In vivo perivascular implantation of encapsulated packaging cells for prolonged retroviral gene transfer

Long-term benefits of coronary angioplasty remain limited by the treatment- induced renarrowing of arteries, termed restenosis. One of the mechanisms l eading to restenosis is the proliferation of smooth muscle cells. Therefore , proliferating cells of the injured arterial wall, which can be selectivel y transduced by retroviruses, are potential targets for gene therapy strate gies. A direct single-dose therapeutic application of retroviral vectors fo r inhibition of cell proliferation is normally limited by too low transduct ion efficiencies. Encapsulated retrovirus-producing cells release viral vec tors from microcapsules, and may enhance the transduction efficiency by pro longed infection. Primary and immortal murine and porcine cells and murine retrovirus-producing cells were encapsulated in cellulose sulphate. Cell vi ability was monitored by analysing cell metabolism. Safety, stability, tran sfer efficiency and extent of restenosis using capsules were determined in a porcine restenosis model for local gene therapy using morphometry, histol ogy, in situ beta-galactosidase assay and PCR. Encapsulation of cells did n ot impair cell viability. Capsules containing retrovirus-producing cells ex pressing the beta -galactosidase reporter gene were implanted into periarte rial tissue or a pig model of restenosis. Three weeks following implantatio n, beta -galactosidase activity was detected in the pericapsular tissue wit h a transduction efficiency of similar to 1 in 500 cells. Adventitial impla ntation of vector-producing encapsulated cells for gene therapy may, theref ore, facilitate successful targeting of proliferating vascular smooth muscl e cells, and allow stable integration of therapeutic genes into surrounding cells. The encapsulation of vector-producing cells could represent a novel and feasible way to optimize local retroviral gene therapy.