Establishment and characterization of an Epstein-Barr virus spontaneously transformed lymphocytic cell line derived from a hairy cell leukemia patient.

Hairy cell leukemia is a rare, B-cell malignancy uniquely sensitive to the antitumor effects of alpha and beta interferons (IFN). In order to further study the effects of IFN in this disease, we derived a cell line (HC1) from the peripheral blood mononuclear cells of a patient with hairy cell leukemia (HCL). Cells exhibited the typical morphological features of HCL, including the characteristic cytoplasmic projections by light, transmission, and scanning electron microscopy. HC1 cells were of B-cell lineage, as evidenced by immunophenotypic analysis. Although originally TRAP positive, HC1 cells lost this biochemical marker following 3 months in culture. Monoclonality of the cell line was confirmed by a clonal karyotypic abnormality characteristic of B-cell malignancies, and the presence of a single, distinctive fused terminal EBV fragment. The cells formed colonies in soft agar and were tumorigenic in irradiated nude mice. HC1 cells were sensitive to the antiproliferative effects of IFN-a and IFN-beta, but only moderately sensitive to the growth inhibitory effects of IFN-gamma. Incubating the cells in the presence of Type 1 IFN resulted in stabilization of cell numbers, without cellular proliferation or loss. Cell cycle analysis revealed that IFN-alpha resulted in a build-up of cells in the S phase of the cell cycle, suggesting a cytostatic effect of IFN on the growth of these cells. The HC1 cell line provides a model system which will be useful for in vitro studies of the biology and treatment of this disease.