Introduction: The current approach of clinical islet transplantation into the liver is suboptimal, resulting in significant islet loss and reduced vascularization limiting long term engraftment. The subcutaneous space has also posed challenges as a transplantation site, as it is an inhospitable environment for islets to acquire the rapid blood supply needed for survival. Endothelial cells (ECs) can provide a vascular niche to foster islet homeostasis and survival; however, adult ECs lack the plasticity and ability to interact with islets, thus presenting a major barrier in prior efforts.

Method: Given the limitations of adult ECs, we have engineered adaptable human endothelium by transient transduction of ETS variant transcription factor 2, Reprogramming adult Vascular ECs (R-VECs) to an adaptable tubulogenic state. The ability of R-VECs to sustain islet function and survival was tested via in vitro and in vivo approaches.

Results: Within microfluidic devices, R-VECs assemble into perfused plexi that can carry blood and avidly vascularize islets. Islets arborized by R-VECs in microfluidic devices demonstrate preserved function by glucose stimulated insulin secretion. To test if this rich, expedited vascularization from R-VECs can enable islets to survive in the subcutaneous space, streptozotocin-induced diabetic SCID-Beige mice were transplanted; human islets achieved euglycemia for 6 months, while transplantation with islets alone or islets/generic ECs did not. Furthermore, mice transplanted with R-VEC/islets demonstrated body weight stabilization and improved glucose tolerance testing. Islet grafts retrieved one month after transplantation showed vascularized engraftment only with R-VEC/islets and not with islets alone or islets/generic ECs. Explant of the grafts resulted in the reoccurrence of diabetes. Mice transplanted with human stem cell-derived β cells/R-VECs demonstrated improved glucose control compared to those transplanted without R-VECs. To further understand how R-VECs support islet homeostasis, single cell RNA-sequencing of R-VECs cultured with human islets was performed, and revealed gene expression changes suggesting R-VECs adapt to islets to acquire a supportive islet-specific phenotype.

Conclusion: As a treatment for diabetes, we have engineered adaptable endothelium that supports the survival and function of islets for transplantation. Importantly, this device-less subcutaneous approach obviates the need for intra-liver infusion and holds promise for forthcoming large animal and human trials.