Mannose/stearyl chloride doubly functionalized polyethylenimine as a nucleic acid vaccine carrier to promote macrophage uptake.

Transmembrane transport remains a significant challenge for nucleic acid vaccine vectors. Promoting the ability of immune cells, such as macrophages, to capture foreign stimuli is also an effective approach to improving cross-presentation. In addition, polyethyleneimine (PEI) has gained attention in the field of nucleic acid vaccine carriers due to its excellent gene transfection efficiency and unique proton buffering effect. However, although high molecular weight PEI exhibits high efficiency, its high-density positive charges make it highly toxic, which limits its application. In this study, mannose/stearyl chloride functionalized polyethylenimine (SA-Man-PEI) was prepared by functionalizing PEI (molecular weight of 25 kDa) with mannose with immunomodulatory and phagocyte targeting effects, and an alkyl hydrophobic chain segment, which could easily promote cell uptake. Moreover, the functionalized-PEI retains a strong proton buffering effect, which helps the carrier escape from the lysosome. The particle sizes of the composite particles formed by SA-Man-PEI and ovalbumin (OVA) were below 200 nm, with good storage stability at both 4 °C and 37 °C. At a drug concentration of 2 μg/mL, the cell survival rate of functionalized-PEI was 19.2% higher than that of unfunctionalized PEI. In vitro macrophage endocytosis experiments showed that SA-Man-PEI could significantly enhance the macrophage uptake of composite particles, compared to unfunctionalized PEI or single-functionalized PEI. This study offers a new approach for developing PEI as a nucleic acid vaccine carrier, which could simultaneously enhance cell targeting and promote cell uptake.