The 8th European MELODI workshop entitled "Radiation effects on the Immune System" (REIS-3) was organized at the Maison Minatec in Grenoble on April 28 and 29, 2026. This workshop brought together about sixty participants representing 55 research organizations from 17 different countries to discuss recent advances in the study of interactions between the response to radiation and the immune system in different contexts: after exposure of healthy tissues, in the context of radiotherapy, and in the context of space exploration.