VPREB1 and acute lymphoblastic leukemia: Cells in this hybrid cluster expressed hallmark B-ALL genes such as IGLC7, IGLL1, VPREB1, TCL1A, and IGHM, albeit at lower levels than NALM6 (C1), and expressed MSC genes such as FN1, TAGLN, COL1A1, COL1A2, and LGALS1 (Figure 5D), indicating that this hybrid cluster (C2) is derived from B-ALL cells but had acquired MSC features.