An evaluation of denileukin diftitox for the treatment of relapsed or refractory cutaneous T-cell lymphoma.

Denileukin difitox (DD), a recombinant cytotoxic fusion protein composed of full-length human interleukin-2 (IL-2) conjugated to diphtheria toxin's A and B subunits, has shown activity in patients with relapsed and refractory (R/R) mycosis fungoides and the Sezary Syndrome (MF/SS) whose tumor cells expressed CD25, with response rates of 30-44% in advanced and earlier (Stage I-III) stage patients respectively. Recently a newer version of DD with improved purity and bioactivity (DD-cxdl) was developed. A registrational trial of D-cxdl showed similar response rates in R/R MF/SS. The purpose of this review is to describe efficacy and safety data surrounding these medications and highlight the equivalency of these two drugs. Both DD and DD-cxdl demonstrate activity in R/R MF/SS with higher response rate in tumor and plaque stage disease. Adverse events grade ≥ 3 included infusion reactions in 8%, elevated hepatic transaminases in 22%, and capillary leak syndrome in 8%. In addition to direct targeting of CD25 expressing tumor cells, both drugs are also capable of depleting immunoregulatory T-cells. A clinical trial of DD-cxdl in Japan showed that responses were independent of CD25 expression, suggesting multiple mechanisms of action for DD-cxdl in MF/SS and potentially other malignancies.