645. Improving RAAV Gene Expression Inflammatory Conditions Using Empty Capsids and an Immunosuppressive Compound
Authors: Caroline J. Aalbers, Niels Broekstra, Mariska van Geldorp, Paul P. Tak, Margriet J. Vervoordeldonk, Jonathan D. Finn
Journal: Molecular Therapy (2015)

Objective: Gene therapy has the potential to treat rheumatic diseases. We have shown that rAAV5 is effective in delivering genes to the joint in vivo, however, the presence of macrophages in the inflamed joint might hampering AAV mediated gene delivery. To investigate this further, we determined if administration of agents that influence macrophage activity/number and/or addition of empty capsids had an effect on rAAV5-transgene expression in the joints of arthritic and healthy mice. Material and Methods: Expression of luciferase after i.a. injection of an rAAV5 vector expressing Fire-fly luciferase was investigated in mice with or without arthritis. Mice with collagen-induced arthritis (CIA) were injected with rAAV5.CMV.Fluc or NaCl in both knee joints on day 21 (unless indicated otherwise) and monitored for luciferase expression (from 3 days up till 6 months) by IVIS. Where indicated, empty capsids were co-administered with full particles at a 5:1 or 20:1 (empty: full) ratio. Macrophages were depleted or inhibited by administration of systemic clodronate liposomes (i.v.) or triamcinolone (i.m. or i.a.) 48 hrs prior to vector administration. Healthy mice were administered with vector and empty capsid. Results: We showed that in arthritic mice administration of rAAV5. CMV. Fluc after the onset of inflammation (d24) resulted in lower expression of luciferase compared to vector administration before onset of inflammation (d17). Both the addition of triamcinolone and clodronate improved luciferase expression over a period of 4 weeks (end of experiment). When empty capsids were added to full genome containing capsids in a 1:5 ratio, expression per joint, and the percentage of knee joints with a positive signal improved. A study to assess the duration of expression as well as to investigate the combination of these two approaches was performed. Similar to the previous study, we observed increased expression using triamcinolone or empty capsid alone, however the combination of macrophage inhibition and decoy capsids resulted in a synergistic enhancement of gene expression (5.85 fold, p = 0.001). This increase was sustained for 6 months post vector administration. As triamcinolone is usually administered directly into the inflamed joint of RA patients, we compared the efficacy of i.a. versus i.m. administration of triamcinolone and found that the enhancement of gene expression was independent of the route of administration. Next we wanted to see if empty capsid could enhance expression in non-inflamed joints. We observed increased expression in the presence of empty capsid, 4.8 fold at 5:1 ratio and up to 20 fold with the 20:1 ratio (p<0.05). In all experiments expression was limited to the knee joint region. Conclusions: We demonstrated that either depletion or inhibition of macrophages leads to an increase in gene expression. In addition, empty decoy capsids improve transgene expression in the presence or absence of inflammation. These data have implications for future applications of local gene therapy to the joint, or to other tissues that have an abundance of macrophages.