Subtyping of chronic lymphocytic leukemia of T-type by dipeptidylaminopeptidase IV (DAP IV), monoclonal antibodies, and Fc-receptors.

The authors have recently provided evidence for a restricted occurrence of the enzyme dipeptidylaminopeptidase IV (DAP IV) in normal human Tmu lymphocytes as far as blood and bone marrow cells are concerned. In this report, this issue has been extended to cases of chronic lymphocytic leukemia (CLL) along with T-monoclonal antibodies of OKT series (OKT4, OKT8) and Fc receptors for IgM (Tmu) and IgG (Tgamma). Seven of eight cases of T-CLL were DAP IV-positive, whereas all B-CLL cases like normal B-cells were invariably enzyme-negative. Parallel studies with OKT antibodies and Fc receptors showed that the cases positive to DAP IV also revealed OKT4 reactivity and, to some extent, Fc IgM receptor. In a single DAP IV-negative T-CLL with azurophilic granules, the leukemic cells were shown to be reactive for OKT8 and bore Fc IgG receptor. It was inferred that DAP IV represents a reliable marker for T-CLL derived from the OKT4 and Tmu positive subsets of T-lymphocytes, which encompasses the T-helper cell cohort.