Intratumoral microbiota have been described in various human cancers. In Nature, Bullman and colleagues use in situ spatial-profiling technologies and single-cell RNA sequencing (scRNA-seq) to map host–bacterial interactions within the tumour microenvironment. In oral squamous cell carcinoma (OSCC) and colorectal cancer (CRC), the spatial distribution of microbiota is heterogenous, dominated by Parvimonas, Peptoniphilus and Fusobacterium in OSCC or Fusobacterium and Bacteroides in CRC, with a higher bacterial load in CRC. Bacteria reside in immunosuppressive microniches that contain increased expression of ARG1, CTLA4 and PD-1 and reduced expression of vascular (SMA) or proliferative (Ki-67) marker proteins. Bacteria are associated with macrophages (possibly engulfed), which upregulate genes involved in antibacterial responses (TNF, IFNA, IFNG and IL1B) and chemokines (CCL2 and CXCL8), and with epithelial tumor cells (possibly attached), which upregulate genes involved in cancer progression (hypoxia, metastasis), chemokines (CXCL10, CXCL11 and CCL4) and metalloproteases compared with their bacteria-negative counterparts. The correlations between the distribution of specific bacteria species in OSCC and CRC and the healthy oral and colon mucosa are not discussed.
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