Therapeutic options in B-acute lymphoblastic leukemia (ALL) relapses after anti-CD19 CAR-T cells are still debated. Here, we analysed leukemic cells of a young patient who had several CD19⁺ relapses of B-ALL after hematopoietic stem cells transplant (HSCT) and after anti-CD19 CAR-T cells (tisagenlecleucel). Extensive membrane immunophenotype revealed the appearance of new targets. Lysis sensibility analysis performed by ⁵¹Cr release and long term killing assays revealed the in vitro persistence of sensitivity to cytolytic activity of CAR-T cells. An immunosuppressive monocytic population was identified in the last relapse sample. Mechanisms leading to ALL resistance are analysed and therapeutic options are discussed.