Chitosan Microparticles and Nanoparticles as Biocompatible Delivery Vehicles for Peptide and Protein-Based Immunocontraceptive Vaccines

Parenteral administration of GnRH constructs and adjuvants: immune responses and effects on reproductive tissues of male mice

Two gonadotrophin releasing hormone (GnRH) constructs prepared by either chemical conjugation to keyhole limpet hemocyanin (GnRH-KLH) or as an expressed recombinant fusion protein (Multimer) were evaluated with or without adjuvants (immunostimulating complexes, ISCOMs, or cytosine-phosphate-guanosine oligodeoxynucleotides, CpG ODNs). After subcutaneous administration to Balb/c male mice at Weeks 0, 2 and 4, these preparations were assessed for induction of immune responses and effects on reproductive organs. GnRH-KLH plus ISCOMs formulation induced strong IgG immune responses from Week 4 through Week 12 resulting in consistent reproductive organ atrophy by Week 12 after subcutaneous administration. GnRH-KLH plus CpG ODNs generated immune responses but no atrophy of reproductive tissues by Week 12. Multimer plus ISCOMs induced poor immune responses and no effects on reproductive tissues by Week 12. In the absence of additional adjuvant, none of the GnRH constructs induced reproductive organ atrophy. GnRH-KLH induced stronger immune responses when formulated with ISCOMs or CpG ODN compared to Multimer. GnRH-KLH with ISCOMs could be an effective colloidal alternative for emulsion GnRH vaccine formulations.

Peptide Vaccine: Progress and Challenges

Conventional vaccine strategies have been highly efficacious for several decades in reducing mortality and morbidity due to infectious diseases. The bane of conventional vaccines, such as those that include whole organisms or large proteins, appear to be the inclusion of unnecessary antigenic load that, not only contributes little to the protective immune response, but complicates the situation by inducing allergenic and/or reactogenic responses. Peptide vaccines are an attractive alternative strategy that relies on usage of short peptide fragments to engineer the induction of highly targeted immune responses, consequently avoiding allergenic and/or reactogenic sequences. Conversely, peptide vaccines used in isolation are often weakly immunogenic and require particulate carriers for delivery and adjuvanting. In this article, we discuss the specific advantages and considerations in targeted induction of immune responses by peptide vaccines and progresses in the development of such vaccines against various diseases. Additionally, we also discuss the development of particulate carrier strategies and the inherent challenges with regard to safety when combining such technologies with peptide vaccines.

Designing improved poly lactic-co-glycolic acid microspheres for a malarial vaccine: incorporation of alginate and polyinosinic-polycytidilic acid

Vaccination using proteins and peptides is currently gaining importance. One of the major drawbacks of this approach is the lack of an efficient immune response when the antigens are administered without adjuvants. In this study, we have taken the advantage of a combined adjuvant system in order to improve the immunogenicity of the SPf66 malarial antigen. For that purpose, we have combined poly (lactic-co-glycolic) acid microspheres, alginate, and polyinosinic polycytidilic acid. Our results show that microspheres can enhance the IgG production obtained with Freund's complete adjuvant. We have attributed this improvement to the presence of polyinosinic polycytidilic acid, since formulations comprising this adjuvant overcame the immune response from the others. In addition, our microspheres produced both IgG1 and IgG2a, leading to mixed Th1/Th2 activation, optimal for malaria vaccination. In conclusion, we have designed a preliminary formulation with a high potential for the treatment of malaria.

Chitosan nanoparticle encapsulated hemagglutinin-split influenza virus mucosal vaccine

Subunit/split influenza vaccines are less reactogenic compared with the whole virus vaccines. However, their immunogenicity is relatively low and thus required proper adjuvant and/or delivery vehicle for immunogenicity enhancement. Influenza vaccines administered intramuscularly induce minimum, if any, mucosal immunity at the respiratory mucosa which is the prime site of the infection. In this study, chitosan (CS) nanoparticles were prepared by ionic cross-linking of the CS with sodium tripolyphosphate (TPP) at the CS/TPP ratio of 1:0.6 using 2 h mixing time. The CS/TPP nanoparticles were used as delivery vehicle of an intranasal influenza vaccine made of hemagglutinin (HA)-split influenza virus product. Innocuousness, immunogenicity, and protective efficacy of the CS/TPP-HA vaccine were tested in influenza mouse model in comparison with the antigen alone vaccine. The CS/TPP-HA nanoparticles had required characteristics including nano-sizes, positive charges, and high antigen encapsulation efficiency. Mice that received two doses of the CS/TPP-HA vaccine intranasally showed no adverse symptoms indicating the vaccine innocuousness. The animals developed higher systemic and mucosal antibody responses than vaccine made of the HA-split influenza virus alone. The CS/TPP-HA vaccine could induce also a cell-mediated immune response shown as high numbers of IFN-γ-secreting cells in spleens while the HA vaccine alone could not. Besides, the CS nanoparticle encapsulated HA-split vaccine reduced markedly the influenza morbidity and also conferred 100% protective rate to the vaccinated mice against lethal influenza virus challenge. Overall results indicated that the CS nanoparticles invented in this study is an effective and safe delivery vehicle/adjuvant for the influenza vaccine.

Activation of the NLRP3 inflammasome is not a feature of all particulate vaccine adjuvants

Particulate vaccine formulations, designed to improve the delivery of antigens to antigen-presenting cells (APCs) and to stimulate an immune response, have been shown to activate the NLRP3 inflammasome. This leads to the processing and secretion of interleukin (IL)-1β, which supports the recruitment of pro-inflammatory immune cells into the tissue and can therefore be beneficial for vaccine potency. Recent work suggested that this may be a common mechanism of action for all particulate formulations. The aim of this study was to investigate whether the activation of the NLRP3 inflammasome was common to many delivery systems. We prepared polymer-based chitosan nanoparticles (CNPs), lipid-based cubosomes, a water in oil emulsion of incomplete Freund's adjuvant (IFA) and alum formulations and examined inflammasome activation in vitro using murine bone-marrow-derived dendritic cells and human peripheral blood mononuclear cells and in vivo in mice. The formulations differed in their morphology, size and zeta-potential. Only the positively charged particles (CNPs and alum) were able to activate the inflammasome and increase the secretion of IL-1β. A decrease in the activation of the inflammasome with these particulates was observed when cathepsin B-mediated effects were blocked, implying a role of lysosomal rupture in the activation process. These findings demonstrate a role for the surface charge of particulates in the activation of the NLRP3 inflammasome, which should be considered when designing a novel vaccine formulation.

Key roles of adjuvants in modern vaccines

Vaccines containing novel adjuvant formulations are increasingly reaching advanced development and licensing stages, providing new tools to fill previously unmet clinical needs. However, many adjuvants fail during product development owing to factors such as manufacturability, stability, lack of effectiveness, unacceptable levels of tolerability or safety concerns. This Review outlines the potential benefits of adjuvants in current and future vaccines and describes the importance of formulation and mechanisms of action of adjuvants. Moreover, we emphasize safety considerations and other crucial aspects in the clinical development of effective adjuvants that will help facilitate effective next-generation vaccines against devastating infectious diseases.

Enhanced immune response and protective effects of nano-chitosan-based DNA vaccine encoding T cell epitopes of Esat-6 and FL against Mycobacterium tuberculosis infection

Development of a novel and effective vaccine against Mycobacterium tuberculosis (M.tb) is a challenging for preventing TB infection. In this study, a novel nanoparticle-based recombinant DNA vaccine was developed, which contains Esat-6 three T cell epitopes (Esat-6/3e) and fms-like tyrosine kinase 3 ligand (FL) genes (termed Esat-6/3e-FL), and was enveloped with chitosan (CS) nanoparticles (nano-chitosan). The immunologic and protective efficacy of the nano-chitosan-based DNA vaccine (termed nano-Esat-6/3e-FL) was assessed in C57BL/6 mice after intramuscular prime vaccination with the plasmids DNA and nasal boost with the Esat-6/3e peptides. The results showed that the immunized mice remarkably elicited enhanced T cell responses and protection against M.tb H37Rv challenge. These findings indicate that the nano-chitosan can significantly elevate the immunologic and protective effects of the DNA vaccine, and the nano-Esat-6/3e-FL is a useful vaccine for preventing M.tb infection in mice.

Bioreducible alginate-poly(ethylenimine) nanogels as an antigen-delivery system robustly enhance vaccine-elicited humoral and cellular immune responses

Although polysaccharide nanogels have emerged as a novel antigen delivery system for vaccine development, whether modulating the redox sensitivity of nanogels could improve vaccine efficacy remains unclear. In the present study, we generated bioreducible cationic alginate-polyethylenimine (PEI) nanogels as a novel vaccine delivery system. Briefly, nanogels were prepared by the electrostatic interaction of negatively charged alginate sodium with branched PEI2k, followed by disulfide cross-linking to generate bioreducible nanogels (AP-SS). The AP-SS nanogels demonstrated great antigen-loading capacity and minimal cytotoxicity. The in vitro study showed that reducible AP-SS nanogels not only facilitated antigen uptake by mouse bone marrow dendritic cells (BMDCs), but also promoted intracellular antigen degradation and cytosolic release. Moreover, AP-SS nanogels significantly enhanced both MHC class I and II antigen presentation by BMDCs. Compared with the non-reducible nanogels, AP-SS nanogels more potently enhanced vaccine-induced antibody production and CD8+ T cell-mediated tumor cell lysis. Hence, the bioreducible alginate-PEI nanogels could serve as a potent adjuvant to improve vaccine-elicited humoral and cellular immune responses.

Micro and nanoparticle-based delivery systems for vaccine immunotherapy: an immunological and materials perspective

The development and widespread application of vaccines has been one of the most significant achievements of modern medicine. Vaccines have not only been instrumental in controlling and even eliminating life-threatening diseases like polio, measles, diphtheria, etc., but have also been immensely powerful in enhancing the worldwide outlook of public health over the past century. Despite these successes, there are still many complex disorders (e.g., cancer, HIV, and other emerging infectious diseases) for which effective preventative or therapeutic vaccines have been difficult to develop. This failure can be attributed primarily to our inability to precisely control and modulate the highly complex immune memory response, specifically the cellular response. Dominated by B and T cell maturation and function, the cellular response is primarily initiated by potent immunostimulators and antigens. Efficient and targeted delivery of these immunomodulatory and immunostimulatory molecules to appropriate cells is key to successful development of next generation vaccine formulations. Over the past decade, particulate carriers have emerged as an attractive means for enhancing the delivery efficacy and potency of vaccines and associated immunomodulatory molecules. Specifically, polymer-based micro and nanoparticles are being extensively studied for a wide variety of applications. In this review, we discuss the immunological fundamentals for developing effective vaccines and how materials and material properties can be exploited to improve these therapies. Particular emphasis is given to polymer-based particles and how the route of administration of particulate systems affects the phenotype and robustness of an immune response. Comparison of various strategies and recent advancements in the field are discussed along with insights into current limitations and future directions.

Biodegradable microparticles covalently linked to surface antigens of the scuticociliate parasite P. dicentrarchi promote innate immune responses in vitro

The histiophagous scuticociliate endoparasite Philasterides dicentrarchi is an emerging pathogen that infects the turbot Scophthalmus maximus and thus causes important economic losses in turbot aquaculture. This in vitro study investigated the adjuvant capacity of biodegradable microspheres (MS) composed of two polymers (chitosan and Gantrez(®)) covalently coupled to surface antigens (Ag) of P. dicentrarchi. The coupled MS-Ag significantly stimulated the phagocytic response of both murine macrophages (RAW 264.7 cells) and leukocytes from the anterior kidney of turbot (HLK), at a level similar to that induced by zymosan A. The MS-Ag also significantly increased production of reactive oxygen and nitrogen species, as shown by the increased O(2) consumption and stimulation of the respiratory burst and nitric oxide production by murine and in particular by turbot HLK. The MS-Ag stimulated the production of the proinflammatory cytokine tumour necrosis factor alpha (TNFα) by murine and turbot HLK. The results confirm the high adjuvant capacity of biodegradable MS covalently bound to Ag as regards stimulating the innate immune response, and they justify the use of MS in the production of safe and effective vaccines against fish pathogens.