In this study, the short-term results are encouraging and demonstrate that knee arthroscopy with IPFP cell concentrates containing MSCs provide assistance in reducing pain and improving function in patients with knee cartilage lesion, especially 6 months and 12 months after surgery. In addition, no significant difference was found in the WOMAC and VAS scores in early stages of surgery between the two groups. This may probably because the main effect of MSCs in cell concentrates focuses more on cartilage regeneration other than anti-inflammation effect in early stage [12, 24]. In the aspect of safety, this kind of therapy did not enhance the probability of postoperative infection and had no obvious influence on hepatic and renal function of patients.
Cartilage lesion has a very limited intrinsic healing capacity. With less vessels, nerves, and lymphoid tissue around, cartilage with large lesion undergo repairment only with the production of fibrous tissue or fibrocartilage [3]. Therefore, degeneration occurs subsequently and can progress to osteoarthritic changes in many cases [25].
MSCs, such as bone marrow mesenchymal stem cells (BMSCs), synovial-derived mesenchymal stem cells (SDMSCs), and adipose-derived mesenchymal stem cells (ADMSCs), can be extracted from different kinds of tissue, whereas only MSCs derived from bone marrow and adipose can be acquired in a large amount for clinical use [14–16, 26–29]. Compared with BMSCs,ADMSCs have more active proliferative capacity, and the acquiring procedure of them causes less damage to the donor zone [24, 30–32]. Meanwhile, studies have also showed that MSCs from different kinds of tissue have significantly different ability of proliferation and differentiation. According to Zhang et. al[33], compared with MSCs derived from synovium lining the joint capsule, and synovium surrounding the cranial cruciate ligament, MSCs from infrapatellar adipose tissue shows a higher ability of proliferation and differentiation.
Recent studies have suggested that MSCs treating knee cartilage lesion is a save way to alleviate pain and improve knee function[34–36]. Toghraie et al[37] used scaffold free MSCs obtained from IPFP in an experimental animal model of osteoarthritis by direct intraarticular injection. Rabbits receiving MSCs showed lower degree of cartilage degeneration, osteophyte formation, and subchondral sclerosis than control experiment group 20 weeks after surgery. According to the study by Liu et al[38], it is possible to generate robust, flexible cartilage-like grafts of scale, opening up the possibility that tissues engineered using IPFP-MSCs derived from OA patients could potentially be used to resurface large areas of joint surfaces damaged by trauma or disease. Skalska U et al[39] shows that MSCs derived from IPFP of rheumatoid arthritis (RA) patients have comparable or slightly stronger osteogenic potential than that from osteoarthritis patients. Koh et al[40, 41] launched several stem cell injections combined with arthroscopic debridement to patients with knee OA. The short-term results demonstrats that IPFP-MSCs therapy with intraarticular injections is safe and aids in reducing pain and improving function in patients with knee osteoarthritis. Based on the in vivo studies above, our study provided a larger sample and more controlled experiments. Meanwhile, MOCART scores were added to evaluate cartilage regeneration. Moreover, flow cytometry was also used to examine the positive rate of MSCs among cell concentrates derived from IPFP through knee arthroscopy.
In our study, cell concentrates containing MSCs instead of pure stem cells were injected into knee cavity. Compared with pure stem cells, the procedure to acquire cell concentrates could be simple and quick, thus decreasing the operating time and reducing the risk of infection caused by times of injection. On the other hand, as cell concentrates were derived from IPFP abandoned during regular arthroscopy surgery, it could be a kind of waste recycling and significantly reduce the cost of surgery, thus increasing the compliance of patients.
Instead of being cultured like other research, cell concentrates containing MSCs were injected into the corresponding joint cavity directly during the arthroscopy surgery. It is widely believed that local microenvironment during culture can affect the differentiation of MSCs[27, 28, 42–46], and the culturing process can add the risk of infection. According to the studies, it is known that the proliferation and differentiation of MSCs can be influenced by the paracrine effects of the cytokines and growth factors released by the grafted cells, which can trigger host-associated signaling pathways, increase angiogenesis, and decrease apoptosis. López-Ruiz et al[47] proves that cells exposed to chondrocyte extracts acquires a characteristic morphological and ultrastructural chondrocyte phenotype that is confirmed by the increased proteoglycan formation and enhanced collagen II immunostaining. Moreover, chondrocyte extracts induces an increase in mRNA expression of chondrogenic genes such as Sox9, L-Sox5, Sox6 and Col2a1.
According to the identification standards proposed by International Society for Cellular Therapy (ISCT) in 2006, MSCs should meet the standards below: (1) cell adhesion growth in vitro; (2) positive expression of CD44, CD73, CD90, and CD105 (positive detection rate of flow cytometry > 95%) and negative expression of CD11b, CD14, CD19, CD34, CD45, CD79α, and HLA-DR (the positive detection rate of flow cytometry < 2%); and (3) having the capabilities to differentiate into osteoblasts, adipocytes, and cartilage cells in vitro in specific culture conditions[21]. In this study, according to the results of flow cytometry, an average of 4.38 ± 2.29% of cells extracted were found to be stem cells, meeting the standards above.
It is shown that clinical effect of treating knee cartilage lesion with knee IPFP cell concentrates is positive. But as the number of cells derived is limited, this kind of therapy is only suitable for small area of cartilage injury. According to a review by Richter. D. L[48], for cartilage lesion of small area (> 2 cm2), microfracture and cartilage autotransplantation are the best choice. As for areas between 2 and 4 cm2, cartilage autotransplantation and chondrocyte autotransplantation have the similar therapeutic effect. For areas beyond 4 cm2, chondrocyte autotransplantation is the best choice. Although clinical effect of treating knee cartilage lesion with knee IPFP cell concentrates is positive, randomized controlled trials with larger sample and further follow-up period are still needed. So far, there are still several technical obstacles to be conquered, such as finding a better method to extract and purify, keeping the multipotential differentiation, promoting the specificity and function, and enhancing the ability of survival and cartilage regeneration of IPFP-MSCs.
The present study has some other limitations. The first is that the number of cells to be injected was limited and not equal among patients. Second, the sample size was small, while the follow-up period was short. Last, we were unable to perform either a routine second-look arthroscopy or a pathologic examination. In addition, we lost nearly 5% of our patients when these individuals refused to participate in some parts of follow-up visits.
In the future, tissue-engineering techniques with cell concentrates containing MSCs hold promise for repairing damaged cartilage within joints. At present, although further randomized controlled clinical trials of this treatment, with more patients and longer follow-up periods are still needed, this study proposes a new option for clinical treatment of knee cartilage lesion.