Mice were irradiated for 13 weeks, and upon tumor growth ≥4 mm, mice were assigned to a group and treated for 1 week (Group 1 and 2) with topical and systemic antibiotics followed by 3 weeks of bacterial application and ICI (Groups 1A and 2A) or isotype (Groups 1B and 2B) or 4 weeks with antibiotics and ICI or isotype (Group 3A and 3B). Week 0: enrollment (arrow), Week 1-5: antibiotics, bacteria and ICI treatment till end point. Skin and fecal samples were collected at weeks 1, 2, and 5. Antibiotics were applied topically and systemically. Details are described in the Supplementary Materials and Methods. Table 1 shows the Groups and animal numbers in more detail. ICI: Immunotherapy; UV-B: ultraviolet B; Abx: Antibiotics.