CK2 inhibition overcomes the protective effect of OP9 stromal cells. Purified CLL cells were cultured alone (−OP9) or cocultured with OP9 stromal cells (+OP9), and treated or not with the indicated doses of TBB. Viability was assessed after 48 hours by annexin V/7-AAD staining and flow cytometric analysis. Results are representative of 4 patients analyzed. Numbers represent the percentage of cells in each quadrant.