Restricted Expression of the Constant Region 1 of T-Cell Receptor β by Flow Cytometry Facilitates Detection of T-Cell Neoplasms With High Specificity but Moderate Predictive Value.

OBJECTIVES

To determine the diagnostic value of disclosing monotypic T-cell populations by expression analysis of the constant region 1 of T-cell receptor β (TRBC1) by flow cytometry, for the detection of T-cell neoplasms, in a routine hematopathology practice setting.

METHODS

A panel of antibodies ECD-CD16/PECy5.5-CD4/PECy7-CD2/APCAF700-CD7/KO-CD8/FITC-TCRγδ/PE-TRBC1/APC-CD26/APC-CD57/APC-CD30/APCH7-CD45/BV421-CD3 was applied. One thousand and twenty-nine cases investigated during 26 months were reviewed and categorized as monotypic or polytypic depending on the expression of TRBC1 in all identifiable CD3+ T-cell subsets.

RESULTS

Although TRBC1 restriction proved to be sensitive (90.7%) with a high negative predictive value (99.1%), in some T-cell neoplasms, particularly those with significant inflammation, including angioimmunoblastic T-cell lymphoma, monotypic T-cells were not detected. The specificity was high (95.6%) albeit with a modest positive predictive value (67.1%), reflecting T-cell clones of uncertain significance (T-CUS) without T-cell neoplasm. Of these clones, 53.6% exhibited a T-cell large granular lymphocytic leukemia-like phenotype, most commonly found in the peripheral blood or bone marrow, while others were identified in association with unrelated primary tumors or other comorbidities. Seventy-nine percent of the T-CUS cases remained stable over time during 1-77 months of follow-up.

CONCLUSION

Including TRBC1 antibodies in a routine flow cytometry panel facilitates the identification of T-cell neoplasms. The analysis must be interpreted within its clinical context since T-cell lymphomas with a small and sometimes surface CD3-negative neoplastic T cell population, may display normal patterns of TRBC1-expression with a background of reactive T cells. Conversely, monotypic T-cells can be found in the absence of T-cell neoplasm.