Figure 1. Comparison of clonality of reactive T cells and neoplastic T cells by TRBC1 (clones JOVI.1) FITC. Left: Reactive T cells show a polytypic pattern with 42.6% of cells positive for TRBC1 and 57.4% of cells negative for TRBC1. Right: Neoplastic T cells show a monotypic pattern with 8.7% of cells positive for TRBC1. Evaluated by Wei Wang from MD Anderson Cancer Center.
TRBC1, an Addition Makes Rapid and Easy T Cell Clonality Assessment for Your Assay
T cell clonality testing has important clinical and research value. The gene rearrangement of the TCR β chain locus involves the selection of one of two mutually exclusive TRBC genes, and one of 52 TCR-Vβ genes. TCR β chain constant region is encoded by two genes, namely T-cell receptor β chain constant region 1 (TRBC1) and T-cell receptor β chain constant region 2 (TRBC2). Nonpathological polyclonal T cells express a mixture of TRBC1 and TRBC2, while malignancy T cells are usually monoclonal for one β chain constant region variant 1. Both NGS-based TCR γ PCR and Vbeta repertoire analysis are highly complex, expensive, and labor-intensive. Due to poor specificity or lack of immunophenotypic clonal characterization, it provides ambiguous information in solving clonality 2.
JOVI.1 is an antibody developed for CAR-T treatment of T-cell lymphoma, showing that the expression of TRBC1 in healthy peripheral blood samples and peripheral T-cell lymphoma is significantly different 3. Studies have also shown that 25% to 47% of peripheral blood T cells express TRBC1. Recently, several leading clinical laboratories have shown important data for clonality evaluation using JOVI.1 antibody for TRBC1 assay 4-7, proving that, compared with NGS-based TCR γ PCR or Vbeta repertoire analysis, flow cytometric TRBC1 assay can provide comparable sensitivity and specificity, but faster and lower cost. The TRBC1 test provides real-time information about the T cell clonality of T cell subsets defined by the immunophenotyping. In all tested specimens, including peripheral blood and bone marrow 4,5,7, lymph nodes7, as well as tissues and body fluids 6, the neoplastic T cell population with restricted (monotype) TRBC1 expression can be distinguished from non-neoplastic T cells.
The expression of TRBC1 in all healthy donor blood is polytypic. The ratio of TRBC1+ to TRBC1– T cells is approximately in in the range of 1:1 to 1:2 (Figure 1). According to the observations from multiple laboratories, the cut-off value of neoplasms (monotypic TRBC1 expression) on which the phenotypic distinction from background benign T-cells is >85% or <15% 5
- The expression of TRBC1 can only be assessed in CD3-positive, TCRaβ-positive T cells, therefore accurate gating of immunophenotypically distinct T-cell subsets is critical; CD4/CD8-double negative populations should be divided into subsets of α/β and γ/δ-expressing T cell.
- Flow cytometric assessment of TRBC1 expression may be used to distinguish subsets of tumors that have obvious morphological overlap with other reactive or neoplastic processes.
Limitation of TRBC1 assessment
- Surface CD3-negative neoplasms and/or TCR γ/δ positive T cells
- B cells or NK cells and Benign thymocytes
TRBC1 assessment provides an opportunity for a simplified immunophenotypic evaluation of T-cell clonality, which can be easily implemented in the clinical workflow of routine flow cytometry practice.
Panel and Materials:
T cell Panel with TRBC1