Association of chitosan and aluminium as a new adjuvant strategy for improved vaccination

Role of NLRP3 inflammasome in nanoparticle adjuvant-mediated immune response

The nucleotide-binding oligomerization domain (NOD)-like receptor (NLR) family pyrin domain-containing 3 (NLRP3) inflammasome is pivotal in orchestrating the immune response induced by nanoparticle adjuvants. Understanding the intricate mechanisms underlying the activation of NLRP3 inflammasome by these adjuvants is crucial for deciphering their immunomodulatory properties. This review explores the involvement of the NLRP3 inflammasome in mediating immune responses triggered by nanoparticle adjuvants. It delves into the signaling pathways and cellular mechanisms involved in NLRP3 activation, highlighting its significance in modulating the efficacy and safety of nanoparticle-based adjuvants. A comprehensive grasp of the interplay between NLRP3 inflammasome and nanoparticle adjuvants holds promise for optimizing vaccine design and advancing immunotherapeutic strategies.

Bridging nanoplatform and vaccine delivery, a landscape of strategy to enhance nasal immunity

Vaccination is an urgently needed and effective option to address epidemic, cancers, allergies, and other diseases. Nasal administration of vaccines offers many benefits over needle-based injection including high compliance and less risk of infection. Inactivated or attenuated vaccines as convention vaccine present potential risks of pathogenic virulence reversal, the focus of nasal vaccine development has shifted to the use of next-generation (subunit and nucleic acid) vaccines. However, subunit and nucleic acid vaccine intranasally have numerous challenges in development and utilization due to mucociliary clearance, mucosal epithelial tight junction, and enzyme/pH degradation. Nanoplatforms as ideal delivery systems, with the ability to enhance the retention, penetration, and uptake of nasal mucosa, shows great potential in improving immunogenic efficacy of nasal vaccine. This review provides an overview of delivery strategies for overcoming nasal barrier, including mucosal adhesion, mucus penetration, targeting of antigen presenting cells (APCs), enhancement of paracellular transportation. We discuss methods of enhancing antigen immunogenicity by nanoplatforms as immune-modulators or multi-antigen co-delivery. Meanwhile, we describe the application status and development prospect of nanoplatforms for nasal vaccine administration. Development of nanoplatforms for vaccine delivery via nasal route will facilitate large-scale and faster global vaccination, helping to address the threat of epidemics.

ROS antagonizes the protection of Parkin-mediated mitophagy against aluminum-induced liver inflammatory injury in mice

Aluminum (Al) is a food pollutant that has extensive deleterious effects on the liver. Our previous research proposed that E3 ubiquitin ligase PARK2 knockout (Parkin^-/-) could aggravate Al-induced liver damage by inhibiting mitophagy, during which the reactive oxygen species (ROS) content increases. Inhibition of mitophagy can activate inflammasome. But the link between Parkin-mediated mitophagy and liver inflammatory injury caused by Al, and the role of ROS in it remain unclear. In this study, we applied Al, Parkin^-/- and N-acetyl-L-cysteine (NAC) to act on C57BL/6N mice to investigate them. We found that Al could induce liver inflammatory injury and Parkin^-/- could aggravate it. Meanwhile, inhibition of ROS alleviated oxidative stress, mitochondrial damage, mitophagy and inflammatory injury caused by Al in Parkin^-/- mice liver. These results indicated that ROS antagonized the protection of Parkin-mediated mitophagy against Al-induced liver inflammatory damage in mice.

An oral vaccine based on chitosan/aluminum adjuvant induces both local and systemic immune responses in turbot (Scophthalmus maximus)

Oral vaccination is the most convenient method for disease protection in aquaculture due to possibility of adding vaccines as part of fish diet. However, low protective efficiency is the major problem of oral vaccination owing to some reasons, especially for antigens degradation. In this study, we developed an oral inactivated vaccine based on a chitosan/aluminum adjuvant system, and investigated immune response induced by the vaccine. As a result, Th1 and Th2 cells mediated immune responses were observed after the vaccination according to the upregulation of IL-6, IL-12, IFNγ and IgM genes expression that were deemed as the driver cytokines for triggering the responses. Moreover, ratio of IgT⁺/IgM⁺ B cells was elevated in intestine after vaccination, while IgM antibodies were also observed in the sera of vaccinated fish, suggested that both local and systemic immune responses were induced by the inactivated vaccine. Totally, this oral vaccine can be used for V. anguillarum protection and this chitosan/aluminum system is an efficient candidate adjuvant for developing more vaccines in the future.

Chitosan modified squalene nanostructured lipid carriers as a promising adjuvant for freeze-dried ovalbumin vaccine

As immune adjuvants assisting vaccines, nanoparticle delivery systems have been widely exploited. Squalene, the major ingredient of approved adjuvant MF59, has great potential in activating immune responses. In the current study, model antigen ovalbumin (OVA) was encapsulated into squalene-based nanostructured lipid carriers (NLCs), and the chitosan, a cationic polysaccharide, was used for modifying nanoparticles to develop a functionalized and cationic nanoparticle delivery system (OVA-csNLCs). Firstly, the optimal formulation of csNLCs was successfully screened out, and had hydrodynamic diameter of 235.80 ± 5.99 nm and zeta potential of 34.90 ± 6.95 mV. Then, the generated OVA-csNLCs had no significant difference in hydrodynamic diameter and exhibited lower zeta potential of 19.03 ± 0.31 mV and high encapsulation efficiency of 83.4%. Sucrose (10%, w/w) was selected as optimal lyoprotectant, exhibiting good stability of OVA-csNLCs in the form of freeze-dried powder. More importantly, the OVA-csNLCs effectively promoted OVA antigen uptake by macrophage, significantly enhanced the level of OVA-specific IgG, and induced a Th2-based immune response in vivo. Furthermore, mice immunization experiment demonstrated that OVA-csNLCs had well biocompatibility and facilitated spleen lymphocytes proliferation. Above findings indicate that chitosan modified squalene nanostructured lipid carriers show promise as antigen delivery system and an open adjuvant platform.

Loading Effect of Chitosan Derivative Nanoparticles on Different Antigens and Their Immunomodulatory Activity on Dendritic Cells

Drug carrier nanoparticles (NPs) were prepared by the polyelectrolyte method, with chitosan sulfate, with different substituents and quaternary ammonium chitosan, including C236-HACC NPs, C36-HACC NPs, and C6-HACC NPs. To evaluate whether the NPs are suitable for loading different antigens, we chose bovine serum albumin (BSA), ovalbumin (OVA), and myoglobin (Mb) as model antigens to investigate the encapsulation effect of the NPs. The characteristics (size, potential, and encapsulation efficiency) of the NPs were measured. Moreover, the NPs with higher encapsulation efficiency were selected for the immunological activity research. The results showed that chitosan derivative NPs with different substitution sites had different loading effects on the three antigens, and the encapsulation rate of BSA and OVA was significantly better than that of Mb. Moreover, the NPs encapsulated with different antigens have different immune stimulating abilities to DCS cells, the immune effect of OVA-coated NPs was significantly better than that of BSA-coated NPs and blank NPs, especially C236-HACC-OVA NPs. Furthermore, we found that C236-HACC-OVA NPs could increase the phosphorylation level of intracellular proteins to activate cell pathways. Therefore, C236-HACC NPs are more suitable for the loading of antigens similar to the OVA structure.

Adjuvants: friends in vaccine formulations against infectious diseases

Infectious diseases represent a major cause of deaths worldwide. No vaccine or effective treatment exists nowadays, especially against intracellular pathogens. The increase in multiple drug and superbug antibiotic resistance strains, excessive medication, or misuse of drugs has prompted the search for other safe and effective alternatives. Consistent with this, adjuvants (Latin word "adjuvare": "help or aid") co-administered (Exo) in vaccines have emerged as a promising alternative to initiate and boost an innate, downstream signal that led to adaptative immune response. Nowadays, a promising model of strong immunogens and adjuvants at mucosal sites are the microbial bacterial toxins. Other adjuvants that are also used and might successfully replace aluminum salts in combination with nanotechnology are CpG-ODN, poly IC, type I IFNs, mRNA platforms. Therefore, in the present review, we focused to revisit the old to the new adjuvants compounds, the properties that make them friends in vaccine formulations against infectious diseases.

Chitosan hydrogel loaded with recombinant protein containing epitope C from HSP90 of Candida albicans induces protective immune responses against systemic candidiasis

We reported previously a recombinant protein (rP-HSP90C) containing epitope C from heat shock protein 90 of Candida albicans mediates protective immune responses against systemic candidiasis. However, it exhibits weak immunogenicity. Therefore, we evaluated the potential and mechanisms of thermosensitive chitosan hydrogel (CH-HG) as an adjuvant in rP-HSP90C vaccine. CH-HG synthesized by ionic cross-linking showed buffering capacity and control-released rP-HSP90C in vitro. In comparison to naked rP-HSP90C, CH-HG-loaded rP-HSP90C (CH-HG/rP-HSP90C) not only evoked a long-lasting rP-HSP90C-specific IgG, but also enhanced Th1, Th2, Th17 responses and the ratio of Th1/Th2 in vivo; Meanwhile, CH-HG/rP-HSP90C provoked a stronger CTL response than rP-HSP90C. Notably, CH-HG increased the protective immune responses against systemic candidiasis in rP-HSP90C-immunized mice since CH-HG/rP-HSP90C enhanced the survival rate of infected mice, and diminished the CFUs in kidneys compared to rP-HSP90C, which were similar to that of QuilA. Further in vitro investigation displayed CH-HG upgraded the expressions of costimulators, MHCs and cytokines in BMDCs compared to rP-HSP90C；CH-HG also promoted cellular uptake, endosomal escape and "cross-presentation" of rP-HSP90C. In addition, it recruited immune cells at the injection site. Our study demonstrated that CH-HG can be an efficient adjuvant in fungal vaccines.

Cloning and Expression of the Tibetan Pig Interleukin-23 Gene and Its Promotion of Immunity of Pigs to PCV2 Vaccine

Vaccines against Porcine circovirus type 2 (PCV2) have been studied intensely and found to be effective in decreasing mortality and improving growth in swine populations. In this study, interleukin-23 (IL-23) gene was cloned from peripheral blood mononuclear cells (PBMCs) of Tibetan pigs and inserted into a eukaryotic VR1020 expression vector-VRIL23. Coated with chitosan (CS), the VRIL23-CS was intramuscularly injected into 3-week-old piglets with PCV2 vaccine. The blood was collected after vaccination at 0, 1, 2, 4, 8, and 12 weeks, respectively, to detect the immunological changes. The IgG2a and specific PCV2 antibodies were detected using ELISA, and blood CD4+ and CD8+ T cells were quantified by flow cytometry. Quantitative fluorescence PCR was used to evaluate the expression of immune genes. The results indicate that leukocytes, erythrocytes, and CD4+ and CD8+ T cells increased significantly in the blood of VRIL23-CS inoculated piglets in comparison with the control (p < 0.05) and so did the IgG2a and PCV2 antibodies. In addition, the expressions of Toll-like receptor (TLR) 2, TLR7, cluster of differentiation (CD) 45, IL-15, IL-12, signal transducer and activator of transcription (STAT)1, STAT2, STAT3, STAT4, and B-cell lymphoma (Bcl)-2 genes were also obviously higher in the VRIL23-CS inoculated pigs at different time points (p < 0.05). Overall, the results demonstrated that VRIL23-CS can enhance the comprehensive immune responses to PCV2 vaccine in vivo and has the promising potential to be developed into a safe and effective adjuvant to promote the immunity of pig against PCV disease.

Immunomodulation as a Novel Strategy for Prevention and Treatment of Bordetella spp. Infections

Well-adapted pathogens have evolved to survive the many challenges of a robust immune response. Defending against all host antimicrobials simultaneously would be exceedingly difficult, if not impossible, so many co-evolved organisms utilize immunomodulatory tools to subvert, distract, and/or evade the host immune response. Bordetella spp. present many examples of the diversity of immunomodulators and an exceptional experimental system in which to study them. Recent advances in this experimental system suggest strategies for interventions that tweak immunity to disrupt bacterial immunomodulation, engaging more effective host immunity to better prevent and treat infections. Here we review advances in the understanding of respiratory pathogens, with special focus on Bordetella spp., and prospects for the use of immune-stimulatory interventions in the prevention and treatment of infection.

Glucan Particles Are a Powerful Adjuvant for the HBsAg, Favoring Antiviral Immunity

The lack of vaccine adjuvants that are able to induce robust T cell responses fosters the search for more powerful options. Pathogen-like particles are a promising approach. The adjuvant activity of pathogen-like particles is highly influenced by size and surface composition. This study aimed to evaluate the adjuvant potential of two different β-glucan-based particles, blend chitosan/β-glucan particles (ChiGluPs), which are positively charged and have mean size of 1276 nm, and neutral yeast-derived glucan particles (GPs), with a mean size of 3 μm. Additionally, chitosan particles (ChiPs) were used to understand the effect of β-glucan addition (ChiGluPs). Mouse spleen cells responded through the production of either TNF-α or RANTES, following in vitro stimulation with particles containing either β-glucan (ChiGluPs and GPs) or chitosan (ChiGluPs and ChiPs). Human monocytes responded to all particles through TNF-α secretion. Subcutaneous vaccination of mice with the hepatitis B surface antigen (HBsAg) showed increased serum IgG for all particles compared to HBsAg alone (435-, 4500-, or 2500-fold increase for either ChiPs, ChiGluPs, or GPs). Interestingly, only GPs elicited the secretion of HBsAg-specific Th1, Th2, Th9, Th17, Th22, and Treg-related cytokines. This study demonstrates, for the first time, that GPs can have a significant role against the hepatitis B virus by favoring antiviral immunity.

Chitosan Plus Compound 48/80: Formulation and Preliminary Evaluation as a Hepatitis B Vaccine Adjuvant

Current vaccine research is mostly based on subunit antigens. Despite the better toxicity profile of these antigens they are often poorly immunogenic, so adjuvant association has been explored as a strategy to obtain a potent vaccine formulation. Recently, mast cell activators were recognized as a new class of vaccine adjuvants capable of potentiating mucosal and systemic immune responses. In this study, a co-adjuvanted delivery system was developed and characterized, combining the mast cell activator C48/80 with chitosan nanoparticles (Chi-C48/80 NPs), and the results were compared with plain chitosan nanoparticles. The adsorption of model antigens onto the NP surface as well as the biocompatibility of the system was not affected by the incorporation of C48/80 in the formulation. The stability of the nanoparticles was demonstrated by studying the variation of size and zeta potential at different times, and the ability to be internalized by antigen presenting cells was confirmed by confocal microscopy. Vaccination studies with hepatitis B surface antigen loaded Chi-C48/80 NPs validated the adjuvanticity of the delivery system, demonstrating for the first time a successful association between a mast cell activator and chitosan nanoparticles as a vaccine adjuvant for hepatitis B virus, applied to a nasal vaccination strategy.

Mechanistic study of the adjuvant effect of chitosan-aluminum nanoparticles

The use of tailored particle-based adjuvants constitutes a promising way to enhance antigen-specific humoral and cellular immune responses. However, a thorough understanding of the mechanisms underlying their adjuvanticity is crucial to generate more effective vaccines. We studied the ability of chitosan-aluminum nanoparticles (CH-Al NPs), which combine the immunostimulatory effects of chitosan and aluminum salts, to promote dendritic cell activation, assess their impact on innate and adaptive immune responses, and compare the results to those reported for conventional chitosan particles (CH-Na NPs). All tested CH-NP formulations were capable of modulating cytokine secretion by dendritic cells. CH-Al NPs promoted NLRP3 inflammasome activation, enhancing the release of IL-1β without significantly inhibiting Th1 and Th17 cell-polarizing cytokines, IL-12p70 or IL-23, and induced DC maturation, but did not promote pro-inflammatory cytokine production on their own. In vivo results showed that mice injected with CH-Al NPs generated a local inflammatory response comparable to that elicited by the vaccine adjuvant alum. Importantly, after subcutaneous immunization with CH-Al NPs combined with the hepatitis B surface antigen (HBsAg), mice developed antigen-specific IgG titers in serum, nasal and vaginal washes. Overall, our results established CH-Al NPs as a potential adjuvant to enhance both innate and adaptive immune responses.

Chitosan:β-glucan particles as a new adjuvant for the hepatitis B antigen

The development of new vaccine adjuvants is urgently needed not only to enable new routes of vaccine administration but mostly to go beyond protective humoral immunity, often insufficient to fight infectious diseases. The association of two or more immunopotentiators or mimicking pathogen physicochemical properties are strategies that can favor powerful and more balanced Th1/Th2 immune responses. Therefore, the present work aimed to combine both chitosan and β-glucan biopolymers in the same particle, preferably with surface β-glucan localization to simulate the cell wall of some pathogens and to stimulate the immune cells expressing the Dectin-1 receptor. Chitosan:β-glucan particles (ChiGluPs) were developed through a chitosan precipitation method. The chitosan was precipitated into a β-glucan alkaline solution followed by genipin crosslink. The optimized method produced particles with a mean diameter of 837 nm for ChiPs and 1274 nm for ChiGluPs. β-glucan surface location was confirmed by zeta potential measurements (+24 mV for ChiGluPs and +36 mV for ChiPs) and zeta potential titration. These new particles showed high antigen loading efficacy and low cytotoxicity. Mice vaccination studies revealed that both ChiPs and ChiGluPs had an adjuvant effect for the hepatitis B surface antigen (HBsAg), with ChiGluPs resulting in serum anti-HBsAg total IgG 16-fold higher than ChiPs, when administered with 1.5 µg HBsAg per dose. Specifically, IgG1 subclass was 5-fold higher and IgG3 subclass was 4-fold higher for ChiGluPs comparing to ChiPs. Overall, the preparation method developed allowed the advantageous combination of β-glucan with chitosan, without chemical functionalization, which represents an additional step toward tailor-made adjuvants production using simple precipitation techniques.

Adjuvant Activity of Poly-ε-caprolactone/Chitosan Nanoparticles Characterized by Mast Cell Activation and IFN-γ and IL-17 Production

Polymeric nanoparticles (NPs) are extremely attractive vaccine adjuvants, able to promote antigen delivery and in some instances, exert intrinsic immunostimulatory properties that enhance antigen specific humoral and cellular immune responses. The poly-ε-caprolactone (PCL)/chitosan NPs were designed with the aim of being able to combine the properties of the 2 polymers in the preparation of an adjuvant for the hepatitis B surface antigen (HBsAg). This article reports important results of an in vitro mechanistic study and immunization studies with HBsAg associated with different concentrations of the nanoparticles. The results revealed that PCL/chitosan NPs promoted mast cell (MC) activation (β-hexosaminidase release) and that its adjuvant effect is not mediated by the TNF-α secretion. Moreover, we demonstrated that HBsAg loaded PCL/chitosan NPs, administered through the subcutaneous (SC) route, were able to induce higher specific antibody titers without increasing IgE when compared to a commercial vaccine, and that the IgG titers are nanoparticle-dose dependent. The results also revealed the NPs' capability to promote a cellular immune response against HBsAg, characterized by the production of IFN-γ and IL-17. These results demonstrated that PCL/chitosan NPs are a good hepatitis B antigen adjuvant, with direct influence on the intensity and type of the immune response generated.