Recruitment of the CTL repertoire specific for subdominant epitopes that have a low MHC class I-binding affinity could be the way to achieve an efficient protective immunity against spontaneous tumors and viruses with high mutation rate. However, we have reported recently that subdominant peptides of influenza A Puerto Rico/8/34 (flu PR8) nucleoprotein (NP) with low Db affinity are only partially able to protect mice against lethal influenza infection. This seems to be due to their inability to recruit the specific CTL repertoire, and suggests that subdominant peptides could be used for vaccination only if they become highly immunogenic. In this work, we describe an approach that allows enhancement of the immunogenicity of every low affinity peptide presented by the Db molecule. It consists in producing chimeric peptides composed by amino acids from a high Db affinity peptide (NP366) in positions that interact with the MHC, and amino acids from low Db affinity nonimmunogenic influenza NP-derived peptides (NP17, NP97, NP330, and NP469) in positions that are exposed to the TCR. All chimeric peptides tested exhibited a high Db affinity and efficiently recruited the CTL repertoire specific for the corresponding low Db affinity peptide. Furthermore, vaccination with chimeric peptides that corresponded to subdominant NP17 and NP97 peptides induced a very potent anti-flu PR8 protective immunity.

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