Enhanced DNA vaccine potency by mannosylated lipoplex after intraperitoneal administration

Harnessing Nanovaccines for Effective Immunization─A Special Concern on COVID-19: Facts, Fidelity, and Future Prospective

Nanotechnology has emerged as a transformative pathway in vaccine research and delivery. Nanovaccines, encompassing lipid and nonlipid formulations, exhibit considerable advantages over traditional vaccine techniques, including enhanced antigen stability, heightened immunogenicity, targeted distribution, and the potential for codelivery with adjuvants or immune modulators. This review provides a comprehensive overview of the latest advancements and applications of lipid and non-lipid-based nanovaccines in current vaccination strategies for immunization. The review commences by outlining the fundamental concepts underlying lipid and nonlipid nanovaccine design before delving into the diverse components and production processes employed in their development. Subsequently, a comparative analysis of various nanocarriers is presented, elucidating their distinct physicochemical characteristics and impact on the immune response, along with preclinical and clinical studies. The discussion also highlights how nanotechnology enables the possibility of personalized and combined vaccination techniques, facilitating the creation of tailored nanovaccines to meet the individual patient needs. The ethical aspects concerning the use of nanovaccines, as well as potential safety concerns and public perception, are also addressed. The study underscores the gaps and challenges that must be overcome before adopting nanovaccines in clinical practice. This comprehensive analysis offers vital new insights into lipid and nonlipid nanovaccine status. It emphasizes the significance of continuous research, collaboration among interdisciplinary experts, and regulatory measures to fully unlock the potential of nanotechnology in enhancing immunization and ensuring a healthier, more resilient society.

Carbohydrate anchored lipid nanoparticles

Nanotechnology has been a dynamic field for formulation scientists with multidisciplinary research being conducted worldwide. Advancements in development of functional nanosystems have led to evolution of breakthrough technologies. Lipidic nanosystems, in particular, are highly preferred owing to their non-immunogenic safety profiles along with a range of versatile intrinsic properties. Surface modification of lipid nanoparticles by anchoring carbohydrates to these systems is one such attractive drug delivery technology. Carbohydrates confer interesting properties to the nanosystems such as stealth, biostability, bioavailability, reduced toxicity due to decreased immunogenic response, targeting potential as well as ease of commercial availability. The carbohydrate anchored systems can be developed using methods such as adsorption, incorporation (nanoprecipitation or solvent displacement method), crosslinking and grafting. Current review provides a detailed overview of potential lipid based nanoparticulate systems with an emphasis on liposomes, solid lipid nanoparticles, nanostructures lipid carriers and micelles. Review further explores basics of surface modification, methods applied therein, advantages of carbohydrates as surface modifiers, their versatile applications, techniques for characterization of carbohydrate anchored systems and vital regulatory aspects concerned with these specialized systems.

Nanovaccine Delivery Approaches and Advanced Delivery Systems for the Prevention of Viral Infections: From Development to Clinical Application

Viral infections causing pandemics and chronic diseases are the main culprits implicated in devastating global clinical and socioeconomic impacts, as clearly manifested during the current COVID-19 pandemic. Immunoprophylaxis via mass immunisation with vaccines has been shown to be an efficient strategy to control such viral infections, with the successful and recently accelerated development of different types of vaccines, thanks to the advanced biotechnological techniques involved in the upstream and downstream processing of these products. However, there is still much work to be done for the improvement of efficacy and safety when it comes to the choice of delivery systems, formulations, dosage form and route of administration, which are not only crucial for immunisation effectiveness, but also for vaccine stability, dose frequency, patient convenience and logistics for mass immunisation. In this review, we discuss the main vaccine delivery systems and associated challenges, as well as the recent success in developing nanomaterials-based and advanced delivery systems to tackle these challenges. Manufacturing and regulatory requirements for the development of these systems for successful clinical and marketing authorisation were also considered. Here, we comprehensively review nanovaccines from development to clinical application, which will be relevant to vaccine developers, regulators, and clinicians.

Vitamin E Scaffolds of pH-Responsive Lipid Nanoparticles as DNA Vaccines in Cancer and Protozoan Infection

DNA vaccinations are promising strategies for treating diseases that require cellular immunity (i.e., cancer and protozoan infection). Here, we report on the use of a liposomal nanocarrier (lipid nanoparticles (LNPs)) composed of an SS-cleavable and pH-activated lipidlike material (ssPalm) as an in vivo DNA vaccine. After subcutaneous administration, the LNPs containing an ssPalmE, an ssPalm with vitamin E scaffolds, elicited a higher gene expression activity in comparison with the other LNPs composed of the ssPalms with different hydrophobic scaffolds. Immunization with the ssPalmE-LNPs encapsulating plasmid DNA that encodes ovalbumin (OVA, a model tumor antigen) or profilin (TgPF, a potent antigen of Toxoplasma gondii) induced substantial antitumor or antiprotozoan effects, respectively. Flow cytometry analysis of the cells that had taken up the LNPs in draining lymph nodes (dLNs) showed that the ssPalmE-LNPs were largely taken up by macrophages and a small number of dendritic cells. We found that the transient deletion of CD169⁺ macrophages, a subpopulation of macrophages that play a key role in cancer immunity, unexpectedly enhanced the activity of the DNA vaccine. These data suggest that the ssPalmE-LNPs are effective DNA vaccine carriers, and a strategy for avoiding their being trapped by CD169⁺ macrophages will be a promising approach for developing next-generation DNA vaccines.

Targeting C-type lectin receptors: a high-carbohydrate diet for dendritic cells to improve cancer vaccines

There is a growing understanding of why certain patients do or do not respond to checkpoint inhibition therapy. This opens new opportunities to reconsider and redevelop vaccine strategies to prime an anticancer immune response. Combination of such vaccines with checkpoint inhibitors will both provide the fuel and release the brake for an efficient anticancer response. Here, we discuss vaccine strategies that use C-type lectin receptor (CLR) targeting of APCs, such as dendritic cells and macrophages. APCs are a necessity for the priming of antigen-specific cytotoxic and helper T cells. Because CLRs are natural carbohydrate-recognition receptors highly expressed by multiple subsets of APCs and involved in uptake and processing of Ags for presentation, these receptors seem particularly interesting for targeting purposes.

γ-Tilmanocept, a New Radiopharmaceutical Tracer for Cancer Sentinel Lymph Nodes, Binds to the Mannose Receptor (CD206)

γ-Tilmanocept ((99m)Tc-labeled-tilmanocept or [(99m)Tc]-tilmanocept) is the first mannose-containing, receptor-directed, radiolabeled tracer for the highly sensitive imaging of sentinel lymph nodes in solid tumor staging. To elucidate the mannose-binding receptor that retains tilmanocept in this microenvironment, human macrophages were used that have high expression of the C-type lectin mannose receptor (MR; CD206). Cy3-labeled tilmanocept exhibited high specificity binding to macrophages that was nearly abolished in competitive inhibition experiments. Furthermore, Cy3-tilmanocept binding was markedly reduced on macrophages deficient in the MR by small interfering RNA treatment and was increased on MR-transfected HEK 293 cells. Finally, confocal microscopy revealed colocalization of Cy3-tilmanocept with the macrophage membrane MR and binding of labeled tilmanocept to MR(+) cells (macrophages and/or dendritic cells) in human sentinel lymph node tissues. Together these data provide strong evidence that CD206 is a major binding receptor for γ-tilmanocept. Identification of CD206 as the γ-tilmanocept-binding receptor enables opportunities for designing receptor-targeted advanced imaging agents and therapeutics for cancer and other diseases.

Design and characterization of novel recombinant listeriolysin O-protamine fusion proteins for enhanced gene delivery

To improve the efficiency of gene delivery for effective gene therapy, it is essential that the vector carries functional components that can promote overcoming barriers in various steps leading to the transport of DNA from extracellular to ultimately nuclear compartment. In this study, we designed genetically engineered fusion proteins as a platform to incorporate multiple functionalities in one chimeric protein. Prototypes of such a chimera tested here contain two domains: one that binds to DNA; the other that can facilitate endosomal escape of DNA. The fusion proteins are composed of listeriolysin O (LLO), the endosomolytic pore-forming protein from Listeria monocytogenes, and a 22 amino acid sequence of the DNA-condensing polypeptide protamine (PN), singly or as a pair: LLO-PN and LLO-PNPN. We demonstrate dramatic enhancement of the gene delivery efficiency of protamine-condensed DNA upon incorporation of a small amount of LLO-PN fusion protein and further improvement with LLO-PNPN in vitro using cultured cells. Additionally, the association of anionic liposomes with cationic LLO-PNPN/protamine/DNA complexes, yielding a net negative surface charge, resulted in better in vitro transfection efficiency in the presence of serum. An initial, small set of data in mice indicated that the observed enhancement in gene expression could also be applicable to in vivo gene delivery. This study suggests that incorporation of a recombinant fusion protein with multiple functional components, such as LLO-protamine fusion protein, in a nonviral vector is a promising strategy for various nonviral gene delivery systems.

Macrophage immunoregulatory pathways in tuberculosis

Macrophages, the major host cells harboring Mycobacterium tuberculosis (M.tb), are a heterogeneous cell type depending on their tissue of origin and host they are derived from. Significant discord in macrophage responses to M.tb exists due to differences in M.tb strains and the various types of macrophages used to study tuberculosis (TB). This review will summarize current concepts regarding macrophage responses to M.tb infection, while pointing out relevant differences in experimental outcomes due to the use of divergent model systems. A brief description of the lung environment is included since there is increasing evidence that the alveolar macrophage (AM) has immunoregulatory properties that can delay optimal protective host immune responses. In this context, this review focuses on selected macrophage immunoregulatory pattern recognition receptors (PRRs), cytokines, negative regulators of inflammation, lipid mediators and microRNAs (miRNAs).

Exploitation of the Macrophage Mannose Receptor (CD206) in Infectious Disease Diagnostics and Therapeutics

The macrophage mannose receptor (MR, CD206) is a C-type lectin expressed predominantly by most tissue macrophages, dendritic cells and specific lymphatic or endothelial cells. It functions in endocytosis and phagocytosis, and plays an important role in immune homeostasis by scavenging unwanted mannoglycoproteins. More attention is being paid to its particularly high expression in tissue pathology sites during disease such the tumor microenvironment. The MR recognizes a variety of microorganisms by their mannan-coated cell wall, which is exploited by adapted intracellular pathogens such as Mycobacterium tuberculosis, for their own survival. Despite the continued development of drug delivery technologies, the targeting of agents to immune cells, especially macrophages, for effective diagnosis and treatment of chronic infectious diseases has not been addressed adequately. In this regard, strategies that optimize MR-mediated uptake by macrophages in target tissues during infection are becoming an attractive approach. We review important progress in this area.

Targeting antigens to dendritic cell receptors for vaccine development

Dendritic cells (DCs) are highly specialized antigen presenting cells of the immune system which play a key role in regulating immune responses. Depending on the method of antigen delivery, DCs stimulate immune responses or induce tolerance. As a consequence of the dual function of DCs, DCs are studied in the context of immunotherapy for both cancer and autoimmune diseases. In vaccine development, a major aim is to induce strong, specific T-cell responses. This is achieved by targeting antigen to cell surface molecules on DCs that efficiently channel the antigen into endocytic compartments for loading onto MHC molecules and stimulation of T-cell responses. The most attractive cell surface receptors, expressed on DCs used as targets for antigen delivery for cancer and other diseases, are discussed.

VLPs and particle strategies for cancer vaccines

Effective delivery of tumor antigens to APCs is one of the key steps for eliciting a strong and durable immune response to tumors. Several cancer vaccines have been evaluated in clinical trials, based on soluble peptides, but results have not been fully satisfactory. To improve immunogenicity particles provide a valid strategy to display and/or incorporate epitopes which can be efficiently targeted to APCs for effective induction of adaptive immunity. In the present review, we report some leading technologies for developing particulate vaccines employed in cancer immunotherapy, highlighting the key parameters for a rational design to elicit both humoral and cellular responses.

Targeting C-type lectin receptors with multivalent carbohydrate ligands

C-type lectin receptors (CLRs) represent a large receptor family including collectins, selectins, lymphocyte lectins, and proteoglycans. CLRs share a structurally homologous carbohydrate-recognition domain (CRD) and often bind carbohydrates in a Ca²⁺-dependent manner. In innate immunity, CLRs serve as pattern recognition receptors (PRRs) and bind to the glycan structures of pathogens and also to self-antigens. In nature, the low affinity of CLR/carbohydrate interactions is overcome by multivalent ligand presentation at the surface of cells or pathogens. Thus, multivalency is a promising strategy for targeting CLR-expressing cells and, indeed, carbohydrate-based targeting approaches have been employed for a number of CLRs, including asialoglycoprotein receptor (ASGPR) in the liver, or DC-SIGN expressed by dendritic cells. Since CLR engagement not only mediates endocytosis but also influences intracellular signaling pathways, CLR targeting may allow for cell-specific drug delivery and also the modulation of cellular functions. Glyconanoparticles, glycodendrimers, and glycoliposomes were successfully used as tools for CLR-specific targeting. This review will discuss different approaches for multivalent CLR ligand presentation and aims to highlight how CLR targeting has been employed for cell specific drug delivery. Major emphasis is directed towards targeting of CLRs expressed by antigen-presenting cells to modulate immune responses.

Dendritic cell targeted liposomes-protamine-DNA complexes mediated by synthetic mannosylated cholesterol as a potential carrier for DNA vaccine

To construct mannosylated liposomes/protamine/DNA (LPD) carriers for DNA vaccine targeting to dendritic cells (DCs), a mannosylated cholesterol derivative (Man-C6-Chol) was synthesized via simple ester linkage and amide bonds. Then, the Man-C6-Chol was applied to LPD formulation as a synthetic ligand. The physicochemical properties of mannosylated LPD (Man-LPD) were first evaluated, including the size and zeta potential, morphology and the ability to protect DNA against DNase I degradation. Man-LPD showed a small size with a stable viral-like structure. In comparison to non-mannose liposomes/LPD (Man-free liposomes/LPD), mannosylated liposomes/LPD (Man-liposomes/Man-LPD) exhibited higher efficiency in both intracellular uptake (2.3-fold) and transfection (4.5-fold) in vitro. Subsequent MTT assays indicated that the LPD carriers had low toxicity on the tested cells. Afterwards, the investigation into the maturation activation on primary bone marrow-derived DCs (BMDCs) showed that both Man-LPD and Man-free LPD induced remarkable up-regulation of CD80, CD86 and CD40 on BMDCs. Inspired by these studies, we can conclude that the synthetic mannosylated LPD targeting to DCs was a potential carrier for DNA vaccine.

Effective targeted gene delivery to dendritic cells via synergetic interaction of mannosylated lipid with DOPE and BCAT

The efficient delivery of plasmids encoding antigenic determinants into dendritic cells (DCs) that control immune response is a promising strategy for rapid development of new vaccines. In this study, we prepared a series of targeted cationic lipoplex based on two synthetic lipid components, mannose-poly(ethylene glycol, MW3000)-1,2-distearoyl-sn-glycero-3-phosphoethanolamine (Mannose-PEG3000-DSPE) and O-(2R-1,2-di-O-(1'Z-octadecenyl)-glycerol)-3-N-(bis-2-aminoethyl)-carbamate (BCAT), that were formulated with 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) for evaluation as nonviral vectors for transgene expression in DCs. First, we optimized the N/P ratio for maximum transfection and then screened the effects of mannose targeting for further enhancement of transfection levels. Our results indicate that efficient delivery of gWIZ GFP plasmid into DCs was observed for mannose compositions of ∼10%, whereas low transfection efficiencies were observed with nontargeted formulations. Mannose-targeted lipofectamine complexes also showed high GFP expression levels in DCs relative to nontargeted lipofectamine controls. The best transfection performance was observed using 10 mol % Mannose-PEG3000-DSPE, 60 mol % BCAT, and 30 mol % DOPE, indicating that the most efficient delivery into DCs occurs via synergistic interaction between mannose targeting and acid-labile, fusogenic BCAT/DOPE formulations. Our data suggest that mannose-PEG3000-DSPE/BCAT/DOPE formulations may be effective gene delivery vehicles for the development of DC-based vaccines.

Mannosylated dextran nanoparticles: a pH-sensitive system engineered for immunomodulation through mannose targeting

Biotherapeutic delivery is a rapidly growing field in need of new materials that are easy to modify, are biocompatible, and provide for triggered release of their encapsulated cargo. Herein, we report on a particulate system made of a polysaccharide-based pH-sensitive material that can be efficiently modified to display mannose-based ligands of cell-surface receptors. These ligands are beneficial for antigen delivery, as they enhance internalization and activation of APCs, and are thus capable of modulating immune responses. When compared to unmodified particles or particles modified with a nonspecific sugar residue used in the delivery of antigens to dendritic cells (DCs), the mannosylated particles exhibited enhanced antigen presentation in the context of major histocompatibility complex (MHC) class I molecules. This represents the first demonstration of a mannosylated particulate system that enables enhanced MHC I antigen presentation by DCs in vitro. Our readily functionalized pH-sensitive material may also open new avenues in the development of optimally modulated vaccine delivery systems.

N-glycan targeted gene delivery to the dendritic cell SIGN receptor

A novel nonviral gene delivery vector composed of a high-mannose N-glycan conjugated to a polyacridine peptide was prepared. The glycopeptide was designed to bind to plasmid DNA by a combination of polyintercalation and ionic binding, and to the DC-SIGN (dendritic cell-specific intracellular adhesion molecule-3 grabbing nonintegrin) receptor expressed on CHO cells by recognition of the high-mannose N-glycan. The glycopeptide conjugate was prepared by purification of a high-mannose N-glycan from affinity fractionated soybean agglutinin (SBA). The SBA was proteolyzed to release the N-glycan which was then modified on its N-terminus with Tyr and a propionate maleimide. A DNA binding polyacridine peptide, Cys-(Acr-Lys)(4), was prepared by solid-phase peptide synthesis using Fmoc-Lys(Acr), then conjugated to the maleimide on the N-glycan to produce a glycopeptide. The glycopeptide bound to DNA with high affinity as determined by fluorophore displacement assay and DNA band shift on agarose gel. When bound to Cy5 labeled DNA, the glycopeptide mediated specific uptake in DC-SIGN CHO (+) cells as determined by FACS analysis. In vitro gene transfer studies established that the glycopeptide increased the specificity of gene transfer in DC-SIGN CHO (+) cells 100-fold relative to CHO (-) cells. These studies suggest that a high-mannose N-glycan conjugated to a polyacridine peptide may also facilitate receptor mediated gene delivery in dendritic cells and thereby find utility in the delivery of DNA vaccines.

Synthetic vehicles for DNA vaccination

DNA vaccination is an attractive immunization method able to induce robust cellular immune responses in pre-clinical models. However, clinical DNA vaccination trials performed thus far have resulted in marginal responses. Consequently, strategies are currently under development to improve the efficacy of DNA vaccines. A promising strategy is the use of synthetic particle formulations as carrier systems for DNA vaccines. This review discusses commonly used synthetic carriers for DNA vaccination and provides an overview of in vivo studies that use this strategy. Future recommendations on particle characteristics, target cell types and evaluation models are suggested for the potential improvement of current and novel particle delivery systems. Finally, hurdles which need to be tackled for clinical evaluation of these systems are discussed.

Mannosylated liposomes for targeted vaccines delivery

Mannosylated liposomes appear to be a promising and potential carrier system for delivery of proteins, peptides, or nucleic acids. The present chapter describes novel mannosylated liposomes, which increase the intracellular targeting of immunogen to dendritic cells and macrophages possessing the specific receptors. The liposomes used in the present investigation were prepared by hand-shaken method and characterized for size, shape, surface charge, encapsulation efficiency, ligand binding, and specificity and uptake studies. The immune-stimulating activity of the liposomes was studied by measuring antigen-specific antibody titer following subcutaneous administration of different liposomal formulations in BALB/c mice. It was found that O-palmitoyl mannan (OPM)-coated liposomes showed better uptake efficiency. In vivo studies revealed that the OPM-coated liposomes exhibited significant higher serum antibody response and stronger TH1/TH2-based cellular responses. In conclusion, novel vesicular constructs are useful nanosized carriers having superior surface characteristics--for active interaction with the antigen-presenting cells and subsequent processing and presentation of antigen.

Targeting the porcine immune system--particulate vaccines in the 21st century

During the last decade, the propagation of immunological knowledge describing the critical role of dendritic cells (DC) in the induction of efficacious immune responses has promoted research and development of vaccines systematically targeting DC. Based on the promise for the rational design of vaccine platforms, the current review will provide an update on particle-based vaccines of both viral and synthetic origin, giving examples of recombinant virus carriers such as adenoviruses and biodegradable particulate carriers. The viral carriers carry pathogen-associated molecular patterns (PAMP), used by the original virus for targeting DC, and are particularly efficient and versatile gene delivery vectors. Efforts in the field of synthetic vaccine carriers are focussing on decorating the particle surface with ligands for DC receptors such as heparan sulphate glycosaminoglycan structures, integrins, Siglecs, galectins, C-type lectins and toll-like receptors. The emphasis of this review will be placed on targeting the porcine immune system, but reference will be made to advances with murine and human vaccine delivery systems where information on DC targeting is available.

Protein/peptide and DNA vaccine delivery by targeting C-type lectin receptors

C-type lectin receptors (CLRs) are a class of pathogen-recognition receptors that are actively investigated in the field of vaccine delivery. Many of their properties have functions linked to the immune system. These receptors are expressed abundantly on antigen-presenting cells and are considered to be the sentinels of immune surveillance owing to their endocytic nature and the ability to recognize a diverse range of pathogens through recognition of pathogen-associated molecular patterns. CLRs are also involved in the processes of antigen presentation mediated through the induction of dendritic cell maturation and cytokine production. These properties engender CLRs to be ideal for vaccine targeting. Conversely, CLRs also function to recognize glycosylated self-antigens to induce homeostatic control and tolerance. In this review, we will describe the various preclinical/clinical vaccination strategies to target antigens and plasmid DNA to this diverse class of receptors.

Mannose-based molecular patterns on stealth microspheres for receptor-specific targeting of human antigen-presenting cells

The targeting of antigen-presenting cells has recently gained strong attention for both targeted vaccine delivery and immunomodulation. We prepared surface-modified stealth microspheres that display various mannose-based ligands at graded ligand densities to target phagocytic C-type lectin receptors (CLRs) on human dendritic cells (DCs) and macrophages. Decoration of microspheres with carbohydrate ligands was achieved (i) by electrostatic surface assembly of mannan onto previously formed adlayers of poly( l-lysine) (PLL) or a mix of PLL and poly( l-lysine)- graft-poly(ethylene glycol) (PLL-PEG), or (ii) through assembly of PLL-PEG equipped with small substructure mannoside ligands, such as mono- and trimannose, as terminal substitution of the PEG chains. Microspheres carrying mannoside ligands were also studied in combination with an integrin-targeting RGD peptide ligand. Because of the presence of a mannan or PEG corona, such microspheres were protected against protein adsorption and opsonization, thus allowing the formation of specific ligand-receptor interactions. Mannoside density was the major factor for the phagocytosis of mannoside-decorated microspheres, although with limited efficiency. This strengthens the recent hypothesis by other authors that the mannose receptor (MR) only acts as a phagocytic receptor when in conjunction with yet unidentified partner receptor(s). Analysis of DC surface markers for maturation revealed that neither surface-assembled mannan nor mannoside-modified surfaces on the microspheres could stimulate DC maturation. Thus, phagocytosis upon recognition by CLRs alone cannot trigger DC activation toward a T helper response. The microparticulate platform established in this work represents a promising tool for systematic investigations of specific ligand-receptor interactions upon phagocytosis, including the screening for potential ligands and ligand combinations in the context of vaccine delivery and immunomodulation.

Use of mannosylated cationic liposomes/ immunostimulatory CpG DNA complex for effective inhibition of peritoneal dissemination in mice

BACKGROUND

Immunotherapy using immunostimulatory CpG DNA could be a promising new therapeutic approach to combat refractory peritoneal dissemination. In the present study, we report the use of a mannosylated cationic liposomes/immunostimulatory CpG DNA complex (Man/CpG DNA lipoplex) for effective inhibition of peritoneal dissemination in mice.

METHODS

The immune response characteristics of the Man/CpG DNA lipoplex were evaluated by measuring tumor necrosis factor (TNF)-alpha production using primary cultured mouse peritoneal macrophages. Subsequently, Man/CpG DNA lipoplex was administered intraperitoneally (i.p.) to peritoneal dissemination model mice, and the number of tumor cells (colon26/Luc) was quantitatively evaluated by measuring luciferase activity. The effect on survival time of the Man/CpG DNA lipoplex was also investigated. The serum transaminase levels of mice receiving i.p. Man/CpG DNA lipoplex treatment were measured to evaluate systemic toxicity.

RESULTS

The Man/CpG DNA lipoplex induced higher TNF-alpha production from macrophages than CpG DNA complexed with conventional cationic liposomes and galactosylated cationic liposomes (Bare/CpG DNA lipoplex and Gal/CpG DNA lipoplex), suggesting mannose receptor-mediated CpG DNA transfer. Intraperitoneal administration of Man/CpG DNA lipoplex inhibited the proliferation of tumor cells in the greater omentum and the mesentery more efficiently than Bare/CpG DNA lipoplex and Gal/CpG DNA lipoplex. Furthermore, the survival time of the peritoneal dissemination model mice was prolonged by i.p. administration of Man/CpG DNA lipoplex. The serum transaminase levels of mice receiving i.p. Man/CpG DNA lipoplex were found to be the same as those of untreated mice.

CONCLUSIONS

The results obtained suggest that i.p. administered Man/CpG DNA lipoplex can be used for efficient immunotherapy to combat peritoneal dissemination.

Nonviral approaches for targeted delivery of plasmid DNA and oligonucleotide

Successful gene therapy depends on the development of efficient delivery systems. Although pDNA and ODN are novel candidates for nonviral gene therapy, their clinical applications are generally limited owing to their rapid degradation by nucleases in serum and rapid clearance. A great deal of effort had been devoted to developing gene delivery systems, including physical methods and carrier-mediated methods. Both methods could improve transfection efficacy and achieve high gene expression in vitro and in vivo. As for carrier-mediated delivery in vivo, since gene expression depends on the particle size, charge ratio, and interaction with blood components, these factors must be optimized. Furthermore, a lack of cell-selectivity limits the wide application to gene therapy; therefore, the use of ligand-modified carriers is a promising strategy to achieve well-controlled gene expression in target cells. In this review, we will focus on the in vivo targeted delivery of pDNA and ODN using nonviral carriers.

[Immunotherapy against peritoneal dissemination by immunostimulatory CpG DNA]

Peritoneal dissemination is one of the most common causes of metastasis from malignancies in the abdominal cavity. However, the treatment of peritoneal dissemination is difficult; patients receiving normal chemotherapy have a 0-1% chance of surviving for 5 years. Milky spots in the greater omentum are considered to facilitate the adhesion and invasion of abdominal free cancer cells, and subsequently lymph node metastasis occurs. Since immune cells such as macrophages and lymphocytes are present in the greater omentum and lymph nodes, the activation of immune cells would be a promising strategy for treatment. Single-stranded oligonucleotides containing CpG dinucleotides (CpG DNA) are recognized by Toll-like receptor-9 on antigen-presenting cells such as macrophages to stimulate Th-1-type immune responses. However, a delivery system for CpG DNA to immune cells is essential to develop effective therapy against peritoneal dissemination. Here we review the pathophysiologic basis of peritoneal dissemination and introduce our approach that employs cationic liposomes as a carrier for CpG DNA as a new approach in the treatment of peritoneal dissemination.

Non-coding pDNA bearing immunostimulatory sequences co-entrapped with leishmanial antigens in cationic liposomes elicits almost complete protection against experimental visceral leishmaniasis in BALB/c mice

The difficulty in making successful vaccines against leishmaniasis is partly due to lack of an appropriate adjuvant. Non-coding plasmid DNA (pDNA) bearing immunostimulatory sequences (ISS) is a potent activator of innate immunity, and can thus act as an adjuvant with vaccine antigen. We therefore evaluated the efficacy of pDNA and soluble leishmanial antigens (SLA) to protect against challenge with Leishmania donovani infection. We demonstrate that immunomodulatory activity of pDNA, which potentiated a Th1 immune responses, led to enhanced protection with SLA. Importantly, adding cationic liposomes as vehicle to the antigen, with pDNA either complexed or entrapped within, significantly increased the potentiating effect of pDNA. Further, comparison of the two vaccine formulations demonstrated an impressive increase in the protective efficacy up to two folds when both antigen and pDNA were within the vehicle. Thus, these studies establish the utility of non-coding pDNA bearing ISS as strong promoters of vaccine potency of liposomal antigens especially when co-entrapped with the antigen in cationic liposomes.

Development of an antigen-presenting cell-targeted DNA vaccine against melanoma by mannosylated liposomes

As part of our research involving the targeted delivery of plasmid DNA (pDNA) to antigen-presenting cells (APCs), we developed mannosylated cationic liposomes: N-[1-(2,3-dioleyloxy)propyl]-N,N,N-trimethylammonium chloride (DOTMA)/cholesten-5-yloxy-N-(4-((1-imino-2-D-thiomannosyl-ethyl)amino)butyl)formamide (Man-C4-Chol)/Chol (Man liposomes). In this study, we used melanoma-associated antigen expressing pDNA; pUb-M and Man liposomes to create a novel APC-targeted DNA vaccine against melanoma and examined its potency by measuring the Ub-M mRNA expression in splenic dendritic cells and macrophages, the cytotoxic T lymphocyte (CTL) activity against melanoma B16BL6 cells and the melanoma B16BL6-specific anti-tumor effect after intraperitoneal (i.p.) administration. We verified that Man lipoplex induces significantly higher pUb-M gene transfection into dendritic cells and macrophages than unmodified lipoplex and naked DNA and it also strongly induces CTL activity against melanoma, inhibits its growth and prolongs the survival after tumor challenge compared with unmodified liposomes and the standard method (naked pDNA, intramuscular (i.m.)). These results demonstrate that Man liposomes are a potent APCs-targeted vector that induce strong immunopotency of DNA vaccine against melanoma.

Optimization and delivery of plasmid DNA for vaccination

Vaccination with DNA is one of the most promising novel immunization techniques against a variety of pathogens and tumors, for which conventional vaccination regimens have failed. DNA vaccines are able to stimulate both arms of the immune system simultaneously, without carrying the safety risks associated with live vaccines, therefore representing not only an alternative to conventional vaccines but also significant progress in the prevention and treatment of fatal diseases and infections. However, translation of the excellent results achieved in small animals to similar success in primates or large animals has so far proved to be a major hurdle. Moreover, biosafety issues, such as the removal of antibiotic resistance genes present in plasmid DNA used for vaccination, remain to be addressed adequately. This review describes strategies to improve the design and production of conventional plasmid DNA, including an overview of safety and regulatory issues. It further focuses on novel systems for the optimization of plasmid DNA and the development of diverse plasmid DNA delivery systems for vaccination purposes.

Mannan-modified adenovirus as a vaccine to induce antitumor immunity

Tumor vaccine is a useful strategy for cancer therapy. However, priming of the immune system requires the relevant antigen to be presented by antigen-presenting cells (APCs). Here, we employed telomerase reverse transcriptase as a model antigen to explore the feasibility of using mannan-modified adenovirus as a tumor vaccine. We found that tumor immunogene therapy with the vaccine was effective at protective antitumor immunity in mice. The antigen-specific cytotoxic T lymphocytes were found in in vitro cytotoxicity assay. The elevation of the killing activity could be abrogated by anti-CD8 or anti-major histocompatibility complex-I antibodies. Adoptive transfer of purified CD8+ cells, and CD4+ cells to a less extent, was effective at antitumor activity. In vivo antitumor activity could be abrogated by depleting CD4+ T lymphocytes. A possible explanation for the antitumor effects may be the antigen was transferred to APCs in the presence of mannan. These observations provide insights into the design of novel vaccine strategies and might be important for the future application of antigens identified in other diseases.

Efficient Gene Transfer into Macrophages and Dendritic Cells by in Vivo Gene Delivery with Mannosylated Lipoplex via the Intraperitoneal Route

In this study, we developed an antigen-presenting cell (APC)-selective intraperitoneal (i.p.) gene delivery system with mannosylated cationic liposomes (Man-liposomes)/plasmid DNA complex (Man-lipoplex). An in vitro study using cultured peritoneal macrophages demonstrated that Man-liposomes could transfect luciferase-encoding plasmid DNA (pCMV-Luc) more efficiently than cationic liposomes via a mannose receptor-mediated mechanism. In vivo gene transfection studies revealed that Man-lipoplex showed a higher gene expression in the liver, spleen, peritoneal exuded cells, and mesenteric lymph nodes than cationic liposomes/plasmid DNA complex (lipoplex) or naked pCMV-Luc after i.p. administration, and this gene expression lasted for at least 24 h. The transfection activity of Man-lipoplex after i.p. administration was significantly higher than that after i.v. gene delivery with the Man-liposomes we developed previously, indicating that gene delivery via the i.p. route seems to be an efficient approach for in vivo gene delivery to APCs. Furthermore, it was demonstrated that Man-lipoplex could enhance gene expression in both F4/80+ and CD11c+ cells in the spleen. These results show that gene delivery with Man-liposomes via the i.p. route could be an effective approach for APC-selective gene transfection.