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78 Alternative Peptide Analogues (“Mimic Peptides”) of the HIV-1-Gag77-85(SL9) Identified by Screening a Combinatorial Nonapeptide Library in Positional Scanning Format with Specific HLA-2.1-Restricted Cytotoxic T Lymphocytes (CTL) Primed ex Vivo
J. Kan-Mitchell*1, M. Bereta1, B. Bisikirska1, S. E. Blondelle2, C. Boggiano2, and D. B. Wilson2
1Karmanos Cancer Inst., Wayne State Univ. Sch. of Med., Detroit, MI, USA and 2Torrey Pines Inst. of Mol. Studies, San Diego, CA, USA
Background: Despite the very robust and effective virus-specific cytotoxic T-lymphocyte (CTL) response early in the course of HIV-1 infection, the majority of patients progress and eventually succumb. This led to the suggestion that HIV vaccines must do more than the natural infection.
Methods: Since the T-cell repertoire of patients may be distorted by the infection, we used an ex vivo primed SL9-specific CTL line from a healthy donor to screen a nonameric combinatorial peptide library to identify altered peptide ligands of this epitope. CD8+ T cells were primed in vitro with monocyte-derived dendritic cells pulsed with 20 mug/ml peptides and cultured in RPMI supplemented with 10% autologous serum. T cells were restimulated with SL9-pulsed monocytes weekly. SL9-specific CTL lines generally contain ~50% tetramer-binding CD8+ T cells. The lines are highly avid, with EC50 values to SL9 in the range of nanomolar to femtomolar. A tetramer-sorted CTL line (PW1) containing ~90% tetramer+ cells was used to screen the library.
Results: A set of 75 potential SL9 peptide analogues were thus identified and studied for their ability (1) to induce IFN-gamma release assays by the PW1 cell line, and (2) to render peptide pulsed T2 target cells susceptible to lysis by the original index PW1 line and an additional second SL9-specific T-cell line (BH1) derived from a different A*0201 individual. Our results showed that the 11 most active peptide analogues are 10(100 times more active than the native SL9 peptide. Many of the most active peptides differed from the native sequence by 5 or 6 amino acid substitutions, with 4 of these “superagonist” peptides detected by CTL lines from 2 donors.
Conclusions: Approximately 40% of these analogues (4/11) are capable of being detected by a SL9-specific CTL line derived from a different donor. And, some of these highly effective peptide sequences differ from SL9 by multiple amino acid substitutions. These data suggest that optimized peptide analogues of HIV-1 epitopes are important to include in epitope-based HIV vaccines.
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