BCR and acute lymphoblastic leukemia: Nevertheless, the CD79a/CD79b heterodimer is already expressed at the pro-B-cell stage before a productive immunoglobulin gene rearrangement is accomplished, even without associated μHC.5 Moreover, we recently reported that the pre-BCR signaling unit CD79a is crucial for BCP-ALL engraftment in vivo, particularly in the central nervous system (CNS), in BCR-ABL1+ and E2A-PBX1+ patient-derived xenograft (PDX) models.6 We therefore hypothesized that CD79b may also serve as a therapeutic target in BCP-ALL.