Usefulness of KIR3DL2 to Diagnose, Follow-Up, and Manage the Treatment of Patients with Sézary Syndrome.

KIR3DL2 is a recently discovered marker of the malignant clonal cell population in Sézary syndrome. We intended to evaluate the expression of KIR3DL2 on blood T cells as a diagnostic, prognostic, and follow-up marker of Sézary syndrome. Sixty-four patients diagnosed with Sézary syndrome were included in this monocentric study. We collected the percentage of KIR3DL2 cells among CD3 T cells, obtained by flow cytometry, and other classical diagnostic criteria for Sézary syndrome at diagnosis and during the follow-up. Compared with the classical diagnostic factors, KIR3DL2 was the most sensitive diagnostic factor for Sézary syndrome. Univariate and multivariate analyses established that an eosinophil cell count >700/mm and a percentage of KIR3DL2 cells within the CD3 T cells >85% at diagnosis were associated with a significantly reduced disease-specific survival. Moreover, KIR3DL2 immunostaining allowed the assessment of treatment efficiency and specificity toward tumor cells, the detection of the residual disease following treatment, and the occurrence of relapse, even though patients clinically experienced complete remission and/or undetectable circulating Sézary cells by cytomorphologic analysis. We show that KIR3DL2 expression is the most sensitive diagnostic criterion of Sézary syndrome when compared with all other available biological criteria. It also represents the best independent prognostic factor for Sézary syndrome-specific death and the most relevant feature for the follow-up of Sézary syndrome, showing the invasion of the functional lymphocytes pool by Sézary cells. KIR3DL2 therefore represents a valuable tool for routine use as a clinical parameter at diagnosis, for prognosis and during patient follow-up. .