MOLECULAR ANALYSIS OF THE LEUKEMIC B-CELL IN ADULT AND CHILDHOOD ACUTE LYMPHOBLASTIC-LEUKEMIA

Immunoglobulin heavy chain gene (IgH gene) rearrangements are found in the majority of cases of B-lineage acute lymphoblastic leukaemia (ALL ). We have examined bone marrow samples taken at presentation or relap se from 109 patients (79 adults and 30 children) and have performed se quence analysis of the complementarity determining region 3 (CDR3) on 65 alleles from 54 patients. We aimed to define immunoglobulin heavy c hain (IgH) variable segment family use and investigate biological and structural features of the B cell in adult and childhood ALL. Using th e FR1 fingerprinting method, a rearranged band was identified in 70 (8 9%) of 79 adult ALL and in 29 (97%) of 30 childhood ALL. This study fo und no preferential use or selection of IgH VH genes and no statistica lly significant structural differences between normal and leukaemic B cells in either adult and childhood ALL. An equal proportion of amplif iable cases of adult and childhood ALL uses more than one VH family ge ne (24/70, 34%, and 8/29, 27 . 5%, respectively). There were no signif icant differences in the structure or size of the CDR3 region and the variable (V) or joining (J) segment use in ALL patients compared to no rmal B cells. We observed that the N2 region was shorter than N1 in ch ildren whereas the opposite was observed in adults (not statistically significant). The J4 segment was a more common rearrangement in childr en than in adults, and in both groups J4 was more frequently associate d with multiple D segment VDJ rearrangements. An increase in VH6 use i n leukaemic alleles compared to normal B lymphocytes (2%) was observed but it was not statistically significant in our group of patients. Am ongst children and adults, in-frame CDR3 junctions occurred in 78% and 64% of rearranged alleles, respectively, compared to 75% of inframe s equences reported by others to occur among normal B cells.