Overall, the results indicate that a loss of a number of contacts between the NPN3A peptide and the MHC-I molecule and lower functional and structural pMHC-I avidity (for wt D b NP 366 ) D b NPN3A selects a narrowed TCR repertoire of ''best fit'' TCRs from a spectrum of naïve clonotypes that, once activated, clonally expanded and engaged in an immune response, have sufficient avidity to be recalled by exposure to the wt D b NP 366 epitope. Conversely, the ''better'' fit D b NP 366 finds a sufficient spectrum of high avidity TCRs within that available naive repertoire and does not (likely because of clonal competition) select most of the TCR ab pairs that interact optimally with D b NPN3A. Priming with the wt virus thus establishes memory for only a very limited secondary response to the mutant. Similar to our results, subtle variations within the anchor residue of H b peptide/I-E k also decreased peptide-MHC class II affinity and the activation of responding T cells [44] .