Neuro-Oncology n J U LY 2 0 0 1 201 Gene therapy using viral vectors has to date failed to reveal its de nitive clinical usefulness. Cell encapsulation technology represents an alternative, nonviral approach for the delivery of biologically active compounds to tumors. This strategy involves the use of genetically engineered producer cells that secrete a protein with therapeutic potential. The cells are encapsulated in an immunoisolating material that makes them suitable for transplantation. The capsules, or bioreactors, permit the release of recombinant proteins that may assert their effects in the tumor microenvironment. During the last decades, there has been signi cant progress in the development of encapsulation technologies that comprise devices for both macro-and microencapsulation. The polysaccharide alginate is the most commonly used material for cell encapsulation and is well tolerated by various tissues. A wide spectrum of cells and tissues has been encapsulated and implanted, both in animals and humans, indicating the general applicability of this approach for both research and medical purposes, including CNS malignancies. Gliomas most frequently recur at the resection site. To provide local and sustained drug delivery, the bioreactors can be implanted in the brain parenchyma or in the ventricular system. The development of comprehensive analyses of geno-and phenotypic pro les of a tumor (genomics and proteomics) may provide new and important guidelines for choosing the optimal combination of bioreactors and recombinant proteins for therapeutic use. Neuro-Oncology 3, 201-210, 2001 (Posted to Neuro-Oncology [serial online], Doc. 00-064,