This is an interventional, single arm, phase I/IIa clinical trial to investigate the efficacy and safety of ABCB5+ mesenchymal stem cells (MSCs) on wound healing in patients with chronic venous ulcer (CVU). Autologous MSCs will be isolated ex vivo from a small skin biopsy and will be expanded in vitro. The IMP APZ2 incorporating the ABCB5+ will then be applied on the wound surface of CVU under local anesthesia.