Characterization of immunogenic Neu5Gc in bioprosthetic heart valves

Calcification of surgical aortic bioprostheses and its impact on clinical outcome

AIMS

Aortic valve calcification (AVC) of surgical valve bioprostheses (BPs) has been poorly explored. We aimed to evaluate in vivo and ex vivo BP AVCs and its prognosis value.

METHODS AND RESULTS

Between 2011 and 2019, AVC was assessed using in vivo computed tomography (CT) in 361 patients who had undergone surgical valve replacement 6.4 ± 4.3 years earlier. Ex vivo CT scans were performed for 37 explanted BPs. The in vivo CT scans were interpretable for 342 patients (19 patients [5.2%] were excluded). These patients were 77.2 ± 9.1 years old, and 64.3% were male. Mean in vivo AVC was 307 ± 500 Agatston units (AU). The AVC was 562 ± 570 AU for the 183 (53.5%) patients with structural valve degeneration (SVD) and 13 ± 43 AU for those without SVD (P < 0.0001). In vivo and ex vivo AVCs were strongly correlated (r = 0.88, P < 0.0001). An in vivo AVC > 100 AU (n = 147, 43%) had a specificity of 96% for diagnosing Stage 2-3 SVD (area under the curve = 0.92). Patients with AVC > 100 AU had a worse outcome compared with those with AVC ≤ 100 AU (n = 195). In multivariable analysis, AVC was a predictor of overall mortality (hazard ratio [HR] and 95% confidence interval = 1.16 [1.04-1.29]; P = 0.006), cardiovascular mortality (HR = 1.22 [1.04-1.43]; P = 0.013), cardiovascular events (HR = 1.28 [1.16-1.41]; P < 0.0001), and re-intervention (HR = 1.15 [1.06-1.25]; P < 0.0001). After adjustment for Stage 2-3 SVD diagnosis, AVC remained a predictor of overall mortality (HR = 1.20 [1.04-1.39]; P = 0.015) and cardiovascular events (HR = 1.25 [1.09-1.43]; P = 0.001).

CONCLUSION

CT scan is a reliable tool to assess BP leaflet calcification. An AVC > 100 AU is tightly associated with SVD and it is a strong predictor of overall mortality and cardiovascular events.

Serum antibody screening using glycan arrays

Humans and other animals produce a diverse collection of antibodies, many of which bind to carbohydrate chains, referred to as glycans. These anti-glycan antibodies are a critical part of our immune systems' defenses. Whether induced by vaccination or natural exposure to a pathogen, anti-glycan antibodies can provide protection against infections and cancers. Alternatively, when an immune response goes awry, antibodies that recognize self-glycans can mediate autoimmune diseases. In any case, serum anti-glycan antibodies provide a rich source of information about a patient's overall health, vaccination history, and disease status. Glycan microarrays provide a high-throughput platform to rapidly interrogate serum anti-glycan antibodies and identify new biomarkers for a variety of conditions. In addition, glycan microarrays enable detailed analysis of the immune system's response to vaccines and other treatments. Herein we review applications of glycan microarray technology for serum anti-glycan antibody profiling.

Comparison of sialylated and fucosylated N-glycans attached to Asn 6 and Asn 41 with different roles in hyaluronan and proteoglycan link protein 1 (HAPLN1)

Hyaluronan and proteoglycan link protein 1 (HAPLN1) is an extracellular matrix protein stabilizing interactions between hyaluronan and proteoglycan. Although HAPLN1 is being investigated for various biological roles, its N-glycosylation is poorly understood. In this study, the structure of N-glycopeptides of trypsin-treated recombinant human HAPLN1 (rhHAPLN1) expressed from CHO cells were identified by nano-liquid chromatography-tandem mass spectrometry. A total of 66 N-glycopeptides were obtained, including 16 and 12 N-glycans at sites Asn 6 (located in the N-terminal region) and Asn 41 (located in the Ig-like domain, which interacts with proteoglycan), respectively. The quantities (%) of each N-glycan relative to the totals (100 %) at each site were calculated. Tri- and tetra-sialylation (to resist proteolysis and extend half-life) were more abundant at Asn 6, and di- (core- and terminal-) fucosylation (to increase binding affinity and stability) and sialyl-Lewis X/a epitope (a major ligand for E-selectin) were more abundant at Asn 41. These results indicate that N-glycans attached to Asn 6 (protecting HAPLN1) and Asn 41 (supporting molecular interactions) play different roles in HAPLN1. This is the first study of site-specific N-glycosylation in rhHAPLN1, which will be useful for understanding its molecular interactions in the extracellular matrix.

Embedding and Backscattered Scanning Electron Microscopy (EM-BSEM) Is Preferential over Immunophenotyping in Relation to Bioprosthetic Heart Valves

Hitherto, calcified aortic valves (AVs) and failing bioprosthetic heart valves (BHVs) have been investigated by similar approaches, mostly limited to various immunostaining techniques. Having employed multiple immunostaining combinations, we demonstrated that AVs retain a well-defined cellular hierarchy even at severe stenosis, whilst BHVs were notable for the stochastic degradation of the extracellular matrix (ECM) and aggressive infiltration by ECM-digesting macrophages. Leukocytes (CD45+) comprised ≤10% cells in the AVs but were the predominant cell lineage in BHVs (≥80% cells). Albeit cells with uncertain immunophenotype were rarely encountered in the AVs (≤5% cells), they were commonly found in BHVs (≥80% cells). Whilst cell conversions in the AVs were limited to the endothelial-to-mesenchymal transition (represented by CD31+α-SMA+ cells) and the formation of endothelial-like (CD31+CD68+) cells at the AV surface, BHVs harboured numerous macrophages with a transitional phenotype, mostly CD45+CD31+, CD45+α-SMA+, and CD68+α-SMA+. In contrast to immunostaining, which was unable to predict cell function in the BHVs, our whole-specimen, nondestructive electron microscopy approach (EM-BSEM) was able to distinguish between quiescent and matrix-degrading macrophages, foam cells, and multinucleated giant cells to conduct the ultrastructural analysis of organelles and the ECM, and to preserve tissue integrity. Hence, we suggest EM-BSEM as a technique of choice for studying the cellular landscape of BHVs.

Differential Immune Response to Bioprosthetic Heart Valve Tissues in the α1,3Galactosyltransferase-Knockout Mouse Model

Structural valve deterioration (SVD) of bioprosthetic heart valves (BHVs) has great clinical and economic consequences. Notably, immunity against BHVs plays a major role in SVD, especially when implanted in young and middle-aged patients. However, the complex pathogenesis of SVD remains to be fully characterized, and analyses of commercial BHVs in standardized-preclinical settings are needed for further advancement. Here, we studied the immune response to commercial BHV tissue of bovine, porcine, and equine origin after subcutaneous implantation into adult α1,3-galactosyltransferase-knockout (Gal KO) mice. The levels of serum anti-galactose α1,3-galactose (Gal) and -non-Gal IgM and IgG antibodies were determined up to 2 months post-implantation. Based on histological analyses, all BHV tissues studied triggered distinct infiltrating cellular immune responses that related to tissue degeneration. Increased anti-Gal antibody levels were found in serum after ATS 3f and Freedom/Solo implantation but not for Crown or Hancock II grafts. Overall, there were no correlations between cellular-immunity scores and post-implantation antibodies, suggesting these are independent factors differentially affecting the outcome of distinct commercial BHVs. These findings provide further insights into the understanding of SVD immunopathogenesis and highlight the need to evaluate immune responses as a confounding factor.

Genetic knockout of porcine GGTA1 or CMAH/GGTA1 is associated with the emergence of neo-glycans

BACKGROUND

Pig-derived tissues could overcome the shortage of human donor organs in transplantation. However, the glycans with terminal α-Gal and Neu5Gc, which are synthesized by enzymes, encoded by the genes GGTA1 and CMAH, are known to play a major role in immunogenicity of porcine tissue, ultimately leading to xenograft rejection.

METHODS

The N-glycome and glycosphingolipidome of native and decellularized porcine pericardia from wildtype (WT), GGTA1-KO and GGTA1/CMAH-KO pigs were analyzed by multiplexed capillary gel electrophoresis coupled to laser-induced fluorescence detection.

RESULTS

We identified biantennary and core-fucosylated N-glycans terminating with immunogenic α-Gal- and α-Gal-/Neu5Gc-epitopes on pericardium of WT pigs that were absent in GGTA1 and GGTA1/CMAH-KO pigs, respectively. Levels of N-glycans terminating with galactose bound in β(1-4)-linkage to N-acetylglucosamine and their derivatives elongated by Neu5Ac were increased in both KO groups. N-glycans capped with Neu5Gc were increased in GGTA1-KO pigs compared to WT, but were not detected in GGTA1/CMAH-KO pigs. Similarly, the ganglioside Neu5Gc-GM3 was found in WT and GGTA1-KO but not in GGTA1/CMAH-KO pigs. The applied detergent based decellularization efficiently removed GSL glycans.

CONCLUSION

Genetic deletion of GGTA1 or GGTA1/CMAH removes specific epitopes providing a more human-like glycosylation pattern, but at the same time changes distribution and levels of other porcine glycans that are potentially immunogenic.

An In Silico Functional Analysis of Non-Synonymous Single-Nucleotide Polymorphisms of Bovine CMAH Gene and Potential Implication in Pathogenesis

The sugar molecule N-glycolylneuraminic acid (Neu5Gc) is one of the most common sialic acids discovered in mammals. Cytidine monophospho-N-acetylneuraminic acid hydroxylase (CMAH) catalyses the conversion of N-acetylneuraminic acid (Neu5Ac) to Neu5Gc, and it is encoded by the CMAH gene. On the one hand, food metabolic incorporation of Neu5Gc has been linked to specific human diseases. On the other hand, Neu5Gc has been shown to be highly preferred by some pathogens linked to certain bovine diseases. We used various computational techniques to perform an in silico functional analysis of five non-synonymous single-nucleotide polymorphisms (nsSNPs) of the bovine CMAH (bCMAH) gene identified from the 1000 Bull Genomes sequence data. The c.1271C>T (P424L) nsSNP was predicted to be pathogenic based on the consensus result from different computational tools. The nsSNP was also predicted to be critical based on sequence conservation, stability, and post-translational modification site analysis. According to the molecular dynamic simulation and stability analysis, all variations promoted stability of the bCMAH protein, but mutation A210S significantly promoted CMAH stability. In conclusion, c.1271C>T (P424L) is expected to be the most harmful nsSNP among the five detected nsSNPs based on the overall studies. This research could pave the way for more research associating pathogenic nsSNPs in the bCMAH gene with diseases.

Immunogenicity of decellularized extracellular matrix scaffolds: a bottleneck in tissue engineering and regenerative medicine

Tissue-engineered decellularized extracellular matrix (ECM) scaffolds hold great potential to address the donor shortage as well as immunologic rejection attributed to cells in conventional tissue/organ transplantation. Decellularization, as the key process in manufacturing ECM scaffolds, removes immunogen cell materials and significantly alleviates the immunogenicity and biocompatibility of derived scaffolds. However, the application of these bioscaffolds still confronts major immunologic challenges. This review discusses the interplay between damage-associated molecular patterns (DAMPs) and antigens as the main inducers of innate and adaptive immunity to aid in manufacturing biocompatible grafts with desirable immunogenicity. It also appraises the impact of various decellularization methodologies (i.e., apoptosis-assisted techniques) on provoking immune responses that participate in rejecting allogenic and xenogeneic decellularized scaffolds. In addition, the key research findings regarding the contribution of ECM alterations, cytotoxicity issues, graft sourcing, and implantation site to the immunogenicity of decellularized tissues/organs are comprehensively considered. Finally, it discusses practical solutions to overcome immunogenicity, including antigen masking by crosslinking, sterilization optimization, and antigen removal techniques such as selective antigen removal and sequential antigen solubilization.

Absorption and Transport Mechanism of Red Meat-Derived N-glycolylneuraminic Acid and Its Damage to Intestinal Barrier Function through the NF-κB Signaling Pathway

N-glycolylneuraminic acid (Neu5Gc) is a specific factor in red meat that induces intestinal disease. Our aim was to investigate the effect of Neu5Gc on the intestinal barrier as well as its mechanism of endocytosis and exocytosis. Ten specific inhibitors were used to explore the mechanism of Neu5Gc endocytosis and exocytosis by Caco-2 cells. Amiloride hydrochloride and cytochalasin D had the strongest inhibitory effect on the endocytosis of Neu5Gc. Sodium azide, dynasore, chlorpromazine hydrochloride, and nystatin also inhibited Neu5Gc endocytosis. Dynasore exhibited a stronger inhibitory effect than that of chlorpromazine hydrochloride or nystatin alone. Exocytosis inhibitors, including nocodazole, brefeldin A, monensin, and bafilomycin A, inhibited the transmembrane transport of Neu5Gc. Monensin promoted the exocytosis of Neu5Gc from Caco-2 cells. In another experiment, we observed no significant inhibitory effects of monensin and brefeldin A. Dietary concentrations of Neu5Gc induced prominent damage to intestinal tight junction proteins zonula occludens-1 (ZO-1), occludin, and claudin-1 and promoted the phosphorylation of IκB-α and P65 to activate the canonical Nuclear Factor kappa-B (NF-κB) pathway. Neu5Gc increased the RNA levels of pro-inflammatory factors IL-1β, IL-6, and TNF-α and inhibited those of anti-inflammatory factors TGF-β and IL-10. BAY, an NF-κB signaling pathway inhibitor, attenuated these changes. Reductions in the levels of ZO-1, occludin, and claudin-1 were recovered in response to BAY. Our data reveal the endocytosis and exocytosis mechanism of Neu5Gc and prove that Neu5Gc can activate the canonical NF-κB signaling pathway, regulate the transcription of inflammatory factors, thereby damaging intestinal barrier function.

Will previous palliative surgery for congenital heart disease be detrimental to subsequent pig heart xenotransplantation?

INTRODUCTION

Pig heart xenotransplantation might act as a bridge in infants with complex congenital heart disease (CHD) until a deceased human donor heart becomes available. Infants develop antibodies to wild-type (WT, i.e., genetically-unmodified) pig cells, but rarely to cells in which expression of the 3 known carbohydrate xenoantigens has been deleted by genetic engineering (triple-knockout [TKO] pigs). Our objective was to test sera from children who had undergone palliative surgery for complex CHD (and who potentially might need a pig heart transplant) to determine whether they had serum cytotoxic antibodies against TKO pig cells.

METHODS

Sera were obtained from children with CHD undergoing Glenn or Fontan operation (n = 14) and healthy adults (n = 8, as controls). All of the children had complex CHD and had undergone some form of cardiac surgery. Seven had received human blood transfusions and 3 bovine pericardial patch grafts. IgM and IgG binding to WT and TKO pig red blood cells (RBCs) and peripheral blood mononuclear cells (PBMCs) were measured by flow cytometry, and killing of PBMCs by a complement-dependent cytotoxicity assay.

RESULTS

Almost all children and adults demonstrated relatively high IgM/IgG binding to WT RBCs, but minimal binding to TKO RBCs (p < 0.0001 vs WT), although IgG binding was greater in children than adults (p < 0.01). All sera showed IgM/IgG binding to WT PBMCs, but this was much lower to TKO PBMCs (p < 0.0001 vs WT) and was greater in children than in adults (p < 0.05). Binding to both WT and TKO PBMCs was greater than to RBCs. Mean serum cytotoxicity to WT PBMCs was 90% in both children and adults, whereas to TKO PBMCs it was only 20% and < 5%, respectively. The sera from 6/14 (43%) children were cytotoxic to TKO PBMCs, but no adult sera were cytotoxic.

CONCLUSIONS

Although no children had high levels of antibodies to TKO RBCs, 13/14 demonstrated antibodies to TKO PBMCs, in 6 of these showed mild cytotoxicity. As no adults had cytotoxic antibodies to TKO PBMCs, the higher incidence in children may possibly be associated with their exposure to previous cardiac surgery and biological products. However, the numbers were too small to determine the influence of such past exposures. Before considering pig heart xenotransplantation for children with CHD, testing for antibody binding may be warranted.

Immune disguise: the mechanisms of Neu5Gc inducing autoimmune and transplant rejection

Organ (stem cell) transplantation is the most effective treatment for advanced organ failure. Neu5Gc (N-hydroxyacetylneuraminic acid) is a pathogenic non-human sialic acid, which is very similar to the molecular structure of Neu5Ac (N-acetylneuraminic acid) in human body. Neu5Gc has the function of "immune disguise", which is the main obstacle to transplantation. Gene knockout such as cytidine monophosphate-N-acetylneuraminidase (CMAH) reduces donor antigenicity, making xenotransplantation from fiction to reality. Exploring the immune disguise event in this emerging field has become a hot topic in the research of transplantation immune tolerance mechanism.

The hybrid crosslinking method improved the stability and anti-calcification properties of the bioprosthetic heart valves

The bioprosthetic heart valves (BHVs) are the best option for the treatment of valvular heart disease. Glutaraldehyde (Glut) is commonly used as the golden standard reagent for the crosslinking of BHVs. However, the obvious defects of Glut, including residual aldehyde toxicity, degradation and calcification, increase the probability of valve failure in vivo and motivated the exploration of alternatives. Thus, the aim of this study is to develop a non-glutaraldehyde hybrid cross-linking method composed of Neomycin Trisulfate, Polyethylene glycol diglycidyl ether and Tannic acid as a substitute for Glut, which was proven to reduce calcification, degradation, inflammation of the biomaterial. Evaluations of the crosslinked bovine pericardial included histological and ultrastructural characterization, biomechanical performance, biocompatibility and structural stability test, and in vivo anti-inflammation and anti-calcification assay by subcutaneous implantation in juvenile Sprague Dawley rats. The results revealed that the hybrid crosslinked bovine pericardial were superior to Glut crosslinked biomaterial in terms of better hydrophilicity, thermodynamics stability, hemocompatibility and cytocompatibility, higher Young’s Modulus, better stability and resistance to enzymatic hydrolysis, and lower inflammation, degradation and calcification levels in subcutaneous implants. Considering all above performances, it indicates that the hybrid cross-linking method is appropriate to replace Glut as the method for BHV preparation, and particularly this hybrid crosslinked biomaterials may be a promising candidate for next-generation BHVs.

Mechanisms and Drug Therapies of Bioprosthetic Heart Valve Calcification

Valve replacement is the main therapy for valvular heart disease, in which a diseased valve is replaced by mechanical heart valve (MHV) or bioprosthetic heart valve (BHV). Since the 2000s, BHV surpassed MHV as the leading option of prosthetic valve substitute because of its excellent hemocompatible and hemodynamic properties. However, BHV is apt to structural valve degeneration (SVD), resulting in limited durability. Calcification is the most frequent presentation and the core pathophysiological process of SVD. Understanding the basic mechanisms of BHV calcification is an essential prerequisite to address the limited-durability issues. In this narrative review, we provide a comprehensive summary about the mechanisms of BHV calcification on 1) composition and site of calcifications; 2) material-associated mechanisms; 3) host-associated mechanisms, including immune response and foreign body reaction, oxidative stress, metabolic disorder, and thrombosis. Strategies that target these mechanisms may be explored for novel drug therapy to prevent or delay BHV calcification.

Placental colonization by Fusobacterium nucleatum is mediated by binding of the Fap2 lectin to placentally displayed Gal-GalNAc

While the existence of an indigenous placental microbiota remains controversial, several pathogens are known to be involved in adverse pregnancy outcomes. Fusobacterium nucleatum is an oral bacterium that is one of several bacteria associated with preterm birth. Oral fusobacteria translocate to the placenta hematogenously; however, the mechanisms localizing them to the placenta remain unclear. Here, using peanut agglutinin, we demonstrate that the level of Gal-GalNAc (Galβ1-3GalNAc; Thomsen Friedenreich antigen) found on trophoblasts facing entering maternal blood rises during gestation and is recognized by the fusobacterial Fap2 Gal-GalNAc lectin. F. nucleatum binding to human and mouse placenta correlates with Gal-GalNAc levels and is reduced upon O-glycanase treatment or with soluble Gal-GalNAc. Fap2-inactivated F. nucleatum shows reduced binding to Gal-GalNAc-displaying placental sections. In a mouse model, intravenously injected Fap2-expressing F. nucleatum, but not a Fap2 mutant, reduces mouse fetal survival by 70%.

The role of antibody responses against glycans in bioprosthetic heart valve calcification and deterioration

Bioprosthetic heart valves (BHVs) are commonly used to replace severely diseased heart valves but their susceptibility to structural valve degeneration (SVD) limits their use in young patients. We hypothesized that antibodies against immunogenic glycans present on BHVs, particularly antibodies against the xenoantigens galactose-α1,3-galactose (αGal) and N-glycolylneuraminic acid (Neu5Gc), could mediate their deterioration through calcification. We established a large longitudinal prospective international cohort of patients (n = 1668, 34 ± 43 months of follow-up (0.1–182); 4,998 blood samples) to investigate the hemodynamics and immune responses associated with BHVs up to 15 years after aortic valve replacement. Early signs of SVD appeared in <5% of BHV recipients within 2 years. The levels of both anti-αGal and anti-Neu5Gc IgGs significantly increased one month after BHV implantation. The levels of these IgGs declined thereafter but anti-αGal IgG levels declined significantly faster in control patients compared to BHV recipients. Neu5Gc, anti-Neu5Gc IgG and complement deposition were found in calcified BHVs at much higher levels than in calcified native aortic valves. Moreover, in mice, anti-Neu5Gc antibodies were unable to promote calcium deposition on subcutaneously implanted BHV tissue engineered to lack αGal and Neu5Gc antigens. These results indicate that BHVs manufactured using donor tissues deficient in αGal and Neu5Gc could be less prone to immune-mediated deterioration and have improved durability.

In a large cohort of patients who underwent aortic valve replacement, antibody responses to glycans present in bioprosthetic heart valves, notably galactose-α1,3-galactose and N-glycolylneuraminic acid, were implicated in valve calcification and deterioration.

Residual Bioprosthetic Valve Immunogenicity: Forgotten, Not Lost

Despite early realization of the need to control inherent immunogenicity of bioprosthetic replacement heart valves and thereby mitigate the ensuing host response and its associated pathology, including dystrophic calcification, the problem remains unresolved to this day. Concerns over mechanical stiffness associated with prerequisite high cross-link density to effect abrogation of this response, together with the insinuated role of leaching glutaraldehyde monomer in subsequent dystrophic mineralization, have understandably introduced compromises. These have become so entrenched as a benchmark standard that residual immunogenicity of the extracellular matrix has seemingly been relegated to a very subordinate role. Instead, focus has shifted toward the removal of cellular compartment antigens renowned for their implication in the failure of vascularized organ xenotransplants. While decellularization certainly offers advantages, this review aims to refocus attention on the unresolved matter of the host response to the extracellular matrix. Furthermore, by implicating remnant immune and inflammatory processes to bioprosthetic valve pathology, including pannus overgrowth and mineralization, the validity of a preeminent focus on decellularization, in the context of inefficient antigen and possible residual microbial remnant removal, is questioned.

Yak Pericardium as an Alternative Biomaterial for Transcatheter Heart Valves

Transcatheter aortic valve implantation (TAVI) has received much attention and development in the past decade due to its lower risk of complication and infections compared to a traditional open thoracotomy. However, the current commercial transcatheter heart valve does not fully meet clinical needs; therefore, new biological materials must be found in order to meet these requirements. We have discovered a new type of biological material, the yak pericardium. This current research studied its extracellular matrix structure, composition, mechanical properties, and amino acid content. Folding experiment was carried out to analyze the structure and mechanics after folding. We also conducted a subcutaneous embedding experiment to analyze the inflammatory response and calcification after implantation. Australian bovine pericardium, local bovine pericardium, and porcine pericardium were used as controls. The overall structure of the yak pericardium is flat, the collagen runs regularly, it has superior mechanical properties, and the average thickness is significantly lower than that of the Australian bovine and the local bovine pericardium control groups. The yak pericardium has a higher content of elastic fibers, showing that it has a better compression resistance effect during the folding experiment as well as having less expression of transplantation-related antigens. We conducted in vivo experiments and found that the yak pericardium has less inflammation and a lower degree of calcification. In summary, the yak pericardium, which is thin and strong, has lower immunogenicity and outstanding anti-calcification effects may be an excellent candidate valve leaflet material for TAVI.

Current views on N-glycolylneuraminic acid in therapeutic recombinant proteins

The incorporation of the non-human N-glycolylneuraminic acid (Neu5Gc) in therapeutic recombinant proteins raises clinical concerns due to its immunogenic potential and the high prevalence of pre-existing anti-Neu5Gc antibodies in humans. The scientific literature is ambiguous regarding the actual impact of Neu5Gc-containing biotherapeutics as no severe adverse clinical manifestations were unequivocally attributed to Neu5Gc for currently marketed biotherapeutics. This review discusses structural and functional considerations of Neu5Gc-containing glycans regarding the potential impact on drug clearance, their recognition by pre-existing antibodies, and recent hypotheses regarding the tolerance to low Neu5Gc levels. Furthermore, it provides recommendations regarding the standardization of analysis and reporting, analytical aspects relevant for assessing risks associated with Neu5Gc-containing biotherapeutics, and approaches to minimize Neu5Gc incorporation in recombinant protein manufacturing.

Generation of glycans depleted decellularized porcine pericardium, using digestive enzymatic supplements and enzymatic mixtures for food industry

BACKGROUND

Xenogeneic pericardium has been used largely for various applications in cardiovascular surgery. Nevertheless, xenogeneic pericardial patches fail mainly due to their antigenic components. The xenoantigens identified as playing a major role in recipient immune response are the Galα1-3Gal (α-Gal) epitope, the non-human sialic acid N-glycolylneuraminic acid (Neu5Gc), and the porcine SDa antigen, associated with both proteins and lipids. The reduction in glycans from porcine pericardium might hinder or reduce the immunogenicity of xenogeneic scaffolds.

METHODS

Decellularized porcine pericardia were further treated at different time points and dilutions with digestive enzymatic supplements and enzymatic mixtures applied for food industry, for the removal of potentially immunogenic carbohydrates. Carbohydrates removal was investigated using up to 8 different lectin stains for the identification of N- and O-glycosylations, as well as glycolipids. Histoarchitectural changes in the ECM were assessed using Elastica van Gieson stain, whereas changes in mechanical properties were investigated via uniaxial tensile test and burst pressure test.

RESULTS

Tissues after enzymatic treatments showed a dramatic decrease in lectin stainings in comparison to tissues which were only decellularized. Histological assessment revealed cell-nuclei removal after decellularization. Some of the enzymatic treatments induced elastic lamellae disruption. Tissue strength decreased after enzymatic treatment; however, treated tissues showed values of burst pressure higher than physiological transvalvular pressures.

CONCLUSIONS

The application of these enzymatic treatments for tissue deglycosylation is totally novel, low cost, and appears to be very efficient for glycan removal. The immunogenic potential of treated tissues will be further investigated in subsequent studies, in vitro and in vivo.

A review of the immune response stimulated by xenogenic tissue heart valves

Valvular heart disease continues to afflict millions of people around the world. In many cases, the only corrective treatment for valvular heart disease is valve replacement. Valve replacement options are currently limited, and the most common construct utilized are xenogenic tissue heart valves. The main limitation with the use of this valve type is the development of valvular deterioration. Valve deterioration results in intrinsic permanent changes in the valve structure, often leading to hemodynamic compromise and clinical symptoms of valve re-stenosis. A significant amount of research has been performed regarding the incidence of valve deterioration and determination of significant risk factors for its development. As a result, many believe that the underlying driver of valve deterioration is a chronic immune-mediated rejection process of the foreign xenogenic-derived tissue. The underlying mechanisms of how this occurs are an area of ongoing research and active debate. In this review, we provide an overview of the important components of the immune system and how they respond to xenografts. A review of the proposed mechanisms of xenogenic heart valve deterioration is provided including the immune response to xenografts. Finally, we discuss the role of strategies to combat valve degeneration such as preservation protocols, epitope modification and decellularization.

Association between Neu5Gc carbohydrate and serum antibodies against it provides the molecular link to cancer: French NutriNet-Santé study

BACKGROUND

High consumption of red and processed meat is commonly associated with increased cancer risk, particularly colorectal cancer. Antibodies against the red meat-derived carbohydrate N-glycolylneuraminic acid (Neu5Gc) exacerbate cancer in "human-like" mice. Human anti-Neu5Gc IgG and red meat are both independently proposed to increase cancer risk, yet how diet affects these antibodies is largely unknown.

METHODS

We used world global data to demonstrate that colorectal cancer incidence and mortality are associated with increased national meat consumption. In a well-defined large cohort, we used glycomics to measure daily Neu5Gc intake from red meat and dairy, and investigated serum as well as affinity-purified anti-Neu5Gc antibodies. Based on 24-h dietary records, daily Neu5Gc intake was calculated for 19,621 subjects aged ≥ 18 years of the NutriNet-Santé study. Serum and affinity-purified anti-Neu5Gc antibodies were evaluated by ELISA and glycan microarrays in representative 120 individuals, each with at least eighteen 24-h dietary records (aged 45-60, Q1-Q4; aged > 60, Q1 and Q4; 10 men/women per quartile).

RESULTS

We found that high-Neu5Gc diet, gender, and age affect the specificity, levels, and repertoires of anti-Neu5Gc IgG immune responses, but not their affinity. Men consumed more Neu5Gc than women, mostly from red meat (p = 0.0015), and exhibited higher overall serum anti-Neu5Gc IgG levels by ELISA (3.94 ng/μl versus 2.22 ng/μl, respectively; p = 0.039). Detailed glycan microarray analysis against 56 different glycans revealed high Neu5Gc-specificity with increased anti-Neu5Gc IgG and altered repertoires, associated with higher consumption of Neu5Gc from red meat and cow dairy. Affinity purification of serum anti-Neu5Gc antibodies revealed increased levels and biased array repertoire patterns, without an increase in antibody affinity, in individuals consuming higher Neu5Gc levels. Furthermore, in a high-meat diet, antibody diversity patterns on glycan microarrays shifted towards Neu5Gcα3-linked glycans, increasing the α3/α6-glycans ratio score.

CONCLUSIONS

We found a clear link between the levels and repertoire of serum anti-Neu5Gc IgG and Neu5Gc intake from red meat and dairy. These precise rational methodologies allowed to develop a Gcemic index to simplify the assessment of Neu5Gc in foods that could potentially be adapted for dietary recommendations to reduce cancer risk.

Identification by mass spectrometry and immunoblotting of xenogeneic antigens in the N- and O-glycomes of porcine, bovine and equine heart tissues

Animal bioprosthetic heart valves (BHV) are used to replace defective valves in patients with valvular heart disease. Especially young BHV recipients may experience a structural valve deterioration caused by an immune reaction in which α-Gal and Neu5Gc are potential target antigens. The expression of these and other carbohydrate antigens in animal tissues used for production of BHV was explored. Protein lysates of porcine aortic and pulmonary valves, and porcine, bovine and equine pericardia were analyzed by Western blotting using anti-carbohydrate antibodies and lectins. N-glycans were released by PNGase F digestion and O-glycans by β-elimination. Released oligosaccharides were analyzed by liquid chromatography – tandem mass spectrometry. In total, 102 N-glycans and 40 O-glycans were identified in animal heart tissue lysates. The N- and O-glycan patterns were different between species. α-Gal and Neu5Gc were identified on both N- and O-linked glycans, N,N´-diacetyllactosamine (LacdiNAc) on N-glycans only and sulfated O-glycans. The relative amounts of α-Gal-containing N-glycans were higher in bovine compared to equine and porcine pericardia. In contrast to the restricted number of proteins carrying α-Gal and LacdiNAc, the distribution of proteins carrying Neu5Gc-determinants varied between species and between different tissues of the same species. Porcine pericardium carried the highest level of Neu5Gc-sialylated O-glycans, and bovine pericardium the highest level of Neu5Gc-sialylated N-glycans. The identified N- and O-linked glycans, some of which may be immunogenic and remain in BHVs manufactured for clinical use, could direct future genetic engineering to prevent glycan expression rendering the donor tissues less immunogenic in humans.

The Possible Role of Anti-Neu5Gc as an Obstacle in Xenotransplantation

Seventy to ninety percentage of preformed xenoreactive antibodies in human serum bind to the galactose-α(1,3)-galactose Gal epitope, and the creation of Gal knockout (KO) pigs has eliminated hyperacute rejection as a barrier to xenotransplantation. Now other glycan antigens are barriers to move ahead with xenotransplantation, and the N-glycolyl neuraminic acid, Neu5Gc (or Hanganutziu-Deicher antigen), is also a major pig xenoantigen. Humans have anti-Neu5Gc antibodies. Several data indicate a strong immunogenicity of Neu5Gc in humans that may contribute to an important part in antibody-dependent injury to pig xenografts. Pig islets express Neu5Gc, which reacted with diet-derived human antibodies and mice deleted for Neu5Gc reject pancreatic islets from wild-type counterpart. However, Neu5Gc positive heart were not rejected in Neu5Gc KO mice indicating that the role of Neu5Gc-specific antibodies has to be nuanced and depend of the graft situation parameters (organ/tissue, recipient, implication of other glycan antigens). Recently generated Gal/Neu5Gc KO pigs eliminate the expression of Gal and Neu5Gc, and improve the crossmatch of humans with the pig. This review summarizes the current and recent experimental and (pre)clinical data on the Neu5Gc immunogenicity and emphasize of the potential impact of anti-Neu5Gc antibodies in limiting xenotransplantation in humans.

Glycosylated Biotherapeutics: Immunological Effects of N-Glycolylneuraminic Acid

The emerging field of biotherapeutics provides successful treatments for various diseases, yet immunogenicity and limited efficacy remain major concerns for many products. Glycosylation is a key factor determining the pharmacological properties of biotherapeutics, including their stability, solubility, bioavailability, pharmacokinetics, and immunogenicity. Hence, an increased attention is directed at optimizing the glycosylation properties of biotherapeutics. Currently, most biotherapeutics are produced in non-human mammalian cells in light of their ability to produce human-like glycosylation. However, most mammals produce the sialic acid N-glycolylneuraminic acid (Neu5Gc), while humans cannot due to a specific genetic defect. Humans consume Neu5Gc in their diet from mammalian derived foods (red meat and dairy) and produce polyclonal antibodies against diverse Neu5Gc-glycans. Moreover, Neu5Gc can metabolically incorporate into human cells and become presented on surface or secreted glycans, glycoproteins, and glycolipids. Several studies in mice suggested that the combination of Neu5Gc-containing epitopes and anti-Neu5Gc antibodies could contribute to exacerbation of chronic inflammation-mediated diseases (e.g., cancer, cardiovascular diseases, and autoimmunity). This could potentially become complicated with exposure to Neu5Gc-containing biotherapeutics, bio-devices or xenografts. Indeed, Neu5Gc can be found on various approved and marketed biotherapeutics. Here, we provide a perspective review on the possible consequences of Neu5Gc glycosylation of therapeutic protein drugs due to the limited published evidence of Neu5Gc glycosylation on marketed biotherapeutics and studies on their putative effects on immunogenicity, drug efficacy, and safety.

Studying Xenograft Rejection of Bioprosthetic Heart Valves

Millions of patients with valvular heart disease have benefitted from heart valve replacement since the procedure was first introduced in the 1960s; however, there are still many patients who get early structural valve deterioration (SVD) of their bioprosthetic heart valves (BHV). BHV are porcine, bovine, or equine tissues that have been glutaraldehyde fixed to preserve the tissue and presumably make the tissue immunologically inert. These glutaraldehyde-fixed BHV with anti-calcification treatments last long periods of time in older adults but develop early SVD in younger patients. The consensus at present is that the early SVD in younger patients is due to more "wear and tear" of the valves and higher calcium turnover in younger patients. However, as younger patients likely have a more robust immune system than older adults, there is a new hypothesis that BHV xenografts may undergo xenograft rejection, and this may contribute to the early SVD seen in younger patients.At present, the technology to noninvasively study in vivo whether an implanted BHV in a human patient is undergoing rejection is not available. Thus, a small animal discordant xenotransplant model in young rodents (to match the young patient getting a pig/bovine/equine BHV) was developed to study whether the hypothesis that glutaraldehyde-fixed BHV undergo xenograft rejection had any merit. In this chapter, we describe our model and its merits and the results of our investigations. Our work provides clear evidence of xenograft rejection in glutaraldehyde-fixed tissue, and our small animal model offers an opportunity to study this process in detail.

N-Glycolylneuraminic Acid (Neu5Gc) Null Large Animals by Targeting the CMP-Neu5Gc Hydroxylase (CMAH)

The two major sialic acids described in mammalian cells are the N-glycolylneuraminic acid (Neu5Gc) and the N-acetylneuraminic acid (Neu5Ac). Neu5Gc synthesis starts from the N-acetylneuraminic acid (Neu5Ac) precursor modified by an hydroxylic group addition catalyzed by CMP-Neu5Ac hydroxylase enzyme (CMAH). In humans, CMAH was inactivated by a 92 bp deletion occurred 2-3 million years ago. Few other mammals do not synthetize Neu5Gc, however livestock species used for food production and as a source of biological materials for medical applications carry Neu5Gc. Trace amounts of Neu5Gc are up taken through the diet and incorporated into various tissues including epithelia and endothelia cells. Humans carry "natural," diet-induced Anti-Neu5Gc antibodies and when undertaking medical treatments or receiving transplants or devices that contain animal derived products they can cause immunological reaction affecting pharmacology, immune tolerance, and severe side effect like serum sickness disease (SSD). Neu5Gc null mice have been the main experimental model to study such phenotype. With the recent advances in genome editing, pigs and cattle KO for Neu5Gc have been generated always in association with the αGal KO. These large animals are normal and fertile and provide additional experimental models to study such mutation. Moreover, they will be the base for the development of new therapeutic applications like polyclonal IgG immunotherapy, Bioprosthetic Heart Valves, cells and tissues replacement.

Synthesis of N-Glycolylneuraminic Acid (Neu5Gc) and Its Glycosides

Sialic acids constitute a family of negatively charged structurally diverse monosaccharides that are commonly presented on the termini of glycans in higher animals and some microorganisms. In addition to N-acetylneuraminic acid (Neu5Ac), N-glycolyl neuraminic acid (Neu5Gc) is among the most common sialic acid forms in nature. Nevertheless, unlike most animals, human cells loss the ability to synthesize Neu5Gc although Neu5Gc-containing glycoconjugates have been found on human cancer cells and in various human tissues due to dietary incorporation of Neu5Gc. Some pathogenic bacteria also produce Neu5Ac and the corresponding glycoconjugates but Neu5Gc-producing bacteria have yet to be found. In addition to Neu5Gc, more than 20 Neu5Gc derivatives have been found in non-human vertebrates. To explore the biological roles of Neu5Gc and its naturally occurring derivatives as well as the corresponding glycans and glycoconjugates, various chemical and enzymatic synthetic methods have been developed to obtain a vast array of glycosides containing Neu5Gc and/or its derivatives. Here we provide an overview on various synthetic methods that have been developed. Among these, the application of highly efficient one-pot multienzyme (OPME) sialylation systems in synthesizing compounds containing Neu5Gc and derivatives has been proven as a powerful strategy.

The Structural Complexity and Animal Tissue Distribution of N-Glycolylneuraminic Acid (Neu5Gc)-Terminated Glycans. Implications for Their Immunogenicity in Clinical Xenografting

N-Glycolylneuraminic acid (Neu5Gc)-terminated glycans are present in all animal cells/tissues that are already used in the clinic such as bioprosthetic heart valves (BHV) as well as in those that potentially will be xenografted in the future to overcome end stage cell/organ failure. Humans, as a species lack this antigen determinant and can react with an immune response after exposure to Neu5Gc present in these products/cells/tissues. Genetically engineered source animals lacking Neu5Gc has been generated and so has animals that in addition lack the major αGal xenoantigen. The use of cells/tissues/organs from such animals may improve the long-term performance of BHV and allow future xenografting. This review summarizes the present knowledge regarding structural complexity and tissue distribution of Neu5Gc on glycans of cells/tissue/organs already used in the clinic or intended for treatment of end stage organ failure by xenografting. In addition, we briefly discuss the role of anti-Neu5Gc antibodies in the xenorejection process and how knowledge about Neu5Gc structural complexity can be used to design novel diagnostics for anti-Neu5Gc antibody detection.

Elicited and pre-existing anti-Neu5Gc antibodies differentially affect human endothelial cells transcriptome

Humans cannot synthesize N-glycolylneuraminic acid (Neu5Gc) but dietary Neu5Gc can be absorbed and deposited on endothelial cells (ECs) and diet-induced anti-Neu5Gc antibodies (Abs) develop early in human life. While the interaction of Neu5Gc and diet-induced anti-Neu5Gc Abs occurs in all normal individuals, endothelium activation by elicited anti-Neu5Gc Abs following a challenge with animal-derived materials, such as following xenotransplantation, had been postulated. Ten primary human EC preparations were cultured with affinity-purified anti-Neu5Gc Abs from human sera obtained before or after exposure to Neu5Gc-glycosylated rabbit IgGs (elicited Abs). RNAs of each EC preparation stimulated in various conditions by purified Abs were exhaustively sequenced. EC transcriptomic patterns induced by elicited anti-Neu5Gc Abs, compared with pre-existing ones, were analyzed. qPCR, cytokines/chemokines release, and apoptosis were tested on some EC preparations. The data showed that anti-Neu5Gc Abs induced 967 differentially expressed (DE) genes. Most DE genes are shared following EC activation by pre-existing or anti-human T-cell globulin (ATG)-elicited anti-Neu5Gc Abs. Compared with pre-existing anti-Neu5Gc Abs, which are normal component of ECs environment, elicited anti-Neu5Gc Abs down-regulated 66 genes, including master genes of EC function. Furthermore, elicited anti-Neu5Gc Abs combined with complement-containing serum down-regulated most transcripts mobilized by serum alone. Both types of anti-Neu5Gc Abs-induced a dose- and complement-dependent release of selected cytokines and chemokines. Altogether, these data show that, compared with pre-existing anti-Neu5Gc Abs, ATG-elicited anti-Neu5Gc Abs specifically modulate genes related to cytokine responses, MAPkinase cascades, chemotaxis, and integrins and do not skew the EC transcriptome toward a pro-inflammatory profile in vitro.

Generation of cattle knockout for galactose-α1,3-galactose and N-glycolylneuraminic acid antigens

Two well‐characterized carbohydrate epitopes are absent in humans but present in other mammals. These are galactose‐α1,3‐galactose (αGal) and N‐glycolylneuraminic acid (Neu5Gc) which are introduced by the activities of two enzymes including α(1,3) galactosyltransferase (encoded by the GGTA1 gene) and CMP‐Neu5Gc hydroxylase (encoded by the CMAH gene) that are inactive in humans but present in cattle. Hence, bovine‐derived products are antigenic in humans who receive bioprosthetic heart valves (BHVs) or those that suffer from red meat syndrome. Using programmable nucleases, we disrupted (knockout, KO) GGTA1 and CMAH genes encoding for the enzymes that catalyse the synthesis of αGal and Neu5Gc, respectively, in both male and female bovine fibroblasts. The KO in clonally selected fibroblasts was detected by polymerase chain reaction (PCR) and confirmed by Sanger sequencing. Selected fibroblasts colonies were used for somatic cell nuclear transfer (SCNT) to produce cloned embryos that were implanted in surrogate recipient heifers. Fifty‐three embryos were implanted in 33 recipients heifers; 3 pregnancies were carried to term and delivered 3 live calves. Primary cell cultures were established from the 3 calves and following molecular analyses confirmed the genetic deletions. FACS analysis showed the double‐KO phenotype for both antigens confirming the mutated genotypes. Availability of such cattle double‐KO model lacking both αGal and Neu5Gc offers a unique opportunity to study the functionality of BHV manufactured with tissues of potentially lower immunogenicity, as well as a possible new clinical approaches to help patients with red meat allergy syndrome due to the presence of these xenoantigens in the diet.

ABO blood type and risk of porcine bioprosthetic aortic valve degeneration: SWEDEHEART observational cohort study

OBJECTIVE

Blood type A antigen on porcine aortic bioprostheses might initiate an immune reaction leading to an increased frequency of structural valve deterioration in patients with blood type B or O. The aim was to analyse the association between ABO blood type and porcine bioprosthetic aortic valve degeneration.

DESIGN

Observational nationwide cohort study.

SETTING

Swedish population-based study.

PARTICIPANTS

Adult patients (n=3417) who underwent surgical aortic valve replacement and received porcine bioprosthetic aortic valves between 1995 and 2012 from the Swedish Web system for Enhancement and Development of Evidence-based care in Heart disease Evaluated According to Recommended Therapies register. The study database was enriched with information from other national registers.

EXPOSURE

The patients were categorised into type A/AB and type B/O blood groups.

PRIMARY AND SECONDARY OUTCOME MEASURES

Primary outcome measure was aortic valve reoperation, and secondary outcomes were heart failure and all-cause mortality. We report risk estimates that account for the competing risk of death.

RESULTS

In total, 3417 patients were identified: 1724 (50.5%) with blood type A/AB and 1693 (49.5%) with blood type B/O. Both groups had similar baseline characteristics. The cumulative incidence of aortic valve reoperation was 3.4% (95% CI 2.5% to 4.4%) and 3.6% (95% CI 2.6% to 4.6%) in the type B/O and the A/AB group, respectively, at 15 years of follow-up (absolute risk difference: -0.2% (95% CI -1.5% to 1.2%)). There was no significantly increased risk for aortic valve reoperation in patients with blood type B/O compared with type A/AB (HR 0.95, 95% CI 0.62 to 1.45). There was no significant difference in absolute or relative risk of heart failure or death between the groups.

CONCLUSIONS

We found no significant association between patient blood type and clinical manifestations of structural valve deterioration following porcine aortic valve replacement. Our findings suggest that it is safe to use porcine bioprosthetic valves without consideration of ABO blood type in the recipient.

TRIAL REGISTRATION NUMBER

NCT02276950.

Differential Recognition of Diet-Derived Neu5Gc-Neoantigens on Glycan Microarrays by Carbohydrate-Specific Pooled Human IgG and IgA Antibodies

Sialic acids (Sias) cover vertebrate cell surface glycans. N-Acetylneuraminic acid (Neu5Ac) and its hydroxylated form N-glycolylneuraminic acid (Neu5Gc) are common Sia in mammals. Humans cannot synthesize Neu5Gc but accumulate it on cells through red-meat rich diets, generating numerous immunogenic Neu5Gc-neoantigens. Consequently, humans have diverse anti-Neu5Gc antibodies affecting xenotransplantation, cancer, atherosclerosis, and infertility. Anti-Neu5Gc antibodies circulate as IgG, IgM, and IgA isotypes; however, repertoires of the different isotypes in a large population have not been studied yet. Here, we used glycan microarrays to investigate anti-Neu5Gc IgGs and IgAs in intravenous immunoglobulin (IVIG) or pooled human IgA, respectively. Binding patterns on microarrays fabricated with Neu5Gc- and Neu5Ac-glycans, together with inhibition assays, revealed that different IVIG preparations have highly specific anti-Neu5Gc IgG reactivity with closely related repertoires, while IgAs show cross-reactivity against several Neu5Ac-glycans. Such different anti-Neu5Gc IgG/IgA repertoires in individuals could possibly mediate distinctive effects on human diseases.

From "Serum Sickness" to "Xenosialitis": Past, Present, and Future Significance of the Non-human Sialic Acid Neu5Gc

The description of "serum sickness" more than a century ago in humans transfused with animal sera eventually led to identification of a class of human antibodies directed against glycans terminating in the common mammalian sialic acid N-Glycolylneuraminic acid (Neu5Gc), hereafter called "Neu5Gc-glycans." The detection of such glycans in malignant and fetal human tissues initially raised the possibility that it was an oncofetal antigen. However, "serum sickness" antibodies were also noted in various human disease states. These findings spurred further research on Neu5Gc, and the discovery that it is not synthesized in the human body due to a human-lineage specific genetic mutation in the enzyme CMAH. However, with more sensitive techniques Neu5Gc-glycans were detected in smaller quantities on certain human cell types, particularly epithelia and endothelia. The likely explanation is metabolic incorporation of Neu5Gc from dietary sources, especially red meat of mammalian origin. This incorporated Neu5Gc on glycans appears to be the first example of a "xeno-autoantigen," against which varying levels of "xeno-autoantibodies" are present in all humans. The resulting chronic inflammation or "xenosialitis" may have important implications in human health and disease, especially in conditions known to be aggravated by consumption of red meat. In this review, we will cover the early history of the discovery of "serum sickness" antibodies, the subsequent recognition that they were partly directed against Neu5Gc-glycans, the discovery of the genetic defect eliminating Neu5Gc production in humans, and the later recognition that this was not an oncofetal antigen but the first example of a "xeno-autoantigen." Further, we will present comments about implications for disease risks associated with red meat consumption such as cancer and atherosclerosis. We will also mention the potential utility of these anti-Neu5Gc-glycan antibodies in cancer immunotherapy and provide some suggestions and perspectives for the future. Other reviews in this special issue cover many other aspects of this unusual pathological process, for which there appears to be no other described precedent.

Bioprosthetic Heart Valves: Upgrading a 50-Year Old Technology

Prosthetic heart valves have been commonly used to address the increasing prevalence of valvular heart disease. The ideal prosthetic heart valve substitute should closely mimic the characteristics of a normal native heart valve. Despite the development of various interventions, an exemplary valve replacement does not exist. This review provides an overview of the novel engineering valve designs and explores emergent immunologic insights into age-dependent structural valve degeneration (SVD).

Quantitative and qualitative changes in anti-Neu5Gc antibody response following rabbit anti-thymocyte IgG induction in kidney allograft recipients

Antibodies of non-human mammals are glycosylated with carbohydrate antigens, such as galactose-α-1-3-galactose (α-Gal) and N-glycolylneuraminic acid (Neu5Gc). These non-human carbohydrate antigens are highly immunogenic in humans due to loss-of-function mutations of the key genes involved in their synthesis. Such immunogenic carbohydrates are expressed on therapeutic polyclonal rabbit anti-human T-cell IgGs (anti-thymocyte globulin; ATG), the most popular induction treatment in allograft recipients. To decipher the quantitative and qualitative response against these antigens in immunosuppressed patients, particularly against Neu5Gc, which may induce endothelial inflammation in both the graft and the host. We report a prospective study of the antibody response against α-Gal and Neu5Gc-containing glycans following rabbit ATG induction compared to controls. We show a drop in the overall levels of anti-Neu5Gc antibodies at 6 and 12 months post-graft compared to the pre-existing levels due to the major early immunosuppression. However, in contrast, in a cross-sectional study there was a highly significant increase in anti-Neu5Gc IgGs levels at 6 months post-graft in the ATG-treated compared to non-treated patients(P = 0.007), with a clear hierarchy favouring anti-Neu5Gc over anti-Gal response. A sialoglycan microarray analysis revealed that the increased anti-Neu5Gc IgG response was still highly diverse against multiple different Neu5Gc-containing glycans. Furthermore, some of the ATG-treated patients developed a shift in their anti-Neu5Gc IgG repertoire compared with the baseline, recognizing different patterns of Neu5Gc-glycans. In contrast to Gal, Neu5Gc epitopes remain antigenic in severely immunosuppressed patients, who also develop an anti-Neu5Gc repertoire shift. The clinical implications of these observations are discussed.

Recent approaches for directly profiling cell surface sialoform

Sialic acids (SAs) are nine-carbon monosaccharides existing at the terminal location of glycan structures on the cell surface and secreted glycoconjugates. The expression levels and linkages of SAs on cells and tissues, collectively known as sialoform, present the hallmark of the cells and tissues of different systems and conditions. Accordingly, detecting or profiling cell surface sialoforms is very critical for understanding the function of cell surface glycans and glycoconjugates and even the molecular mechanisms of their underlying biological processes. Further, it may provide therapeutic and diagnostic applications for different diseases. In the past decades, several kinds of SA-specific binding molecules have been developed for detecting and profiling specific sialoforms of cells and tissues; the experimental materials have expanded from frozen tissue to living cells; and the analytical technologies have advanced from histochemistry to fluorescent imaging, flow cytometry and microarrays. This review summarizes the recent bioaffinity approaches for directly detecting and profiling specific SAs or sialylglycans, and their modifications of different cells and tissues.

Presentation Mode of Glycans Affect Recognition of Human Serum anti-Neu5Gc IgG Antibodies

Recognition of carbohydrates by antibodies can be affected by antigen composition and density. This had been investigated in a variety of controllable multivalent systems using synthetic carbohydrate antigens, yet such effects on anticarbohydrate antibodies in circulating human serum have not been fully addressed thus far. All humans develop a polyclonal and diverse response against carbohydrates containing a nonhuman sialic acid form, N-glycolylneuraminic acid (Neu5Gc). This red meat-derived monosaccharide is incorporated into a diverse collection of human glycans resulting in circulating anti-Neu5Gc antibodies in human sera. Such antibodies can cause exacerbation of diseases mediated by chronic inflammation such as cancer and atherosclerosis. We aimed to evaluate how different presentation modes of Neu5Gc-glycans can affect the detection of anti-Neu5Gc IgGs in human serum. Here, we compare serum IgG recognition of Neu5Gc-containing glycoproteins, glycopeptides, and synthetic glycans. First, Neu5Gc-positive or Neu5Gc-deficient mouse strains were used to generate glycopeptides from serum glycoproteins. Then we developed a reproducible ELISA to screen human sera against Neu5Gc-positive glycopeptides for detection of human serum anti-Neu5Gc IgGs. Finally, we evaluated ELISA screens against glycopeptides in comparison with glycoproteins, as well as against elaborated arrays displaying synthetic Neu5Gc-glycans. Our results demonstrate that the presentation mode and diversity of Neu5Gc-glycans are critical for detection of the full collection of human serum anti-Neu5Gc IgGs.

Bioengineered tissue solutions for repair, correction and reconstruction in cardiovascular surgery

The treatment of cardiac alterations is still nowadays a dramatic issue in the cardiosurgical practice. Synthetic materials applied in this surgery have failed in their long-term therapeutic efficacy due to low biocompatibility and compliance, especially when used in contractile sites. In order to overcome these treatment pitfalls, novel solutions have been developed based on biological tissues. Patches in pericardium, small intestinal submucosa, as well as engineered tissues of myocardium, heart valves and blood vessels have undergone a large preclinical investigation in regenerative medicine studies. Clinical translation has been started or reached by several of these new bioengineered treatment alternatives. This review will describe the preclinical and clinical experiences realized so far with the application of biological tissues in cardiovascular surgery. It will depict the progressive steps realized in the evolution of this research, as well as it will point out the challenges yet to face in order to generate the ideal biomaterial for cardiovascular repair, corrective and reconstructive surgery.

Evolution of sialic acids: Implications in xenotransplant biology

All living cells are covered with a dense “sugar-coat” of carbohydrate chains (glycans) conjugated to proteins and lipids. The cell surface glycome is determined by a non-template driven process related to the collection of enzymes that assemble glycans in a sequential manner. In mammals, many of these glycans are topped with sialic acids (Sia), a large family of acidic sugars. The “Sialome” is highly diverse owing to various Sia types, linkage to underlying glycans, range of carriers, and complex spatial organization. Presented at the front of cells, Sia play a major role in immunity and recognition of “self” versus “non-self,” largely mediated by the siglecs family of Sia-binding host receptors. Albeit many mammalian pathogens have evolved to hijack this recognition system to avoid host immune attack, presenting a fascinating host-pathogen evolutionary arms race. Similarly, cancer cells exploit Sia for their own survival and propagation. As part of this ongoing fitness, humans lost the ability to synthesize the Sia type N-glycolylneuraminic acid (Neu5Gc), in contrast to other mammals. While this loss had provided an advantage against certain pathogens, humans are continuously exposed to Neu5Gc through mammalian-derived diet (eg, red meat), consequently generating a complex immune response against it. Circulating anti-Neu5Gc antibodies together with Neu5Gc on some human tissues mediate chronic inflammation “xenosialitis” that exacerbate various human diseases (eg, cancer and atherosclerosis). Similarly, Neu5Gc-containing xenografts are exposed to human anti-Neu5Gc antibodies with implications to sustainability. This review aimed to provide a glimpse into the evolution of Sia and their implications to xenotransplantation.

Glycosphingolipids of porcine, bovine, and equine pericardia as potential immune targets in bioprosthetic heart valve grafts

BACKGROUND

Pericardial tissue from various animal species is utilized for the production of the bioprosthetic heart valves (BHV) used clinically. Experimental data show that the eventual breakdown of BHV is partly due to immunological interactions with carbohydrate tissue antigens. To understand these processes, we have examined the glycolipid-based carbohydrate antigens in naïve porcine, bovine, and equine pericardia.

EXPERIMENTAL

Total non-acid and acid glycosphingolipid fractions were isolated from porcine, bovine, and equine pericardia, and individual glycolipid compounds were characterized by thin-layer chromatography, mass spectrometry, and binding of monoclonal antibodies, lectins and bacteria in chromatogram binding assays.

RESULTS

The non-acid glycolipid fractions from all species contained glycosphingolipids based on the globo- and neolacto-series, including pentaglycosylceramides with terminal Galα3 determinants. Terminal blood group A and H (O) structures based on type 2 core chains were present in porcine pericardium, while the Forssman pentaosylceramide was found in equine pericardium. All acid glycolipid fractions contained sulfatide and several gangliosides with both N-acetyl- and N-glycolyl-neuraminic acid as terminal saccharide chain determinants.

CONCLUSION

Several carbohydrate antigens which are potential targets for the human immune system have been identified in the animal pericardial tissues used for the production of BHV. Which of these antigens are left in the tissues after industrial BHV production processes, as well as their potential role in eventual BHV degradation, remains to be elucidated.

Polyclonal human antibodies against glycans bearing red meat-derived non-human sialic acid N-glycolylneuraminic acid are stable, reproducible, complex and vary between individuals: Total antibody levels are associated with colorectal cancer risk

BACKGROUND

N-glycolylneuraminic acid (Neu5Gc) is a non-human red-meat-derived sialic acid immunogenic to humans. Neu5Gc can be metabolically incorporated into glycan chains on human endothelial and epithelial surfaces. This represents the first example of a "xeno-autoantigen", against which circulating human "xeno-autoantibodies" can react. The resulting inflammation ("xenosialitis") has been demonstrated in human-like Neu5Gc-deficient mice and contributed to carcinoma progression via antibody-mediated inflammation. Anti-Neu5Gc antibodies have potential as biomarkers for diseases associated with red meat consumption such as carcinomas, atherosclerosis, and type 2 diabetes.

METHODS

ELISA assays measured antibodies against Neu5Gc or Neu5Gc-glycans in plasma or serum samples from the Nurses' Health Studies, the Health Professionals Follow-up Study, and the European Prospective Investigation into Cancer and Nutrition, including inter-assay reproducibility, stability with delayed sample processing, and within-person reproducibility over 1-3 years in archived samples. We also assessed associations between antibody levels and coronary artery disease risk (CAD) or red meat intake. A glycan microarray was used to detected antibodies against multiple Neu5Gc-glycan epitopes. A nested case-control study design assessed the association between total anti-Neu5Gc antibodies detected in the glycan array assay and the risk of colorectal cancer (CRC).

RESULTS

ELISA assays showed a wide range of anti-Neu5Gc responses and good inter-assay reproducibility, stability with delayed sample processing, and within-person reproducibility over time, but these antibody levels did not correlate with CAD risk or red meat intake. Antibodies against Neu5Gc alone or against individual Neu5Gc-bearing epitopes were also not associated with colorectal cancer (CRC) risk. However, a sialoglycan microarray study demonstrated positive association with CRC risk when the total antibody responses against all Neu5Gc-glycans were combined. Individuals in the top quartile of total anti-Neu5Gc IgG antibody concentrations had nearly three times the risk compared to those in the bottom quartile (Multivariate Odds Ratio comparing top to bottom quartile: 2.98, 95% CI: 0.80, 11.1; P for trend = 0.02).

CONCLUSIONS

Further work harnessing the utility of these anti-Neu5Gc antibodies as biomarkers in red meat-associated diseases must consider diversity in individual antibody profiles against different Neu5Gc-bearing glycans. Traditional ELISA assays for antibodies directed against Neu5Gc alone, or against specific Neu5Gc-glycans may not be adequate to define risk associations. Our finding of a positive association of total anti-Neu5Gc antibodies with CRC risk also warrants confirmation in larger prospective studies.

Reducing immunoreactivity of porcine bioprosthetic heart valves by genetically-deleting three major glycan antigens, GGTA1/β4GalNT2/CMAH

Bioprosthetic heart valves (BHVs) originating from pigs are extensively used for heart valve replacement in clinics. However, recipient immune responses associated with chronic calcification lead to structural valve deterioration (SVD) of BHVs. Two well-characterized epitopes on porcine BHVs have been implicated in SVD, including galactose-α1,3-galactose (αGal) and N-glycolylneuraminic acid (Neu5Gc) whose synthesis are catalyzed by α(1,3) galactosyltransferase (encoded by the GGTA1 gene) and CMP-Neu5Ac hydroxylase (encoded by the CMAH gene), respectively. It has been reported that BHV from αGal-knockout pigs are associated with a significantly reduced immune response by human serum. Moreover, valves from αGal/Neu5Gc-deficient pigs could further reduce human IgM/IgG binding when compared to BHV from αGal-knockout pigs. Recently, another swine xenoantigen, Sd(a), produced by β-1,4-N-acetyl-galactosaminyl transferase 2 (β4GalNT2), has been identified. To explore whether tissue from GGTA1, CMAH, and β4GalNT2 triple gene-knockout (TKO) pigs would further minimize human antibody binding to porcine pericardium, TKO pigs were successfully produced by CRISPR/Cas9 mediated gene targeting. Our results showed that the expression of αGal, Neu5G and Sd(a) on TKO pigs was negative, and that human IgG/IgM binding to pericardium was minimal. Moreover, the analysis of collagen composition and physical characteristics of porcine pericardium from the TKO pigs indicated that elimination of the three xenoantigens had no significant impact on the physical proprieties of porcine pericardium. Our results demonstrated that TKO pigs would be an ideal source of BHVs.

STATEMENT OF SIGNIFICANCE

Surgical heart valve replacement is an established lifesaving treatment for diseased heart valve. Bioprosthetic heart valves (BHVs) made from glutaraldehyde-fixed porcine or bovine tissues are widely used in clinics but exhibit age-dependent structural valve degeneration (SVD) which is associated with the immune response against BHVs. Three major xenoantigens present on commercial BHVs, Galactosea α1,3 galactose (αGal), N-glycolylneuraminic acid (Neu5Gc) and glycan products of β-1,4-N-acetyl-galactosaminyl transferase 2 (β4GalNT2) are eliminated through CRISPR/Cas9 mediated gene targeting in the present study. The genetically modified porcine pericardium showed reduced immunogenicity but comparable collagen composition and physical characteristics of the pericardium from wild-type pigs. Our data suggested that BHVs from TKO pigs is a promising alternative for currently available BHVs from wild-type pigs.

Xenotransplantation: past, present, and future

PURPOSE OF REVIEW

To review the progress in the field of xenotransplantation with special attention to most recent encouraging findings which will eventually bring xenotransplantation to the clinic in the near future.

RECENT FINDINGS

Starting from early 2000, with the introduction of galactose-α1,3-galactose (Gal)-knockout pigs, prolonged survival especially in heart and kidney xenotransplantation was recorded. However, remaining antibody barriers to non-Gal antigens continue to be the hurdle to overcome. The production of genetically engineered pigs was difficult requiring prolonged time. However, advances in gene editing, such as zinc finger nucleases, transcription activator-like effector nucleases, and most recently clustered regularly interspaced short palindromic repeats (CRISPR) technology made the production of genetically engineered pigs easier and available to more researchers. Today, the survival of pig-to-nonhuman primate heterotopic heart, kidney, and islet xenotransplantation reached more than 900, more than 400, and more than 600 days, respectively. The availability of multiple-gene pigs (five or six genetic modifications) and/or newer costimulation blockade agents significantly contributed to this success. Now, the field is getting ready for clinical trials with an international consensus.

SUMMARY

Clinical trials in cellular or solid organ xenotransplantation are getting closer with convincing preclinical data from many centers. The next decade will show us new achievements and additional barriers in clinical xenotransplantation.

Heart valve tissue engineering: an overview of heart valve decellularization processes

Despite recent advances in medicine and surgery, many people still suffer from cardiovascular diseases, which affect their life span and morbidity. Regenerative medicine and tissue engineering are novel approaches based on restoring or replacing injured tissues and organs with scaffolds, cells and growth factors. Scaffolds are acquired from two major sources, synthetic materials and naturally derived scaffolds. Biological scaffolds derived from native tissues and cell-derived matrix offer many advantages. They are more biocompatible with a higher affinity to cells, which facilitate tissue reconstruction. Interestingly, xenogeneic recipients generally tolerate their components. Therefore, heart valve tissue engineering is increasingly benefiting from naturally derived scaffolds. In this review, we investigated the different protocols and methods that have been used for heart valve decellularization.

Comparison of valvar and right ventricular function following transcatheter and surgical pulmonary valve replacement

OBJECTIVE

Trans-catheter (TC) pulmonary valve replacement (PVR) has become common practice for patients with right ventricular outflow tract obstruction (RVOTO) and/or pulmonic insufficiency (PI). Our aim was to compare PVR and right ventricular (RV) function of patients who received TC vs surgical PVR.

DESIGN

Retrospective review of echocardiograms obtained at three time points: before, immediately after PVR, and most recent.

PATIENTS

Sixty-two patients (median age 19 years, median follow-up 25 months) following TC (N = 32) or surgical (N = 30) PVR at Yale-New Haven Hospital were included.

OUTCOME MEASURES

Pulmonary valve and right ventricular function before, immediately after, and most recently after PVR.

RESULTS

At baseline, the TC group had predominant RVOTO (74% vs 10%, P < .001), and moderate-severe PI was less common (61% vs 100%, P < .001). Immediate post-procedural PVR function was good throughout. At last follow-up, the TC group had preserved valve function, but the surgical group did not (moderate RVOTO: 6% vs 41%, P < .001; >mild PI: 0% vs 24%, P = .003). Patients younger than 17 years at surgical PVR had the highest risk of developing PVR dysfunction, while PVR function in follow-up was similar in adults. Looking at RV size and function, both groups had a decline in RV size following PVR. However, while RV function remained stable in the TC group, there was a transient postoperative decline in the surgical group.

CONCLUSIONS

TC PVR in patients age <17 years is associated with better PVR function in follow-up compared to surgical valves. There was a transient decline in RV function following surgical but not TC PVR. TC PVR should therefore be the first choice in children who are considered for PVR, whenever possible.

The Rapidly Evolving Concept of Whole Heart Engineering

Whole heart engineering represents an incredible journey with as final destination the challenging aim to solve end-stage cardiac failure with a biocompatible and living organ equivalent. Its evolution started in 2008 with rodent organs and is nowadays moving closer to clinical application thanks to scaling-up strategies to human hearts. This review will offer a comprehensive examination on the important stages to be reached for the bioengineering of the whole heart, by describing the approaches of organ decellularization, repopulation, and maturation so far applied and the novel technologies of potential interest. In addition, it will carefully address important demands that still need to be satisfied in order to move to a real clinical translation of the whole bioengineering heart concept.

Different approaches to heart valve decellularization: A comprehensive overview of the past 30 years

Xenogeneic decellularized heart valve scaffolds have the potential to overcome the limitations of existing bioprosthetic heart valves that have limited duration due to calcification and tissue degeneration phenomena. This article presents a review of 30 years of decellularization approaches adopted in cardiovascular tissue engineering, with a focus on the use, either individually or in combination, of different detergents. The safety and efficacy of cell-removal procedures are specifically reported and discussed, as well as the structure and biomechanics of the treated extracellular matrix (ECM). Detergent residues within the ECM, production of hyaluronan fragments, safe removal of cellular debris, and the persistence of the alpha-Gal epitope after the decellularization treatments are of particular interest as parameters for the identification of the best tissue for the manufacture of bioprostheses. Special attention has also been given to key factors that should be considered in the manufacture of the next generation of xenogeneic bioprostheses, where tissues must retain the ability to be remodeled and to grow in weight along with body reshaping.