Potentiating the Efficacy of mRNA Vaccines through NIR-II Imaging-Guided Precise Vaccination.

mRNA vaccines have been widely implemented and revolutionized the landscape of oncology and epidemiology. Potent vaccination demands precise control over injection depth to ensure optimal lymphatic drainage, driving the development of non-invasive imaging techniques to visualize the distribution and efficacy of mRNA vaccines. Herein, near-infrared-II (NIR-II) lipid nanoparticles (NIR-II-LNPs) are fabricated for mRNA delivery by integrating a cationic fluorophore amphiphile (IR780-C16) into traditional LNPs, enabling longitudinal, quantitative, and non-invasive trafficking of mRNA vaccines. The in vivo behaviors of mRNA vaccines are characterized with different vaccination protocols in mice and rabbits by NIR-II fluorescence imaging. Results proved that following a 25 µL injection of mRNA vaccines into the mouse thigh at a depth of 4 mm or a 500 µL injection volume into a rabbit at a depth of 7 mm via the intramuscular route, the vaccines rapidly and abundantly accumulated in the inguinal lymph nodes. Flow cytometry and tissue immunofluorescence analyses further validated that optimized vaccination parameters effectively activated antitumor immunity and greatly boosted the therapeutic efficacy in B16-OVA and HPV-associated mouse tumor models. NIR-II-LNPs offer a unique modality for non-invasively monitoring the fate of vaccines, reinforcing its role in preclinical and clinical mRNA therapeutics.