JAK1 mutation–positive T-ALL cells show a type I IFN transcriptional signature. The gene expression profile of human JAK1 mutation–positive and mutation–negative T-ALL cells was assessed with pangenomic microarrays. (A) The list of the 10 gene sets most enriched in cells with a mutated JAK1 allele, according to a GSEA analysis, is shown. (B) The figure represents the GSEA enrichment plot of one of the most enriched gene sets. The lower part of this plot shows the ranking of the genes relative to their enrichment in JAK1 mutation–positive cells. The medium part shows the ranking of the hits from the IFN-induced gene set and the top part shows the resulting enrichment profile. (C) Hierarchical clustering based on the genes induced by IFN-α in PBMCs. (D) The mean microarray signal for the IFN targets hIRF-7 (right) and hMX1 (left) is represented for 3 JAK1 mutation–positive compared with 8 mutation-negative T-ALL samples. The differences between JAK1 mutation–positive and mutation–negative samples were extremely significant (***P < .001, t test). Results are mean ± SEM. (E) Quantitative analysis hIRF-7 (left) and hMX1 (right) expression, based on an independent set of 6 JAK1 mutation–positive and 11 mutation–negative T-ALL samples. Transcripts were normalized to the level of the β-actin transcripts. The differences between JAK1 mutation–positive and mutation–negative ALL samples were significant (**P < .007, *P < .035, t test). Results are mean ± SEM.