CD4 T cell epitope abundance in ferritin core potentiates responses to hemagglutinin nanoparticle vaccines

Abstract

Nanoparticle vaccines based on H. pylori ferritin are increasingly used as a vaccine platform for many pathogens, including RSV, influenza, and SARS-CoV-2. They have been found to elicit enhanced, long-lived B cell responses. The basis for improved efficacy of ferritin nanoparticle vaccines remains unresolved, including whether recruitment of CD4 T cells specific for the ferritin component of these vaccines contributes to cognate help in the B cell response. Using influenza HA-ferritin nanoparticles as a prototype, we have performed an unbiased assessment of the CD4 T cell epitope composition of the ferritin particles relative to that contributed by influenza HA using mouse models that express distinct constellations of MHC class II molecules. The role that these CD4 T cells play in the B cell responses was assessed by quantifying follicular helper cells (TFH), germinal center (GC) B cells, and antibody secreting cells. When mice were immunized with equimolar quantities of soluble HA-trimers and HA-Fe nanoparticles, HA-nanoparticle immunized mice had an increased overall abundance of TFH that were found to be largely ferritin-specific. HA-nanoparticle immunized mice had an increased abundance of HA-specific isotype-switched GC B cells and HA-specific antibody secreting cells (ASCs) relative to mice immunized with soluble HA-trimers. Further, there was a strong, positive correlation between CD4 TFH abundance and GC B cell abundance. Thus, availability of helper CD4 T cell epitopes may be a key additional mechanism that underlies the enhanced immunogenicity of ferritin-based HA-Fe-nanoparticle vaccines.

Generation of antigen-specific memory CD4 T cells by heterologous immunization enhances the magnitude of the germinal center response upon influenza infection

“…However, vaccination strategies or adjuvants specifically to target the recall of CD4+ Tfh cells to enhance the GC and its products have been slow to develop beyond the preclinical stage. We found that specifically targeting the recall and expansion of memory antigen-specific CD4+ T cells induced an increase in GC Tfh and HA-specific GC B cells early compared to mice that lacked antigen-specific memory CD4+ T cell during primary influenza infection, indicating that our findings concur with previous studies that targeting CD4+ T cells is a successful strategy to enhance the GC reaction (40, 44, 107). While heterologous infection/immunization priming enhanced the early GC Tfh and GC B cell magnitude, we did not see increases in HA-specific antibody titers, but we did see selection for specific clones in the resultant B cell repertoires.…”

“…We further compared the numbers of HA-specific GC B cells to the number of GC Tfh cells and found that in the GP(1°)PR8(2°) group, there was a significantly higher number of HA-specific GC B cells to every GC Tfh cell ( Fig 3J ). These data suggest that while the number of GC Tfh cells in the GP(1°)PR8(2°) group were similar to the PR8(1°) group, the GC Tfh cells may be of a higher quality as to sustain support for higher numbers of HA-specific GC B cells, as has been previously suggested (41, 44). Together, these data suggest that heterologous priming with adjuvanted rGP immunization or LCMV infection significantly enhanced the early anti-influenza germinal center B cell response following influenza infection compared to primary influenza infection.…”

“…In influenza-related studies, adjuvanted inactivated influenza vaccine was shown to increase GC responses and enhance cross-reactivity and long-term detectability of HA-specific antibodies (43). In addition, vaccination with influenza HA-ferritin nanoparticles showed a positive correlation between increased ferritin-specific CD4+ GC Tfh cells and increased HA-specific GC B cells and antibody secreting cells (44). Overall, these studies suggest that current influenza vaccine strategies are ill-equipped at generating universal broadly neutralizing antibodies, possibly in part to mechanisms such as epitope masking by pre-existing antibodies (11, 45–47).…”

Viral immunity: Basic mechanisms and therapeutic applications—a Keystone Symposia report

“…Importantly, the single mouse strain lacking CD4 + T cell epitopes in the ferritin core (C57BL/6) did not display enhanced B or CD4 + T cell responses relative to the conventional trimer construct, showing that the ferritin core CD4 + T cell epitope composition is a central and requisite feature of its enhanced B cell immunogenicity of the ferritin nanoparticle. Thus, low CD4 + T cell activity can limit the high‐affinity B cell response to clinically relevant vaccines and this feature needs to be optimized in vaccination strategies designed to elicit robust B cell responses to multimeric viral antigens 90 …”

Self‐Assembled Multiepitope Nanovaccine Provides Long‐Lasting Cross‐Protection against Influenza Virus

“…[ 21 ] The self‐assembled ferritin, as a natural and safe biomaterial, has good biocompatibility, biodegradability, stability, and surface modifiability. [ 22 ] The antigen of interest can be fused with the N ‐terminal (Asp5) of the ferritin subunit, and subsequently, multiple antigens can be displayed on the surface of ferritin nanoparticles, thereby enhancing its immunogenicity. [ 23 ] Ferritin nanoplatforms have been widely used to display antigens from different pathogens, including IV, [ 24 ] enterovirus 71 (EV71), respiratory syncytial virus, [ 25 ] canine distemper virus, [ 26 ] and SARS‐CoV‐2.…”