Four subclones with distinct immunoglobulin light chain phenotypes (κ⁺λ⁺, κ⁺, λ⁺ and κ^-λ^-) from acute leukemia

A human acute lymphoblastic leukemia (ALL) cell line, BALM-9, was established from the peripheral blood specimen of a patient with B cell ALL (L3 type). In contrast to the original immunoglobulin (Ig) phenotype, the established BALM-9 cell line expressed both κ and λ light (L) chains simultaneously in a range of 30-80%. Two-color flow cytometric analysis demonstrated that there was a distinct population of κλ double positive cells as well as κ single, A single and double negative populations. Therefore, subclones were obtained from each population by limiting dilution and were designated BALM-9KL (κ⁺λ⁺), BALM-9K (κ⁺λ^-), BALM-9L (κ^-λ⁺) and BALM-9N (κ^-λ_-). Western blotting confirmed the results of the immunofluorescence test at the protein level. In BALM-9N, L chains were absent even in the cytoplasm as demonstrated by Western blotting. Evidence that the subclones have the same ancestry was provided both by cytogenetic analysis and by Southern blotting, which revealed the 14q32 chromosomal rearrangement as a common abnormality and the same IgH gene rearrangement among the subclones. The existence of a κλ positive B cell population suggests a transient stage of normal B cell maturation. These subclones might represent such a stage and thus provide a useful means of analyzing the mechanism of this double light chain expression.