This project focuses on CAR-T cell therapy, an innovative immunotherapy for the treatment of relapsed and refractory pediatric acute lymphoblastic leukemia. The expansion, function, and long-term persistence of CAR-T cells, associated with long-term disease-free survival, might be hampered by immunosuppressive characteristics within the leukemic bone marrow microenvironment (the leukemic niche). In this project, we will therefore study the effector function of CAR-T cells in relation to their cellular environment by modelling the dynamic interactions between CAR-T cells, leukemic blasts, and bone marrow components. This project aims to characterize factors that influence these interactions and the function of CAR-T cells using (3D) co-cultures and innovative imaging systems resembling an artificial bone marrow microenvironment. With these efforts, we hope to gain more insights in the mechanisms behind CAR-T cell therapy failure, to eventually reduce relapses and improve survival outcome of treated patients.