Th1 and Tc1 cell expansion to alloantigen in vivo is inhibited by CGS: reversal by exogenous IL-2. (A) In vitro-generated congenic CD45.1⁺ donor Th1/Tc1 cells (10 × 10⁶ cells) were injected intravenously into sublethally irradiated syngeneic (C57Bl/6) or semiallogeneic (CB6F₁) recipients. After transplantation (BMT), mice were injected daily (intraperitoneally) with either DMSO vehicle (VEH) or the adenosine agonist CGS (2 mg/kg per day). On day 4 after transplantation, spleens were harvested, and the absolute number of Th1 cells (left panel; CD45.1⁺CD4⁺ cells) and Tc1 cells (right panel; CD45.1⁺CD8⁺ cells) were enumerated by FACS data and total spleen cell counts (n = 5 per treatment cohort; ^*statistically significant difference). (B) In vitro-generated congenic CD45.1⁺ donor Th1/Tc1 cells (10 × 10⁶ cells) were injected intravenously into sublethally irradiated semiallogeneic (CB6F₁) recipients. After transplantation, mice were injected daily (intraperitoneally) with either DMSO vehicle (VEH) or CGS (2 mg/kg per day) with or without recombinant human IL-2 (10 000 IU/day). On day 5 after transplantation, spleens were harvested, and the absolute numbers of Th1 and Tc1 cells were determined (values are mean ± SEM of n = 5 per treatment cohort). ^* Statistically significant difference.