PDCD1 and neoplasm: Remarkably, subcutaneously grafted CT26.CL25 tumours were significantly bigger in germ-free Balb/c mice repopulated with decR mutant E. coli plus A. muciniphila than those in germ-free Balb/c mice repopulated with WT E. coli plus A. muciniphila after anti-PD-1 treatment (Fig. 7e).