A device is provided containing cells or tissue distributed on a filamentous cell-supporting matrix which is encapsulated by a semi-permeable membrane which can be immunoisolatory. The matrix may be formed of a plurality of monofilaments twisted into yarn that is in non-woven strands, or of the monofilaments or yarn woven into a mesh. Configurations of the matrix include a hollow cylinder, tube, solid cylinder or cord. A coating of extracellular matrix molecules may be on the matrix, or the matrix may be treated with plasma irradiation to enhance cell adhesion. The device can be made by inserting the matrix in a hollow membrane tube, injecting cells or tissue into the tube and sealing ends of the tube. The device is particularly useful for implantation into a mammalian host to provide therapy resulting from a biologically active molecule produced by the cells and tissue.