Interaction of Cells with Decellularized Biological Materials - Tissue Engineering: Cell-Surface Interactions for Tissue Culture - page 109

removal of all cellular components via hypotonic solutions, Huynh et al. [ 26 ]
tested autologous, allogeneic, and xenogeneic grafts in large-animal models and
reported excellent patency rates. In the histological analysis they found that these
primary decellularized implanted grafts were spontaneously reseeded in vivo and,
therefore, obviously underwent regenerative processes. However, in experiments
using smaller animals such as rats, these small-caliber vessel grafts were found to
be occluded at a very early stage owing to thrombus formation [ 27 ].
4 Reseeding Concepts
Trying to avoid the immunological influence of residual cellular fragments,
Gulbins et al. [ 28 ] reseeded cryopreserved human allografts with autologous
endothelial cells in vitro without prior decellularization and implanted these
prostheses in animals—with moderate success. Another concept which can be
taken as a logical consequence of the previously described method was the
autologous endothelial reseeding of decellularized allogeneic and xenogeneic heart
valve prostheses. Following very promising data in animal models, initial results in
human patients are now available (xenogeneic heart valves reseeded with autol-
ogous human endothelial cells) [ 29 ].
Another approach to autologous endothelial reseeding of decellularized heart
valve prostheses was implemented in Hanover in close cooperation with the
University of Chis in˘u (Moldava). On the basis of the consideration that decell-
ularized, i.e., xenogeneic, matrix scaffolds may still induce immunological reac-
tions because of interspecies differences, human allografts which had been
decellularized using an elaborate protocol were reseeded with autologous endo-
thelial cells obtained as mononuclear cells isolated from individual blood samples.
Positive stains for von Willebrand factor, CD31 (platelet/endothelial cell adhesion
molecule 1) and flk-1, as observed in monolayers of cells cultivated and differ-
entiated on the luminal surface of the scaffolds in a dynamic bioreactor system,
indicated the endothelial nature of these cells. Reseeded valves were implanted in
a pulmonary position of two pediatric patients (aged 13 and 11 years) with con-
genital pulmonary valve failure. Postoperatively, a mild pulmonary regurgitation
was documented in both children. On the basis of regular echocardiographic
investigations, the hemodynamic parameters and cardiac morphology changed in
3.5 years as follows: increase of the pulmonary valve annulus diameter (18-22.5
and 22-26 mm, respectively), decrease of valve regurgitation (trivial/mild and
trivial, respectively), one decrease (16-9 mmHg) and one increase (8-9.5 mmHg)
of the mean transvalvular gradient, and one remaining (26 mm) and one
decreasing (32-28 mm) right ventricular end-diastolic diameter. The body surface
area increased (1.07-1.42 and 1.07-1.46 m 2 , respectively) and no signs of valve
degeneration were observed in either of the patients 7 years after the procedure.
Thus, it could be shown that the tissue engineering of heart valves using autolo-
gous endothelial progenitor cells is a feasible and safe method—at least for