Bioengineering implantable bone tissue for treating nonhealing defects
The availability of materials to treat slow or nonhealing bone defects is a significant clinical challenge for the more than 600,000 bone graft procedures performed annually. As an alternative to the gold standard of grafting bone from the patient themselves, which is limited by extensive tissue loss and limited availability, we propose to produce functional bone tissue from unrelated donor bone marrow-derived mesenchymal stem cells (MSCs). MSCs will be seeded on biodegradable implants fabricated from FDA-approved polymers and synthetic minerals and maintained in a bioreactor that applies force to the cells for promoting bone formation on the implant. The bioreactor will be developed, housed, and maintained under Good Manufacturing Practice (GMP) standards, thereby allowing the production of a construct for implantation in human patients. We will determine the importance of these forces on the secretion of bone-like mineral by human MSCs when seeded on our engineered implants, as well as other parameters including the volume of implantable bone that can be created and degradation of the underlying polymer. The resulting cellularized implant will then be infused with cells isolated from adipose tissue (stromal vascular fraction), recently shown in two clinical trials to promote vascularization, cell survival, and improve tissue function. The capacity of the engineered construct to promote bone healing will be validated in rodent and sheep models of bone repair widely used by our group. Together with input from the FDA, successful results from small and large animal models will provide the blueprint for the appropriate development candidate to test in a Phase I/II clinical trial.
The properties of our single development candidate, primarily derived from human cells, will be similar to that of native bone with regard to stiffness and mineral content. We anticipate this implant will integrate with surrounding bone much better than other currently available materials while eliminating tissue morbidity. Unlike other implants such as metals and pure bioceramics, this implant will resorb over time while functioning as native bone. The infusion of the mineralized tissue with cells from the patient’s own fat tissue before implantation will offer a patient-specific component to accelerate vascularization and enhance graft survival. We anticipate initiating the clinical trial within the period of this award due to the FDA’s familiarity with the individual components of the development candidate and our team’s broad experience with MSCs and engineered biomaterials for bone repair in a number of small and large animal models.
Congenital bone abnormalities, bone loss, and defects resulting from trauma pose a significant health problem that impacts individuals across their lifespan. Many of the most severe fractures have significant bone loss and require surgical treatment to restore function. Conventional therapies for bone-related abnormalities commonly require the grafting of bone segments into the defect (more than 600,000 procedures annually at a cost of more than $5 billion), yet a lack of sufficient material often precludes such therapies. Moreover, at least 10% of all bone defects are nonhealing, with an even higher prevalence of nonunions in the elderly. Given that at least 20% of California’s population will be over the age of 65 by 2025, it is imperative that new approaches to bone repair are developed. This proposal has two primary goals. First, we seek to develop a novel approach for generating functional pieces of implantable bone using mesenchymal stem cells (MSCs) from unrelated donors by combining MSCs with an engineered resorbable implant stimulated by a bioreactor to promote bone formation. Second, we propose to complete IND-enabling studies and carry out a Phase I/II clinical trial to treat traumatic, critical size bone defects or as an alternative to autogenous grafting for fractures than have failed to heal. Successfully achieving these primary goals will benefit the State of California and its citizens in several ways. Our findings will likely provide a novel means to treat nonhealing and traumatic bone defects by developing a novel bone graft. Clinical utilization of this system could markedly accelerate limb salvage, reduce the need for repeated surgical procedures, and conceivably improve the quality of life for these patients. These approaches could also have value in other health conditions where accelerated bone formation is warranted including osteogenesis imperfecta and osteoporosis. Also, the versatile technology developed here will have applications to other tissue engineering approaches that could benefit the biotechnology companies of California investing in regenerative medicine. Finally, we anticipate that the proposed studies will also directly benefit young scientists and researchers in training among the respective collaborating laboratories. Exposure of students to novel stem cell-related research may provide the greatest benefit to California by inspiring future leaders in science to pursue their research efforts within the state or develop products and therapies at California-based biotechnology companies.