Lactobacillus gallinarum ̧ instead, seems to improve anti-PD-1 efficacy in both MSI-high and MSI-low CRC tumors by suppressing the intratumoral infiltration of Treg and enhancing effector function of CD8+ T cells, as described by Fong et al. L. gallinarum-derived indole-3-carboxylic acid was identified as the functional metabolite capable of modulating antitumor immunity by antagonizing the activation of a pathway that leads to Treg differentiation [113]. Here, PDCD1 is linked to colorectal carcinoma.