CD4 and T-cell leukemia: In an analysis of the phenotype of leukemic CD4+ T cells from patients with adult T-cell leukemia (ATL), we found that a number of primary CD4+ T cells became positive for cell surface CD83 after short-term culture, and that most of these CD83+ CD4+ T cells were positive for human T-cell leukemia virus type-I (HTLV-I) Tax (Tax1).