In vitro, BH3 profiling demonstrates that primary CLL cells cocultured for 24 hours with a variety of stroma are less primed to undergo apoptosis. Priming of CLL cells from individual patients cocultured without and with CD154⁺ L-cell (A; n = 5), StromaNKTert (B; n = 4), or primary human nurse-like cells (C; n = 5) stroma for 24 hours, measured by 0.03μM BIM BH3 peptide (complete BH3 profiling data from individual patients are provided in supplemental Figure 2). All BH3 profiles are via the FACS-based method, except for 2 samples in panel B and 3 samples in panel C, which were via the plate-based method (see Methods). (D) Aggregate data from all 3 stroma (n = 14) reveals significantly decreased priming in stroma-exposed CLL cells (P = .020 by paired t test).