A study evaluated the effectiveness of CTLA4-Ig and anti-CD40 ligand (5C8) in preventing and reversing renal allograft rejection in rhesus monkeys. Both agents inhibited T cell proliferation in vitro and significantly prolonged graft survival in vivo. When used together, they were 100 times more effective than either agent alone. In a study of four rhesus monkeys, two animals treated with both agents experienced extended (>150 days) rejection-free survival. Two animals treated with 5C8 alone and one treated with both 5C8 and CTLA4-Ig experienced late rejection, but subsequent treatment restored normal graft function. Neither drug affected peripheral T or B cell counts, and there were no clinically evident side effects or rejections during treatment. The study concluded that CTLA4-Ig and 5C8 can prevent and reverse acute allograft rejection, significantly prolonging the survival of MHC-mismatched renal allografts in primates without chronic immunosuppression. The study also discussed the mechanisms of T cell activation and the role of costimulation in allograft rejection. T cell activation requires both TCR-mediated signals and costimulatory signals, which are provided by B7 molecules on antigen-presenting cells. CD40 and CD40L also play a role in T cell activation and B cell activity. CTLA4-Ig and 5C8 inhibit T cell activation by blocking costimulatory signals, potentially by competing with CD28 for B7. These agents were tested in rodents and shown to prolong allograft survival, leading to the hypothesis that they might be effective in humans. The study used a preclinical model of rhesus monkeys with MHC-mismatched renal allografts. The agents were tested in vitro and in vivo, with in vitro studies showing significant inhibition of T cell proliferation. In vivo, the agents prolonged graft survival and reversed rejection in some cases. The study also noted that the agents did not cause adverse effects or changes in peripheral blood parameters. The results suggest that CTLA4-Ig and 5C8 could be used to prevent and reverse allograft rejection in humans without the need for chronic immunosuppression. The study highlights the potential of these agents as a new class of reagents targeting T cell costimulation rather than T cell suppression. The findings suggest that prolonged rejection-free allograft survival is achievable in primates, and that allograft tolerance might be an achievable goal in humans. The study also emphasizes the importance of further research to fully assess the potential of this new therapy.A study evaluated the effectiveness of CTLA4-Ig and anti-CD40 ligand (5C8) in preventing and reversing renal allograft rejection in rhesus monkeys. Both agents inhibited T cell proliferation in vitro and significantly prolonged graft survival in vivo. When used together, they were 100 times more effective than either agent alone. In a study of four rhesus monkeys, two animals treated with both agents experienced extended (>150 days) rejection-free survival. Two animals treated with 5C8 alone and one treated with both 5C8 and CTLA4-Ig experienced late rejection, but subsequent treatment restored normal graft function. Neither drug affected peripheral T or B cell counts, and there were no clinically evident side effects or rejections during treatment. The study concluded that CTLA4-Ig and 5C8 can prevent and reverse acute allograft rejection, significantly prolonging the survival of MHC-mismatched renal allografts in primates without chronic immunosuppression. The study also discussed the mechanisms of T cell activation and the role of costimulation in allograft rejection. T cell activation requires both TCR-mediated signals and costimulatory signals, which are provided by B7 molecules on antigen-presenting cells. CD40 and CD40L also play a role in T cell activation and B cell activity. CTLA4-Ig and 5C8 inhibit T cell activation by blocking costimulatory signals, potentially by competing with CD28 for B7. These agents were tested in rodents and shown to prolong allograft survival, leading to the hypothesis that they might be effective in humans. The study used a preclinical model of rhesus monkeys with MHC-mismatched renal allografts. The agents were tested in vitro and in vivo, with in vitro studies showing significant inhibition of T cell proliferation. In vivo, the agents prolonged graft survival and reversed rejection in some cases. The study also noted that the agents did not cause adverse effects or changes in peripheral blood parameters. The results suggest that CTLA4-Ig and 5C8 could be used to prevent and reverse allograft rejection in humans without the need for chronic immunosuppression. The study highlights the potential of these agents as a new class of reagents targeting T cell costimulation rather than T cell suppression. The findings suggest that prolonged rejection-free allograft survival is achievable in primates, and that allograft tolerance might be an achievable goal in humans. The study also emphasizes the importance of further research to fully assess the potential of this new therapy.