An increasing number of large granular lymphocytic leukemia (T-LGLL) patients have also been reported to possess the STAT5BN642H mutation (Fig. 1a), most of which had a CD4+ disease burden20,21, but one STAT5BN642H-positive CD8+ T-LGLL case was reported to be particularly aggressive and fatal22. The gene discussed is CD4; the disease is T-cell large granular lymphocyte leukemia.