To construct mannosylated liposomes/protamine/DNA (LPD) carriers for DNA vaccine targeting to dendritic cells (DCs), a mannosylated cholesterol derivative (Man-C6-Chol) was synthesized via simple ester linkage and amide bonds. Then, the Man-C6-Chol was applied to LPD formulation as a synthetic ligand. The physicochemical properties of mannosylated LPD (Man-LPD) were first evaluated, including the size and zeta potential, morphology and the ability to protect DNA against DNase I degradation. Man-LPD showed a small size with a stable viral-like structure. In comparison to non-mannose liposomes/LPD (Man-free liposomes/LPD), mannosylated liposomes/LPD (Man-liposomes/Man-LPD) exhibited higher efficiency in both intracellular uptake (2.3-fold) and transfection (4.5-fold) in vitro. Subsequent MTT assays indicated that the LPD carriers had low toxicity on the tested cells. Afterwards, the investigation into the maturation activation on primary bone marrow-derived DCs (BMDCs) showed that both Man-LPD and Man-free LPD induced remarkable up-regulation of CD80, CD86 and CD40 on BMDCs. Inspired by these studies, we can conclude that the synthetic mannosylated LPD targeting to DCs was a potential carrier for DNA vaccine.

Background: To establish a potential gene-delivery system with the ability to deliver plasmid DNA to dendritic cells (DCs) more efficiently and specifically, we designed and synthesized a low-molecular-weight polyethyleneimine and triethyleneglycol polymer (PEI-TEG) and a series of its mannosylated derivatives. Methods: PEI-TEG was synthesized from PEI2000 and PEI600 with TEG as the cross-linker. PEI-TEG was then linked to mannose via a phenylisothiocyanate bridge to obtain man-PEI-TEG conjugates. The DNA conveyance abilities of PEI-TEG, man-PEI-TEG, as well as control PEI25k were evaluated by measuring their zeta potential, particle size, and DNA-binding abilities. The in vitro cytotoxicity, cell uptake, and transfection efficiency of these PEI/DNA complexes were examined on the DC2.4 cell line. Finally, a maturation experiment evaluated the effect of costimulatory molecules CD40, CD80, and CD86 on murine bone marrow-derived DCs (BMDCs) using flow cytometry. Results: PEI-TEG and man-PEI-TEG were successfully synthesized and were shown to retain the excellent properties of PEI25k for condensing DNA. Compared with PEI-TEG as well as PEI25k, the man-PEI-TEG had less cytotoxicity and performed better in both cellular uptake and transfection assays in vitro. The results of the maturation experiment showed that all the PEI/ DNA complexes induced an adequate upregulation of surface markers for DC maturation. Conclusion: These results demonstrated that man-PEI-TEG can be employed as a DC-targeting gene-delivery system.