Phosphorylated peptides can be transported by TAP molecules, presented by class I MHC molecules, and recognized by phosphopeptide-specific CTL

CTL recognize short peptide fragments presented by class I MHC molecules, I n this study, we examined the effect of phosphorylation on TAP transport, b inding to class I MHC molecules, and recognition by CTL of peptide fragment s from known phosphorylated oncogene proteins or virus phosphoproteins, We show that phosphopeptides can be efficiently transported from the cytosol t o the endoplasmic reticulum by the TAP. Furthermore, we show that phosphory lation can have a neutral, negative, or even a positive effect on peptide b inding to class I MHC. Finally, we hale generated phosphopeptide-specific C TL that discriminate between the phosphorylated and the nonphosphorylated v ersions of the peptide. We conclude that phosphopeptide-specific CTL respon ses are likely to constitute a subset of the class I MHC-restricted CTL rep ertoire in vivo.