1 Abstract 2 The temporomandibular joint (TMJ) is a complex joint system critical for dental occlusion, 3 mastication, respiration and speech. The TMJ is comprised of a network of muscles, 4 ligaments, and a fibrocartilaginous disc and condyle. Temporomandibular disorders (TMDs) 5 are a complex, heterogeneous group of pathologies involving the TMJ and associated 6 musculature. Degenerative types of TMDs, including TMJ osteoarthritis (OA), are debilitating, 7 compromise the quality of life. TMDs afflict over 10 million Americans at an annual cost of 8 ~$4 billion, per the NIDCR. Current TMJ OA treatments are typically two-fold, involving either 9 pain management or invasive surgeries, such as total joint replacements with high failure rates. 10 Regenerative medicine promises the recreation functional tissue that is lost from diseases. 11 Thus exploiting the regenerative capabilities of resident stem cells to repair TMJ may 12 represent a minimally invasive stem cell based treatment for TMJ OA. Sponsored by NIH 13 small business grant, we further developed StemGel®, a sustained-release formulation by 14 encapsulating sclerostin in hyaluronic acid (HA). Monthly injection of StemGel® efficiently 15 inhibits TMJ OA progression and regenerates cartilage in both rabbit and minipig TMJ OA 16 models. 17 The active ingredient of StemGel®, sclerostin is a glycosylated protein with 213 amino acids. 18 A mammalian expressing system is required to faithfully produce the post-translational 19 modification. Cell line development is a critical inflection point for therapeutic protein 20 manufacturing. The properties of the cell substrate and the events linked to cell substrate 21 can affect protein quality and safety, and further, the effective quality control on all aspects of 22 handling the cell substrate. The goal of this proposal is to develop Master Cell Bank 23 (MCB)/stable cell line expressing sclerostin to be readily transferred to the Contract 24 Development and Manufacturing Organization (CDMO) for massive production of the GMP 25 grade protein for pharmacokinetics and safety tests.