• Male or female aged 20 to 79 years at informed consent.

• Diagnosis of OAK classified as Kellgren-Lawrence (K-L) Grade 2 to 4 based on plain lower extremity X-ray.

• OAK eligible for proximal tibial osteotomy based on the following criteria: Range of motion (ROM): \>=120 degree flexion, \<=5 degree extension

• Preoperative cartilage defect of the femoral condyle/trochlear groove or medial tibial condyle with an area of \>=4 cm2 per defect site.

• Total defect area of \<=21 cm2 in individuals with multiple cartilage defects.

• Body mass index (BMI) \<30.

• No coexisting ligament injury requiring surgery, and no meniscal injury requiring suturing or surgical repair other than partial resection, in the target knee.

• No history of ligament reconstruction, meniscal suturing, total meniscectomy or bone marrow stimulation, and no history of treatment with regenerative medicine products (including investigational products), cell processing products or gene therapy, in the target knee.

• No history of treatment with hyaluronic acid products and/or opioid for severe pain in the target knee within 1 month prior to informed consent.

⁃ No history of treatment with corticosteroid products and/or immunosuppressive drug in the target knee within 3 months prior to informed consent.

⁃ No history of platelet-rich plasma (PRP) therapy within 6 months prior to informed consent.

⁃ Non-smoker; provided, however, that smokers will be eligible for study entry if they consent to abstain from smoking from 3 months prior to proximal tibial osteotomy or proximal tibial osteotomy+RMSC until postoperative bone healing.

⁃ Written informed consent to participate in the study on a voluntary basis.