SOCS3 within T cells limits T-cell proliferation and apoptosis after allogeneic SCT. Splenocytes from G-CSF–treated WT or SOCS3^−/ΔLck mice were CFSE labeled, and grafts containing 2 million T cells were transplanted into lethally irradiated (1100 cGy) B6D2F1 recipient mice. (A) Spleens were harvested from recipients 3 days later, and CFSE dilution in the CD4⁺ T-cell compartment was examined by flow cytometry. (B) Modfit CFSE dilution analysis of splenic and lymph node T-cell proliferation. Data are representative of 2 similar experiments with 4 to 5 animals/group. (C) Splenocytes from G-CSF–treated WT or SOCS3^−/ΔLck mice were transplanted into lethally irradiated (1100 cGy) B6D2F1 recipient mice. On days 7 and 14 after transplantation, spleens were harvested, total cellularity was determined with an automated cell counter, and CD4⁺ and CD8⁺ T cells were quantified by flow cytometry. (D) On day 7 after transplantation, spleens were stained with annexin V and 7-amino-actinomycin (7AAD), and the frequency of apoptotic splenocytes (annexin V⁺7AAD⁻) was determined by flow cytometric analysis. Black bars and white bars represent G-CS–treated WT or SOCS3^−/ΔLck mice, respectively.