Morphologic studies of cell endogenous repopulation in decellularized aortic and pulmonary homografts implanted in sheep

PurposesThe rationale of this study was to assess morphologically the effects of implantation of decellularized aortic and pulmonary homografts into growing sheep, with the objective to establish type and extent of cell repopulation and propensity to dystrophic calcification over a prolonged period of time.MethodsPulmonary and aortic homografts were obtained from healthy euthanized juvenile sheep (35–45 kg). Complete decellularization was accomplished in 0.5% sodium deoxycholate and 0.5% sodium dodecylsulfate for 24 h.Twelve homografts from 11 animals were studied as follows:-2 native (1 pulmonary and 1 aortic) from the same animal;-2 decellularized unimplanted (1 aortic and 1 pulmonary), from two different animals;-8 decellularized (2 aortic and 6 pulmonary), implanted in 8 female animals for 14–21 months.Gross, X-ray, histology, immunohistochemistry, morphometry, transmission electron microscopy and calcium content spectroscopy investigations were carried out.ResultsDecellularization appeared complete in unimplanted homografts. The extracellular matrix was intact. Explanted homografts showed soft, pliable cusps without gross calcium deposits and tears; calcium content showed slight difference between aortic and pulmonary cusps (5.505±2.04 vs. 2.77±1.06 mg/g dry weight, P= .04). Microscopic calcifications were observed in two aortic homografts on smooth muscle cells of repopulated homograft wall and on valvular interstitial cells, respectively. Inflammatory infiltrates were never seen.Cell repopulation occurred in homograft wall with actin smooth muscle and vimentin positive cells in media lamellar units (cell density per millimeter squared, 885.4±424.38 in native vs. 172.64±160.33 in implanted homograft, P< .01) as well as in cusps (cell density per millimeter squared, 495.96±63.92 in native vs. 184.66±140.74 in implanted homograft, P< .01). The percentage area of recellularization was 71.27±3.03 in the homograft wall and 22.16±3.06 in the cusps.Thickness of pulmonary explanted homograft wall and cusps was 900.68±321.52 μm vs. 994.36±135.92 μm and 204.75±66.64 μm vs. 231.04±105.94, respectively (P= NS), whereas in aortic homograft wall and cusps it was 1358.604±423.79 μm vs. 2065.32±431.46 μm, P= .016, and 248.01±93.95 μm vs. 390.30±104.81 μm, P= .03, respectively. The endothelial lining was restored.ConclusionEndogenous cell repopulation in decellularized homografts occurs and persists following implantation, at both wall and cusp level, without evidence of immune reaction.Even in the long term, the cusps exhibit no structural deterioration and negligible calcification.