Chitosan and alginate salt as biomaterials are potential natural adjuvants for killed cholera vaccine

An Injectable Chitosan Hydrochloride-Sodium Alginate Hydrogel Adjuvant Capable of Eliciting Potent Humoral and Cellular Immunity

Adjuvants can enhance the immune effects of vaccines. Currently, the most commonly used and validated are aluminum and oil-emulsion adjuvants. However, these adjuvants are not without flaws; for instance, aluminum adjuvants can cause adverse reactions and irritation at the injection site. Consequently, the development of new, safe, and effective adjuvants remains a prominent topic in vaccine research. In this study, we synthesized a composite hydrogel by combining sodium alginate (SA) and the chitosan derivative chitosan hydrochloride (CHCL) to explore the feasibility of this polymer composite hydrogel as a novel immunoadjuvant. Our results indicate that this hydrogel material possesses good biocompatibility and antibacterial properties, is easily injectable, and locally initiates vaccine responses by stimulating the phagocytosis of protein antigens by dendritic cells (DCs). Additionally, they offer sustained exposure to vaccine antigens. After administration, a transient inflammatory niche is created to prolong immune system activation. Importantly, our study demonstrated that the CHCL-SA hydrogel loaded with antigens effectively stimulated the body to produce a humoral immune response and enhance the maturation of the CD8+ T lymphocyte subset. In murine tumor challenge experiments, the CHCL-SA supplemented antigen group significantly inhibited tumor cell growth and improved mouse survival rates. In summary, we developed an injectable CHCL-SA hydrogel adjuvant with great potential for enhancing the efficacy of vaccines.

A Thermosensitive and Degradable Chitin-Based Hydrogel as a Brucellosis Vaccine Adjuvant

Brucellosis is a zoonotic infectious disease that has long endangered the development of animal husbandry and human health. Currently, vaccination stands as the most efficacious method for preventing and managing brucellosis. Alum, as the most commonly used adjuvant for the brucellosis vaccine, has obvious disadvantages, such as the formation of granulomas and its non-degradability. Therefore, the aims of this study were to prepare an absorbable, injectable, and biocompatible hydroxypropyl chitin (HPCT) thermosensitive hydrogel and to evaluate its immunization efficacy as an adjuvant for Brucella antigens. Specifically, etherification modification of marine natural polysaccharide chitin was carried out to obtain a hydroxypropyl chitin. Rheological studies demonstrated the reversible temperature sensitivity of HPCT hydrogel. Notably, 5 mg/mL of bovine serum albumin can be loaded in HPCT hydrogels and released continuously for more than one week. Furthermore, the L929 cytotoxicity test and in vivo degradation test in rats proved that an HPCT hydrogel had good cytocompatibility and histocompatibility and can be degraded and absorbed in vivo. In mouse functional experiments, as adjuvants for Brucella antigens, an HPCT hydrogel showed better specific antibody expression levels and cytokine (Interleukin-4, Interferon-γ) expression levels than alum. Thus, we believe that HPCT hydrogels hold much promise in the development of adjuvants.

Immunostimulatory Polymers as Adjuvants, Immunotherapies, and Delivery Systems

Activating innate immunity in a controlled manner is necessary for the development of next-generation therapeutics. Adjuvants, or molecules that modulate the immune response, are critical components of vaccines and immunotherapies. While small molecules and biologics dominate the adjuvant market, emerging evidence supports the use of immunostimulatory polymers in therapeutics. Such polymers can stabilize and deliver cargo while stimulating the immune system by functioning as pattern recognition receptor (PRR) agonists. At the same time, in designing polymers that engage the immune system, it is important to consider any unintended initiation of an immune response that results in adverse immune-related events. Here, we highlight biologically derived and synthetic polymer scaffolds, as well as polymer–adjuvant systems and stimuli-responsive polymers loaded with adjuvants, that can invoke an immune response. We present synthetic considerations for the design of such immunostimulatory polymers, outline methods to target their delivery, and discuss their application in therapeutics. Finally, we conclude with our opinions on the design of next-generation immunostimulatory polymers, new applications of immunostimulatory polymers, and the development of improved preclinical immunocompatibility tests for new polymers.