BM cytokines rescue FLT3-ITD AML. (A) Colony-forming assay of primary human FLT3-ITD AML in cytokine-rich methylcellulose treated with or without crenolanib. Brackets denote high (≥50%) or low (<50%) FLT3-ITD mutant to wild-type allelic ratio (ITD AR) expressed as a percentage of total alleles. Colony-forming assay of sample #3073 (B) or MV4;11 cells (n = 3) (C) in methylcellulose with or without cytokines and treated with crenolanib. (D) Colony-forming assay of MV4;11 cells in methylcellulose supplemented with the indicated cytokine and treated with crenolanib (n = 3). (E) Immunoblot of MV4;11 cells treated with crenolanib ± the indicated cytokine for 24 hours. (F) Adenosine triphosphate–based survival assay of primary human FLT3-ITD AML treated with crenolanib ± the indicated cytokine. Supplemental Table 1 provides characteristics of patient samples. Dashed line represents DMSO-treated control (n = 5). Error bars represent standard error of the mean (SEM). *P < .05; ****P < .0001. Cren10/50, crenolanib 10 or 50 nM; PBS, phosphate-buffered saline.