Conversion of a human immunodeficiency virus cytotoxic T lymphocyte epitope into a high affinity HLA-Cw3 ligand

To elucidate the residues important for the binding of peptides to HLA-Cw3, a substitutional analysis of two HLA-Cw*0304-binding peptides was performed. The optimal registry and length for a Cw3-restricted epitope from HIV-1 p24gag was determined to be a nonamer, p24gag 144-152. Substituted analogs of this nonamer peptide revealed that substitutions at position 3 (P3) and the carboxyl-terminal P9 were inhibitory to binding, while certain substitutions at the amino-terminal P1 or P2 increased binding significantly. Substituted analogs of another Cw3-restricted peptide, the Cw3 consensus peptide, which binds to HLA-Cw*0304 with a 1,000-fold higher affinity and with a greater stability than the HIV p24gag nonamer revealed that the P1, P2, P6, and P9 residues play important roles in the ligand's binding to Cw*0304. The incorporation of the amino-terminal P1 and P2 residues from the Cw3 consensus peptide into the HIV p24gag 144-152 peptide created a hybrid peptide with profoundly enhanced affinity for and stability with Cw*0304. Collectively, these findings provide a clear insight into how peptides interact with HLA-Cw3 and how high affinity Cw3 ligands can be constructed.