Approaching clinical application of xenotransplantation

Accommodation after lung xenografting from hamster to rat

BACKGROUND

Long-term xenograft survival can be achieved in hamster hearts transplanted into rats treated with cobra venom factor (CVF) and cyclosporine A (CsA). This phenomenon of "accommodation" is associated with expression of protective genes such as bcl-2, bcl-X(L), and heme-oxygenase-1. We examined whether accommodation could be induced in hamster-to-rat lung xenografts and whether the pattern of protective genes is similar to cardiac xenografts.

METHODS

We used hamster-to-rat cardiac and lung xenotransplantation models. Cardiac xenotransplants were treated with CVF+CsA and compared with untreated controls. Lung xenotransplants were treated with either CVF+CsA or FK506 and cyclophosphamide (Cp) and compared with untreated controls. All recipients were killed by 21 days after transplantation. We examined graft survival and protein expression of protective genes, and we performed histologic and immunohistologic analyses.

RESULTS

Rejection occurred rapidly in untreated rats. CVF+CsA or FK506+Cp treatment significantly influenced graft survival. Eight of 12 CVF+CsA-treated heart transplants survived 21 days. Seven of 16 CVF+CsA-treated lung grafts and five of 12 FK506+Cp-treated lung xenografts survived 21 days. We observed significant protein expression of bcl-2, bcl-X(L), and heme-oxygenase-1 in cardiac xenografts treated with CVF+CsA at 2, 14, and 21 days after transplantation, compared with normal hamster hearts. We also observed significant expression of these proteins in lung xenografts treated with either CVF+CsA or FK506+Cp at 21 days after transplantation, compared with normal lungs.

CONCLUSIONS

Accommodation may be a general phenomenon for all organs, mediated through protective genes. Induction of accommodation does not require disruption of the complement system.

Histological and immunohistological study of cryopreserved aortic valve grafts: the possibility of a clinical application for cryopreserved aortic valve xenograft

The influence of preservation techniques on xenogeneic immune responses was examined to investigate the possibility of their clinical use. Mongrel dogs and pigs were used as allogeneic and discordant xenogeneic donors of aortic valve grafts, respectively. The allografts and xenografts were implanted in the abdominal aorta of mongrel dogs after cryopreservation or after fresh preservation. Allografts and xenografts were explanted at Days 7 and 42 for histological and immunohistochemical examination. In the fresh preserved allografts and the fresh preserved xenografts, the media of aortic wall grafts were significantly acellular at 7 days. Significant aortic medial destruction and neointimal proliferation with significant destruction of the valve leaflets was observed at 42 days. However, no differences were found among the preservation techniques in the xenogeneic grafts. To alleviate the lack of homografts, approaches such as the tissue-engineered graft may become an alternative in patients who are acceptable candidates.