Immune responses to alpha1,3 galactosyltransferase knockout pigs

Research on gene editing and immunosuppressants in kidney xenotransplantation

Gene-edited pig organ transplantation can solve the serious shortage of human donor organs. Currently, xenotransplantation is rapidly developing and has made significant breakthroughs. The use of GTKO (Gal knockout) pigs is an important step forward. The subsequent knockout of three genes combined with the transfer of immune-related genes effectively prolonged the survival time of non-human primate (NHP) transplantation in xenotransplantation. Due to the success of allogeneic kidney transplantation on NHP, this gene editing protocol was recently applied to clinical patients. Two patients underwent allogeneic kidney transplantation and survived for 51 days and 47 days. Exceeding the hyperacute rejection period proves that appropriate gene editing strategies and the combination of immunosuppressive agents contribute to the success of xenotransplantation. To further enhance the feasibility of pig kidney xenograft, this article mainly explores the effects of the NHP xenograft gene editing scheme and immunosuppressants on prolonging transplant survival time.

Comparative Study of Immunodeficient Rat Strains in Engraftment of Human-Induced Pluripotent Stem Cell-Derived Airway Epithelia

The airway epithelia (AE) play a role in the clearance of foreign substances through ciliary motility and mucus secreted. We developed an artificial trachea that is made of collagen sponges and polypropylene mesh for the regeneration of the tracheal defect, and it was used for a clinical study. Then, a model in which the luminal surface of an artificial trachea was covered with a human-induced pluripotent stem cell-derived AE (hiPSC-AE) was transplanted into the tracheal defect of nude rats to promote epithelialization. In the future, this model was expected to be applied to research on infectious diseases and drug discovery as a trachea-humanized rat model. However, at present, sufficient engraftment has not been achieved to evaluate functional recovery in transplanted cells. Therefore, this study focused on immunosuppression in recipient rats. Nude rats lack T cell function and are widely used for transplantation experiments; however, more severe immunosuppressed recipients are preferred for xenotransplantation. Several strains of immunodeficient rats were created as rats that exhibit more severe immunodeficiency until now. In this study, to establish a trachea-humanized rat model in which human AE function can be analyzed to improve engraftment efficiency, engraftment efficiency in nude rats and X-linked severe combined immunodeficiency (X-SCID) rats following hiPSC-AE transplantation was compared. In the analysis of the proportion of engrafted cells in total cells at the graft site, the engraftment efficiency of epithelial cells tended to be high in X-SCID rats, although no statistical difference was found between the two groups, whereas the engraftment efficiency of mesenchymal cells was higher in X-SCID rats. Furthermore, the number of immune cells that accumulated in the grafts showed that a pan T cell marker, that is, CD3-positive cells, did not differ between the two strains; however, CD45-positive cells and major histocompatibility complex (MHC) class II-positive cells significantly decreased in X-SCID rats. These results indicate that X-SCID rats are more useful for the transplantation of hiPSC-AE into the tracheae to generate trachea-humanized rat models.

Mechanisms of Formation of Antibodies against Blood Group Antigens That Do Not Exist in the Body

The system of the four different human blood groups is based on the oligosaccharide antigens A or B, which are located on the surface of blood cells and other cells including endothelial cells, attached to the membrane proteins or lipids. After transfusion, the presence of these antigens on the apical surface of endothelial cells could induce an immunological reaction against the host. The final oligosaccharide sequence of AgA consists of Gal-GlcNAc-Gal (GalNAc)-Fuc. AgB contains Gal-GlcNAc-Gal (Gal)-Fuc. These antigens are synthesised in the Golgi complex (GC) using unique Golgi glycosylation enzymes (GGEs). People with AgA also synthesise antibodies against AgB (group A [II]). People with AgB synthesise antibodies against AgA (group B [III]). People expressing AgA together with AgB (group AB [IV]) do not have these antibodies, while people who do not express these antigens (group O [0; I]) synthesise antibodies against both antigens. Consequently, the antibodies are synthesised against antigens that apparently do not exist in the body. Here, we compared the prediction power of the main hypotheses explaining the formation of these antibodies, namely, the concept of natural antibodies, the gut bacteria-derived antibody hypothesis, and the antibodies formed as a result of glycosylation mistakes or de-sialylation of polysaccharide chains. We assume that when the GC is overloaded with lipids, other less specialised GGEs could make mistakes and synthesise the antigens of these blood groups. Alternatively, under these conditions, the chylomicrons formed in the enterocytes may, under this overload, linger in the post-Golgi compartment, which is temporarily connected to the endosomes. These compartments contain neuraminidases that can cleave off sialic acid, unmasking these blood antigens located below the acid and inducing the production of antibodies.

Possible Link Between the ABO Blood Group of Bioprosthesis Recipients and Specific Types of Structural Degeneration

Background Pigs/bovines share common antigens with humans: α-Gal, present in all pigs/bovines close to the human B-antigen; and AH-histo-blood-group antigen, identical to human AH-antigen and present only in some animals. We investigate the possible impact of patients' ABO blood group on bioprosthesis structural valve degeneration (SVD) through calcification/pannus/tears/perforations for patients ≤60 years at implantation. Methods and Results This was a single-center study (Paris, France) that included all degenerative bioprostheses explanted between 1985 and 1998, mostly porcine bioprostheses (Carpentier-Edwards second/third porcine bioprostheses) and some bovine bioprostheses. For the period 1998 to 2014, only porcine bioprostheses with longevity ≥13 years were included (total follow-up ≥29 years). Except for blood groups, important predictive factors for SVD were prospectively collected (age at implantation/longevity/number/site/sex/SVD types) and analyzed using logistic regression. All variables were available for 500 explanted porcine bioprostheses. By multivariate analyses, the A group was associated with an increased risk of: tears (odds ratio[OR], 1.61; P=0.026); pannus (OR, 1.5; P=0.054), pannus with tears (OR, 1.73; P=0.037), and tendency for lower risk of: calcifications (OR, 0.63; P=0.087) or isolated calcification (OR, 0.67; P=0.17). A-antigen was associated with lower risk of perforations (OR 0.56; P=0.087). B-group patients had an increased risk of: perforations (OR, 1.73; P=0.043); having a pannus that was calcified (OR, 3.0, P=0.025). B-antigen was associated with a propensity for calcifications in general (OR, 1.34; P=0.25). Conclusions Patient's ABO blood group is associated with specific SVD types. We hypothesize that carbohydrate antigens, which may or may not be common to patient and animal bioprosthetic tissue, will determine a patient's specific immunoreactivity with respect to xenograft tissue and thus bioprosthesis outcome in terms of SVD.

Comparison of Bone Regeneration between Porcine-Derived and Bovine-Derived Xenografts in Rat Calvarial Defects: A Non-Inferiority Study

The present study aimed to compare the bone-regeneration capacity of porcine-derived xenografts to bovine-derived xenografts in the rat calvarial defect model. The observation of surface morphology and in vitro cell studies were conducted prior to the animal study. Defects with a diameter of 8 mm were created in calvaria of 20 rats. The rats were randomly treated with porcine-derived (Bone-XP group) or bovine-derived xenografts (Bio-Oss group) and sacrificed at 4 and 8 weeks after surgery. The new bone regeneration was evaluated by micro-computed tomography (μCT) and histomorphometric analyses. In the cell study, the extracts of Bone-XP and Bio-Oss showed a positive effect on the regulation of osteogenic differentiation of human mesenchymal stem cells (hMSCs) without cytotoxicity. The new bone volume of Bone-XP (17.52 ± 3.78% at 4 weeks and 32.09 ± 3.51% at 8 weeks) was similar to that of Bio-Oss (11.6 ± 3.88% at 4 weeks and 25.89 ± 7.43% at 8 weeks) (p > 0.05). In the results of new bone area, there was no significant difference between Bone-XP (9.08 ± 5.47% at 4 weeks and 25.22 ± 13.56% at 8 weeks) and Bio-Oss groups (5.83 ± 2.56% at 4 weeks and 21.68 ± 11.11% at 8 weeks) (p > 0.05). It can be concluded that the porcine-derived bone substitute may offer a favorable cell response and bone regeneration similar to those of commercial bovine bone mineral.

Recipients with blood group A associated with longer survival rates in cardiac valvular bioprostheses

Background

Pigs/bovines share with humans some of the antigens present on cardiac valves. Two such antigens are: the major xenogenic Ag, “Gal” present in all pig/bovine very close to human B-antigen of ABO-blood-group system; the minor Ag, pig histo-blood-group AH-antigen identical to human AH-antigen and present by some animals. We hypothesize that these antigens may modify the immunogenicity of the bioprosthesis and also its longevity. ABO distribution may vary between patients with low (<6 years) and high (≥15 years) bioprostheses longevity.

Methods

Single-centre registry study (Paris, France) including all degenerative porcine bioprostheses (mostly Carpentier-Edwards 2nd/3rd generation heart valves) explanted between 1985 and 1998 and some bovine bioprostheses. For period 1998–2014, all porcine bioprostheses with longevity ≥13 years (follow-up ≥29 years). Important predictive factors for bioprosthesis longevity: number, site of implantation, age were collected. Blood group and other variables were entered into an ordinal logistic regression analysis model predicting valve longevity, categorized as low (<6 years), medium (6–14.9 years), and high (≥15 years).

Findings

Longevity and ABO-blood group were obtained for 483 explanted porcine bioprostheses. Mean longevity was 10.2 ± 3.9 years [0–28] and significantly higher for A-patients than others (P = 0.009). Using multivariate analysis, group A was a strong predictive factor of longevity (OR 2.09; P < 0.001). For the 64 explanted bovine bioprosthesis with low/medium longevity, the association, with A-group was even more significant.

Interpretation

Patients of A-group but not B have a higher longevity of their bioprostheses. Future graft-host phenotyping and matching may give rise to a new generation of long-lasting bioprosthesis for implantation in humans, especially for the younger population.

Fund

None.

Transplant Tolerance: Current Insights and Strategies for Long-Term Survival of Xenografts

Xenotransplantation is an attractive solution to the problem of allograft shortage. However, transplants across discordant species barriers are subject to vigorous immunologic and pathobiologic hurdles, some of which might be overcome with the induction of immunologic tolerance. Several strategies have been designed to induce tolerance to a xenograft at both the central (including induction of mixed chimerism and thymic transplantation) and peripheral (including adoptive transfer of regulatory cells and blocking T cell costimulation) levels. Currently, xenograft tolerance has been well-established in rodent models, but these protocols have not yet achieved similar success in nonhuman primates. This review will discuss the major barriers that impede the establishment of immunological tolerance across xenogeneic barriers and the potential solution to these challenges, and provide a perspective on the future of the development of novel tolerance-inducing strategies.

The Role of NK Cells in Pig-to-Human Xenotransplantation

Recruitment of human NK cells to porcine tissues has been demonstrated in pig organs perfused ex vivo with human blood in the early 1990s. Subsequently, the molecular mechanisms leading to adhesion and cytotoxicity in human NK cell-porcine endothelial cell (pEC) interactions have been elucidated in vitro to identify targets for therapeutic interventions. Specific molecular strategies to overcome human anti-pig NK cell responses include (1) blocking of the molecular events leading to recruitment (chemotaxis, adhesion, and transmigration), (2) expression of human MHC class I molecules on pECs that inhibit NK cells, and (3) elimination or blocking of pig ligands for activating human NK receptors. The potential of cell-based strategies including tolerogenic dendritic cells (DC) and regulatory T cells (Treg) and the latest progress using transgenic pigs genetically modified to reduce xenogeneic NK cell responses are discussed. Finally, we present the status of phenotypic and functional characterization of nonhuman primate (NHP) NK cells, essential for studying their role in xenograft rejection using preclinical pig-to-NHP models, and summarize key advances and important perspectives for future research.

Characteristics of α-Gal epitope, anti-Gal antibody, α1,3 galactosyltransferase and its clinical exploitation (Review)

The α-Gal epitope (Galα1,3Galα1,4GlcNAc-R) is ubiquitously presented in non-primate mammals, marsupials and New World Monkeys, but it is absent in humans, apes and Old World monkeys. However, the anti-Gal antibody (~1% of immunoglobulins) is naturally generated in human, and is found as the immunoglobulin G (IgG), IgM and IgA isotypes. Owing to the specific binding of the anti-Gal antibody with the α-Gal epitope, humans have a distinct anti-α-gal reactivity, which is responsible for hyperacute rejection of organs transplanted from α-gal donors. In addition, the α1,3 galactosyltransferases (α1,3GT) can catalyze the synthesis of the α-Gal epitope. Therefore, the α1,3GT gene, which encodes the α1,3GT, is developed profoundly. The distributions of the α-Gal epitope and anti-Gal antibody, and the activation of α1,3GT, reveal that the enzyme of α1,3GT in ancestral primates is ineffective. Comparison of the nucleotide sequence of the human α1,3-GT pseudogene to the corresponding different species sequence, and according to the evolutionary tree of different species, the results of evolutionary inactivation of the α1,3GT gene in ancestral primates attribute to the mutations under a stronger selective pressure. However, on the basis of the structure, the mechanism and the specificity of the α-Gal epitope and anti-Gal antibody, they can be applied to clinical exploitation. Knocking out the α1,3GT gene will eliminate the xenoantigen, Gal(α1,3)Gal, so that the transplantation of α1,3GT gene knockout pig organ into human becomes a potential clinically acceptable treatment for solving the problem of organ shortage. By contrast, the α-Gal epitope expressed through the application of chemical, biochemical and genetic engineering can be exploited for the clinical use. Targeting anti-Gal-mediated autologous tumor vaccines, which express α-Gal epitope to antigen-presenting cells, would increase their immunogenicity and elicit an immune response, which will be potent enough to eradicate the residual tumor cells. For tumor vaccines, the way of increasing immunogenicity of certain viral vaccines, including flu vaccines and human immunodeficiency virus vaccines, can also be used in the elderly. Recently, α-Gal epitope nanoparticles have been applied to accelerate wound healing and further directions on regeneration of internally injured tissues.

Monocytic MDSCs regulate macrophage-mediated xenogenic cytotoxicity

BACKGROUND

Xenotransplantation is considered to be one of the most attractive strategies for overcoming the worldwide shortage of organs. However, many obstructions need to be overcome before it will achieve clinical use in patients. One such obstacle is the development of an effective immunosuppressive strategy. We previously reported that myeloid-derived suppressor cells (MDSCs), a heterogeneous population of progenitor and immature myeloid cells, suppress xenogenic CTL-mediated cytotoxicity. Because of their heterogeneous nature, MDSC can function via several suppressive mechanisms that disrupt both innate and adaptive immunity. Since macrophages play a pivotal role in the rejection of a xenograft, in this study, we evaluated the suppressive effects of MDSC against macrophage-mediated xenogenic rejection.

MATERIALS AND METHODS

To evaluate the effect of monocyte-derived MDSCs on xenogenic immune reactions, a CFSE(carboxyfluorescein diacetate, succinimidyl ester)assay was employed to assess cytotoxicity.

RESULTS

While, in the absence of activation, primed MDSCs had no detectable effect on macrophage-induced cytotoxicity against SEC cells, LPS-activated MDSCs were found to significantly suppress xenogenic cytotoxicity. A CFSE cytotoxicity assay revealed that MDSCs significantly suppressed macrophage-induced cytotoxicity. Furthermore, an indoleamine 2,3 dioxygenase (IDO) inhibitor, 1-methyl tryptophan (1-MT), abolished the MDSC-induced suppression of macrophage-mediated xeno-rejection, indicating that MDSCs may suppress macrophage-mediated cytotoxicity in an IDO-dependent manner.

CONCLUSION

These findings indicate that MDSCs have great potential for immunosuppressing macrophage-mediated xeno-rejection.

Osteogenic effect of low-temperature-heated porcine bone particles in a rat calvarial defect model

The current study was designed to investigate the chemical and physical properties of porcine-derived xenografts of different crystallinity (low and high) and to evaluate their osteogenic potential. Porcine femur bone underwent a heat treatment process at 400°C (P400) and 1200°C (P1200) and was then milled into particles of 1 mm or less. In X-ray diffraction, P400 exhibited a low crystallinity compared with that of P1200, as indicated by the relatively wide diffraction peaks. Brunauer-Emmett-Teller analysis revealed that P400 also had a wider surface area than P1200. In micro-CT scan analysis of specimens in a rat calvarial defect model, bone mineral density of the P400 group was significantly higher than that of the P1200 group (p < 0.01). New bone formation was also remarkably higher at 8 weeks in the P400 group, which showed more new osteocytes in the lacuna compared with the P1200 group. In this study, low crystalline bone particles were obtained at low processing temperature (at temperature of 400°C) and achieved superior new bone formation compared with the high crystalline bone particles created at a higher process temperature (1200°C). It can be concluded that lower process temperature bone particles might provide a more effective graft material for enhancing bone formation. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 102A: 3609-3617, 2014.

Carbohydrate antigens

PURPOSE OF REVIEW

To summarize the current knowledge of carbohydrate antigens as related to xenotransplantation. The emphasis is on non-Gal carbohydrate antigens identified in many institutes. In addition, several topics such as glycosyltransferase-transgenic pigs, innate cell receptors and porcine endogenous retrovirus (PERV) will be discussed.

RECENT FINDINGS

Studies related to iGb3 and neoantigens after knocking out GalT (GGTA1) were reviewed. Available data do not support the conclusion that GalT-KO remains iGb3 and/or that neoantigens are produced in the pigs. Concerning non-Gal antigen, in addition to the Hanganutziu-Deicher (H-D) antigen (NeuGc), Forrsman antigen, Galα1-3Lew(x), α-linked or β-linked GalNAc, β3 linked Gal, NeuAc, such as Neu5Acα2-3Galβ1-3GlcNAc, and Sid blood group (Sd(a))-like antigens are candidates. However, to date some of these remain controversial and others need further study to completely identify them. Regarding the H-D antigen, different from the α-Gal, it has a complicated expression system, but has cytotoxic effects toward pig cells. To modify other carbohydrate antigen apart from α-Gal, only the overexpression of GnT-III appears to have an effect on the suppression of the N-linked sugar of non-Gal antigen. Concerning innate cell receptors related to carbohydrates (ligands), the focus turned from natural killer (NK) receptor to others, such as monocytes. Finally, PERV contains a ligand with an N-linked sugar. Modification of the glycosylation pattern appears to be associated with regulating PERV infectivity.

SUMMARY

A considerable amount of data related to carbohydrate antigens is now available. At the same time, however, discrepancies between studies complicate this issue. Further studies will be needed to completely understand this complicated area of interest.

Complete absence of the αGal xenoantigen and isoglobotrihexosylceramide in α1,3galactosyltransferase knock-out pigs

BACKGROUND

Anti-Galα1,3Galβ-R natural antibodies are responsible for hyperacute rejection in pig-to-primate xenotransplantation. Although the generation of pigs lacking the α1,3galactosyltransferase (GalT) has overcome hyperacute rejection, antibody-mediated rejection is still a problem. It is possible that other enzymes synthesize antigens similar to Galα1,3Gal epitopes that are recognized by xenoreactive antibodies. The glycosphingolipid isoglobotrihexosylceramide (iGb₃) represents such a candidate expressing an alternative Galα1,3Gal epitope. The present work determined whether the terminal Galα1,3Gal disaccharide is completely absent in Immerge pigs lacking the GalT using several different highly sensitive methods.

METHODS

The expression of Galα1,3Gal was evaluated using a panel of antibodies and lectins by flow cytometry and fluorescent microscopy; GalT activity was detected by an enzymatic assay; and ion trap mass spectroscopy of neutral cellular membranes extracted from aortic endothelial was used for the detection of sugar structures. Finally, the presence of iGb₃ synthase mRNA was tested by RT-PCR in pig thymus, spleen, lymph node, kidney, lung, and liver tissue samples.

RESULTS

Aortic endothelial cells derived from GalT knockout pigs expressed neither Galα1,3Gal nor iGb₃ on their surface, and GalT enzymatic activity was also absent. Lectin staining showed an increase in the blood group H-type sugar structures present in GalT knockout cells as compared to wild-type pig aortic endothelial cells (PAEC). Mass spectroscopic analysis did not reveal Galα1,3Gal in membranes of GalT knockout PAEC; iGb₃ was also totally absent, whereas a fucosylated form of iGb₃ was detected at low levels in both pig aortic endothelial cell extracts. Isoglobotrihexosylceramide 3 synthase mRNA was expressed in all pig tissues tested whether derived from wild-type or GalT knockout animals.

CONCLUSIONS

These results confirm unequivocally the absence of terminal Galα1,3Gal disaccharides in GalT knockout endothelial cells. Future work will have to focus on other mechanisms responsible for xenograft rejection, in particular non-Galα1,3Gal antibodies and cellular responses.

Immunobiology of liver xenotransplantation

Pigs are currently the preferred species for future organ xenotransplantation. With advances in the development of genetically modified pigs, clinical xenotransplantation is becoming closer to reality. In preclinical studies (pig-to-nonhuman primate), the xenotransplantation of livers from pigs transgenic for human CD55 or from α1,3-galactosyltransferase gene-knockout pigs+/- transgenic for human CD46, is associated with survival of approximately 7-9 days. Although hepatic function, including coagulation, has proved to be satisfactory, the immediate development of thrombocytopenia is very limiting for pig liver xenotransplantation even as a 'bridge' to allotransplantation. Current studies are directed to understand the immunobiology of platelet activation, aggregation and phagocytosis, in particular the interaction between platelets and liver sinusoidal endothelial cells, hepatocytes and Kupffer cells, toward identifying interventions that may enable clinical application.

Gal/non-Gal antigens in pig tissues and human non-Gal antibodies in the GalT-KO era

Our knowledge regarding Gal and non-Gal antigens in GalT-KO pig tissues can be summarized as α3Galactosyl-tranferase gene knock out eliminates the Galα3Galβ4GlcNAc-R antigen expression in pig tissues as well as anti-Gal antibody binding. Other Galα-terminating saccharides (e.g. iGb3 glycolipids and Galα2 determinants) may be present but have not been documented. α3Galactosyl-tranferase gene knock out slightly changes the carbohydrate antigen expression but no "new" antigens recognized by the human immune system have been found. Non-Gal antigens are both of protein and carbohydrate nature but their exact chemical structures are poorly defined. Regarding human non-Gal antibodies our knowledge is as Non-Gal antibodies exist naturally and increase in humans/non-human primate (NHP) receiving WT or GalT-KO pig grafts. Non-Gal antibodies with new antigen epitope recognition can be induced in humans/NHP after challenge by WT or GalT-KO pig grafts. Non-Gal antibodies react with both carbohydrates and proteins. Part of the protein reactivity is directed to glycoprotein carbohydrates chains. Non-Gal antibodies reacting with neuraminic acid terminated saccharides (both N-Acetyl and N-Glycoloyl variants) are present in humans/NHP. Anti-neuraminic acid antibodies are increased, as well as induced, after grafting pig organs into humans/NHP. Non-Gal antibodies does not cause hyperacute xenorejection but can be cytotoxic and cause xenoorgan damage. If humans sensitized to HLA antigens are at a higher risk of rejecting pig xenograft compared with non-sensitized individuals is not fully clarified. Clinical trials are needed to evaluate the relevance of non-Gal antigens/antibodies and for the xenofield to advance.

Studies on carbohydrate xenoantigens

Naturally occurring and elicited anti-carbohydrate antibodies play a major role in immune responses to xenografts. The original obstacles associated with the Gal antigen have been largely resolved by the generation of knockout pigs. In contrast, much less is known about the nature and role of non-Gal carbohydrate antigens and the antibodies recognizing these. These antibodies can be identified and characterized by enzyme-linked immunosorbent assay. Furthermore, the biological significance of the non-Gal antigen(s) can be determined by expression of the relevant glycosyltransferase(s) by transfection and analyzed by antibody and/or lectin binding.

Structural biology of carbohydrate xenoantigens

Transplantation of organs across species (xenotransplantation) is being considered to overcome the shortage of human donor organs. However, unmodified pig organs undergo an antibody-mediated hyperacute rejection that is brought about by the presence of natural antibodies to Galalpha(1,3)Gal, which is the major carbohydrate xenoantigen. Genetic modification of pig organs to remove most of the Galalpha(1,3)Gal epitopes has been achieved, but the human immune system may still recognize residual lipid-linked Galalpha(1,3)Gal carbohydrates, new (cryptic) carbohydrates or additional non-Galalpha(1,3)Gal carbohydrate xenoantigens. The structural basis for lectin and antibody recognition of Galalpha(1,3)Gal carbohydrates is starting to be understood and is discussed in this review. Antibody binding to Galalpha(1,3)Gal carbohydrates is predicted to primarily involve end-on insertion of the terminal alphaGal residue, but it is possible that groove-type binding can occur, as for some lectins. It is likely that similar antibody and lectin recognition will occur with other non-Galalpha(1,3)Gal xenoantigens, which potentially represent new barriers for pig-to-human xenotransplantation.

Current status of xenotransplantation and prospects for clinical application

Xenotransplantation is one promising approach to bridge the gap between available human cells, tissues, and organs and the needs of patients with diabetes or end-stage organ failure. Based on recent progress using genetically modified source pigs, improving results with conventional and experimental immunosuppression, and expanded understanding of residual physiologic hurdles, xenotransplantation appears likely to be evaluated in clinical trials in the near future for some select applications. This review offers a comprehensive overview of known mechanisms of xenograft injury, a contemporary assessment of preclinical progress and residual barriers, and our opinions regarding where breakthroughs are likely to occur.