Two CD19‐deficient cell lines were constructed to simulate the loss or downregulation of target antigens in B‐ALL, CD19‐KO‐Nalm6 (CD19 knock out Nalm6, CD19 negative cells), and CD19‐KO‐697 (CD19 knockout 697, CD19 negative cells) using the CRISPR/Cas9 system (Figure S12a, Supporting Information). This evidence concerns the gene CD19 and acute lymphoblastic leukemia.