Only specific Bifidobacterium strains (i.e., B. HIF-K57, B. HIF-K18, and B. HIF-MG731 [B. HIF-M31]) act synergistically with anti–PD-1 therapy to reduce tumor growth, while other Bifidobacterium bifidum strains (i.e., B. bifidum_B06, B. bifidum_R71 and B. bifidum CKDB001 (B. Bifidum_C01)) show no synergistic effect with anti-PD-1 therapy (62). The gene discussed is PDCD1; the disease is neoplasm.