Hyperbranched Polylysine‐Based Lipopolyplexes Enable Efficient mRNA Delivery With Long‐Term Storage Stability

ABSTRACT

Clinical translation of messenger RNA (mRNA) therapeutics is often hampered by the poor storage stability of lipid‐based delivery vectors. Many lipopolyplex (LPP) delivery systems struggle to achieve efficient nucleic acid release through the membrane fusion pathway. Herein, we developed a novel ternary lipopolyplex (LPP) platform of lipid/HBPL/mRNA LPPs by incorporating hyperbranched poly‐L‐lysine (HBPL) as a functional polymeric core. The highly branched architecture of HBPL enabled a unique balance between high mRNA encapsulation efficiency, efficient intracellular release, and exceptional colloidal stability, thereby overcoming a key limitation of conventional lipid nanoparticles. This platform primarily promoted cellular uptake through a membrane fusion mechanism in vitro, thereby achieving highly efficient cytoplasmic delivery, while the HBPL core enabled superior mRNA release compared to its linear ε ‐Polylysine ( ε ‐PLL, hereafter referred to as PLL)‐based counterpart. These attributes collectively yielded high transfection efficiency across multiple cell lines, significantly enhanced dendritic cell (DC) maturation, and superior biocompatibility over a commercial transfection reagent. Efficient mRNA delivery to the lungs and spleen was also confirmed in vivo, with protein expression sustained even after 1 month of storage. By successfully integrating long‐term stability with high delivery efficiency, this HBPL‐based LPP platform represents a highly promising candidate for advancing mRNA therapeutics and vaccines.