Detection of minimal residual disease in B chronic lymphocytic leukemia (CLL)

In the absence of specific chromosomal translocations the best method for detecting minimal residual disease (MRD) in B cell malignancies is based on the uniqueness of immunoglobulin (Ig) genes rearrangement. We here report a very sensitive method for assessing MRD in complete hematological remission (CHR) chronic lymphocytic leukemia (CLL) patients as defined by the international workshop on CLL (IWCLL).

Twelve CLL patients in CHR and complete phenotypic remission (CPR) were included in the study. Eight of them received Fludarabine (FDR), one was treated by Chop regimen, and the remaining 3 were rescued by polychemotherapy followed by autologous bone marrow transplantation (ABMT).

DNA extracted from peripheral blood lymphocytes (PBL) of each patient was amplified with VH family specific and framework 3 primers in 5' and a consensus JH primer in 3', before treatment and sequentially after the CPR completion. When no clonal rearrangement could be detected by this assay, the CDR3 sequence specific probe of the clone was used as the 3' primer, associated to the VH family specific primer in 5'. PCR products were analyzed by classical procedures in agarose and/or acrylamide gels.

Mixtures of leukemic cells and normal PBL showed detection of a single leukemic cell among more than 10(5) normal cells. Four out of the 12 patients achieved molecular remission (MR) when employing CDR3 amplification. All 3 autografted patients were in MR, whereas only one out of the 9 patients treated by chemotherapy alone achieved MR. When using a clone specific probe, a clonal signal was observed in all cases but one (ABMT). Results presented here confirm that MR may be achieved in a few cases of B-CLL. Further studies are needed to determine the exact relationship between MRD and clinical outcome.