Down-regulation of JAK targets with ruxolitinib treatment. Levels of phosphophorylated (p) and total STAT proteins in the spleens of ETP-ALL xenografts. Xenografts (2-3 mice per arm, replicates shown) were treated with ruxolitinib (rux) or vehicle (con) for 72 hours, spleens were harvested, and protein lysates were subjected to immunoblot. Protein levels by immunoblot of replicates were quantitated relative to actin and analyzed by the Welch-Satterthwaite t test. Levels of pSTAT1 were reduced by >50% in treated mice compared with control for all 6 samples (P < .05). There was a >50% reduction in pSTAT3, which was statistically significant (P < .05) for ETP1, 5, 8, and 14 but not significant for ETP12 and 13. There was a 70% or greater reduction in pSTAT5 for all 6 samples (P < .05).