Structurally-optimised HPV16 E7/E6 mRNA–LPP mediates dose-sparing efficacy via tumour microenvironment reprogramming

Abstract The development of therapeutic vaccines against human papillomavirus (HPV)–associated malignancies remains challenging due to the immunosuppressive tumour microenvironment and the limited efficacy of existing delivery platforms. In this study, we designed and systematically compared two mRNA vaccine strategies based on a core–shell structured lipopolyplex (LPP) delivery system: a codon- and untranslated region-optimised non-replicating mRNA (nr-mRNA) and a self-amplifying mRNA (sa-mRNA). In the TC-1 murine model of HPV-driven cancer, both vaccine formulations effectively activated systemic antitumour immune responses, significantly enhancing the infiltration of functional CD8⁺ T cells and natural killer cells into tumours and promoting the repolarisation of tumour-associated macrophages towards an M1 phenotype. Notably, the sa-mRNA–LPP platform achieved comparable therapeutic efficacy at only one-fifth the dose of nr-mRNA–LPP, highlighting its superior potency and dose-sparing potential. Further analysis revealed that immune response induced by sa-mRNA–LPP was predominantly localised to the tumour site, with no significant immune activation detected in peripheral lymphoid organs such as lymph nodes and spleen, suggesting a stronger capacity for localised immunomodulation within the tumour. In summary, this study validates the high efficiency of the LPP platform in delivering different mRNA vaccines and elucidates the unique mechanism by which sa-mRNA exerts potent antitumour effects at low doses through localised immune remodelling. These findings provide important experimental support for the clinical translation of LPP-based mRNA vaccines targeting HPV-associated cancers.