IL-15 levels in the serum of patients who relapsed with FLT3-ITD+ AML after allo-HCT. Sorafenib–DLI responders and nonresponders are shown separately. Each data point represents the IL-15 level in the serum of a patient before sorafenib (so.) treatment (day 0) and after the start of sorafenib treatment (day 3; before the patients received donor lymphocyte infusions). The dashed line indicates the detection limit (4 pg/mL) of the IL-15 ELISA. n values represent biologically independent patients. p value was determined using the twosided Wilcoxon matched-pairs signed-rank test.