An evaluation of minimal residual disease in childhood acute lymphoblastic leukaemia

Evaluation of minimal residual disease (MRD) in acute lymphoblastic leukaemia (ALL) is important for disease prognostication and early relapse detection. In this study, the rearranged third complementarity-determining-region (CDR-III) of immunoglobulin heavy chain (IgH) was used as a surrogate tumour marker for MRD evaluation. DNA obtained from marrows at diagnosis was amplified by the polymerase chain reaction (PCR) using a pair of consensus primers. After 2 rounds of DNA amplification and polyacrylamide gel separation, the nucleotide sequences of 87.5% (21/24) consecutive children with B-lineage ALL were obtained by automated sequencing. There were between 1-4 rearrangements per patient. Although the J5 and J6 joining regions were preferentially used, the rearranged sequences were unique for all 25 sequences obtained. Oligoprobes to the DNJ region were constructed and quantitation in 7 patients showed a detection sensitivity of 1 leukaemic cell in 10(4) to 10(5) normal cells compared to 3 in 100 using conventional morphological criteria. Serial bone marrow showed progressive decrease in the quantity of leukaemic cells, and no leukaemic sequences were detected during cessation of therapy in 4/7 patients. One patient with detectable MRD, absconded treatment and eventually relapsed. These results are consistent with the need to eliminate the leukaemic clones below MRD detection levels before the end of therapy at 2 years. In conclusion, this study describes a novel, simplified and sensitive method of MRD detection in childhood leukaemia.