Potential Applications of Gene Therapy in Sports Medicine

Advanced Gene Therapy Strategies for the Repair of ACL Injuries

The anterior cruciate ligament (ACL), the principal ligament for stabilization of the knee, is highly predisposed to injury in the human population. As a result of its poor intrinsic healing capacities, surgical intervention is generally necessary to repair ACL lesions, yet the outcomes are never fully satisfactory in terms of long-lasting, complete, and safe repair. Gene therapy, based on the transfer of therapeutic genetic sequences via a gene vector, is a potent tool to durably and adeptly enhance the processes of ACL repair and has been reported for its workability in various experimental models relevant to ACL injuries in vitro, in situ, and in vivo. As critical hurdles to the effective and safe translation of gene therapy for clinical applications still remain, including physiological barriers and host immune responses, biomaterial-guided gene therapy inspired by drug delivery systems has been further developed to protect and improve the classical procedures of gene transfer in the future treatment of ACL injuries in patients, as critically presented here.

Gene delivery to cartilage defects using coagulated bone marrow aspirate

The long-term goal of the present study is to develop a clinically applicable approach to enhance natural repair mechanisms within cartilage lesions by targeting bone marrow-derived cells for genetic modification. To determine if bone marrow-derived cells infiltrating osteochondral defects could be transduced in situ, we implanted collagen-glycosaminoglycan (CG) matrices preloaded with adenoviral vectors containing various marker genes into lesions surgically generated in rabbit femoral condyles. Analysis of the recovered implants showed transgenic expression up to 21 days; however, a considerable portion was found in the synovial lining, indicating leakage of the vector and/or transduced cells from the matrix. As an alternative medium for gene delivery, we investigated the feasibility of using coagulated bone marrow aspirates. Mixture of an adenoviral suspension with the fluid phase of freshly aspirated bone marrow resulted in uniform dispersion of the vector throughout, and levels of transgenic expression in direct proportion to the density of nucleated cells in the ensuing clot. Furthermore, cultures of mesenchymal progenitor cells, previously transduced ex vivo with recombinant adenovirus, were readily incorporated into the coagulate when mixed with fresh aspirate. These vector-seeded and cell-seeded bone marrow clots were found to maintain their structural integrity following extensive culture and maintained transgenic expression in this manner for several weeks. When used in place of the CG matrix as a gene delivery vehicle in vivo, genetically modified bone marrow clots were able to generate similarly high levels of transgenic expression in osteochondral defects with better containment of the vector within the defect. Our results suggest that coagulates formed from aspirated bone marrow may be useful as a means of gene delivery to cartilage and perhaps other musculoskeletal tissues. Cells within the fluid can be readily modified with an adenoviral vector, and the matrix formed from the clot is completely natural, native to the host and is the fundamental platform on which healing and repair of mesenchymal tissues is based.