Sé zary syndrome (SS) is a rare form of cutaneous T-cell lymphoma (CTCL) characterized by a distinct metastatic pattern mainly involving blood and skin. Chemokines and their receptors play a critical role in cellular recruitment and homing to tissues and in the metastatic process of several tumors including non-Hodgkin Tcell lymphomas (NHLs). Here we report that SS cells express a functionally active CXCR4 and that its ligand SDF-1 is abundantly produced in the skin, which represents the main destination of SS cell spreading. SDF-1 is normally inactivated by proteolytic cleavage by the CD26/ dipeptidylpeptidase IV (DPPIV). The lack of CD26 from the cell surface is a hallmark of circulating SS cells. We also show that the CD26 ؊ phenotype is maintained also in skin-infiltrating neoplastic T lymphocytes and that SS-affected individuals exhibit a reduced activity of plasma soluble CD26. Finally, we observe that the addition of soluble CD26 reduces the migratory response of SS cells to SDF-1 whereas the inhibition of the CD26 peptidase activity in Hut78, a CD26 ؉ CTCL cell line, enhances the SDF-1-induced migration of these cells. Our findings suggest that the SDF-1-CXCR4 axis could play an important role in skin homing of SS through the regulatory activity of CD26. IntroductionCutaneous T-cell lymphomas (CTCLs) are a heterogeneous group of non-Hodgkin lymphomas (NHLs) that show a considerable variability in clinical presentation, histology, immunophenotype, and prognosis. They represent a clonal malignancy 1 of CD4 ϩ helper T cells 2,3 with a memory phenotype 4 and tendency to accumulate in the skin. 5 Mycosis fungoides (MF) and Sézary syndrome (SS) are the 2 major clinical variants of CTCLs. While MF shows a skinrestricted infiltration of the clonal T-cell population and an indolent course, SS is a leukemic and erythrodermic variant of CTCL characterized by the presence of tumor lymphocytes in the skin, lymph nodes, and peripheral blood. These tumor cells, named SS cells, have major abnormalities like a low mitotic index, aberrant but nonuniform chromosomal alterations, 6 monoclonal rearrangement 7 with a loss of T-cell receptor repertoire complexity 8 and loss of surface molecules such as CD7, CD26, and CD49d. 9-11 SS cells mainly localize to the skin and express cutaneous lymphocyteassociated antigen (CLA) that has been implicated in skin-specific homing patterns. 4,9 However, the mechanisms underlying the accumulation of these atypical lymphocytes to the skin are poorly defined. Extravasation and active locomotion of malignant lymphocytes could suggest the involvement of secreted factors such as chemokines. Chemokines regulate multiple cell functions, including cell chemotaxis, proliferation, and apoptosis, and are involved in leukocyte transendothelial migration and homing to tissues.These biologic activities are mediated through their interaction with G protein-coupled chemokine receptors expressed by target cells such as leukocytes, hematopoietic cells, neuronal cells, glial cells, and cells of the vasculat...

Key Points• PTEN is downregulated in Sézary syndrome by different mechanisms, mostly by gene deletions and microRNAs.• PTEN deficiency activates AKT in skin resident but not circulating Sezary cells.Sézary syndrome (SS) is an incurable leukemic variant of cutaneous T-cell lymphoma characterized by recurrent chromosomal alterations, among which, chromosome 10q deletion is very frequent. In this study, we investigated the PTEN status, on locus 10q23, in 44 SS patients; our findings show that PTEN is deleted in 36% of SS cases, whereas PTEN downregulation is observed in almost all of the samples evaluated by quantitative reverse-transcriptase polymerase chain reaction and Western blotting analysis. Neither DNA sequence mutation nor promoter hypermethylation were found at the PTEN locus, but we demonstrate that PTEN level can be also reduced by a group of miRs previously found upregulated and of prognostic relevance in SS; particularly, miR-21, miR-106b, and miR-486 were able to control PTEN abundance either in vitro or in vivo. Finally, because reduced PTEN activates the PI3/AKT-mediated pathway of cell growth and survival, we demonstrate that PTEN deficiency is associated with activated AKT in skin resident but not circulating SS cells, suggesting that the cutaneous milieu may strongly contribute to the SS cell growth. To our knowledge, this is the first study fully exploring the PTEN status in a large cohort of SS patients, unveiling potential elements of clinical utility in this malignancy. (Blood. 2013; 122(20):3511-3520)

Sézary syndrome (SS) is a rare and aggressive variant of Cutaneous T-Cell Lymphoma characterized by neoplastic distribution mainly involving blood, skin, and lymph-node. Although a role of the skin microenvironment in SS pathogenesis has long been hypothesized, its function in vivo is poorly characterized. To deepen this aspect, here we compared skin to blood-derived SS cells concurrently obtained from SS patients highlighting a greater proliferation-index and a PI3K/AKT/mTORC1 pathway activation level, particularly of mTOR protein, in skin-derived-SS cells. We proved that SDF-1 and CCL21 chemokines, both overexpressed in SS tissues, induce mTORC1 signaling activation, cell proliferation and Ki67 up-regulation in a SS-derived cell line and primary-SS cells. In a cohort of 43 SS cases, we observed recurrent copy number variations (CNV) of members belonging to this cascade, namely: loss of LKB1 (48%), PTEN (39%) and PDCD4 (35%) and gains of P70S6K (30%). These alterations represent druggable targets unraveling new therapeutic treatments as metformin here evaluated in vitro. Moreover, CNV of PTEN, PDCD4, and P70S6K, evaluated individually or in combination, are associated with reduced survival of SS patients. These data shed light on effects in vivo of skin-SS cells interaction underlying the prognostic and therapeutic relevance of mTORC1 pathway in SS.