Schematic description of the clinical-scale photodepletion approach. Stimulator cells from study subjects were prepared directly from leukapheresed mononuclear cells or from selected CD3⁺ cells and cultured using anti-CD3 antibody (OKT-3) and 100 IU interleukin-2 (IL-2) for 10 to 12 days, irradiated, and kept frozen thereafter. Donor cells (non–granulocyte–colony-stimulating factor [G-CSF]–mobilized leukapheresis mononuclear cells) were cocultured 1:1 with thawed, irradiated stimulator cells for 72 hours followed by incubation with the photosensitizer TH9402 at 5 × 10⁶/mL cells for 40 minutes. Afterward, cells were transferred to an “extrusion” medium for 90 minutes and exposed to 514 nm visible light in the photodepletion light source at a cell concentration of 5 × 10⁶/mL, in plastic bags. The total light energy delivered was 5 J/cm². After light exposure, cells were rested for different time periods, separated by Ficoll Hypaque, washed, and used for the readout assays or frozen down for later analysis. *Optional.