Table 2. Pathways of gut microbes affecting ICB therapy.

Variables	Mechanism	Effects	Ref.
ICB, immune checkpoint blockade; SCFAs, short-chain fatty acids; BA, bile acid; PD-L1, programmed death ligand 1; NKT, natural killer T; AhR, aryl hydrocarbon receptor; I3A, indole-3-aldehyde; PFS, progression-free survival; ICI, immune checkpoint inhibitor.
Gut microbial metabolite
SCFAs	Regulating immune cell response and improving the curative effect of PD-L1	Longer PFS	(52)
Inosine	Enhancing the anti-tumor ability of T cells	Enhancing the effect of checkpoint blockade immunotherapy	(53)
BAs	Controlling a chemokine-dependent accumulation of hepatic NKT cells	Inhibiting the growth of liver tumor	(54)
Bacterial translocation
Lactobacillus 　reuteri	Releasing AhR agonist I3A	Promoting ICI efficacy and survival	(55)