Previously, PI3Kδi have been reported to reduce the in vitro viability of malignant B-cells, presumably through BCR inhibition.18 GS-9820 reduced cellular viability in both Eμ-Tcl1 Tg leukemias and CLL samples (Figure 4a); albeit with significant heterogeneity in individual Eμ-Tcl1 Tg tumors. Here, BCR is linked to B-cell chronic lymphocytic leukemia.