Effect of Chitosan and Liposome Nanoparticles as Adjuvant Codelivery on the Immunoglobulin G Subclass Distribution in a Mouse Model

In vivo evaluation of new adjuvant systems based on combination of Salmonella Typhi porins with particulate systems: Liposomes versus polymeric particles

Subunit vaccines that have weak immunogenic activity require adjuvant systems for enhancedcellular and long-acting humoral immune responses. Both lipid-based and polymeric-based particulate adjuvants have been widely investigated to induce the desired immune responses against the subunit vaccines. The adjuvant efficacy of these particulate adjuvants depends upon their physicochemical properties such as particle size, surface charge, shape and their composition. Previously, we showed in vitro effect of adjuvant systems based on combination of chitosan and Salmonella Typhi porins in microparticle or nanoparticle form, which were spherical with positive surface charge. In the present study, we have further developed an adjuvant system based on combination of porins with liposomes (cationic and neutral) and investigated the adjuvant effect of both the liposomal and polymeric systems in BALB/c mice using a model antigen, ovalbumin. Humoral immune responses were determined following priming and booster dose at 15-day intervals. In overall, IgM and IgG levels were induced in the presence of both the liposomal and polymeric adjuvant systems indicating the positive impact of combination with porins. The highest IgM levels were obtained on Day 8, and liposomal adjuvant systems were found to elicit significantly higher IgM levels compared to polymeric systems. IgG levels were increased significantly after booster, particularly more profound with the micro-sized polymeric system when compared to cationic liposomal system with nano-size. Our results demonstrated that the developed particulate systems are promising both as an adjuvant and delivery system, providing enhanced immune responses against subunit antigens, and have the potential for long-term protection.

Semisynthetic Pneumococcal Glycoconjugate Nanovaccine

Pneumococcal conjugate vaccines offer an excellent safety profile and high protection against the serotypes comprised in the vaccine. However, inclusion of protein antigens fromStreptococcus pneumoniaecombined with potent adjuvants and a suitable delivery system are expected to both extend protection to serotype strains not represented in the formulation and stimulate a broader immune response, thus more effective in young children, elderly, and immunocompromised populations. Along this line, nanoparticle (NP) delivery systems can enhance the immunogenicity of antigens by protecting them from degradation and increasing their uptake by antigen-presenting cells, as well as offering co-delivery with adjuvants. We report herein the encapsulation of a semisynthetic glycoconjugate (GC) composed of a synthetic tetrasaccharide mimicking theS. pneumoniae serotype 14 capsular polysaccharide (CP14) linked to the Pneumococcal surface protein A (PsaA) using chitosan NPs (CNPs). These GC-loaded chitosan nanoparticles (GC-CNPs) were not toxic to human monocyte-derived dendritic cells (MoDCs), showed enhanced uptake, and displayed better immunostimulatory properties in comparison to the naked GC. A comparative study was carried out in mice to evaluate the immune response elicited by the glycoconjugate-administered subcutaneously (SC), where the GC-CNPs displayed 100-fold higher IgG response as compared with the group treated with nonencapsulated GC. Overall, the study demonstrates the potential of this chitosan-based nanovaccine for efficient delivery of glycoconjugate antigens.

Differences in HPV-specific antibody Fc-effector functions following Gardasil® and Cervarix® vaccination

Gardasil® (Merck) and Cervarix® (GlaxoSmithKline) both provide protection against infection with Human Papillomavirus 16 (HPV16) and Human Papillomavirus 18 (HPV18), that account for around 70% of cervical cancers. Both vaccines have been shown to induce high levels of neutralizing antibodies and are known to protect against progression beyond cervical intraepithelial neoplasia grade 2 (CIN2+), although Cervarix® has been linked to enhanced protection from progression. However, beyond the transmission-blocking activity of neutralizing antibodies against HPV, no clear correlate of protection has been defined that may explain persistent control and clearance elicited by HPV vaccines. Beyond blocking, antibodies contribute to antiviral activity via the recruitment of the cytotoxic and opsonophagocytic power of the immune system. Thus, here, we used systems serology to comprehensively profile Gardasil®- and Cervarix®- induced antibody subclass, isotype, Fc-receptor binding, and Fc-effector functions against the HPV16 and HPV18 major capsid protein (L1). Overall, both vaccines induced robust functional humoral immune responses against both HPV16 and HPV18. However, Cervarix® elicited higher IgG3 and antibody-dependent complement activating responses, and an overall more coordinated response between HPV16 and 18 compared to Gardasil®, potentially related to the distinct adjuvants delivered with the vaccines. Thus, these data point to robust Fc-effector functions induced by both Gardasil® and Cervarix®, albeit with enhanced coordination observed with Cervarix®, potentially underlying immunological correlates of post-infection control of HPV.

Chitosan-Based Nanomaterial as Immune Adjuvant and Delivery Carrier for Vaccines

With the support of modern biotechnology, vaccine technology continues to iterate. The safety and efficacy of vaccines are some of the most important areas of development in the field. As a natural substance, chitosan is widely used in numerous fields-such as immune stimulation, drug delivery, wound healing, and antibacterial procedures-due to its good biocompatibility, low toxicity, biodegradability, and adhesion. Chitosan-based nanoparticles (NPs) have attracted extensive attention with respect to vaccine adjuvants and delivery systems due to their excellent properties, which can effectively enhance immune responses. Here, we list the classifications and mechanisms of action of vaccine adjuvants. At the same time, the preparation methods of chitosan, its NPs, and their mechanism of action in the delivery system are introduced. The extensive applications of chitosan and its NPs in protein vaccines and nucleic acid vaccines are also introduced. This paper reviewed the latest research progress of chitosan-based NPs in vaccine adjuvant and drug delivery systems.

Polymeric Nanoparticle-Based Vaccine Adjuvants and Delivery Vehicles

As vaccine formulations have progressed from including live or attenuated strains of pathogenic components for enhanced safety, developing new adjuvants to more effectively generate adaptive immune responses has become necessary. In this context, polymeric nanoparticles have emerged as a promising platform with multiple advantages, including the dual capability of adjuvant and delivery vehicle, administration via multiple routes, induction of rapid and long-lived immunity, greater shelf-life at elevated temperatures, and enhanced patient compliance. This comprehensive review describes advances in nanoparticle-based vaccines (i.e., nanovaccines) with a particular focus on polymeric particles as adjuvants and delivery vehicles. Examples of the nanovaccine approach in respiratory infections, biodefense, and cancer are discussed.

Polymeric nanoencapsulation of alpha interferon increases drug bioavailability and induces a sustained antiviral response in vivo

Polymeric nanoparticulate systems allow the encapsulation of bio-active substances, giving them protection against external agents and increasing the drug's bioavailability. The use of biocompatible and biodegradable polymers usually guarantees the harmless character of the formulation, and a controlled drug release is also assured. A relatively easy procedure to obtain polymeric formulations of bioactive agents is ionotropic gelation, which allows the synthesis of chitosan (CS) - sodium tri-polyphosphate nanoparticles (NPs) loading encapsulated proteins. In this work, Bovine serum albumin (BSA) model protein and a recombinant porcine alpha interferon variant were used to obtain nanoparticulate formulations. The internalization of the encapsulated material by cells was studied using a BSA-fluorescein system; the fluorescent conjugate was observable inside the cells after 20 h of incubation. The therapeutic CS-alpha interferon formulation showed a maximum of protein released in vitro at around 90 h. This system was found to be safe in a cytotoxicity assay, while biological activity experiments in vitro showed antiviral protection of cells in the presence of encapsulated porcine alpha interferon. In vivo experiments in pigs revealed a significant and sustained antiviral response through overexpression of the antiviral markers OAS2 and PKR. This proves the preservation of porcine alpha interferon biological activity, and also that a lasting response was obtained. This procedure is an effective and safe method to formulate drugs in nanoparticulate systems, representing a significant contribution to the search for more effective drug delivery strategies.

Nanoparticle-Based Vaccines for Brucellosis: Calcium Phosphate Nanoparticles-Adsorbed Antigens Induce Cross Protective Response in Mice

Introduction

Vaccine formulation with appropriate adjuvants is an attractive approach to develop protective immunity against pathogens. Calcium phosphate nanoparticles (CaPNs) are considered as ideal adjuvants and delivery systems because of their great potential for enhancing immune responses. In the current study, we have designed nanoparticle-based vaccine candidates to induce immune responses and protection against B. melitensis and B. abortus.

Materials and Methods

For this purpose, we used three Brucella antigens (FliC, 7α-HSDH, BhuA) and two multi-epitopes (poly B and poly T) absorbed by CaPNs. The efficacy of each formulation was evaluated by measuring humoral, cellular and protective responses in immunized mice.

Results

The CaPNs showed an average size of about 90 nm with spherical shape and smooth surface. The CaPNs-adsorbed proteins displayed significant increase in cellular and humoral immune responses compared to the control groups. In addition, our results showed increased ratio of specific IgG2a (associated with Th1) to specific IgG1 (associated with Th2). Also, immunized mice with different vaccine candidate formulations were protected against B. melitensis 16M and B. abortus 544, and showed same levels of protection as commercial vaccines (B. melitensis Rev.1 and B. abortus RB51) except for BhuA-CaPNs.

Discussion

Our data support the hypothesis that these antigens absorbed with CaPNs could be effective vaccine candidates against B. melitensis and B. abortus.

Development of Next Generation Streptococcus pneumoniae Vaccines Conferring Broad Protection

Streptococcus pneumoniae is a major pathogen causing pneumonia with over 2 million deaths annually, especially in young children and the elderly. To date, at least 98 different pneumococcal capsular serotypes have been identified. Currently, the vaccines for prevention of S. pneumoniae infections are the 23-valent pneumococcal polysaccharide-based vaccine (PPV23) and the pneumococcal conjugate vaccines (PCV10 and PCV13). These vaccines only cover some pneumococcal serotypes and are unable to protect against non-vaccine serotypes and unencapsulated S. pneumoniae. This has led to a rapid increase in antibiotic-resistant non-vaccine serotypes. Hence, there is an urgent need to develop new, effective, and affordable pneumococcal vaccines, which could cover a wide range of serotypes. This review discusses the new approaches to develop effective vaccines with broad serotype coverage as well as recent development of promising pneumococcal vaccines in clinical trials. New vaccine candidates are the inactivated whole-cell vaccine strain (Δpep27ΔcomD mutant) constructed by mutations of specific genes and several protein-based S. pneumoniae vaccines using conserved pneumococcal antigens, such as lipoprotein and surface-exposed protein (PspA). Among the vaccines in Phase 3 clinical trials are the pneumococcal conjugate vaccines, PCV-15 (V114) and 20vPnC. The inactivated whole-cell and several protein-based vaccines are either in Phase 1 or 2 trials. Furthermore, the recent progress of nanoparticles that play important roles as delivery systems and adjuvants to improve the performance, as well as the immunogenicity of the nanovaccines, are reviewed.

The Combinations Chitosan-Pam3CSK4 and Chitosan-Monophosphoryl Lipid A: Promising Immune-Enhancing Adjuvants for Anticaries Vaccine PAc

We previously demonstrated that recombinant protein PAc could be administered as an anticaries vaccine. However, the relatively weak immunogenicity of PAc limits its application. In the present study, we investigated the effect of two adjuvant combinations of chitosan plus Pam₃CSK₄ (chitosan-Pam₃CSK₄) and of chitosan plus monophosphoryl lipid A (chitosan-MPL) in the immune responses to the PAc protein in vivo and in vitro PAc-chitosan-Pam₃CSK₄ or PAc-chitosan-MPL promoted significantly higher PAc-specific antibody titers in serum and saliva, inhibited Streptococcus mutans colonization onto the tooth surfaces, and endowed better protection effect with significantly less caries activities than PAc alone. Chitosan-Pam₃CSK₄ and chitosan-MPL showed no statistically significant differences. In conclusion, our study demonstrated that the chitosan-Pam₃CSK₄ and chitosan-MPL combinations are promising for anticaries vaccine development.

Polyglutamic acid-trimethyl chitosan-based intranasal peptide nano-vaccine induces potent immune responses against group A streptococcus

Peptide-based vaccines have the potential to overcome the limitations of classical vaccines; however, their use is hampered by a lack of carriers and adjuvants suitable for human use. In this study, an efficient self-adjuvanting peptide vaccine delivery system was developed based on the ionic interactions between cationic trimethyl chitosan (TMC) and a peptide antigen coupled with synthetically defined anionic α-poly-(l-glutamic acid) (PGA). The antigen, possessing a conserved B-cell epitope derived from the group A streptococcus (GAS) pathogen and a universal T-helper epitope, was conjugated to PGA using cycloaddition reaction. The produced anionic conjugate formed nanoparticles (NP-1) through interaction with cationic TMC. These NP-1 induced higher systemic and mucosal antibody titers compared to antigen adjuvanted with standard mucosal adjuvant cholera toxin B subunit or antigen mixed with TMC. The produced serum antibodies were also opsonic against clinically isolated GAS strains. Further, a reduction in bacterial burden was observed in nasal secretions, pharyngeal surface and nasopharyngeal-associated lymphoid tissue of mice immunized with NP-1 in GAS challenge studies. Thus, conjugation of defined-length anionic polymer to peptide antigen as a means of formulating ionic interaction-based nanoparticles with cationic polymer is a promising strategy for peptide antigen delivery. STATEMENT OF SIGNIFICANCE: A self-adjuvanting delivery system is required for peptide vaccines to enhance antigen delivery to immune cells and generate systemic and mucosal immunity. Herein, we developed a novel self-adjuvanting nanoparticulate delivery system for peptide antigens by combining polymer-conjugation and complexation strategies. We conjugated peptide antigen with anionic α-poly-(l-glutamic acid) that in turn, formed nanoparticles with cationic trimethyl chitosan by ionic interactions, without using external crosslinker. On intranasal administration to mice, these nanoparticles induced systemic and mucosal immunity, at low dose. Additionally, nanoparticles provided protection to vaccinated mice against group A streptococcus infection. Thus, this concept should be particularly useful in developing nanoparticles for the delivery of peptide antigens.