Abnormalities by Multicolor Flow Cytometry for Detection of Minimal Residual Disease in Recipients of Allo-HSCT Originating from Donors: A Cohort Study

OBJECTIVE: In minimal residual disease (MRD) analysis after allogeneic hematopoietic stem cell transplantation (allo-HSCT), abnormal immunophenotyping is commonly considered as evidence of a secondary recurrence or complications, leading to overtreatment. We aimed to confirm whether such phenotypic abnormality might originate from donors using multicolor flow cytometry (MFC). MATERIALS AND METHODS: The MRD of bone marrow specimens of 3395 patients who had received allo-HSCT were analyzed using the conventional two-tube, eight-color MFC panel. The frequencies of abnormal immunophenotypes were also evaluated in three groups of patients without malignancies. RESULTS: The frequency of new abnormal polymorphisms was 0.088% (3/3395) among patients who received allo-HSCT. The abnormal cells seen in three patients in complete remission were Fcγ receptor IIIB (FcγRIIIB) gene deletion (CD16- neutrophils), CD2-CD159a(-)CD159c(+) natural killer (NK) cells, and monoclonal B lymphocytosis (MBL), respectively. In addition, abnormal T-cells (CD4(+)CD8(+)) were detected in one donor before allo-HSCT. Identical abnormalities were found in the peripheral blood of the corresponding donors of the three patients via MFC. Among the individuals without malignancies, the incidence of FcγRIIIB deletion was 0.2% (11/5256), that of NK cells with the absence of CD2 and single-positive CD159c was 0.05% (1/2000), that of monoclonal CD4/CD8 double-positive T-cells was 0.05% (1/2000), and that of MBL was 1.3% (14/1100). The frequency of NK cells with the absence of CD2 was 1.3% (1/79) and with CD8dim was 14% (11/79) in NK cell lymphoma. The following abnormalities could be identified by the two-tube, eight-color MFC panel: cκ/cλ/CD19/CD5/CD20/CD38/CD45/CD56 (adding CD10 and CD34 as the ninth and tenth colors) and CD16(+)CD56/CD5/CD3/CD7/CD4/CD8/CD2/CD45 (adding CD117 as the ninth color). CONCLUSION: Abnormalities in recipients of allo-HSCT detected by MRD analysis may originate from their donors. Screening of donor specimens with a suitable two-tube, eight- to ten-color MFC panel may be a promising method for minimizing misdiagnoses.