Lack of KIR3DS1 binding to MHC class I Bw4 tetramers in complex with CD8+ T cell epitopes

In HIV-1 infection, the synergistic association of a subset of Bw4 MHC class I molecules and the activating killer inhibitory receptor (KIR), KIR3DS1, with prolonged AIDS-free survival has been reported. As KIRs represent a diverse group of MHC class I receptors, we questioned whether Bw4 MHC class I molecules expressing isoleucine at position 80 (Bw4Ile80) and in complex with HIV-1-derived T cell epitopes represented KIR3DS1 ligands. MHC class I tetramers are powerful tools for the detection of T cell receptor-MHC class I interactions, and have recently been used to evaluate KIR-MHC class I binding ex vivo. Specifically, this approach has been successfully utilized to assess binding of Bw4 MHC class I tetramers to KIR3DL1, an inhibitory KIR and allele of KIR3DS1. In this study we generated a diverse panel of HIV-1-specific Bw4Ile80 MHC class I tetramers and tested its ability to bind transiently expressed KIR3DS1 on 293-T cells. Using flow cytometry analysis, the expression of KIR3DS1 on 293-T cells was confirmed by anti-FLAG BioM2 staining, prior to incubation with PE-conjugated MHC class I tetramers. Despite choosing a broad array of peptide epitopes and diverse Bw4Ile80 MHC class I molecules, we were unable to detect tetramer binding to KIR3DS1. We speculate that our negative finding may be a consequence of the MHC class I molecules and peptide epitopes chosen, but could also relate to key amino acid differences that distinguish KIR3DS1 from KIR3DL1.