NOTCH1 and B-cell chronic lymphocytic leukemia: To provide further evidence for the gene repressive functions of NOTCH1, we cultured CLL cells from 4 donors with endogenous exon 34 mutations of NOTCH1 under identical conditions on MM1-stroma cells in the presence or absence of γ-secretase inhibitors (GSI) to block ligand-mediated activation of NOTCH1.