Immunoisolation: at a turning point.

The principle of immunoisolation is to separate transplanted cells from the hostile immunological environment of the host by a selectively permeable membrane. Low-molecular-weight substances such as nutrients, electrolytes, oxygen and biotherapeutic agents are exchanged across the membrane, while immunocytes, antibodies and other transplant-rejection effector mechanisms are excluded. Here, Robert Lanza and William Chick review these systems.