Vecabrutinib treatment prolongs survival in the Eμ-TCL1 adoptive transfer model. (A) Syngeneic recipient mice were transplanted with 5 million Eµ-TCL1 tumor cells through tail vein injection and monitored for engraftment. Treatment with vehicle (n = 6), vecabrutinib (n = 6) or ibrutinib (n = 6) was initiated on day 14 upon reaching >10% tumor load (CD19⁺CD5⁺) in peripheral blood and continued until reaching a humane end point for euthanization (described in “Materials and methods”). Comparison of responses of tumor cells isolated from vecabrutinib (Veca)-treated mice (B), ibrutinib (Ibru)-treated mice (C), or vehicle-treated mice (n = 5 per group) to treatment with venetoclax (Ven) as a single agent or in combination with the corresponding BTK inhibitors. The ex vivo treatments were performed in triplicates and analyzed using DiOC6/PI staining and flow cytometry on day 4. Dynamic BH3 profiling of WT BTK primary CLL cells (D), BTK mutant patient sample #1 (E), and BTK mutant patient sample #2 (F) (supplemental Table 3) subjected to treatment with ibrutinib (1 µM) or vecabrutinib (1 µM) for 16 hours. % Delta Priming indicates the difference in the percentage of mitochondrial cytochrome c release between the treatment and control condition in response to BAD peptide, indicating BCL-2 dependence. Each data point in (D) represents a single patient sample, whereas each data point in (E-F) represents technical replicates within individual patient samples. The dashed lines at 0 in (D-F) represent normalization to DMSO control. P values in individual columns in (D-F) represent comparison with DMSO control. *P ≤ .05, **P ≤ .01, ***P < .001, log-rank (Mantel-Cox) test (A), Mann-Whitney U test (B-C), paired Student t test (D), unpaired Student t test (E-F). ns, not significant (P > .05).