R406, GS-9973, and idelalisib overcome anti-IgM–mediated ABT-199 resistance more potently than ibrutinib. CLL cells (n = 22) were preincubated for 2 hours with 1 μM of R406, GS-9973, ibrutinib, or idelalisib prior to the addition of imm-aIgM. ABT-199 was added 3 hours later. The percentage of viable cells was determined by annexin V/PI staining and flow cytometry 24 hours after the addition of the SYK inhibitors. Significance of differences between ABT-199/aIgM-cultured cells in the presence or absence of the various inhibitors was evaluated with one-way analysis of variance.