Psychologist Kimberley Wilson and Dr Xand van Tulleken take a journey around the human body, asking what it can tell us about our innate capacity for change. In this episode, they zoom in on T cells: a type of white blood cell that forms a critical part of the body’s ability to fight off infection. Xand and Kimberley discover how scientists are hacking into the immune system and hear the story of 5-year-old Zac, who has undergone an innovative form of immunotherapy for leukemia. Producer: Dan Hardoon Researcher: Emily Finch Executive Producer: Kate Holland A Whistledown Production for BBC Radio 4