Detection of minimal residual disease (MRD) following BMT by multi-parameter flow cytometry (MPFC)

Cell mediated immunotherapy (CMI) is able to reinduce remission in patients (pts) with MRD post-BMT. MPFC is effective in detecting MRD with a sensitivity of 0.05-1 %. We therefore used MPFC for detection of MRD following BMT in 21 pts (Allo BMT-16 ABMT-5) (M-14, F-7) age 21 (6-48) years. Eleven pts had AML, 9 ALL, and 1 MDS. Eleven pts were transplanted in complete remission (CR) as defined by clinical, morphological, and cytogenetical criteria and 10 pts in relapse (>20% blasts in BM). Bone marrow was analyzed pretransplant and 3-4 months post-BMT. MPFC detects MRD by identifying cells with aberrant antigen expression and/or leukemia-associated phenotype (LAP). MPFC analysis of normal BM resulted in 72.0±10.7% CD33+, 3.0±2.1% CD14. 6.0±3.6% CD71+, 0.7+0.2,% CD34+, 14.0±6.7% CD3+, 5.0±2.6 CD19+ with a ratio of CD4/8 I.4±0.8 (n=4). 8/21 pts had a normal MPFC while 13 had abnormal results prc-BMT. Pre-BMT MPFC was abnormal in all pts not in CR. In addition, 3 pts (ALL) that were in CR had an abnormal MPFC prc-BMT. In ALL, an abnormal uniform B cell population was observed (CD34+, CD10+, CD19+, CD20+'-, CD22+'-) and antigen densities varied greatly between pts. In AML, the main finding was abnormal distribution in CD34. In all but one AML pt, pre-BMT abnormal MPFC with LAP was observed following BMT. Only 2/8 pts that had normal MPFC pre-BMT, relapsed (AML, ABMT) while 2/3 pts that were transplanted in clinical CR but had abnormal MPFC pre-BMT, relapsed and died. 2/13 (15%) of the pts with abnormal and 3/8 (37%) pts with normal MPFC pre-BMT, respectively are alive 36 (20-38) months post-BMT. In summary, MPFC is an effective tool for detection of MRD pre-BMT and can detect LAP in CR mainly in ALL. In most of the cases LAP persists post-BMT. Pre-transplant MPFC abnormality may predict outcome and response to CMI post-BMT.