The SUP-T1 established from the pleural effusion of an 8-year-old boy with T-lymphoblastic lymphoma in relapse. These cells are E-rosette, Leu 5, OKT9 and CALLA negative. They also express β2M, Leu 1, 2, 3a, 4, 6, 9 and OKT10 antigens and are CD4 positive. These cells are negative for Tac, HLA-DR and surface immunoglobulin.