Overexpression of haem oxygenase 1 protects allogeneic thyroid grafts from rejection in naive mice

Abstract

Abstract Background Endocrine allografts are an option for the treatment of endocrine failure. This study examined whether anti-CD4 monoclonal antibody (mAb) could induce survival of allogeneic thyroid grafts and investigated the mechanisms involved in graft survival. Methods and Results One lobe of thyroid was transplanted under the kidney capsule and graft survival was examined histologically. C57BL/10 (H2b) thyroids were rejected in naive CBA (H2k) mice within 14 days after transplantation. When mice were treated with a depleting anti-CD4 mAb (YTA 3·1; 100 μg on day −1, 0 and 3), all C57BL/10 thyroid grafts survived for over 30 days. In order to determine if donor-specific tolerance had been induced, mice with the surviving C57BL/10 thyroid grafts were transplanted with second C57BL/10 or Balb/c (H2d) thyroids under the left kidney capsule at 30 days. Interestingly, all of the second grafts were rejected in the left kidney capsule but the first C57BL/10 thyroid grafts continued to survive in the right kidney capsule for a further 30 days. These findings suggest that grafts themselves were modified under anti-CD4 mAb treatment. To confirm this hypothesis, C57BL/10 thyroid grafts in mice treated with anti-CD4 mAb were resected and retransplanted into naive mice 30 days after transplantation. All of the grafts survived when retransplanted to naive mice and this was found to correlate with overexpression of haem oxygenase 1 in the thyroid grafts. In an attempt to demonstrate the pivotal role of haem oxygenase 1 on graft survival, an inhibitor of haem oxygenase 1 (zinc protoporphyrin) or control compound (copper protoporphyrin) that did not inhibit the enzyme was injected intraperitoneally (30 mmol l−1 every day) after transplantation of C57BL/10 thyroid grafts into the primary CBA recipients treated with anti-CD4 mAb. The grafts in mice treated with zinc protoporphyrin but not copper protoporphyrin were rejected when retransplanted to naive recipients. Conclusion Overexpression of haem oxygenase 1 protects allogeneic thyroid grafts from rejection in recipients treated with anti-CD4 mAb. This observation may be applied for clinical endocrine grafts using gene transfer of haem oxygenase 1.