CLONAL EVOLUTION IN B-LINEAGE ACUTE LYMPHOBLASTIC-LEUKEMIA BY CONTEMPORANEOUS V-H-V-H GENE REPLACEMENTS AND V-H-DJ(H) GENE REARRANGEMENTS

B-cell acute lymphoblastic leukemia (B-ALL), more frequently than any other B-lineage neoplasm, exhibits oligoclonal Ig heavy chain (IgH) ge ne rearrangement in 15% to 43% of all cases studied. To study the mole cular processes that promote multiple IgH rearrangements, a comprehens ive sequence analysis of a B-ALL case was performed in which seven clo nal IgH gene rearrangements were identified. The genetic profiles sugg ested that a single leukemic progenitor clone evolved into several sub clones through dual processes of variable (V-H) to preexisting diversi ty-joining (DJ(H)) gene segment rearrangement and V-H to V-H gene repl acement, Predominant IgH-V usage and the uniquely rearranged clonotype -specific V(H)DJ(H) region gene sequences were identified using a nove l DNA-based gene amplification strategy. Polymerase chain reaction (PC R) 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 res olution denaturant gel electrophoretic analysis. Sequence patterns of the amplified V(H)DJ(H) fragments segregated into two groups defined b y common DJ(H) sequences. Partial N region homology at the VHD junctio n 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 g roup. In the second subset, oligoclonality was propagated by independe nt V-H gene rearrangements to a common DJ(H) precursor. The contributi ons of all clonal lg-V(H)DJ(H) repertoires for each group was approxim ately 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 m echanisms, All seven clones displayed nonfunctional Ig-V(H)DJ(H) recom binations. These observations may have relevance to the recombinatoria l opportunities available during normal B-cell maturation. (C) 1996 by The American Society of Hematology.