Selective deletion of antigen-specific CD8 + T cells by MHC class I tetramers coupled to the type I ribosome-inactivating protein, saporin Running title: Deletion of CD8 + T cells by a cytotoxic tetramer

CD8 + cytotoxic T lymphocytes (CTL) are important effector cells responsible for tissue destruction in several autoimmune and allograft-related diseases. To discover if pathogenic T cells could be selectively deleted, we investigated the ability of a toxin coupled to major histocompatibility complex (MHC) class I tetramers to kill antigen-specific CD8 + T cells. H2-D b tetramers were assembled using streptavidin conjugated to the ribosome-inactivating protein (RIP), saporin (SAP). These tetramers inhibited ribosome activity in vitro, retained the T cell receptor (TCR) binding specificity of their non-toxic counterparts, and were internalized by 100% of target cells, leading to cell death in 72 hours. Cytotoxicity was dependent on the tetramer dose and avidity for the T cell. A single injection of the SAP-coupled tetramer eliminated >75% of cognate, but not control, T cells. This work demonstrates the therapeutic potential of cytotoxic tetramers to selectively eradicate pathogenic clonotypes, while leaving overall T cell immunity intact.