Relevance of sample preparation for flow cytometry.

INTRODUCTION: Flow cytometry is a useful tool for diagnosis and minimal residual disease (MRD) study of hematological diseases. Standard sample preparation protocols are characterized by stain-lyse-wash (SLW). To prevent nonspecific bindings and achieve high sensitivity in MRD studies, lyse-wash-stain-wash (LWSW) is required. To our knowledge, no comparison between the two methods has been performed. METHODS: We compared mean fluorescence intensity (MFI), stain index, signal-to-noise ratio, and percentage of positive cells of 104 antibodies and of 13 selected antibodies tested in 10 samples simultaneously prepared with the two methods. RESULTS: MFI and percentages of positive cells obtained by the two methods did not show significant differences and showed a very high correlation. Stain index and signal-to-noise ratio presented higher values for kappa and lambda surface chains in LWSW samples and a trend of higher values for the other antibodies in SLW samples. CONCLUSIONS: We suggest to use LWSW method also at diagnosis to obtain more comparable antibody intensity expressions when samples from the same patient are processed for MRD evaluation after bulk lysis. Moreover, LWSW can prevent nonspecific bindings, shows no differences in the identification and quantitation of the populations of interest, and reduces acquisition of cell debris.

Clinical impact of immunophenotypic remission after allogeneic hematopoietic cell transplantation in multiple myeloma.

Immunophenotypic remission (IR) is a strong prognostic factor in myeloma patients. The combination of IR and conventional CR was retrospectively evaluated in 66 patients after allografting. IR was defined as the absence of monoclonal plasma cells in BM aspirates by multiparameter flow cytometry. Conditioning was non-myeloablative in 55 patients; reduced-intensity in 10 and myeloablative in 1 patient. The allograft was given upfront in 35/66 (53%) patients. After a median follow-up of 7.1 years, 24 patients achieved both CR and IR (CR/IR group), 21 achieved IR but not CR with persistence of a urine/serum M-component (no CR/IR group) and 21 did not achieve either CR or IR (no CR/no IR group). Median OS and EFS were 'not reached' and 59 months in the CR/IR group; 64 and 16 months in the no CR/IR; and 36 and 6 months in the no CR/no IR, respectively (P<0.001). Cumulative incidence of extramedullary disease was 4.4% in the CR/IR, 38.1% in the no CR/IR and 14.3% in the no CR/no IR groups, respectively, at 4 years (P<0.001). IR was a valid tool to monitor residual disease after allografting, and allowed definition of a cohort of patients at higher incidence of extramedullary relapse.