Ultrasound-Activatable Lipid Nanoplatform for Region-Confined Innate Immune Stimulation and mRNA Vaccination Therapy of Cancer

Adjuvant-integrated lipid nanoparticle (LNP) formulations have been extensively investigated to potentiate mRNA vaccine therapy by promoting innate immune stimulation in antigen-presenting cells (APCs). However, these strategies are challenged by the non-specific and "always on" innate immunostimulatory effects of adjuvants, largely impeding their clinical translation. In this study, we developed a novel LNP component, sono-adjuvant lipid, to endow clinically approved LNP formulations with region-confined adjuvanticity. The engineered ultrasound (US)-activatable LNP (ULNP) precisely boosted innate immune responses in the lymph nodes (LN) through US-triggered activation of the cytosolic DNA-sensing pathways in APCs. Compared to conventional LNP integrating toll-like receptor adjuvant, the combination of ULNP with localized US stimulation (ULNP + US) not only enhanced LN-specific mRNA transfection but also elicited 2.5-fold higher antigen-specific CD8⁺ T cell responses to inhibit established tumor growth. More importantly, the US-activatable adjuvanting strategy was readily applicable to potentiate tumor neoantigen-encoding circular RNA (circRNA) vaccine therapy. Combining circRNA-loaded ULNP (ci-ULNP) with US stimulation elicited potent antitumor T cell immunity and completely eliminated orthotopic liver tumors in mice. Overall, the sono-adjuvant lipid-integrated ULNP offered a robust platform for spatiotemporally tunable innate immune stimulation and mRNA vaccination therapy of cancer.