JAK3 mutation data in T-ALL and investigation of JAK3 as a competitive factor for JAK3-mutant signaling. (A) Graph shows variant allele frequency (VAF) of JAK3 mutations in patients with T-ALL; 34% of JAK3-mutant patient cases either have a second JAK3 mutation or a homozygous JAK3 mutation. (B-D) Proliferation curves of Ba/F3 cells expressing JAK3 (M511I), JAK3 (L875H), or JAK3 wild type in the absence of cytokines: parental Ba/F3 cells (B), Ba/F3 cells lacking common γ chain (guide RNA [gRNA] targeting exon 3 of Il2rg) (C), and Ba/F3 cells lacking common γ chain (gRNA targeting exon 5 of Il2rg) (D). Significance was calculated compared with wild-type control using the Kruskal-Wallis test and Dunn’s multiple comparisons correction. (E-F) Graph showing relative percentage of Ba/F3 cells expressing wild-type JAK3 or empty vector in cells transformed by JAK3 M511I (E) or JAK3 L857Q (F). Competition between wild-type JAK3 and mutant JAK3 results in the disappearance of wild-type JAK3–expressing cells, which is observed only in panel E. Experiment was performed in biological triplicate. Standard error of the mean is shown. Significance was calculated using 1-way analysis of variance and the Bonferroni correction. ***P ≤ .001, **P ≤ .01, *P ≤ .05, not significant [ns] P ≥ .05. GFP, green fluorescent protein.