1. ¹Interdepartmental Program in Cell and Molecular Biology, Baylor College of Medicine, Houston, TX
2. ²Center for Cell and Gene Therapy, Baylor College of Medicine, Houston, TX
3. ³Molecular and Human Genetics, Baylor College of Medicine, Houston, TX
4. ⁴Howard Hughes Medical Institute, Baylor College of Medicine, Houston, TX
5. ⁵Cartela AB, Lund, Sweden
6. ⁶Rice University, Houston, TX

Abstract

Osteoarthiritis (OA) is a significant social and economic problem without adequate therapies. OA is characterized by focal erosion of articular cartilage in the joints of affected individuals. Recent advances in the field of gene therapy have identified potential transgenes that may alleviate symptoms and potentially regenerate the damaged intra-articular surfaces of the OA joint. Injecting adenovirus into the articular capsule results in preferential transduction of the synovium. Unfortunately, therapeutic growth factor expression from the synovial tissue results in ectopic cartilage formation and may cause osteophyte formation. One solution to overcome this is to express chondrogenic growth factors within the cartilage by transducing chondrocytes. However, poor transduction of articular chondrocytes limits efficient adenoviral mediated gene transfer strategies for the treatment of OA. To this end, we tested whether including adenovirus in a calcium phosphate co-precipitate (Ad:CaPi) would increase gene transfer efficiency in rat chondrosarcoma cells (RCS) in vitro. When cells were transduced with equivalent MOI, we found a significant increase in |[beta]|gal expression (2-log) in Ad:CaPi transduced cells compared to adenovirus alone. Moreover, a dose response comparison between adenovirus and Ad:CaPi showed a significant increase in efficiency, where 1 log fewer particles of adenovirus in calcium phosphate complexes were required to transduce the same number of cells as adenovirus alone. Since Ad:CaPi complexes increase gene transfer to different cell types through a receptor independent mechanism, it is likely that these complexes will increase gene transfer to all cell types in the articular space including the surrounding synovial tissue, and therefore would require genetic modification to achieve chondrocyte specific gene expression. Therefore, we tested an alternative approach to re-direct adenoviral gene transfer specifically to chondrocytes. We utilized a biotinylated anti-|[alpha]|₁₀ integrin antibody that is specific for chondrocytes. We coupled the antibody with a multivalent neutravidin, and complexed this with a metabolically biotinylated adenovirus. The results indicate a 5-fold increase in gene transfer with the antibody-targeted adenovirus compared to the biotinylated adenovirus alone. Importantly, since this virus has significantly reduced CAR binding, this increase may signify a selectable advantage for transducing chondrocytes within the joint capsule. From this data, we identify novel methods to increase gene transfer to chondrocytes in vitro, and indicate a potential local and chondrocyte targeted gene therapy strategy in vivo.