aim to protect against or treat diseases through manipulation of the immune response, promoting either immunity or tolerance. In the former case, vaccines generate antibodies and T cells poised to protect against future pathogen encounter or attack diseased cells such as tumours; in the latter case, which is far less developed, vaccines block pathogenic autoreactive T cells and autoantibodies that target self tissue. Enormous challenges remain, however, as a consequence of our incomplete understanding of human immunity. A rapidly growing field of research is the design of vaccines based on synthetic materials to target organs, tissues, cells or intracellular compartments; to co-deliver immunomodulatory signals that control the quality of the immune response; or to act directly as immune regulators. There exists great potential for well-defined materials to further our understanding of immunity. Here we describe recent advances in the design of synthetic materials to direct immune responses, highlighting successes and challenges in prophylactic, therapeutic and tolerance-inducing vaccines.

Antigen-displaying lipid-enveloped PLGA nanoparticles as delivery agents for a Plasmodium vivax malaria vaccine

The parasite Plasmodium vivax is the most frequent cause of malaria outside of sub-Saharan Africa, but efforts to develop viable vaccines against P. vivax so far have been inadequate. We recently developed pathogen-mimicking polymeric vaccine nanoparticles composed of the FDA-approved biodegradable polymer poly(lactide-co-glycolide) acid (PLGA) “enveloped” by a lipid membrane. In this study, we sought to determine whether this vaccine delivery platform could be applied to enhance the immune response against P. vivax sporozoites. A candidate malaria antigen, VMP001, was conjugated to the lipid membrane of the particles, and an immunostimulatory molecule, monophosphoryl lipid A (MPLA), was incorporated into the lipid membranes, creating pathogen-mimicking nanoparticle vaccines (VMP001-NPs). Vaccination with VMP001-NPs promoted germinal center formation and elicited durable antigen-specific antibodies with significantly higher titers and more balanced Th1/Th2 responses in vivo, compared with vaccines composed of soluble protein mixed with MPLA. Antibodies raised by NP vaccinations also exhibited enhanced avidity and affinity toward the domains within the circumsporozoite protein implicated in protection and were able to agglutinate live P. vivax sporozoites. These results demonstrate that these VMP001-NPs are promising vaccines candidates that may elicit protective immunity against P. vivax sporozoites.

A comparative analysis of HIV-specific mucosal/systemic T cell immunity and avidity following rDNA/rFPV and poxvirus-poxvirus prime boost immunisations

In this study we have firstly compared a range of recombinant DNA poxvirus prime-boost immunisation strategies and shown that combined intramuscular (i.m.) 2× DNA-HIV/intranasal (i.n.) 2× FPV-HIV prime-boost immunisation can generate high-level of HIV-specific systemic (spleen) and mucosal (genito-rectal nodes, vaginal tissues and lung tissues) T cell responses and HIV-1 p24 Gag-specific serum IgG1, IgG2a and mucosal IgG, SIgA responses in vaginal secretions in BALB/c mice. Data indicate that following rDNA priming, two rFPV booster immunisations were necessary to generate good antibody and mucosal T cell immunity. This data also revealed that mucosal uptake of recombinant fowl pox (rFPV) was far superior to plasmid DNA. To further evaluate CD8+ T cell immunity, i.m. 2× DNA-HIV/i.n. 1× FPV-HIV immunisation strategy was directly compared with single shot poxvirus/poxvirus, i.n. FPV-HIV/i.m. VV-HIV immunisation. Results indicate that the latter strategy was able to generate strong sustained HIV-specific CD8+ T cells with higher avidity, broader cytokine/chemokine profiles and better protection following influenza-K(d)Gag(197-205) challenge compared to rDNA poxvirus prime-boost strategy. Our findings further substantiate the importance of vector selection/combination, order and route of delivery when designing effective vaccines for HIV-1.

Antibody-mediated protection against mucosal simian-human immunodeficiency virus challenge of macaques immunized with alphavirus replicon particles and boosted with trimeric envelope glycoprotein in MF59 adjuvant

We have previously shown that rhesus macaques were partially protected against high-dose intravenous challenge with simian-human immunodeficiency virus SHIV(SF162P4) following sequential immunization with alphavirus replicon particles (VRP) of a chimeric recombinant VEE/SIN alphavirus (derived from Venezuelan equine encephalitis virus [VEE] and the Sindbis virus [SIN]) encoding human immunodeficiency virus type 1 HIV-1(SF162) gp140DeltaV2 envelope (Env) and trimeric Env protein in MF59 adjuvant (R. Xu, I. K. Srivastava, C. E. Greer, I. Zarkikh, Z. Kraft, L. Kuller, J. M. Polo, S. W. Barnett, and L. Stamatatos, AIDS Res. Hum. Retroviruses 22:1022-1030, 2006). The protection did not require T-cell immune responses directed toward simian immunodeficiency virus (SIV) Gag. We extend those findings here to demonstrate antibody-mediated protection against mucosal challenge in macaques using prime-boost regimens incorporating both intramuscular and mucosal routes of delivery. The macaques in the vaccination groups were primed with VRP and then boosted with Env protein in MF59 adjuvant, or they were given VRP intramuscular immunizations alone and then challenged with SHIV(SF162P4) (intrarectal challenge). The results demonstrated that these vaccines were able to effectively protect the macaques to different degrees against subsequent mucosal SHIV challenge, but most noteworthy, all macaques that received the intramuscular VRP prime plus Env protein boost were completely protected. A statistically significant association was observed between the titer of virus neutralizing and binding antibodies as well as the avidity of anti-Env antibodies measured prechallenge and protection from infection. These results highlight the merit of the alphavirus replicon vector prime plus Env protein boost vaccine approach for the induction of protective antibody responses and are of particular relevance to advancing our understanding of the potential correlates of immune protection against HIV infection at a relevant mucosal portal of entry.

The potency of the adjuvant, CpG oligos, is enhanced by encapsulation in PLG microparticles

The objective of this work was to evaluate the potency of the CpG containing oligonucleotide encapsulated within poly(lactide-co-glycolide), and coadministered with antigen adsorbed to poly(lactide-co-glycolide) microparticles (PLG particles). The formulations evaluated include, CpG added in soluble form, CpG adsorbed, and CpG encapsulated. The antigen from Neisseria meningitidis serotype B (Men B) was used in these studies. The immunogenicity of these formulations was evaluated in mice. Poly(lactide-co-glycolide) microparticles were synthesized by a w/o/w emulsification method in the presence of a charged surfactant for the formulations. Neisseria meningitidis B protein was adsorbed to the PLG microparticles, with binding efficiency and initial release measured. CpG was either added in the soluble or adsorbed or encapsulated form based on the type of formulation. The binding efficiency, loading, integrity and initial release of CpG and the antigen were measured from all the formulations. The formulations were then tested in mice for their ability to elicit antibodies, bactericidal activity and T cell responses. Encapsulating CpG within PLG microparticles induced statistically significant higher antibody, bactericidal activity and T cell responses when compared to the traditional method of delivering CpG in the soluble form.

TLR ligands and antigen need to be coencapsulated into the same biodegradable microsphere for the generation of potent cytotoxic T lymphocyte responses

Dendritic cells phagocytose pathogens leading to maturation and cross-presentation on MHC class I. We found that the efficiency of cross-priming in mice after vaccination with biodegradable poly(D,L-lactide-co-glycolide) microspheres (MSs) was enhanced when ovalbumin was coencapsulated together with either a CpG oligonucleotide or polyI:C as compared to co-inoculation of ovalbumin-bearing MS with soluble or separately encapsulated adjuvants. A single immunization with MS containing coencaspsulated CpG and ovalbumin yielded 9% SIINFEKL/H-2K(b) tetramer positive CTLs, production of IFN-gamma, efficient cytolysis, and protection from vaccinia virus infection. Taken together, coencapsulation of adjuvant and antigen is an important paradigm for the generation of potent CTL responses.

Characterization of immune responses elicited in mice by intranasal co-immunization with HIV-1 Tat, gp140 DeltaV2Env and/or SIV Gag proteins and the nontoxicogenic heat-labile Escherichia coli enterotoxin

The development of a vaccine against HIV/AIDS capable of inducing broad humoral and cellular responses at both systemic and mucosal sites, able to stop or reduce viral infection at the portal of entry, represents the only realistic way to control the infection caused by HIV world-wide. The promising results obtained with the HIV-1 Tat-based vaccines in preclinical and clinical settings, the evidence that a broad immunity against HIV correlates with reduced viral load or virus control, as well as the availability of novel gp140 V2-loop deleted HIV-1 Env (DeltaV2Env) immunogens capable of inducing cross-reactive neutralizing antibodies, have led to the design of new vaccine strategies based on the combination of non-structural and structural proteins. In this study, we demonstrate that immunization with a biologically active HIV-1 Tat protein in combination with the oligomeric HIV-1 gp140 DeltaV2Env and/or SIV Gag proteins, delivered intranasally with the detoxified LTK63 mucosal adjuvant, whose safety has been recently shown in humans, elicits long-lasting local and systemic antibody and cellular immune responses against the co-administered antigens in a fashion similar to immune responses induced by vaccination with Tat, DeltaV2Env and Gag proteins alone. The results indicate lack of antigen interference implying that HIV-1 Tat is an optimal co-antigen for combined vaccine strategies employing DeltaV2Env and/or Gag proteins.

MF59 is a safe and potent vaccine adjuvant that enhances protection against influenza virus infection

In preclinical studies, MF59 adjuvant offered improved protection against influenza virus challenge and significantly reduced the viral load in the lungs of challenged mice. In humans, MF59 is a safe and potent vaccine adjuvant that has been licensed in more than 20 countries (Fluad [Novartis Vaccines and Diagnostics Inc., MA, USA]). The safety profile of an MF59-adjuvanted vaccine is well established through a large safety database. MF59 adjuvant has had a significant impact on the immunogenicity of influenza vaccines in the elderly and in adults who are chronically ill. MF59 has also been shown to have a significant impact on the immunogenicity of pandemic influenza vaccines. MF59 allows for broader cross-reactivity against viral strains not included in the vaccine. MF59 has been shown to be more potent for both antibody and T-cell responses than aluminum-based adjuvants. MF59 has broad potential to be used as a safe and effective vaccine adjuvant for a wide range of vaccine types.

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

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

Induction of potent CD8+ T-cell responses by novel biodegradable nanoparticles carrying human immunodeficiency virus type 1 gp120

The mainstream of recent anti-AIDS vaccines is a prime/boost approach with multiple doses of the target DNA of human immunodeficiency virus type 1 (HIV-1) and recombinant viral vectors. In this study, we have attempted to construct an efficient protein-based vaccine using biodegradable poly(gamma-glutamic acid) (gamma-PGA) nanoparticles (NPs), which are capable of inducing potent cellular immunity. A significant expansion of CD8+ T cells specific to the major histocompatibility complex class I-restricted gp120 epitope was observed in mice intranasally immunized once with gp120-carrying NPs but not with gp120 alone or gp120 together with the B-subunit of cholera toxin. Both the gp120-encapsulating and -immobilizing forms of NPs could induce antigen-specific spleen CD8+ T cells having a functional profile of cytotoxic T lymphocytes. Long-lived memory CD8+ T cells could also be elicited. Although a substantial decay in the effector memory T cells was observed over time in the immunized mice, the central memory T cells remained relatively constant from day 30 to day 238 after immunization. Furthermore, the memory CD8+ T cells rapidly expanded with boosting with the same immunogen. In addition, gamma-PGA NPs were found to be a much stronger inducer of antigen-specific CD8+ T-cell responses than nonbiodegradable polystyrene NPs. Thus, gamma-PGA NPs carrying various HIV-1 antigens may have great potential as a novel priming and/or boosting tool in current vaccination regimens for the induction of cellular immune responses.

Preparation and Characterization of Innovative Protein-coated Poly(Methylmethacrylate) Core-shell Nanoparticles for Vaccine Purposes

PURPOSE

This study aims at developing novel core-shell poly(methylmethacrylate) (PMMA) nanoparticles as a delivery system for protein vaccine candidates.

MATERIALS AND METHODS

Anionic nanoparticles consisting of a core of PMMA and a shell deriving from Eudragit L100/55 were prepared by an innovative synthetic method based on emulsion polymerization. The formed nanoparticles were characterized for size, surface charge and ability to reversibly bind two basic model proteins (Lysozyme, Trypsin) and a vaccine relevant antigen (HIV-1 Tat), by means of cell-free studies. Their in vitro toxicity and capability to preserve the biological activity of the HIV-1 Tat protein were studied in cell culture systems. Finally, their safety and immunogenicity were investigated in the mouse model.

RESULTS

The nanoparticles had smooth surface, spherical shape and uniform size distribution with a mean diameter of 220 nm. The shell is characterized by covalently bound carboxyl groups negatively charged at physiological pH, able to reversibly adsorb large amounts (up to 20% w/w) of basic proteins (Lysozyme, Trypsin and HIV-1 Tat), mainly through specific electrostatic interactions. The nanoparticles were stable, not toxic to the cells, protected the HIV-1 Tat protein from oxidation, thus preserving its biological activity and increasing its shelf-life, and efficiently delivered and released it intracellularly. In vivo experiments showed that they are well tolerated and elicit strong immune responses against the delivered antigen in mice.

CONCLUSIONS

This study demonstrates that these new nanoparticles provide a versatile platform for protein surface adsorption and a promising delivery system particularly when the maintenance of the biologically active conformation is required for vaccine efficacy.

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.

Characterization of immune responses elicited in macaques immunized sequentially with chimeric VEE/SIN alphavirus replicon particles expressing SIVGag and/or HIVEnv and with recombinant HIVgp140Env protein

In the present study, macaques were coimmunized with VEErep/SINenv chimeric alphavirus replicon particles expressing SIVp55Gag and HIVDeltaV2gp140Env or only with replicon particles expressing HIVDeltaV2gp140Env. All animals were subsequently immunized with recombinant trimeric HIVDeltaV2gp140Env protein. During alphavirus immunization, anti-SIVGag and anti-HIVEnv-specific interferon (IFN)-gamma responses, as well as high titers of anti-HIVEnv binding (gp120 but not gp41 specific) and anti-HIV neutralizing antibodies, were generated. The subsequent immunization with recombinant HIVDeltaV2gp140 enhanced the neutralizing antibody titers and Env-specific IFN-gamma responses. Following intravenous challenge with the R5- tropic SHIV(SF162P4) virus, significantly lower primary plasma viremia levels were recorded in the immunized animals, as compared to control animals immunized with replicon particles expressing influenza virus HA. Our results show that this method of immunization elicits both strong cellular immunity and neutralizing antibodies in primates and, thus, merits further investigation.

Hepatitis C virus polyprotein vaccine formulations capable of inducing broad antibody and cellular immune responses

Although approximately 3 % of the world's population is infected with Hepatitis C virus (HCV), there is no prophylactic vaccine available. This study reports the design, cloning and purification of a single polyprotein comprising the HCV core protein and non-structural proteins NS3, NS4a, NS4b, NS5a and NS5b. The immunogenicity of this polyprotein, which was formulated in alum, oil-in-water emulsion MF59 or poly(dl-lactide co-glycolide) in the presence or absence of CpG adjuvant, was then determined in a murine model for induction of B- and T-cell responses. The addition of adjuvants or a delivery system to the HCV polyprotein enhanced serum antibody and T-cell proliferative responses, as well as IFN-gamma responses, by CD4+ T cells. The antibody responses were mainly against the NS3 and NS5 components of the polyprotein and relatively poor responses were elicited against NS4 and the core components. IFN-gamma responses, however, were induced against all of the individual components of the polyprotein. These data suggest that the HCV polyprotein delivered with adjuvants induces broad B- and T-cell responses and could be a vaccine candidate against HCV.

Evaluation of fowlpox–vaccinia virus prime-boost vaccine strategies for high-level mucosal and systemic immunity against HIV-1

We have tested the efficacy of recombinant fowl pox (rFPV) and recombinant vaccinia virus (rVV) encoding antigens of AE clade HIV-1 in a prime-boost strategy, using both systemic and mucosal delivery routes. Of the various vaccine routes tested, intranasal/intramuscular (i.n./i.m.) AE FPV/AE VV prime-boosting generated the highest mucosal and systemic T cell responses. Peak mucosal T cell responses occurred as early as 3 days post-boost vaccination. In contrast only low systemic responses were observed at this time with the peak response occurring at day 7. Current data also revealed that, due to better uptake of the rFPV, intranasal viral priming was much more effective than intranasal rDNA priming tested previously. The i.m./i.m. prime-boost delivery also generated strong systemic but poor mucosal responses to Gag peptides. Interestingly, the oral administration of AE FPV followed by i.m. AE VV delivery elicited strong systemic responses to sub-dominant Pol 1 peptides that were absent in mice that received vaccine by other routes. Moreover, priming with AE FPV co-expressing cytokine IL-12 significantly enhanced the T cell responses to target antigens, whilst co-expression of IFNgamma decreased these responses. The results also indicated that the route of inoculation and the vaccine vector combination could radically influence not only the magnitude but also the antigen specificity of the immune response generated. Further, in contrast to the generally protracted HIV rDNA/rFPV multiple delivery prime-boosting, this single rFPV prime and rVV boost approach was more flexible and generated excellent mucosal and systemic immune responses to HIV vaccine antigens.

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.

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.

Antigen expression kinetics and immune responses of mice immunized with noninfectious simian-human immunodeficiency virus DNA

In a previous report we demonstrated that three injections of an rt-deleted noninfectious genome of the simian-human immunodeficiency virus SHIV(KU2) induced protection against AIDS in macaques (D. K. Singh, Z. Liu, D. Sheffer, G. A. Mackay, M. Smith, S. Dhillon, R. Hegde, F. Jia, I. Adany, and O. Narayan, J. Virol 79:3419-3428, 2005). To make this DNA safer, we deleted two more genes, the integrase gene and vif, along with the 3' long terminal repeat. We also replaced the gag, pro, and nef genes (SIVmac239 origin) with those of human immunodeficiency virus (HIV) type 1 strain SF2. The resultant construct, designated delta4SHIV(KU2) DNA, was used in this study to evaluate gene expression and immunogenicity in BALB/c mice. DNA-transfected human embryonic kidney epithelial cells (HEK 293) produced all of the major viral proteins and released p24 in the supernatant for 12 days. Inoculation of the vaccine DNA into the gastrocnemius muscles resulted in intense mononuclear cell infiltration at the inoculated sites and the production of viral p24 in myocytes, in infiltrating mononuclear cells, and in cells in the spleen and draining lymph nodes between 3 and 10 days postinoculation. Expression of p24 in the muscle cells peaked at day 7 and became undetectable after day 12. The same 12-day period of expression of p24 was observed in mice that were given a second injection 4 weeks after the first. Evaluation of immune responses in BALB/c mice revealed that the DNA induced enzyme-linked immunospot and antigen-specific proliferative cell-mediated immunity responses. The responses were stronger in mice that were coinjected with a second plasmid expressing granulocyte-macrophage colony-stimulating factor. Since new waves of viral antigen production could be induced with each boosting injection of the vaccine DNA, this DNA could be a safe and efficient agent to induce long-term protection against HIV.

Encapsulation of proteins and peptides into biodegradable poly(D,L-lactide-co-glycolide) microspheres prolongs and enhances antigen presentation by human dendritic cells

Dendritic cell (DC)-based immunotherapy has been hampered by the lack of suitable methods for antigen delivery. Here, we use biodegradable poly(D,L-lactide-co-glycolide) microspheres (PLGA-MS) as carriers of peptides and proteins for antigen delivery to human monocyte-derived DC (MoDC). Compared to soluble proteins, MHC classes I and II-restricted presentation of PLGA-MS-encapsulated proteins and peptides by MoDC was markedly prolonged and proteins were presented 50-fold more efficiently on class I molecules. The vaccination of mice with DC loaded with PLGA-MS-encapsulated proteins raised strong and persisting cytotoxic T cell responses. In conclusion, antigen delivery via PLGA-MS markedly enhanced the duration of antigen presentation by human MoDC and the potency of DC-based vaccination.

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.

Non-human primate models for AIDS vaccine research

Since the discovery of simian immunodeficiency viruses (SIV) causing AIDS-like diseases in Asian macaques, non-human primates (NHP) have played an important role in AIDS vaccine research. A multitude of vaccines and immunization approaches have been evaluated, including live attenuated viruses, DNA vaccines, viral and bacterial vectors, subunit proteins, and combinations thereof. Depending on the particular vaccine and model used, varying degrees of protection have been achieved, including prevention of infection, reduction of viral load, and amelioration of disease. In a few instances, potential safety concerns and vaccine-enhanced pathogenicity have also been noted. In the past decade, sophisticated methodologies have been developed to define the mechanisms of protective immunity. However, a clear road map for HIV vaccine development has yet to emerge. This is in part because of the intrinsic nature of the surrogate model and in part because of the improbability of any single model to fully capture the complex interactions of natural HIV infection in humans. The lack of standardization, the limited models available, and the incomplete understanding of the immunobiology of NHP contribute to the difficulty to extrapolate findings from such models to HIV vaccine development. Until efficacy data become available from studies of parallel vaccine concepts in humans and macaques, the predictive value of any NHP model remains unknown. Towards this end, greater appreciation of the utility and limitations of the NHP model and further developments to better mimic HIV infection in humans will likely help inform future AIDS vaccine efforts.

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.

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.

Charged polylactide co-glycolide microparticles as antigen delivery systems

Polymeric microparticles with encapsulated antigens have become well-established in the last decade as potent antigen delivery systems and adjuvants, with experience being reported from many groups. However, the authors have recently shown that an alternative approach involving charged polylactide co-glycolide (PLG) microparticles with surface adsorbed antigen(s) can also be used to deliver antigen into antigen-presenting cell populations. The authors have described the preparation of cationic and anionic PLG microparticles that have been used to adsorb a variety of agents, to include plasmid DNA, recombinant proteins and adjuvant active oligonucleotides. These novel PLG microparticles were prepared using a w/o/w solvent evaporation process in the presence of the anionic surfactants, such as dioctyl sodium sulfosuccinate, or cationic surfactants, such as hexadecyl trimethyl ammonium bromide. Antigen binding to the charged PLG microparticles was influenced by both electrostatic interaction and other mechanisms, including hydrophobic interactions. Adsorption of antigens to microparticles resulted in the induction of significantly enhanced immune responses in comparison with alternative approaches. The surface adsorbed microparticle formulation offers an alternative way of delivering antigens as a vaccine formulation.

New poly(lactic-co-glycolic acid) derivatives: Modular polymers with tailored properties

Poly(lactic-co-glycolic acid) (PLGA) is one of the most widely used polymers in drug delivery, despite several well-characterized shortcomings. Polymer modification is one approach to improve PLGA-based formulation properties, such as drug stability, drug release profiles, mechanism of polymer degradation and the possibility of drug targeting. A brief summary of recent reports on PLGA modifications is provided and a new class of branched polyester derivatives is introduced. In vitro and in vivo applications of the new branched polyesters as protein carriers, gene delivery vehicles, vaccine adjuvants and pulmonary drug delivery vehicles are described.:

The role of branched polyesters and their modifications in the development of modern drug delivery vehicles

Branched polyesters consisting of poly (vinyl alcohol) (PVA) grafted with chains of poly (lactic-co-glycolic acid) (PLGA) represent a new class of biodegradable polymers showing significant potential for the development of a variety of drug delivery vehicles. The amphiphilic character and the resulting increase in hydrophilicity of this class of polymers provide advantages when packaging sensitive drug molecules, such as proteins, peptides or DNA. Furthermore, the PVA backbone can be modified, for example, with sulfobutyl moieties or amine structures, to create polymers with negative or positive charges. The ability to modify not only the backbone but also the length of the PLGA side chains results in an extremely flexible polymer system, which can be adapted to meet the needs of almost any drug substance. Further, the rate of biodegradation may also be manipulated through polymer modification to achieve half-lives ranging from several hours to several weeks. This review provides an overview of the three major groups of branched polyesters based upon poly (vinyl alcohol)-grafted poly (lactic-co-glycolic acid) (PVA-g-PLGA), namely, the neutrally charged PVA-g-PLGA, the negatively charged sulfobutyl-modified PVA-g-PLGA and the positively charged amine-modified PVA-g-PLGA, as well as their use in various drug delivery systems.

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.

Novel biocompatible anionic polymeric microspheres for the delivery of the HIV-1 Tat protein for vaccine application

Two novel classes of biocompatible core-shell anionic microspheres, composed of an inner hard insoluble core, either made of poly(styrene) (PS) or poly(methyl methacrylate) (PMMA), and a soft outer tentacular shell made of long soluble negatively charged arms derived from the steric stabilizer, hemisuccinated poly(vinyl alcohol) or Eudragit L100/55, respectively, were prepared by dispersion polymerization and characterized. Five types of these novel microspheres, two made of poly(styrene) and hemisuccinated poly(vinyl alcohol) (A4 and A7), and three made of poly(methyl methacrylate) and Eudragit L100/55 (1D, 1E, H1D), differing for chemical composition, size, and surface charge density were analyzed for the delivery of the HIV-1 Tat protein for vaccine applications. All microspheres reversibly adsorbed the native biologically active HIV-1 Tat protein preventing Tat from oxidation and maintaining its biological activity, therefore increasing the shelf-life of the Tat protein vaccine. The microspheres efficiently delivered Tat intracellularly, and were not toxic in vitro nor in mice, even after multiple administrations. These results indicate that these novel microparticles are safe and represent a promising delivery system for vaccination with Tat, as well as for other subunit vaccines, particularly when a native protein conformation is required.

Anionic microparticles are a potent delivery system for recombinant antigens from Neisseria meningitidis serotype B

The adsorption behavior of model proteins onto anionic poly(lactide-co-glycolide) (PLG) microparticles was evaluated. PLG microparticles were prepared by a w/o/w solvent evaporation process in the presence of the anionic surfactant dioctyl sodium sulfosuccinate (DSS). The effect of surfactant concentration and adsorption conditions on the adsorption efficiency and release rates in vitro was also studied. Subsequently, the microparticle formulation was tested to evaluate the efficacy of anionic microparticles as delivery systems for recombinant antigens from Neisseria meningitides type B (Men B), with and without CpG adjuvant. Protein (antigen) binding to anionic PLG microparticles was influenced by both electrostatic interaction and by other mechanisms, including hydrophobic attraction. The Men B antigens adsorbed efficiently onto anionic PLG microparticles and, following immunization in mice, induced potent enzyme-linked immunosorbent assay (ELISA) and serum bactericidal activity in comparison to alum-adsorbed formulations. These Men B antigens represent an attractive approach for vaccine development.

Progress on new vaccine strategies against chronic viral infections

Among the most cost-effective strategies for preventing viral infections, vaccines have proven effective primarily against viruses causing acute, self-limited infections. For these it has been sufficient for the vaccine to mimic the natural virus. However, viruses causing chronic infection do not elicit an immune response sufficient to clear the infection and, as a result, vaccines for these viruses must elicit more effective responses--quantitative and qualitative--than does the natural virus. Here we examine the immunologic and virologic basis for vaccines against three such viruses, HIV, hepatitis C virus, and human papillomavirus, and review progress in clinical trials to date. We also explore novel strategies for increasing the immunogenicity and efficacy of vaccines.

Progress on new vaccine strategies against chronic viral infections

Among the most cost-effective strategies for preventing viral infections, vaccines have proven effective primarily against viruses causing acute, self-limited infections. For these it has been sufficient for the vaccine to mimic the natural virus. However, viruses causing chronic infection do not elicit an immune response sufficient to clear the infection and, as a result, vaccines for these viruses must elicit more effective responses--quantitative and qualitative--than does the natural virus. Here we examine the immunologic and virologic basis for vaccines against three such viruses, HIV, hepatitis C virus, and human papillomavirus, and review progress in clinical trials to date. We also explore novel strategies for increasing the immunogenicity and efficacy of vaccines.

Enhancement of vaccine potency through improved delivery

The need for more potent, safe and well-characterised vaccines has necessitated the discovery and development of new vaccine technologies. These include adjuvants to target the innate immune system to provide a stimulus that potentiates the development of an antigen-specific immune response, and delivery systems to ensure that the antigen and adjuvant are localised to the appropriate immune compartments. Several such technologies are being tested in human clinical trials and a few have been licensed for limited use in human vaccines. This review will highlight some of the promising technologies that may have an impact on how vaccines are administered.

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.

DNA vaccines against human immunodeficiency virus type 1 in the past decade

This article reviews advances in the field of human immunodeficiency virus type 1 (HIV-1) and AIDS vaccine development over the last decade, with an emphasis on the DNA vaccination approach. Despite the discovery of HIV-1 and AIDS in humans nearly 20 years ago, there is no vaccine yet that can prevent HIV-1 infection. The focus has shifted toward developing vaccines that can control virus replication and disease progression by eliciting broadly cross-reactive T-cell responses. Among several approaches evaluated, the DNA-based modality has shown considerable promise in terms of its ability to elicit cellular immune responses in primate studies. Of great importance are efforts aimed at improvement of the potency of this modality in the clinic. The review discusses principles of DNA vaccine design and the various mechanisms of plasmid-encoded antigen presentation. The review also outlines current DNA-based vaccine strategies and vectors that have successfully been shown to control virus replication and slow disease progression in animal models. Finally, it lists recent strategies that have been developed as well as novel approaches under consideration to enhance the immunogenicity of plasmid-encoded HIV-1 antigen in various animal models.

DNA vaccines and their application against parasites--promise, limitations and potential solutions

DNA or nucleic acid vaccines are being evaluated for efficacy against a range of parasitic diseases. Data from studies in rodent model systems have provided proof of principle that DNA vaccines are effective at inducing both humoral and T cell responses to a variety of candidate vaccine antigens. In particular, the induction of potent cellular responses often gives DNA vaccination an immunological advantage over subunit protein vaccination. Protection against parasite challenge has been demonstrated in a number of systems. However, application of parasite DNA vaccines in large animals including ruminants, primates and humans has been compromised by the relative lack of immune responsiveness to the vaccines, but the reasons for this hyporesponsiveness are not clear. Here, we review DNA vaccines against protozoan parasites, in particular vaccines for malaria, and the use of genomic approaches such as expression library immunization to generate novel vaccines. The application of DNA vaccines in ruminants is reviewed. We discuss some of the approaches being evaluated to improve responsiveness in large animals including the use of cytokines as adjuvants, targeting molecules as delivery ligands, electroporation and CpG oligonucleotides.

Recent advances in the discovery and delivery of vaccine adjuvants

Adjuvant design has historically had a touch of alchemy at its heart due to its reliance on the complex biology of innate immune activation. However, a new mechanistic understanding of innate immunity, combined with new adjuvant and delivery platforms for exploiting this knowledge, has led to significant advances recently. Although many challenges remain, the field is moving rapidly and the proper tools and methodologies are in place for the use of traditional drug discovery engines in guiding the development of vaccine adjuvants. In this review, we outline the current trends in immune potentiator, delivery system and adjuvant design that will shape the vaccines of the future.