Molecular analysis of lineage-specific chimerism and minimal residual disease by RT-PCR of p210BCR-ABLand p190BCR-ABLafter allogeneic bone marrow transplantation for chronic myeloid leukemia: increasing mixed myeloid chimerism and p190BCR-ABLdetection precede cytogenetic relapse

We studied lineage-specific chimerism and minimal residual disease (MRD) in sequential posttransplant samples from 55 patients who underwent unmanipulated (n = 44) or partially T-cell–depleted (n = 11) allogeneic bone marrow transplantation (BMT) for chronic myeloid leukemia (CML). Chimerism was assessed by polymerase chain reaction (VNTR [variable number of tandem repeats]-PCR) analysis in highly purified CD19+, CD3+, CD15+, and CD56+ cell fractions, whereas MRD was investigated in whole blood by reverse transcriptase–PCR (RT-PCR) of both p210BCR-ABLand p190BCR-ABLhybrid transcripts. Of 55 patients, 14 (including 6 T-cell–depleted patients) had cytogenetic relapse at 5-80 months and progressed to hematologic relapse, while 41 patients remained in prolonged cytogenetic remission 12-107 months post-BMT. Before leukemia recurrence, patients in the relapse group showed a consistent evolution pattern sequentially featured by persistent p210BCR-ABLpositivity, increasing mixed chimerism (MC) in myeloid cells, p190BCR-ABLpositivity, and, finally, cytogenetic relapse. Myeloid MC preceded cytogenetic relapse by 2-12 months, whereas p190BCR/ABLwas detected 1-6 months prior to cytogenetic relapse in 11 patients and concomitant with cytogenetic relapse in 3 patients. In the remission group, all patients invariably tested negative for p190BCR-ABL; 10 patients tested positive for p210BCR-ABLat variable time-points but showed persistent full donor chimerism (DC), whereas 31 patients tested p210BCR-ABLnegative and displayed full DC or transient MC due to the persistence of recipient T cells. Two patients in the relapse group were successfully reinduced into molecular remission with donor lymphocyte infusion. Sequential molecular analysis after such treatment showed the inverse pattern to that observed prior to relapse, ie, progressive disappearance of p190BCR-ABLtranscripts, conversion of myeloid chimerism to donor type, and, finally, p210BCR-ABLnegativity. We conclude that lineage-specific chimerism and p190BCR-ABLmessenger RNA (mRNA) analyses contribute a better characterization of CML evolution after BMT and enable early identification of patients at the highest risk of relapse.