Inbred or outbred? An evaluation of the functional allogenicity of farm sheep used in cardiac valve studies

Modified uterine allotransplantation and immunosuppression procedure in the sheep model

Objective

To develop an orthotopic, allogeneic, uterine transplantation technique and an effective immunosuppressive protocol in the sheep model.

Methods

In this pilot study, 10 sexually mature ewes were subjected to laparotomy and total abdominal hysterectomy with oophorectomy to procure uterus allografts. The cold ischemic time was 60 min. End-to-end vascular anastomosis was performed using continuous, non-interlocking sutures. Complete tissue reperfusion was achieved in all animals within 30 s after the vascular re-anastomosis, without any evidence of arterial or venous thrombosis. The immunosuppressive protocol consisted of tacrolimus, mycophenolate mofetil and methylprednisolone tablets. Graft viability was assessed by transrectal ultrasonography and second-look laparotomy at 2 and 4 weeks, respectively.

Results

Viable uterine tissue and vascular patency were observed on transrectal ultrasonography and second-look laparotomy. Histological analysis of the graft tissue (performed in one ewe) revealed normal tissue architecture with a very subtle inflammatory reaction but no edema or stasis.

Conclusion

We have developed a modified procedure that allowed us to successfully perform orthotopic, allogeneic, uterine transplantation in sheep, whose uterine and vascular anatomy (apart from the bicornuate uterus) is similar to the human anatomy, making the ovine model excellent for human uterine transplant research.

Functional restoration of endothelial cells of the cryopreserved heart valve

PURPOSE

Although several approaches have been tried to improve the durability of cryopreserved valves, cellular restoration after thawing remains to be investigated. The aim of our study was to assess the functional restoration of endothelial cells of cryopreserved heart valves by in vitro culture for an alternative step to improving longevity.

METHODS

Cryopreserved human umbilical vein endothelial cells (HUVECs) and porcine aortic cusps were cultivated for 14 days after thawing. Then the cellular activity of the enzymes cytosolic esterase and mitochondrial dehydrogenase was measured. The cellular viability of cryopreserved cusps was also assessed using confocal laser scanning microscopy.

RESULTS

The number of viable HUVECs decreased markedly after cryopreservation and thawing but recovered to pre-cryopreservation level after 14 days of culture. In contrast, the enzyme activity of the cryopreserved porcine aortic cusps showed recovery at 7 days of in vitro tissue culture after thawing. Confocal laser scanning microscopy findings showed that the cellular cytosolic esterase activity of cryopreserved cusps deteriorated after thawing but displayed considerable recovery by day 14 of culture.

CONCLUSION

The functional recovery of endothelial cells in cryopreserved heart valves seems to require tissue culture of at least 14 days. Ex vivo endothelial restoration of cryopreserved heart valves may add to heart valve durability.

Decellularization reduces immunogenicity of sheep pulmonary artery vascular patches

OBJECTIVES

Allograft vascular tissue is important in the repair of complex structural lesions of the heart and great vessels, but induces a deleterious immune response that might shorten the effective lifespan of the tissue and sensitize the recipient. We hypothesized that decellularizing allograft vascular tissue reduces the host allogeneic immune response.

METHODS

Allograft ovine pulmonary artery patches were decellularized, cryopreserved, and implanted into the descending thoracic aorta. The humoral immune response was measured by means of flow cytometry at regular intervals over 6 months. Graft histology, immunohistochemistry, and calcification were assessed after 4 weeks or 6 months.

RESULTS

Leukocyte infiltration was reduced in decellularized grafts. A trend toward decreased in-patch calcification was observed in the decellularized group (7.6 ± 4.3 vs 40.0 ± 15.9 mg of calcium/mg of protein, P = .107). Decellularization reduced IgG antibody binding to donor splenocytes (9.8% ± 3.3% vs 57.8% ± 13.7% [control value], P = .010), as assessed by means of flow cytometry. All cytokines examined were detected in nondecellularized tissues after 4 weeks but not at 6 months, indicating complete graft rejection at that time. In contrast, transforming growth factor β1 and interleukin 10 were the only prominent cytokines in all decellularized grafts at 4 weeks after transplantation.

CONCLUSIONS

Decellularization of allograft vascular tissue minimized the recipient cellular immune response and eliminated the production of anti-donor antibodies in recipients.