Phenotypic modulation of chronic lymphocytic, prolymphocytic, and lymphoplasmacytic leukemia cells by TPA: induction of TRAP isoenzyme 5 and HD6 (CD22) antigen and enhancement of IgM messenger RNA.

B-cell neoplasias such as CLL can be viewed as models of monoclonal populations restricted within discrete ranges of B-cell maturation. It is unknown whether other B-cell leukemias such as prolymphocytic leukemia (PLL), lymphoplasmacytoid immunocytoma (IC), and hairy cell leukemia (HCL) involve different B lineages or are malignant variants of B cells in successive stages of development along the same lineage. Therefore in vitro maturation was induced with the phorbol ester TPA in leukemic cell samples from 10 CLL, 4 PLL, and 4 IC patients. Morphologically, both plasmacytic and hairy cell-like phenomena were induced. The latter unexpected finding was confirmed by reaction with HD6 (CD22) antibody which stains HCL but is unreactive with plasma cells, multiple myeloma, and CLL cells. Tartrate-resistant acid phosphatase was demonstrated in TPA-cultured CLL, PLL, and IC cells, and the same isoenzyme band as in HCL was revealed by isoelectrofocusing. On the other hand, an increase of IgM messenger RNA was detected in up to 20% of the cells in CLL cultures by single-cell in situ hybridization with fluoro-chrome-labeled DNA probes. An abundance of IgM messenger RNA characterizes lymphoplasmacytoid cells as found in IC. Our data demonstrate that CLL, PLL, and IC can be induced to realize a common genetic program which bears characteristics of HCL indicating that these four entities are more closely related than previously thought.