Although the etiology of CTCL is not fully understood, it is believed to be a malignancy proliferation of a "memory" T-cell in the context of Th2-type cytokine profile and suppressed cytotoxic T-cell (CTL) immunity. T-regulatory (T-regs) cells may be important in CTCL in the setting of immunotherapy. Removal of T-regs would result in enhanced immune responses in vitro, which may translate into augmentation of the anti-tumor immune response and durable clinical responses in vivo. We propose to evaluate effects of ONTAK on the T-reg cell subset in patients undergoing routine therapy with ONTAK. We will evaluate T-reg subsets in peripheral blood and tumor tissues from the patients both phenotypically using multi-color FACS analysis and confocal microscopy, and functionally in MLRs and ELISpot assays with baseline, day 5 and 19 blood samples in up to four cycles.

Inclusion Criteria:

• 18 and older
• diagnosed with CTCL
• able and willing to provide informed consent
• will be receiving denileukin diftitox per standard guidelines

Exclusion Criteria:

• prior history of receiving Ontak
• pregnancy