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

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.