IKZF1 deletion reduces survival in NSG mice and leads to profound dexamethasone resistance that is rescuable by IK1 overexpression. NSG mice xenografts transplanted with Nalm-6 clonal cell lines. (A) Flow cytometry for human HLA-ABC marker in peripheral blood samples taken on day 18. Horizontal bar shows mean, and error bars are standard error of the mean (SEM). Statistical significance was calculated by using the Student t test. (B) Kaplan-Meier survival curve; n = total number of mice in each group. Statistical significance was calculated by using the log-rank test. (C) Tissue engraftment of Nalm-6 cells in moribund mice at time of euthanasia. Horizontal bar shows mean, and error bars are SEM. Statistical significance was calculated by using the Student t test. (D, E, and G) Seventy-two-hour dexamethasone treatment of Nalm-6 clonal cell lines showing percent annexin V/7-AAD double-negative population as measured by flow cytometry. Samples were performed in triplicate; error bars show SEM. Asterisks denote statistical significance at the specified dose of KO compared with WT control (*P < .05; **P < .01; ***P < .001). (F) IKAROS immunoblotting of single cell–derived Nalm-6 clones and IK1 lentivirus overexpression (55-7 + IK1 rescue shown in purple). (G) Partial restoration of dexamethasone sensitivity in IKZF1 KO after IK1 rescue. (H) RNAseq gene expression levels plotted as fragments per kilobase of transcript per million mapped reads (FPKM) in untreated samples (NR3C1) or fold increase of FPKM after 48-hour, 50-nM dexamethasone treatment (FKBP5 and TSC22D3) (supplemental Figure 6C). BM, bone marrow; LIV, liver; ns, not significant; PB, peripheral blood; PBS, phosphate-buffered saline; SPL, spleen.