CD19 and acute lymphoblastic leukemia: Our previous studies have shown that non‐killer cell‐derived CD19‐targeting effector cells can cause target cell death.[36] Consistent with these findings, we found that CD19‐targeting HEK 293 (CD19‐293) cells expressing a CD19‐targeting module (CD19‐TM) consisting of a CD19‐specific scFv and a CD8 hinge/transmembrane domain (Figure S1, Supporting Information) effectively deplete CD19 on B‐ALL target cells and induce target cell death[36] (Figure S2, Supporting Information).