T follicular helper cell differentiation programs immunogenicity of prototypic influenza vaccines 4602

Abstract Description The influenza HA stem domain is a promising vaccine antigen to elicit broadly protective antibody responses. In vivo, however, trimeric stem is poorly immunogenic due to a lack of MHC class II epitopes. To address this, we designed a series of stem antigens that incorporate individual CD4 T cell epitopes derived from viral proteins or model antigens. 14 days post-vaccination in WT BL/6 mice, these antigens elicited stem IgG titres ranging from undetectable (<1:100) to > 2x104. Novel MHC class II tetramers revealed that vaccine immunogenicity was unrelated to the total frequency of antigen-specific CD4 T cells. Rather, a bias toward TFH differentiation dictated whether prototypic vaccines were immunogenic or not. Our data suggest that between 60-450 ag-specific TFH are required in the draining lymph node to support a robust germinal centre (GC) response and the proliferation of stem-specific GC B cells. Incorporation of a single, TFH-competent class II epitope into the stem immunogen elicited antibody titres that were 19-fold higher than the full-length HA protein, and 8-fold higher than stem-ferritin nanoparticles, demonstrating the extent to which CD4 T cell help can augment the intrinsic immunogenicity of an antigen. Understanding the factors that underpin variability in TFH differentiation across polyclonal, epitope-specific CD4 T cell populations will further inform rational design of potently immunogenic vaccines. Funding Sources Supported by the NHMRC (Australia; GNT2004398 and 2009308) and Sylvia and Charles Viertel Foundation. Topic Categories Vaccines and Immunotherapy (VAC)