A novel decellularization protocol with cryopreservation of pulmonary allografts in an ovine model.

Objectives: Pulmonary allografts are commonly used for right ventricular outflow tract reconstruction. Cryopreserved allografts may develop degeneration and stenosis over time due to immune-related issues. Fresh decellularized aortic and pulmonary allografts have shown favourable early outcomes. We used a sheep model to evaluate the safety of a novel decellularization protocol combined with cryopreservation applied on pulmonary allografts, aiming to improve availability and reduce cost.

Methods: Pulmonary valve replacement was performed in juvenile female sheep using cryopreserved pulmonary allograft (n = 9) and decellularized cryopreserved pulmonary allograft (n = 10). Haemodynamics were investigated by transthoracic echocardiography and magnetic resonance imaging. Allografts were explanted at 6 months for macroscopic comparison, calcium quantification using X-ray imaging and spectrometry, histological and immunohistochemical characterization.

Results: There was one operative death in each group. There were no significant haemodynamic differences between groups regarding peak gradient (P = 0.14) or degree of regurgitation (P = 0.67) at 6 months. Calcium content of macroscopically non-calcified tissue was statistically similar (P = 0.16). Overall, decellularized tissues were smooth and supple. Cryopreserved allografts developed pannus formation and pronounced subvalvular calcifications. Some grafts in both groups showed luminal fibrin thrombi, calcified in cryopreserved grafts. Histologically, cryopreserved tissues contained more inflammatory cells. Decellularized grafts had lower cell presence, acellular inner media and valve with occasional fibrin covering. No true endothelium was seen in the stained samples except at the anastomoses.

Conclusions: Haemodynamically, both cryopreserved allografts and allografts decellularized according to the newly-developed protocol produced equivalent and favourable outcomes. Decellularized allografts showed less inflammation, less pannus formation and less calcification on X-ray imaging.