NUDT21 and precursor B-cell acute lymphoblastic leukemia: In addition to CD81, nudix hydrolase 21 encoded by NUDT21, a protein that regulates the polyadenosine tailing and stability of CD19 mRNA, was found in elevated expression level that resulted in CD19-negative relapses in B-ALL patients after treatment with anti-CD19 CAR-T cells or blinatumomab [9].