Islet immuno‐isolation: The use of hybrid artificial organs to prevent islet tissue rejection

Immuno‐isolation protects islet tissue from rejection by enclosing it within semi‐permeable membranes. Four major techniques have been developed to achieve this goal: (1) Extravascular diffusion chambers. These can be implanted in many locations but are limited by host fibroblastic responses which further reduce diffusion capability. (2) Intravascular diffusion chambers. These have improved diffusion characteristics dependent on design but have serious vascular access problems. (3) Intravascular ultrafiltration chambers. These have a more rapid response since they do not rely on diffusion but have an additional problem of protein deposition on their membranes. (4) Microencapsulation. This technique incorporates the islet tissue inside a biochemical membrane making it more efficient. Yet the technique is limited by membrane instability. Immuno‐isolation offers an alternative to immunosuppression, but the biotechnology must be improved to develop suitable materials for effective clinical trials .