Abstract
B-cell acute lymphoblastic leukemia (B-ALL), more frequently than any other B-lineage neoplasm, exhibits oligoclonal Ig heavy chain (IgH) gene rearrangement in 15% to 43% of all cases studied. To study the molecular processes that promote multiple IgH rearrangements, a comprehensive sequence analysis of a B-ALL case was performed in which seven clonal IgH gene rearrangements were identified. The genetic profiles suggested that a single leukemic progenitor clone evolved into several subclones through dual processes of variable (V-H) to preexisting diversity-joining (DJ(H)) gene segment rearrangement and V-H to V-H gene replacement, Predominant IgH-V usage and the uniquely rearranged clonotype-specific V(H)DJ(H) region gene sequences were identified using a novel DNA-based gene amplification strategy. Polymerase chain reaction (PCR) was directed by an IgH-J generic primer and a complement of family-specific IgH-V primers that defined the major B-cell IgH-V gene usage, Clonality of rearranged V(H)DJ(H) bands was substantiated by high resolution denaturant gel electrophoretic analysis. Sequence patterns of the amplified V(H)DJ(H) fragments segregated into two groups defined by common DJ(H) sequences. Partial N region homology at the VHD junction as well as shared DJ(H) sequences firmly established V-H to V(H)DJ(H) gene replacement as a mechanism generating clonal evolution in one group. In the second subset, oligoclonality was propagated by independent V-H gene rearrangements to a common DJ(H) precursor. The contributions of all clonal lg-V(H)DJ(H) repertoires for each group was approximately 50% and reflected a symmetric distribution of leukemic subclones generated by either process, Thus, oligoclonal rearrangements evolved by two independent, yet seemingly contemporaneous molecular genetic mechanisms, All seven clones displayed nonfunctional Ig-V(H)DJ(H) recombinations. These observations may have relevance to the recombinatorial opportunities available during normal B-cell maturation. (C) 1996 by The American Society of Hematology.