Synthetic lethality approach to killing residual tumor cells in CD127⁺ T-ALL/T-LBL. Glucocorticoids efficiently reduce the tumor burden and induce acute in vivo PIM1 expression in residual tumor cells through the cell-non-autonomous activation of the IL7RA/JAK-STAT signaling pathway. Combination therapy with the PIM inhibitor PIM447 allows for a synergistic antileukemic effect on residual tumor cells.