BACKGROUND:Freeze-dried bone has strong immunogenicity due to insufficient removal of xenoantigen.Deproteinized bone and completely-decalcified bone have weak antigenicity,but the fomer has no osteoinductive property,and the latter has poor biomechanical property,so both of tem are limited in clinical application.OBJECTIVE:To observe the change of rabbit peripheral blood T lymphocyte subsets after transplantation of tissue engineered bone constituted by partially-decalcified freeze-dried bone scaffold and the histological changes of transplanted tissue.DESIGN,TIME AND SETTlNG:Randomized grouping,controlled animal observation.Performed in the State Key Laboratory of Biotherapy(I.E.Department of Stem cells and Tissue Engineering),Huaxi Hospital,Sichuan University between June 2006 and June 2007.MATERlALS:Tissue-engineered bone was in vitro constructed using osteoblasts.Which were derived from rabbit periosteum and used as seeding cells,and xenogeneic cancellous bone,which were antigen self-digested,partially-decalcified freeze-dried bone.METHODS:Forty-eight rabbits were randomly divided into the following 4 groups,with 12 rabbits in each group:partially-decalcified freeze-dried bone group(partially-decalcified bone group),tissue engineered bone group,autogenous bone group.And allogeneic bone group.Partially-decalcified freeze-dried bone,tissue engineered bone,autogenous bone,and allogeneic bone were respectively implanted into the 1 cm segmental defect in rabbit radius in above-mentioned groups.MAINOUTCOME MEASURES:Prior to and 1,2,and 4 weeks after implantation,the change of rabbit peripheraI blood T lymphocyte subsets were examined by flow cytometry；At 2,4,8,and 12 weeks after implantation,osteogenesis of the 4 materials was examined by routine histological examination.RESULTS:①In the partially-decalcifled bone group,peripheral blood CD4+and CD8+1r lymphocytes were significantly increased at 1 and 2weeks afterimplantationthan priortoimplantation(P<0.05).At 4 weeks after implantation.CD4+T lymphocytes were increased,but not significantly,compared with prior to implantation(P>0.05).In the autogenous bone group,CD4’and CD8+T lymphocytes were increased,but not significantly(P>0.05).In the allogeneic bone group,CD4’and CD8+T lymphocytes were significantly increased at weeks 1,2,and 4 after implantation than prior to implantation and the synchroale phase in the other groups(P<0.05).②inthetissue engineeredbonegroup,at week 2 after implantation,osteoblasts and chondroblasts were visible in the material porous,in addition,a new mixed tissue containing bone and cartilage formed and surrounded by osteoclasts,and partial rack was destroved and absorbed.At week 4,newly formed bone had turned into woven bone.At week 8.Lamellar bone was foand.And partially-decalcified freeze-dried bone was completely degraded and absorbed.At week 12,the implant had been completely substituted by lamellar bone,and medullary cavity was recanalized.CONCLUSION:Tissue-engineered bone constituted by taking partially-decalcified freeze-dried bone as scaflfold led to an increase in peripheral blood T lymphocytes,but which did not influence its good repair capabmtv of bone defects.