Third complementarity determining region (CDR III) sequence analysis in childhood B-lineage acute lymphoblastic leukaemia: implications for the design of oligonucleotide probes for use in monitoring minimal residual disease.

The genetic sequence of the third complementarity determining region (CDR III) of the immunoglobulin heavy chain (IgH) gene was analysed in 55 rearranged alleles from 36 children presenting with B-lineage acute lymphoblastic leukaemia (ALL). This confirmed the unique nature of these rearrangements. However, contrary to the hypothesis that the CDR III is produced by a random process of rearrangement, biased utilisation of diversity (D) segments and of joining (J) regions 4, 5 and 6 was demonstrated. Moreover, preferred sequence boundaries were seen in J regions 1 to 5 and were suggested at the 3'-end of certain D regions, notably D21/9 and DK1. Similar patterns of rearrangement have been noted in normal B-lymphocyte clones. Together with relatively limited N nucleotide addition, these factors may restrict the potential sequence variability at the D-N-J junction. The occurrence of clonal progression by secondary gene rearrangements, such as V-V replacement, favours the use of this site when designing clone-specific oligonucleotide probes for use in monitoring minimal residual disease (MRD). In cases where biased features of D-J rearrangement are shared by both the leukaemic and normal B-lymphocyte clones this could reduce the sensitivity of these probes in detecting low levels of residual disease.