Proportion of lymphoid organ-homing T cells and magnitude of antigen (Ag)-specific T-cell responses in severe combined immunodeficient (SCID) mice treated with placebo or FTY720 after receiving complete donor lymphocyte transfer (T cells along with non-T cells as Ag-presenting cells) and in SCID mice receiving T cell-depleted transfer. T-cell proportions in the (a) joint-draining lymph nodes (JDLNs) and (b) spleens were measured by flow cytometry and expressed as percentage of CD3+ of total CD45+ cells. Data shown are the mean ± standard error of the mean (SEM) (n = 9 to 11 mice per group; *P < 0.05). (c) Ag (human proteoglycan)-specific spleen cell proliferation and (d) Ag-specific production of bioactive interleukin-2 (IL-2) by the same spleen cell cultures were assayed on the basis of [3H]thymidine incorporation into splenocytes and CTLL-2 cells, respectively. Results are expressed as stimulation index and are the mean ± SEM (n = 4 to 5 mice per group; *P < 0.01). Isotope incorporation by non-stimulated cell cultures was less than 1,700 cpm per well and was comparable among the three groups of mice. PG, proteoglycan.