Patients receiving intensive cancer treatments – such as radiation or stem cell transplantation – often suffer from severe damage to the intestinal lining. This not only causes pain and complications but also worsens long-term outcomes. A “Nature Communications” study from the LIT Cooperation Group “Innate Immune Sensing in Cancer and Transplantation” reveals how a microbial metabolite safeguards the intestinal barrier and drives stem cell-mediated regeneration after injury. The results also show that the microbial product simultaneously reinforces the immune defense against leukemia.