Engineered endocrine objects tolerate hypoxia in macroencapsulation devices and enable subcutaneous engraftment in diabetic mice

Islet encapsulation has been pursued for decades as a potential immunosuppression-free transplantation strategy to treat type 1 diabetes (T1D). The encapsulation device protects islets from immune cell-contact mediated killing, but it also prevents vascular penetration and intra-islet vascularization, leading to poor mass transfer and islet central necrosis. In healthy pancreas, islets with sizes > ~40 m are vascularized while non-islet endocrine cell clusters below ~40 m exist without internal capillaries. Here, we developed scalable and reproducible engineered endocrine objects (EEOs) as small as ~47 m by mesh-induced fragmentation of native islets, followed by a recovery culture. Under hypoxic culture condition (1% O2 for 24 hours), EEOs showed enhanced viability of >90%, compared to 49% for the native islet control. With a flat, thin (0.5-mm-thick) alginate-based macroencapsulation device, rat EEOs at a marginal dose of 300 islet equivalents (IEQ) achieved glycemic control for over 5 weeks in the challenging, hypoxic subcutaneous space of immunocompetent diabetic mice. The engrafted mice displayed near-physiological glycemic profiles upon glucose challenge, and the retrieved EEOs showed enhanced viability with significantly reduced central necrosis compared with native islets. Overall, engineering hypoxia-resistance into cellular products mitigates intrinsic constraints of encapsulation devices, offering a promising strategy for convenient, immunosuppression-free subcutaneous islet transplantation.