CD19 and acute lymphoblastic leukemia: The success of autologous CD19 CAR‐T cell therapy against hematological malignancies, such as chronic lymphocytic leukemia (CLL), acute lymphocytic leukemia (ALL), and non‐Hodgkin lymphoma (NHL), represents one of the most exceptional breakthroughs in cancer immunotherapy in the past decade.2, 3, 4, 5