A Human CD4⁺T Cell Epitope in the Influenza Hemagglutinin Is Cross-Reactive to Influenza A Virus Subtypes and to Influenza B Virus

Abstract

The hemagglutinin protein (HA) of the influenza virus family is a major antigen for protective immunity. Thus, it is a relevant target for developing vaccines. Here, we describe a human CD4 + T cell epitope in the influenza virus HA that lies in the fusion peptide of the HA. This epitope is well conserved in all 16 subtypes of the HA protein of influenza A virus and the HA protein of influenza B virus. By stimulating peripheral blood mononuclear cells (PBMCs) from a healthy adult donor with peptides covering the entire HA protein based on the sequence of A/Japan/305/1957 (H2N2), we generated a T cell line specific to this epitope. This CD4 + T cell line recognizes target cells infected with influenza A virus seasonal H1N1 and H3N2 strains, a reassortant H2N1 strain, the 2009 pandemic H1N1 strain, and influenza B virus in cytotoxicity assays and intracellular-cytokine-staining assays. It also lysed target cells infected with avian H5N1 virus. We screened healthy adult PBMCs for T cell responses specific to this epitope and found individuals who had ex vivo gamma interferon (IFN-γ) responses to the peptide epitope in enzyme-linked immunospot (ELISPOT) assays. Almost all donors who responded to the epitope had the HLA-DRB1*09 allele, a relatively common HLA allele. Although natural infection or standard vaccination may not induce strong T and B cell responses to this highly conserved epitope in the fusion peptide, it may be possible to develop a vaccination strategy to induce these CD4 + T cells, which are cross-reactive to both influenza A and B viruses.

Endocine™, N3OA and N3OASq; Three Mucosal Adjuvants That Enhance the Immune Response to Nasal Influenza Vaccination

“…In this study we used TIV and it was surprising to see that the serum response against the Influenza B/Brisbane/60/08 (WHO-Victoria-like influenza B) antigen was so strong also without any adjuvant. Previously studies have shown that there is cross-reactive antibody and CD4+ T cell responses between influenza B and A HAs in both humans and mice [32], [33], [34] and there is an estimated 23–27% amino acid homology between influenza B and A HA proteins [34], [35], [36]; which may be a reason for a strong IgG response towards influenza B. Also, in close proximity to the fusion peptide in the stalk of the HA, a highly conserved B cell epitope have been identified and shown to be cross-reactive within influenza A subtypes and influenza B HA [37].…”

Cytotoxic CD4 T Cells—Friend or Foe during Viral Infection?

“…This approach may therefore be a good candidate for generating adaptive memory responses at the site of infection that are capable of limiting the replication of heterotypic viruses, particularly if well-conserved epitopes were chosen for vaccination. To that end, Babon et al (165) identified a CD4 T cell epitope in the fusion peptide of the HA that is conserved across all influenza A HA subtypes as well as the influenza B HA protein. A CD4 T cell clone recognizing this epitope exhibits cytotoxicity to a variety of influenza strains, including avian H5N1 virus.…”

Broad-Based CD4+ T Cell Responses to Influenza A Virus in a Healthy Individual Who Lacks Typical Immunodominance Hierarchy

“…Otherwise, specific CD4 + T cell responses were proven to be indispensable for the clearance of IAV in both animal models (8, 9) and in human volunteers (10). CD4 + T cells can exert their protective effect directly through cytotoxic activity (11) or indirectly through providing “help” to both CD8 + T cells and B-cells to eliminate virus and virus-infected cells via cytotoxicity and antibody neutralization, respectively (12, 13). Furthermore, the generation of strong memory CD4 + and CD8 + T cell responses are also CD4 + helper T cell dependent (14, 15).…”