Direct alloreactivity by human cytotoxic T lymphocytes can be inhibited byaltered peptide ligand antagonism

Alloreactive T lymphocytes that respond directly to foreign major histocomp atibility complex (MHC) molecules and bound peptide are known to be central mediators of graft-versus-host disease (GVHD) and allograft rejection. We have recently identified a peptide from the human protein, cytochrome P450 (isotypes IIC9, 10, or 18), that is recognized in association with human le ukocyte antigen (HLA) B*3501 by alloreactive cytotoxic T lymphocytes (CTLs) , These CTLs with this specificity were isolated from several unrelated ind ividuals and were found to express a common T-cell receptor (ICR), Syntheti c analogs of the cytochrome P450 peptide were generated by introducing sing le amino acid substitutions at putative TCR contact positions. Four altered peptide ligands were powerful competitive antagonists of these CTL clones, reducing lysis levels of target cells expressing the alloantigen HLA B*350 1 by over 80%, This first demonstration that it is possible to suppress CTL alloreactivity with structural variants of allodeterminants raises the pro spect that such TCR antagonists could be exploited within the clinical aren a to specifically modulate GVHD and allograft rejection. (C) 1999 by The Am erican Society of Hematology.