Man, apes, and Old World monkeys differ from other mammals in the expression of alpha-galactosyl epitopes on nucleated cells

Production of α1,3-galactosyltransferase targeted pigs using transcription activator-like effector nuclease-mediated genome editing technology

Recent developments in genome editing technology using meganucleases demonstrate an efficient method of producing gene edited pigs. In this study, we examined the effectiveness of the transcription activator-like effector nuclease (TALEN) system in generating specific mutations on the pig genome. Specific TALEN was designed to induce a double-strand break on exon 9 of the porcine α1,3-galactosyltransferase (GGTA1) gene as it is the main cause of hyperacute rejection after xenotransplantation. Human decay-accelerating factor (hDAF) gene, which can produce a complement inhibitor to protect cells from complement attack after xenotransplantation, was also integrated into the genome simultaneously. Plasmids coding for the TALEN pair and hDAF gene were transfected into porcine cells by electroporation to disrupt the porcine GGTA1 gene and express hDAF. The transfected cells were then sorted using a biotin-labeled IB4 lectin attached to magnetic beads to obtain GGTA1 deficient cells. As a result, we established GGTA1 knockout (KO) cell lines with biallelic modification (35.0%) and GGTA1 KO cell lines expressing hDAF (13.0%). When these cells were used for somatic cell nuclear transfer, we successfully obtained live GGTA1 KO pigs expressing hDAF. Our results demonstrate that TALEN-mediated genome editing is efficient and can be successfully used to generate gene edited pigs.

Initial in vitro studies on tissues and cells from GTKO/CD46/NeuGcKO pigs

BACKGROUND

The impact that the absence of expression of NeuGc in pigs might have on pig organ or cell transplantation in humans has been studied in vitro, but only using red blood cells (pRBCs) and peripheral blood mononuclear cells (pPBMCs) as the target cells for immune assays. We have extended this work in various in vitro models and now report our initial results.

METHODS

The models we have used involve GTKO/hCD46 and GTKO/hCD46/NeuGcKO pig aortas and corneas, and pRBCs, pPBMCs, aortic endothelial cells (pAECs), corneal endothelial cells (pCECs), and isolated pancreatic islets. We have investigated the effect of the absence of NeuGc expression on (i) human IgM and IgG binding, (ii) the T-cell proliferative response, (iii) human platelet aggregation, and (iv) in an in vitro assay of the instant blood-mediated inflammatory reaction (IBMIR) following exposure of pig islets to human blood/serum.

RESULTS

The lack of expression of NeuGc on some pig tissues (aortas, corneas) and cells (RBCs, PBMCs, AECs) significantly reduces the extent of human antibody binding. In contrast, the absence of NeuGc expression on some pig tissues (CECs, isolated islet cells) does not reduce human antibody binding, possibly due to their relatively low NeuGc expression level. The strength of the human T-cell proliferative response may also be marginally reduced, but is already weak to GTKO/hCD46 pAECs and islet cells. We also demonstrate that the absence of NeuGc expression on GTKO/hCD46 pAECs does not reduce human platelet aggregation, and nor does it significantly modify the IBMIR to pig islets.

CONCLUSION

The absence of NeuGc on some solid organs from GTKO/hCD46/NeuGcKO pigs should reduce the human antibody response after clinical transplantation when compared to GTKO/hCD46 pig organs. However, the clinical benefit of using certain tissue (e.g., cornea, islets) from GTKO/hCD46/NeuGcKO pigs is questionable.

Modifying the sugar icing on the transplantation cake

As a transplant surgeon, my interest in glycobiology began through my research into ABO-incompatible allotransplantation, and grew when my goal became overcoming the shortage of organs from deceased human donors by the transplantation of pig organs into patients with terminal organ failure (xenotransplantation/cross-species transplantation). The major target for human "natural" (preformed) anti-pig antibodies is galactose-α(1,3)-galactose (the "Gal" epitope), which is expressed on many pig cells, including the vascular endothelium. The binding of human IgM and IgG antibodies to Gal antigens initiates the process of hyperacute rejection, resulting in destruction of the pig graft within minutes or hours. This major barrier has been overcome by the production of pigs in which the gene for the enzyme α(1,3)-galactosyltransferase (GT) has been deleted by genetic engineering, resulting in GT knockout (GTKO) pigs. The two other known carbohydrate antigenic targets on pig cells for human anti-pig antibodies are (i) the product of the cytidine monophosphate-N-acetylneuraminic acid hydroxylase (CMAH) gene, i.e., N-glycolylneuraminic acid, and (ii) the product of the β1,4 N-acetylgalactosaminyltransferase gene, i.e., the Sd(a) antigen. Expression of these two has also been deleted in pigs. These genetic manipulations, together with others directed to overcoming primate complement and coagulation activation (the latter of which also relates to glycobiology) have contributed to the prolongation of pig graft survival in nonhuman primate recipients to many months rather than a few minutes. Clinical trials of the transplantation of pig cells are already underway and transplantation of pig organs may be expected within the relatively near future.

Inhalation of α-gal/sialic acid liposomes: a novel approach for inhibition of influenza virus infection?

Effective inhibition of influenza virus infection in symptomatic patients may be feasible by inhalation of aerosol-containing liposomes presenting α-gal epitopes and sialic acid epitopes. The virus binds to sialic acid epitopes and the natural anti-Gal antibody binds to α-gal epitopes on the liposomes and activates the complement system to generate chemotactic peptides that recruit macrophages. These macrophages bind and internalize via their Fc receptors, anti-Gal-coated liposomes and the influenza virus bound to them, process the viral antigens and transport them to the regional lymph nodes for eliciting a rapid, protective immune response that prevents progression of the virus infection.

The pathobiology of pig-to-primate xenotransplantation: a historical review

The immunologic barriers to successful xenotransplantation are related to the presence of natural anti-pig antibodies in humans and non-human primates that bind to antigens expressed on the transplanted pig organ (the most important of which is galactose-α1,3-galactose [Gal]), and activate the complement cascade, which results in rapid destruction of the graft, a process known as hyperacute rejection. High levels of elicited anti-pig IgG may develop if the adaptive immune response is not prevented by adequate immunosuppressive therapy, resulting in activation and injury of the vascular endothelium. The transplantation of organs and cells from pigs that do not express the important Gal antigen (α1,3-galactosyltransferase gene-knockout [GTKO] pigs) and express one or more human complement-regulatory proteins (hCRP, e.g., CD46, CD55), when combined with an effective costimulation blockade-based immunosuppressive regimen, prevents early antibody-mediated and cellular rejection. However, low levels of anti-non-Gal antibody and innate immune cells and/or platelets may initiate the development of a thrombotic microangiopathy in the graft that may be associated with a consumptive coagulopathy in the recipient. This pathogenic process is accentuated by the dysregulation of the coagulation-anticoagulation systems between pigs and primates. The expression in GTKO/hCRP pigs of a human coagulation-regulatory protein, for example, thrombomodulin, is increasingly being associated with prolonged pig graft survival in non-human primates. Initial clinical trials of islet and corneal xenotransplantation are already underway, and trials of pig kidney or heart transplantation are anticipated within the next few years.

Amblyomma sculptum tick saliva: α-Gal identification, antibody response and possible association with red meat allergy in Brazil

The anaphylaxis response is frequently associated with food allergies, representing a significant public health hazard. Recently, exposure to tick bites and production of specific IgE against α-galactosyl (α-Gal)-containing epitopes has been correlated to red meat allergy. However, this association and the source of terminal, non-reducing α-Gal-containing epitopes have not previously been established in Brazil. Here, we employed the α-1,3-galactosyltransferase knockout mouse (α1,3-GalT-KO) model and bacteriophage Qβ-virus like particles (Qβ-VLPs) displaying Galα1,3Galβ1,4GlcNAc (Galα3LN) epitopes to investigate the presence of α-Gal-containing epitopes in the saliva of Amblyomma sculptum, a species of the Amblyomma cajennense complex, which represents the main tick that infests humans in Brazil. We confirmed that the α-1,3-galactosyltransferase knockout animals produce significant levels of anti-α-Gal antibodies against the Galα1,3Galβ1,4GlcNAc epitopes displayed on Qβ-virus like particles. The injection of A. sculptum saliva or exposure to feeding ticks was also found to induce both IgG and IgE anti-α-Gal antibodies in α-1,3-galactosyltransferase knockout mice, thus indicating the presence of α-Gal-containing epitopes in the tick saliva. The presence of α-Gal-containing epitopes was confirmed by ELISA and immunoblotting following removal of terminal α-Gal epitopes by α-galactosidase treatment. These results suggest for the first known time that bites from the A. sculptum tick may be associated with the unknown etiology of allergic reactions to red meat in Brazil.

Decellularized Renal Matrix and Regenerative Medicine of the Kidney: A Different Point of View

Over the past years, extracellular matrix (ECM) obtained from whole organ decellularization has been investigated as a platform for organ engineering. The ECM is composed of fibrous and nonfibrous molecules providing structural and biochemical support to the surrounding cells. Multiple decellularization techniques, including ours, have been optimized to maintain the composition, microstructure, and biomechanical properties of the native renal ECM that are difficult to obtain during the generation of synthetic substrates. There are evidences suggesting that in vivo implanted renal ECM has the capacity to induce formation of vasculature-like structures, but long-term in vivo transplantation and filtration activity by these tissue-engineered constructs have not been investigated or reported. Therefore, even if the process of renal decellularization is possible, the repopulation of the renal matrix with functional renal cell types is still very challenging. This review aims to summarize the current reports on kidney tissue engineering with the use of decellularized matrices and addresses the challenges in creating functional kidney units. Finally, this review discusses how future studies investigating cell-matrix interaction may aid the generation of a functional renal unit that would be transplantable into patients one day.

Glycomics: revealing the dynamic ecology and evolution of sugar molecules

Sugars are the most functionally and structurally diverse molecules in the biological world. Glycan structures range from tiny single monosaccharide units to giant chains thousands of units long. Some glycans are branched, their monosaccharides linked together in many different combinations and orientations. Some exist as solitary molecules; others are conjugated to proteins and lipids and alter their collective functional properties. In addition to structural and storage roles, glycan molecules participate in and actively regulate physiological and developmental processes. Glycans also mediate cellular interactions within and between individuals. Their roles in ecology and evolution are pivotal, but not well studied because glycan biochemistry requires different methods than standard molecular biology practice. The properties of glycans are in some ways convenient, and in others challenging. Glycans vary on organismal timescales, and in direct response to physiological and ecological conditions. Their mature structures are physical records of both genetic and environmental influences during maturation. We describe the scope of natural glycan variation and discuss how studying glycans will allow researchers to further integrate the fields of ecology and evolution.

Guided tissue regeneration in heart valve replacement: from preclinical research to first-in-human trials

Heart valve tissue-guided regeneration aims to offer a functional and viable alternative to current prosthetic replacements. Not requiring previous cell seeding and conditioning in bioreactors, such exceptional tissue engineering approach is a very fascinating translational regenerative strategy. After in vivo implantation, decellularized heart valve scaffolds drive their same repopulation by recipient's cells for a prospective autologous-like tissue reconstruction, remodeling, and adaptation to the somatic growth of the patient. With such a viability, tissue-guided regenerated conduits can be delivered as off-the-shelf biodevices and possess all the potentialities for a long-lasting resolution of the dramatic inconvenience of heart valve diseases, both in children and in the elderly. A review on preclinical and clinical investigations of this therapeutic concept is provided with evaluation of the issues still to be well deliberated for an effective and safe in-human application.

Quantification of α-Gal Antigen Removal in the Porcine Dermal Tissue by α-Galactosidase

The α-Gal (Galα1,3-Galβ1-4GlcNAc-R) epitope, the major xenoantigen, is the first barrier in a porcine-to-man tissue and organ xenotransplantation. The elimination or reduction of the α-Gal epitopes is therefore an important step for a successful xenotransplantation. The present study is to evaluate the α-Gal elimination in the porcine skin with α-galactosidase treatment, and to assess two methods (immunohistochemistry and inhibition ELISA) that may be used in quality control for quantifying the extent of the α-Gal elimination. Enzymatic cleavage in a single-step process is extremely efficient and affordable at eliminating the α-Gal epitope even in a tissue as dense as the porcine dermis. The cost of enzymatic cleavage is found to be less than US$7 for a 10 × 10 cm piece of porcine skin (0.5 mm thick) or about US$140 for 100 g of 3-dimensional soft tissues. After enzymatic cleavage, the α-Gal-positive immunostaining was essentially undetectable in enzyme-treated porcine skin. The inhibition rate constant of the monoclonal anti-Gal antibody M86 binding to α-Gal-bovine serum albumin in ELISA was reduced from 15.0 ± 4.3 (n = 10) to 6.1 ± 2.6 (n = 7) after enzyme treatment, in comparison to 4.4 ± 1.8 (n = 9) background inhibition of decellularized human skin (the ultimate negative control), which demonstrates ∼ 84% elimination of α-Gal epitopes in treated porcine skin. To examine the suitability of two detection methods for the routine quality control application, comparative studies were made with control and enzyme-treated porcine skin, porcine skin from the α-Gal knockout animal, as well as decellularized human skin. The data show that the traditional immunohistochemistry and, to a less extent, the inhibition ELISA with further modifications can be used as quality control tools in the production and selection of biocompatible bioprosthetic devices. The biological evaluation of enzyme-treated porcine skin is ongoing with a small animal model and a nonhuman primate model.

Histologic examination of decellularized porcine intestinal submucosa extracellular matrix (CorMatrix) in pediatric congenital heart surgery

BACKGROUND

CorMatrix is a decellularized porcine small intestinal submucosa extracellular matrix that has gained attention as a promising alternative to current materials used in cardiac repair. While animal models demonstrate integration of CorMatrix material with host tissue, the histologic characteristics of CorMatrix used in humans are less well-characterized. In this retrospective study, we report our experience with CorMatrix material used in pediatric congenital heart surgery and describe the histology of CorMatrix material and of surrounding native tissue in explanted specimens.

METHODS

Records were reviewed of all pediatric patients implanted with CorMatrix from a single institution (2011-2014). Histologic examinations were performed on CorMatrix and other tissues removed. Explanted samples of CorMatrix and adherent tissues were evaluated for inflammation (acute and chronic), fibrosis, necrosis, degenerative changes, eosinophil response, foreign-body giant cell reaction, neovascularization, and calcification of tissues on a semiquantitative basis (0, none; 1, mild; 2, moderate; 3, marked). Presence of degeneration within CorMatrix and necrosis of surrounding tissue were noted.

RESULTS

CorMatrix was utilized in 532 pediatric heart reconstruction procedures since 2011. Twelve explanted CorMatrix specimens from 11 pediatric patients including 4 valves (2 mitral and 2 aortic) and 8 outflow/septal/conduit patches were identified and evaluated. Six cases (5 patients) demonstrated clinical evidence of graft failure prior to surgery (n=6, 1%). Chronic inflammation was seen in adjacent native tissue in 11/12 cases and consisted predominantly of a mixed population of lymphocytes, macrophages, and plasma cells. Acute inflammation was seen in three cases (3/12). Fibrosis of the surrounding native tissue was seen in all CorMatrix specimens. Eosinophils were present in 6/12 cases. Calcification in surrounding tissue was present in 3/12 cases. Giant cell reaction in adjacent native tissue was seen in 8/12 cases. Neovascularization was seen in surrounding native tissue in 5/12 cases. Degeneration of CorMatrix material was seen in 9/12 cases. Necrosis of surrounding tissue was also identified in 5/12 cases. CorMatrix was not resorbed and no cases demonstrated any remodeling of CorMatrix material by integration of native mesenchymal cells or myocytes.

CONCLUSION

CorMatrix may be associated with a marked inflammatory response, including a foreign-body giant cell reaction and fibrosis of the surrounding native tissue. Degenerative changes of CorMatrix material are also seen in a majority of explanted specimens. No histologic differences were seen between patients with clinical evidence of graft failure versus patients requiring graft removal due to other factors. Additionally, no cases showed evidence of tissue integration or recellularization of patch material. Our overall clinical experience with CorMatrix demonstrates a favorable outcome for pediatric patients undergoing cardiac reconstructive surgery. However, there is no histologic evidence that CorMatrix acts as a scaffold for reconstitution of the native cardiovascular structures.

Recent investigations into pig antigen and anti-pig antibody expression

Genetic engineering of donor pigs to eliminate expression of the dominant xenogeneic antigen galactose α1,3 galactose (Gal) has created a sea change in the immunobiology of xenograft rejection. Antibody mediated xenograft rejection of GGTA-1 α-galactosyltransferase (GTKO) deficient organs is now directed to a combination of non-Gal pig protein and carbohydrate antigens. Glycan analysis of GTKO tissues identified no new neo-antigens but detected high levels of N-acetylneuraminic acid (Neu5Gc) modified glycoproteins and glycolipids. Humans produce anti-Neu5Gc antibody and in very limited clinical studies sometimes show an induced anti-Neu5Gc antibody response after challenge with pig tissue. The pathogenicity of anti-Neu5Gc antibody in xenotransplantation is not clear however as non-human transplant models, critical for modelling anti-Gal immunity, do not produce anti-Neu5Gc antibody. Antibody induced after xenotransplantation in non-human primates is directed to an array of pig endothelial cells proteins and to a glycan produced by the pig B4GALNT2 gene. We anticipate that immune suppression will significantly affect the T-cell dependent and independent specificity of an induced antibody response and that donor pigs deficient in synthesis of multiple xenogeneic glycans will be important to future studies.

Current status of pig lung xenotransplantation

Human organ transplantation has improved duration and quality of life for many people, but its full potential is critically limited by short supply of available organs. One solution is xenotransplantation, although this comes with its own set of challenges. Lungs in particular are highly sensitive to injury, during the transplantation process generally, and to multiple immune rejection mechanisms. Using pig lung donors, our lab has been working on lung transplants into baboons as a surrogate for a human recipient. Several ex vivo human blood perfusion models have also proven useful. The combination of these experiments allows us to test large animal models as well as whole organ or isolated endothelial reactions to perfusion with human blood. We have found that a multi-modality therapeutic approach to prevent various pathogenic cascades - such as antibody-driven complement activation, other immune pathway activation, thrombosis, and tissue ischemia-reperfusion injury - has met with progressively greater success to protect the xeno lung from injury. Pig gene knockout and human gene transfer has been perhaps the greatest contributor. This review will discuss mechanisms of xeno lung injury, relevant experimental models, as well as recent results and future targets for research.

Neuronally produced versican V2 renders C-fiber nociceptors IB4 -positive

A subpopulation of nociceptors, the glial cell line-derived neurotrophic factor (GDNF)-dependent, non-peptidergic C-fibers, expresses a cell-surface glycoconjugate that can be selectively labeled with isolectin B4 (IB4 ), a homotetrameric plant lectin from Griffonia simplicifolia. We show that versican is an IB4 -binding molecule in rat dorsal root ganglion neurons. Using reverse transcriptase polymerase chain reaction (RT-PCR), in situ hybridization and immunofluorescence experiments on rat lumbar dorsal root ganglion, we provide the first demonstration that versican is produced by neurons. In addition, by probing Western blots with splice variant-specific antibodies we show that the IB4 -binding versican contains only the glycosaminoglycan alpha domain. Our data support V2 as the versican isoform that renders this subpopulation of nociceptors IB4 -positive (+). A subset of nociceptors, the GDNF-dependent non-peptidergic C-fibers can be characterized by its reactivity for isolectin B4 (IB4), a plant lectin from Griffonia simplicifolia. We have previously demonstrated that versican V2 binds IB4 in a Ca2 + -dependent manner. However, given that versican is thought to be the product of glial cells, it was questionable whether versican V2 can be accountable for the IB4-reactivity of this subset of nociceptors. The results presented here prove - for the first time - a neuronal origin of versican and suggest that versican V2 is the molecule that renders GDNF-dependent non-peptidergic C-fibers IB4-positive.

Acceleration of wound healing by α-gal nanoparticles interacting with the natural anti-Gal antibody

Application of α-gal nanoparticles to wounds and burns induces accelerated healing by harnessing the natural anti-Gal antibody which constitutes ~1% of human immunoglobulins. α-gal nanoparticles present multiple α-gal epitopes (Galα1-3Galβ1-4GlcNAc-R), the carbohydrate ligand of anti-Gal. Studied α-gal nanoparticles were comprised of glycolipids with α-gal epitopes, phospholipids, and cholesterol. Binding of anti-Gal to α-gal nanoparticles in wounds activates the complement cascade, resulting in formation of chemotactic complement cleavage peptides that induce rapid recruitment of many macrophages. The Fc/Fcγ receptors interaction between anti-Gal coating α-gal nanoparticles and the recruited macrophages activates macrophages to produce cytokines/growth factors that promote wound healing and recruit stem cells. Studies of wound healing by α-gal nanoparticles were feasible in α1,3galactosyltransferase knockout mice and pigs. In contrast to other nonprimate mammals, these mice and pigs lack the α-gal epitope, and thus they are not immunotolerant to it and produce anti-Gal. Treatment of skin wounds and burns with α-gal nanoparticles resulted in 40-60% decrease in healing time in comparison with control wounds treated with saline. This accelerated healing is associated with increased recruitment of macrophages and extensive angiogenesis in wounds, faster regrowth of epidermis, and regeneration of the dermis. The accelerated healing further decreases and may completely eliminate fibrosis and scar formation in wounds. Since healing of internal injuries is mediated by mechanisms similar to those in external wound healing, it is suggested that α-gal nanoparticles treatment may also improve regeneration and restoration of biological function following internal injuries such as surgical incisions, myocardial ischemia following infarction, and nerve injuries.

Xenotransplantation: immunological hurdles and progress toward tolerance

The discrepancy between organ need and organ availability represents one of the major limitations in the field of transplantation. One possible solution to this problem is xenotransplantation. Research in this field has identified several obstacles that have so far prevented the successful development of clinical xenotransplantation protocols. The main immunologic barriers include strong T-cell and B-cell responses to solid organ and cellular xenografts. In addition, components of the innate immune system can mediate xenograft rejection. Here, we review these immunologic and physiologic barriers and describe some of the strategies that we and others have developed to overcome them. We also describe the development of two strategies to induce tolerance across the xenogeneic barrier, namely thymus transplantation and mixed chimerism, from their inception in rodent models through their current progress in preclinical large animal models. We believe that the addition of further beneficial transgenes to Gal knockout swine, combined with new therapies such as Treg administration, will allow for successful clinical application of xenotransplantation.

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.

NKT cell networks in the regulation of tumor immunity

CD1d-restricted natural killer T (NKT) cells lie at the interface between the innate and adaptive immune systems and are important mediators of immune responses and tumor immunosurveillance. These NKT cells uniquely recognize lipid antigens, and their rapid yet specific reactions influence both innate and adaptive immunity. In tumor immunity, two NKT subsets (type I and type II) have contrasting roles in which they not only cross-regulate one another, but also impact innate immune cell populations, including natural killer, dendritic, and myeloid lineage cells, as well as adaptive populations, especially CD8⁺ and CD4⁺ T cells. The extent to which NKT cells promote or suppress surrounding cells affects the host’s ability to prevent neoplasia and is consequently of great interest for therapeutic development. Data have shown the potential for therapeutic use of NKT cell agonists and synergy with immune response modifiers in both pre-clinical studies and preliminary clinical studies. However, there is room to improve treatment efficacy by further elucidating the biological mechanisms underlying NKT cell networks. Here, we discuss the progress made in understanding NKT cell networks, their consequent role in the regulation of tumor immunity, and the potential to exploit that knowledge in a clinical setting.

In situ conversion of tumors into autologous tumor-associated antigen vaccines by intratumoral injection of α-gal glycolipids

The immunogenicity of autologous tumor-associated antigens (TAAs) is markedly increased upon the intratumoral injection of α-gal glycolipids, which insert into tumor cell membranes. The binding of natural anti-Gal antibodies to these glycolipids activates the complement system and recruits antigen-presenting cells (APCs), which internalize anti-Gal-coated tumor cells upon Fc/FcγR interactions. Eventually, TAA-derived peptides presented by APCs activate a T cell-mediated tumor-specific immune response.

Genetically modified porcine split-thickness skin grafts as an alternative to allograft for provision of temporary wound coverage: preliminary characterization

Temporary coverage of severely burned patients with cadaver allograft skin represents an important component of burn care, but is limited by availability and cost. Porcine skin shares many physical properties with human skin, but is susceptible to hyperacute rejection due to preformed antibodies to α-1,3-galactose (Gal), a carbohydrate on all porcine cells. Our preliminary studies have suggested that skin grafts from α-1,3-galactosyltransferase knock out (GalT-KO) miniature swine might provide temporary wound coverage comparable to allografts, since GalT-KO swine lack this carbohydrate. To further evaluate this possibility, eight non-human primates received primary autologous, allogeneic, GalT-KO, and GalT+xenogeneic skin grafts. Additionally, secondary grafts were placed to assess whether sensitization would affect the rejection time course of identical-type grafts. We demonstrate that both GalT-KO xenografts and allografts provide temporary coverage of partial- and full-thickness wounds for up to 11 days. In contrast, GalT+xenografts displayed hyperacute rejection, with no signs of vascularization and rapid avulsion from wounds. Furthermore, secondary GalT-KO transplants failed to vascularize, demonstrating that primary graft rejection sensitizes the recipient. We conclude that GalT-KO xenografts may provide temporary coverage of wounds for a duration equivalent to allografts, and thus, could serve as a readily available alternative treatment of severe burns.

Significance of the evolutionary α1,3-galactosyltransferase (GGTA1) gene inactivation in preventing extinction of apes and old world monkeys

The α1,3-galactosyltransferase (α1,3GT or GGTA1) gene displays unique evolutionary characteristics. This gene appeared early in mammalian evolution and is absent in other vertebrates. The α1,3GT gene is active in marsupials, nonprimate placental mammals, lemurs (prosimians) and New World monkeys, encoding the α1,3GT enzyme that synthesizes a carbohydrate antigen called "α-gal epitope." The α-gal epitope is present in large numbers on cell membrane glycolipids and glycoproteins. The α1,3GT gene was inactivated in ancestral Old World monkeys and apes by frameshift single-base deletions forming premature stop codons. Because of this gene inactivation, humans, apes, and Old World monkeys lack α-gal epitopes and naturally produce an antibody called the "anti-Gal antibody" which binds specifically to α-gal epitopes and which is the most abundant antibody in humans. The evolutionary event that resulted in the inactivation of the α1,3GT gene in ancestral Old World primates could have been mediated by a pathogen endemic to Eurasia-Africa landmass that exerted pressure for selection of primate populations lacking the α-gal epitope. Once the α-gal epitope was eliminated, primates could produce the anti-Gal antibody, possibly as means of defense against pathogens expressing this epitope. This assumption is supported by the fossil record demonstrating an almost complete extinction of apes in the late Miocene and failure of Old World monkeys to radiate into multiple species before that period. A present outcome of this evolutionary event is the anti-Gal-mediated rejection of mammalian xenografts expressing α-gal epitopes in humans, apes, and Old World monkeys.

Cloning and expression of porcine β1,4 N-acetylgalactosaminyl transferase encoding a new xenoreactive antigen

Background

Xenograft rejection of pigs organs with an engineered mutation in the GGTA-1 gene (GTKO) remains a predominantly antibody mediated process which is directed to a variety of non-Gal protein and carbohydrate antigens. We previously used an expression library screening strategy to identify six porcine endothelial cell cDNAs which encode pig antigens that bind to IgG induced after pig-to-primate cardiac xenotransplantation. One of these gene products was a glycosyltransferase with homology to the bovine β1,4 N-acetylgalactosaminyltransferase (B4GALNT2). We now characterize the porcine B4GALNT2 gene sequence, genomic organization, expression, and functional significance.

Methods

The porcine B4GALNT2 cDNA was recovered from the original library isolate, subcloned, sequenced, and used to identify a bacterial artificial chromosome (BAC) containing the entire B4GALNT2 locus from the Children's Hospital Oakland Research Institute BACPAC Resource Centre (#AC173453). PCR primers were designed to map the intron/exon genomic organization in the BAC clone. A stable human embryonic kidney (HEK) cell line expressing porcine B4GALNT2 (HEK-B4T) was produced. Expression of porcine B4GALNT2 in HEK-B4T cells was characterized by immune staining and siRNA transfection. The effects of B4GALNT2 expression in HEK-B4T cells was measured by flow cytometry and complement mediated lysis. Antibody binding to HEK and HEK-B4T cells was used to detect an induced antibody response to the B4GALNT2 produced glycan and the results were compared to GTKO PAEC specific non-Gal antibody induction. Expression of porcine B4GALNT2 in pig cells and tissues was measured by qualitative and quantitative real time reverse transcriptase PCR and by Dolichos biflorus agglutinin (DBA) tissue staining.

Results

The porcine B4GALNT2 gene shares a conserved genomic organization and encodes an open reading frame with 76 and 70% amino acid identity to the human and murine B4GALNT2 genes, respectively. The B4GALNT2 gene is expressed in porcine endothelial cells and shows a broadly distributed expression pattern. Expression of porcine B4GALNT2 in human HEK cells (HEK-B4T) results in increased binding of antibody to the B4GALNT2 enzyme, and increased reactivity with anti-Sd^a and DBA. HEK-B4T cells show increased sensitivity to complement mediated lysis when challenged with serum from primates after pig to primate cardiac xenotransplantation. In GTKO and GTKO:CD55 cardiac xenotransplantation recipients there is a significant correlation between the induction of a non-Gal antibody, measured using GTKO PAECs, and the induction of antibodies which preferentially bind to HEK-B4T cells.

Conclusion

The functional isolation of the porcine B4GALNT2 gene from a PAEC expression library, the pattern of B4GALNT2 gene expression and its sensitization of HEK-B4T cells to antibody binding and complement mediated lysis indicates that the enzymatic activity of porcine B4GALNT2 produces a new immunogenic non-Gal glycan which contributes in part to the non-Gal immune response detected after pig-to-baboon cardiac xenotransplantation.

Distribution of non-gal antigens in pig cornea: relevance to corneal xenotransplantation

PURPOSE

The aim of this study was to investigate the distribution of antigens other than galactose-α-1,3-galactose (Gal) (non-Gal) recognized by human and rhesus monkey serum antibodies in the α-1,3-galactosyltransferase gene-knockout (GTKO) pig cornea.

METHODS

The distribution of non-Gal, specifically N-glycolylneuraminic acid (NeuGc), in the corneas from wild-type (WT) and GTKO pigs was identified. Corneal sections from WT and GTKO pigs were incubated with human or rhesus monkey serum to determine immunoglobulin (Ig)M and IgG binding to corneal tissue by means of fluorescent microscopy.

RESULTS

Strong expression of NeuGc was found in all layers of both WT and GTKO pig corneas. In both humans and monkeys, antibody binding (IgG > IgM) to GTKO was found to be weaker than that to entire WT pig corneas, but in both, most antibody binding, especially IgG, was to the epithelium. There was weak diffuse antibody binding, especially of IgG, to the corneal stroma, suggesting binding to antigens expressed on collagen. There was no or minimal binding of IgM/IgG to the corneal endothelium.

CONCLUSIONS

Although the cornea is avascular, antibodies in primate serum can bind to pig antigens, especially on epithelial cells and stromal collagen. Although the binding to entire GTKO corneas was weaker than that to WT corneas, deletion of the expression of NeuGc and expression of human complement-regulatory proteins in the pig cornea will be important if prolonged clinical corneal xenograft survival is to be achieved.

Lack of cross-sensitization between α-1,3-galactosyltransferase knockout porcine and allogeneic skin grafts permits serial grafting

BACKGROUND

The current standard of care for burns requiring operative treatment consists of early burn excision and autologous split-thickness skin grafting. However, in large burns, sufficient donor sites may not be available to achieve total coverage, necessitating temporary coverage with allogeneic human cadaver skin grafts or synthetic skin substitutes. A previous study from this laboratory demonstrated that skin grafts from alpha-1,3 galactosyltransferase knockout (GalT-KO) miniature swine enjoyed survival comparable to that of allogeneic skin grafts in baboons.

METHODS

In the present study, we have evaluated the immune response against sequential GalT-KO and allogeneic skin grafts to determine whether such serial grafts could extend the period of temporary wound coverage before definitive grafting with autologous skin.

RESULTS

We report that rejection of primary GalT-KO skin grafts led to an anti-xenogeneic humoral response with no evidence for sensitization to alloantigens nor acceleration of rejection of allogeneic skin grafts. Similarly, presensitization with allogeneic skin did not lead to accelerated rejection of xenogeneic skin.

CONCLUSIONS

These data suggest that GalT-KO skin grafts could provide an early first-line treatment in the management of severe burns that would not preclude subsequent use of allografts, and that serial grafting of GalT-KO skin and allogeneic skin could potentially be used to provide an extended period of temporary burn wound coverage.

Rhamnose glycoconjugates for the recruitment of endogenous anti-carbohydrate antibodies to tumor cells

Immunotherapy is a promising strategy for targeting tumors. One emerging approach is to harness the immune effector functions of natural antibodies to destroy tumor cells. Dinitrophenyl (DNP) and the galactose-α-1,3-galactose (αGal) epitope are two haptens that bind endogenous antibodies. One potential alternative is the deoxysugar L-rhamnose. We compared these candidates by using a biosensor assay to evaluate human sera for endogenous antibody concentration, antibody isotype distribution, and longevity of antibody-hapten interactions. Antibodies recognizing α-rhamnose are of equal or greater abundance and affinity as those recognizing αGal. Moreover, both rhamnose and αGal epitopes are more effective than DNP at recruiting the IgG antibody subtype. Exposure of tumor cells to rhamnose-bearing glycolipids and human serum promotes complement-mediated cytotoxicity. These data highlight the utility of α-rhamnose-containing glycoconjugates to direct the immune system to target cells.

CD55 limits sensitivity to complement-dependent cytolysis triggered by heterologous expression of α-gal xenoantigen in colon tumor cells

Engineering cancer cells to express heterologous antigen α-gal and induce the destruction of tumor cells depending on the complement cascade may be a promising strategy of tumor therapy. However, the feasibility and effect of using α-gal to induce colorectal adenocarcinoma cell line cytolysis is not yet known. In this study, we evaluated α-gal expression's ability to sensitize human colorectal adenocarcinoma cell lines to complement attack in cell lines LoVo, SW620, and Ls-174T. Nearly all α-gal-expressing LoVo and SW620 cells were killed by normal human serum (NHS), but α-gal-expressing Ls-174T cells showed no significant lysis. We analyzed the expression levels of membrane-bound complement regulatory proteins (mCRPs) on the three cell lines, and their protective role in α-gal-mediated activation of the complement. LoVo showed no expression of any of the three proteins. CD59 was strongly expressed by SW620 and Ls-174T. CD46 and CD55 varied between the two cell lines. CD46 on SW620 was only half the intensity of CD46 on Ls-174T. Ls-174T showed a notable expression of CD55, while expression of CD55 on SW620 was not detected. The sensitivity of Ls-174T expressing α-gal to NHS greatly increased following the downregulation of CD46 and CD55 with short hairpin RNA (shRNA). However, there is no increase in cell killing when CD59 expression was diminished. Our findings suggest that the use of α-gal as antigen to induce tumor cell killing may be a potential therapeutic strategy in colon cancer and that CD55 plays a primary role in conferring resistance to lysis.

Complementary innate (anti-A-specific) IgM emerging from ontogenic O-GalNAc-transferase depletion: (Innate IgM complementarity residing in ancestral antigen completeness)

The murine and the human genome have global properties in common. So the murine anti-A-specific complementary IgM and related human innate isoagglutinin represent developmental, 2-mercaptoethanol-sensitive, complement-binding glycoproteins, which do not arise from any measurable environmentally-induced or auto- immune response. The murine anti-A certainly originates from a cell surface- or cell adhesion molecule, which in the course of germ cell development becomes devoid of O-GalNAc-transferase and is released into the circulation. In human sera the enzyme occurs exclusively in those of blood group A- and AB subjects, while in group O(H) an identically encoded protein lets expect an opposite function and appears in conjunction with a complementary anti-A reactive glycoprotein. Since O-glycosylations rule the carbohydrate metabolism in growth and reproduction processes, we propose that the ancestral histo-(blood)-group A molecule arises in the course of O-GalNAc-glycosylations of glycolipids and protein envelops at progenitor cell surfaces. Germ cell development postulates embryonic stem cell fidelity, which is characterised by persistent production of α-linked O-GalNAc-glycans. They are determined by the A-allele within the human, "complete" histo (blood) group AB(O) structure that in early ontogeny is hypothesised to be synthesised independently from the final phenotype. The structure either passes "completely" through the germline, in transferase-secreting mature tissues becoming the "complete" phenotype AB, or disappears in exhaustive glycotransferase depletion from the differentiating cell surfaces and leaves behind the "incomplete" blood group O-phenotype, which has released a transferase- and O-glycan-depleted, complementary glycoprotein (IgM) into the circulation. The process implies, that in humans the different blood phenotypes evolve from a "complete" AB(O) molecular complex in a distinct enzymatic and/or complement cascade suggesting O-glycanase involvements. While the murine and human oocyte zona pellucida express identical O-glycans, the human phenotype O might be explainable by the kinetics of the murine ovarian O-GalNAc glycan synthesis and the complementary anti-A released in parallel. The maturing murine ovary may provide insight into encoding of the physiologically superior α-linked GalNAc ancestral epitope that becomes essential in reproduction as well as in tissue renewal events. According to recent reports, O-GalNAc-transferase-determined blood group A suggests superiority in human female fertility and was called even "protective". So the minor fertility of blood-group-O females may reside in a critical timing in developmental shifting of enzyme functions affecting the formation of GalNAc-determined hormone receptors on the way to maturation. Experiments that had inserted an oocyte genome into a somatic one to generate pluripotent stem cells, might elucidate a developmental dilemma by testing oocytes from different blood group AB donors donors. Perhaps they will unmask the molecular basis of an evolutionary trend, while stem cell generation itself capitalises on the enzymatically-advantaged, lineage-maintaining (histo) blood group A-allele, which guaranties ancestral functional completeness.

Preliminary experience with porcine intestinal submucosa (CorMatrix) for valve reconstruction in congenital heart disease: histologic evaluation of explanted valves

OBJECTIVE

We compared the histologic findings in explanted CorMatrix (9 patients) and autologous pericardium (9 patients) used for valvuloplasty of the aortic (7 patients) and/or mitral (11 patients) valve in patients with congenital heart defects.

METHODS

We used standard tissue stains and immunohistochemistry to identify the inflammatory cell type.

RESULTS

CorMatrix was associated with an intense inflammatory response in the surrounding native tissue, extending into CorMatrix in 8 of 9 cases, continuing to the longest follow-up point (9 months). The typical response included macrophages and giant cells in contact with the material, surrounded by lymphocytes, macrophages, plasma cells, and eosinophils. The thickness of the residual CorMatrix material was 280 to 300 μm, similar to the nominal thickness at implantation and unrelated to the implantation duration. Only at the longest follow-up interval was any significant resorption of CorMatrix material evident. A neointima had formed on the surface of CorMatrix, increasing in thickness with the period in situ. Mild cellular infiltration of CorMatrix was noted in all cases; however, in no case, did it appear that CorMatrix was being remodeled into tissue resembling a 3-layered native valve. In contrast, a near absence of any inflammatory reaction was seen and no eosinophilia associated with autologous pericardium was present, irrespective of the duration in situ. Furthermore, we observed more tissue infiltration, remodeling, vascularization, and neointima formation with autologous pericardium.

CONCLUSIONS

Although CorMatrix used for valve repair induced an intense inflammatory response, little or no remodeling to form tissue resembling a 3-layered native valve was seen at ≤9 months after implantation.

Kidney xenotransplantation

Xenotransplantation using pigs as donors offers the possibility of eliminating the chronic shortage of donor kidneys, but there are several obstacles to be overcome before this goal can be achieved. Preclinical studies have shown that, while porcine renal xenografts are broadly compatible physiologically, they provoke a complex rejection process involving preformed and elicited antibodies, heightened innate immune cell reactivity, dysregulated coagulation, and a strong T cell-mediated adaptive response. Furthermore, the susceptibility of the xenograft to proinflammatory and procoagulant stimuli is probably increased by cross-species molecular defects in regulatory pathways. To balance these disadvantages, xenotransplantation has at its disposal a unique tool to address particular rejection mechanisms and incompatibilities: genetic modification of the donor. This review focuses on the pathophysiology of porcine renal xenograft rejection, and on the significant genetic, pharmacological, and technical progress that has been made to prolong xenograft survival.

New concepts of immune modulation in xenotransplantation

The shortage of human organs for transplantation has focused research on the possibility of transplanting pig organs into humans. Many factors contribute to the failure of a pig organ graft in a primate. A rapid innate immune response (natural anti-pig antibody, complement activation, and an innate cellular response; e.g., neutrophils, monocytes, macrophages, and natural killer cells) is followed by an adaptive immune response, although T-cell infiltration of the graft has rarely been reported. Other factors (e.g., coagulation dysregulation and inflammation) appear to play a significantly greater role than in allotransplantation. The immune responses to a pig xenograft cannot therefore be controlled simply by suppression of T-cell activity. Before xenotransplantation can be introduced successfully into the clinic, the problems of the innate, coagulopathic, and inflammatory responses will have to be overcome, most likely by the transplantation of organs from genetically engineered pigs. Many of the genetic manipulations aimed at protecting against these responses also reduce the adaptive response. The T-cell and elicited antibody responses can be prevented by the biological and/or pharmacologic agents currently available, in particular, by costimulation blockade-based regimens. The exogenous immunosuppressive regimen may be significantly reduced by the presence of a graft from a pig transgenic for a mutant (human) class II transactivator gene, resulting in down-regulation of swine leukocyte antigen class II expression, or from a pig with "local" vascular endothelial cell expression of an immunosuppressive gene (e.g., CTLA4-Ig). The immunomodulatory efficacy of regulatory T cells or mesenchymal stromal cells has been demonstrated in vitro but not yet in vivo.

Anti-Gal: an abundant human natural antibody of multiple pathogeneses and clinical benefits

Anti-Gal is the most abundant natural antibody in humans, constituting ~ 1% of immunoglobulins. Anti-Gal is naturally produced also in apes and Old World monkeys. The ligand of anti-Gal is a carbohydrate antigen called the 'α-gal epitope' with the structure Galα1-3Galβ1-4GlcNAc-R. The α-gal epitope is present as a major carbohydrate antigen in non-primate mammals, prosimians and New World monkeys. Anti-Gal can contributes to several immunological pathogeneses. Anti-Gal IgE produced in some individuals causes allergies to meat and to the therapeutic monoclonal antibody cetuximab, all presenting α-gal epitopes. Aberrant expression of the α-gal epitope or of antigens mimicking it in humans may result in autoimmune processes, as in Graves' disease. α-Gal epitopes produced by Trypanosoma cruzi interact with anti-Gal and induce 'autoimmune like' inflammatory reactions in Chagas' disease. Anti-Gal IgM and IgG further mediate rejection of xenografts expressing α-gal epitopes. Because of its abundance, anti-Gal may be exploited for various clinical uses. It increases immunogenicity of microbial vaccines (e.g. influenza vaccine) presenting α-gal epitopes by targeting them for effective uptake by antigen-presenting cells. Tumour lesions are converted into vaccines against autologous tumour-associated antigens by intra-tumoral injection of α-gal glycolipids, which insert into tumour cell membranes. Anti-Gal binding to α-gal epitopes on tumour cells targets them for uptake by antigen-presenting cells. Accelerated wound healing is achieved by application of α-gal nanoparticles, which bind anti-Gal, activate complement, and recruit and activate macrophages that induce tissue regeneration. This therapy may be of further significance in regeneration of internally injured tissues such as ischaemic myocardium and injured nerves.

α1,3Galactosyltransferase knockout pigs produce the natural anti-Gal antibody and simulate the evolutionary appearance of this antibody in primates

BACKGROUND

Anti-Gal is the most abundant natural antibody in humans and Old World primates (apes and Old World monkeys). Its ligand, the α-gal epitope (Galα1-3Galβ1-4GlcNAc-R), is abundant in nonprimate mammals, prosimians and New World monkeys whereas it is absent in humans and Old World primates as a result of inactivation of the α1,3galactosyltransferase (α1,3GT) gene in ancestral Old World primates, as recent as 20-28 million years ago. Since anti-Gal has been a "forbidden" autoantibody for >140 million years of evolution in mammals producing α-gal epitopes it was of interest to determine whether ancestral Old World primates could produce anti-Gal once α-gal epitopes were eliminated, i.e. did they carry anti-Gal encoding immunoglobulin genes, or did evolutionary selection eliminate these genes that may be detrimental in mammals synthesizing α-gal epitopes. This question was studied by evaluating anti-Gal prodution in α1,3GT knockout (GT-KO) pigs recently generated from wild-type pigs in which the α-gal epitope is a major self-antigen.

METHODS

Anti-Gal antibody activity in pig sera was assessed by ELISA, flow cytometry and complement mediated cytolysis and compared to that in human sera.

RESULTS

The study demonstrates abundant production of the natural anti-Gal antibody in GT-KO pigs at titers even higher than in humans. The fine specificity of GT-KO pig anti-Gal is identical to that of human anti-Gal.

CONCLUSIONS

Pigs and probably other mammals producing α-gal epitopes carry immunoglobulin genes encoding anti-Gal as an autoantibody. Once the α-gal epitope is eliminated in GT-KO pigs, they produce anti-Gal. These findings strongly suggest that similar to GT-KO pigs, inactivation of the α1,3GT gene in ancestral Old World primates enabled the immediate production of anti-Gal, possibly as a protective antibody against detrimental microbial agents carrying α-gal epitopes.

Human T cell activation results in extracellular signal-regulated kinase (ERK)-calcineurin-dependent exposure of Tn antigen on the cell surface and binding of the macrophage galactose-type lectin (MGL)

The C-type lectin macrophage galactose-type lectin (MGL) exerts an immunosuppressive role reflected by its interaction with terminal GalNAc moieties, such as the Tn antigen, on CD45 of effector T cells, thereby down-regulating T cell receptor signaling, cytokine responses, and induction of T cell death. Here, we provide evidence for the pathways that control the specific expression of GalNAc moieties on human CD4(+) T cells. GalNAc epitopes were readily detectable on the cell surface after T cell activation and required de novo protein synthesis. Expression of GalNAc-containing MGL ligands was completely dependent on PKC and did not involve NF-κB. Instead, activation of the downstream ERK MAPK pathway led to decreased mRNA levels and activity of the core 1 β3GalT enzyme and its chaperone Cosmc, favoring the expression of Tn antigen. In conclusion, expression of GalNAc moieties mirrors the T cell activation status, and thus only highly stimulated T cells are prone to the suppressive action of MGL.

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.

Discovery of the natural anti-Gal antibody and its past and future relevance to medicine

This is a personal account of the discovery of the natural anti-Gal antibody, the most abundant natural antibody in humans, the reciprocal distribution of this antibody and its ligand the α-gal epitope in mammals and the immunological barrier this antibody has formed in porcine to human xenotransplantation. This barrier has been overcome in the recent decade with the generation of α1,3-galactosyltransferase gene-knockout pigs. However, anti-Gal continues to be relevant in medicine as it can be harnessed for various therapeutic effects. Anti-Gal converts tumor lesions injected with α-gal glycolipids into vaccines that elicit a protective anti-tumor immune response by in situ targeting of tumor cells for uptake by antigen-presenting cells. This antibody further accelerates wound and burn healing by interaction with α-gal nanoparticles applied to injured areas and induction of rapid recruitment and activation of macrophages. Anti-Gal/α-gal nanoparticle immune complexes may further induce rapid recruitment and activation of macrophages in ischemic myocardium and injured nerves, thereby inducing tissue regeneration and prevention of fibrosis.

Distribution of the Galβ1-4Gal epitope among birds: species-specific loss of the glycan structure in chicken and its relatives

The Galβ1-4Gal epitope is rarely found in mammals, and the natural antibody against Galβ1-4Gal is rich in human. In contrast, we have previously demonstrated the presence of Galβ1-4Gal in pigeon and ostrich, and the absence of this epitope in chicken. Here, to further investigate the expression of this glycan among birds, egg white glycoproteins and egg yolk IgG from nine species of birds, namely, chicken, duck, emu, guineafowl, ostrich, peafowl, pigeon, quail, and turkey, were analyzed by western blot using an anti-(Galβ1-4Gal) antibody. The results indicated that some egg white glycoproteins from emu, ostrich, and quail, and heavy chains of IgG from all of the birds, except chicken and quail, were stained with the antibody. The presence of Galβ1-4Gal on N-glycans of IgGs from guineafowl, peafowl, and turkey were confirmed by mass spectrometry (MS), MS/MS, and MS(n) analyses. In quail, the presence of Galβ1-4Gal was confirmed by detecting the activities of UDP-galactose: β-galactoside β1,4-galactosyltransferase (β4GalT(Gal)) in various tissues, and by detecting Galβ1-4Gal by western blotting. In contrast, bamboo partridge, which is a close relative of chicken, did not show any detectable activities of β4GalT(Gal) or Galβ1-4Gal on glycoproteins. Because quail, peafowl, turkey, chicken, and bamboo partridge belong to the same family, i.e., Phasianidae, expression of Galβ1-4Gal was most likely differentiated within this family. Considering that Galβ1-4Gal is also expressed in ostrich, emu, and pigeon, which are phylogenetically distant relatives within modern birds, Galβ1-4Gal expression appears to be widely distributed among birds, but might have been abolished in the ancestors of chicken and bamboo partridge.

Lectin glycoprofiling of recombinant therapeutic interleukin-7

Lectins array is a powerfull and complementary method of glycans analysis allowing fast identification of specific motifs on molecules or cells. This technology is of increased interest for the development of therapeutic recombinant glycoproteins and particularly relevant for a first study of lot-to-lot comparison, or detection of unwanted glycans. In this chapter, we describe a lectin array-type method specifically designed for the study of recombinant therapeutic interleukin-7 (rhIL-7). This specific method allows the analysis of the glycans motifs, the distribution of the glycoforms population, and the detection of potential immunogen glycans in rhIL-7 purified CHO-produced batches.

Immunotherapy updates in pancreatic cancer: are we there yet?

Pancreatic cancer is a lethal disease and remains one of the most resistant cancers to traditional therapies. Historically, chemotherapy or radiotherapy did not provide meaningful survival benefit in advanced pancreatic cancer. Gemcitabine and recently FOLFIRINOX (5-flourouracil, leucovorin, oxaliplatin and irinotecan) have provided some limited survival advantage in advanced pancreatic cancer. Targeted agents in combination with gemcitabine had not shown significant improvement in the survival. Current therapies for pancreatic cancer have their limitations; thus, we are in dire need of newer treatment options. Immunotherapy in pancreatic cancer works by recruiting and activating T cells that recognize tumor-specific antigens which is a different mechanism compared with chemotherapy and radiotherapy. Preclinical models have shown that immunotherapy and targeted therapies like vascular endothelial growth factor and epidermal growth factor inhibitors work synergistically. Hence, new immunotherapy and targeted therapies represent a viable option for pancreatic cancer. In this article, we review the vaccine therapy for pancreatic cancer.

Changes of the Structural and Biomechanical Properties of the Bovine Pericardium after the Removal of α-Gal Epitopes by Decellularization and α-Galactosidase Treatment

Background

Bovine pericardium is one of the most widely used materials in bioprosthetic heart valves. Immunologic responses have been implicated as potential causes of limited durability of xenogenic valves. This study aimed to determine the effectiveness of decellularization and α-galactosidase (α-gal) to remove major xenoreactive antigens from xenogenic tissues.

Materials and Methods

Recombinant Bacteroides thetaiotaomicron (B. thetaiotaomicron) α-gal or decellularization, or both were used to remove α-gal from bovine pericardium. It was confirmed by α-gal-bovine serum albumin-based enzyme-linked immunosorbent assay (ELISA), high-performance anion exchange chromatography, flow cytometry, 3,3'-diaminobenzidine-staining, and lectin-based ELISA. The mechanical properties of bovine pericardium after decellularization or α-gal treatment were investigated by tests of tensile-strength, permeability, and compliance. Collagen fiber rearrangement was also evaluated by a 20,000× transmission electron microscope (TEM).

Results

Recombinant B. thetaiotaomicron α-gal could effectively remove α-gal from bovine pericardium B. thetaiotaomicron (0.1 U/mL, pH 7.2) while recombinant human α-gal removed it recombinant human α-gal (10 U/mL, pH 5.0). There was no difference in the mechanical properties of fresh and recombinant α-gal-treated bovine pericardium. Furthermore, the TEM findings demonstrated that recombinant α-gal made no difference in the arrangement of collagen fiber bundles with decellularization.

Conclusion

Recombinant B. thetaiotaomicron α-gal effectively removed α-gal from bovine pericardium with a small amount under physiological conditions compared to human recombinant α-gal, which may alleviate the harmful xenoreactive immunologic responses of α-gal. Recombinant α-gal treatment had no adverse effects on the mechanical properties of bovine pericardium.

Histologic Characteristics and Mechanical Properties of Bovine Pericardium Treated with Decellularization and α-Galactosidase: A Comparative Study

Background

Bioprostheses for cardiovascular surgery have limitations in their use following as calicification. α-galactosidase epitope is known as a stimulant of immune response and then shows a progressing calcification. The objective of this study was to evaluate histologic characteristics and mechanical properties of decellularization and treated with α-galactosidase.

Materials and Methods

Bovine pericardial tissues were allocated into three groups: fixation only with glutaraldehyde, decellularization with sodium dodesyl sulfate and decellularization plus treatment with α-galactosidase. We confirmed immunohistological characteristics and mechanical properties as fatigue test, permeability test, compliance test, tensile strength (strain) test and thermal stability test.

Results

Decellularization and elimination of α-gal were confirmed through immunohistologic findings. Decellularization had decreased mechanical properties compared to fixation only group in permeability (before fatigue test p=0.02, after fatigue test p=0.034), compliance (after fatigue test p=0.041), and tensile strength test (p=0.00). The group of decellularization plus treatment with α-galactosidase had less desirable mechanical properties than the group of decellularization in concerns of permeability (before fatigue test p=0.043) and strain test (p=0.001).

Conclusion

Favorable decellularization and elimination of α-gal were obtained in this study through immunohistologic findings. However, those treatment including decellularization and elimination of α-gal implied the decreased mechanical properties in specific ways. We need more study to complete appropriate ioprosthesis with decellularization and elimination of α-gal including favorable mechanical properties too.

Porcine sialoadhesin: a newly identified xenogeneic innate immune receptor

Extracorporeal porcine liver perfusion is being developed as a bridge to liver allotransplantation for patients with fulminant hepatic failure. This strategy is limited by porcine Kupffer cell destruction of human erythrocytes, mediated by lectin binding of a sialic acid motif in the absence of antibody and complement. Sialoadhesin, a macrophage restricted lectin that binds sialic acid, was originally described as a sheep erythrocyte binding receptor. Given similarities between sialoadhesin and the unidentified macrophage lectin in our model, we hypothesized porcine sialoadhesin contributed to recognition of human erythrocytes. Two additional types of macrophages were identified to bind human erythrocytes-spleen and alveolar. Expression of sialoadhesin was confirmed by immunofluorescence in porcine tissues and by flow cytometry on primary macrophages. A stable transgenic cell line expressing porcine sialoadhesin (pSn CHO) bound human erythrocytes, while a sialoadhesin mutant cell line did not. Porcine macrophage and pSn CHO recognition of human erythrocytes was inhibited approximately 90% by an antiporcine sialoadhesin monoclonal antibody and by human erythrocyte glycoproteins. Furthermore, this binding was substantially reduced by sialidase treatment of erythrocytes. These data support the hypothesis that porcine sialoadhesin is a xenogeneic receptor that mediates porcine macrophage binding of human erythrocytes in a sialic acid-dependent manner.

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.

Anti-gal antibodies in α1,3-galactosyltransferase gene-knockout pigs

Serum anti-galactose-α1,3-galactose (Gal) IgM and IgG antibody levels were measured by ELISA in α1,3-galactosyltransferase gene-knockout (GTKO) pigs (78 estimations in 47 pigs). A low level of anti-Gal IgM was present soon after birth, and rose to a peak at 4-6 m, which was maintained thereafter even in the oldest pigs tested (at >2 yr). Anti-Gal IgG was also present at birth, peaked at 3 m, and after 6 m steadily decreased until almost undetectable at 20 m. No differences in this pattern were seen between pigs of different gender. Total IgM followed a similar pattern as anti-Gal IgM, but total IgG did not decrease after 6m. The data provide useful baseline data for future experimental studies in GTKO pigs, e.g., relating to the antibody response to WT pig allografts.