Tissue transplantation by stealth—Coherent alginate microcapsules for immunoisolation

Several of today's most prominent diseases arise as a result of aberrant secretory or enzymatic function, or loss of the corresponding tissue. While an obvious approach to treating these diseases is to simply replace the malfunctioning, damaged, or lost tissue, the need to immunosuppress recipients places them at increased risk of pathogenic infection and development of cancer. Limited availability of donor tissue is also problematic, and while xenogenic tissue could be used in some instances, immunosuppression alone is insufficient to prevent rejection. As an alternative, a physical barrier could be employed to mask the implanted tissue from immune surveillance at a local level, without the need for systemic immunosuppression. This approach is embodied through tissue microencapsulation. We review the underlying rationale of alginate based tissue microencapsulation technologies, current challenges, and possible solutions to these challenges in the form of a simple emulsion coating system incorporating functionalized alginate for local immunomodulation.