Immunomodulatory properties of chitosan polymers

The introduction of vaccines is regarded as one of the most successful medical interventions to date. However, there is a clear need for the development of new vaccines for diseases which require the induction of a potent cellular immune response. Advancements in the field of vaccine research have resulted in a move away from the use of whole organisms and towards the use of subunit vaccines which consist of highly purified antigens with an improved safety profile. Adjuvants are immunostimulatory components that are included in subunit vaccine formulations to help direct and amplify adaptive immune responses. Chitosan is a cationic polysaccharide that has been examined in an adjuvant setting due to its biocompatible and biodegradable nature. The polysaccharide has been shown to have the capacity to induce Th1 cell responses following vaccination by injection or mucosal routes, supporting its application as an alternative to alum for vaccines that promote cell-mediated immunity. Here, we provide an overview of the physico-chemical properties of chitosan with a focus on the specific characteristics that dictate the type and scale of the immune responses induced. The potential to finely tailor chitosan polymers in order to direct specific types of immune responses can provide invaluable tools for the design of novel chitosan-based adjuvants and biomaterials.