The efficacy of immune checkpoint blockade (ICB) for cancer therapy has been correlated with the presence of certain intestinal commensal bacteria in both pre-clinical animal models and human clinical studies. However, the mechanisms by which intestinal bacteria can affect tumour immunity at distant sites, such as the skin in the case of melanoma, has been unclear. Choi et al. show that ICB facilitates the translocation of gut bacteria into secondary lymphoid organs (SLOs) and tumours, as well as lymph node remodelling, leading to increased priming of anti-tumour immune responses.