Insights into how diet-related factors may influence immune response for cancer patients

Dietary fiber and probiotics impact gut bacteria and immunotherapy responses in melanoma patients, a new study in patients shows. A high-fiber diet was associated with improved survival and response to immunotherapy, the results reveal. The influence of the gut microbiome on therapeutic response has now been demonstrated in numerous human cohorts and in preclinical models. The human gut microbiome is shaped by a wide variety of environmental exposures, including diet and medication use. But whether factors such as dietary fiber intake and the use of commercially available probiotics affect immunotherapy responses in cancer patients remains unclear. To understand how dietary habits impact microbiota and clinical outcomes to immunotherapy, Christine Spencer et al. performed an observational study that began with analyzing the gut microbiome profiles of 438 melanoma patients. The majority of these patients (87%) received immune checkpoint blockade (ICB) therapy. As they began therapy, the patients were asked to complete a lifestyle survey of usage of antibiotics and probiotics, as well as a dietary questionnaire. Among those who completed the survey and questionnaire, the authors found no significant difference in outcomes in progression-free survival for patients who did take probiotics, versus those who did not. They next sought to assess the effect of dietary fiber intake on response to ICB. The patients with sufficient fiber intake had improved survival compared to the patients with insufficient fiber intake. After this, the authors evaluated whether dietary fiber intake and probiotic use may jointly affect clinical outcomes. The most marked benefit was observed for patients reporting a combination of high fiber consumption and no use of over-the-counter probiotic supplements. Further work in preclinical models supported the authors’ hypothesis that dietary fiber and probiotics modulate the microbiome and that antitumor immunity is impaired in mice receiving a low-fiber diet and in those receiving probiotics. Ongoing dietary intervention studies in the setting of immune checkpoint blockade therapy are critical for establishing whether a targeted and achievable diet change at the initiation of therapy can safely and effectively improve outcomes, the authors say.