Monitoring of minimal residual disease among multiple myeloma patients after autologous stem cell transplantation Fidan Akhundova, Larisa Mendeleeva, Irina Galtseva, Olga Pokrovskaya, Evdokiya Urnova, Elena Parovichnikova, Valeriy Savchenko Research Center for Hematology (Moscow, RU) Introduction Results Multiparameter flow cytometry (MFC) immunophenotyping (IF) can be a sensitive method for analyzing the plasma cells (PCs) compartment in patients with multiple myeloma (MM), allows discrimination between myelomatous and normal PCs. 1 patient achieved complete response (CR) before SCM, that was confirmed by immunofixation (IMF) and by morphology (0,8 % BMPCs) and was MRD (-) by MFC. 4 patients were in very good partial response (VGPR) (trace secretion in serum and/or urine M-protein and 0-1,2 % BMPCs), among 3 of them was MRD (+) by IF, in 1 case MRD was undetectable. Partial response (PR) was achieved in 1 patient (serum M-protein-13 g/l; 3,5 % BMPCs) and MRD (+) by IF (table). IF of BMC among 4 patients after ASCT confirmed achievement of stringent complete response (sCR): absence of abberant antigen expression CD 19, CD 117, CD 56 on cells with coexpression 138/38, absence of M-protein in serum and urine, 0-0,5 % PCs in BM. There were 1 patient in CR before SCM and 3 patients with VGPR. Another patient with VGPR before SCM still had the same data after ASCT: trace secretion in serum; 1,2 % BMPCs and MRD (+).Only 1 patient in PR after ASCT hasn't get responder rate: without having any changes in serum M-protein, he was otherwise MRD negative due to a few-celled BM. Purpose The aim of this study was evaluation of residual tumor cells in bone marrow by MFC. Materials and methods In this study 6 patients with MM were screened, age 33-66 (M-55). IF of bone marrow cells (BMC) was performed before stem cell mobilization (SCM) and after 2-6 months after autologous stem cell transplantation (ASCT). SCM included cyclophosphamide 4g/m2 plus G-CSF 5 µg/kg/day. Prior ASCT conditioning included melphalan200mg/m2. Quantification of neoplastic cells was perfomed by using Beckman Coulter FC-500 flow cytometer. IF studies were perfomed on erythrocyte-lysed BM aspirate samples: CD 138 FITC/CD 38 PE/CD 19 PerCP; CD 138 FITC/CD 38 PE/CD 117 PerCP (c-cit) Cy 5.5; CD 138 FITC/CD 38 PerCP Cy 5.5/ CD 56 PE (monoclonal antibodies BD). Minimal residual disease (MRD) was estimated according to abberant antigen expression CD 19, CD 117, CD 56 from gate with coexpression CD 138/38. The analysis was based on at least 50,000 events. Threshold level of cells with abnormal antigen expression of CD 138/CD 38 population was 10 %. The IF results were compared with immunofixation and morphology studies. Conclusions Immunophenotyping of bone marrow cells among MM patients by multiparameter flow cytometry allows to identify stringent CR after ASCT. Before ASCT gate G gate B gate B Efficiency of ASCT Table 1. № patient S.F.M. BM plasma cells % Response SPEP and UPEP + IF MFC MRD 1. F.A.Z., 55 y.o. Before ASCT After ASCT 3,5 % 0,8 % PR SPEP 13 g/l SPEP 6,4 g/l + 2. K.L.V., 59 y.o. absent VGPR CR Traces UPEP - 3. S.O.I., 54 y.o. 0,5 % 4. G.G.A., 59 y.o. 1,2 % 0,4 % Traces SPEP and UPEP Traces SPEP 5. D.Z.I., 55 y.o. 6. B.V.V., 43 y.o. 1 2 3 4 5 gate B gate B gate B gate B 6 7 After ASCT 8 9 gate N gate G gate N 10 11 12 13 14 gate N gate N gate N gat e N 15 16 18 17 Figure 1. Office address: National Research Center For Hematology, Noviy Zykovskiy pr., 4A, Moscow, 125167,Russia. E-mail: mlp@blood.ru Flow cytometry analysis of MRD from patient S.O.I. with MM before and after ASCT.