The Impact of Intratumoral Bacterial Response to Vaccine Therapy in Cancer Treatment

Therapeutic Human papillomavirus (HPVs) vaccines are designed to enhance the immunogenicity of HPV and promote the elimination of tumor cells effectively. Mounting evidence implies that tumor-resident microbiomes may influence therapeutic outcomes through immune modulation. In this study, we evaluated whether the intratumoral microbiota affects the efficacy of the therapeutic HPV vaccine. We analyzed RNA sequencing data from tumor tissues of C57BL/6N female mice treated with a DNA vaccine incorporating HPV16 E6/E7 antigens fused with the chemokine CCL11. Microbial community data were acquired using the PathSeq bioinformatics pipeline. Alpha diversity was estimated using the Shannon index and the number of observed taxonomic features, while beta diversity was assessed via principal coordinate analysis (PCoA) based on Bray–Curtis distance. Linear discriminant analysis Effect Size (LEfSe) analysis was performed to identify differentially abundant microbial taxa. Immune cell infiltration was characterized using the xCell deconvolution method. The analysis revealed significant divergence in both the alpha- and beta-diversity metrics of intratumoral microbiota, associated with treatment responsiveness. Vaccinated groups exhibited enriched abundances of the phyla Proteobacteria, together with a concomitant reduction in Firmicutes and Actinobacteria, and were associated with a positive response to cancer immunotherapy. Additionally, intratumoral microbiome composition and diversity correlated with the increased infiltration of CD8+ T cells, natural killer T (NKT) cells, and myeloid cells. This study identifies intratumoral microbiota remodeling as a key feature of therapeutic HPV vaccine response. The observed coordination between bacterial signatures and immune cell infiltration is associative and raises the hypothesis that intratumoral bacteria may modulate, rather than drive, antitumor immunity. These findings support the development of intratumoral microbiota profiling and highlight the potential for microbiota-targeted strategies to enhance cancer immunotherapy efficacy.