A targeted single mutation in influenza A virus universal epitope transforms immunogenicity and protective immunity via CD4+ T cell activation.

CD4⁺ T cells are central to adaptive immunity. Their role in cross-protection in viral infections such as influenza and severe acute respiratory syndrome (SARS) is well documented; however, molecular rules governing T cell receptor (TCR) engagement of peptide-human leukocyte antigen (pHLA) class II are less understood. Here, we exploit an aspect of HLA class II presentation, the peptide-flanking residues (PFRs), to "tune" CD4⁺ T cell responses within an in vivo model system of influenza. Using a recombinant virus containing targeted substitutions at immunodominant HLA-DR1 epitopes, we demonstrate limited weight loss and improved clinical scores after heterosubtypic re-challenge. We observe enhanced protection linked to lung-derived influenza-specific CD4⁺ and CD8⁺ T cells prior to re-infection. Structural analysis of the ternary TCR:pHLA complex identifies that flanking amino acids influence side chains in the core 9-mer peptide, increasing TCR affinity. Augmentation of CD4⁺ T cell immunity is achievable with a single mutation, representing a strategy to enhance adaptive immunity that is decoupled from vaccine modality. [Display omitted] • Modifying CD4⁺ T cell epitope of influenza HA transforms immunogenicity and long-term immunity • Modified HA also induces increased CD8⁺ T cells to influenza NP in HLA-DR1+ mice • Long-term heterosubtypic protection is mediated by antigen-specific lung CD4⁺ and CD8⁺ T cells • A single mutation of a peptide-flanking residue alters TCR-pHLA-II interface and affinity Hulin-Curtis et al. demonstrate that a single targeted mutation in an HLA-DR1-presented epitope enhances control of primary influenza infection and long-term immunity after heterosubtypic re-challenge in HLA-DR1 mice. Enhanced protection appears to be mainly mediated by lung-derived T cells. [ABSTRACT FROM AUTHOR]