Moreover, indole-3-carboxaldehyde enhances anti-PD-1 efficacy in CRC by inhibiting CD4+ Treg differentiation and modulating the IDO1-kynurenine-AhR axis to bolster CD8+ T-cell function, enhances anti-PD-1 efficacy in CRC [45]. This evidence concerns the gene CD4 and colorectal carcinoma.