Background: This study aimed to develop a functional, vascularized endocrine pancreas using decellularized human placental cotyledons (hPLCs), human blood outgrowth endothelial cells (BOECs), and pancreatic islets. BOECs can be derived from transplant recipients, were utilized to enhance vascularization and improve graft integration.

Methods: hPLCs were decellularized using 1% SDS and 0.1% Triton to obtain acellular scaffold.  These scaffolds were repopulated with BOECs before being seeded with 1500 human islet equivalents (IEQ). Successful recellularization was confirmed via histological and immunohistochemical analyses, while endocrine function was assessed using glucose-stimulated insulin secretion assays. Engineered constructs were transplanted into the subcutaneous (SC) space of STZ-induced diabetic NSG mice (PLCs+Islets+BOECs). Control groups included mice receiving non-endothelialized scaffolds (PLCs+Islets) with the same number of islets, as well as free islets transplanted into prevascularized SC spaces and under the kidney capsule (KC).

Results: The vascularized endocrine constructs exhibited a continuous CD31+ endothelial network within the hPLC scaffold, with islets embedded in a well-vascularized matrix. These constructs demonstrated physiological insulin secretion in response to glucose stimulation. Within the first week post-transplant, 80% of mice in the PLCs+Islets+BOECs group achieved normoglycemia, compared to 60% in the PLCs+Islets group. In contrast, mice receiving islets in prevascularized SC spaces failed to restore normoglycemia. Removal of the graft-bearing construct resulted in hyperglycemia recurrence within 24 hours, confirming graft-dependent glucose regulation. Immunohistochemical analysis at 90 days post-transplant revealed a significantly larger β-cell mass (assessed by insulin-positive area per field) in the PLCs+Islets+BOECs group compared to the PLCs+Islets group. Additionally, CD31 staining of explanted grafts showed significantly greater vessel density in PLCs+Islets+BOECs constructs than in non-endothelialized scaffolds.

Conclusion: The engineered vascularized endocrine pancreas represents a fully biocompatible construct that mimics the native islet microenvironment, enhances graft vascularization, and provides mechanical protection. This approach promotes long-term islet engraftment and function, offering a promising strategy for improving cell-based therapies in diabetes treatment.