Intermediate TCR Cells with Self-Reactive Clones Are Effector Cells Which Induce Syngeneic Graft-versus-Host Disease in Mice

It has been established that, even after syngeneic bone marrow transplantation, animals treated with immunosuppressive drugs may suffer from graft-versus-host disease, showing autoimmune-like symptoms. Although the major effector cells are known to be T-cell subsets, detailed characterization of such T cells remains to be investigated. In the present study, we characterized them, especially as to whether they are thymus-derived T cells or extrathymic T cells, and how self-reactive clones were distributed among the above T-cell subsets. BALB/c mice (Mls-1b2a) were irradiated (9 Gy), subjected to bone marrow transplantation, and then treated with cyclosporin A (CsA) for 6 weeks. From 2 weeks after the cessation of CsA, these mice displayed signs of GVH disease. The major target organs included the liver and colon. Two-color staining for CD3 and IL-2Rβ was applied to identify CD3−IL-2Rβ+NK cells, CD3-intermediate+IL-2Rβ+cells (i.e., intermediate CD3 or TCR cells of extrathymic origin) and CD3-high+IL-2Rβ−cells (i.e., high CD3 cells of thymic origin). It was demonstrated that the major expanding lymphocytes were intermediate TCR cells and that self-reactive clones (Vβ3+and Vβ11+cells in this strain of mice) were confined to this population. Interestingly, these self-reactive clones had ability to respond to immobilized anti-Vβ3 and anti-Vβ11 mAbs. Liver MNC in mice with GVH disease which contained the highest proportion of intermediate TCR cells were able to mediate the adoptive transfer of GVH disease to other irradiated (6.5 Gy) mice. Intermediate TCR cells also showed potent cytotoxic activity against syngeneic leukemia cells. These results suggest that intermediate TCR cells are the major effector cells for the induction of syngeneic GVH disease.