Tissue Reactions of Adenoviral, Adeno-Associated Viral, and Liposome–Plasmid Vectors in Tendons and Comparison With Early-Stage Healing Responses of Injured Flexor Tendons

Delivery of growth factor genes that may substantially increase the healing rate of injured digital flexor tendons is a new application of gene therapy. Adenoviral, adeno-associated viral (AAV), and liposome–plasmid vectors have been used to deliver genes to tendons, but the tendon reactions to these vectors—particularly in contrast to the healing responses in the injured tendons—were unknown. This study was designed to compare the tissue reactions of the earlier-mentioned vectors in tendons with the healing responses of injured flexor tendons. Forty-two flexor digitorum profundus tendons of 6 New Zealand white rabbits were used. Eighteen tendons were divided into 3 groups of 6 each and injected with different vectors: adenoviral vector, AAV2-luciferase vector, or pCMV-β vector with liposome. Another 12 tendons were cut and repaired. At 3, 7, and 14 days, the tendons were harvested and stained with hematoxylin and eosin. Normal flexor tendons were harvested as controls. The tissue reactions of the liposome–plasmid vector in tendons were the most prominent among the 3 vectors tested. The adenoviral vector elicited a moderate degree of tissue reaction. The AAV2 vector caused remarkable reactions in epitenon but almost no reactions in endotenon. Early-stage tissue reactions were more robust in the injured tendons. Compared with early-stage inflammatory and healing responses, the reactions elicited by these vectors were less severe. The 3 gene delivery systems tested elicit less severe tissue reactions in flexor tendons compared with early-stage inflammatory changes in injured tendons. Adenoviral and AAV vectors elicit less severe tissue reactions than liposome–plasmid vectors. The AAV2 vector appears to cause almost no reaction in endotenon. In terms of tissue reactions, the adenoviral and AAV2 vectors, in particular AAV2, are suitable gene delivery systems for future gene transfer to the tendon in vivo.