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In the past 5 years, several novel immunotherapies for cancer have emerged (NEJM JW Gen Med Jun 16 2015; [e-pub] and Science 2015; 348:62). One of the most exciting is “checkpoint inhibitors.” When malignant cells elicit a T-cell response, the activated T cells paradoxically produce “checkpoint” molecules (including CTLA-4 and PD-1) that abort the T-cell attack. However, monoclonal antibodies that inhibit these checkpoint molecules can unleash the T-cell attack on the tumor. Dramatic responses have been reported in some patients, but, in other patients, the therapies don't work.
Using a mouse model of melanoma, two teams have found that particular gut bacteria might play a key role in determining the efficacy of checkpoint-inhibitor drugs. A…