Intratumoral microbial abundance and load influence the immune microenvironment of oral squamous cell carcinoma

Objective This study aimed to explore the characteristics intratumoral microbiome in oral squamous cell carcinoma, and elucidate the interplay between intratumoral microbial profiles (relative abundance/absolute load) and tumor-infiltrating lymphocytes markers (CD4 + /CD8 + /FOXP3) and PD-L1 in oral squamous cell carcinoma Methods We analyzed 45 OSCC tissue samples alongside paired paracancerous (n=10) and normal oral microbiota controls (n=8). Microbial composition was characterized by 16S rRNA sequencing (V3-V4 regions), with bacterial load quantified via qPCR targeting the V4–1 region. Tumor-infiltrating lymphocytes markers were assessed by immunohistochemistry. Results Spirochaetota was concentrated in the CD4 + as well as CD8 + low infiltration groups, Proteobacteria in the CD8 + high infiltration group and Actinobacteriota in the FOXP3 low infiltration group. Tumor microbial load was negatively correlated with CD4 + , CD8 + , and FOXP3, but of these, only the correlation coefficient of -0.309 for CD4 + was statistically significant. However, no significant correlation was observed in the analysis of PD-L1 expression with the relative abundance of intratumoral microbiome, α-diversity, and intratumoral microbial load values Conclusion Changes in the abundance of specific intratumoral microbiome affect the infiltration of TILs markers, and there is a negative relationship between intratumoral microbial load and T-cell infiltration, suggesting that intratumoral microbiome contribute to the processes of the tumor immunosuppressive microenvironment.