Heterologous prime-boost with an mRNA vaccine and an oncolytic virus enhances tumor regression through overcoming intratumoral immune suppression

Therapeutic mRNA vaccines are limited in inducing tumor shrinkage in advanced cancers due to their inability to overcome immune-suppressive mechanisms within tumors. In this study, we developed an HPV-immunogen-expressing oncolytic virus (OV) using HSV-1 for HPV-related cancer treatment. A mouse syngeneic tumor model evaluates the effectiveness of intratumoral OV application for E6⁺E7⁺ tumors. Comparative analysis of OV and mRNA vaccines reveals distinct mechanisms in tumor treatment. Single-cell RNA sequencing and flow cytometry show that OV enhances cytotoxic T cell infiltration, polarizes neutrophils and macrophages toward anti-tumor phenotypes, and promotes immune activation within the tumor. In contrast, the mRNA vaccine more effectively activates peripheral antigen-specific T cell responses. A heterologous prime-boost strategy using the mRNA vaccine to prime systemic T cells, followed by OV therapy to direct these cells into the tumor, leads to significant tumor regression. This combination optimizes both systemic and intratumoral immune responses for advanced HPV-related cancers.