OKM1-positive T-cell leukemias. Relationships among morphologic features, phenotype, and functional activities.

The morphologic features, phenotype, and functions of OKM1+ leukemic T-cells were studied. The leukemic T-cells in two patients with chronic lymphocytic leukemia (CLL) had specific features of large granular lymphocytes (LGL), and those in two patients with acute lymphocytic leukemia (ALL) had L2 morphologic characteristics. The phenotype of the leukemic cells from one patient with CLL was OKM1+, ER+, OKT3+, OKT4+, OKT8-, OKIa1-, IgGFc receptor (EA gamma)+, Leu-7+, Leu-11b+, and anti-Tac-. The cells had antibody-dependent cell-mediated cytotoxicity (ADCC), but no natural killer (NK) activity. They had a definitive helper effect on pokeweed mitogen-induced normal B-cell differentiation. The leukemic cells from the other patient with CLL were Leu-7-, and Leu-11b-, and lacked both ADCC and NK activity. The leukemic cells in the two patients with ALL were ER+, OKM1+, Leu-7-, and Leu-11-, and did not have any cytotoxicity. One was EA gamma +, and the other was EA gamma -. These findings suggest that OKM1+ leukemic T-cells consist of at least two subgroups: (1) T-cells with the morphologic features of LGL; and (2) those with a lymphoblastic morphologic type. In either case, the phenotype is novel and suggests the emergence of a small, distinct lymphocyte subset.