title: The relevance of the CD4+ CD26- subset in the identification of circulating Sézary cells.
abstract: BACKGROUND
  The lack of specific markers for the phenotyping of circulating neoplastic T cells in Sézary syndrome (SS) patients makes it difficult both to ascertain the presence of clonal cells and to quantify the tumour burden in the peripheral blood. In previous reports we showed that the lack of CD26 (dipeptidyl-aminopeptidase IV) is a characteristic feature of circulating Sézary cells (SC).
  
  
  OBJECTIVE
  The purpose of this study was to ascertain, by means of high-resolution two-, three- or four-parameter flow cytometry, the relationship between CD26 expression on peripheral blood lymphocytes and peripheral blood involvement in cutaneous T-cell lymphoma patients and to assess its significance in SS diagnosis.
  
  
  METHODS
  The patient population included 52 SS patients, 151 mycosis fungoides (MF) patients at different clinical stages (including 14 with blood involvement, B1-MF), 88 patients with erythrodermic inflammatory skin diseases (EISD) and 72 healthy donors (HD). CD26+ values were available in all cases, whereas CD4+ CD26- level measurement was performed in 23 SS, 141 MF, 71 EISD and 72 HD.
  
  
  RESULTS
  CD4+ CD26- percentage values were higher than 30% in all but one B1-MF and higher than 40% in all SS cases, whereas HD, EISD and B0-MF patient values were always lower than 30%. A statistically significant difference was found in both CD26- and CD4+ CD26- percentage and absolute values between SS and HD, EISD and B0-MF patients. The CD26- and CD4+ CD26- percentage values (but not the absolute values) were significantly higher in B1-MF compared with HD, EISD and B0-MF patients (P < 0.001). Moreover, CD26- absolute values and CD4+ CD26- percentage and absolute values were significantly higher in SS than in B1-MF (P < 0.001). A statistically significant direct relationship was found between CD4+ CD26- percentage values and the percentage of circulating SC within the lymphoid population in SS and B1-MF (r = 0.77; P < 0.001). The lack of CD26 was confirmed on phenotypically clonal cells in patients with an expanded circulating TCRvbeta population or a T-cell antigen loss. Sorted CD4+ CD26- cells from both SS patients and HD showed the characteristic cerebriform nuclei of SC.
  
  
  CONCLUSIONS
  We feel that a CD4+ CD26- percentage value higher than 30% of peripheral blood lymphocytes could correctly identify the presence of peripheral blood involvement in SS and MF patients.
authors.affiliation: Department of Medical and Surgical Specialities, First Dermatologic Clinic, University of Turin, Via Cherasco 23, 10126 Torino, Italy. bernengo@ddmc.unito.it
authors.forename: M G
authors.initials: MG
authors.lastname: Bernengo
authors.forename: M
authors.initials: M
authors.lastname: Novelli
authors.forename: P
authors.initials: P
authors.lastname: Quaglino
authors.forename: F
authors.initials: F
authors.lastname: Lisa
authors.forename: A
authors.initials: A
authors.lastname: De Matteis
authors.forename: P
authors.initials: P
authors.lastname: Savoia
authors.forename: N
authors.initials: N
authors.lastname: Cappello
authors.forename: M T
authors.initials: MT
authors.lastname: Fierro
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D014408:Biomarkers, Tumor / Q000097:blood*; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology / Q000648:ultrastructure; D002467:Cell Nucleus / Q000648:ultrastructure; D003937:Diagnosis, Differential; D018819:Dipeptidyl Peptidase 4 / Q000097:blood*; D005260:Female; D005434:Flow Cytometry; D006801:Humans; D016130:Immunophenotyping / Q000379:methods; D018655:Lymphocyte Count; D008297:Male; D008875:Middle Aged; D009182:Mycosis Fungoides / Q000276:immunology; D012751:Sezary Syndrome / Q000175:diagnosis* / Q000276:immunology; D012878:Skin Neoplasms / Q000175:diagnosis* / Q000276:immunology; D016176:T-Lymphocyte Subsets / Q000276:immunology / Q000648:ultrastructure
chemical_list: D014408:Biomarkers, Tumor; D018819:Dipeptidyl Peptidase 4