The principle of immunoisolation is to separate transplanted cells fro
m the hostile immunological environment of the host by a selectively p
ermeable membrane. Low-molecular-weight substances such as nutrients,
electrolytes, oxygen and biotherapeutic agents are exchanged across th
e membrane, while immunocytes, antibodies and other transplant-rejecti
on effector mechanisms are excluded. Here, Robert Lanza and William Ch
ick review these systems.