Immuno-Isolation Strategy with Tacrolimus-Loaded Nanofilm Promotes Stable Stem Cell-Based Cartilage Regeneration

Bone marrow stem cells (BMSCs)-engineered cartilage (BEC) shows promise for clinically repairing cartilage defects. However, when implanted in immunocompetent large animals, BEC becomes susceptible to ossification due to inflammatory infiltration. To address this, a nanofilm isolation approach is developed to enhance BEC's chondrogenic stability. Tacrolimus (FK506), known for its immunosuppressive effect, is integrated into adipic dihydrazide (ADH)-modified hyaluronic acid (HA), creating an acid-responsive macromolecular prodrug called FK506@HA-ADH. This prodrug is then blended with poly(lactic-co-glycolic acid) (PLGA) to form electrospun FK506@HA/PLGA nanofilm. Goat-derived BMSCs are induced in vitro to form BEC, which is enclosed within the FK506@HA/PLGA nanofilm and subcutaneously implanted in autologous goats. The nanofilm acted as a physical barrier, preventing immunocyte infiltration. Additionally, in response to the acidic environment triggered by inflammation and the gradual degradation of PLGA, the FK506@HA-ADH prodrug is cleaved, releasing FK506 as needed. The released FK506 effectively countered inflammatory cytokines and promoted cartilaginous maturity. These combined mechanisms significantly inhibited BEC hypertrophy and improved its chondrogenic stability within an immunocompetent goat model. This nanofilm-based isolation strategy established an immunosuppressive niche, successfully preventing endochondral ossification and promoting stable cartilage formation in BEC. These advancements are crucial for translating stem cell-based therapies into clinical use for cartilage repair.