CD19 and precursor B-cell acute lymphoblastic leukemia: In the development of B-cell malignancies such as B-ALL (Fig. 1a) [68], malignant initiating clones with expression of CD19 molecule (ubiquitously expressed in normal B cells) can differentiate into highly heterogeneous subclones at the genetic and epigenetic levels, resulting in difficulties of T-cell therapy for their eradication.