The established impact of gut microbiota- and probiotic-derived metabolites on immune-checkpoint blockade (ICB) has spurred extensive efforts to identify strains and druggable bioactive molecules of microbial origin that can improve tumor immune therapy. In this issue, Kawanabe-Matsuda and colleagues show that the exopolysaccharide EPS-R1 produced by the probiotic strain Lactobacillus delbrueckii subsp. bulgaricus augments the response to ICB therapy by expanding the population of Peyer's patches CCR6+ CD8+ T cells, which can subsequently migrate from the gut into CCL20-expressing tumors to enhance antitumor activity. See related article by Kawanabe-Matsuda et al., p. 1336 (10).
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