YS- and P-Sp–derived T cells engrafted in the recipient spleen are functional. YS- and P-Sp–derived T cells engrafted in the recipient spleen are proliferative on CD3 stimulation and secrete IL-2. Spleen cells from recipient mice 2 weeks after transplantation were plated in RPMI medium with anti-CD3 and anti-CD28 Abs. Donor cell proliferation was analyzed with the use of CFSE staining (left panel: CD45.2⁺CD4⁺ gated cells are depicted; CD45.2⁺CD8⁺ cells showed a similar proliferation pattern). Nontransplanted BL/6 spleen cells were used as a control. IL-2 secretion was confirmed by intracellular staining (middle panel). CD25 expression was up-regulated in all samples (right panel). Nonstimulated spleen cells were used as a negative control. Filled histogram is at 0 hour, and solid line is at 48 hours after stimulation. YS- and P-Sp–derived spleen cells (n = 5).