Stabilizing Macrophage Immune States through Fusion-Enabled Nanoparticle-Based Intracellular Drug Depots for Durable Ulcerative Colitis Therapy

Ulcerative colitis (UC) is characterized by persistent colonic inflammation accompanied by the accumulation of pro-inflammatory M1-like macrophages, which sustain cytokine production and impair mucosal repair. Promoting a shift toward a pro-resolving M2-like phenotype is therefore a promising strategy, but current macrophage-modulating approaches are often limited by insufficient intracellular drug persistence and rapid phenotypic reversion after treatment withdrawal. Herein, we report a therapeutic strategy designed to achieve prolonged immunomodulation of macrophages. Specifically, we develop an orally administrable, fusion-enabled nanoparticle (OFEN) to enable improved intracellular availability of immunomodulatory agents in macrophages. By tuning the cholesterol content of milk-derived exosome membranes, OFEN exhibited gastrointestinal stability and fusion-biased cellular entry with reduced endolysosomal sequestration. Following cellular uptake, the poly(lactic-co-glycolic acid) (PLGA) core served as an intracellular reservoir for the prolonged release of tumor necrosis factor-α (TNF-α) siRNA and curcumin, thereby combining sequence-specific suppression of a central inflammatory mediator with broader immunomodulatory and antioxidative regulation. This intracellular exposure sustained M2-associated phenotypic modulation and reduced pro-inflammatory cytokine production. In a chronic colitis model, intermittent OFEN administration alleviated disease activity, preserved colonic architecture, and promoted epithelial barrier-associated recovery, producing greater therapeutic benefit than 5-aminosalicylic acid (5-ASA) and the less fusogenic counterpart under the same intermittent dosing schedule. In a dextran sulfate sodium (DSS) rechallenge model, protective effects remained detectable at the day-12 assessment following a single oral administration of OFEN. Collectively, these findings support fusion-biased, depot-like intracellular retention as a strategy for prolonging macrophage-directed immunomodulation in UC.