Comment from Anonymous

Docket No. FDA-2026-N-4162 To: Vaccines and Related Biological Products Advisory Committee (VRBPAC) Meeting Date: June 18, 2026 Subject: Notice Regarding Systemic Distribution, Endothelial Transfection, and Antigen Presentation Pathways of the SM-102 LNP Platform for MFLUSIVA (BLA STN 125869/0) 1. Executive Summary This submission assesses the lipid nanoparticle (LNP) delivery vehicle utilized in Moderna’s seasonal influenza formulation, MFLUSIVA. Peer-reviewed literature, cellular assays, and regulatory filings demonstrate that the synthetic ionizable amino lipid SM-102 exhibits wide systemic distribution and transfects non-immune structural tissues, specifically vacular endothelial cells. By forcing these cells to synthesize viral antigens endogenously, the platform initiates a Major Histocompatibility Complex Class I (MHC-I) intracellular pathway. This mechanism models an intracellular viral infection within vascularized structures, rendering transfected host cells targets for cell-mediated cytotoxic destruction—a pathway distinct from traditional antigen-based vaccines. 2. Technical Evaluation of SM-102 Mechanics I. Systemic Transit and Endothelial Homing Preclinical tracking studies demonstrate that the SM-102 LNP formulation does not remain sequestered within localized muscle tissue. A measurable fraction moves beyond the injection site, draining into the local lymphatic network and entering the systemic circulation (Pardi et al., 2015; Hassett et al., 2019). In plasma, SM-102 LNPs adsorb blood proteins to form a dynamic biomolecular corona. Endogenous Apolipoprotein E (ApoE) binds with high affinity to this surface, acting as a targeting ligand for Low-Density Lipoprotein Receptors (LDLR) natively expressed across human vascular endothelial cell walls (Sebastiani et al., 2021; Kulkarni et al., 2021). This promotes receptor-mediated endocytosis by off-target vascular endothelial cells. II. Intracellular Release and Presentation Divergence Following endocytosis, structural pKa​ shifts of the ionizable lipid SM-102 during endosomal acidification destabilize the membrane, releasing the mRNA payload into the host cell cytoplasm for ribosomal translation (Kulkarni et al., 2021; Cayman Chemical Company, 2023). Traditional vaccine platforms utilize pre-formed antigens captured externally by professional antigen-presenting cells (APCs) and processed via the extracellular pathway on MHC-II molecules to stimulate helper T cells without marking host cells for destruction. In contrast, the SM-102 vehicle mimics an active intracellular viral infection by forcing structural somatic cells to manufacture viral antigens endogenously. These proteins are cleaved by the immunoproteasome, translocated via TAP molecules into the endoplasmic reticulum, loaded onto MHC-I molecules, and presented on the cell surface (Szabo et al., 2022). III. Cytotoxic T-Cell Attack and Localized Histopathology Antigen-specific CD8+ Cytotoxic T Lymphocytes (CTLs) recognize these surface peptide-MHC-I complexes via matching T-Cell Receptors (TCRs). This establishes an active immunological synapse, causing CTLs to release perforin and granzymes that induce targeted, cell-mediated apoptosis of the antigen-displaying structural host cells. Clinical pathology reports, tissue biopsies, and autopsy series confirm that where transfected host cells aggregate near sensitive vascularized structures, this cytotoxic pathway manifests as focal clusters of CD8+ T-cell infiltration, localized structural cell necrosis, and microvascular wall inflammation (Schwab et al., 2023; Baumeier et al., 2022). Because immunological memory establishes long-lived antigen-specific T-cell populations, any persistent or repeated expression of the target peptide via this endogenous MHC-I pathway can reactivate this localized cell-mediated cytotoxic response. 3. Conclusion The scientific literature and regulatory filings indicate that the mRNA-LNP platform functions as an active delivery architecture that shifts antigen processing from traditional extracellular immune consumption to an intracellular, cell-mediated presentation pathway. This notice provides the committee with these verified pharmacokinetic and cytotoxic profiles to ensure a rigorous evaluation of BLA STN 125869/0. References Baumeier, C., et al. (2022). J. Pers. Med., 12(8), 1348. Cayman Chemical Company. (2023). Ionizable Lipid Composition Influences LNP Efficacy In Vitro. Application Note. EMA. (2021). Assessment Report: COVID-19 Vaccine Moderna. EMA/156877/2021. Hassett, K. J., et al. (2019). Mol. Ther., 27(4), 850-863. Kulkarni, J. A., et al. (2021). Nat. Nanotechnol., 16(6), 630-643. Pardi, N., et al. (2015). J. Control. Release, 217, 345-351. Schwab, C., et al. (2023). Clin. Res. Cardiol., 112(3), 431-440. Sebastiani, F., et al. (2021). ACS Nano, 15(4), 6709–6722. Szabo, G. T., Mahiny, A. J., & Vlatkovic, I. (2022). Mol. Ther., 30(5), 1850-1868.