SOCS3 within donor T cells attenuates GVHD after G-CSF–mobilized allogeneic SCT. Donor B6 mice were treated with G-CSF (10 μg/animal per day for 4 days) or were untreated. Unfractionated splenic grafts containing 2 million T cells were transplanted into lethally irradiated (1100 cGy) B6D2F1 recipient mice. Survival curves by Kaplan-Meier analysis, pooled from 2 experiments. ***P < .001 for recipients of G-CSF Socs3−/Δlck versus G-CSF WT spleen; *P < .05 for recipients of G-CSF SOCS3−/Δvav versus G-CSF WT spleen.