Dipeptidylaminopeptidase IV (DAP IV) Activity in Normal and Malignant T‐Cell Subsets as Defined by Monoclonal Antibodies

Abstract

The activity of dipeptidylaminopeptidase IV (DAP IV) was investigated by a cytochemical method in isolated fractions of normal peripheral blood mononuclear cells and malignant cells from 9 patients with chronic T-cell leukemia. A positive DAP IV reaction was observed in 52% of normal T-cells, a consistent negative reaction in normal B cells and monocytes, 2 distinct T-cell subsets, helper/inducer cells (T4+/T8-) and cytotoxic/suppressor cells (T4-/T8+), were negatively selected by complement-mediated cytolysis utilizing the monoclonal antibodies OKT4 and OKT8. On examination of these T-cell subsets a positive DAP IV reaction was restricted to the majority of normal T4+/T8- cells. The malignant cells from 3 patients with T-chronic lymphocytic leukemia, expressing the cytoxic/suppressor phenotype (T4-/T8+) lacked DAP IV activities. Almost all leukemic cells from 3 other cases, expressing the helper/inducer phenotype (T4+/T8-), were strongly positive. Despite their T4+/T8- phenotype, the malignant cells from 3 patients with Sezary syndrome were completely DAP IV negative. The DAP IV reaction may be helpful in the further characterization of normal and malignant T-cell subsets.