Memory CD8+ T lymphocytes (CTLs) specific for antigenic peptides derived from internal viral proteins confer broad protection against distinct strains of influenza A virus (IAV). However, immune efficacy can be undermined by the emergence of escape mutants. To determine how T-cell receptor (TCR) composition relates to IAV epitope variability, we used ex vivo peptide-HLA tetramer enrichment and single-cell multiplex analysis to compare TCRs targeted to the largely conserved HLA-A*0201-M1 58 and the hypervariable HLA-B*3501-NP 418 antigens. The TCRαβs for HLA-B*3501-NP 418 + CTLs varied among individuals and across IAV strains, indicating that a range of mutated peptides will prime different NP 418 -specific CTL sets. Conversely, a dominant public TRAV27/TRBV19+ TCRαβ was selected in HLA-A*0201+ donors responding to M1 58 . This public TCR cross-recognized naturally occurring M1 58 variants complexed with HLA-A*0201. Ternary structures showed that induced-fit molecular mimicry underpins TRAV27/TRBV19 + TCR specificity for the WT and mutant M1 58 peptides, suggesting the possibility of universal CTL immunity in HLA-A*0201 + individuals. Combined with the high population frequency of HLA-A*0201, these data potentially explain the relative conservation of M1 58 . Moreover, our results suggest that vaccination strategies aimed at generating broad protection should incorporate variant peptides to elicit cross-reactive responses against other specificities, especially those that may be relatively infrequent among IAV-primed memory CTLs.influenza infection | human CD8 + T cells | T-cell receptor

Newly-emerged and vaccine-mismatched influenza A viruses (IAVs) result in a rapid global spread of the virus due to minimal antibody-mediated immunity. In that case, established CD8+ T-cells can reduce disease severity. However, as mutations occur sporadically within immunogenic IAV-derived T-cell peptides, understanding of T-cell receptor (TCRαβ) cross-reactivity towards IAV variants is needed for a vaccine design. Here, we investigate TCRαβ cross-strain recognition across IAV variants within two immunodominant human IAV-specific CD8+ T-cell epitopes, HLA-B*37:01-restricted NP338-346 (B37-NP338) and HLA-A*01:01-restricted NP44-52 (A1-NP44). We find high abundance of cross-reactive TCRαβ clonotypes recognizing distinct IAV variants. Structures of the wild-type and variant peptides revealed preserved conformation of the bound peptides. Structures of a cross-reactive TCR-HLA-B37-NP338 complex suggest that the conserved conformation of the variants underpins TCR cross-reactivity. Overall, cross-reactive CD8+ T-cell responses, underpinned by conserved epitope structure, facilitates recognition of distinct IAV variants, thus CD8+ T-cell-targeted vaccines could provide protection across different IAV strains.

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