Gut bacteria are known to modulate the response to immune checkpoint blockade (ICB) treatment in cancer; however, the effect of diet and supplements on this interaction is not sufficiently studied. 

Spencer et al, in their recent study, assessed fecal microbiota profiles, dietary habits and commercially available probiotic supplement benefits in melanoma patients along with conducting parallel preclinical studies. 

They found that the higher dietary fiber was associated with significantly improved progression-free survival in 128 patients on ICB. Patients with sufficient dietary fiber intake and no probiotic use showed the most pronounced benefit. They recapitulated these findings in preclinical models, which demonstrated impaired treatment response to anti-programmed cell death 1 (anti-PD-1)-based therapy in mice receiving a low-fiber diet or probiotics. They also found a lower frequency of interferon-γ-positive cytotoxic T cells in the tumor microenvironment of these mice. 

Thus, these results are clinically relevant for patients receiving ICB for cancer. 

Although this study indicates that undirected use of commercially available probiotics may be harmful in the setting of ICB, further investigation of rationally designed and targeted probiotics or bacterial consortia is required.

Source: Spencer CN, McQuade JL, Gopalakrishnan V, et al. Dietary fiber and probiotics influence the gut microbiome and melanoma immunotherapy response. Science. 2021;374(6575):1632-40.