5.1 Bone tissue structure
Bone, bone marrow, and cartilage have different blood supplies, matrix, and cell turnover rates; osteoblasts, osteocytes, chondrocytes, or bone marrow cells should be designated first.
5.2 AAV serotype selection
Native AAV9/AAV-DJ can be used as a starting point, and systemic bone targeting usually requires capsid or ligand optimization.
5.3 Bone-specific promoter
COL1A1 is biased toward the osteogenic lineage, BGLAP is biased toward mature osteoblasts, and COL2A1 is biased toward chondrocytes.
5.4 Administration method and dosage reference
Intra-articular injection (IA): Targets the synovium. For mice, 0.5×10^10-1×10^11 vg/joint, 5 μL, 30 G Hamilton, insert the needle at the medial edge of the patellar tendon of the knee joint; for rats, 1×10^10-2.5×10^10 vg/joint, 50 μL; expression can last for >6 months [5-4,5-5].
Local/systemic administration: 1×10^10-1×10^11 vg for local fracture; 1×10^11-1×10^12 vg/for system. The joint cavity mainly transduces synovial lining cells, and the cartilage matrix barrier restricts AAV from penetrating cartilage and reaching chondrocytes. Treatment of cartilage lesions requires direct intrachondral injection or optimization of capsid engineering [5-5].
Coverage and limitations: Mainly synovial fibroblasts, with very limited chondrocyte transduction; intra-articular injection of AAV2.5-IL-1Ra in the equine OA model achieves sustained intra-articular IL-1Ra expression, no structural progression, and reduced lameness [5-6]. Bone tissue sampling and decalcification will affect nucleic acid, protein and fluorescence readout, and the detection method needs to be matched in advance.
5.5 Key research evidence
Xing et al. confirmed that intra-articular AAV-PRG4 gene therapy prevents post-traumatic osteoarthritis [5-4]; Frisch et al. reported the persistence and localization of transgene expression after a single AAV joint injection [5-5]; AAV2.5-IL-1Ra achieved safe and sustained intra-articular expression in the human OA knee joint in Phase I clinical trials [5-6].
5.6 References for this chapter
[5-1] Yang YS, et al. Bone-targeting AAV silencing of Schnurri-3 prevents bone loss. Nat Commun. 2019;10:2958. [H]
[5-2] Lee LR, et al. AAV vectors for local fracture and systemic skeleton delivery. Mol Ther Methods Clin Dev. 2019;15:101-111. [H]
[5-3] Yoon DS, et al. AAV serotype selectivity for chondrocytes and cartilage. Int J Med Sci. 2021;18:3353-3360. [H]
[5-4] Xing Y, et al. Intra-articular AAV-mediated PRG4 gene therapy for preventing posttraumatic osteoarthritis. Mol Ther. 2022;30:1864-1876. DOI:10.1016/j.ymthe.2022.02.015. [N]
[5-5] Frisch J, et al. Persistence, localization, and external control of transgene expression after single injection of AAV into injured joints. Hum Gene Ther. 2013;24:423-433. DOI:10.1089/hum.2012.118. [H]
[5-6] A phase 1 clinical trial shows safe, sustained AAV-mediated expression of IL-1Ra in human OA knee. Sci Transl Med. 2025. DOI:10.1126/scitranslmed.adu9804. [N]