Weiran Chen

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]-gamma, interleukin [IL]-2, and tumor necrosis factor-alpha). 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-beta). 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-gamma 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-gamma 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.

Unexpected T-cell diversity in syngeneic graft-versus-host disease revealed by interaction with peptide-loaded soluble MHC class II molecules.

Background. Administration of cyclosporine after syngeneic bone marrow transplantation elicits a systemic autoaggression syndrome termed syngeneic graft-versus-host disease (SGVHD). The effector T cells recognize a peptide from the invariant chain termed CLIP (MHC class II invariant chain peptide) presented on MHC class II molecules. Moreover, the N-terminal flanking region of CLIP interacts with the T-cell receptor (TcR) &bgr; chain. Methods. The current study uses a novel approach to isolate and examine the responding T cells ex vivo. A soluble MHC class II molecule using immunoglobulin (Ig)G (MHC class II-Ig) as a scaffold was constructed. The MHC class II-Ig molecule loaded with different peptide variants of CLIP (lacking the N-terminal or C-terminal flanking regions of CLIP) was used to isolate antigen-specific T cells from animals with SGVHD by panning or by flow cytometric sorting. Results. Two subsets of antigen specific T cells restricted by the N- and C-terminal flanking regions of CLIP can be isolated during acute SGVHD that express the V&bgr;8.5 TcR determinant but secrete different cytokines (interferon [IFN]-&ggr;, interleukin [IL]-10) as detected by real-time quantitative polymerase chain reaction (PCR). Spectratyping of the complementarity-determining region 3 regions reveals that the N-terminal CLIP reactive population has greater diversity in both the CDR3 and J regions than the C-terminal CLIP reactive subset. Interestingly, the N-terminal CLIP reactive cells can be preferentially detected in the target tissues during acute SGVHD. However, only IFN-&ggr; messenger (m)RNA was detected in the tissues. Conclusion. The ability to isolate and examine antigen specific T cells ex vivo has revealed unexpected differences in TcR diversity and cytokine production in SGVHD.