Gene transfer into the mammalian kidney: first steps towards renal gene therapy

In this review we discuss two strategies for successful retrovirally-mediated transfer (transduction) of a reporter gene (bacterial beta-galactosidase) into the mammalian kidney. Retroviruses only integrate into dividing cells, but the adult kidney has a very low cell turnover. One approach used is the rapidly-dividing metanephros, or precursor of the adult kidney, as a target for proviral integration. After infection and microtransplantation of fragments of this tissue into the renal cortex of neonatal mice, the implants grew and developed within the host kidney and reporter gene expression was located in glomerular and interstitial cells. A similar approach has been used by other investigators to grow genetically-engineered metanephros in a subcapsular location in the kidney. However, access of the gene product to the parenchyma of the kidney may be limited using this approach. A second strategy was to induce renal tubular cell replication by causing nephrotoxic damage with a folic acid injection. This created a 'biological window' in which a specific cell population, that is, tubular cells, was targeted for retroviral infection. One to four weeks later foci of tubular cells were found to express the reporter gene product. In both models, 50 to 90% of the experiments showed evidence of proviral integration as judged by the presence of a 559 base-pair DNA fragment amplified by the polymerase chain reaction. This persisted for four to seven weeks, the limit of the period of observation.