Microbiome-derived inosine modulates response to checkpoint inhibitor immunotherapy

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Science  18 Sep 2020:
Vol. 369, Issue 6510, pp. 1481-1489
DOI: 10.1126/science.abc3421

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Inosine modulates antitumor immunity

Checkpoint blockade immunotherapy harnesses the immune system to kill cancer cells and has been used with great success to treat certain tumors, but not all cancer patients respond. The efficacy of checkpoint blockade immunotherapy has been shown to depend on the presence of distinct, beneficial bacteria residing in the gut of patients, but how the microbiome mediates such beneficial effects is unclear. Mager et al. found that specific bacteria produce a metabolite called inosine that enhances the effect of checkpoint blockade immunotherapy (see the Perspective by Shaikh and Sears). In mouse models, inosine, together with proinflammatory stimuli and immunotherapy, strongly enhanced the antitumor capacities of T cells in multiple tumor types, including colorectal cancer, bladder cancer, and melanoma.

Science, this issue p. 1481; see also p. 1427


Several species of intestinal bacteria have been associated with enhanced efficacy of checkpoint blockade immunotherapy, but the underlying mechanisms by which the microbiome enhances antitumor immunity are unclear. In this study, we isolated three bacterial species—Bifidobacterium pseudolongum, Lactobacillus johnsonii, and Olsenella species—that significantly enhanced efficacy of immune checkpoint inhibitors in four mouse models of cancer. We found that intestinal B. pseudolongum modulated enhanced immunotherapy response through production of the metabolite inosine. Decreased gut barrier function induced by immunotherapy increased systemic translocation of inosine and activated antitumor T cells. The effect of inosine was dependent on T cell expression of the adenosine A2A receptor and required costimulation. Collectively, our study identifies a previously unknown microbial metabolite immune pathway activated by immunotherapy that may be exploited to develop microbial-based adjuvant therapies.

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