CD19 and acute lymphoblastic leukemia: Three types of relapse after tisagenlecleucel are described: CD19‐positive (CD19POS) relapse (around 50% of cases), CD19‐negative (CD19NEG) relapse (around 40%) and relapse with a lineage switch from ALL to AML (around 5%–10%) [6, 7, 9, 10].