DIRECT SYNOVIAL GENE-TRANSFER WITH RETROVIRAL VECTORS IN RAT ADJUVANTARTHRITIS

Objective. To evaluate the feasibility of direct in vivo gene transfer in an animal model of arthritis using a retroviral vector. Methods. T he timing and dose of retroviral vector was examined using very high t iter retroviral vector (greater than or equal to 10(9) CFU) in rat adj uvant arthritis. Retroviral vector expressing beta-galactosidase (beta -gal) or vehicle alone was injected into the right ankle of rats with adjuvant arthritis. Ankles were injected either on Day 7 (pre-arthriti s), Day 10 (early arthritis), Day 15 (accelerating arthritis), or Day 28 (chronic arthritis) after adjuvant immunization. Joints were harves ted 3 days later and extracts were assayed for beta-gal activity. Resu lts. Synovial beta-gal expression was minimal in the Day 7 group and e levated in the Day 10, Day 15, and Day 28 groups. Gene transfer with r etroviral vector did not exacerbate the local inflammatory response. M inimal or no beta-gal expression was observed in the contralateral uni njected paw or in the spleen, lung, liver, and kidneys. Frozen section s of retroviral vector injected joints were stained with X-gal and rev ealed transduced cells in the lining and superficial sublining layers, To determine the longevity of gene expression, ankle joints were inje cted with vector on Day 15 post-adjuvant, harvested, and assayed for b eta-gal activity for up to 49 days after injection. Expression of the enzyme peaked from Day 3 to 7 and was still readily detected up to 49 days after retrovirus infection. Conclusion. This is the first report of successful direct in vivo gene transfer in the rat adjuvant arthrit is model using a retroviral vector. Appropriate timing of administrati on and very high titer retroviral vector preparations are key determin ants of adequate gene transduction.