The purpose of this study is to investigate the efficacy and safety of transplantation of umbilical cord mesenchymal stem cells（UCMSCs） in patient with Knee cartilage damage.

Human cartilage only has limited regenerative potential. Transplantation of umbilical cord mesenchymal stem cells (UCMSCs) is a promising strategy given the high proliferative capacity of MSCs and their potential to differentiate into cartilage-producing cells - chondrocytes. The acquisition of ucMSCs does not require invasive surgical intervention or cartilage extraction from other sites as required by other cell-based strategies. The investigators inject allogeneic human mesenchymal stem cells to the cartilage lesions in patients via intra-articular injection method, and to investigate the efficacy and safety。

Inclusion Criteria:

• Patients whose lesion (single joint) should be in the range of 2 cm^2-8 cm^2.
• Patients with pain in affected joint of 60 mm- 100 mm VAS (visual analogue scale)
• Patients with articular swelling, tenderness and active range of motion of Grade 2 or below
• Patients with knee joint cartilage defect or injury of ICRS (International Cartilage Repair Society) Grade 4 confirmed by arthroscopy (At screening, patients diagnosed as such with an MRI may be included)
• Patients who needs invasive interventions of arthroplasty due to no response from existing pain medication
• Patients voluntarily agreed to participate in the study and signed informed consent

Exclusion Criteria:

• Patients with autoimmune diseases or medical history
• Patients with infections requiring injection of antibiotics
• Patients with severe internal diseases
• Patients who are currently pregnant or lactation
• Patients who had participated in any other clinical trials within the past four weeks
• Patients who had been administered with immunosuppressants within the past four weeks
• Patients whom the principal investigator considers inappropriate for the clinical trial due to any other reasons than those listed above