New approach to reduce allograft tissue immunogenicity. Experimental data

Objectives: Rejection is thought to contribute to the degeneration of valved allografts. Most proposed methods of decellularisation allow usage of treated valves in pulmonic position. We developed a new protocol of devitalization, which provides cell death and suppression of calcification using digitonin and ethylenediaminetetraacetic acid. The aim of the study was to evaluate new allografts in a chronic canine model. Methods: Two groups of adult mongrel dogs (5 in each) were used for allograft implantation. The cryopreserved viable (group 1) and devitalized (group 2) heart valve aorta allografts were tested. Allografts were implanted as valved patches into the thoracic aorta and explanted after four months. Histologic examination and fluorescence microscopy were used to test tissue matrix and cells in allografts. Mineralized calcium in the samples was detected using absorption spectroscopy. Results: The fluorescence microscopy proved that a significant number of cells were viable in the allografts after their cryopreservation (group 1) and all the cells were dead after anticalcinosis devitalisation (group 2). No damage of tissue matrix was observed in group 2 after devitalisation. After explantation, the cusps in both groups were either stuck to aorta wall of the allografts, or there were thrombus clots between the cusps and the wall. Internal surface was covered with neointima. Media of aortic wall was acellular. Repopulation of the viable and devitalized tissues with recipient cells during a 4-month follow-up period was not observed. In non-treated allografts, aortic walls had areas of dissection and infiltration of lymphoid cells. Devitalized patches were homogenous without dissection areas. There was no immune-cell infiltration in devitalized matrix as opposed to cryopreserved vital tissue. Conclusions: The new devitalizing technology seems effective in decreasing immune response to homologous tissue. It does not affect elasto-mechanic properties and collagenous structure of allografts. The presented data stimulate interest to the anticalcinosis devitalisation technology as an affective tool for improving biocompatibility of allografts. (c) 2010 Published by European Association for Cardio-Thoracic Surgery. All rights reserved.