任意のT細胞エピトープ同定法の開発

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1) Positional scanning of MHC calss Imolecules.Peptide binding specificities of Kb, Db and Ld were analyzed with 9-mer peptide libraries. The basic design of the libraries is Oxxxxxxxx, for instance, to evaluate the relative fitness of an amino acid at position, O.xdesignates the positions where 19 am ino acids but Cys are equally represented. Binding of peptides was quantitated by stabilization of empty MHC class Imolecules expressed on TAP deficient cell lines. Energetic advantages and disadvantages among different amino acids in MHC binding are most prominent at the positions that have been previously identified as major anchors by pool sequencing. Positions 4,6,7 and 8 exhibited the least selectivity.2) Prediction of T cell epitopes.A scoring system was devised from the positional scanning data by assuming that the energetic contribution of each amino acid can be additive in binding of the whole peptide. Most of known T cell epitope peptides are scored 1-5th among the highest scoring 9-mers present in parental proteins.3) Correlation of predicted vs actual binding.Arbitorarily chosen peptides were synthesized and their MHCbinding capacities were compared with the predicted binding scores. A positive correlation between these values were observed, but there were also substantial fluctuations, indicating a limit in predicting power by the positional scannning.4) Prediction of repertoire overlap of MHC binding peptides among different MHC molecules.By using the above mentioned scoring system, MHC binding peptides were predicted for thres murine MHC allomorphs. Their repertoiree are suggested to share relatively small overlaps.