Engineering of human vascular aortic tissue based on a xenogeneic starter matrix

The goal for tissue engineering of vascular grafts is the replacement of a diseased vessel with a functional and stable graft. We now introduce a new concept for the tissue engineering of vessels. The idea was to humanize a previously acellularized, but structurally intact, xenogeneic vessel by repopulation with human autologous cells. To this purpose, a gentle nondenaturing and nondeterging acellularization procedure for xenogeneic aortas was developed. This structure was reseeded with pre-expanded peripheral vascular endothelial cells (EC) and myofibroblasts using specifically designed bioreactors.

Aortas from 15-30 kg female landrace pigs were acelullarized with a 0.1% trypsin solution for between 24 and 96 hr. Human vascular cells were harvested from saphenous vein biopsy specimens. Acellularized vessels were reseeded with EC and myofibroblasts. Cell viability after reseeding was assayed by fluorescence staining. Morphologic features of the acellularized matrix and tissue engineered vessel was assayed by transmission and scanning electron microscopy and histologic analysis. Nitric oxide-synthetase activity was investigated by mass spectrometric analysis of bioreactor supernatants. The in vivo immune response was tested by subcutaneous implantation of acellularized porcine aortic tissue in a rat model.

The acellularization procedure resulted in an almost complete removal of the original resident cells, and the 3-D matrix was loosened at interfibrillar zones. However, the 3-D arrangement of the matrix fibers was grossly maintained. The 3-D matrix was covered with a fully confluent human endothelial cell layer obtained by continuous stress challenge in the bioreactor. Myofibroblasts migrated into positions formerly occupied by the xenogeneic cells. Nitric oxide synthetase activity was maintained in the bioartificial graft. T-lymphocyte and CD18 positive leukocyte infiltrate were greatly reduced after acellularization of porcine aortic specimens after implantation in the rat.

Porcine vessels were acellularized and consecutively fully repopulated with human EC and myofibroblasts. This approach may eventually lead to the engineering of vessels immunologically acceptable to the host using a relatively short preparation period of 2-3 weeks. We expect matrix turnover in vivo leading to a gradual assimilation of the matrix structure by the host mediated by the hosts autologous cells.