Unexpected immunoglobulin light chain gene rearrangements in myeloid antigen positive acute lymphoid leukemia

Blast cells from 10 immunologically diagnosed adult acute lymphoid leukemias expressing myeloid antigens (M⁺ ALL) were studied for immunoglobulin heavy (IgH) and light chain as well as T-cell receptor (TCR)-β chain gene rearrangements. All but one leukemic isolate met the FAB criteria for ALL. DNA from 2 patients with pre-pre-B-ALL (CD10^-) and 1 patient with common ALL contained rearranged Ig light chain (κ in two, λ in one case) in addition to rearranged IgH genes. The TCR-β chain gene was germline in all pre-pre-B leukemias and rearranged in common ALLs (bigenotypic features). One patient with mature B-ALL showed IgH and light chain gene rearrangements. DNA from 2 pre-T-ALLs contained rearranged TCR-β chain genes plus rearranged IgH genes in one case. Ig light chain gene rearrangements in immature M⁺ ALL were not associated with gross chromosomal abnormalities except for one Philadelphia chromosome positive case. The occurrence of Ig light chain gene rearrangements in M^- ALL with immature lymphoid immunophenotype might represent an hitherto unrecognized aberrant differentiation potential of transformed multipotential stem cells with commitment towards the lymphoid lineage.