Adult T-cell leukemia cells expressing OKT 17 antigen in the activated state.

The surface phenotype and the functional activities of leukemic cells from seven patients with adult T-cell leukemia (ATL) were studied using monoclonal antibodies OKT 3, 4 and 8, anti-Tac, and OKT 17. The latter defines the heterogeneity of the activated T4+ T cell subset. In all cases, ATL cells with the typical OKT3-T4+ T8- phenotype expressed OKT 17 antigen. In addition, in five out of the seven cases the fresh ATL cells possessed Tac antigen which is expressed on activated T cells in varying degree. After cultivation with PWM, most populations of ATL cells acquired Tac even in the cases expressing little antigen in uncultured preparations. However the PWM activated ATL cells did not lose OKT 17 antigen. Functional assays showed the suppressor activity of ATL cells on normal B cell differentiation in three out of six cases examined. These results suggest that ATL cells most probably arise from a particular subset characterized by OKT 17 antigen within the activated OKT4+ T cell subset.