SUBCUTANEOUS XENOTRANSPLANTATION OF HYBRID ARTIFICIAL PANCREAS ENCAPSULATING PANCREATIC B-CELL LINE (MIN6) - FUNCTIONAL AND HISTOLOGICAL STUDY

The biohybrid artificial pancreas is designed to enclose pancreatic en docrine tissues with a selectively permeable membrane that immunoisola tes the graft from the host immune system, allowing those endocrine ti ssues to survive and control glucose metabolism for an extended period of time, The pancreatic B cell line MIN6 is established from a pancre as B cell tumor occurring in transgenic mice harboring the human insul in promoter gene connected to the SV40 T-antigen hybrid gene. It has b een proven that glucose-stimulated insulin secretion in MIN6 cells ret ain; a concentration-dependent response similar to that of normal isle ts, In this study, we performed the histological and functional examin ation of three-layer microbeads employing MIN6 cells after subcutaneou s xenotransplantation to evaluate this device as bioartificial pancrea s, MINE cells were microencapsulated in three-layer microbeads formula ted with agarose, polystyrene sulfonic acid, polybrene, and carboxymet hyl cellulose, Microbeads were xenogenically implanted in the subcutan eous tissue of the back of Lewis rats with streptozotocin-induced diab etes. One week after implantation, microbeads were retrieved and cultu red for 24 h before the static incubation, There was no evidence of ad hesion to the graft and the fibrosis in the transplantation site as de termined by gross visual inspection, Microscopic examination demonstra ted that retrieved microbeads maintained normal shape, containing inta ct MIN6 cells, Histological study showed that these MIN6 cells in the microbeads appeared to be viable without cellular infiltration within or around the microbeads. Immunohistochemical analysis of the microbea ds clearly revealed the intense staining of insulin in the cytoplasm o f encapsulated MIN6 cells, Insulin productivity of MIN6 cells in the m icrobeads is strongly suggested to be preserved, In response to 16.7 m M glucose stimulation, static incubation of microbeads 1 wk after impl antation caused the 2.3 times increase in insulin secretion seen after 3.3 mM glucose stimulation (84.3 +/- 10.0 vs, 37.4 +/- 10.7 mu U/3 x 10(6) cells/hr, n = 5 each, p < 0.01), This study demonstrates that th ree-layer microbeads encapsulating MIN6 cells retain excellent biocomp atibility and maintain good insulin secretion even after subcutaneous xenotransplantation, suggesting the possible future clinical applicati on of this unique bioartificial pancreas to subcutaneous xenotransplan tation. (C) 1997 Elsevier Science Inc.