Comment from Anonymous

Docket No. FDA-2026-N-4162 TO: Food and Drug Administration (FDA) Vaccines and Related Biological Products Advisory Committee — June 2026 Meeting SUBJECT: Public Comment – MFLUSIVA (Influenza Vaccine, mRNA); BLA STN 125869/0 PURPOSE: To add to the record a concise, literature-anchored rationale regarding the distinct pharmacokinetic and biophysical profiles of mRNA lipid nanoparticle (LNP) platforms compared to traditional influenza vaccines. Fixed Antigen Dosage vs. Cellular Transfection Kinetics Traditional influenza vaccines deliver a precise, pre-measured dose of a static antigen that remains largely localized. Conversely, mRNA platforms utilize LNPs as transfection vehicles to deliver genetic blueprints, prompting host cells to manufacture the antigen in vivo. Because individual cellular uptake, translation efficiency, and the kinetics of antigen production vary among recipients, the internal pharmacokinetic profile differs fundamentally from conventional vaccines. Consequently, standard bioequivalence and safety models must account for these platform-specific variables. Literature-Anchored Biophysical Considerations 1. Biomolecular Corona Formation and Biodistribution Unlike traditional vaccines with highly predictable surface characteristics, LNPs adsorb host plasma proteins upon systemic entry, forming a dynamic "protein corona" (Cedervall et al., 2007; Monopoli et al., 2012). This biomolecular layer influences cellular targeting, interactions with receptor pathways, and clearance mechanisms (Francia et al., 2020; Schöttler et al., 2016). Characterizing these corona dynamics is critical to modeling LNP pharmacokinetics accurately across diverse patient populations. 2. Innate Immune and Complement Interactions Synthetic lipid formulations can interact with the innate immune system, including the complement cascade (Moghimi et al., 2011). Transient complement activation by nanomedicines can influence early reactogenicity profiles and accelerate the rate of particle clearance by the mononuclear phagocyte system (Szebeni, 2005). This specific lipid-mediated pathway requires distinct safety and monitoring considerations not typically associated with highly purified traditional protein antigens. 3. Surface Interactions and Protein Conformation The binding of plasma proteins to nanoparticle surfaces can induce localized changes in native protein secondary structure (Lynch & Dawson, 2008; Nel et al., 2009). These structural alterations can modify how the adsorbed proteins interact with cell-surface receptors (Fleischer & Payne, 2014). Understanding these soft-matter surface properties is necessary for mapping out downstream cellular interactions and verifying platform-specific biocompatibility. 4. Influence on Protein Microenvironments In model environments, nanoscale surfaces can affect the local behavior and kinetics of surrounding macromolecules (Linse et al., 2007; Mahmoudi et al., 2013). The specific lipid composition, phase behavior, and surface charge density of an LNP dictate its immediate microenvironment. Evaluating these biophysical surface interactions is an established component of nanomedicine characterization. References Cedervall, T., Lynch, I., et al. (2007). Understanding the nanoparticle–protein corona. PNAS, 104(7), 2050–2055. Fleischer, C. C., & Payne, C. K. (2014). Secondary structure of corona proteins determines cell surface receptors. J. Phys. Chem. B, 118(49), 14017–14026. Francia, V., Schiffelers, R. M., Cullis, P. R., & Witzigmann, D. (2020). The biomolecular corona of lipid nanoparticles for gene therapy. Bioconjugate Chem., 31(9), 2046–2059. Linse, S., Cabaleiro‑Lago, C., et al. (2007). Nucleation of protein fibrillation by nanoparticles. PNAS, 104(21), 8691–8696. Lynch, I., & Dawson, K. A. (2008). Protein‑nanoparticle interactions. Nano Today, 3(1-2), 40–47. Mahmoudi, M., Kalhor, H., Laurent, S., & Lynch, I. (2013). The protein corona slows amyloid beta fibrillation. ChemBioChem, 14(5), 568–572. Moghimi, S. M., Peer, D., & Hunter, A. C. (2011). Activation of the complement system by nanomedicines. Adv. Drug Deliv. Rev., 63(12), 1000–1007. Monopoli, M. P., Åberg, C., Salvati, A., & Dawson, K. A. (2012). Biomolecular coronas provide the biological identity. Nat. Nanotechnol., 7(12), 779–786. Nel, A. E., Mädler, L., et al. (2009). Understanding biophysicochemical interactions at the nano–bio interface. Nat. Mater., 8(7), 543–557. Schöttler, S., et al. (2016). Protein adsorption is required for stealth effect of poly(ethylene glycol)-coated nanocarriers. Nat. Nanotechnol., 11(4), 372–378. Szebeni, J. (2005). Complement activation‑related pseudoallergy: A new class of drug‑induced acute toxicity. Toxicology, 216(2-3), 106–121.