Bioactivity of a tissue-engineered product: bridging the gap between academic and clinical studies

The translation of cell-based therapeutics from academic and fundamental sciences to clinical trial settings follows a preclinical pathway with rigorous regulatory oversights to ensure the cellmediated therapeutic effect. Although international guidelines thoroughly describe single-dose toxicity and biodistribution studies, the quantitative evaluation of the biological activity remains a major challenge for biotechnology companies and authorities. Here we discuss a strategy to demonstrate the bioactivity of an osteogenic tissue-engineered product intended to promote angiogenesis and osteogenesis in a bone defect. Osteogenic 3-dimensional (3D) grafts were manufactured as a pharmaceutical batch. A sequence of chemical treatment was applied on the native graft in view to obtained a decellularized 3D-matrix as confirmed by a reduction of >90% and 40-80% of the cellular and growth factors (VEGF, IGF1) contents, respectively. Decellularized and native grafts were implanted intra-muscularly (after cauterization of the lumbar region, n=10 nude rats) to assess the mineralization (X-ray microCT and histomorphometry on Von Kossa staining) and angiogenesis (histomorphometry on Masson’s Trichrome and Von Willebrand Factor immunostaining) at day 29 postimplantation. Human cells detection (in the explanted tissue) were also quantified after KU80/HLA type I immunostaining at the implantation site. A significant higher mineralization was found for explanted samples from the native osteogenic 3D grafts in comparison to the decellularized tissues (Bone volume/tissue volume of 2.92 ± 1.12% vs. 0.38 ± 0.59%, respectively.