Spacer-engineered carboxylated curdlan derivatives for dendritic cell activation and cancer immunotherapy

• Spacer-engineered carboxylated curdlan derivatives integrate adjuvant activity and pH-responsive antigen delivery in a single material. • Cyclohexyl-modified curdlan (Chex-Curd) exhibits superior dendritic cell activation property. • Chex-Curd–antigen conjugates strongly promote MHC class I antigen presentation and CD8⁺ T-cell responses. • Immunization with Chex-Curd conjugates achieves near-complete tumor suppression in a mouse lymphoma model. • Spacer hydrophobicity governs protonation behavior and membrane interaction, enabling rational design of next-generation cancer vaccines. Effective cancer immunotherapy requires cytosolic delivery of antigens into dendritic cells together with their maturation to elicit robust cellular immunity. Conventional vaccine carriers often combine multiple components to achieve both adjuvant activity and antigen delivery, which increases formulation complexity and raises safety concerns. Here, we present a strategy to integrate these functions into a single material by synthesizing carboxylated curdlan derivatives with tailored spacer structures. Introducing carboxy groups into curdlan, a representative polysaccharide adjuvant, conferred pH-sensitivity and improved water solubility, while spacer hydrophobicity modulated protonation behavior and interactions with lipid membranes. Among the derivatives, Chex-Curd, bearing a cyclohexyl spacer within carboxylated units, exhibited strong adjuvant activity and enhanced antigen presentation via the MHC class I pathway, which might result from cytosolic delivery of antigen. Chex-Curd also induced high levels of TNF-α and IL-12 secretion and upregulated dendritic cell maturation markers. Conjugates of Chex-Curd with a model antigenic protein elicited strong CD8⁺ T-cell responses and achieved significant tumor growth suppression in a mouse tumor model. These findings demonstrate that spacer engineering of polysaccharide-based adjuvants enables simultaneous dendritic cell activation and cytosolic antigen delivery, providing a promising platform for next-generation cancer vaccines.