(555f) Peptide Amphiphile Micelles As a Biomaterials Platform for Universal Influenza Vaccination

Despite 48% of adults receiving the flu vaccine this past year, there were still at least 4 million cases and 40,000 hospitalizations due to influenza during the 2021-2022 flu season. The yearly influenza vaccine protects against three or four specific influenza viruses, using forecasting to predict which strains will have the most significant impact in the upcoming year. Unfortunately, the predictions are not always accurate, sometimes reducing the efficacy of the flu vaccine for a given season. A universal vaccine could address this problem with broader protection against many, or even all, strains of influenza. A possible way to generate a universal vaccine is to focus on viral genomic regions that have considerable homology across various influenza strains. From those, subunit vaccines, contrary to the current live attenuated influenza vaccines, can be generated that consist of just the antigenic peptide epitope(s) associated with the virus. While these do not possess the complications associated with the replication and infection potential of the virus itself, peptides are known to be poorly immunostimulatory on their own, requiring a drug delivery system to enhance their efficacy.

A variety of biomaterials systems have been studied for subunit vaccine delivery, though a specific biomolecular material in peptide amphiphile micelles (PAMs) possess a number of exciting features for use in this application. PAMs are made of amphiphilic lipopeptides that self-assemble into nanoparticles in aqueous environments. Our previous research has shown that PAMs possess the capacity to self-adjuvant incorporated peptides to improve their overall vaccine potential. Building on this foundational work, we have focused on using our platform to deliver the M2_1-24 antigen, a potential universal influenza peptide vaccine candidate consisting of the first 24 residues of the M2 protein which are highly conserved and known to contain a B cell epitope. To further enhance the immune response to the incorporated antigen, adjuvants can also be packaged with the micelles, either associated with the micellar corona or core depending on adjuvant properties.

To fabricate various PAMs for this research, peptide amphiphiles (PAs) containing the M2_1-24 antigen were synthesized using solid-phase peptide synthesis. These PAs were hydrated with and without the TLR-2 agonist Pam₂CSK₄ adjuvant for which their micellization was characterized by standard techniques including the critical micelle concentration assay and transmission electron microscopy. Mice were immunized with formulations consisting of peptide or PAMs with or without adjuvant in PBS at days 0 and 21. Blood was collected 14 days after each vaccination and enzyme-linked immunosorbent assays were conducted on the samples to quantify antigen-specific antibody production induced by each vaccine formulation. PAMs supplemented with adjuvant showed similar levels of M2-specific IgG production as the positive control (i.e., M2 peptide plus Pam₂CSK₄). Even PAMs without adjuvant showed high levels of IgG production; however, antibodies were specific to an antigen on the peptide amphiphile that was not restricted to the M2 antigen, which could reduce protection against a live viral challenge. The inherent immunogenicity of the PAMs, even without adjuvant, is a positive, though ongoing work is underway to better understand how to restrict antigenic drift and shift within peptide amphiphiles and help to improve their overall performance as a universal influenza vaccine.