Sivan et al. compared the effects of anti-PD-1/PD-L1 mAbs by observing the subcutaneous B16.SIY melanoma growth in genetically similar C57BL/6 mice obtained from Jackson Laboratory (JAX) and Taconic Farms (TAC) (Sivan et al. 2015), which harbored a disparate commensal microbiota. This evidence concerns the gene PDCD1 and melanoma.