Preclinical Safety and Efficacy of an Allogeneic Adipose-Derived Mesenchymal Stem Cell Medicinal Product for Rotator Cuff Repair: A Two-Phase Experimental Study.

Abstract

Cell therapy with adipose-derived mesenchymal stem cells (ASCs) is a promising biological augmentation strategy for rotator cuff repair; however, before clinical translation, regulatory frameworks mandate rigorous preclinical characterization of safety. We report the complete preclinical program evaluating both the safety of an allogeneic ASC-based cell therapy medicinal product (CTMP) and its efficacy in a chronic rotator cuff tear model. Phase I (safety, 164 immunodeficient nude BALB/c mice) assessed toxicity, biodistribution, and tumorigenicity after intra-articular (IA) and intravenous (IV) administration at doses ranging from 10× to 1000× the projected clinical dose. Toxicity was evaluated by biochemical panels and full-body histopathology at 90 days. Biodistribution was quantified by FDG-PET/CT (days 45 and 90) and human-specific qPCR (Alu-repeat) at 90 days. Tumorigenicity used an HT-29 positive-control model. Phase II (efficacy, 48 Sprague-Dawley rats) used a validated 4-week chronic supraspinatus tear-and-repair model; after repair, animals received ASCs in suspension (n=24) or Hypothermosol vehicle (n=24) and were assessed histologically (Åström-Rausing scale) and biomechanically (Instron 4411) at 4 months. In Phase I, no biochemical or histopathological toxicity attributable to the CTMP was detected at any dose or route. Three animals showed FDG-PET findings compatible with neoplasm but were histologically negative, confirming assay specificity. qPCR detected strong human DNA signals exclusively at the highest IV doses (≥500×), limited to the injection site (tail) and one heart sample; maximum retention was 1.75% at 90 days. After IA administration at the clinical dose (10×), human ASCs persisted locally in 21% of animals at 90 days with no systemic dissemination. In Phase II, no statistically significant differences between groups were found in total histological score (median: 2 vs 1; p=0.811), any individual histological parameter, maximum load to failure (51.99±9.1 N vs 50.97±9.1 N; p=0.770), tendon displacement (5.33±1.2 mm vs 5.53±1.4 mm; p=0.852), or stiffness (17.28±4.96 N/mm vs 14.85±4.01 N/mm; p=0.669). This allogeneic ASC-based CTMP demonstrated a favorable safety profile across all tested doses and administration routes, supporting its candidacy for clinical development. Efficacy in suspension delivery over a repaired chronic tear was not demonstrated; immune-mediated rejection and mechanical displacement represent additional explanatory factors alongside cell retention failure, and should guide the design of next-generation delivery strategies.