Objective To evaluate the effect of the osteoprotegerin（OPG） gene-modified autologous bone marrow stromal cells（BMSCs） on regeneration of periodontal defects, and to provide new experimental evidence to explore the gene therapy for periodontal disease. Methods pSecTag2/B-opg was transduced into BMSCs by lipofectamine 2000. The expression of OPG protein in the BMSCs was detected by immunocytochemistry and Western blot. Inverted phase contrast microscope and scanning electron microscopy（SEM） were used to observe the morphology and proliferation of the MSCsOPG on the surface of the poly lactic-co-glycolic（PLGA）. Horizontal alveolar bone defect（4 mm×4 mm× 3 mm） were surgically created in the buccal aspect of the mandibular premolar, and were randomly assigned to receive BMSCsOPG -PLGA（cells/material/OPG）, BMSCs -PLGA（cells/material）, PLGA（material）, or root planning only （blank control）. The animals were euthanized at 6 weeks post surgery for histological analysis. The height of new alveolar bone and cementum and the formation of new connective tissue were analyzed and compared. All data were statistically analyzed using the q test. Results The BMSCs transfected by human OPG gene can highly express OPG protein. SEM observations demonstrated that BMSCsOPG were able to proliferate and massively colonize on the scaffolds structure. After 6 weeks, the height of new alveolar bone and cementum and the formation of new connective tissue were significantly greater in the experimental group than in the control groups P
