A novel flow cytometric assay for detection of residual disease in patients with B-lymphoblastic leukemia/lymphoma post anti-CD19 therapy.

BACKGROUND: Residual disease detection following therapy is an important prognostic variable in B-lymphoblastic leukemia (B-LL). Most flow cytometric strategies for detecting B cell malignancy utilize CD19 to identify B cells. With growing use of anti-CD19 targeted therapies, alternative strategies are needed for residual disease detection. We describe an approach for residual disease detection in this setting. METHODS: A novel combination was designed using expression of CD22 or CD24 (without CD66b) for B cell detection in combination with markers aberrantly expressed in B-LL (CD10, CD20, CD34, CD38, and CD45). The performance characteristics of this combination were evaluated and compared to a standard, validated B-LL MRD assay using 10 known negative samples, 10 overtly positive samples, and 11 post-therapy samples (prior therapy other than anti-CD19 therapy). Subsequently, results from the first 100 samples on which the new tube was performed were reviewed. RESULTS: The described combination performed well in the initial analysis of 31 samples with all negative and positive samples correctly classified. In positive samples, the percentage of abnormal cells correlated well between the standard and new assay. Evaluation of the first 100 samples demonstrated good performance with adequate detection of CD19-positive and CD19-negative B-LL. Additionally, it was observed that patients receiving anti-CD19 therapies demonstrate an increased proportion of CD19-negative progenitors. CONCLUSIONS: These preliminary findings describe a strategy that performs well for residual disease detection in B-LL post anti-CD19 therapy. Such alternative strategies will become more important as the use of targeted immunotherapies becomes more common. © 2016 International Clinical Cytometry Society.

Expression of CD2 and CD25 on mast cell populations can be seen outside the setting of systemic mastocytosis.

BACKGROUND: Systemic mastocytosis (SM) is a diagnosis made using clinical, laboratory, and histologic parameters. Aberrant CD2 and/or CD25 expression on mast cells provides one minor criterion for a diagnosis of SM. To validate a tube (CD45/CD117/CD2/CD25) for mast cell evaluation, flow cytometry (FC) on residual material from marrow aspirates samples submitted to the hematopathology laboratory was performed. METHODS: Samples evaluated (n = 98) had no clinical or morphologic suspicion for SM. Samples were excluded if there was history of a myeloid stem cell neoplasm. Ten documented cases of SM were evaluated for comparison. RESULTS: Among cases without history of SM, 17.3% (n = 17) showed expression of CD2 and/or CD25 on ≥10% of the mast cell population (CD25 alone in 14 cases, CD2 alone in 2 cases, both in one case), while 82.6% (n = 81) showed no expression of these antigens. The percentage of mast cells showing aberrant CD2 and/or CD25 expression respectively ranged from 12.1% to 98.8% and 22.2% to 95.7% Interestingly, all of the cases with evidence of aberrant antigen expression on mast cells were collected post-therapy while 22.1% of the negative samples were collected pre-therapy. A cut-off of 60% CD25 expression on mast cells identified all cases of SM while minimizing false positives. CONCLUSIONS: These findings demonstrate that aberrant expression of CD2 and/or CD25 may be seen on mast cells outside of the setting of SM. The data suggests that this phenomenon may be seen more commonly following chemotherapy and that FC of mast cells should be interpreted with caution in the post-chemotherapy setting. © 2015 International Clinical Cytometry Society.