The expression of CADM1/TSLC1 in leukemic cutaneous T-cell lymphoma: A possible diagnostic marker for Sézary syndrome

Cell Adhesion Molecule 1 (CADM1/TSLC1) is known to be expressed in adult T-cell leukemia/lymphoma (ATLL) cells as well as other cancer cells. To explore a potential biomarker for primary cutaneous T-cell lymphoma (CTCL), we examined the CADM1/TSLC1 expression in leukemic cells from three patients with Sézary syndrome (SS), and three cell lines established from patients with mycosis fungoides (MF)/SS. As a control, we examined the expression in four and two cell lines derived from anaplastic large cell lymphoma (ALCL) and ATLL, respectively, normal peripheral blood mononuclear cells (PBMCs), and reactive lymphocytosis in patients with mycosis fungoides (MF) (n = 9) and non-CTCL erythroderma (n = 4), including actinic reticuloid, non-clonal CD8+ T-cell atypical lymphocytosis, drug- induced erythroderma, and erythroderma of unknown etiology. In all three patients with SS, the CADM1/TSLC1+ cells were increased to 65.1%, 38.0% and 74.5% in the CD3+CD4+ cell fractions, respectively, but absent or a background level in normal PBMCs and reactive lymphocytosis. In conventional Sézary cell markers, the CD4+CD7- and CD4+CD26- cells were observed in 82.7% and 97.7%, 9.6% and 92.4%, and 84.0% and 83.6%, respectively, in the three patients. In the cell lines examined, the CADM1/TSLC1+ cells ranged from 8.0 to 99.7% and 11.3 to 22.4% in the MF/SS- and ATLL-derived cell lines, respectively, whereas they ranged from 1.3 to 7.5% in the ALCL cell lines. These results indicate that the CADM1/TSLC1 is expressed frequently in the leukemic cells of MF/SS and ATLL, and suggest that the CADM1/TSLC1 is an additional diagnostic marker for the B2 criteria of leukemic CTCL, or Sézary syndrome, and might be a therapeutic target.