Flow Cytometry Evaluation of T-Cell Receptor Constant Beta Chain-1 (TRBC1) Expression and Characterization of T-Cell Clones of Uncertain Significance

• Published in: Blood 2024-11, Vol.144, p.6218-6218
• Main Authors: George, Giby V., LaBarge, Tia, Burack, W. Richard, El Hussein, Siba, Wallace, Danielle S, Syposs, Chauncey R.
• Format: Article
• Language: English
• ISSN: 0006-4971
• DOI: 10.1182/blood-2024-204156

Background: Although T-cell clones may be observed as part of the normal immune response, the detection of an aberrant T-cell population often raises the possibility of a T-cell malignancy. Here, we describe the occurrence of T-cell clones of uncertain significance (T-CUS) in peripheral blood, tissue, and body fluids in patients with no documented evidence of T-cell malignancies. Methods: Expression of cell surface markers was measured using the ClearLLab 10C 10-color B-cell, T-cell, M1, and M2 panels on the Navios, Beckman Coulter flow cytometer. TRBC1 expression was assessed in CD3/TCRaβ-positive T-cells and subpopulations with abnormal CD5, CD2, CD4, CD8, CD7, and CD57 expression. Clonality was defined as the percent positivity/negativity of TRBC1 ≥80% or ≤20% in CD3/TCRaβ-positive T-cells in each subset. Relevant clinical information was obtained for all patients. All statistical calculations were performed using JMP Pro 18.0.1. The association of T-CUS with age was assessed using an unpaired two-tailed t test, while its association with other variables was evaluated using Pearson and likelihood ratio chi-square tests. Results: One hundred and seventeen samples from 108 patients (median age: 63 years [range: 2 - 96 years], 47% [51/108] female) were tested. Sample types included blood (N=72), bone marrow (N=15), lymph node (N=17), pleural fluid (N=5), cerebrospinal fluid (N=1), thyroid (N=1), breast (N=2), bone (N=2), and skin (N=2). Based on TRBC1 expression, flow cytometry identified phenotypically discrete clonal T-cell populations in 38.5% (30/78) of patients in the absence of a history of a T-cell malignancy (positive or ≥80% in six patients and negative or ≤20% in 24 patients). A median T-CUS size of 1.3% (range: 0.11-9.54%) was observed with a single clonal subset observed in the majority of patients. Polymerase chain reaction for T-cell receptor gamma rearrangement was only available for 10% (3/30) of these patients and was concordant with clonality observed by TRBC1 expression. Of the 30 patients, 40% (12/30) were diagnosed with a non-T cell malignancy, such as a B-cell lymphoma, a monoclonal B-cell population, or a myeloid malignancy. Aberrant T-cell clones were identified in 60% (18/30) of patients with non-malignant diagnoses. Of the 30 total T-cell clones, 18 (60%) were CD8-positive, 1 (3%) was CD4/CD8-double-negative, 5 (17%) were CD4/CD8-double-positive, and 6 (20%) were CD4-positive. Additional phenotyping revealed at least partial expre