Complexity of Effector Mechanisms in Cyclosporine-Induced Syngeneic Graft-Versus-Host Disease

Administration of the immunosuppressive drug cyclosporine after syngeneic or autologous bone marrow transplantation elicits a T-lymphocyte-dependent autoimmune syndrome similar to graft-versus-host disease (GVHD). The onset of this autoaggression syndrome, termed syngeneic GVHD, is associated with the development of a highly restricted repertoire of CD8⁺ autoreactive T cells that recognize a peptide from the invariant chain, termed CLIP, presented by major histocompatibility complex (MHC) class II molecules. Clonal analysis reveals 2 distinct subsets of autoreactive T cells defined by their activation requirement for either the N-terminal or the C-terminal flanking regions of CLIP and by their cytokine profile. The studies here reveal that the autoreactive T-cell clones requiring the N-terminal flanking region of CLIP produce type 1 cytokines (interferon [IFN]-γ, interleukin [IL]-2, and tumor necrosis factor-α). In contrast, the autoreactive T-cell clones that require the C-terminal flanking region of CLIP produce type 2 cytokines (IL-4, IL-10, transforming growth factor-β). As assessed in a local graft-versus-host reaction assay, the N-terminal flanking-restricted clones mediate changes consistent with acute GVHD, whereas the clones responsive to the C-terminal flanking region do not. Moreover, the autoreactive T-cell clones restricted by the C-terminal flanking region of CLIP ameliorate the pathogenic potential of the cells responsive to the N-terminal flanking region of CLIP. The mechanism accounting for this regulatory affect appears to be the downregulation of mRNA message for type 1 cytokines (IFN-γ and IL-2). The C-terminal-restricted autoreactive T-cell clones, however, could manifest disease with dermal changes similar to those seen in chronic syngeneic GVHD, provided that IFN-γ was present. Consistent with these observations was the demonstration that type 1 cytokines are preferentially detected during the acute phase of syngeneic GVHD, whereas type 2 cytokines dominate during the chronic phase. The results suggest that acute and chronic syngeneic GVHD is mediated by distinct autoreactive T cells, which are separated by their fine specificity for the CLIP-MHC class II complex and by their cytokine profiles.