SUSTAINED PRODUCTION OF HUMAN TRANSFERRIN BY TRANSDUCED FIBROBLASTS IMPLANTED INTO ATHYMIC MICE - A MODEL FOR SOMATIC GENE-THERAPY

Somatic gene therapy has been proposed as a means of treating inherite d diseases involving defective or absent plasma proteins, viral diseas es, and cancer, Introduction of the gene of interest into fibroblasts and implantation of these genetically modified fibroblasts using a ski n equivalent system may be an attractive model for gene therapy becaus e skin fibroblasts are easily obtained and propagated in culture, This study evaluated expression of the gene for human transferrin (hTf) by genetically modified fibroblasts in vitro and in vivo. NIH 3T3 fibrob lasts, which form non-metastasizing tumors in athymic mice, mere trans duced with a retroviral vector encoding hTf. The transduced cells were cloned by limiting dilution and hTf production by the cloned cells me asured, Two clones of cells producing high levels of hTf were used to seed collagen-coated nylon matrices, which were maintained in culture for up to 53 d. The rate of synthesis of hTf by the seeded matrices wa s constant after 22 d in vitro. Matrices seeded with cloned, transduce d cells were implanted subcutaneously into seven athymic mice, and pla sma levels of hTf were assessed biweekly, In all animals, the plasma l evel of hTf was detectable at week 6 after implantation, Levels of hTf remained elevated in the animals until the implants were removed at w eek 12. At week 10, the level of hTf in the plasma correlated with tum or volume in tumors less than 2000 mm(3) in size, The half-life of hTf in the mice was 39.5 h. In this model, gene expression did not declin e for the 12-week observation period.