Rearrangement and expression of immunoglobulin genes and expression of Tac antigen in hairy cell leukemia.

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Abstract
The origin and exact stage of differentiation of [human] neoplastic cells that comprise hairy cell leukemia remained uncertain. As Ig H and L chain genes must both undergo a DNA rearrangement during B cell development but rarely do so within other hematopoietic lineages, these genes in this leukemia were examined. The neoplastic cells of all 8 cases demonstrated rearranged H and L chain genes and, in 2 cases examined, contained the corresponding mRNA for H and L chain Ig. Consistent with this B cell genotype, all cases displayed cell surface HLA-DR and B cell-associated antigens. Unexpectedly, all cases demonstrated cell surface Tac antigen, which previously was restricted predominantly to select T cell malignancies and activated T cells. Prior studies suggested that the anti-Tac monoclonal antibody recognized a peptide associated with the binding of interleukin 2 (T cell growth factor) in such T cells. Immunoprecipitation with anti-Tac and NaDodSO4[sodium dodecyl sulfate]/polyacrylamide gel electrophoresis revealed an antigen on leukemic hairy cells with a MW of 53,000-57,000, identical in size to the receptor on activated T cells. This apparent biphenotypic status might reflect a transformation-associated expression of the Tac antigen in this leukemia. Alternatively, hair cell leukemia may be a malignancy of a unique stage of normal B cell differentiation in which the Tac antigen is expressed.