California's Stem Cell Agency

Resulting from injuries or wear-and-tear that leads to osteoarthritis, cartilage degeneration is a problem that costs in excess of $65B per annum. Toward developing a long-term solution for this vexing problem, cellular therapies hold the promise of replacing degenerated cartilage with healthy tissue. This Development Candidate Feasibility Award is a first step toward the overall goal of developing a cell-based cartilage repair therapy using stem cells derived from the skin. The therapy would begin with a biopsy of the patient’s own skin to harvest dermis isolated, adult stem cells (DIAS cells), which will undergo processing to yield neocartilage. This neocartilage will then be implanted into the patient’s joint to restore or improve mobility. During this progress report period, a major milestone has been completed. Previously, DIAS cells have been isolated from various animal models, including sheep, goat, and rabbit. Comparing animal skin and human skin showed notable differences, including morphology, response to enzymatic digestion, and the rate at which cells attach to tissue culture plastic. As a result, protocols that successfully yielded DIAS cells using animal models could not be directly applied to isolating DIAS cells from human skin. During the first six months of this reporting period, human DIAS cells were isolated and used to engineer neocartilage. Characterizing the human DIAS cell population showed that cells shared similar characteristics with stem and progenitor cells previously identified by other groups as originating from various niches of the skin. Neocartilage constructs formed using human DIAS cells were found to contain twice as much glycosaminoglycans and three times more collagen; these are cartilage extracellular matrix component important in imparting mechanical function to the tissue. Neocartilage constructs generated from human DIAS cells also contained five times higher compressive modulus and close to twice the tensile modulus of constructs generated using sheep DIAS cells. The completion of this important milestone allowed for progression to the next milestones of this award. Milestone 2 of this award consists of examining safety of the engineered constructs in a small animal model. For the scaling-up of constructs to be used in an athymic mouse study, an experiment was conducted to finalize our protocol for generating human DIAS cell constructs, using what have been learned both from Milestone 1 and also from literature sources. Three methods for generating neocartilage constructs were examined. While the resultant constructs did not differ in mechanical properties, one method nonetheless yielded constructs of more uniform size and greater cell and glycosaminoglycan content. For milestones 3 and 4, the originally proposed studies were to implant autologous neocartilage constructs in intermediate and large animal studies to examine efficacy of repair. To improve the translational potential of this project, CIRM has requested that neocartilage constructs of human origin be used instead. To ensure that the implanted constructs are not rejected, progress during this reporting period also includes identifying methods to immunosuppress intermediate and large animal models. To summarize, progress during this reporting period includes the completion of Milestone 1 and work toward all other milestones of this award. Additionally, two papers have been published thus far to disseminate scientific findings to the public.