Structure-Guided Design of CD4 T cell Memory-Enhanced rHA H7N9 Influenza Vaccine

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ABSTRACT Routine influenza exposure and vaccination generate inadequate cross-protective immunity against novel avian influenza. This fuels concerns for pandemics that may cause high numbers of severe illness and deaths in immune naïve populations. Avian H7N9 influenza poses a threat to human health because of its high case fatality rate consistently observed in annual epidemic waves since it emergence in 2013. The potential for virus adaptations that increase human-to-human transmissibility raises concern for an H7N9 influenza virus pandemic. H7N9 influenza HA elicits weak neutralizing antibody responses in natural infection and vaccination. To prepare for an H7N9 influenza pandemic, vaccine strategies that overcome the poor immunogenicity of H7N9 HA are needed. We hypothesize that a stronger CD4+ T cell response to H7N9 HA will support an improved hemagglutination inhibition (HI) antibody response. To address this hypothesis, we propose to introduce seasonal HA-specific CD4+ T cell epitopes into H7N9 HA, using a structure-guided approach, to produce a novel immunogen capable of priming protective HI responses by inducing CD4+ T cell memory. The proposed studies are grounded in our prior work showing that the H3-HA306-318 CD4+ T cell epitope introduced into the corresponding site in H7N9 HA boosts effector T cell and antibody immune responses while preserving neutralizing antibody epitopes that would be encountered in natural infection. Here, we propose to introduce more memory CD4+ T cell epitopes into the existing optimized H7-HA because the frequency of CD4+ T cells that recognize the H3-HA306-318 epitope varies among individuals depending on their history of seasonal influenza exposure. Aim 1 will evaluate novel HAs composed of different numbers of engineered CD4+ T cell epitopes. A new HA containing the fewest engineered seasonal HA CD4+ T cell epitopes that best approximates the biophysical properties of wild type H7N9 HA and demonstrates enhanced mouse and human immune responses over wild type H7N9 HA will be selected to go forward to Aim 2 refinement studies. In Aim 2, we will reduce the mutational load of the immunogen that emerges from Aim 1 to generate an improved design that maintains the gain in protective immunity while more closely preserving structural and biophysical properties of wild type H7- HA. The benefits of a lower mutational load will be minimized perturbation to neutralizing antibody targets and improved manufacturability. The proposed studies will identify a lead candidate with minimum mutational load and maximal immunogenicity and protective efficacy that is ready for IND enabling studies by the end of this Partnerships program.