LONG-TERM BIOLOGICAL RESPONSE OF INJURED RAT CAROTID-ARTERY SEEDED WITH SMOOTH-MUSCLE CELLS EXPRESSING RETROVIRALLY INTRODUCED HUMAN GENES

Cultured vascular smooth muscle cells (SMCs) containing retrovirally i ntroduced genes are a potential vehicle for gene replacement therapy. Because the cultured SMCs are selected for their ability to proliferat e in vitro, it is possible that the SMCs might be permanently altered and lose their capacity to respond to growth-suppressing conditions af ter being seeded back into blood vessels. To investigate this possibil ity we measured SMC proliferation and intimal thickening in balloon-in jured Fischer 344 rat carotid arteries seeded with SMCs stained with t he fluorescent marker dioctadecyl-3,3,3',3'-tetramethylindo-carbocyani ne perchlorate (DiI) and infected with replication-defective retroviru s expressing human adenosine deaminase or human placental alkaline pho sphatase. The majority of the seeded SMCs remained in the intima while a few of the cells appeared to migrate into the first layer of the me dia. Intimal SMC proliferation returned to background levels (< 0.1% t hymidine labeling index) by 28 d. At late times (1 and 12 mo) the morp hological appearance of the intima was the same for balloon-injured ar teries with or without seeded SMC, except that the seeded arteries con tinued to express human adenosine deaminase or alkaline phosphatase. T hese results support the conclusion that cultured SMC infected with a replication-defective virus containing human adenosine deaminase or al kaline phosphatase are not phenotypically altered and do not become tr ansformed. After seeding onto the surface of an injured artery, they s top replicating but continue to express the introduced human genes eve n over the long term.