Chitosan (CS), a cationic polysaccharide comprising
β (1–4)-linked glucosamine and
N-acetyl-glucosamine, is derived from chitin that is one of the most abundant polymers in nature. Due to its biocompatible and biodegradable, chitosan has been widely used in medicine, food, chemical industry, cosmetics and so on [
15,
16]. Chitosan is also considered as a potential vaccine adjuvant because of its abilities to enhance humoral and cellular immunity [
17]. Depending on the deacetylation degree, chitosan has various amount of –NH
2 exposure which leads to rich positive charge. This cationic polysaccharide has the superiority to easily attach the cell surface that is negative charged by electrostatic interaction, which may play an important role during the antigen uptake and presentation [
18]. The positive charge of chitosan can also improve the adjuvanticity including antigen protection and depot formation when the chitosan mixed with antigens. Besides, the protonation of the –NH
2 group at C-2 position of the d-glucosamine repeat unit also improves the solubility of chitosan which is critical for an adjuvant [
19]. In addition to these advantages as a delivery cargo, chitosan has specific immunostimulatory activities. It has been proved that chitosan induces type Ⅰ interferon (IFNs) secretion following with dendritic cells (DCs) activation and Th1 cellular immunity through the cGAS-STING pathway and NLRP3 inflammasome [
17]. Moreover, after the chitosan capsulated into the lysosome, the protonation of amino groups causes proton sponge effect that may induce endosomal escape and promote the cross-presentation of antigens. It is especially important for provoking CD8+ killer T cells after interacting with major histocompatibility complex (MHC) class Ⅰ molecules [
20]. Given the potential adjuvant property of chitosan, it is an excellent candidate for constructing MUC1-based vaccine to improve the immunogenicity of MUC1 peptide.