Atypical pattern of light chain gene rearrangement in hairy cell leukemia

Molecular genetic analysis was exploited to determine the lineage of the neoplastic cells in nine patients affected by hairy cell leukemia (HCL). In all cases the B-lineage of the cells was confirmed at the molecular level. In four cases a relatively advanced maturation stage was suggested by the expression of lambda light chain genes. Surprisingly, in two patients lambda light chain gene rearrangement was observed in spite of a germ-line kappa light chain gene. In at least one case the rearrangement was productive, as a full length messenger RNA (mRNA) was shown by Northern blot analysis and lambda light chain-restricted surface immunoglobulins (sIg) were found. These data suggest that exceptions to the hierarchy that regulates light chain gene rearrangements are not uncommon in this type of leukemia and that molecular genetic analysis should include lambda gene locus to determine more precisely the lineage origin of some leukemic cell populations.