Background & aims: In the context of xenotransplantation, cellular encapsulation is a promising strategy to evade the host immune system whilst providing a nurturing environment for islet cell survival and function. We have previously shown that transgenic InsGLP-1M3R porcine islets have human-like insulin secretory response and that they can efficiently cure insulin-dependent diabetes in an immunosuppressed xenotransplantation model. Here, our aim was to use such functionally-improved islets to prepare macroencapsulated islet pouches that were then tested both in vitro and in vivo.
Material & methods: Pancreatic islets were isolated from transgenic neonatal piglets and kept in culture in a maturation medium for 8 days. Islet pouches were prepared by seeding 15000 IEQ on a 1 cm2 sheet of decellularized pig skin, covering the islets with a thin layer of an alginate-agarose gel solution and encasing the ensemble between two sheets of PET membranes (0.4 µm pore size) that were then heat-sealed. Obtained pouches were kept in culture over a period of 3-4 weeks with glucose stimulation tests performed on a weekly basis. Streptozotocin-induced diabetic rats received a pouch each behind the seminal vesicle and were kept in an 80% oxygen atmosphere for 48 hours following implantation. Blood glucose was monitored weekly, and blood samples were taken to evaluate the immunologic anti-pig response by FACS analysis of serum samples. Normoglycemic rats had their pouches removed 6 months post-implantation and follow-up continued for hyperglycemia to occur.
Results: Weekly glucose stimulation of incubated islet pouches showed a robust 3.5-fold increase of insulin secretion in response to 15 mM glucose. Interestingly, the amount of both basal and stimulated insulin increased during the in vitro culture period. Out of 10 pouch recipients, 5 became normoglycemic (< 200 mg/dl) within 30 days of implantation. 100% of these recipients remained so during a 6-month follow-up period. Upon graft removal, an irreversible rise of blood glucose was observed in 5 out of 5 rats as shown in figure 1. FACS analysis of serum samples showed absence of anti-pig antibodies (IgM and IgG) in 9 out of 10 recipients with one individual showing a 30% increase of IgG within 30 days post-implantation. Macroscopic observation of explanted pouches showed no signs of fibrosis nor physical damage to the pouches. Moreover, a well-developed capillary network surrounding each pouch was observed.      
Conclusion & perspectives: Neonatal porcine islet macroencapsulation on an acellular collagen matrix sustains islet survival and function both in vitro and in vivo. Host immune reaction was successfully evaded using a combination of alginate-agarose gel and microporous PET membranes. The ensemble showed good biocompatibility and integration.