Antigen-presenting cells (APCs) have unique properties in initiating primary immune responses and thus can be an excellent target for DNA vaccination. Polyion complex made of poly(ethylene glycol)-block-poly(ethylene imine) (PEG-b-PEI) conjugates are known to self-assemble in aqueous media with DNA into a spherical polymeric, which reduces non-specific interactions with blood components. However, the PEG shielding lowers the transfection efficiency. The attachment of a specific ligand may increase cellular uptake via receptor-mediated endocytosis. The mannose receptor (ManR) involved in the uptake of particulate and soluble antigenic products of bacterial origin represents therefore a promising receptor for targeting APCs having ManR. Amino-terminated mannose (Man) ligand, in a mono- (Man–PAP) and tri- (Man3-AHT) valency were first synthesized and conjugated with PEG (3,500Da) via the N-hydroxy succinimide (NHS) activated terminal. PEI (25,000Da) containing terminal thiol group was then conjugated to the mannosylated PEG via the Maleimide (MAL) activated terminal. The resulted positively charged mannosylated di-block copolymers (Man-PEG-b-PEI and Man3-PEG-b-PEI) can self-assemble with DNA to form polymer/DNA polyion complexes. The ζ-potential and particle size were determined by laser Doppler-anemometry and Dynamic light scattering, respectively. Man-PEG-b-PEI and Man3-PEG-b-PEI showed good in vitro complexation with DNA at N/P ratios > 4, and had lower surface charge relative to their PEI building block. Man3-PEG-b-PEI demonstrated a 3-4 fold greater transfection efficiency relative to Man-PEG-b-PEI in ManR positive dendritic cell lines. Furthermore, the mannosylated block copolymers exhibited low cytotoxicity when compared with PEI and showed low transfection efficiency in the non-dendritic HeLa cells. Finally, 24h after subcutaneous injection of C57/BL6 mice, Man3-PEG-b-PEI demonstrated 2-3 fold greater transfection efficiency relative to Man-PEG-PEI and PEI, in DCs hosted at the injection site draining lymph nodes. The results suggest that the mannosylated polyion complexes are a safe and efficient gene delivery system for APCs'.
