Cell surface phenotype and in vitro function of adult T-cell leukemia cells

The cell surface phenotypes of leukemic cells obtained from 30 patients with adult T-cell leukemia (ATL) were examined by means of a panel of OKT monoclonal antibodies and an anti-Tac monoclonal antibody. These leukemic cells were reactive with OKT1, OKT3, OKT4, OKT10, and OKT11 but not with OKT5, OKT6, OKT8 antibodies, suggesting that they were derived from peripheral mature cells included in the OKT4+ "helper/inducer" T-cell subset. Functionally, leukemic cells from none of the nine patients studied stimulated pokeweed mitogen (PWM)-driven immunoglobulin (Ig) synthesis by normal B cells. Suppressor cell activity, however, was found in 17 of 25 patients in PWM-induced Ig production. Fresh or cultured ATL cells from 22 of 23 patients tested expressed Tac antigen (interleukin-2 receptor) on the cell surface. The significance of Tac antigen on ATL cells is discussed in relation to the abnormal regulation of Tac antigen and leukemogenesis.