Clinical benefit of TTI-621 in Sézary syndrome is accompanied by a decrease in circulating clone of Sézary cells. (A) Percentage change in clonal (Vβ⁺) CD4 cells in patients with Sézary syndrome (n = 5) who received a single dose of TTI-621. Comparison between day 1 pretreatment and 8 days after infusion. (B) Decrease in lactate dehydrogenase (LDH; right y-axis, blue) and absolute lymphocyte count (ALC; left y-axis, red) during treatment with TTI-621 (a representative patient). (C) A 52-year-old man with stage IVA1 (T4N1M0B2) SS enrolled in phase 1a of clinical trial NCT02663518. Images taken at screening and week 4 on study.