CD274 and B-cell chronic lymphocytic leukemia: To demonstrate that the upregulation of PD-L1 by NOTCH1 was functionally important and could indeed impair T-cell activation, we co-cultured primary CLL cells, either transfected with EV or NOTCH1ΔPEST, with Jurkat T cells, expressing luciferase under the control of the NFAT responsive element (Fig. 5h).