Increased sensitivity of TCB mice to venetoclax. (A) The viability of murine splenocytes (purified B cells) relative to corresponding untreated samples was assessed via annexin V binding or adenosine triphosphate (ATP) content after overnight in vitro treatment with 10 or 100 nM venetoclax, respectively. P values refer to the comparison of isolated B splenocytes from TC and TCB mice. (B) Five 28-week-old TCB mice were subjected to intragastric (p.o.) administration of venetoclax (200 mg/kg) on the indicated days for 4 weeks. Their white blood cell counts and Cd19⁺ population (day 0 n = 4; day 14 n = 5; day 28 n = 4; day 0 to day 14, ∗P = .0159; day 0 to day 28, ∗P= .0286) were longitudinally followed during the treatment period. There is a significant reduction of white blood cell count in TCB mice within 14 days of venetoclax (VTX) treatment (day 0 to day 14, ∗∗P = .0079; day 0 to day 28, ∗P = .159). Numbers of B cells were calculated as follows: white blood cells × (% of B cells of viable cells per 100). After 28 days of treatment all mice were sacrificed and immunophenotyped. (C) Viable splenocytes were counted and multiplied by the proportion of B cells in the spleen. The absolute numbers of CD19⁺ splenocytes between untreated and venetoclax treated TCB mice were compared. (D) Splenocytes of 30-week-old TC (n = 12), TCB (n = 5), and TCB-V (n = 4) mice were analyzed by flow cytometry and the relative amounts of different B-cell developmental stages were quantified. Debris and doublets were excluded from singlets. Viable cells were defined via FS INT/SS INT. GFP⁺ population was gated. The total B-cell population (GFP⁺) was gated in the IgM vs IgD plot defining the subpopulations. (E) Among splenic T cells from untreated or venetoclax-treated mice, subpopulations with CD4 or CD8 expression were distinguished by flow cytometry. ∗P < .05; ∗∗P < .01; ∗∗∗P < .001; ∗∗∗∗P < .0001. Welch unpaired 2-tailed t test performed for panels A-E.