Immunoisolation of pancreatic B cells by microencapsulation. An in vitro study

The selective permeability of alginate microcapsules, containing isolated rat islets of Langerhans or insulin secreting RINm5F cells, was investigated in vitro. An increase in insulin release was observed when microencapsulated islets were stimulated by glucose+theophylline, and when microencapsulated RINm5F cells were stimulated by arginine+theophylline. These findings demonstrate the permeability of the microcapsule membrane to these B-cell secretagogues and to insulin. Immunoisolation of RINm5F cells by microencapsulation was assessed using a 51chromium cytotoxicity test. Significant 51Cr release was observed when nonencapsulated cells were incubated with complement and either the serum of a rabbit immunized with RIN cells or the sera of two patients with recently diagnosed Type 1 (insulin-dependent) diabetes. This effect was not observed with encapsulated cells. Both free and encapsulated cells released 80% of their initial radioactivity when incubated in the presence of HC1. These results clearly demonstrate pancreatic cell immunoisolation by microencapsulation. They also provide a method for the in vitro evaluation of the functional characteristics of microcapsules, in terms of both insulin permeability and immunoprotection.