NP23/Bcor pro-B1 ALL cell lines are sensitive to JAK inhibitors. (A) V-Ab1, T259, A1929, and A1942 B-cell line (pro-B1 cell line) were stained with the indicated antibodies. Expression of AA4.1 and IL7-Ra were detected when B-cell line were cultured in RPMI medium without IL7 and serum for 6 hours. (B) Growth curve for T259, A1929, and A1942 B-cell line. A total of 1 × 10⁴ T259, A1929, and A1942 B-cell lines were plated and cultured for 11 days in RPMI medium with or without 5 ng/mL IL-7. Growth curves of a v-Abl transformed B-cell line (C), T259 B-cell line (D), and A1929 B-cell line (E) treated with ruxolitinib (left) or tofacitinib (right) for 5 days. Cell number was determined by trypan blue exclusion. Each point represents the mean ± standard deviation (n = 3). Student t test: *P < .05; **P < .01; ***P < .001. (F) Survival curve for leukemic mice treated with tofacitinib. Mice were transplanted with 1 × 10⁶ T259 B-cell line and treated daily for 21 days (treatment duration shaded in gray), beginning day 3 posttransplant, with either 40 mg/kg/d tofacitinib or vehicle control via oral gavage. P value is indicated (log-rank Mantel-Cox test). DMSO, dimethyl sulfoxide.