PERMEABILITY OF ALGINATE MICROCAPSULES TO SECRETORY RECOMBINANT GENE-PRODUCTS

Non-autologous somatic gene therapy is an alternate approach to delive ring recombinant gene products through implantation of a ''universal'' donor cell line engineered to produce a therapeutic gene product. The cells are immunologically isolated by enclosure in immunoprotective m icrocapsules fabricated from alginate-poly-L-lysine-alginate. The mole cular weight cutoff of these microcapsules was thought to be <100 kd, thus, excluding the immunoglobulins. However, when such microcapsules are fabricated to enclose cells, they show a higher permeability thres hold than expected. The secretion rates of recombinant gene products r anging from 21 through 150 to 300 kd (human growth hormone, rat serum albumin, human arylsulfatase A, human immunoglobulin, mouse beta-hexos aminidase, mouse beta-glucuronidase) were similar between the nonencap sulated and encapsulated recombinant cells with the exception of the l argest molecular species, the 300-kd beta-glucuronidase. Its secretion was reduced about eightfold after encapsulation, Increasing the thick ness of the membrane by prolonging the coating time with poly-L-lysine did not provide a lower molecular weight cutoff. An additional coatin g with alginate, however, reduced the leakage of the larger molecular species, but the effect was short lived: After 2 weeks in culture, the double- and single-coated microcapsules were equally permeable. Both the increased poly-L-lysine and alginate coating were detrimental to t he long-term viability and proliferation of the encapsulated cells. He nce, immunoisolation of encapsulated cells with alginate-poly-L-lysine -alginate microcapsules cannot provide a molecular weight cutoff below 300 kd. (C) 1996 John Wiley & Sons, Inc.