Alginate/Poly-L-Ornithine Microcapsules for Pancreatic Islet Cell Immunoprotection

Abstract

Over the past few decades several laboratory procedures have been developed for immobilization and encapsulation of either animal or plant cellular products, or cells/tissues for different applications. Encapsulation techniques usually reflected the physical-chemical properties associated with the microcapsule’s membrane, depending upon its specific employment. In fact, use of microcapsules for drug or metabolite time-controlled release or delivery poses a number of technical problems that substantially differ from those that arise when the membranes are to be rigorously immunoselective so as to protect the enveloped cell/tissue graft (TX) from the host’s immune reponse. This being the case, it seems critical that microcapsules keep their constituent physicalchemical structure as immutable as possible throughout the post-TX period. Moreover, encapsulated cell TX addresses those recipients that may require replacement of a function that has been lost, thus introducing additional variables. For instance, in the specific case of insulin-dependent diabetes mellitus (IDDM), it is not sufficient that microcapsules serve as a biocompatible and competent physical immunobarrier for the implanted islets, but it is also necessary that the membranes be specially engineered so as not to interfere with normal β-cell insulin secretory kinetics, which are indispensable for the prevention of blood glucose spikes. In other words, here it is not only a matter of immunoprotecting cells that release a certain product, but also, and rather, of preserving an extremely complex sensing apparatus that is finely tuned to maintain the glucose homeostasis. Of course, as a further variable, IDDM is an autoimmune disorder, which means that an extra immunoprotection may be required to avoid recurrence of the disease.