Reduction-sensitive dextran nanogels aimed for intracellular delivery of antigens

Targeting of antigens to dendritic cells (DCs) to induce strong cellular immune response can be established by loading in a nano-sized carrier and keeping the antigen associated with the particles until they are internalized by DCs. In the present study, a model antigen (ovalbumin, OVA) is immobilized in cationic dextran nanogels via disulfide bonds. These bonds are stable in the extracellular environment but are reduced in the cytosol of DCs due to the presence of glutathione. Reversible immobilization of OVA in the nanogels is demonstrated by the fact that hardly any release of the protein occurred at pH 7 in the absence of glutathione, whereas rapid release of OVA occurs once the nanogels are incubated in buffer with glutathione. Furthermore, these OVA conjugated nanogels show intracellular release of the antigen in DCs and boost the MHC class I antigen presentation, demonstrating the feasibility of this concept for the aimed intracellular antigen delivery. The model antigen ovalbumin is chemically conjugated to the cationic nanogels via disulfide bonds. The protein is thereby covalently immobilized in the nanogels in the extracellular environment. Rapid release of conjugated protein occurs once the nanogels are internalized into cells, due to cleavage of the disulfide bonds in the presence of relatively high intracellular levels of glutathione (2.5-10 × 10-3 m).