Induction of features characteristic of hairy cell leukemia in chronic lymphocytic leukemia and prolymphocytic leukemia cells.

In vitro maturation was induced with 12-O-tetradecanoylphorbol-13-acetate in leukemic cell samples from patients with chronic lymphocytic leukemia (n = 10) and prolymphocytic leukemia (n = 4). The cells were studied for morphology, for immunological markers using the fluorescence activated cell sorter, and for acid phosphatase isoenzymes using both cytochemistry and isoelectrofocusing. Morphologically the induced changes included appearance of cells with an excentric nucleus and basophilic cytoplasm and eventually of cells with many fine cytoplasmic projections ("hairs"). Analysis of immunological markers by flow cytometry revealed that the monoclonal antibody defined cell surface molecule HD6 (CD22), which is strongly expressed on hairy cell leukemia (HCL) but absent from plasmacytoma and plasma cells, can be induced or enhanced in the leukemic samples. In the study of acid phosphatase isoenzymes using cytochemistry we observed the induction of the tartrate resistant isoenzyme. Further, using isoelectrofocusing we could demonstrate the induction of the same band of tartrate resistant acid phosphatase with an isoelectric point of 9.0-9.7 as detected also in HCL. This particular isoenzyme is considered characteristic of HCL but is absent in plasmacytoma. Our data demonstrate that chronic lymphocytic leukemia and prolymphocytic leukemia cells can be induced to realize a common genetic program which bears characteristics of HCL, indicating that these three entities are much more closely related than previously thought.