Efficacy of combination treatment with vecabrutinib and PI3K-δ inhibitor (PI-3065) or venetoclax in vivo. Syngeneic recipient mice were transplanted with 10 million Eµ-TCL1 tumor cells through tail vein injection. After engraftment for 14 days, mice were randomized to treatment with vehicle (n = 5), vecabrutinib (n = 6), PI-3065 (n = 6), venetoclax (n = 6), vecabrutinib with venetoclax (n = 5), or vecabrutinib with PI-3065 (n = 5) for 10 days. Comparison of tumor burden, as measured by spleen weights (A), percentage of CD19⁺CD5⁺ tumor cells in spleen (B), and absolute CD19⁺CD5⁺ cell count per spleen (C). (D) Representative flow cytometry plots for CD8⁺ and CD4⁺ T cells in the different treatment groups. (E) Comparison of percentage of CD4⁺ and CD8⁺ T-cell populations between the single and combination treatment subgroups. Changes in percentage of effector (CD8⁺CD127^lowCD44^int-hi), memory (CD8⁺CD44⁺CD127⁺), naive (CD8⁺CD44⁻CD127⁺) T-cell populations (F) and Tregs (CD4⁺ CD25⁺ FOXP3⁺) (G) upon single and combination treatment using vecabrutinib with PI3K-δ and BCL2 inhibitors. One animal each from the vehicle and the 2 combination treatment groups was excluded from the study because of low tumor engraftment resulting from technical error in IV injection. (H) Syngeneic recipient mice were transplanted with 7 million Eµ-TCL1 tumor cells through tail vein injection and monitored for engraftment. Treatment with vehicle (n = 5), vecabrutinib (n = 5), venetoclax (n = 5) or the combination of vecabrutinib and venetoclax (n = 4) was initiated on day 14 after reaching 10% tumor load (CD19⁺CD5⁺) in peripheral blood and continued until reaching a humane end point for euthanization (described in “Materials and methods”). One animal that died during the treatment procedure in the combination treatment group on day 31 with a very small spleen (0.17 g) was excluded from analysis. *P ≤ .05, **P ≤ .01, Mann-Whitney U test (A-C,E-G), log-rank (Mantel-Cox) test (H). ns, not significant (P > .05); Veca, vecabrutinib; Ven, venetoclax.