Enhanced in vivo gene expression mediated by listeriolysin O incorporated anionic LPDII: Its utility in cytotoxic T lymphocyte-inducing DNA vaccine

The relationship between Listeria infections and host immune responses: Listeriolysin O as a potential target

Listeria monocytogenes (Lm), a foodborne bacterium, can infect people and has a high fatality rate in immunocompromised individuals. Listeriolysin O (LLO), the primary virulence factor of Lm, is critical in regulating the pathogenicity of Lm. This review concludes that LLO may either directly or indirectly activate a number of host cell viral pathophysiology processes, such as apoptosis, pyroptosis, autophagy, necrosis and necroptosis. We describe the invasion of host cells by Lm and the subsequent removal of Lm by CD8 T cells and CD4 T cells upon receipt of the LLO epitopes from major histocompatibility complex class I (MHC-I) and major histocompatibility complex class II (MHC-II). The development of several LLO-based vaccines that make use of the pore-forming capabilities of LLO and the immune response of the host cells is then described. Finally, we conclude by outlining the several natural substances that have been shown to alter the three-dimensional conformation of LLO by binding to particular amino acid residues of LLO, which reduces LLO pathogenicity and may be a possible pharmacological treatment for Lm.

Biopolymer-based Carriers for DNA Vaccine Design

Over the last 30 years, genetically engineered DNA has been tested as novel vaccination strategy against various diseases, including human immunodeficiency virus (HIV), hepatitis B, several parasites, and cancers. However, the clinical breakthrough of the technique is confined by the low transfection efficacy and immunogenicity of the employed vaccines. Therefore, carrier materials were designed to prevent the rapid degradation and systemic clearance of DNA in the body. In this context, biopolymers are a particularly promising DNA vaccine carrier platform due to their beneficial biochemical and physical characteristics, including biocompatibility, stability, and low toxicity. This article reviews the applications, fabrication, and modification of biopolymers as carrier medium for genetic vaccines.

Journey to the Center of the Cell: Current Nanocarrier Design Strategies Targeting Biopharmaceuticals to the Cytoplasm and Nucleus

New biopharmaceutical molecules, potentially able to provide more personalized and effective treatments, are being identified through the advent of advanced synthetic biology strategies, sophisticated chemical synthesis approaches, and new analytical methods to assess biological potency. However, translation of many of these structures has been significantly limited due to the need for more efficient strategies to deliver macromolecular therapeutics to desirable intracellular sites of action. Engineered nanocarriers that encapsulate peptides, proteins, or nucleic acids are generally internalized into target cells via one of several endocytic pathways. These nanostructures, entrapped within endosomes, must navigate the intracellular milieu to orchestrate delivery to the intended destination, typically the cytoplasm or nucleus. For therapeutics active in the cytoplasm, endosomal escape continues to represent a limiting step to effective treatment, since a majority of nanocarriers trapped within endosomes are ultimately marked for enzymatic degradation in lysosomes. Therapeutics active in the nucleus have the added challenges of reaching and penetrating the nuclear envelope, and nuclear delivery remains a preeminent challenge preventing clinical translation of gene therapy applications. Herein, we review cutting-edge peptide- and polymer-based design strategies with the potential to enable significant improvements in biopharmaceutical efficacy through improved intracellular targeting. These strategies often mimic the activities of pathogens, which have developed innate and highly effective mechanisms to penetrate plasma membranes and enter the nucleus of host cells. Understanding these mechanisms has enabled advances in synthetic peptide and polymer design that may ultimately improve intracellular trafficking and bioavailability, leading to increased access to new classes of biotherapeutics.

Antibody-mediated neutralization of perfringolysin o for intracellular protein delivery

Perfringolysin O (PFO) is a member of the cholesterol-dependent cytolysin (CDC) family of bacterial pore-forming proteins, which are highly efficient in delivering exogenous proteins to the cytoplasm. However, the indiscriminate and potent cytotoxicity of PFO limits its practical use as an intracellular delivery system. In this study, we describe the design and engineering of a bispecific, neutralizing antibody against PFO, which targets reversibly attenuated PFO to endocytic compartments via receptor-mediated internalization. This PFO-based system efficiently mediated the endosomal release of a co-targeted gelonin construct with high specificity and minimal toxicity in vitro. Consequently, the therapeutic window of PFO was improved by more than 5 orders of magnitude. Our results demonstrating that the activity of pore-forming proteins can be controlled by antibody-mediated neutralization present a novel strategy for utilizing these potent membrane-lytic agents as a safe and effective intracellular delivery vehicle.

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.

Liposomes as vaccine delivery systems: a review of the recent advances

Liposomes and liposome-derived nanovesicles such as archaeosomes and virosomes have become important carrier systems in vaccine development and the interest for liposome-based vaccines has markedly increased. A key advantage of liposomes, archaeosomes and virosomes in general, and liposome-based vaccine delivery systems in particular, is their versatility and plasticity. Liposome composition and preparation can be chosen to achieve desired features such as selection of lipid, charge, size, size distribution, entrapment and location of antigens or adjuvants. Depending on the chemical properties, water-soluble antigens (proteins, peptides, nucleic acids, carbohydrates, haptens) are entrapped within the aqueous inner space of liposomes, whereas lipophilic compounds (lipopeptides, antigens, adjuvants, linker molecules) are intercalated into the lipid bilayer and antigens or adjuvants can be attached to the liposome surface either by adsorption or stable chemical linking. Coformulations containing different types of antigens or adjuvants can be combined with the parameters mentioned to tailor liposomal vaccines for individual applications. Special emphasis is given in this review to cationic adjuvant liposome vaccine formulations. Examples of vaccines made with CAF01, an adjuvant composed of the synthetic immune-stimulating mycobacterial cordfactor glycolipid trehalose dibehenate as immunomodulator and the cationic membrane forming molecule dimethyl dioctadecylammonium are presented. Other vaccines such as cationic liposome-DNA complexes (CLDCs) and other adjuvants like muramyl dipeptide, monophosphoryl lipid A and listeriolysin O are mentioned as well. The field of liposomes and liposome-based vaccines is vast. Therefore, this review concentrates on recent and relevant studies emphasizing current reports dealing with the most studied antigens and adjuvants, and pertinent examples of vaccines. Studies on liposome-based veterinary vaccines and experimental therapeutic cancer vaccines are also summarized.

Enhancement of nasal HIV vaccination with adenoviral vector-based nanocomplexes using mucoadhesive and DC-targeting adjuvants

PURPOSE

To investigate the vaccine effect of a replication-defective recombinant adenovirus 5 (rAd5)-based nanocomplex with chitooligosaccharides (Oligo) and mannosylated polyethyleneimine-triethyleneglycol (mPEI) as adjuvants for human immunodeficiency virus (HIV) infection.

METHODS

Physical characteristics were determined through detecting the size, zeta potential and morphology of Oligo-mPEI-rAd5 nanocomplex, and in vitro vaccine uptake and transduction efficiency were estimated. Nanocomplexes were then administered intranasally to Balb/c mice to evaluate in vivo rAd5 residence in nasal cavity and HIVgag-specific immune responses using cytotoxic T lymphocyte (CTL), intracellular cytokine staining (ICS) and ELISA assay.

RESULTS

The mucoadhesivity of Oligo prolonged nasal residence time, while the dendritic cell (DC) specificity of mPEI improved vaccine uptake. These two adjuvants jointly enhanced transduction efficiency of rAd5. Oligo-mPEI-rAd5 nanocomplex elicited potent HIVgag-specific CTL response and increased IFN-γ positive CD8(+)T and IL-4 positive CD4(+)T cells, indicating high cellular immune responses. This vaccine candidate also led to strong humoral immune responses (IgG/IgG1/IgG2a) with balanced Th1/Th2 CD4(+)T cell activity. Moreover, mice nasally immunized with Oligo-mPEI-rAd5 showed higher levels of SIgA in nasal washes than did mice immunized with rAd5.

CONCLUSIONS

Intranasal delivery of Oligo-mPEI-rAd5 with a prime-boost regimen is a potential immunization for HIV infection, inducing HIVgag-specific cellular, humoral and mucosal immune responses.

Targeted cytolysins synergistically potentiate cytoplasmic delivery of gelonin immunotoxin

Targeted endocytic uptake is a first step toward tissue-specific cytoplasmic macromolecular delivery; however, inefficient escape from the endolysosomal compartment makes this generally impractical at present. We report here a targeted cytolysin approach that dramatically potentiates endosomal release of an independently targeted potent gelonin immunotoxin. Fibronectin domains engineered for affinity to EGF receptor or carcinoembryonic antigen were fused to the plant toxin gelonin or bacterial pore-forming cytolysins. These fusion proteins display synergistic activity in both antigen-specific cytotoxicity in vitro, enhancing potency by several orders of magnitude, and in tumor growth inhibition in vivo. In addition, the number of internalized gelonin molecules required to induce apoptosis is reduced from approximately 5 × 10(6) to less than 10(3). Targeted potentiation shows promise for enhancing cytoplasmic delivery of other macromolecular payloads such as DNA, siRNA, and miRNA.

Listeriolysin O as a strong immunogenic molecule for the development of new anti-tumor vaccines

The pore-forming toxin listeriolysin O (LLO), which is produced by Listeria monocytogenes, mediates bacterial phagosomal escape and facilitates bacterial multiplication during infection. This toxin has recently gained attention because of its confirmed role in the controlled and specific modulation of the immune response. Currently, cancer immunotherapies are focused on conquering the immune tolerance induced by poorly immunogenic tumor antigens and eliciting strong, lasting immunological memory. An effective way to achieve these goals is the co-administration of potent immunomodulatory adjuvant components with vaccine vectors. LLO, a toxin that belongs to the family of cholesterol-dependent cytolysins (CDCs), exhibits potent cell type-non-specific toxicity and is a source of dominant CD4(+) and CD8(+) T cell epitopes. According to recent research, in addition to its effective cytotoxicity as a cancer immunotherapeutic drug, the non-specific adjuvant property of LLO makes it promising for the development of efficacious anti-tumor vaccines.

Triolein-based polycation lipid nanocarrier for efficient gene delivery: characteristics and mechanism

We proposed to develop a polycation lipid nanocarrier (PLN) with higher transfection efficiency than our previously described polycation nanostrucutred lipid nanocarrier (PNLC). PLN was composed of triolein, cetylated low-molecular-weight polyethylenimine, and dioleoyl phosphatidylethanolamine. The physicochemical properties of PLN and the PLN/DNA complexes (PDC) were characterized. The in vitro transfection was performed in human lung adenocarcinoma (SPC-A1) cells, and the intracellular mechanism was investigated as well. The measurements indicated that PLN and PDC are homogenous nanometer-sized particles with a positive charge. The transfection efficiency of PDC significantly increased with the content of triolein and was higher than that of PNLC and commercial Lipofectamine™ 2000. In particular, the transfection of PLN in the presence of 10% serum was more effective than that in its absence. With the help of specific inhibitors of chlorpromazine and filipin, the clathrin-dependent endocytosis pathway was determined to be the main contributor to the successful transfection mediated by PLN in SPC-A1 cells. The captured images verified that the fluorescent PDC was localized in the lysosomes and nuclei after endocytosis. Thus, PLN represents a novel efficient nonviral gene delivery vector.

Polymer-mediated DNA vaccine delivery via bystander cells requires a proper balance between transfection efficiency and cytotoxicity

Direct targeting of dendritic cells is an ideal goal for DNA vaccine delivery in order to stimulate both arms of the immune system. However, dendritic cells are often difficult to transfect using nonviral polyplexes. Here we show that transfecting bystander cells such as fibroblasts with PEI/DNA complexes leads to efficient cross-presentation of a model antigen by dendritic cells and subsequent activation of antigen-specific CD8(+) T cells. Maturation of dendritic cells is also stimulated after co-culture with transfected fibroblasts. Such outcomes depend on a proper balance between transfection efficiency and polyplex-induced cytotoxicity in the fibroblasts. In fact, substantial cytotoxicity is desirable and even necessary for cross-presentation and cross-priming of T cells. This study illustrates a new pathway of polymer-based DNA vaccine delivery via bystander cells without direct targeting of antigen-presenting cells and highlights the importance of exploiting polymer-induced cytotoxicity for the benefit of immune activation.

Conjugation of lipid and CpG-containing oligonucleotide yields an efficient method for liposome incorporation

For optimal stimulation of T cells, protein-based vaccines must deliver protein antigens to antigen-presenting cells while simultaneously providing immunostimulatory signals. Listeriolysin O (LLO)-containing liposomes have been utilized to efficiently deliver protein antigens to the cytosolic pathway for antigen processing and major histocompatibility complex class I-dependent presentation while codelivering immunostimulatory CpG-oligodeoxyribonuceotides (ODNs). In this report, we describe the synthesis of lipid-CpG-ODN conjugates utilizing maleimide-phosphatidylethanolamine (PE) lipids and 5'-sulfhdryl-containing CpG-ODNs as a method for facile incorporation of CpG-ODNs in liposomal vaccine carriers, an alternative to co-encapsulation inside liposomes and as a means to enhance delivery of CpG-ODNs to their major receptor, Toll-like receptor 9 (TLR9), in the endosome. The characterization and biological evaluation of the vaccine delivery system made of liposomes, which contain the lipid-CpG-ODN conjugates inserted in the liposomal membrane, is described. We demonstrate in vitro in bone marrow derived macrophages that the lipid-CpG-ODN conjugates incorporated onto the liposome bilayers interact with their receptor TLR9 as readily as liposome-encapsulated ODNs and exert their immunostimulatory capabilities. The liposomal vaccine delivery systems were evaluated in mice using ovalbumin (OVA) as a model antigen, and the results indicate equally robust OVA-specific cytotoxic T lymphocyte responses and similar Th1 immune skewing capabilities between liposomes containing lipid-conjugated or encapsulated CpG-ODNs. Overall, this work indicates that conjugating PE lipids and CpG-ODNs results in an efficient method that allows facile incorporation of CpG-ODNs into a liposome-based delivery platform while retaining the immune-stimulating capabilities of CpG-ODNs.