Notch-1 is a signaling component known to be essential for IL-2 production as well as GVHD development (20–23), and, because Fli-1 has already been shown to be positively associated with Notch-1+ mutations in pre–T cell lymphoblastic lymphoma (pre-TLL) (3), we investigated whether this phenomenon would also apply to murine activated primary T cells. The gene discussed is NOTCH1; the disease is graft versus host disease.