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


METHODS
Pulmonary and aortic homografts were obtained from healthy euthanized juvenile sheep (35-45kg). Complete decellularization was accomplished in 0.5% sodium deoxycholate and 0.5% sodium dodecylsulfate for 24h. Twelve homografts from 11 animals were studied as follows: Gross, X-ray, histology, immunohistochemistry, morphometry, transmission electron microscopy and calcium content spectroscopy investigations were carried out.


RESULTS
Decellularization 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±1.06mg/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±321.52μm vs. 994.36±135.92μm and 204.75±66.64μm vs. 231.04±105.94, respectively (P=NS), whereas in aortic homograft wall and cusps it was 1358.604±423.79μm vs. 2065.32±431.46μm, P=.016, and 248.01±93.95μm vs. 390.30±104.81μm, P=.03, respectively. The endothelial lining was restored.


CONCLUSION
Endogenous 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.