Combined transgenic expression of alpha-galactosidase and alpha1,2-fucosyltransferase leads to optimal reduction in the major xenoepitope Galalpha(1,3)Gal

Comparing the application of various engineered xenografts for skin defects: A systematic review

INTRODUCTION

Xenografts are a now a cornerstone in the management of wound dressings. Promising results were achieved since 1960 in the application of skin substitute for skin defects.

OBJECTIVE

The objective of this study was to evaluate the efficacy of various xenografts.

METHODS

A literature research was conducted using the following query: 'Porcine skin dermatology substitute', 'bovine skin dermatology substitute', 'xenograft skin substitute dermatology', 'xenografts skin defect', 'porcine skin defect', 'bovine skin defect'.

RESULTS

The review yielded 35 articles pertaining to the topic. Main indications for porcine and bovine xenograft application were burn wounds and post-traumatic wounds, respectively. Mean discharge date or length of stay was at the 6th day after porcine application, and the time of graft healing was reported for 33.7% (n = 510) of patients. Promising results were seen with Matriderm and split-thickness skin graft. Most wounds achieved an excellent cosmetic result with full range of motion and a smooth contour appearance. A great variety of tissue substitutes exist, and the choice of graft application should depend on a patient's factors, product availability, wound type, size, and physician's factors.

CONCLUSION

In summary, xenografts are more economic and affordable but have higher risk of infections compared to allografts.

Characterization of Mono- and Bi-Transgenic Pig-Derived Epidermal Keratinocytes Expressing Human FUT2 and GLA Genes-In Vitro Studies

Pig-to-human xenotransplantation seems to be the response to the contemporary shortage of tissue/organ donors. Unfortunately, the phylogenetic distance between pig and human implies hyperacute xenograft rejection. In this study, we tested the hypothesis that combining expression of human α1,2-fucosyltransferase (hFUT2) and α-galactosidase A (hGLA) genes would allow for removal of this obstacle in porcine transgenic epidermal keratinocytes (PEKs). We sought to determine not only the expression profiles of recombinant human α1,2-fucosyltransferase (rhα1,2-FT) and α-galactosidase A (rhα-Gal A) proteins, but also the relative abundance (RA) of Galα1→3Gal epitopes in the PEKs stemming from not only hFUT2 or hGLA single-transgenic and hFUT2×hGLA double-transgenic pigs. Our confocal microscopy and Western blotting analyses revealed that both rhα1,2-FT and rhα-Gal A enzymes were overabundantly expressed in respective transgenic PEK lines. Moreover, the semiquantitative levels of Galα1→3Gal epitope that were assessed by lectin fluorescence and lectin blotting were found to be significantly diminished in each variant of genetically modified PEK line as compared to those observed in the control nontransgenic PEKs. Notably, the bi-transgenic PEKs were characterized by significantly lessened (but still detectable) RAs of Galα1→3Gal epitopes as compared to those identified for both types of mono-transgenic PEK lines. Additionally, our current investigation showed that the coexpression of two protective transgenes gave rise to enhanced abrogation of Galα→3Gal epitopes in hFUT2×hGLA double-transgenic PEKs. To summarize, detailed estimation of semiquantitative profiles for human α-1,2-FT and α-Gal A proteins followed by identification of the extent of abrogating the abundance of Galα1→3Gal epitopes in the ex vivo expanded PEKs stemming from mono- and bi-transgenic pigs were found to be a sine qua non condition for efficiently ex situ protecting stable lines of skin-derived somatic cells inevitable in further studies. The latter is due to be focused on determining epigenomic reprogrammability of single- or double-transgenic cell nuclei inherited from adult cutaneous keratinocytes in porcine nuclear-transferred oocytes and corresponding cloned embryos. To our knowledge, this concept was shown to represent a completely new approach designed to generate and multiply genetically transformed pigs by somatic cell cloning for the needs of reconstructive medicine and dermoplasty-mediated tissue engineering of human integumentary system.

Trichostatin A-Assisted Epigenomic Modulation Affects the Expression Profiles of Not Only Recombinant Human α1,2-Fucosyltransferase and α-Galactosidase A Enzymes But Also Galα1→3Gal Epitopes in Porcine Bi-Transgenic Adult Cutaneous Fibroblast Cells

This study was conducted to explore whether trichostatin A-assisted epigenomic modulation (TSA-EM) can affect the expression of not only recombinant human α1,2-fucosyltransferase (rhα1,2-FT) and α-galactosidase A (rhα-Gal A) immune system enzymes but also Galα1→3Gal epitopes in ex vivo proliferating adult cutaneous fibroblast cells (ACFCs) derived from hFUT2×hGLA bi-transgenic pigs that had been produced for the needs of future xenotransplantation efforts. The ACFC lines were treated with 50 nM TSA for 24 h and then the expression profiles of rhα1,2-FT and rhα-Gal A enzymes were analyzed by Western blot and immunofluorescence. The expression profiles of the Galα1→3Gal epitope were determined by lectin blotting and lectin fluorescence. The ACFCs derived from non-transgenic (nTG) pigs were served as the negative (TSA-) and positive (TSA+) control groups. For both hFUT2×hGLA and nTG samples, the expression levels of α1,2-FT and α-Gal A proteins in TSA+ cells were more than twofold higher in comparison to TSA- cells. Moreover, a much lower expression of the Galα1→3Gal epitopes was shown in TSA- hFUT2×hGLA cells as compared to the TSA- nTG group. Interestingly, the levels of Galα1→3Gal expression in TSA-treated hFUT2×hGLA and nTG ACFCs were significantly higher than those noticed for their TSA-untreated counterparts. Summing up, ex vivo protection of effectively selected bi-transgenic ACFC lines, in which TSA-dependent epigenetic transformation triggered the enhancements in reprogrammability and subsequent expression of hFUT2 and hGLA transgenes and their corresponding transcripts, allows for cryopreservation of nuclear donor cells, nuclear-transferred female gametes, and resultant porcine cloned embryos. The latter can be used as a cryogenically conserved genetic resource of biological materials suitable for generation of bi-transgenic cloned offspring in pigs that is targeted at biomedical research in the field of cell/tissue xenotransplantation.

Porcine genome engineering for xenotransplantation

The extreme shortage of human donor organs for treatment of patients with end-stage organ failures is well known. Xenotransplantation, which might provide unlimited organ supply, is a most promising strategy to solve this problem. Domestic pigs are regarded as ideal organ-source animals owing to similarity in anatomy, physiology and organ size to humans as well as high reproductive capacity and low maintenance cost. However, several barriers, which include immune rejection, inflammation and coagulative dysfunctions, as well as the cross-species transmission risk of porcine endogenous retrovirus, blocked the pig-to-human xenotransplantation. With the rapid development of genome engineering technologies and the potent immunosuppressive medications in recent years, these barriers could be eliminated through genetic modification of pig genome together with the administration of effective immunosuppressants. A number of candidate genes involved in the regulation of immune response, inflammation and coagulation have been explored to optimize porcine xenograft survival in non-human primate recipients. PERV inactivation in pigs has also been accomplished to firmly address the safety issue in pig-to-human xenotransplantation. Many encouraging preclinical milestones have been achieved with some organs surviving for years. Therefore, the clinical trials of some promising organs, such as islet, kidney and heart, are aimed to be launched in the near future.

Skin xenotransplantation: technological advances and future directions

PURPOSE OF REVIEW

To summarize the evolution of skin xenotransplantation and contextualize technological advances and the status of clinically applicable large animal research as well as prospects for translation of this work as a viable future treatment option.

RECENT FINDINGS

Porcine xenografts at the start of the millennium were merely biologic dressings subject to rapid rejection. Since then, numerous important advances in swine to nonhuman primate models have yielded xenotransplant products at the point of clinical translation. Critical genetic modifications in swine from a designated pathogen-free donor herd have allowed xenograft survival reaching 30 days without preconditioning or maintenance immunosuppression. Further, xenograft coverage appears not to sensitize the recipient to subsequent allograft placement and vice versa, allowing for temporary coverage times to be doubled using both xeno and allografts.

SUMMARY

Studies in large animal models have led to significant progress in the creation of living, functional skin xenotransplants with clinically relevant shelf-lives to improve the management of patients with extensive burns.

Clustered Regularly Interspaced Short Palindromic Repeats/Cas9 Gene Editing Technique in Xenotransplantation

Genetically modified pigs have been considered favorable resources in xenotransplantation. Microinjection of randomly integrating transgenes into zygotes, somatic cell nuclear transfer, homologous recombination, zinc finger nucleases, transcription activator-like effector nucleases, and most recently, clustered regularly interspaced short palindromic repeats-cas9 (CRISPR/Cas9) are the techniques that have been used to generate these animals. Here, we provide an overview of the CRISPR approaches that have been used to modify genes which are vital in improving xenograft survival rate, including cytidine monophosphate-N-acetylneuraminic acid hydroxylase, B1,4N-acetylgalactosaminyltransferase, isoglobotrihexosylceramide synthase, class I MHC, von Willebrand factor, C3, and porcine endogenous retroviruses. In addition, we will mention the importance of potential candidate genes which could be targeted using CRISPR/Cas9.

Analysis of swine leukocyte antigen class I gene profiles and porcine endogenous retrovirus viremia level in a transgenic porcine herd inbred for xenotransplantation research

Molecular characterization of swine leukocyte antigen (SLA) genes is important for elucidating the immune responses between swine-donor and human-recipient in xenotransplantation. Examination of associations between alleles of SLA class I genes, type of pig genetic modification, porcine endogenous retrovirus (PERV) viral titer, and PERV subtypes may shed light on the nature of xenograft acceptance or rejection and the safety of xenotransplantation. No significant difference in PERV gag RNA level between transgenic and non-transgenic pigs was noted; likewise, the type of applied transgene had no impact on PERV viremia. SLA-1 gene profile type may correspond with PERV level in blood and thereby influence infectiveness. Screening of pigs should provide selection of animals with low PERV expression and exclusion of specimens with PERV-C in the genome due to possible recombination between A and C subtypes, which may lead to autoinfection. Presence of PERV-C integrated in the genome was detected in 31.25% of specimens, but statistically significant increased viremia in specimens with PERV-C was not observed. There is a need for multidirectional molecular characterization (SLA typing, viremia estimation, and PERV subtype screening) of animals intended for xenotransplantation research in the interest of xeno-recipient safety.

Recent advances in genome editing and creation of genetically modified pigs

The field of xenotransplantation is benefiting greatly from recent advances in genetic engineering. The efficiency and pace with which new model animals are being created has dramatically sped progress towards clinical relevance. Endonuclease-driven genome editing now allows for the efficient generation of targeted genetic alterations. Herein we review the available methods of genetic engineering that have been successfully employed to create genetically modified pigs.

The current state of xenotransplantation

Pigs as a source of grafts for xenotransplantation can help to overcome the rapidly growing shortage of human donors. However, in the case of pig-to-human transplantation, the antibody-xenoantigen complexes lead to the complement activation and immediate hyperacute rejection. Methods eliminating hyperacute rejection (HAR) include α1,3-galactosyltransferase (GGTA1) inactivation, regulation of the complement system and modification of the oligosaccharide structure of surface proteins. The humoral immune response control and reduction of the risk of coagulation disorders are the priority tasks in attempts to overcome acute humoral xenograft rejection that may occur after the elimination of HAR. The primary targets for research are connected with the identification of obstacles and development of strategies to tackle them. Because of the magnitude of factors involved in the immune, genetic engineers face a serious problem of producing multitransgenic animals in the shortest possible time.

Immune modulation in xenotransplantation

The use of animals as donors of tissues and organs for xenotransplantations may help in meeting the increasing demand for organs for human transplantations. Clinical studies indicate that the domestic pig best satisfies the criteria of organ suitability for xenotransplantation. However, the considerable phylogenetic distance between humans and the pig causes tremendous immunological problems after transplantation, thus genetic modifications need to be introduced to the porcine genome, with the aim of reducing xenotransplant immunogenicity. Advances in genetic engineering have facilitated the incorporation of human genes regulating the complement into the porcine genome, knockout of the gene encoding the formation of the Gal antigen (α1,3-galactosyltransferase) or modification of surface proteins in donor cells. The next step is two-fold. Firstly, to inhibit processes of cell-mediated xenograft rejection, involving natural killer cells and macrophages. Secondly, to inhibit rejection caused by the incompatibility of proteins participating in the regulation of the coagulation system, which leads to a disruption of the equilibrium in pro- and anti-coagulant activity. Only a simultaneous incorporation of several gene constructs will make it possible to produce multitransgenic animals whose organs, when transplanted to human recipients, would be resistant to hyperacute and delayed xenograft rejection.

Double transgenic pigs with combined expression of human α1,2-fucosyltransferase and α-galactosidase designed to avoid hyperacute xenograft rejection

Hyperacute rejection (HAR) depends on the response of xenoreactive antibodies principally against porcine α-Gal epitope. Methods eliminating HAR include GGTA1 inactivation, regulation of the complement system and modification of the oligosaccharide structure of surface proteins in donor's cells. Transgenic animals designed for the purpose of xenotransplantation with single modification do not display full reduction of the α-Gal epitope level, which means that a accumulation of several modifications in one transgenic individual is needed. The aim of the study was to create a molecular and cytogenetic profile of a double transgenic animal with α1,2-fucosyltransferase and α-galactosidase expression. As a result of interbreeding of an individual with α1,2-fucosyltransferase expression with an individual with α-galactosidase expression 12 living piglets were obtained. PCR revealed the pCMVFUT gene construct was present in four individuals and pGAL-GFPBsd in three, including one with a confirmed integration of both the gene constructs. Fluorescence in situ hybridization confirmed the site of transgene integration, which corresponded to the mapping site of the transgenes which occurred in the parental generations. Karyotype analysis did not show any changes in the structure or the number of chromosomes (2n = 38, XX). As for the results pertaining to the single transgenic individuals, expression analysis demonstrated a high extent of α-Gal epitope level reduction on the surface of cells, whereas human serum cytotoxicity tests revealed the smallest decrease in longevity of cells in the obtained double transgenic individual (4.35 %). The tests suggest that the co-expression of both the transgenes leads to a considerable reduction of the α-Gal antigen level on the surface of cells and a decrease of xenotransplant immunogenicity.

Transgenic pigs designed to express human α-galactosidase to avoid humoral xenograft rejection

The use of animals as a source of organs and tissues for xenotransplantation can overcome the growing shortage of human organ donors. However, the presence of xenoreactive antibodies in humans directed against swine Gal antigen present on the surface of xenograft donor cells leads to the complement activation and immediate xenograft rejection as a consequence of hyperacute reaction. To prevent hyperacute rejection, it is possible to change the swine genome by a human gene modifying the set of donor’s cell surface proteins. The gene construct pGal-GFPBsd containing the human gene encoding α-galactosidase enzyme under the promoter of EF-1α elongation factor ensuring systemic expression was introduced by microinjection into a male pronucleus of the fertilised porcine oocyte. As a result, the founder male pig was obtained with the transgene mapping to chromosome 11p12. The polymerase chain reaction (PCR) analysis revealed and the Southern analysis confirmed transgene integration estimating the approximate number of transgene copies as 16. Flow cytometry analysis revealed a reduction in the level of epitope Gal on the cell surface of cells isolated from F0 and F1 transgenic animals. The complement-mediated cytotoxicity assay showed increased viability of the transgenic cells in comparison with the wild-type, which confirmed the protective influence of α-galactosidase expression.

Carbohydrate biomarker recognition using synthetic lectin mimics

Carbohydrate biomarkers play very important roles in a wide range of biological and pathological processes. Compounds that can specifically recognize a carbohydrate biomarker are useful for targeted delivery of imaging agents and for development of new diagnostics. Furthermore, such compounds could also be candidates for the development of therapeutic agents. A tremendous amount of active work on synthetic lectin mimics has been reported in recent years. Amongst all the synthetic lectins, boronic-acid-based lectins (boronolectins) have shown great promise. Along this line, four classes of boronolectins including peptide-, nucleic-acid-, polymer-, and small-molecule-based ones are discussed with a focus on the design principles and recent advances. We hope that by presenting the potentials of this field, this review will stimulate more research in this area.

Carbohydrate-mediated binding and induction of acrosomal exocytosis in a boar sperm-somatic cell adhesion model

The molecular basis underlying the binding of spermatozoa to their homologous eggs and the subsequent induction of acrosomal exocytosis remain a major unresolved issue in mammalian fertilization. Novel cell adhesion systems are now being explored to advance this research. Triantennary and tetraantennary N-glycans have previously been implicated as the major carbohydrate sequences that mediate the initial binding of spermatozoa to the specialized egg coat (zona pellucida) in the murine and porcine models. Mouse spermatozoa also undergo binding to rabbit erythrocytes (rRBCs), presumably via the interaction of their lectin-like egg-binding proteins with branched polylactosamine sequences present on these somatic cells. Experiments presented in this study confirm that boar spermatozoa also bind to rRBCs. However, unlike mouse spermatozoa, boar spermatozoa also undergo acrosomal exocytosis within 30 min after binding to rRBCs. Both binding and induction of acrosomal exocytosis in this system did not require the participation of terminal Galalpha1-3Gal sequences that are found on rRBCs. Pronase glycopeptides derived from rRBCs inhibited the binding of boar sperm to porcine oocytes by 91% at a final concentration of 0.3 mg/ml under standard IVF conditions. Binding in this porcine cell adhesion model was also completely blocked at this concentration of glycopeptide. Thus, adhesion results from the interaction of the egg-binding protein expressed on the surface of boar spermatozoa with the glycans presented on rRBCs. This cell adhesion model will be useful for investigating the molecular basis of gamete binding and the induction of acrosomal exocytosis in the pig.

Brief report: a new profile of terminal N-acetyllactosamines glycans on pig red blood cells and different expression of alpha-galactose on Sika deer red blood cells and nucleated cells

It has been reported that: (1) large variations were found in the number of sialic acid (SA) capped with N-acetyllactosamines (SA-Galbeta1-4GlcNAc-R) and alpha-Gal epitopes (Galalpha1-3Galbeta1-4GlcNAc-R) or uncapped N-acetyllactosamines (Galbeta1-4GlcNAc-R) on different mammalian red blood cells, and on nucleated cells originating from a given tissue in various species; (2) goat, sheep, horse and mouse red blood cells lack alpha-Gal epitopes, despite the expression of this epitope on a variety of nucleated cells in these species, including lymphocytes differentiated from the same hematopoietic origin. In this study, flow cytometry and Western blot analyses of pig red blood cells showed that alpha-Gal epitopes on pig red cells developed concomitantly after treatment with neuraminidase, suggesting that the terminal N-acetyllactosaminide glycans were capped with SA-alpha-Gal epitopes. Whereas, the expression of the alpha-Gal epitopes on red blood cells from Sika deer (Cevus nippon hortulorum) were found to be absent even though the epitopes were present on their white blood cells. Thus, these results add new data not only for the terminal carbohydrate structures on cell surface glycans of various mammalian cells, but also for wide variety of epitope expression on the cells from different tissues, which might be useful for understanding their unique states resulting from differentiation and evolution.

Carbohydrate recognition by boronolectins, small molecules, and lectins

Carbohydrates are known to mediate a large number of biological and pathological events. Small and macromolecules capable of carbohydrate recognition have great potentials as research tools, diagnostics, vectors for targeted delivery of therapeutic and imaging agents, and therapeutic agents. However, this potential is far from being realized. One key issue is the difficulty in the development of "binders" capable of specific recognition of carbohydrates of biological relevance. This review discusses systematically the general approaches that are available in developing carbohydrate sensors and "binders/receptors," and their applications. The focus is on discoveries during the last 5 years.

Carrageenan-induced innate immune response is modified by enzymes that hydrolyze distinct galactosidic bonds

The common food additive carrageenan (CGN) predictably induces intestinal inflammation in animal models. Mechanisms of CGN-induced nuclear factor κB and interleukin-8 (IL-8) stimulation include an immune-mediated pathway involving toll-like receptor 4 (TLR4) and B-cell lymphoma/leukemia 10 (BCL10) and a reactive oxygen species (ROS)-mediated pathway. To determine how the structure of CGN contributes to its initiation of inflammation through these two distinct mechanisms, we treated CGNs with galactosidases and carrageenases (CGNases) and determined the impact on IL-8 secretion and BCL10 production. Hydrolysis of CGN by the enzyme α-1→(3,6)-galactosidase significantly reduced increases in IL-8 and BCL10, but other galactosidases tested, including α-1→6-galactosidase, β-1→4-galactosidase and β-1→3,6-galactosidase, had no effect. In contrast, specific κ-CGNases or ι-CGNases, which hydrolyze β-1,4-galactosidic bonds, produced increases in IL-8 and BCL10 attributable to increased exposure of the immunogenic α-1→3-galactosidic epitope of CGN to TLR4. These results were consistent with induction of innate immune response by an interaction of TLR4 with the unusual α-d-Gal-(1→3)-d-Gal epitope present in CGN. Activation of the ROS-mediated pathway was unaffected by treatment of κ-CGN with either κ-CGNase (3 mg/L), α-1→(3,6)-galactosidase (20 mU/ml) or these enzymes in combination, indicating that changes in IL-8 production were attributable to the effects of induction of inflammation on the TLR4-BCL10-mediated innate immune pathway. These findings provide new information about the specificity of carbohydrate-protein interaction between CGN and TLR4 and may help to devise treatments that modify the immune reactivity induced by carbohydrate antigens.

Novel Leb-like Helicobacter pylori-binding glycosphingolipid created by the expression of human alpha-1,3/4-fucosyltransferase in FVB/N mouse stomach

The "Le(b) mouse" was established as a model for investigations of the molecular events following Le(b)-mediated adhesion of Helicobacter pylori to the gastric epithelium. By the expression of a human alpha-1,3/4-fucosyltransferase in the gastric pit cell lineage of FVB/N transgenic mice, a production of Le(b) glycoproteins in gastric pit and surface mucous cells was obtained in this "Le(b) mouse," as demonstrated by binding of monoclonal anti-Le(b) antibodies. To explore the effects of the human alpha-1,3/4-fucosyltransferase on glycosphingolipid structures, neutral glycosphingolipids were isolated from stomachs of transgenic alpha-1,3/4-fucosyltransferase-expressing mice. A glycosphingolipid recognized by BabA-expressing H. pylori was isolated and characterized by mass spectrometry and proton NMR as Fuc alpha 2Gal beta 3(Fuc alpha 4)GalNAc beta 4 Gal beta 4 Glc beta 1Cer, i.e., a novel Le(b)-like glycosphingolipid on a ganglio core. In addition, two other novel glycosphingolipids were isolated from the mouse stomach epithelium that were found to be nonbinding with regard to H. pylori. The first was a pentaglycosylceramide, GalNAc beta 3 Gal alpha 3(Fuc alpha 2)Gal beta 4 Glc beta 1Cer, in which the isoglobotetrasaccharide has been combined with Fuc alpha 2 to yield an isoglobotetraosylceramide with an internal blood group B determinant. The second one was an elongated fucosyl-gangliotetraosylceramide, GalNAc beta 3(Fuc alpha 2)Gal beta 3GalNAc beta 4Gal beta 4 Glc beta 1Cer.

Toll-like receptor 4 mediates induction of the Bcl10-NFkappaB-interleukin-8 inflammatory pathway by carrageenan in human intestinal epithelial cells

The sulfated polysaccharide carrageenan (CGN) induces activation of NFkappaB and interleukin 8 (IL-8) in human colonic epithelial cells through a pathway of innate immunity mediated by Bcl10 (B-cell CLL/lymphoma 10). In this report, we identify Toll-like receptor 4 (TLR4), a member of the family of innate immune receptors, as the surface membrane receptor for CGN in human colonic epithelial cells. Experiments with fluorescence-tagged CGN demonstrated a marked reduction in binding of CGN to human intestinal epithelial cells and to RAW 264.7 mouse macrophages, following exposure to TLR4 blocking antibody (HTA-125). Binding of CGN to 10ScNCr/23 mouse macrophages, which are deficient in the genetic locus for TLR4, was absent. Additional experiments with TLR4 blocking antibody and TLR4 small interfering RNAs showed 80% reductions in CGN-induced increases in Bcl10 and IL-8. Transfection with dominant-negative MyD88 plasmid demonstrated MyD88 dependence of the CGN-TLR4-triggered increases in Bcl10 and IL-8. Therefore, these results indicate that CGN-induced inflammation in human colonocytes proceeds through a pathway of innate immunity, perhaps related to the unusual alpha-1,3-galactosidic linkage characteristic of CGN, and suggest how dietary CGN intake may contribute to human intestinal inflammation. Because CGN is a commonly used food additive in the Western diet, clarification of its effects and mechanisms of action are vital to issues of food safety.

Carrageenan-induced NFkappaB activation depends on distinct pathways mediated by reactive oxygen species and Hsp27 or by Bcl10

Carrageenans are highly sulfated polysaccharides that are widely used as food additives due to their ability to improve food texture. They are also widely recognized for their ability to induce inflammation in animal models of colitis. Recently, we reported that carrageenan (CGN) activated a pathway of innate immunity in human colonic epithelial cells mediated by Bcl10 (B-cell CLL/lymphoma 10). However, increases in phospho-IkappaBalpha and Interleukin-8 (IL-8) were not completely inhibited by silencing Bcl10, suggesting that CGN also influenced another mechanism, or mechanisms, of inflammation. In this report, we demonstrate that CGN increases production of reactive oxygen species (ROS) in human colonic epithelial cells. The combination of ROS quenching by the free radical scavenger Tempol and of Bcl10 silencing by siRNA completely inhibited the CGN-induced increases in nuclear NFkappaB (p65), phospho-IkappaBalpha, and secretion of IL-8. The CGN-induced increase in ROS was associated with declines in phosphorylation of MAPK 12 (p38gamma), MAPK 13 (p38delta), and heat-shock protein (Hsp) 27. The CGN-induced decline in phospho-Hsp27 was reversed by co-administration of Tempol (100 nM), but unaffected by silencing Bcl10. Since Hsp27 phosphorylation is inversely associated with phosphorylation of the IkappaBalpha kinase (IKK) signalosome, CGN exposure appears to affect the IKK signalosome by both the catalytic component, mediated by ROS-phospho-Hsp27, and the regulatory component, mediated by Bcl10 interaction with IKKgamma (Nemo). Hence, the CGN-activated inflammatory cascades related to innate immunity and to generation of ROS may be integrated at the level of the IKK signalosome.

Carrageenan induces cell cycle arrest in human intestinal epithelial cells in vitro

Multiple studies in animal models have shown that the commonly used food additive carrageenan (CGN) induces inflammation and intestinal neoplasia. We performed the first studies to determine the effects of CGN exposure on human intestinal epithelial cells (IEC) in tissue culture and tested the effect of very low concentrations (1-10 mg/L) of undegraded, high-molecular weight CGN. These concentrations of CGN are less than the anticipated exposure of the human colon to CGN from the average Western diet. In the human colonic epithelial cell line NCM460 and in primary human colonic epithelial cells that were exposed to CGN for 1-8 d, we found increased cell death, reduced cell proliferation, and cell cycle arrest compared with unexposed control cells. After 6-8 d of CGN exposure, the percentage of cells reentering G0-G1 significantly decreased and the percentages of cells in S and G2-M phases significantly increased. Increases in activated p53, p21, and p15 followed CGN exposure, consistent with CGN-induced cell cycle arrest. Additional data, including DNA ladder, poly ADP ribose polymerase Western blot, nuclear DNA staining, and activities of caspases 3 and 7, indicated no evidence of increased apoptosis following CGN exposure and were consistent with CGN-induced necrotic cell death. These data document for the first time, to our knowledge, marked adverse effects of low concentrations of CGN on survival of normal human IEC and suggest that CGN exposure may have a role in development of human intestinal pathology.

Studies on glycolipid antigens in small intestine and pancreas from alpha1,3-galactosyltransferase knockout miniature swine

BACKGROUND

To avoid hyperacute rejection of xeno-organs, alpha1,3-galactosyltransferase knockout (GalT-KO) pigs have been produced. Galalpha1,3Gal determinant elimination may expose cryptic carbohydrate antigens and/or generate new antigens. This is the first biochemical study of carbohydrate antigens in GalT-KO pig organs.

METHODS

Neutral and acidic glycolipids were isolated from small intestine and pancreas of two GalT-KO and one wild-type (WT) pig. Glycolipid immune reactivity was tested on thin-layer chromatograms. Small intestine neutral glycolipids were separated by high-performance liquid chromatography and selected fractions were analyzed by proton nuclear magnetic resonance spectroscopy. Total gangliosides were quantified on thin-layer chromatograms and in microtiter wells.

RESULTS

Using Galalpha1,3nLc4 glycolipid reference, total Galalpha1,3Gal glycolipid antigens in the WT animal was estimated at about 30 microg (small intestine) and 3 microg (pancreas) per gram of dry tissue. Galalpha1,3Gal determinants were not detected in GalT-KO tissues at a detection limit of less than 0.25% (small intestine) and 0.5% (pancreas) of the WT tissues. Isoglobotriaosylceramide (iGb3) was absent but trace amounts of Fuc-iGb3 was found in both GalT-KO and WT pig small intestine. Blood group H type 2 core saccharide compounds were increased in GalT-KO pancreas. Total amount of gangliosides was decreased in GalT-KO tissues. The alpha1,3-galactosyltransferase acceptor, N-acetyllactosamine determinant, was not increased in GalT-KO tissues. Human serum antibodies reacted with WT organ Galalpha1,3Gal antigens and gangliosides, of which the ganglioside reactivity remained in GalT-KO tissues.

CONCLUSIONS

Knockout of porcine alpha1,3-galactosyltransferase gene results in elimination of Galalpha1,3Gal-terminated glycolipid compounds. GalT-KO genetic modification did not produce new compensatory glycolipid compounds reactive with human serum antibodies.

Xenotransfusions, past and present

The first blood transfusions in humans were xenotransfusions, carried out by Jean-Baptiste Denis beginning in 1667. Richard Lower, Matthäus Purmann and Georges Mercklin also experimented with the use of animal blood for transfusion until this practice was forbidden in 1670, after the death of one of Denis's patients. In the middle of the 19th century, xenotransfusion was rescued from oblivion by the work of Pierre Cyprien Oré. Franz Gesellius and Oscar Hasse fervently defended xenotransfusion, but Emil Ponfick and Leonard Landois stressed the potentially harmful effects of inter-species transfusion from 1874 onward. Xenotransfusion was abandoned completely following the discovery of blood groups by Karl Landsteiner in 1900. From 2000, because of progress in xenotransplantation and the need of blood supply, xenotransfusion is again being considered. Pigs are the best potential donors. The development of alpha-1,3-galactosyltransferase gene-knockout pigs has overcome the first hurdle to xenotransfusion. The main obstacle to porcine red blood cell transfusion is now the cellular response involving macrophages or natural killer cells.

Reducing Gal expression on the pig organ - a retrospective review

The rejection caused by the presence of Galalpha1,3Gal (Gal) on the pig vascular endothelium and of natural anti-Gal antibodies in human blood has recently been prevented by the breeding of pigs that do not express Gal, achieved by knocking out the gene for the enzyme, alpha1,3-galactosyltransferase. However, prior to the introduction of nuclear transfer/embryo transfer techniques, a major effort was directed towards reducing Gal expression on pig cells by other methods, such as by cleaving Gal from the underlying substrate, or replacing Gal with an alternative, innocuous oligosaccharide by a process that has been termed 'competitive glycosylation'. Gal has been cleaved by alpha-galactosidase or endo-beta-galactosidase C. Competitive glycosylation has largely targeted replacement of Gal by insertion of a gene for a fucosyltransferase or a sialyltransferase, or by insertions of the gene for N-acetylglucosaminyltransferase III to reduce cell-surface expression of several oligosaccharides. The results of these approaches to render the pig cells less immunogenic to the human immune system are summarized. With regard to the problem provided by Gal expression, the above approaches may be considered by some to be largely obsolete, but the principles underlying them may prove valuable when other antigen targets for human antibodies are definitively identified, if these prove to be carbohydrates.

Foundation Review: Transgenic animals and their impact on the drug discovery industry

The ability to direct genetic changes at the molecular level has resulted in a revolution in biology. Nowhere has this been more apparent than in the production of transgenic animals. Transgenic technology lies at the junction of several enabling techniques in such diverse fields as embryology, cell biology and molecular genetics. A host of techniques have been used to effect change in gene expression and develop new pharmaceutical and nutraceutical compounds cost-effectively. Scientific advances gained by transgenic capabilities enable further understanding of basic biological pathways and yield insights into how changes in fundamental processes can perturb programmed development or culminate in disease pathogenesis.

Effect of RNA interference on Gal alpha 1,3 Gal expression in PIEC cells

Xenotransplantation from pigs to human beings is viewed as a potential solution for the acute organ shortage. However, consequent xenorejection induced by Gal alpha 1,3 Gal (a Gal, Gal antigen) prevents xenotransplantation from clinical application. Thus, the most attracting attempt to prevent xenorejection is the elimination of Gal. Our study suggested that compared with the human alpha 1,2 fucosyltransferase (FT) gene and the porcine antisense alpha 1,3 galactosyltransferase gene, sequence-specific siRNA targeting Gal was capable of suppressing Gal expression markedly, and therefore, significantly inhibiting xenoreactivity and the complement activation with human serum in PIEC cells. We also demonstrated the concordant inhibitory effect of siRNA and the human FT gene on Gal and corresponding functions, which implied a practical significance of combined transgenic strategy. The successful application of vector-based dsRNA-GT may extend the list of available modalities in the abrogation of xenorejection in xenotransplantation.

Effect of RNA interference on Gal alpha 1,3 Gal expression in PIEC cells

Xenotransplantation from pig to human being is viewed as a potential solution for the acute organ shortage. However, consequent xenorejection induced by Gal alpha 1,3 Gal (Gal, Gal antigen) prevents xenotransplantation from clinical application. Thus, the most attracting attempt to prevent xenorejection is the elimination of Gal. Our study suggested that compared with the human alpha 1,2 fucosyltransferase (FT) gene and porcine antisense alpha 1,3 galactosyltransferase gene, sequence-specific siRNA targeting Gal were capable of suppressing Gal expression markedly, and therefore, significantly inhibiting xenoreactivity and the complement activation with human serum in PIEC cells. We also demonstrated the concordant inhibitory effect of siRNA and human FT gene on Gal and corresponding functions, which implied a practical significance of combined transgenic strategy. The successful application of vector-based dsRNA-GT may extend the list of available modalities in the abrogation of xenorejection in xenotransplantation.

Progress in xenotransplantation

Organ transplantation is considered the most effective treatment for end-stage organ failure; currently it is limited by a severe worldwide shortage of human donor organs. This has led to investigation of the potential use of animals as organ donors. For a number of reasons, the pig represents the most likely organ donor candidate. Transplantation of a vascularised porcine organ into a human or non-human primate results in an immediate and dramatic rejection process, known as hyperacute rejection, which is mediated by the binding of pre-existing antibody to the porcine graft and the subsequent activation of host complement. Strategies aimed at preventing this initial rejection have been largely successful in experimental models. This has allowed attention to turn towards an understanding of the immunological barriers comprising the next phase of xenograft rejection, termed acute vascular rejection. This delayed rejection process appears to be a humoral event, and it is likely that the control of antibody synthesis will play a pivotal role in overcoming the current barrier to successful xenotransplantation.

Xenotransplantation: a tool for reproductive biology and animal conservation?

The transplantation of reproductive organs, including ovaries and ovarian tissue, was pioneered over 100 years ago. In the 1960s, ovarian grafting was used as a tool to investigate ovarian function, but with the recent development of more effective cryopreservation protocols for ovarian tissue, germline preservation and propagation have now become realistic goals. This review describes progress in ovarian banking and ovarian tissue transplantation, with emphasis on how fresh and frozen ovarian tissue can be used in assisted reproduction for both humans and animals. This paper focuses most closely on the potential value of xenotransplantation, the transplantation of gonads from one species to another, to conserve rare and endangered species. Specific attention is drawn to the use of xenotransplantation as a strategy for generating viable gametes that can be used to produce live fertile offspring. Other upcoming xenogeneic technologies that may be of potential significance in animal conservation, such as transplantation of whole ovaries or isolated growing follicles, and even male germ cells, are discussed.

Xenotransplantation in the 21st century

Xenotransplantation, i.e. transplantation across species, is increasingly being viewed a potential solution to the problem of severe shortage of transplant donors. Clinical application of xenotransplantation is, however, limited in large part by the pre-eminent hurdle of the immune response of the recipient against the graft. This immunologic reaction is mediated initially by natural xenoreactive antibodies, complement and natural killer cells, and later by elicited humoral and cellular immune responses that ultimately lead to graft failure. Progress in understanding the cellular and molecular basis of xenograft rejection has characterized the past few years. Additional hurdles to xenotransplantation include physiologic incompatibility of the transplant and the risk of infections. The recent development of novel strategies to overcome xenograft rejection has brought about great optimism that xenotransplantation may be attainable in the near future.

Genetic modification of xenografts

For nearly a century, xenotransplantation has been seen as a potential approach to replacing organs and tissues damaged by disease. Until recently, however, the application of xenotransplantation has seemed only a remote possibility. What has changed this perspective is the advent of genetic engineering of large animals; that is, the ability to add genes to and remove genes from lines of animals that could provide an enduring source of tissues and organs for clinical application. Genetic engineering could address the immunologic, physiologic and infectious barriers to xenotransplantation, and could allow xenotransplantation to provide a source of cells with defined and even controlled expression of exogenous genes. This communication will consider one perspective on the application of genetic engineering in xenotransplantation.

Fetal porcine thymus engraftment, survival and CD4 reconstitution in alphaGal-KO mice is impaired in the presence of high levels of antibodies against alphaGal

Xenospecific T-cell tolerance can be induced among murine and human T-cells by porcine thymic grafting. However, anti-alpha 1,3-galactosyltranserase (alphaGal) (Galalpha1-3Galbeta1-4GlcNAc-R) natural antibodies (NAbs) pose a major barrier to porcine xenografts in humans. We used alphaGal knockout (KO) and muchain KO mice to explore the effect of natural anti-alphaGal and other xenoantibodies on porcine thymic engraftment and to examine the potential of thymic tissue to tolerize anti-alphaGal antibody-producing cells. Thymectomized [adult thymectomy (ATX)] non-immunized and rabbit red blood cell (RRBC) pre-transplant immunized alphaGal-KO (knockout), wild-type (WT) and mu chain KO B6 mice were treated with 3Gy total body irradiation (TBI), and T and natural killer (NK) cell depleting monoclonal antibodies (mAbs). These conditioned mice were grafted with fetal porcine thymus and liver (FP THY/LIV) tissue under the kidney capsule. Flow cytometric analysis was performed to follow CD4 reconstitution as a measure of FP THY engraftment and function. Only mice with >10% CD4+ peripheral blood lymphocytes (PBL) were considered successfully engrafted. Enzyme-linked immunosorbent assay (ELISA) was used to assess the kinetics of immunoglobulin M (IgM) and IgG anti-alphaGal antibodies. Anti-pig antibodies were monitored by flow cytometry (FCM). FP THY engrafted successfully in most of the immunoglobulin deficient mice (11 out of 12, 92%) and the outcome was similar in WT B6 controls (8 out of 12, 67%). Non-immunized alphaGal-KO mice grafted with FP THY had a similar success rate (7 out of 11) to that observed in non-immunized alphaGal-WT controls (2 out of 4). In contrast, alphaGal-KO mice immunized pre-transplant with RRBC, then grafted with FP THY/LIV, showed a significant reduction in the success of thymic grafting (2 out of 9, 22%) compared with pre-transplant immunized WT controls (4 out of 7; 57%) and non-immunized alphaGal-KO mice (7 out of 11, 64%). Anti-Gal and anti-pig antibody levels were not markedly augmented by porcine thymus grafts in mice with successful thymus grafts. FP THY engraftment is impaired in the presence of high levels of anti-alphaGal xenoantibodies. However, low levels of anti-alphaGal antibodies and other mouse anti-pig NAbs appear not to play a major role in the rejection of FP THY. Although grafting FP THY expressing the alphaGal epitope did not tolerize B cells producing anti-alphaGal antibodies in a T-cell independent manner, it prevented T-cell dependent sensitization by inducing T-cell tolerance to porcine antigens.

Reduction of alpha-Gal expression by relocalizing alpha-galactosidase to the trans-Golgi network and cell surface

Historically, the most effective means of modifying cell surface carbohydrates has required the intracellular overexpression of glycosyltransferases or glycosidases and is dependent on the enzymes occupying a cellular localization close to the carbohydrate structures they modify. We report on relocalizing the lysosomal resident glycosidase human alpha-galactosidase to other regions of the cell, Golgi and cell surface, where it is in closer proximity for cleaving the carbohydrate structure Galalpha(1,3)Gal. Relocalization of alpha-galactosidase was achieved by using the transmembrane and cytoplasmic domains from the human protein furin, which is known to localize in the trans-Golgi network (TGN) and cell surface. Two chimeric forms of alpha-galactosidase were generated, one directing it to the TGN of the cell and the other to the cell surface, as shown by confocal microscopy. The relocalized enzymes have the ability to cleave terminal alpha-galactose as detected by expression on the cell surface. Furthermore, when expressed as a transgene in mice, the TGN form of alpha-galactosidase was more effective at decreasing cell surface terminal alpha-galactose than was the native lysosomal form. When expressed in conjunction with the alpha1,2fucosyltransferase that also decreases Galalpha(1,3)Gal, the reduction was additive. The ability to relocalize enzymes that modify cell surface carbohydrate structures has far-reaching implications in biology and may be useful in such fields as xenotransplantation and treatment of glycosidase disorders.

Efficient production by sperm-mediated gene transfer of human decay accelerating factor (hDAF) transgenic pigs for xenotransplantation

A large number of hDAF transgenic pigs to be used for xenotransplantation research were generated by using sperm-mediated gene transfer (SMGT). The efficiency of transgenesis obtained with SMGT was much greater than with any other method. In the experiments reported, up to 80% of pigs had the transgene integrated into the genome. Most of the pigs carrying the hDAF gene transcribed it in a stable manner (64%). The great majority of pigs that transcribed the gene expressed the protein (83%). The hDAF gene was transmitted to progeny. Expression was stable and found in caveolae as it is in human cells. The expressed gene was functional based on in vitro experiments performed on peripheral blood mononuclear cells. These results show that our SMGT approach to transgenesis provides an efficient procedure for studies involving large animal models.

Enzymatic removal of alphaGal antigen in pig kidneys by ex vivo and in vivo administration of endo-beta-galactosidase C

Xenotransplantation using the pig as a donor species is considered to be a promising solution to the serious shortage of organ donors. Both hyperacute and acute vascular rejection (AVR) are believed to be associated with xenoreactive antibody binding to alphaGal epitopes on the pig vascular endothelial cells. Thus, suppression of this antigen-antibody reaction would appear essential for successful long-term xenograft survival. The purpose of this study was to examine the efficacy of ex vivo and in vivo administration of recombinant endo-beta-galactosidase C (EndoGalC which, in previous in vitro studies, has been proven to digest alphaGal antigens completely) on alphaGal epitopes expressed in pig kidneys. Excised pig kidneys were perfused with University of Wisconsin solution containing EndoGalC and preserved for 4 h. After cold storage, the pig kidney was transplanted into another pig. Ex vivo perfusion and cold storage with EndoGalC reduced alphaGal epitope expression on vascular endothelial cells to an undetectable level. However, alphaGal antigens began to be expressed again as early as 1 day after transplantation. The digestion of alphaGal epitopes by EndoGalC did not cause any damage to the kidney graft. EndoGalC was intravenously administered to two pigs (15 kg), without causing any serious adverse effect. Twelve hours later, >98% of alphaGal antigens on pig red blood cells (RBCs) had been digested. Immunohistochemical study revealed almost complete elimination of alphaGal expression on vascular endothelial cells of the kidney graft 4 and 8 h after in vivo administration, but reappearance within 24 h. EndoGalC was administered to a baboon after an interval of 2 months. The second administration did not result in any serious toxicity or reduction in efficacy. These results suggest that ex vivo and in vivo administration of EndoGalC is simple and useful in removing alphaGal epitopes from pig organs. As the effect of EndoGalC is temporary, multiple in vivo administrations of EndoGalC would be required to inhibit the reappearance of alphaGal epitopes. Alternatively, transgenic techniques of introducing the gene for EndoGalC into the donor organ might permanently prevent alphaGal expression.

Activation of natural killer cells and macrophages by porcine endothelial cells augments specific T-cell xenoresponse

The rejection of xenografts is characterized by infiltration of monocytes and natural killer (NK) cells into the graft, suggesting an important role for the innate immune system in xenorecognition. In this study, purified human NK or T cells were cocultured with porcine endothelial cells, and cytokines were analyzed by ELISA and intracellular FACS. We demonstrated a vigorous human anti-porcine xenoresponse that was associated with a strong T-cell proliferation against porcine endothelial cells. Limiting dilution cloning and T-cell receptor (TCR) Vbeta gene usage revealed a low number of xenoreactive T-cell precursors. We demonstrated that xenogeneic porcine but not allogeneic human endothelial cells induced the early production of interferon (IFN)-gamma by human NK cells but not by CD3+ T cells. Porcine xenoantigen-induced IFN-gamma production was only partially dependent on IL-12. Blocking IL-12 with neutralizing antibodies or by depletion of human macrophages partially decreased IFN-gamma production by CD56+ NK cells. Three-color flow cytometry revealed that IL-12 was produced through a species-specific activation of human macrophages by porcine endothelial cells. Our results indicate that the direct activation of NK cells and macrophages by porcine endothelial cells provides a unique pathway of xenorecognition that augments downstream specific T-cell immunity and represents a powerful effector mechanism in xenograft rejection.

Viral vector-mediated delivery of competing glycosyltransferases modifies epitope expression cell specifically

The glycoconjugate epitopes 3-fucosyl-N-acetyllactosamine (CD15) and sulfoglucuronylcarbohydrate (SGC) mediate cell adhesion events in several systems, and are regulated both spatially and temporally during cerebellar development. In cotransfection studies using COS-1 cells, competition between glycosyltransferases that utilize a common precursor involved in the final synthetic steps of these epitopes, can modulate epitope expression. For example, cotransfection of rat alpha1,3-fucosyltransferase IV (Fuc-TIV) and either rat glucuronic acid transferase P (GlcAT) or pig alpha1,3-galactosyltransferase (GalT) resulted in the dominance of either SGC or GalalphaGal epitope expression, respectively, with blockage of CD15 epitope expression. Viral vectors expressing these glycosyltransferases were used to determine whether competition plays a role in establishing epitope dominance in cerebellar cells, and whether overexpression of competing glycosyltransferases could be used to block epitope expression. Infection of cerebellar astrocytes with viral vectors expressing either Fuc-TIV, or Fuc-TIX, caused dramatic increases in CD15 expression in the presence of continued endogenous SGC epitope expression. Likewise, viral transduction with GalT resulted in GalalphaGal expression without affecting endogenous CD15 or SGC expression. Thus, competition between these enzymes does not appear to play a role in establishing epitope expression in astrocytes, and transduction of these enzymes does not provide a method of blocking the expression of endogenous epitopes. In contrast to what was observed for astrocytes, infection with viral vectors expressing either Fuc-T, GlcAT, or GalT did not result in significant expression of the relevant epitopes (CD15, SGC or GalalphaGal, respectively) on granule neurons. These results suggest a different complement of precursors are present in granule neurons and astrocytes, presumably due to the presence of different complements of glycosyltransferases in these cells.

Genetic engineering for xenotransplantation

Xenotransplantation is being pursued vigorously to solve the shortage of allogeneic donor organs. Experimental studies of the major xenoantigen (Gal) and of complement regulation enable model xenografts to survive hyperacute rejection. When the Gal antigen is removed or reduced and complement activation is controlled, the major barriers to xenograft survival include unregulated coagulation within the graft and cellular reactions involving macrophages, neutrophils, natural killer (NK) cells, and T lymphocytes. Unlike allografts, where specific immune responses are the sole barrier to graft survival, molecular differences between xenograft and recipient that affect normal receptor-ligand interactions (largely active at the cell surface and which may not be immunogenic), are also involved in xenograft failure. Transgenic strategies provide the best options to control antigen expression, complement activation, and coagulation. Although the Gal antigen can be eliminated by gene knockout in mice, that outcome has only become a possibility in pigs due to the recent cloning of pigs after nuclear transfer. Instead, the use of transgenic glycosyl transferase enzymes and glycosidases, which generate alternative terminal carbohydrates on glycolipids and glycoproteins, has reduced antigen in experimental models. As a result, novel strategies are being tested to seek the most effective solution. Transgenic pigs expressing human complement-regulating proteins (DAF/CD55, MCP/CD46, or CD59) have revealed that disordered regulation of the coagulation system requires attention. There will undoubtedly be other molecular incompatibilities that need addressing. Xenotransplantation, however, offers hope as a therapeutic solution and provides much information about homeostatic mechanisms.

The immunological hurdles to cardiac xenotransplantation

The main hurdle to clinical application of cardiac xenotransplantation is the immune response of the recipient against the graft. Although all xenografts arouse an intense immune response, the effect of that response depends very much on whether the graft consists of isolated cells or an intact organ, such as the heart. Intact organs, which are transplanted by primary vascular anastomosis, are subject to severe vascular injury owing to the reaction of immune elements with the endothelial lining of donor blood vessels. Vascular injury leads to hyperacute rejection, acute vascular rejection, and chronic rejection. The immunological basis for these types of rejection and potential therapies, which might be used to avert them, are discussed.

Remodeling of the major pig xenoantigen by N-acetylglucosaminyltransferase III in transgenic pig

We have been successful in generating several lines of transgenic mice and pigs that contain the human beta-d-mannoside beta-1,4-N-acetylglucosaminyltransferase III (GnT-III) gene. The overexpression of the GnT-III gene in mice and pigs reduced their antigenicity to human natural antibodies, especially the Galalpha1-3Galbeta1-4GlcNAc-R, as evidenced by immunohistochemical analysis. Endothelial cell studies from the GnT-III transgenic pigs also revealed a significant down-regulation in antigenicity, including Hanganutziu-Deicher antigen, and dramatic reductions in both the complement- and natural killer cell-mediated pig cell lyses. Changes in the enzymatic activities of other glycosyltransferases, such as alpha1,3-galactosyltransferase, GnT-IV, and GnT-V, did not support cross-talk between GnT-III and these enzymes in the transgenic animals. In addition, we demonstrated the effect of GnT-III in down-regulating the xenoantigen of pig heart grafts, using a pig to cynomolgus monkey transplantation model, suggesting that this approach may be useful in clinical xenotransplantation in the future.

The pig as a source of cardiac xenografts

The inadequate availability of human donor hearts and other organs has inspired interest in the field of xenotransplantation. Historically, ten attempts to transplant animal hearts into human recipients have been reported. Those who received hearts from nonhuman primates (i.e., baboons and chimpanzees) survived rather longer than did those who received hearts from nonprimates (i.e., sheep and pigs). Nevertheless, current opinion is that the pig is the best candidate as a source of hearts for humans despite the considerable immunologic disparity between the two species. Pigs are available in large numbers and can be bred easily and rapidly. They grow to appropriate sizes and their cardiovascular system is similar to that of humans. Substantial knowledge has been accumulated regarding both genetic engineering and tolerance induction in pigs, two strategies that may help to overcome the existing immunologic barriers. Concern has been raised, however, with regard to the potential for the transfer of a porcine infection with the pig organ to the human recipient. This brief review addresses these and other aspects of the use of the pig as a source of hearts for patients with end-stage cardiac disease.

The α-Gal epitope (Galα1-3Galβ1-4GlcNAc-R) in xenotransplantation

Many patients with failing organs (e.g., heart, liver or kidneys), do not receive the needed organ because of an insufficient number of organ donors. Pig xenografts have been considered as an alternative source of organs for transplantation. The major obstacle currently known to prevent pig to human xenotransplantation is the interaction between the human natural anti-Gal antibody and the α-gal epitope (Galα1-3Galβ1-4GlcNAc-R), abundantly expressed on pig cells. This short review describes the characteristics of anti-Gal and of the alpha-gal epitope, their role in inducing xenograft rejection and some experimental approaches for preventing this rejection.

Adenovirus-mediated expression of pig alpha(1, 3) galactosyltransferase reconstructs Gal alpha(1, 3) gal epitope on the surface of human tumor cells

Gal alpha(1, 3) Gal (gal epitope) is a carbohydrate epitope and synthesized in large amount by alpha(1, 3) galactosyltransferase [alpha(1, 3) GT] enzyme on the cells of lower mammalian animals such as pigs and mice. Human has no gal epitope due to the inactivation of alpha(1, 3) GT gene but produces a large amount of antibodies (anti-Gal) which recognize Gal alpha(1, 3) Gal structures specifically. In this study, a replication-deficient recombinant adenoviral vector Ad5sGT containing pig alpha(1, 3) GT cDNA was constructed and characterized. Adenoviral vector-mediated transfer of pig alpha(1, 3) GT gene into human tumor cells such as malignant melanoma A375, stomach cancer SGC-7901, and lung cancer SPC-A-1 was reported for the first time. Results showed that Gal epitope did not increase the sensitivity of human tumor cells to human complement-mediated lysis, although human complement activation and the binding of human IgG and IgM natural antibodies to human tumor cells were enhanced significantly after Ad5sGT transduction. Appearance of gal epitope on the human tumor cells changed the expression of cell surface carbohydrates reacting with Ulex europaeus I (UEA I) lectins, Vicia villosa agglutinin (VVA), Arachis hypogaea agglutinin (PNA), and Glycine max agglutinin (SBA) to different degrees. In addition, no effect of gal epitope on the growth in vitro of human tumor cells was observed in MTT assay.

Antigen expression in xenotransplantation: how low must it go?

BACKGROUND

Acute vascular rejection (AVR) is an important immunological barrier to xenotransplantation. Thought to be initiated by xenoreactive antibodies, acute vascular rejection might, in principle, be avoided by engineering animals to express low levels of antigen. The extent to which antigen expression would have to be decreased to achieve such a goal is unknown.

METHODS

We estimated the decrease in expression of a xenogeneic antigen, Galalpha1-3Gal, which might be needed to avert acute vascular rejection of xenotransplants based on the decrease in antibody binding to endothelium that would prevent tissue damage.

RESULTS

The level of decrease needed in Galalpha1-3Gal expression needed to avoid acute vascular rejection was estimated to exceed 96% of baseline. The extent of the decrease needed reflected, in part, a substantial "excess" of Galalpha1-3Gal on porcine endothelial cell surfaces.

CONCLUSIONS

Although the change in antigen expression required to avoid acute vascular rejection might be conditioned by various factors, the very large magnitude of this change necessitates application of highly efficient approaches to antigen modification.