CD25 expression is correlated with histological grade and response to denileukin diftitox in cutaneous T-cell lymphoma.

Denileukin diftitox (Ontak), a recombinant fusion protein of diphtheria toxin and ligand, IL-2, binds to the IL-2 receptor, is internalized, and causes cell death. Denileukin diftitox was approved for the treatment of cutaneous T-cell lymphomas (CTCLs) with CD25+ expression. We prospectively stained lesional skin biopsy specimens from 113 mycosis fungoides and Sézary Syndrome patients for activation markers CD25 and CD30 to correlate expression with clinical tumor-node metastasis (TNM) stage, histologic grade, and response to denileukin diftitox. High expression was defined as positivity of > or =20% of lesional T-cells using immunohistochemistry (IHC). CD25 and CD30 expression was more common in lesions from advanced patients (P = 0.04 and 0.002, respectively). Advanced TNM (T3 or T4) was significantly associated with intermediate-grade (P = 0.002) and large-cell transformation histology (P = 0.04). Of interest, clinical responses were observed in 78.5% of patients with high CD25 expression versus 20% with low to undetectable CD25 expression (P = 0.01) among 24 patients receiving standard 5-day infusions of denileukin diftitox at 18 microg/kg/day. These data suggest that high CD25 expression by IHC is associated with advanced CTCL and with clinical response to denileukin diftitox therapy.