A high level of T CD8+ in tumor tissue correlated with an increased abundance of the genus Faecalibacterium of the Ruminococcaceae family and of the order Clostridiales. Flow cytometric analysis showed that patients with high levels of Clostridiales, Ruminococcaceae or Faecalibacterium in the gut had higher levels of CD4+ and CD8+ effector T cells in the peripheral blood. The gene discussed is CD4; the disease is neoplasm.