SD-4 on CTCL cells or PBMCs of patients with SS inhibits their anti–CD3 response following binding to DC-HIL. HuT-78 (A), HH cells (B), or PBMCs (C-D) from 2 patients with SS (Pt. 2 and Pt. 3A with Vβ⁺ cells at 98%, in which SD-4⁺ cells were 94%) were cultured with immobilized anti–CD3 Ab (increasing doses) plus 5 μg/mL DC-HIL-Fc (●) or control Ig (○). Activation was measured by IL-2 production for the HuT-78 cells (A) and PBMCs (C), by the frequency of CD69⁺ cells as a percentage for the HH line (B), or by ³H-thymidine (TdR) incorporation (D) as mean (± SD) for n = 3 experiments.