In-depth analyses of the 16S rRNA gene amplicon sequencing of the fecal microbiota of patients with cancer have shown that the enrichment in specific bacterial strains was associated with increased tumor infiltration by cytotoxic T cells and enhanced tumor responses to immune checkpoint blockade.5, 6, 7 An enhanced activity of the CD8+ T cells by short-chain fatty acids (SCFAs) that are metabolites derived from the gut microbiota is thought to play an important role in the improved tumor control.8 Here, CD8A is linked to neoplasm.