IFN-gamma-mediated prevention of graft-versus-host disease: pharmacodynamic studies and influence on proliferative capacity of chimeric spleen cells

Recently we demonstrated that prolonged administration of IFN-gamma prevent ed the development of GVHD in a MHC-mismatched murine BMT model, Treatment with IFN-gamma allowed the development of mature donor-derived allo-toleran t immunocompetent cells in complete chimeric recipients. Here we present da ta on the pharmacodynamics of this cytokine-mediated protection against GVH D, Treatment with 50000 U IFN-gamma twice weekly for a period of 5 weeks, s tarting at the day of BMT, was shown to be the optimal treatment protocol, resulting in complete prevention of GVHD-related mortality, Treatment durin g 1 week with a three-fold higher weekly dose of IFN-gamma (50000 U six tim es) did not result in significantly improved survival. The start of IFN-gam ma administration was a critical factor since a delay of 3 days from the ti me of BMT resulted in substantial GVHD-induced mortality, Furthermore, it w as shown that IFN-gamma treatment inhibited the spontaneous and Con-A-induc ed proliferation of T cells at 7-14 days after BMT, which is the critical p eriod for the initiation of acute GVHD, However, long-term survivors after IFN-gamma treatment showed a recovery of immunity in contrast to long-term survivors of saline-injected animals, as tested by Con-A responsiveness. It seems that injection of high dose IFN-gamma suppresses the response of pot entially alloreactive donor T cells during what normally is the initiation phase of the GVH reaction (GVHR), resulting in the abrogation of GVHD.