Bacteroides fragilis or Bacteroides thetaiotaomicron could enhance the efficacy of anti–CTLA-4 in the mouse model of sarcoma (2), and Bifidobacterium species could enhance the efficacy of anti–PD-L1 in a mouse model of melanoma (1), Therefore, when these two studies, which used different tumor models and were investigating different observations (antibiotic treatment vs. different vendor microbiomes), independently arrived at the same conclusion that the composition of the gut microbiome affects efficacy of ICIs, the field of the microbiome and cancer immunotherapy expanded markedly. Here, CTLA4 is linked to melanoma.