The goal of this clinical trial is to compare a newly developed off-the-shelf cryopreserved "ready to inject" Mesenchymal Stem Cell (MSC) product with the usual MSC preparation the investigators have used in knee osteoarthritis (OA) patients. Since usual MSC therapy requires cell manipulation in GMP (Good Manufacturing Practices)-type facilities, this new formulation would enable wider access to Cell therapy and Multicentric clinical trials in areas devoid of expensive facilities and equipment.

This is a double blind randomized controlled trial testing a modified formulation of an allogenic Umbilical cord (UC) derived MSC therapy that the investigators have used in a prior published clinical trial. It has been modified and characterized according to the standards of quality control that are required for the development an off-the-shelf cryopreserved MSCs product.

This so called "ready to inject" MSC preparation will be compared with the usual MSC formulation that requires centrifugation and resuspension in different media, thus requiring access to advanced (GMP-type) facilities.

A total of 60 symptomatic knee OA patients will be randomized (1.1 ratio) to receive one or the other MSC product at baseline and month 6, to be followed blindly for 12 months with baseline and end of study knee MRI imaging.

The primary endpoint of the trial will be the safety according to the occurrence of adverse events (AEs) as coded by the Common Terminology Criteria for Adverse Event classification. The secondary endpoint will be efficacy, as assessed by the following validated clinical outcome measures: Western Ontario and Mc Master Universities Arthritis Index (WOMAC) Spanish validated version, Pain Visual Analog scale (VAS), Quality of life by the Short-form 36 (SF-36) questionnaire, Patient Global Assessment, and the Outcome Measures in Rheumatology Committee (OMERACT)-Osteoarthritis Research Society International (OARSI) Responder Index Criteria. Baseline MRI will be performed mainly to exclude meniscal lesions associated with accelerated knee OA. Final (12 month) MRI will be performed to assess structural change in response to treatment

The completion of this project represents a main technological advance, eventually leading to the scalability and enhanced quality control of a much needed treatment, within reasonable costs and logistics, and in particular, with no need of a GMP facility at the point of care or of clinical testing

Inclusion Criteria:

• Symptomatic knee OA defined by grade 1-3 Kellgren-Lawrence radiographic changes in the targeted knee.
• Daily pain at the affected joint for at least 3 months before inclusion

Exclusion Criteria:

• Bilateral symptomatic knee OA (only if the contralateral knee has more severe disease)
• Meniscal rupture.
• Condylar or tibial plateau generalized bone marrow edema on MRI
• Major axial deviation defined by valgus (>10°) or varus (5°) deformity of the involved leg
• Use of oral or intra-articular steroids or hyaluronic acid in the past 6 months
• Ipsilateral hip or ankle pain, local or systemic infection
• Any form of secondary arthritis, previous malignancy, or body mass index ≥30.

Sharing upon request after publication of the trial.

At trial termination and publication.

Data will be shared with researchers or scholars with no conflict of interest and once we have confirmed the data are not subject to confidentiality due to intellectual property or other issues.

Participants, providers, investigators and outcome assessments will be blind to randomization except in need to open code for security reasons