Apparent CD19 expression by natural killer cells: a potential confounder for minimal residual disease detection by...

Detection of minimal residual disease (MRD) by flow cytometry (FCM) in B lymphoblastic leukemia (B ALL) is important for guiding patient-specific clinical management. We describe apparent expression of CD19 by natural killer cells as a potential confounder in the detection of B ALL MRD by FCM. This finding was noted in seven different patient samples analyzed on different days as part of routine clinical care in our laboratory, with analysis of different anti-CD19 antibody clones and fluorochrome conjugates in five of the seven samples. Although the etiology of this finding is not clear, possibilities include true low level expression and trogocytosis. We highlight this finding to avoid potential misinterpretation when evaluating samples for MRD in patients with B lineage neoplasms, particularly in B ALL.