Annexin V staining showed that Gfi1 KO thymocytes display higher levels of apoptosis, either at baseline or following exposure to IR, compared to WT controls (Supplementary Fig. 1d), consistent with previous results in T-cell lymphoma and T-cell acute lymphoblastic leukemia (T-ALL)4. Here, GFI1 is linked to T-cell acute lymphoblastic leukemia.