Xenogeneic Tissue Research Articles

BIOTECHNOLOGICAL CONDITIONS OF VALVE PROSTHESES CREATING BY TISSUE ENGINEERING METHOD

Tissue engineering is the advanced biotechnology area focusing on invention of artificial substitutes of biological origin to repair, support and activity improvement of the defective organ or its part [1, 2]. In this case the therapeu tic reconstruction is achieved by delivering support structures (matrix), cells as well as regenerative molecular and mechanical signals to the specific area [3, 4]. Today the tissue engineering covers a range of materials studied as matrices [1, 5]. Nominally they can be divided into two categories: polymer matrix, including biological and synthetic polymers, and connective tissue frameworks of human (allogeneic) and animal (xenogeneic) tissues [6, 7]. According to one of the m ost inspiring hypotheses in cardiological surgery the tissue engineering is an opportunity to create a perfect valvular prosthesis — live, growable, adaptive, autologous and functionally optimally adjustable [8, 9]. The point of this hypothe sis is to use the valvular connective tissue frameworks, which after decellularization [10, 11] become perfect for prosthesis repopulation with recipient cells and creation of a live autologous tissue [12, 13]. Using allogeneic decel lularized grafts is limited by insufficient amount of transplants. That is why xenogeneic tissue becomes increasingly popular as a basis for manufacturing tissue-engineered valvular prostheses [14, 15]. This biotechnological approach will make valvular prosthetic repair procedure more widely applicable due to material availability [6, 16, 17]. It is especially convenient to use porcine valves regarding their 3D structure and extracellular matrix structure, which are much similar to the relevant parameters of the human valve [17]. It is also important that molecules of the extracellular matrix refer to the class of highly conserved proteins (their amino acid composition has low variability among different species), that almost completely explains the absence of immune response after decellularized tissue xenografting [18, 19]. Additionally it is presumed that except immune response decrease the decellularization will contribute to life improvement of valvular transplants [20–22]. Decellularization is an intentional initiation of cell death in the biological tissue [23–25]. It is significan t that there are two basic ways of tissue and human/animal SHORT REVIEWS

Comparison of the biomechanical tensile and compressive properties of decellularised and natural porcine meniscus

Meniscal repair is widely used as a treatment for meniscus injury. However, where meniscal damage has progressed such that repair is not possible, approaches for partial meniscus replacement are now being developed which have the potential to restore the functional role of the meniscus, in stabilising the knee joint, absorbing and distributing stress during loading, and prevent early degenerative joint disease. One attractive potential solution to the current lack of meniscal replacements is the use of decellularised natural biological scaffolds, derived from xenogeneic tissues, which are produced by treating the native tissue to remove the immunogenic cells. The current study investigated the effect of decellularisation on the biomechanical tensile and compressive (indentation and unconfined) properties of the porcine medial meniscus through an experimental–computational approach. The results showed that decellularised medial porcine meniscus maintained the tensile biomechanical properties of the native meniscus, but had lower tensile initial elastic modulus. In compression, decellularised medial porcine meniscus generally showed lower elastic modulus and higher permeability compared to that of the native meniscus. These changes in the biomechanical properties, which ranged from less than 1% to 40%, may be due to the reduction of glycosaminoglycans (GAG) content during the decellularisation process. The predicted biomechanical properties for the decellularised medial porcine meniscus were within the reported range for the human meniscus, making it an appropriate biological scaffold for consideration as a partial meniscus replacement.

Poloxamer 188 as a Supplement to Barium Cross-Linked Ultra-High Viscosity Alginate for Immunoisolation of Transplanted Islet Cells

Transplantation of Langerhans islets is a potential cure for diabetes mellitus. The main problem for routine clinical use remains the prevention of rejection without drastic side effects. Immuno-isolation is an experimental strategy to prevent graft rejection by separating the transplanted cells from the host immune system using a barrier device. The aim of the current study was to improve the physical features of encapsulated islets in a barium cross-linked ultra-high viscosity alginate by adding Poloxamer 188 (P188). Empty alginate capsules, and especially encapsulated islets, could be easily generated using UHV-P188 alginate because of its anti-foaming properties. Diabetic mice were used for evaluation of biocompatibility and graft function. Biocompatibility testing with empty capsules showed no inflammatory reaction or fibrotic overgrowth. The capsules remained intact in the intraperitoneal and intramuscular implant sites over a period of 4 weeks. Transplantation of encapsulated islets, however, led to a strong systemic inflammatory response with fibrotic overgrowth of the islet-containing capsules but no graft failure. This finding likely reflected the complementactivating property of P188. Our results clearly showed that the complex interaction of additives, xenogeneic tissue, and alginate with the host immune system could not be predicted by the behavior of the individual components. Furthermore, the mouse model described herein was an excellent tool to evaluate the physico-chemical properties and the in vivo biocompatibility and functionality of various additives. Our results will improve the biomaterials used for alginate microbeads in a clinical setting in the future.

Differences in xenoreactive immune response and patterns of calcification of porcine and bovine tissues in α-Gal knock-out and wild-type mouse implantation models.

Although bioprostheses are widely used in cardiovascular surgery, their durability is limited due to degeneration. Degeneration of bioprostheses limiting its clinical use results from multiple factors, and immune reaction has been considered to be one of the most important factors. The study objectives were to compare the mechanical characteristic differences of porcine and bovine prostheses, assess the differences in immune reaction among different species and tissues as well as elucidate bioprosthetic failure patterns in α-Gal knock-out (KO) and wild-type mouse implantation models. Six groups of different xenogeneic tissues (porcine pericardium, aortic valve, aortic wall; bovine pericardium, aortic valve and aortic wall) were implanted into the subcutaneous tissue of the wild-type mouse (n = 4) and the KO mouse (n = 4) (four xenogeneic tissue segments per each mouse). Mechanical and chemical tests, including tensile strength measurement and thermal stability test for pericardial tissues and pronase test for different xenogeneic tissues, were performed before implantation. Anti-α-Gal antibody titres (IgM and IgG antibodies) were measured using serum enzyme-linked immunosorbent assay analyses before implantation and 30, 60 and 90 days after implantation. Implanted tissues were harvested after 90 days and studied for histopathology and quantification of calcification. There were no significant differences in tensile strength and shrinkage temperature between the porcine and bovine pericardia, although the bovine pericardia showed a greater elasticity than the porcine pericardia (elongation at tensile strength, 74.8 ± 4.5% vs 50.0 ± 8.7%, P < 0.001). Resistance towards pronase degradation was not different among the groups of tissues (Groups 1-6, 89.1 ± 7.6, 95.1 ± 1.8, 90.3 ± 5.3, 93.7 ± 3.3, 89.1 ± 2.4 and 89.1 ± 3.0%, respectively; P = 0.061). The IgM titres of the α-Gal KO mice were significantly higher at 30 days after implantation (0.71 ± 0.27 vs 1.07 ± 0.48, P = 0.004), whereas the IgG titres of the α-Gal KO mice remained higher until 60 days after implantation (at 30 days, 0.81 ± 0.07 vs 1.28 ± 0.79, P = 0.017; at 60 days, 0.54 ± 0.16 vs 1.43 ± 1.10, P = 0.045) than those of the wild-type mice. Calcium levels of tissues implanted into the α-Gal KO mice were significantly higher than those implanted into the wild-type mice regardless of tissue type (from Groups 1-6, 4.72 ± 1.75 vs 27.76 ± 22.73 μg/mg; 3.05 ± 1.04 vs 15.90 ± 6.98 μg/mg; 2.13 ± 1.48 vs 29.76 ± 30.71 μg/mg; 1.02 ± 0.53 vs 5.97 ± 1.40 μg/mg; 3.18 ± 3.41 vs 30.55 ± 66.69 μg/mg; 6.21 ± 5.56 vs 21.65 ± 17.77 μg/mg, all P ≤ 0.002). Chronic immune response to the α-Gal antigen may cause more severe tissue calcification in α-Gal KO mice. Removal of α-Gal antigenicity is strongly advised in xenogeneic bioprosthetic tissue implantation.

Preventive effects of CTLA4Ig-overexpressing adipose tissue–derived mesenchymal stromal cells in rheumatoid arthritis

Background aimsRheumatoid arthritis is a systemic autoimmune disorder. In this study, we first compared the therapeutic effects of syngeneic and xenogeneic adipose tissue–derived stem cells on a collagen-induced arthritis mouse model. Second, we investigated the synergistic preventive effects of CTLA4Ig and adipose tissue–derived mesenchymal stromal cells (ASCs) as a therapeutic substance. MethodsArthritis was induced in all groups except for the normal, saline (N) group, using chicken type II collagen (CII). Animals were divided into C (control, saline), H (hASCs), M (mASCs) and N groups (experiment I) and C, H, CT (CTLA4Ig-overexpressing human ASC [CTLA4Ig-hASCs]) and N groups (experiment II), according to transplanted material. Approximately 2 × 106 ASCs or 150 μL of saline was intravenously administered on days 24, 27, 30 and 34, and all animals were killed on days 42 to 44 after CII immunization. ResultsAnti-mouse CII autoantibodies were significantly lower in the H, M and CT groups than in the C group. Cartilage damage severity score and C-telopeptide of type II collagen were significantly lower in the CT group than in the C group. The serum levels of IL-6 were significantly lower in the H, M and CT groups than in the C group. The serum levels of keratinocyte chemoattractant were significantly lower in the CT group than the C group. ConclusionsThere were similar effects of ASCs on the decrease of anti-mouse CII autoantibody levels between syngeneic and xenogeneic transplantations, and CTLA4Ig-hASCs showed synergistic preventive effects compared with non-transduced hASCs.

Xenotransplantation of porcine islet cells as a potential option for the treatment of type 1 diabetes in the future.

Solid organ and cell transplantation, including pancreatic islets constitute the treatment of choice for chronic terminal diseases. However, the clinical use of allogeneic transplantation is limited by the growing shortage of human organs. This has prompted us to initiate a unique multi-center and multi-team effort to promote translational research in xenotransplantation to bring xenotransplantation to the clinical setting. Supported by the German Research Foundation, an interdisciplinary group of surgeons, internal medicine doctors, diabetologists, material sciences experts, immunologists, cell biologists, virologists, veterinarians, and geneticists have established a collaborative research center (CRC) focusing on the biology of xenogeneic cell, tissue, and organ transplantation. A major strength of this consortium is the inclusion of members of the regulatory bodies, including the Paul-Ehrlich Institute (PEI), infection specialists from the Robert Koch Institute and PEI, veterinarians from the German Primate Center, and representatives of influential ethical and religious institutions. A major goal of this consortium is to promote islet xenotransplantation, based on the extensive expertise and experience of the existing clinical islet transplantation program. Besides comprehensive approaches to understand and prevent inflammation-mediated islet xenotransplant dysfunction [immediate blood-mediated inflammatory reaction (IBMIR)], we also take advantage of the availability of and experience with islet macroencapsulation, with the goal to improve graft survival and function. This consortium harbors a unique group of scientists with complementary expertise under a cohesive program aiming at developing new therapeutic approaches for islet replacement and solid organ xenotransplantation.

Transplantation of Cultivated Fibroblasts on a Backing of Xenogenic Tissue in the Treatment of Wounds.

IntroductionTrophic ulcers are a common health problem, and there are numerous treatment methods. Irreversible damage in the skin, subcutaneous tissue, and fascia with long-term ulcer existence make standard autotransplantation inneffective. Skin grafts are often complicated by partial or complete rejection of skin flaps. The aim of this study was to examine the feasibility of using transplanted cultivated allogenic fibroblasts on the backing of a cellularless xenogenic fabric for wound healing.MethodsTransplantation of cultured embryonic fibroblasts on a backing of xenogenic tissue was used in the complex treatment of trophic ulcers for stimulation of regenerative processes. Decellularization xenogenic film was previously held. Then allogenic fibroblasts were cultivated on the surface of collagen-elastin matrix. Since 2013, we treated 12 patients with giant ulcers caused by the following: lymphedema (2 patients), vascular disease (3 patients), diabetes (2 patients), after injury (4 patients), and radiation ulcer (1 patient). Dimensions of ulcers were from 150 to 600 cm2. Duration of the lower limb ulcers ranged from 8 months to 10 years. For a number of years, all patients were on a complex therapy, which had not resulted in healing wounds. During the operation when excision of granulation tissue was performed, plastic wounds perforated with the ratio 1:2 autoskin. Xenogenic fabric with cultured fibroblasts was applied on top. In this case, xenogenic film protected the skin from drying, created optimal microclimate, and cultured fibroblasts stimulating regeneration and improving engraftment.ResultsThe first redress was held on the fifth day. In all cases, the results of engraftment skin grafts achieved maximum possible (100%) and optimal (90%). Complete epithelialization of the cell perforation was seen in five patients on the fifth day and three on seventh day after skin plastics. Average period of inpatient treatment was 20.7 days. All patients were discharged with healed wounds.ConclusionThus, the treatment of trophic ulcers can be successfully solved using advances in biotechnology. Transplantation of cultivated allogenic fibroblasts on a backing of cellularless xenogenic fabric shows good clinical results due to the stimulation of regenerative processes and creates the optimum environment for autotransplants.

Fabrication and properties of acellular porcine anulus fibrosus for tissue engineering in spine surgery.

BackgroundOver the last few years, new treatments for a damaged intervertebral disc (IVD) have included strategies to repair, replace, or regenerate the degenerative disc. However, these techniques are likely to have limited success, due to insufficiently effective means to address the damaged anulus fibrosus (AF). Here, we try to develop a bioprocess method for decellularization of the xenogeneic AF tissue, with a view to developing a scaffold as a potential candidate for clinical application in spinal surgery.MethodsPorcine AFs were decellularized using freeze-thaw cycles, followed by various combined treatments with 0.1% sodium dodecyl sulfate (SDS) and nucleases.ResultsHematoxylin and eosin (H & E) staining showed that decellularization was achieved through the decellularization protocols. Biochemical analyses revealed 86% reduction in DNA, but only 15.9% reduction in glycosaminoglycan (GAG) content, with no significant difference in the hydroxyproline content. There was no appreciable cytotoxicity of the acellular AF. Biomechanical testing of the acellular AF found no significant decline in stiffness or Young’s modulus.ConclusionsPorcine AF tissues were effectively decellularized with the preservation of biologic composition and mechanical properties. These results demonstrate that acellular AF scaffolds would be a potential candidate for clinical application in spinal surgery.

Crosslinking strategies for preparation of extracellular matrix-derived cardiovascular scaffolds.

Heart valve and blood vessel replacement using artificial prostheses is an effective strategy for the treatment of cardiovascular disease at terminal stage. Natural extracellular matrix (ECM)-derived materials (decellularized allogeneic or xenogenic tissues) have received extensive attention as the cardiovascular scaffold. However, the bioprosthetic grafts usually far less durable and undergo calcification and progressive structural deterioration. Glutaraldehyde (GA) is a commonly used crosslinking agent for improving biocompatibility and durability of the natural scaffold materials. However, the nature ECM and GA-crosslinked materials may result in calcification and eventually lead to the transplant failure. Therefore, studies have been conducted to explore new crosslinking agents. In this review, we mainly focused on research progress of ECM-derived cardiovascular scaffolds and their crosslinking strategies.

Xeno-immunogenicity of ice-free cryopreserved porcine leaflets

BackgroundUndesirable processes of inflammation, calcification, or immune-mediated reactions are limiting factors in long-term survival of heart valves in patients. In this study, we target the modulatory effects of ice-free cryopreservation (IFC) of xenogeneic heart valve leaflet matrices, without decellularization, on the adaptive human immune responses in vitro. MethodsWe tested porcine leaflet matrices from fresh untreated, conventionally cryopreserved (CFC), and IFC pulmonary valves by culturing them with human blood mononuclear cells for 5 d in vitro. No other tissue treatment protocols to modify possible immune responses were used. Matrices alone or in addition with a low-dose second stimulus were analyzed for induction of proliferation and cytokine release by flow cytometry-based techniques. Evaluation of the α-Gal epitope expression was performed by immunohistochemistry with fluorochrome-labeled B4 isolectin. ResultsNone of the tested leaflet treatment groups directly triggered the proliferation of immune cells. But when tested in combination with a second trigger by anti-CD3, IFC valves showed significantly reduced proliferation of T cells, especially effector memory T cells, in comparison with fresh or CFC tissue. Moreover, the cytokine levels for interferon-γ (IFNγ), tumor necrosis factor α, and interleukin-10 were reduced for the IFC-treated group being significantly different compared with the CFC group. However, no difference between treatment groups in the expression of the α-Gal antigen was observed. ConclusionsIFC of xenogeneic tissue might be an appropriate treatment method or processing step to prevent responses of the adaptive immune system.

Detection of binding of a synthetic granzyme B-like peptide fluorescent conjugate within platelet-like structures in cancer-related peripheral blood specimens and tissue sections.

Platelets and cytotoxic T lymphocytes (CTL) are important whole blood components in peripheral blood. Studies have shown that platelets, from precursor megakaryocytes, are significant factors in cancer prognosis, cancer progression, and metastasis; but a direct platelet-cancer relationship remains unclear. CTL play an essential role in cancer surveillance by inducing cancer cell death with granzyme B. A recent report has shown the presence of binding targets with binding affinity to a synthetic granzyme B-like peptide fluorescent conjugate (GP1R) in different types of cancer cells grown in vitro. It suggests that these binding targets may serve as a "universal-pathologic-biomarker". It is not known if similar biomarkers may be present in platelets of cancer patients. We show with fluoroscopic images that GP1R can bind to binding targets: 1) within platelets in methanol-fixed whole blood smears of patients with breast cancer and lung cancer, and 2) within platelet-like structures in formalin-fixed-paraffin-embedded (FFPE) nude mouse xenogeneic breast tumor tissues. Samples without cancer-association displayed no discernible GP1R-binding in platelet-like structures. Our data demonstrate for the first time that a similar "universal-pathologic-biomarker" detectable by GP1R-binding is present in circulating platelets of cancer patients. The data depict a co-existence of animal-platelets and human-breast cancer cells, both have a common pathologic biomarker detectable by GP1R, in the tumor growth. The fluoroscopic images indicate a visual direct connection between pathologic platelets and cancer. These preliminary results may lead to developments of novel platelet-based cancer diagnostics and therapeutics and a better understanding of the potential multifunction of GP1R and its relationship to megakaryocytes and PD1.

In vitro generation of atrioventricular heart valve neoscaffolds.

Tissue engineering of cardiovascular structures represents a novel approach to improve clinical strategies in heart valve disease treatment. The aim of this study was to engineer decellularized atrioventricular heart valve neoscaffolds with an intact ultrastructure and to reseed them with umbilical cord-derived endothelial cells under physiological conditions in a bioreactor environment. Mitral (n=38) and tricuspid (n=36) valves were harvested from 40 hearts of German Landrace swine from a selected abattoir. Decellularization of atrioventricular heart valves was achieved by a detergent-based cell extraction protocol. Evaluation of the decellularization method was conducted with light microscopy and quantitative analysis of collagen and elastin content. The presence of residual DNA within the decellularized atrioventricular heart valves was determined with spectrophotometric quantification. The described decellularization regime produced full removal of native cells while maintaining the mechanical stability and the quantitative composition of the atrioventricular heart valve neoscaffolds. The surface of the xenogeneic matrix could be successfully reseeded with in vitro-expanded human umbilical cord-derived endothelial cells under physiological flow conditions. After complete decellularization with the detergent-based protocol described here, physiological reseeding of the xenogeneic neoscaffolds resulted in the formation of a confluent layer of human umbilical cord-derived endothelial cells. These results warrant further research toward the generation of atrioventricular heart valve neoscaffolds on the basis of decellularized xenogeneic tissue.

Xenograft Tolerance and Immune Function of Human T Cells Developing in Pig Thymus Xenografts

Transplantation of xenogeneic thymus tissue allows xenograft tolerance induction in the highly disparate pig-to-mouse model. Fetal swine thymus (SW THY) can support the generation of a diverse human T cell repertoire that is tolerant of the pig in vitro. We demonstrate that SW THY generates all human T cell subsets, including regulatory T cells (Tregs), in similar numbers as fetal human thymus (HU THY) grafts in immunodeficient mice receiving the same human CD34(+) cells. Peripheral T cells are specifically tolerant to the mouse and to the human and porcine donors, with robust responses to nondonor human and pig Ags. Specific tolerance is observed to pig skin grafts sharing the THY donor MHC. SW THY-generated peripheral Tregs show similar function, but include lower percentages of naive-type Tregs compared with HU THY-generated Tregs. Tregs contribute to donor-pig specific tolerance. Peripheral human T cells generated in SW THY exhibit reduced proportions of CD8(+) T cells and reduced lymphopenia-driven proliferation and memory-type conversion, accelerated decay of memory-type cells, and reduced responses to protein Ags. Thus, SW thymus transplantation is a powerful xenotolerance approach for human T cells. However, immune function may be further enhanced by strategies to permit positive selection by autologous HLA molecules.

Soft tissue wound healing at teeth, dental implants and the edentulous ridge when using barrier membranes, growth and differentiation factors and soft tissue substitutes

To review the biological processes of wound healing following periodontal and periimplant plastic surgery when different technologies are used in a) the coverage of root and implant dehiscences, b) the augmentation of keratinized tissue (KT) and c) the augmentation of soft tissue volume. An electronic search from The National Library of Medicine (MEDLINE-PubMed) was performed: English articles with research focus in oral soft tissue regeneration, providing histological outcomes, either from animal experimental studies or human biopsy material were included. Barrier membranes, enamel matrix derivatives, growth factors, allogeneic and xenogeneic soft tissue substitutes have been used in soft tissue regeneration demonstrating different degrees of regeneration. In root coverage, these technologies were able to improve new attachment, although none has shown complete regeneration. In KT augmentation, tissue-engineered allogenic products and xenogeneic collagen matrixes demonstrated integration within the host connective tissue and promotion of keratinization. In soft tissue augmentation and peri-implant plastic surgery there are no histological data currently available. Soft tissue substitutes, growth differentiation factors demonstrated promising histological results in terms of soft tissue regeneration and keratinization, whereas there is a need for further studies to prove their added value in soft tissue augmentation.

Theological‐ethical legitimization of xenotransplantation and challenges regarding the hospital chaplaincy including the pastoral psychological companionship

BackgroundIn contrast to allotransplantation, xenotransplantation has thus far attracted lit‐tle interest within the field of theological ethics [6]. This can essentially be attributed to the fear of considerable problems regarding the medical feasibility due to possible immune reac‐tions and the risk of infection [10,11]. Consequently, at the beginning of the 21st century a recommendation was issued to stop all relevant research; this also led to a retardation of theo‐logical‐ethical reflections on xenotransplantation.Ethical questions: Irrespective of technical feasibility, the question whether xenotransplanta‐tion is ethically justifiable or not can systematically be divided into three areas [10]: (i) Ethics regarding animals and nature are concerned with the significance of non‐human rights; (ii) ethics in the areas of medicine, biomedicine and research deal with the importance of human rights; (iii) within the frame of a social‐ethical perspective, these rights need to be debated within the context of distributive justice. The prevalent ethical discussions regarding xeno‐transplantation focus on the following issues [2, 10]: protection of animals, risks of infection and informed consent. These have been the main reasons for the reluctance regarding human experiments [3, 5, 8]. Another range of concerns centers on the creation of human/animal chimeras by Xenotransplantation and the psychosocial and sociocultural acceptance of such procedures. These reservations are especially strong where the heart is concerned, since it has a special value in terms of personal and cultural identity, and a strong symbolic meaning. The morality of breeding transgenic pigs as donor animals has also recently been questioned, rais‐ing the question of whether it is legitimate to transgress the human‐animal boundary [1].Since chimerism raises questions regarding its psychosocial and sociocultural acceptance, the basic levels of the bioethical discourse that underlie the specific normative regulations are addressed. This concerns the anthropological question of human self‐conception and ques‐tions regarding fundamental interpretations of life and essential beliefs regarding the meaning of life. To the extent that the last mentioned levels are inevitably incorporated into the norma‐tive judgments of applied ethics and relate to the psychosocial and sociocultural acceptance of the xenotransplantation of the heart, it is necessary to bear in mind the fundamental anthropo‐logical and ideological implications [4, 9]. These implications are reflected by theological ethics. From a perspective of theological ethics the question of identity also has to be debated within a theological anthropological framework.Most ethical perspectives on xenotransplantation refer explicitly or implicitly to the question of the psychosocial and sociocultural acceptance of Xenotransplantation. As a consequence, the question of personal [7], social and cultural identity as well as the pivotal question con‐cerning the significance of the acceptance category for the ethical argumentation and ethical legitimization of standards are addressed. According to the ethical standards definition, validi‐ty of a standard is also characterized by an opportunity to achieve social recognition and ac‐ceptance.Research areas: The relationship between psychosocial and sociocultural acceptance and ethical legitimization shall be discussed within the context of xenotransplantation, and the relevance of public opinion shall be mapped out with the goal of achieving social acceptance and thereby facilitating the success of xenotransplantation. With reference to the psychosocial conditions for acceptance and success, the relevance as well as the tasks of pastoral compan‐ionship and pastoral‐psychological support for potential organ recipients shall be debated and guidelines shall be drafted. In light of the identity‐related challenges, an ethical and theologi‐cal request for psychosocial counseling and pastoral companionship. Furthermore, special focus shall be given to the particular importance of the spiritual dimension of counseling.This project is funded by DFG (TR CRC 127 “Biology of xenogeneic cell, tissue and organ transplantation – from bench to bedside”).

Evaluating the functionality of xeno‐relevant transgenes

With the scientific progress made in recent years, clinical application of xenotransplantation has become a realistic goal. Besides optimizing immunosuppressive regimens, the development of geneticallytailored donor pigs contributed to this success. Within the CRC 127 “Biology of xenogeneic cell, tissue and organ transplantation – from bench to bedside” we aim at developing novel transgenic donor pigs for islet transplantation, and providing existing transgenic donor lines to German as well as international collaboration partners.Regarding novel donor models, we have established transgenic pigs carrying the x‐linked inhibitor of apoptosis (XIAP) under the control of the porcine insulin promoter to achieve beta‐cell specific expression, as apoptosis has been postulated to play a major role in islet loss during isolation, in vitro cultivation and engraftment. Expression analyses of the first transgenic founders are presently underway. In addition, an advanced donor pig aiming at the temporary expression of vascular endothelial growth factor (VEGF) for improved engraftment of islets is being established. The model is based on the TetOn principle which requires two independent transgenes. First litters of founder pigs carrying a construct for beta‐cell specific expression of the transactivator (TA) have been delivered and qPCR analysis of the pancreas revealed different levels of TA expression in individual animals. Primary cells from a highly expressing founder will be transfected with a construct carrying the regulated VEGF gene under the control of the TA response element.For detailed pre‐clinical evaluation of already characterized transgenic pigs, we have established multitransgenic lines in collaboration with Revivicor Inc. carrying either aGalTKO/CD46/hTM, aGalTKO/CD46/INS‐LEA or aGalTKO/CD46/HLA‐E. We provide these animals, in addition to single‐transgenic INS‐LEA pigs, to the groups of P.Brenner and J.Seissler within the consortium. Furthermore, multi‐transgenic animals are provided to the groups of M.Mohiuddin, D.K.C. Cooper and R. Pierson by D. Ayares and islets of INS‐LEA expressing pigs are supplied to B. Hering in collaboration with J. Seissler.The ongoing evaluation of existing transgenes or their combination will reveal more detailed insight into the complexity of rejection mechanisms and, thus, support the design of optimized future transgenic approaches.

The host response to allogeneic and xenogeneic biological scaffold materials

The clinical use of biological scaffold materials has become commonplace. Such scaffolds are composed of extracellular matrix (ECM), or components of ECM, derived from allogeneic or xenogeneic tissues. Such scaffold materials vary widely in their source tissue, processing methods and sterilization methods. The success or failure of an ECM scaffold for a given application is dependent on the host response following implantation; a response that is largely mediated by the innate immune system and which is influenced by a numerous factors, including the processing methods used in the preparation of biological scaffolds. The present paper reviews various aspects of the host response to biological scaffolds and factors that affect this response. In addition, some of the logistical, regulatory and reconstructive implications associated with the use of biological scaffolds are discussed.

Graft Materials in Oral Surgery: Revision

Oral implantology is a common procedure in dentistry, especially for fully or partially edentulous patients. The implants must be placed in the best location from both the aesthetic and functional point of view. Because of this it is increasingly more frequent to resort to regeneration techniques that use substitutes of the bone itself, in order to be able to insert the implants in the most appropriate location. Material and Methodology: A review was performed on the literature from the last ten years based on the following search limitations: “graft materials, allograft, xenograft, autologous graft” and dentistry”. Results: 241 works were obtained that after reading their respective summaries, they were reduced to 38, and 9 previous works were included in order to summarize the concepts. Discussion: Autologous grafts are the gold standard of the bone regeneration. They have obvious advantages, but they also have drawbacks. This is why allogeneic and xenogeneic tissues are used. The former because of their clear similarity with the recipient's tissue and the latter due to their wide availability. Given that these grafts also have drawbacks, the industry has developed synthetic materials that have properties similar to those of human bone tissue. However, as of today, the ideal material to substitute human bone has not yet been found. In recent years the tendency has been to combine these synthetic materials with the patient's own bone, which is extracted during drilling in implant placement, with bone marrow aspiration, or with bone morphogenetic proteins. Thus the intention is to equip these substances with the osteogenic capacity. Conclusions: There is currently no ideal graft material, with the exception of those materials that come directly from the patient. We hope that in the coming years we will have products that will allow us to perform rehabilitations with better results and provide a better quality of life for our patients, especially those who have more complex situations to resolve, like the patients that are operated on for head and neck cancer.

Tissue engineering of regenerative cardiovascular patch material based on decellularized pericardium

Objectives: Autologous pericardium is often used to substitute small or medium sized vascular or myocardial lesions. However, its use is restricted due to its limited availability. Hence, glutaraldehyde-fixed bovine pericardium is currently being employed more extensively despite potential impact of the xenogenic tissue on the host, possible toxicity of residual fixing solution within the graft, and absence of any regenerative and growing potential. We therefore developed a new biological and viable matrix, based on decellularized and reseeded pericardium.

Formation of multiple conduit aneurysms following Matrix P® conduit implantation in a boy with tetralogy of Fallot and pulmonary atresia

We report on a 6-year old boy with tetralogy of Fallot and pulmonary atresia in whom a 16 m Matrix P conduit was implanted between the pulmonary artery and the right ventricle at the age of 16 months. Five years later he developed severe stenosis of the distal conduit anastomosis. The notable findings were several aneurysms of the conduit proximal to the distal stenosis within the high-pressure region. The wall of the aneurysms contained xenogeneic conduit tissue without inflammatory or foreign-body response. We believe that aneurysm formation of the conduit was a result of fatigue of the conduit wall under suprasystemic pressure.