Pluristem Therapuetics, a regenerative therapy company based in Haifa, Israel, has used placenta-based stem cells to treat animal with tendon damage, and the results of this preclinical study were announced at a poster presentation at the American Academy of Orthopedic Surgeons’ (AAOS) annual meeting in New Orleans.
Dr. Scott Rodeo of New York’s Hospital for Special Surgery (HSS) is the principal investigator for this preclinical trial. His poster session showed placental-based stem cells that were grown in culture and applied to damaged tendons seemed to have an early beneficial effect on tendon healing. In this experiment, animal tendons were injured by treatments with the enzyme collagenase. This enzyme degrades tendon-specific molecules and generates tendon damage, which provides an excellent model for tendon damage in laboratory animals. These placenta-based cells are not rejected by the immune system and can also be efficiently expanded in culture. The potential for “off-the-shelf” use of these cells is attractive but additional preclinical studies are necessary to understand how these cells actually help heal damaged tendons and affect tendon repair.
“Although our findings should be considered preliminary, adherent stromal cells derived from human placenta appear promising as a readily available cell source to aid tendon healing and regeneration,” stated Dr. Rodeo.
“These detailed preclinical results, as well as the favorable top-line results we announced from our Phase I/II muscle injury study in January, both validate our strategy to pursue advanced clinical studies of our PLX cells for the sports and orthopedic market,” stated Pluristem CEO Zami Aberman.
Dr. Rodeo and his orthopedic research team at HSS studied the effects of PLX-PAD cells, which stands for PLacental eXpanded cells in a preclinical model of tendons around the knee that had sustained collagenase-induced injuries. Favorable results from the study were announced by Pluristem on August 14, 2013. Interestingly, Dr. Rodeo, the Principal Investigator for this study is Professor of Orthopedic Surgery at Weill Cornell Medical College; Co-Chief of the Sports Medicine and Shoulder Service at HSS; Associate Team Physician for the New York Giants Football Team; and Physician for the U.S.A. Olympic Swim Team.
A Duke University research team has combined synthetic scaffolding materials with gene delivery techniques to generate replacement cartilage precisely where it’s needed in the body.
The ingenious strategy utilized by this research project circumvents the need for large quantities of growth factors, which are expensive and difficult to apply after implantation. The Duke team led by Farshid Guilak, director of orthopedic research at Duke University Medical Center, used gene therapy to make stem cells that synthesize their own growth factors.
In brief, Guilak and his collaborators used genetically engineered viruses to transfer genes to stem cells embedded in a synthetic matrix. Upon infection, the stem cells grew and differentiated as needed, but the scaffolding provided the necessary structural cues for the stem cells to move to the proper configuration and form cartilage with the proper shape and biomechanical properties.
Guilak has devoted several years to developing biodegradable synthetic scaffolds that mimic the mechanical properties of cartilage. After testing many different scaffolds, he settled on a 3D woven poly(ε-caprolactone) scaffold, which is completely biodegradable and provides an excellent structural matrix for the synthesis of cartilage. However, an additional challenge for engineering good cartilage is to coax stem cells embed themselves in the scaffold while differentiating into cartilage-making cells, known as chondrocytes, after the scaffold has been implanted into a living organism.
One widely used strategy is to treat the stem cells with growth factors to induce chrondrocyte formation and cartilage production. Such cartilage can be implanted after it has been grown in the laboratory. However, this approach has some inherent limitations.
Guilak explained that “a major limitation in engineering tissue replacements has been the difficulty in delivering growth factors to the stem cells once they are implanted in the body.” Guilak continued: “There’s a limited amount of growth factor that you can put into the scaffolding, and once it’s released, it’s all gone. We need a method for long-term delivery of growth factors, and that’s where the gene therapy comes in.”
To tackle this perennial problem, Guilak tapped a talented colleague of his, Charles Gersbach, an assistant professor of biomedical engineering, who happens to also be a gene therapy expert.
Gersbach looked at the tissue engineering problem in an entirely new way and suggested that if the mountain will not come to Mohammed (that is to say if the growth factors cannot be given to stem cells after implantation), then Mohammed should grow his own mountain (the stem cells should be genetically engineered to make their own growth factors). Unfortunately, the conventional gene therapy methods are too complex to be commercially feasible. Typically, stem cells are collected, infected with genetically modified viruses that introduces new genes into them, grown to large numbers, and applied to synthetic cartilage scaffolds and implanted into the patient. Sounds like a headache? That’s because it is.
Fortunately, Gersbach had a slick gene therapy trick up his lab coat sleeve: “There are a few challenges with that process, one of them being that there are way too many extra steps,” said Gersbach. “So we turned to a technique I had previously developed that affixes the viruses that deliver the new genes onto a material’s surface.”
This new study combines Gersbach’s gene therapy technique—dubbed biomaterial-mediated gene delivery—to induce those human mesenchymal stem cells embedded in Guilak’s synthetic cartilage scaffolding to produce growth factor proteins (in particular a molecule called transforming growth factor β3 or TGF-β3). Based on the results of their experiments, the technique works and that the resulting synthetic, composite cartilage-like material is at least as good biochemically and biomechanically as if the growth factors were introduced in the laboratory.
“We want the new cartilage to form in and around the synthetic scaffold at a rate that can match or exceed the scaffold’s degradation,” said Jonathan Brunger, a graduate student who has spent time in both Guilak’s and Gersbach’s laboratories developing and testing the new technique. “So while the stem cells are making new tissue (in the body), the scaffold can withstand the load of the joint. In the ideal case, one would eventually end up with a viable cartilage tissue substitute replacing the synthetic material.”
This particular study examines cartilage regeneration, but Guilak and Gersbach hope that their technique could be applied to the regeneration of many different kinds of tissues, especially orthopaedic tissues such as tendons, ligaments and bones. Also, because the platform comes ready to use with any stem cell, it presents an important step toward commercialization.
“One of the advantages of our method is getting rid of the growth factor delivery, which is expensive and unstable, and replacing it with scaffolding functionalized with the viral gene carrier,” said Gersbach. “The virus-laden scaffolding could be mass-produced and just sitting in a clinic ready to go. We hope this gets us one step closer to a translatable product.”
Citation: “Scaffold-mediated lentiviral transduction for functional tissue engineering of cartilage.” Brunger, J.M., Huynh, N.P.T., Guenther, C.M., Perez-Pinera, P., Moutos, F.T., Sanchez-Adams, J., Gersbach C.A., and Guilak F. PNAS Plus, 2014. DOI: 10.1073/pnas.1321744111/-/DCSupplemental