The perspectives of regenerative medicine are still severely hampered by the host response to biomaterial implantation, despite the robustness of technologies that hold the promise to recover the functionality of damaged organs and tissues. In this scenario, the cellular and molecular events that decide on implant success and tissue regeneration are played at the interface between the foreign body and the host inflammation, determined by innate and adaptive immune responses. To avoid adverse events, rather than the use of inert scaffolds, current state of the art points to the use of immunomodulatory biomaterials and their knowledge-based use to reduce neutrophil activation, and optimize M1 to M2 macrophage polarization, Th1 to Th2 lymphocyte switch, and Treg induction. Despite the fact that the field is still evolving and much remains to be accomplished, recent research breakthroughs have provided a broader insight on the correct choice of biomaterial physicochemical modifications to tune the reaction of the host immune system to implanted biomaterial and to favor integration and healing.

Osteoarthritis (OA) is the most widespread musculoskeletal disorder in adults. It leads to cartilage damage associated with subchondral bone changes and synovial inflammation, causing pain and disability. The present study aimed at evaluating the safety of a dose-escalation protocol of intra-articular injected adipose-derived stromal cells (ASCs) in patients with knee OA, as well as clinical efficacy as secondary endpoint. A bicentric, uncontrolled, open phase I clinical trial was conducted in France and Germany with regulatory agency approval for ASC expansion procedure in both countries. From April 2012 to December 2013, 18 consecutive patients with symptomatic and severe knee OA were treated with a single intra-articular injection of autologous ASCs. The study design consisted of three consecutive cohorts (six patients each) with dose escalation: low dose (2 × 106 cells), medium dose (10 × 106), and high dose (50 × 106). The primary outcome parameter was safety evaluated by recording adverse events throughout the trial, and secondary parameters were pain and function subscales of the Western Ontario and McMaster Universities Arthritis Index. After 6 months of follow-up, the procedure was found to be safe, and no serious adverse events were reported. Four patients experienced transient knee joint pain and swelling after local injection. Interestingly, patients treated with low-dose ASCs experienced significant improvements in pain levels and function compared with baseline. Our data suggest that the intra-articular injection of ASCs is a safe therapeutic alternative to treat severe knee OA patients. A placebo-controlled double-blind phase IIb study is being initiated to assess clinical and structural efficacy. Significance: Although this phase I study included a limited number of patients without a placebo arm, it showed that local injection of autologous adipose-derived stem cells was safe and well tolerated in patients with knee osteoarthritis. This study also provides encouraging preliminary evidence of efficacy. Larger and controlled long-term studies are now mandatory to confirm whether this new strategy of cell therapy can improve pain and induce structural benefit in osteoarthritis.

Objective: To examine the effect of different sources of Good Manufacturing Practice clinical grade adipose‐derived mesenchymal stem cells (AD‐MSCs) on inflammatory factors in osteoarthritic (OA) chondrocytes and synoviocytes.Methods: AD‐MSCs from infrapatellar Hoffa fat, subcutaneous (SC) hip fat, and SC abdominal fat were cocultured in Transwells with chondrocytes or synoviocytes. Inflammatory factors (interleukin‐1β [IL‐1β], tumor necrosis factor α, IL‐6, CXCL1/growth‐related oncogene α, CXCL8/IL‐8, CCL2/monocyte chemotactic protein 1, CCL3/macrophage inflammatory protein 1α, and CCL5/RANTES) were evaluated by quantitative reverse transcription–polymerase chain reaction or multiplex bead–based immunoassay. The role of different immunomodulators was analyzed.Results: All the inflammatory factors analyzed were down‐modulated at the messenger RNA or protein level independently by all 3 AD‐MSC sources or by allogeneic AD‐MSCs used in coculture with chondrocytes or synoviocytes. Inflammatory factor down‐modulation was observed only when AD‐MSCs were cocultured with chondrocytes or synoviocytes that produced high levels of inflammatory factors, but no effect was observed in cells that produced low levels of those factors, thus highlighting a dependence of the AD‐MSC effect on existing inflammation. The immunomodulators IL‐10, IL‐1 receptor antagonist, fibroblast growth factor 2, indoleamine 2,3‐dioxygenase 1, and galectin 1 were not involved in AD‐MSC effects, whereas the cyclooxygenase 2 (COX‐2)/prostaglandin E₂ (PGE₂) pathway exerted a role in the mechanism of antiinflammatory AD‐MSC action.Conclusion: The antiinflammatory effects of AD‐MSCs are probably not dependent on AD‐MSC adipose tissue sources and donors but rather on the inflammatory status of OA chondrocytes and synoviocytes. AD‐MSCs seem to be able to sense and respond to the local environment. Even though a combination of different molecules may be involved in AD‐MSC effects, the COX‐2/PGE₂ pathway may play a role, suggesting that AD‐MSCs may be useful for therapies in osteoarticular diseases.

To define if adipose mesenchymal stromal cell (ASC) treatment mediated switching of the pro-inflammatory profile of M1-like macrophages as a means to develop a tailored in vitro efficacy/potency test. We firstly performed immunohistochemical analysis of CD68, CD80 (M1-like) and CD206 (M2-like) macrophages in osteoarthritic (OA) synovial tissue. ASC were co-cultured in contact and in transwell with activated (GM-CSF + IFNγ)-M1 macrophages. We analyzed IL1β, TNFα, IL6, MIP1α/CCL3, S100A8, S100A9, IL10, CD163 and CD206 by qRT-PCR or immunoassays. Prostaglandin E2 (PGE2) blocking experiments were performed using PGE2 receptor antagonist. In moderate grade OA synovium we did not always find a higher percentage of CD80 with respect to CD206. M1-like-activated macrophage factors IL1β, TNFα, IL6, MIP1α/CCL3, S100A8 and S100A9 were down-modulated both in contact and in transwell by ASC. However, in both systems ASC induced the typical M2-like macrophage markers IL10, CD163 and CD206. Activated-M1-like macrophages pre-treated with PGE2 receptor antagonist failed to decrease secretion of TNFα, IL6 and to increase that of IL10, CD163 and CD206 when co-cultured with ASC confirming a PGE2 specific role. We demonstrated that ASC are responsible for the switching of activated-M1-like inflammatory macrophages to a M2-like phenotype, mainly through PGE2. This evidenced that activated-M1-like macrophages may represent a relevant cell model to test the efficacy/potency of ASC and suggests a specific role of ASC as important determinants in therapeutic dampening of synovial inflammation in OA.