T-cell Receptor (TCR)-Vβ Repertoire Flow Cytometry for T-cell Lymphoproliferative Disorder: a Retrospective Analysis of a Single-Center Real-Life Laboratory Experience.

Background: Discrimination between clonal and reactive cell proliferation is critical for the correct management of T-cell lymphocytosis. Multiparametric flow cytometry (MFC) represents a valuable tool, particularly because it allows the evaluation of the T-cell receptor (TCR) Vβ repertoire to pinpoint eventual clonality in T-cell lymphocytosis. A restricted expansion of a single out of the 24 evaluable families or a "clonogram-off" pattern is highly suggestive of the presence of a clonal T-cell population. However, data available on the concordance between MFC TCR-Vβ repertoire and molecular analysis of TCR gene rearrangements, which is regarded as the gold standard for assessing T-cell clonality, are limited.

Objective And Methods: We performed a retrospective monocentric study involving 307 patients referred to our center for lymphocytosis between 2003 and 2024. The aim of our study was to investigate the diagnostic accuracy of MFC TCR-Vβ repertoire analysis and compare its performance with molecular analysis of TCR gene rearrangements for the identification of T-cell clonality.

Results: In clonally restricted cases, MFC TCR-Vβ repertoire analysis demonstrated a restricted expansion of a single Vβ family in 67.5% of cases, while a "clonogram-off" pattern inferred clonality in the remaining 32.5%. For 215 (70%) patients, both MFC TCR-Vβ repertoire analysis and molecular analysis of TCR gene rearrangements were available, showing an absolute concordance (215 out of 215 cases, 100%) between the two methods.

Conclusion: MFC TCR-Vβ repertoire analysis is a rapid, cheap, sensitive, and reliable tool to identify clonal T-cell lymphocytosis. It represents an absolutely valid first-line diagnostic approach, and it should be included in the routine laboratory work-up performed on MFC analysis for peripheral lymphocytosis.