CD4+CD7- T cells compose the dominant T-cell clone in the peripheral blood of patients with Sezary syndrome

Background: Absence of CD7 antigen expression in T cells defines a subset of normal CD4(+) CD45RO(+) CD45RA(-) memory cells and is furthermore observed in Sezary syndrome (SS). Objective: Our purpose was to identify circulating T-cell clones in patients with SS and to elucidate whether the dominant T-cell clones express the CD7 antigen. Methods: Peripheral blood lymphocytes of patients with SS were analyzed by two-color flow cytometry using antibodies to the V beta region of the T cell receptor (TCR) in combination with an antibody to CD7. In addition, T cells were analyzed for TCR-gamma gene rearrangement by polymerase chain reaction (PCR) techniques. Results: Clonal T-cell expansion was detected in 7 patients with SS by immunostaining of the TCR VP regions. PCR analysis confirmed the presence of dominant T cell clones. Double-immunostaining revealed that in each case cells of the clonal V beta TCR rearrangement homogeneously express the CD4(+)CD7(-) phenotype. Furthermore, CD4(+)CD7(-) cells express the CD15s antigen but lack expression of CD26 and CD49d. Conclusion: Expansion of clonal T cells strongly correlates with the expansion of CD4(+)CD7(-) T cells in 7 tested patients with SS. This supports our model that a subset of late differentiated, normal CD4(+)CD7(-) memory T cells may represent the physiologic counterpart of Sezary cells. Monitoring of circulating T cells with the CD4(+)CD7(-)CD15s(+)CD26(-)CD49d(-) phenotype proved to be useful for the identification of clonal T cells in patients with SS.