Lymph node-targeted mRNA delivery of fine-tuned peptide-nanocomplexes for SARS-CoV-2 Vaccination.

Messenger RNA (mRNA) vaccines require efficient delivery systems to reach antigen-presenting cells (APCs). Lipid nanoparticles (LNPs) are a standard delivery carrier. However, LNPs often accumulate in the liver and exhibit transient protein expression. These limitations can restrict their safety and immunogenic potential. Here, we developed a modular, peptide-based nanocomplex to overcome the current limitations. The system comprises three functional peptides: an RNA-binding peptide (RBP) for condensation, l-polyglutamic acid (PGA) for charge modulation, and an APC-targeting cell-penetrating peptide (A-CPP). This A-CPP features a newly discovered 7-mer immune cell-binding motif identified in this study. We optimized the physicochemical properties by systematically fine-tuning the ratios of these peptide modules. The optimized nanocomplex formed stable particles under 200 nm. Unlike LNPs, which showed significant liver accumulation, the peptide-nanocomplexes remained localized at the injection site and effectively drained to the lymph nodes. Furthermore, the peptide-nanocomplex retained mRNA expression for up to 7 days in vivo, whereas LNP-mediated expression diminished within 48 h. In mice immunized with SARS-CoV-2 spike mRNA, this prolonged antigen exposure elicited robust neutralizing antibody titers comparable to LNPs. Notably, the peptide-nanocomplex induced significantly higher CD8+ T cell responses than LNPs. Moreover, the peptide-nanocomplex demonstrated an excellent safety profile in vivo with no toxicity observed even after daily injections for two weeks at doses up to 200 times higher. This study establishes a data-driven fine-tuning strategy for peptide-based mRNA delivery. The resulting peptide-nanocomplex offers a safer, lymph node-targeted, and longer-lasting efficacy alternative to lipid-based carriers for next-generation vaccines.