Introduction
Distinguishing benign T-cell populations from malignant T-lymphoproliferative disorders (T-LPDs) is challenging. Limitations of molecular T-cell receptor (TCR) gene rearrangement studies include longer turnaround time, reduced sensitivity and increased cost. The flow cytometric method of TCR clonality assessment by Vβ specificities is complex and costly.
During TCR gene rearrangement, alpha/beta T-cells randomly select one of two beta constant genes, either TRBC1 or TRBC2. TRBC1 expression can be detected by flow cytometry. Marked alteration to the ratio of TRBC1 positive and negative cells can be utilized to detect monoclonal T-cell populations. We compared the TRBC1 expression with molecular TCR studies in T-LPD evaluation.
Method
Thirteen patient samples comprising peripheral bloods, bone marrows and tissues with either elevated T-cell counts or aberrant T-cell immunophenotypes were tested for comparison of TRBC1 expression with molecular TCR studies. Fifty-six normal samples were included as controls as a verification cohort. TRBC1 expression was evaluated on CD4 and CD8 subsets and on aberrant T-cell populations. TRCB1 >85% or <15% expression was considered as monoclonal expansion in accordance with published literature.
Results
Control samples demonstrated the normal TRBC1 expression (CD4 T-cells mean 50%, range 35-61% and CD8 T-cells mean 38%, range 22-55%). These samples therefore fell within the cut-off range 15-85%. Of the 13 patient samples, 9 showed evidence of monoclonality by both TRBC1 and molecular TCR studies, while 2 were negative by both methods. Two samples had discrepant results with absence of monoclonal TRBC1 ratios but demonstrating monoclonality in a polyclonal background by molecular TCR studies. This could be attributed to an oligoclonal expansion of the TCR repertoire, a limitation of this flow cytometric assay.
Conclusion
TRBC1 flow cytometric immunophenotyping is a simple rapid method to identify monoclonal T-cell populations and aid diagnosis of T-LPDs.