Enhanced antitumor immunity of mRNA vaccines by bioorthogonal-like delayed activation of exogeneous STING

The development of cGAS-STING (stimulator of interferon genes) agonists as mRNA vaccine adjuvants has been hampered by widespread STING expression and by the observation that codelivered STING agonists suppress antigen mRNA translation. Here, to address these challenges, we engineer synchronized STING (Syn-STING): a lipid nanoparticle (LNP) codelivering antigen mRNA, mRNA encoding full-length STING transmembrane protein and a bioorthogonal-like delayed-release STING activator, DMXAA. DMXAA release is controlled by a biodegradable linker, enabling localized mouse STING activation while avoiding systemic endogeneous human STING recognition. In humanized STING mouse models, we test human papillomavirus E7 and ovalbumin antigens with mouse STING or a human STING mutant engineered for DMXAA specificity. Intratumoral or subcutaneous LNPs are preferentially internalized by myeloid cells, preserving antigen expression fidelity, achieving localized STING activation in antigen-presenting cells and preventing systemic regulatory B cell differentiation and immunocyte apoptosis. The Syn-STING vaccine elicits robust adaptive responses and Th1-biased T cell immunity. It suppresses tumor growth and prolongs survival while exhibiting negligible anti-STING immunity.