Flow Cytometric Clonality Analysis in T Cells

The current WHO classification describes numerous T-lymphatic neoplasms, the diagnostic classification of which remains challenging. In addition to flow cytometry, histopathological, genetic, clinical, and infectious disease parameters are often taken into account. Because flow cytometry provides rapid results, it is frequently employed at the outset of the diagnostic evaluation to guide subsequent testing.

Various antigens are analyzed to diagnose abnormal T-cell populations. These include typical T-cell markers, such as CD2, CD4, CD5, CD7, and CD8. Additionally, the T-cell receptor α/β (TCR α/β), which is expressed on most CD4+ and CD8+ T cells, and its subunit CD3ε are examined. Other markers help distinguish them from other leukocyte populations, such as natural killer (NK) cells.

Unlike the analysis of mature peripheral B cells, determining clonality in T cell populations has only been possible through complex specialized tests in routine diagnostics. Detection is often carried out using molecular biological methods, which are more time-consuming, costly, and, in some cases, less sensitive than flow cytometric methods.

During T cell development, TCR-α/β T cells express either the TRBC1 or TRBC2 chain in the constant region of their T cell receptor. In a healthy T cell pool, both variants are found in roughly equal proportions, similar to the kappa/lambda distribution in B cells.

Antibodies specific to TRBC1 and TRBC2, originally developed for therapeutic applications, can now be used for diagnosis in flow cytometry. This enables the quick and reliable distinction of polyclonal T-cell populations from clonal, potentially neoplastic T-cell populations.

However, the presence of a clonal T-cell population does not necessarily indicate malignant disease. Follow-up examinations and additional tests, such as histopathological or genetic analyses, are necessary to determine the clinical significance in such cases.