Retrovirus mediated in vivo gene transfer to synovium in bacterial cell wall-induced arthritis in rats

Gene therapy may provide an effective alternative to conventional approaches for treating rheumatoid arthritis. Direct in vivo gene delivery to synovium has a distinct advantage with respect to clinical use. To date, retroviral vectors are the best studied constructs for gene delivery, and almost all approved gene therapy trials in humans rely on retroviral vectors. However, the applicability of retroviral transduction is limited by requirement for cell division, and attempts to transduce normal synovium in situ using retroviral vectors are reported to fail. The present study was undertaken in order to investigate susceptibility of inflamed synovium to retroviral infection in vivo. Using an experimental model of bacterial cell wall (BCW)-induced arthritis in rats, we attempted two approaches for delivery of retroviral vectors to synovium. In the first approach, recombinant retroviral vectors carrying reporter genes lacZ and neo were directly injected into inflamed rat ankle joints. Alternatively, inflamed joints were inoculated with gamma-irradiated murine retroviral vector-producing packaging cells. We found that about 1% of cells in explants from joints inoculated with packaging cells were lacZ-neo-positive. The lacZ+ neo+ cells in joint explants proliferated in culture and were of rat origin as determined using species-specific polymerase chain reaction (PCR) analysis. There was no evidence of transduction in explants from joints directly injected with retroviral vectors or from contralateral, control joints. These findings show that arthritic joints have a population of cells susceptible to retroviral infection in situ and demonstrate the possibility of using retroviral vectors for direct gene delivery to inflamed synovium.