Restricted TRBC1 expression: A clonality marker for circulating Sézary cells

Abstract

A 56-year-old woman presented with diffuse xerotic cutaneous plaques and lymphadenopathy. Her peripheral count showed marked lymphocytosis (white cell count 31.8 10/L), mild anemia (hemoglobin 10.7 g/dl), and mild thrombocytosis (platelet count 483 10/L). A blood smear demonstrated numerous small to medium-sized lymphocytes with significantly irregular nuclei, delicately folded/ cerebriform nuclei (Sézary cells) (Image 1A). Flow cytometric immunophenotyping on blood sample showed a 62% population of neoplastic T cells with aberrant immunophenotype of CD3/CD4/ CD7 /CD8 /CD25 /CD26 /TCRαβ/TCRγδ and restricted TRBC1 expression (in contrast to normal T cells with polytypic expression pattern, Image 1B). Polymerase chain reaction (PCR) analysis revealed a monoclonal T-cell receptor gamma gene rearrangement. Serology for HTLV-1 was negative. A concurrent skin biopsy displayed a CD4 positive T cell lymphoma with the similar immunophenotype. The overall findings are diagnostic of Sézary syndrome involving peripheral blood and skin. Use of an antibody against T-cell receptor β constant region 1 (TRBC1) has recently been described to assess clonality of TCRαβ T cell subsets, as T cells randomly express one of two mutually exclusive T-cell receptor β constant (TRBC) regions, TRBC1 or TRBC2. This novel strategy of detecting T-cell clonality, analogous to the assessment of κand λ-immunoglobulin light chains in B-cell lymphoma, is useful in diagnosis of Sézary syndrome,