Upcoming MSC Injection Approvals

Recently, the phase III clinical trial of AlloJoin®, an allogeneic human adipose-derived mesenchymal progenitor cell injection, was officially launched. The results of the completed randomized, double-blind, controlled multi-center phase II clinical trial (96-week follow-up) initially show that AlloJion® has relatively good safety and efficacy in the treatment of knee osteoarthritis. AlloJion® is administered by injection into the knee joint. This is the first stem cell drug for knee osteoarthritis that has entered phase III clinical trials in China, and it is expected to fill the gap in the field of stem cell products in China for the treatment of knee osteoarthritis in the future.

According to the 2019 GBD (Global Burden of Disease Database) statistics, the number of patients with osteoarthritis in China in 2019 was about 133 million, accounting for 9.75% of all-cause patients in China and 18.32% of the global number of patients with osteoarthritis. Osteoarthritis mainly occurs after middle age. Among people aged 40-70, the incidence rate of women is higher than that of men. After the age of 70, the incidence rate of both sexes is equal. The clinical manifestations of osteoarthritis are joint pain, joint stiffness, and severe cases will manifest as loss of joint function. By 2021, osteoarthritis will become the fourth most disabling disease

Since the hyaline cartilage tissue on the surface of the bone joint has no nerves and blood vessels, the self-repair and regeneration ability of the cartilage is poor, and once damaged, it is difficult to recover by itself. At present, the clinical treatment methods for osteoarthritis mainly include non-drug therapy, such as targeted exercise, heat therapy, cold therapy, insoles, acupuncture, etc.; drug therapy and surgical treatment, but these can only relieve pain, to a certain extent Improving symptoms, delaying the disease, and correcting deformities cannot completely delay the development of the disease. Autologous chondrocyte transplantation has been successfully used to repair cartilage, but chondrocytes cultured in vitro show differentiation, which reduces the expression of chondrocyte-specific genes, thereby affecting the therapeutic effect.

In recent years, novel stem cell-based therapies for osteoarthritis have received increasing attention. Mesenchymal stem cells have the potential of self-renewal and directed differentiation, can repair cartilage tissue, inhibit the secretion of inflammatory factors and homing properties of chondrocytes, and are very promising cells for the gradual treatment of osteoarthritis.

The mechanism of action of mesenchymal stem cells

Mesenchymal stem cells exist in various tissues, such as bone marrow, umbilical cord, placenta, tendon, periodontal tissue, and adipose tissue. In 2006, the International Society for Cell Therapy ( ISCT ) defined mesenchymal stem cells with three criteria:

1. Can be attached to the plastic surface to grow;
2. Expression of CD105, CD73 and CD90, and lack of CD45, CD34, CD14 or CD11b, CD79a or CD19 and HLA-DR surface molecules;
3. After in vitro induction, mesenchymal stem cells can differentiate into osteoblasts, adipocytes and chondrocytes.

In addition to their differentiation potential, mesenchymal stem cells also express and secrete a variety of enzymes and secrete a variety of trophic factors involved in paracrine activities, including growth factors, cytokines and chemokines, which nourish cells by activating cellular and angiogenic pathways cartilage .

Mesenchymal stem cells also participate in the local immune regulation mechanism, which can inhibit the proliferation of T cells, the maturation of dendritic cells, the activation and proliferation of B cells, and the secretion of antibodies, thereby affecting the polarization of macrophages and the differentiation of antibody-secreting cells. Eliminates rejection and the spread of disease. Among them, the polarization of macrophages is stimulated by INF-γ and IL-1β, which transform macrophages from pro-inflammatory ( M1 ) to anti-inflammatory ( M2 ); moreover, mesenchymal stem cells can also interact with macrophages Phage cells interact to inhibit the activation of macrophages and the secretion of IL-1β, TGF-α and other inflammatory factors.

Of course, the regulatory functions of MSCs may vary among individuals, species, tissue sources, culture conditions, and activation states. The homing function of mesenchymal stem cells can migrate to cartilage ischemia or damaged sites under the influence of microenvironment in vivo. In addition, mesenchymal stem cells can also repair and rebuild damaged tissues by secreting growth factors, cytokines and extracellular matrix. According to studies, cytokines secreted by mesenchymal stem cells can target synovial and chondrocytes, and they can regulate anabolic and catabolic factors, as well as induce the expression of anti-inflammatory and chondrogenic molecules.

With the deepening of research, most recent studies have shown that mesenchymal stem cells mainly regulate local inflammation, cell apoptosis and proliferation through paracrine mechanisms, rather than directly differentiate into chondrocytes to participate in tissue repair . The researchers pointed out that endogenous mesenchymal stem cells maintain the health of tissues through the resource reserve of cell repair and the sentinel of immune regulation, and the transmission of paracrine signals of mesenchymal stem cells is more important than differentiation in activating the repair response . This means that instead of replacing damaged cartilage, mesenchymal stem cells are orchestrated to enhance the repair response .

Clinical research

Local intra-articular mesenchymal stem cell injection and mixed injection

Mixed injection refers to the mixed injection of growth factors, cytokines and scaffold mixed with mesenchymal stem cells to improve the curative effect. Commonly used scaffolds include polymers such as hemagglutinin and fibrin gel, and nutrient-rich body fluids such as platelet-rich plasma ( PRP ). Among them, there are many clinical studies on intra-articular injection of mesenchymal stem cells ( MSCs )/PRP mixture. PRP is an autologous tissue rich in cartilage-derived growth factors ( such as TGF-β and platelet-derived growth factor ), which can be used as a tissue source for the treatment of damaged cartilage. PRP composite scaffold has high osteoinductive activity and can promote bone healing . PRP combined with MSCs composed of adipose-derived mesenchymal stem cells and adipose tissue vascular matrix can create a suitable microenvironment to promote blood supply, reduce local inflammatory reactions, promote the synthesis of cartilage mechanisms, and improve mesenchymal stem cells in the treatment of knee joints. Therapeutic effect of arthritis. At present, the problem of PRP still lies in the variability of its preparation method and the quantity of expressed biologically active factors . Some growth factors ( such as vascular endothelial growth factor ) secreted by RPR may have adverse effects on both joints and mesenchymal stem cells.

With the increasing evidence of the successful application of stem cell technology in animal and in vitro experiments, the transplantation technology using stem cells in the treatment of osteoarthritis has also shown the potential to regenerate cartilage. To date, nearly 80 relevant clinical studies have been registered on Clinicaltrail.gov, some of which have completed clinical trials and preliminary evaluations of safety and efficacy. According to the existing research results, mesenchymal stem cells ( derived from bone marrow, fat and umbilical cord ) therapy have shown very good curative effect in the treatment of osteoarthritis, and may replace traditional therapy in the future.

Bone marrow mesenchymal stem cells

Bone marrow mesenchymal stem cells are the earliest and most common effective source for the treatment of osteoarthritis, and gratifying results have been obtained in the clinical repair of knee articular cartilage. In 2008, a study reported a case of severe knee osteoarthritis treated with bone marrow mesenchymal stem cells. When injected, bone marrow mesenchymal stem cells are combined with 10% platelet lysate and 10ng dexamethasone to stimulate cartilage. Six months after the injection, MRI showed significant growth of articular cartilage and menisci, and significantly reduced pain. Positive results were achieved with a single injection of bone marrow mesenchymal stem cells into the joint cavity even in the absence of adjuvant analgesics, anti-inflammatory drugs, or immunosuppressants. Studies have shown that bone marrow mesenchymal stem cell transplantation is more effective than autologous chondrocyte therapy with relatively fewer complications. Although the safety and effectiveness of bone marrow mesenchymal stem cells have been widely confirmed, it is difficult to obtain a sufficient amount of primary stem cells in actual clinical applications, which is largely affected by the age of the donor . Different degrees of trauma and differentiation .

Adipose-derived mesenchymal stem cells

Adipose-derived mesenchymal stem cells are also one of the effective sources for the treatment of osteoarthritis. Usually obtained by liposuction or infrapatellar fat pad extraction, liposomes are centrifuged and dissolved by adding collagenase I to prepare concentrated mesenchymal stem cells. Intra-articular injection of 1.0x108 L -MSCs has been reported to significantly improve knee joint pain and function without adverse events. The patients who received the medium dose ( 5.0x10 7 ) showed improvement in clinical indicators, while most patients in the low dose group ( 1.0x10 7 ) did not show improvement in clinical indicators. These results show that the curative effect of intra-articular injection of mesenchymal stem cells is significantly related to the dose , and further clinical trials are needed to prove the long-term safety and clinical advantages of high-dose injection. Compared with bone marrow stem cells, adipose-derived mesenchymal stem cells have a lower potential to generate cartilage, and the ability to generate cartilage-specific matrix proteins and the expression ability of type I collagen genes are also relatively lower. Therefore, the stimulation of cartilage regeneration potential of adipose-derived mesenchymal stem cells needs to be further optimized and improved.

Questions about Mesenchymal Stem Cell Transplantation

Although there is a lot of relevant evidence to prove the ability of mesenchymal stem cells to treat osteoarthritis, the existing problems cannot be ignored.

1. The extremely low number of surviving stem cells after injection cannot predict lasting improvement and cell-cell interactions, and whether sufficient cell banks can be maintained to achieve the desired therapeutic effect;
2. Donor fitness may be another important challenge, as MSCs isolated from old or unhealthy donors have been found to have reduced performance and proliferation ;
3. Before transplantation, long time of in vitro expansion of mesenchymal stem cells may lead to induction of senescence, loss of proliferation ability and reduced differentiation ability (especially more than 10-20 times of population doubling);
4. Since chondrogenically induced calcification is genetically programmed as part of normal endochondral ossification, it is also a question of how to maintain differentiated mesenchymal stem cells in a cartilage phenotype and prevent their calcification from expanding to an osteogenic phenotype;
5. Mesenchymal stem cells are sensitive to some "environmental response" factors , and perform specific modification behaviors in response to trace unknown substances in the microenvironment. Although this response is frequently exploited in regenerative medicine, MSC responses can be negatively affected in the diseased joint setting. It has been reported that human adipose-derived mesenchymal cells, after reacting with tumor necrosis factor (TNF), transform into a pro-inflammatory secretome and enhance the inflammatory response.

Mesenchymal Stem Cell Exosomes

Because of some of the above-mentioned problems of stem cell transplantation, the discovery of mesenchymal stem cell exosomes is expected to avoid these risks.

As mentioned above, more and more studies have shown that the injection of mesenchymal stem cells in the treatment of osteoarthritis really plays a role in the biomolecules secreted by the paracrine system of stem cells, which regulate the microenvironment of the affected area and activate the original stem cells to repair damaged tissues. Stem cell exosomes are also gaining more and more attention. Exosomes are a soluble biological medium isolated from the culture medium of mesenchymal stem cells. Exosomes are produced under pathological and physiological conditions, and they are the main mediators of intercellular communication by transferring mRNA, lipid, siRNA, protein, miRNA and ribosomal RNA to adjacent or distant cells. Studies have found that exosomes from mesenchymal stem cells can protect chondrocytes from apoptosis by increasing chondrocyte markers ( such as type II collagen and aggrecan ), reducing inflammatory markers ( iNOS ), protecting chondrocytes from apoptosis, and blocking giant cells. Phage cells are activated. Mesenchymal stem cell exosomes can attenuate osteoarthritis by stimulating chondrocyte migration and proliferation .

The injection of mesenchymal stem cell exosomes has many similarities with the injection of intact stem cells in biological effects , and has significant advantages compared with the injection of intact mesenchymal stem cells, such as small size, low immunogenicity, and the elimination of direct cell Injection procedural issues. Exosomes are considered to be powerful intercellular messengers that not only mediate pathological processes, but also maintain tissue homeostasis and regulate physiological functions in a variety of therapeutic approaches. Although several studies have used stem cell-derived exosomes to treat joint injuries and osteoarthritis, conclusive evidence is still lacking. As a new cell-free therapy for osteoarthritis and joint damage, a large number of clinical trials are still needed to confirm its effectiveness.

Although osteoarthritis is very common, it seriously affects people's lives. Traditional treatment methods are difficult to fundamentally solve the disease, but also cause a series of side effects, causing great harm to patients. With the in-depth study of mesenchymal stem cells and stem cell exosomes, new therapies based on mesenchymal stem cells have gradually shown advantages in the treatment of osteoarthritis.