Efficacy and Safety of Denileukin Diftitox (Ontak®) in the Treatment of Cutaneous T-Cell Lymphoma (CTCL) According to CD25 Status.

Denileukin diftitox, an interleukin-2 (IL-2)-diphtheria toxin fusion protein, binds to and intoxicates cells expressing the medium (CD122, CD132) and high affinity (CD25, CD122, CD132) IL-2 receptor. Because its role in patients whose tumors tested negative for the CD25 component of the receptor had not been prospectively studied, we initiated a prospective, open label, multi-center study to evaluate the safety and efficacy of denileukin diftitox in CTCL patients according to CD25 status (CD25+ and CD25-). Patients with pathologically proven, persistent or recurrent CTCL Stages IB-IVA were treated with denileukin diftitox at a dose of 18 mcg/kg/day x 5 days every 21 days for up to 8 cycles. Expression of CD25 by tumor cells in skin biopsies was determined by IHC or flow cytometry at a central laboratory and investigators were blinded to CD25 status. Response was based on improvement in skin involvement by weighted skin assessment for lesion type (patch, plaque, tumor) and blood involvement based on quantitation of Sezary cells. Safety was evaluated based on reports of Grade 3 and 4 toxicities (NCI CTC version 2.0). Sixty-one pts were enrolled and treated with denileukin diftitox. Disease stages were: I-IIA (n=14), IIB (n=22), III (n=11) and IV (n=14). Eighteen (29.5%) had blood involvement. Fifty-seven pts completed at least one cycle of treatment and were evaluable for response. Four pts were excluded because they had Stage IVB (visceral) disease (n=2), did not have a post baseline skin assessment recorded (n=1), or did not complete the first cycle (n=1). The median number of cycles of denileukin diftitox was 4 (range 1–13). The overall response rate (CR+PR) was 53% (30/57, 95% CI 40–66%), with 2 CR. Of the 57 evaluable pts, tumor was CD25+ in 34 (70%), CD25- in 14 (25%) and unknown in 9. Response rate was similar in patients whose tumor tested CD25+ (56%, 95% CI: 39–73%), and CD25- (43%, 95% CI: 17–69%) (p=0.41). For the 61 patients the most common grade 3/4 toxicities included constitutional symptoms (11%) and metabolic/laboratory abnormalities (36%). One patient with significant cardiopulmonary disease died of myocardial infarction while on therapy. The frequency of grade 3/4 toxicities was similar in CD25+ 64% (23/36), vs CD25- 75% (12/16) (p=0.62). In conclusion, we found that 70% of the CTCL pts evaluated for this study tested CD25+ and that the response rates and safety profile of denileukin diftitox in CD25+ and CD25- patients were similar. These data support a role for denileukin diftitox in the treatment of CTCL regardless of CD25 status.