Engineered exosome-lymphotropic mRNA vaccine encoding series-connected antigens elicits potent antitumor immunity in pancreatic cancer.

Pancreatic ductal adenocarcinoma (PDAC) is driven by KRAS mutations in over 90% of cases yet remains refractory to most therapies due to poor antigen delivery and a suppressive tumor microenvironment. To address these challenges, we developed an exosome‑augmented, epitope‑focused mRNA nanovaccine. First, we engineered a series-connected (SC) mRNA that condenses five KRAS-derived immunogenic epitope segments, including G12D, G12V, G12R and two additional KRAS-derived sequences into a single open reading frame. This design minimizes non‑productive sequence and enhances antigen presentation compared to a conventional parallel-connected (PC) mixture of full‑length transcripts. Second, we cloaked β‑sitosterol LNPs with mature dendritic‑cell-derived exosomes (LNP@exo), endowing the particles with lymph‑node tropism and intrinsic adjuvanticity. The resulting mKRAS SC-LNP@exo triggered potent dendritic cell activation and Th1 cytokine release in vitro, rapidly accumulated in lymph nodes, and drove superior CD8⁺ T cell infiltration in a Pan02 tumor model. Remarkably, one‑third of mKRAS SC-LNP@exo treated mice achieved complete tumor regression without off‑target toxicity. These findings demonstrate that combining epitope‑condensed mRNA with exosome‑cloaked LNP delivery can convert "cold" KRAS‑mutant PDAC into an immunologically responsive tumor and provide a broadly applicable strategy for next‑generation mRNA cancer vaccines.