397 Real World Utilization of Paired TRBC1/TRBC2 by Flow Cytometry in Identification of Clonal T-Cells

Introduction/Objective T-cell receptor (TCR) beta chains (TRBC1/TRBC2) are isoforms of the αβ TCR, with only one isoform expressed on individual T-cells. There is a characteristic TRBC1/TRBC2 ratio in healthy individuals making TRBC1 and TRBC2 specific diagnostic markers for T-cell clonality. Methods/Case Report TRBC2(SAM5.2)/BV421 antibody was custom manufactured by BDBiosciences and added to our 10-color single tube T-cell clonality panel. The panel consists of TRBC1/FITC, TcRγδ/PE, CD5/PerCP-Cy5.5, CD3/PE-Cy7, CD7/APC, CD8/APC-H7, CD56/APC-R700, CD4/BV605, CD45/V500-C, and TRBC2/BV421, allowing gating of CD3+/αβ+ T-cells, exclusion of TcRγδ T-cells and NK cells, and simultaneous evaluation of TRBC1/TRBC2 expression. 57 samples (blood, bone marrow, vitreous) specimens were analyzed on the 12-color FACSLyric flow cytometer with FACSuite software. Results Of 57 samples, 85.96% were polyclonal, 10.52% showed a T-cell clone of uncertain significance (TCUS), and 3.51% showed a clonal T-cell malignancy. In clonal T-cell samples, 50% were TRBC1 and 50% were TRBC2. Polyclonal samples showed TRBC2 /TRBC1 ratio of 0.761-2.824 (mean 1.655, SD 0.481) in CD3+ TCR αβ T-cell, 0.680-2.677 (mean 1.574, SD 0.449) in CD4+ T-cells, and 0.596-6.114 (mean 1.954, SD 1.008) in CD8+ T-cells. Conclusion The combination of TRBC2/TRBC1 by flow cytometry in multiple specimens is useful in evaluating TCUS and clonal T-cell populations.