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

Abstract

Recently we demonstrated that prolonged administration of IFN-γ prevented the development of GVHD in a MHC-mismatched murine BMT model. Treatment with IFN-γallowed the development of mature donor-derived allo-tolerant immunocompetent cells in complete chimeric recipients. Here we present data on the pharmacodynamics of this cytokine-mediated protection against GVHD. Treatment with 50000 U IFN-γ twice weekly for a period of 5 weeks, starting at the day of BMT, was shown to be the optimal treatment protocol, resulting in complete prevention of GVHD-related mortality. Treatment during 1 week with a three-fold higher weekly dose of IFN-γ (50000 U six times) did not result in significantly improved survival. The start of IFN-γ administration was a critical factor since a delay of 3 days from the time of BMT resulted in substantial GVHD-induced mortality. Furthermore, it was shown that IFN-γ treatment inhibited the spontaneous and Con-A-induced proliferation of T cells at 7–14 days after BMT, which is the critical period for the initiation of acute GVHD. However, long-term survivors after IFN-γ 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-γ suppresses the response of potentially alloreactive donor T cells during what normally is the initiation phase of the GVH reaction (GVHR), resulting in the abrogation of GVHD.