Harmonizing immunogenicity for AAV and LNP/mRNA modalities: best-practice panels for binding, neutralizing, and cellular assays with pre-existing immunity controls

INTRODUCTION: Immunogenicity remains the principal constraint on the efficacy, safety, and re-dosing of adeno-associated virus (AAV) and lipid nanoparticle (LNP) - mRNA therapeutics. Clinical decision-making and comparability between programs are hampered by heterogeneous test formats and matrix effects. AREAS COVERED: This narrative review integrates 2023-2025 bench, translational, clinical, and regulatory evidence. Studies on binding, neutralizing, and cellular/innate tests, anti-PEG epidemiology, complement biology, and ultrasensitive digital immunoassays were identified through searches of PubMed, Web of Science, Google Scholar, and regulatory archives. We propose a panel with tiers: Tier-0 pre-screening using isotype-resolved anti-PEG and total anti-capsid; Tier-1 standardized cell-based transduction inhibition with an optional constant-serum-concentration design to reduce dilution-induced matrix bias; Tier-2 mechanistic cellular and innate panels (e.g. complement split products, cytokines, and capsid-specific T-cell assays); and Tier-3 attomolar digital assays for critical biomarkers. FUTURE PERSPECTIVE: By implementing this harmonized, matrix-aware panel, which is presented as a fit-for-purpose analytical best-practice proposal rather than an evidence-validated clinical standard, screening-failure bias can be minimized, eligibility criteria can be stabilized, and connections between assay results and dosing, monitoring, and re-dosing/deferral may be strengthened.