Oligomeric collagen as an encapsulation material for islet/β cell replacement: Effect of islet source, dose, implant site, and administration format.

Replacement of islets/β cells that provide long-lasting glucose-sensing and insulin-releasing functions has the potential to restore extended glycemic control in individuals with type 1 diabetes. Unfortunately, persistent challenges preclude such therapies from widespread clinical use including cumbersome administration via portal vein infusion, significant loss of functional islet mass upon administration, limited functional longevity, and requirement for systemic immunosuppression. Previously, fibril-forming type I collagen (oligomer) was shown to support subcutaneous injection and in-situ encapsulation of syngeneic islets within diabetic mice, with rapid (<24 hours) reversal of hyperglycemia and maintenance of euglycemia for beyond 90 days. Here, we further evaluated this macroencapsulation strategy, defining effects of islet source (allogeneic and xenogeneic) and dose (500 and 800), injection microenvironment (subcutaneous and intraperitoneal), and macrocapsule format (injectable and preformed implantable) on islet functional longevity and recipient immune response. We found that xenogeneic rat islets functioned similarly to or better than allogeneic mouse islets, with only modest improvements in longevity noted with dose. Additionally, subcutaneous injection led to more consistent encapsulation outcomes, along with improved islet health and longevity, when compared to intraperitoneal administration, while no significant differences were observed between subcutaneous injectable and preformed implantable formats. Collectively, these results document the benefits of incorporating natural collagen for islet/β cell replacement therapies.