sGARP prevents GVHD development. (A) Protection from GVHD by human Treg. Newborn Rag2^−/−γc^−/− mice were transferred with 5 × 10⁶ human PBMC with or without titrated numbers of Treg. Untreated mice served as controls. Percent mean body weight is based on initial weight. Upper panel: One representative experiment (3 mice per group, n = 3) is shown. Percent mean body weight data ± SEM. Lower panel: Kaplan-Meier plots of 9 mice per individual group. (B) Protection by a single GARP injection in the presence of Treg. 5 × 10⁶ PBMC were intraperitoneally injected into newborn Rag2^−/−γc^−/− mice containing a nonprotective number of Treg (PBMC:Treg ratio 20:1) with and without 5 µg sGARP. Untreated mice served as controls. Upper panel: One representative experiment (4 mice per group, n = 3) is shown. Percent mean body weight data ± SEM. Lower panel: Kaplan-Meier plots of 12 mice per individual group. (C) Single injection of sGARP did not protect against GVHD. PBMC were injected with and without 5 µg sGARP into newborn Rag2^−/−γc^−/− mice. Untreated mice served as controls. Upper panel: One representative experiment (5 mice per group, n = 2) is shown. Percent mean body weight data ± SEM. Lower panel: Kaplan-Meier plots with 10 mice per individual group. (D) Protection by repetitive injection of sGARP. PBMC were injected with 5 µg sGARP or control protein into newborn Rag2^−/−γc^−/− mice. sGARP was administered 3 times every other day (sGARP rep.). Untreated mice served as controls. Upper panel: One typical experiment (6 mice per group, n = 4) is shown. Percent mean body weight data ± SEM. Lower panel: Kaplan-Meier plots with 24 mice per individual group. (E) Mice 27 days after transfer of PBMC with and without repetitive injection of sGARP compared with untreated mice (14 mice per group, mean ± SEM, *P < .05, **P < .01).