Hairy cell leukemia has a B-cell genotype.

The phenotype and, by inference, the cell of origin of some lymphocytic neoplasms has been defined by surface marker studies; however, the precise cellular origin of other neoplasms of the lymphoid system is still unknown. For example, with reference to hairy cell leukemia (HCL), cell marker data has been used in support of a monocytic, a T cell, or a B cell origin. If hairy cell leukemia is a B cell-derived neoplasm, the controversy may be resolved by genotyping the cells, using the rearrangement of immunoglobulin genes as a marker of the B cell nature of the process. Rearrangement of these genes is detected using the Southern blot technique and cloned probes specific for the JH segment of the immunoglobulin genes. In this study, the arrangement of the immunoglobulin genes was analysed in normal tissue, in two accepted B cell lymphomas and in nine cases of hairy cell leukemia. DNA from peripheral blood leukocytes (two patients) and from the spleen (seven patients) revealed a discrete new JH restriction fragment length in the leukocytes of hairy cell leukemia cases. The presence of rearranged restriction fragments is interpreted as evidence of the existence of clonal B cell populations. Three of six samples had rearranged kappa light chain fragments. We conclude that most cases of hairy cell leukemia have a B cell genotype. The use of genotyping has wider application in the analysis of hematological malignancies.