Human (HLA) and chimpanzee (Patr) peptide-binding motifs of relevant MHC class I molecules, and the Gag protein regions that are potentially targeted. P2 and PΩ (carboxyl-terminus) represent the anchor-binding positions of the MHC class I molecules; amino acids that are preferred on these positions are indicated by the conventional one-letter code, whereas tolerated amino acids are indicated between brackets. Patr-B*01:01 has a peptide-binding motif that resembles that of HLA-B*57:01, and Patr-B*03:01 has a peptide-binding motif that resembles that of HLA-B*27:05. Parts of the Gag consensus sequences of HIV-1 (HBX2) and SIVcpz are given (http://www.hiv.lanl.gov). A lower-case letter in the SIVcpz consensus indicates a variable position. The HLA-B*27 and -B*57 CTL epitopes are indicated by red arrows. For the respective Patr class I molecules, blue arrows indicate the potential Gag epitopes that are tested in peptide-binding studies. Based on IC50 (μM) values determined in peptide-binding competition assays, high (1) or intermediate (2) binding affinities of the peptides to their respective MHC class I molecule are indicated .