Quantitative imaging of cartilage and bone for functional assessment of gene therapy approaches in experimental arthritis

Anti‐inflammatory gene therapy can inhibit inflammation driven by TNFα in experimental models of rheumatoid arthritis. However, assessment of the therapeutic effect on cartilage and bone quality is either missing or unsatisfactory. A multimodal imaging approach, using confocal laser scanning microscopy (CLSM) and micro‐computed tomography (µCT), was used for gathering 3D quantitative image data on diseased and treated murine joints. As proof of concept, the efficacy of anti‐TNF‐based gene therapy was assessed, comparing imaging techniques with classical investigations. SCID mice knees were injected with human synoviocytes overexpressing TNFα. Two days later, electric pulse‐mediated DNA transfer was performed after injection of the pGTRTT‐plasmid containing a dimeric soluble‐TNF receptor (dsTNFR) under the control of a doxycycline‐inducible promoter. After 21 days the mice were sacrificed, TNFα levels were measured and the joints assessed for cartilage and bone degradation, using CLSM, µCT and histology. TNFα levels were decreased in the joints of mice treated with the plasmid in the presence of doxycycline. Concomitantly, histological analysis showed an increase in cartilage thickness and a decrease in specific synovial hyperplasia and cartilage erosion. Bone morphometry revealed that groups with the plasmid in the presence of doxycycline displayed a higher cortical thickness and decreased porosity. Using an anti-TNF gene therapy approach, known to reduce inflammation, as proof of concept, 3D imaging allowed quantitative evaluation of its benefits to joint architecture. It showed that local delivery of a regulated anti‐TNF vector allowed decreasing arthritis severity through TNFα inhibition. These tools are valuable for understanding the efficacy of gene therapy on whole‐joint morphometry.