BECAR7

T-cell leukaemia is an uncommon type of blood cell cancer that affects white blood cells (T cells). This phase I clinical trial will treat children aged 6 months up to 16 years with T cell leukaemia which has come back (relapsed) after chemotherapy or is not responding to chemotherapy (refractory). The cell therapy is made from white blood cells (T cells) collected from a healthy donor and changed so they can kill other T cells, including leukaemia cells. These 'ready-made' CAR T cells have been made using a new technique called CRISPR base editing to modify them DNA code and have been given the name BE CAR-7. This technique allows them to work after chemotherapy and also disarms them to prevent effects against normal cells. The main aim of this study is to assess the safety of the BE CAR-7 treatment and to see if ready-made CAR T cells can eradicate T cell leukaemia ahead of a planned bone marrow transplant.