Tissue engineered allogeneic cartilage induces local immune privilege in rabbits

Hongliang HU; Yilin CAO; Tingting CHEN; Qishi FAN; Yiqun HU

ABSTRACT

BACKGROUND:

The transplantation of allogeneic cartilage has local immunological rejection, and it is necessary to further reduce the rejection to promote its application in clinic, thus it is significant to perform a series of experiments to induce local immune privilege.

OBJECTIVE:

To observe the in vivo growth of tissue engineered allogeneic cartilage reconstructed by chondrocytes transfected with recombinant retroviral vector pLNCX2-FasL.

DESIGN:

A randomized controlled observation.

SETTING:

Shanghai Jiao Tong University.MATERIALS Thirty-six allogeneic New Zealand rabbits as recipients and 45 1-week-old chinchillas as donors, either sex,were purchased by the experimental animal center of Chinese Academy of Sciences. Amphotropic recombinant retrovirus coated cell line PT67 was purchased from Clontech Company; Dulbecco's modified eagle medium (DMEM), fetal bovine serum (FBS), G418 and Polybrene were bought from GIBCO BRL.

METHODS:

The experiment was carried out in original Shanghai Second Medical University from January 2000 to July 2005. The New Zealand rabbits were randomly divided into three groups FasL-transfected group (n =12), untransfected group (n =12) and blank control group (n =12). The rabbit allogeneic cartilages were constructed by the compound of pLNCX2-FasL transfected chondrocytes and tissue engineered material of pluronic F-127. ① Gross observation and mass changes of the grafts Corresponding materials were infused subcutaneously, the grafts were removed at 1, 2 and 3 months after transplantation for gross observation and the mass changes. ② Staining observation The grafts were removed at 1, 2 and 3 months after transplantation, then prepared into sections, and observed by hematoxylin and eosin (HE), Safranin'O and Masson's trichrome stainings. ③ Antibody detection Blood samples (1 mL) were collected at 1 and 2 months after transplantation, the chondrocytes of the chinchillas were lysed freezingly with lysis antigen as the mixed antigen, and separated by electrophoresis in agarose medium, then acted with serum of recipient to observe whether corresponding antibody generated. ④ Complement dependent cytotoxicity (CDC) test The chondrocytes of chinchillas were prepared into cell suspension (2×109/L), and then seeded into 96-well plate, attached grew for 24 hours, then recipient serum was added for the CDC test, and the percentage of apoptotic cells was counted under microscope.MAIN OUTCOME

MEASURES:

① Gross observation and mass changes of the grafts;② Histological changes; ③ Results of the antibody detection; ④ Percentage of apoptotic cells.

RESULTS:

All the 81 rabbits were involved in the analysis of results. ① Gross observation and mass changes of the grafts Two weeks after inoculation, there were obvious nod formations at the inoculated sites, but no nod formed in the blank control group. The new cartilage tissues became smaller gradually and completely disappeared at 4 months in the untransfected group, whereas those in the FasL-transfected group became smaller, but still existed after 7 months. The masses of grafts in the FasL-transfected group were higher than those in the untransfected group (P ＜ 0.05). ②Histological observation Plenty of lymphocytic infiltrations around cartilage tissue could be observed in the untransfected group, and obviously decreased in the FasL-transfected group. No lymphocyte was observed inside the chondrocytes.Masson's trichrome staining was performed, and it was observed under light microscope that the small white parts in the middle were immature chondrocytes, and there were green collagen around most of the mature chondrocytes. Safranin O staining showed strong positive reaction, suggested that there were rich glycosaminoglycan in matrix. ③ Antibody detection The chondrocytes of the chinchillas were lysed freezingly with lysis antigen as the mixed antigen, then acted with serum of recipient, and the results showed that no corresponding antibody generated. ④ Percentage of apoptotic cells The percentages of serum CDC apoptotic cells in the FasL can ransfected group, untransfected group and blank control group were 5%, 6% and 1%, which were all negative.

CONCLUSION:

Rabbit allogeneic chondrocytes transfected with recombinant retroviral vector pLNCX2-FasL can reconstruct tissue engineered cartilage, and can postpone the degeneration by 3 months.