title: Protective efficacy of cross-reactive CD8+ T cells recognising mutant viral epitopes depends on peptide-MHC-I structural interactions and T cell activation threshold.
abstract: Emergence of a new influenza strain leads to a rapid global spread of the virus due to minimal antibody immunity. Pre-existing CD8(+) T-cell immunity directed towards conserved internal viral regions can greatly ameliorate the disease. However, mutational escape within the T cell epitopes is a substantial issue for virus control and vaccine design. Although mutations can result in a loss of T cell recognition, some variants generate cross-reactive T cell responses. In this study, we used reverse genetics to modify the influenza NP(336-374) peptide at a partially-solvent exposed residue (N->A, NPN3A mutation) to assess the availability, effectiveness and mechanism underlying influenza-specific cross-reactive T cell responses. The engineered virus induced a diminished CD8(+) T cell response and selected a narrowed T cell receptor (TCR) repertoire within two V beta regions (V beta 8.3 and V beta 9). This can be partially explained by the H-2D(b)NPN3A structure that showed a loss of several contacts between the NPN3A peptide and H-2D(b), including a contact with His155, a position known to play an important role in mediating TCR-pMHC-I interactions. Despite these differences, common cross-reactive TCRs were detected in both the naïve and immune NPN3A-specific TCR repertoires. However, while the NPN3A epitope primes memory T-cells that give an equivalent recall response to the mutant or wild-type (wt) virus, both are markedly lower than wt->wt challenge. Such decreased CD8(+) responses elicited after heterologous challenge resulted in delayed viral clearance from the infected lung. Furthermore, mice first exposed to the wt virus give a poor, low avidity response following secondary infection with the mutant. Thus, the protective efficacy of cross-reactive CD8(+) T cells recognising mutant viral epitopes depend on peptide-MHC-I structural interactions and functional avidity. Our study does not support vaccine strategies that include immunization against commonly selected cross-reactive variants with mutations at partially-solvent exposed residues that have characteristics comparable to NPN3A.
authors: Department of Microbiology and Immunology, University of Melbourne, Parkville, Australia.
authors: Sophie A
authors: SA
authors: Valkenburg
authors: Stephanie
authors: S
authors: Gras
authors: Carole
authors: C
authors: Guillonneau
authors: Nicole L
authors: NL
authors: La Gruta
authors: Paul G
authors: PG
authors: Thomas
authors: Anthony W
authors: AW
authors: Purcell
authors: Jamie
authors: J
authors: Rossjohn
authors: Peter C
authors: PC
authors: Doherty
authors: Stephen J
authors: SJ
authors: Turner
authors: Katherine
authors: K
authors: Kedzierska
mesh_terms: D000818:Animals; D000956:Antigens, Viral / Q000276:immunology; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology*; D003429:Cross Reactions / Q000276:immunology; D018360:Crystallography, X-Ray; D018984:Epitopes, T-Lymphocyte / Q000276:immunology*; D015395:Histocompatibility Antigens Class I / Q000276:immunology*; D009980:Influenza A virus / Q000235:genetics / Q000276:immunology*; D007252:Influenza Vaccines / Q000276:immunology; D008213:Lymphocyte Activation / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL; D009154:Mutation; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D010455:Peptides; D017433:Protein Structure, Secondary; D011948:Receptors, Antigen, T-Cell / Q000276:immunology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014758:Viral Core Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology*
chemical_list: D000956:Antigens, Viral; D018984:Epitopes, T-Lymphocyte; D015395:Histocompatibility Antigens Class I; D007252:Influenza Vaccines; D010446:Peptide Fragments; D010455:Peptides; D011948:Receptors, Antigen, T-Cell; D014758:Viral Core Proteins; C102366:nucleoprotein (366-374), influenza virus