Molecular analysis of presentation by HLA-A2.1 of a promiscuously binding V3 loop peptide from the HIV-1 envelope protein to human cytotoxic T lymphocytes

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Abstract
P18IIIB is a highly immunogenic peptide from the V3 loop of the HIV-1 gp160 envelope protein that is presented promiscuously by multiple class I MHC molecules. Understanding the molecular basis for promiscuous presentation may have many practical applications. As the highly prevalent HLA-A2.1 class I molecule is known to present P18IIIB for recognition by cytotoxic T lymphocytes (CTL) found in peripheral blood mononuclear cells of HIV+ donors, a P18III-specific CTL line was generated from an HLA-A2+, HIV- donor in order to define the molecular basis for, and ultimately improve upon the binding of, this peptide to HLA-A2.1. The minimal epitope recognized by the line was a decamer,I10, with the sequence RGPGRAFVTI. Interestingly, this decamer is identical to the minimal epitope from P18IIIB seen by murine CTL restricted by H-2Dd. A panel of Ala-substituted peptides was employed in MHC-binding and T cell response studies to identify MHC- and TCR-binding residues. Notably, many of the agretopic and epitopic residues identified were identical to those involved in the corresponding interactions of l10 with the H-2Dd MHC molecule and murine l10-specific CTL. The l10 peptide does not contain the described HLA-A2.1 binding motif. Instead a Pro at P3, a Phe at P7 and an Me at P10 are utilized for MHC binding. Agretopic residue similarities with the hepatitis B nucleocapsid decamer suggest that these residues may comprise an alternative motif of anchors utilized by decamers for binding to HLA-A2.1.

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