RecruitingDevice studyExtracorporeal Photopheresis in Sezary SyndromeThe primary endpoint is to determine if ECP induces a decrease in % of tumor cells after treatment. 20 patients with Sezary Syndrome will receive ECP weekly x4, then bi-weekly for 5 months. Each patient will donate 5 samples to determine immune responses in peripheral blood. Additional clinical assessments will be a modified skin weighted assessment and flow cytometry at baseline and months 3 and 6. A CT scan will be obtained at baseline and only repeated if pathology is present at baseline. The tumor microenvironment will be studied by comparing transcriptomics of the blood samples before, 1 day after first ECP treatment, cycle 1, 1, 3 and 6 months after ECP treatment by scRNAseq (5 samples total per patient ).