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Sezary's cell Volume 8, issue 4, Juillet - Août 2002

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Authors
Service de dermatologie et Inserm U. 448, hôpital Henri-Mondor et université Paris-XII (IM3), 94010 Créteil, France.

The Sezary's cell is a lymphocyte with a convoluted, cerebriform nucleus on cytomorphologic and ultrastructural samples. It is a major diagnostic feature of Sezary's syndrome, clinically defined by the rapid onset of a pruriginous erythroderma with diffused adenopathies. Sezary's cells can also reveal blood involvement by tumor cells in patients with mycosis fungoides. Large-size Sezary's cells are suggestive of the diagnosis of T-cell lymphoma. In contrast, small-size Sezary's cells lack specificity and can be found in other types of erythrodermas (eczemas, drug reactions). Most Sezary's cells have a phenotype of mature memory T-lymphocytes, CD2+, CD3+, CD4+, CD5+, CD8-, CD45RO+, CD45RA-, TCR alpha/beta+, but rarely they can also exhibit a CD8+CD4- or CD4+CD8+ phenotype, and/or a lack of expression of CD2, CD3, CD4 or CD5 antigens. Patients with a Sezary's syndrome often have an increase in CD4+ lymphocytes, resulting in a CD4/CD8 ratio usually exceeding 10. The CD4+CD7- population is also increased, but tumor cells have been identified both in the CD4+CD7+ and in the CD4+CD7- populations. Sezary's cells are found in the CD4+CD26- population, but there are yet no discrete phenotypic markers of Sezary's cells. IL-7 and IL-15 are growth factors for Sezary's cells, and can induce the establishment of long-term tumor T-cell lines. We recently identified three other surface antigens on Sezary's cells. The natural killer (NK) receptor CD158k/KIR3DL2/p140, normally expressed by NK and CD8+ T-cells was detected on the surface of CTCL cell lines as well as on freshly isolated CD4+ peripheral blood lymphocytes from SS patients. SC5 is a newly described activation-related intracellular inhibitory receptor expressed on the surface of a minor PBL subset. We found that SC5 expression was significantly increased in SS cells and correlated to p140 expression. ILT-2/CD85j is another inhibitory receptor expressed by tumor T-lymphocytes. Both SC5 and ILT-2 molecules are functional on CTCL cells, as their triggering in vitro leads to the recruitment of SHP-1 and to the specific inhibition of CTCL malignant cell proliferation induced by CD3/TCR stimulation. The expression of these antigens and the cytokine-induced upregulation of bcl-2 could partly explain the survival and the inhibition of the apoptosis of Sezary's cells. Their identification on circulating SS tumor cells might be of importance both for the understanding of CTCL pathophysiology and for the treatment of SS patients.