Immunoglobulin gene rearrangements in hairy cell leukemia and other chronic B cell lymphoproliferative disorders.

Immunoglobulin gene rearrangements have been investigated in 11 patients with hairy cell leukemia (HCL), 11 with prolymphocytic Leukemia (PLL), and 34 with chronic lymphocytic leukemia (CLL). Heavy and Light Ig chain gene probes have been used, and Ig genes were found in a rearranged configuration in all cases. Production of kappa and lambda light chains correlated with the respective gene rearrangements. With respect to the heavy chain locus, we found that in 6 of 21 cases of kappa-producing CLL only one allele was rearranged, whereas both alleles were rearranged in nearly all cases of lambda-producing CLL and either kappa- or lambda-producing HCL and PLL. Our data confirm the B cell nature of HCL and lead us to suggest that HCL derives from the clonal expansion of a cell at a later developmental stage than in CLL and PLL.