Enhanced immune activity of cytotoxic T-lymphocyte epitope analogs derivedfrom positional scanning synthetic combinatorial libraries

The pp65(495-503) cytotoxic T-lymphocyte (CTL) epitope from cytomegalovirus (CMV) is universally recognized among CMV+ individuals who express an alle le of the human leukocyte antigen A (HLA-A*0201), The relative binding affi nity of the epitope to HLA-A*0201 is moderate, and its increased activity m ight prove beneficial in its use as a CTL epitope vaccine. A new approach t o enhance the activity of T-cell epitopes is the use of positional scanning synthetic combinatorial libraries (PS-SCLs), Using a nonamer PS-SCL, the p p65495-503 epitope was modified after screening a CMV-specific T-cell clone (ICC) (3-3F4) from which the native peptide sequence was derived. Two pept ides with amino acid substitutions at P1, P3, P7, and P8 are between 10(3) and 10(4) more active than the native epitope, Although the native CTL epit ope terminates as a free acid, both tetrasubstituted peptides only function as CTL epitopes when the carboxyl terminus is amidated, Selective substitu tion of the native sequence based on PS-SCL screening results identified 3 amidated monosubstituted and disubstituted peptides that are better recogni zed than the native epitope by TCCs from a cohort expressing HLA-A*0201. In vitro stimulation of peripheral blood mononuclear cells with each of the p eptide epitope analogs stimulated memory CTLs, which recognized CMV-infecte d targets among a high percentage of CMV+ individuals. Binding studies of p eptide analogs with HLA-Ig (immunoglobulin) dimers and 2 different TCCs cor related with in vitro lysis results. These data suggest that increasing the activity of CTL epitopes while maintaining broad recognition is possible, which holds promise for vaccine development in infectious disease and cance r, (Blood, 2001; 97:1776-1786) (C) 2001 by The American Society of Hematolo gy.