Allogeneic mesenchymal stromal cell injections for knee osteoarthritis: a review of clinical outcomes.

Mesenchymal stromal cell (MSC) therapy is an injectable, orthobiologic treatment for patients with knee osteoarthritis (OA). The purpose of this narrative review is to evaluate the literature on allogeneic MSCs used in knee OA patients and to report on clinical outcomes. A comprehensive literature search was performed using the following keywords: osteoarthritis, knee, stem cell transplantation, allogeneic or allogenic, human mesenchymal stem cells, and human mesenchymal stromal cells. There was no restriction on time, and subjective and objective clinical outcomes were reported. A total of 11 (n = 11) clinical trial studies were included. The most common allogeneic source was adipose tissue (AD-MSCs). Most studies included a control group and included participants with Kellgren-Lawrence grades of II-III or II-IV. The MSC dose used was highly variable. There were no significant adverse safety events. All studies reported an improvement in patient reported outcomes from baseline, with the most common observation being a durable reduction in pain for 6 to 24 months. There were positive effects of AD-MSCs on cartilage imaging in most studies, although outcomes were variable. Allogeneic MSC injections for knee OA resulted in improved OA related symptom scores, are safe, and provided patients with a reduction in pain at long-term follow-up.