3.1. MSC Characterization
The MSCs were spindle-shaped in plastic-adherent culture and capable of differentiation into adipocytes and osteoblasts, as evidenced by lipid vacuole accumulation and the deposition of mineralized matrix, respectively. This was confirmed after cell isolation and sorting as well as for exemplary MSC portions that had been thawed, expanded, and used for treatment. After isolation and sorting, the MSCs were positive for the inclusion markers CD29, CD44, and CD90 (87%, 99%, and 75% positive cells, respectively) but widely negative for CD73 and CD105 (1% and 6%, respectively). They also showed very low expression of the exclusion marker antigens CD14, CD34, CD45, CD79α, and MHCII (2%, 4%, 5%, 0%, and 3%, respectively). The immunophenotype remained similar after thawing and further expansion, albeit with overall decreased percentages of positive cells. An exemplary analysis of the MSCs used for treatment (i.e., after thawing and expansion) is shown in 