JAK3A572V mutation is present in human CTCL. (A) DNA samples from 30 patients with CTCL were PCR amplified and resequenced using M13-tailed primers flanking exon 12 of the human JAK3 gene. Forward (For.) and reverse (Rev.) sequence traces from Patient 7 (Pt.7) sample as well as wild-type trace are shown. (B) PCR products obtained in (A) were cloned and individually sequenced. Eleven of 44 (25%) products showed the mutant JAK3A572V allele. (C) Hematoxylin&Eosin staining of the skin biopsy shown in (A). (D) Sequence traces from Patient 7 (Pt.7) biopsies collected during disease progression. SK1 indicates skin biopsy at diagnosis prior to large-cell transformation shown in panel A; PB0, peripheral blood at diagnosis; PB1, before diagnosis of large cell transformation; and PB2, after diagnosis of large cell transformation.