YAMAGUCHI, A., MIURA, I., MIURA, A. B. and AMANO, Y. Establishment and Characterization of T-Cell Lines (Yana-I and Yana-II) Derived from a Patient with Chronic Adult T -Cell Leukemia (ATL) . Tohoku J. exp. Med., 1987, 152 (2), 139-149-ATL-cell lines producing C-type retroviruses were established by culture of the peripheral blood mononuclear cells from a patient with chronic ATL. These cell lines had the surface feature of inducer/helper T-cells with electron microscopic finding of C-type retrovirus on the cell surface. Chromosome analysis revealed the presence of a marker chromosome, but did not identify 7 trisomy nor 14q⁺. Of the cell lines, the line established by culture with TCGF was named “Yana-I” and the line established by culture of Yana-I without adding TCGF was named “Yana-II”. Serum ATLA-antibody was positive in 1.5% of the healty individuals examined (4/257). Among malignant lymphoma patients, ATLA antibody was positive in none of the patients with B-cell type lymphoma (0/10) and Hodgkin's disease (0/2). In contrast, ATLA antibody was found in half of the patients with T-cell type lymphoma (3/6) and all with ATL (4/4). This suggested that C-type retrovirus in closely associated with ATLL.