Therapeutic Exosomes: From Molecular Biology to Clinical Translation.
INTRODUCTION Exosomes, extracellular vesicles of 30-150 nm generated via fusion of multivesicular bodies with the plasma membrane, have evolved from poorly characterized cellular byproducts into a promising platform for translational medicine. Their intrinsic biological properties, including low immunogenicity, biocompatibility, capacity to cross the blood-brain barrier, and natural tissue tropism, confer fundamental advantages over synthetic nanocarriers. METHODS This review systematically covers biogenesis (ESCRT-dependent and ceramide-mediated pathways), molecular cargo composition, cellular sources and GMP-- compliant manufacturing, pharmacokinetics and biodistribution, clinical experience across major disease areas, engineering strategies for cargo loading and surface modification, and the current regulatory landscape. RESULTS Exosome biogenesis is orchestrated by ESCRT-0-III complexes and the neutral sphingomyelinase pathway, yielding vesicles enriched in tetraspanins (CD63, CD9, CD81), heat-shock proteins, and functional nucleic acids including miRNA and circRNA. Mesenchymal stromal cell-derived exosomes dominate clinical pipelines, with scalable 3D hollow-fiber bioreactor production enabling GMP-grade manufacturing. Circulating half-lives vary markedly by source: most cell line-derived exosomes are cleared within 2-30 minutes, whereas platelet-derived EVs persist in circulation for 5.3-5.8 hours. These values are substantially prolonged by CD47-mediated phagocytosis evasion and PEGylation. Engineering approaches, LAMP-2B-mediated genetic display of targeting ligands, click chemistry conjugation, and hybrid Exosome-Liposome Nanoparticles (HELN)markedly enhance tissue selectivity and therapeutic potency. Completed Phase I-IIb trials in oncology and pulmonology demonstrate favourable safety profiles without severe systemic adverse events. As of 2025-2026, no extracellular vesicle therapeutic has received regulatory approval by the FDA, EMA, or equivalent agencies. DISCUSSION Engineered exosomes combine multicomponent cargo, context-dependent uptake, and tissue tropism in a single platform. Validated potency assays, batch consistency, and regulatory harmonisation remain the principal unresolved barriers to clinical approval. CONCLUSION Convergence of AI-driven manufacturing optimisation, multimodal engineering platforms, and international regulatory harmonisation defines the translational roadmap for exosome-based medicines over the coming decade.