Specifically, the presence of natural Bifidobacterium species in C57Bl/6 mice from The Jackson Laboratory (JAX) or the introduction of Bifidobacterium species by oral gavage into C57Bl/6 mice from Taconic (TAC), which do not naturally harbor these bacteria, correlated with tumor-specific CD8+ T cell responsiveness to α-PD-L1 Ab therapy and tumor control. This evidence concerns the gene CD8A and neoplasm.