TCR-Vβ flow cytometric analysis of peripheral blood for assessing clonality and disease burden in patients with T cell large granular lymphocyte leukaemia

Aims: T cell large granular lymphocytes (T-LGLs) are commonly increased in reactive conditions as well as T-LGL leukaemia. This differential diagnosis often requires a combined assessment of clonality and tumour burden. In this study we assessed the utility of flow cytometric (FC) analysis of T cell receptor β chain variable region (TCR-Vβ) expression by using 24 antibodies reactive to 70% of the TCR-Vβ repertoire. Methods: Analyses were performed on peripheral blood samples obtained from 20 patients with a confirmed diagnosis of T-LGL leukaemia and 18 patients without known T cell lymphoproliferative diseases. Results: The results were compared with TCR gene rearrangement status assessed by PCR. By FC analysis, 19/20 T-LGL leukaemia cases were CD3+CD8+ and one case was CD3+CD4+. All the cases demonstrated at least one immunophenotypic aberration, with altered CD5 expression being most frequent. Abnormal Vβ expression was detected by FC in 19 of 20 (95%) T-LGL leukaemia cases, but in none of the controls; this showed 100% concordance with TCR gene rearrangement studies. In addition to establishing clonality, FC Vβ analysis enables calculation of absolute numbers of clonal T cells; this is important in monitoring tumour burden after treatment. Conclusions: It is concluded that FC Vβ analysis is a fast, reliable and quantitative method that can simultaneously assess T-LGL leukaemia clonality and tumour burden.