Jak3 mutations confer proliferation advantage to cultured pro-B cells. (A) Percentage of GFP⁺ cells over the course of 14 days after infection of WT fetal liver-derived pro-B cells with MSCV empty, MSCV JAK3, MSCV T844M, MSCV R653H, MSCV V670A, or MSCV V670A/T844M cultured at low IL-7 concentration (0.5% conditioned medium). Statistics were performed using repeated measures analysis of variance (ANOVA), *P ≤ .05; **P ≤ .01. (B) Absolute number of viable GFP⁺ cells after 4 days of culture at low IL-7 concentration. WT pro-B cells were infected as described earlier, counted, and analyzed for GFP frequency between day 8 and day 12 of culture. Data are presented as number of GFP⁺ cells/mL; n = 3. Statistics were performed using ANOVA with Tukey's posttest: ***P ≤ .001; ****P ≤ .0001. (C) Percentage of GFP⁺ cells over the course of 14 days after infection of the Spi1/Spib-deficient 660BM cell line with MSCV empty or MSCV T844M at low IL-7 concentration. Statistics were performed using repeated measures ANOVA: **P ≤ .01. (D) Absolute number of viable GFP⁺ cells over 6 days of culture shown in panel C. Spi1/Spib-deficient 660BM pro-B cells were infected with either MSCV empty or MSCV T844M vectors.