OBJECTIVETo compare the leukemia-associated immunophenotypes (LAIP) in patients with B lineage acute lymphoblastic leukemia (B-ALL) at diagnosis and relapse, and investigate its implications for minimal residual disease (MRD) detection.

METHODSThe immunophenotype of leukemia cells from 410 newly diagnosed and 6 relapsed patients with B-ALL were detected by four to six antibody combination, mainly CD34/CD10/CD45/CD19 of 4-color CD45/SSC gating flow cytometry (FCM).

RESULTSThe proportion of CD45 under-expressed or negative in relapsed patients was much higher than that in newly diagnosed patients, being 69.2% and 37.8% respectively. Immunophenotypic changes occurred in 9 relapsed patients (including 8 hematological relapse and 1 central nerves system relapse) when analyzed by paired samples analysis at diagnosis vs at relapse: 4 cases showed CD45 down-modulation and 2 up-modulation; 4 CD34 down-modulation and 2 CD10 up-modulation, while the expression of CD19 remained no change. MRD was observed in all 7 cases of hematological relapse 2 - 4 months before relapse, and the immunophenotype of MRD cells was the same as that in relapse.

CONCLUSIONA high frequency of immunophenotypic changes occurred at relapse and even in MRD before relapse, however the accuracy of MRD monitoring seemed not affected by the FCM strategy used in this investigation.