Polymer-based adjuvant requirements for vaccines

Vaccination is an effective strategy to prevent infectious diseases and, depending on the type of immune response generated, can have a therapeutic applicability. Vaccine adjuvants are key components to direct immunity toward strong humoral and cell-mediated immunity. New and powerful adjuvants are needed and must be included in new vaccines either to stimulate the exhausted immune systems of elderly or immunocompromised individuals or to provide increased stability to the vaccine formulations, benefiting vaccine coverage in developing countries. The development of “pathogen-like” adjuvants, mimicking pathogens’ repetitive surface molecule organization, their particulate nature, and the ability to stimulate both innate and adaptive immune responses are some of the key parameters responsible for their superb immunogenicity, representing a promising alternative to licensed vaccine formulations. The inclusion of biodegradable naturally occurring polymers, present on some microorganisms, may also result in both strong antibody protection and broad cytokine production by T cell populations leading to a global Th1 antiviral protection. Finally, vaccine administration through mucosal routes, such as the oral route, could be the way toward vaccine-preventable diseases eradication, with a high translational potential for mass vaccination in developing countries. Overall, the present chapter aims to provide a brief review of the immunological mechanisms that explain the action of adjuvants and a deepen insight on the most promising features of the awaiting new generation of polymer-based vaccine adjuvants, with special emphasis on β-glucans and chitosan.