Mechanism of skin allograft enhancement across an H-2 class I mutant difference. Evidence for involvement of veto cells.

Intravenous injection of spleen cells across mutant class I H-2 incompatibility results in a drastic donor-specific prolongation of skin allograft survival and a marked decrease in the donor-specific cytotoxic T lymphocyte precursor (CTLp) frequency. This immunosuppressive effect depends on the presence of radiosensitive T cells in the donor cell inoculum. It was excluded that a graft-vs.-host reaction was responsible for the observed effects. In mixing experiments, spleen cells from animals transfused with allogeneic lymphocytes could not suppress a normal CTL response against the alloantigen, despite an excess of putative recipient-derived spleen suppressor cells. The data are compatible with the idea that donor T cells function as veto cells which inactivate recipient CTLp directed against the alloantigen expressed by the veto cell.