A cryptic case of APL

Abstract

Background: The recent discovery of a monoclonal antibody specific for TCR-Cb-1 (encoded by TCRCB1) heralded a new method for ab-T-cell clonality assessment by flow cytometry. Each ab-T-cell contains a b-chain constant region encoded by either TCRCB1 or TCRCB2. 1 Methods: Since 25 March 2021, following non-Hodgkin lymphoma immunophenotyping, selected specimens were further analysed with custom 5-colour panel tube(s) containing mouse monoclonal anti-TCR-Cb-1 (clone JOVI-1) conjugated to fluorescein isothiocyanate, anti-CD45 and additional antibodies to allow gating of T-cell populations of interest, using a stain-lysewash method. TCR-Cb-1 expression of <15% or >85% is considered clonal. Results: 24 clonality assessments were performed to date. Indications include aberrant T-cell immunophenotype (n=10), marked abnormal CD4:CD8 skewing (n=6), monitoring of established abnormal T-cell clones (n=4), mycosis fungoides staging (n=3) and T-cell lymphocytosis (n=1). In cases with negative-clonality (n=13), median TCR-Cb-1positivity was 40% (interquartile range 34-47%). Excluding lost to follow-up (n=1), clinicopathological correlation was established in 21/23 cases. Lack of correlation was secondary to clonality of uncertain significance (n=1) and sampling (n=1, aberrant immunophenotype detected only by immunohistochemistry, T-cells identified by flow cytometry lacked aberrant immunophenotype and were nonclonal). Conclusion: Concordant with published data, 1,2 our experience supports the utility of this method for establishing ab-T-cell clonality.