Exposure to DLL4 upregulated CXCR4 mRNA expression as well as protein levels specifically in NOTCH1-mutated CLL cells (p < 0.05), together with an induction of the CXCL12-induced migratory capacity of these cells (Fig. 5a–c). The gene discussed is CXCR4; the disease is B-cell chronic lymphocytic leukemia.