Microcapsules and microcarriers for in situ cell delivery

In recent years, the use of transplanted living cells pumping out active factors directly at the site has proven to be an emergent technology. However a recurring impediment to rapid development in the field is the immune rejection of transplanted allo- or xenogeneic cells. Immunosuppression is used clinically to prevent rejection of organ and cell transplants in humans, but prolonged usage can make the recipient vulnerable to infections, and increase the likelihood of tumorigenesis of the transplanted cells. Cell microencapsulation is a promising tool to overcome these drawbacks. It consists of surrounding cells with a semipermeable polymeric membrane. The latter permits the entry of nutrients and the exit of therapeutic protein products, obtaining in this way a sustained delivery of the desirable molecule. The membrane isolates the enclosed cells from the host immune system, preventing the recognition of the immobilization cells as foreign. This review paper intends to overview the current situation in the cell encapsulation field and discusses the main events that have occurred along the way. The technical advances together with the ever increasing knowledge and experience in the field will undoubtedly lead to the realization of the full potential of cell encapsulation in the future.