Human antibody reactivity against xenogeneic N-glycolylneuraminic acid and galactose-α-1,3-galactose antigen

Some Human Anti-Glycan Antibodies Lack the Ability to Activate the Complement System

Background. Naturally occurring human antibodies against glycans recognize and quickly eliminate infectious bacteria, viruses and aberrantly glycosylated neoplastic malignant cells, and they often initiate processes that involve the complement system. Methods. Using a printed glycan array (PGA) containing 605 glycoligands (oligo- and polysaccharides, glycopeptides), we examined which of the glycan-binding antibodies are able to activate the complement system. Using this PGA, the specificities of antibodies of the IgM and IgG classes were determined in the blood serum of healthy donors (suggested as mostly natural), and, then, using the same array, it was determined which types of the bound immunoglobulins were also showing C3 deposition. Results. It was found that about 30% of anti-glycan antibodies in human serum detected by the PGA did not activate the complement. They were mostly IgGs and directed to bacterial O-antigens; no apparent common structural motif within their target polysaccharides was found. Antibodies to blood group systems ABO and Forssman, xeno-antigens, a number of polysaccharides from various strains of S. enterica, E. coli and P. alcalifaciens, as well as small fragments of bacterial polysaccharides were recognized by complement-activating antibodies as expected. A complement-activating antibody was affinity-isolated on glycan-Sepharose from human serum, and, in the presence of the complement, it lysed red blood cells coated with the same glycan (kodecytes, where glycans expressed on biological membranes), while an isolated complement non-activating antibody did not, which confirms the validity of the solid-phase PGA results. Conclusions. Thus, ~30% of human anti-glycan antibodies lack the ability to activate the complement system. The function of the widely represented immunoglobulins that do not cause C3 deposition remains unclear.

Genome editing of porcine zygotes via lipofection of two guide RNAs using a CRISPR/Cas9 system

CRISPR/Cas9-based multiplex genome editing via electroporation is relatively efficient; however, lipofection is versatile because of its ease of use and low cost. Here, we aimed to determine the efficiency of lipofection in CRISPR/Cas9-based multiplex genome editing using growth hormone receptor (GHR) and glycoprotein alpha-galactosyltransferase 1 (GGTA1)-targeting guide RNAs (gRNAs) in pig zygotes. Zona pellucida-free zygotes were collected 10 h after in vitro fertilization and incubated with Cas9, gRNAs, and Lipofectamine 2000 (LP2000) for 5 h. In Experiment 1, we evaluated the mutation efficiency of gRNAs targeting either GHR or GGTA1 in zygotes transfected using LP2000 and cultured in 4-well plates. In Experiment 2, we examined the effects of the culture method on the development, mutation rate, and mutation efficiency of zygotes with simultaneously double-edited GHR and GGTA1, cultured using 4-well (group culture) and 25-well plates (individual culture). In Experiment 3, we assessed the effect of additional GHR-targeted lipofection before and after simultaneous double gRNA-targeted lipofection on the mutation efficiency of edited embryos cultured in 25-well plates. No significant differences in mutation rates were observed between the zygotes edited with either gRNA. Moreover, the formation rate of blastocysts derived from GHR and GGTA1 double-edited zygotes was significantly increased in the 25-well plate culture compared to that in the 4-well plate culture. However, mutations were only observed in GGTA1 when zygotes were transfected with both gRNAs, irrespective of the culture method used. GHR mutations were detected only in blastocysts derived from zygotes subjected to GHR-targeted lipofection before simultaneous double gRNA-targeted lipofection. Overall, our results suggest that additional lipofection before simultaneous double gRNA-targeted lipofection induces additional mutations in the zygotes.

A systematic review reveals conflicting evidence for the prevalence of antibodies against the sialic acid 'xenoautoantigen' Neu5Gc in humans and the need for a standardised approach to quantification

Despite an array of hypothesised implications for health, disease, and therapeutic development, antibodies against the non-human sialic acid N-glycolylneuraminic acid (Neu5Gc) remain a subject of much debate. This systematic review of 114 publications aimed to generate a comprehensive overview of published studies in this field, addressing both the reported prevalence of anti-Neu5Gc antibodies in the human population and whether experimental variation accounts for the conflicting reports about the extent of this response. Absolute titres of anti-Neu5Gc antibodies, the reported prevalence of these antibodies, and the individual variation observed within experiments were analysed and grouped according to biological context ('inflammation', 'xenotransplantation', 'biotherapeutic use', 'cancer', and 'healthy populations'), detection method, target epitope selection, and choice of blocking agent. These analyses revealed that the experimental method had a notable impact on both the reported prevalence and absolute titres of anti-Neu5Gc antibodies in the general population, thereby limiting the ability to ascribe reported trends to genuine biological differences or the consequence of experimental design. Overall, this review highlights important knowledge gaps in the study of antibodies against this important xenoautoantigen and the need to establish a standardised method for their quantification if the extent of the importance of Neu5Gc in human health is to be fully understood.

A platform for qualitative and quantitative characterization of α-Gal and NeuGc at the oligosaccharide level

Glycosylation modification serves as a pivotal quality attribute in glycoprotein-based therapeutics, emphasizing its role in drug safety and efficacy. Prior studies have underscored the potential immunogenic risks posed by the presence of galactose-α-1,3-galactose (α-Gal) and N-glycolylneuraminic acid (NeuGc) in glycoprotein formulations. This accentuates the imperative for developing robust qualitative and quantitative analytical methods to monitor these immunogenic epitopes, thereby ensuring drug safety. In the present investigation, α-Gal and NeuGc were accurately quantified using UPLC-FLR-MS/MS at the oligosaccharide level. Remarkably, α-Gal could be identified when the ion intensity ratio or the mass-to-charge ratio (m/z) of 528.19 to 366.14 exceeded 1. Concurrently, NeuGc and N-acetylneuraminic acid (NeuAc) could be unambiguously identified through their respective fragment ions at m/z 673.23 and m/z 657.23. Furthermore, relative quantification of α-Gal and NeuGc was achieved using fluorescence signals. This study introduces a sensitive and reliable analytical approach for the qualitative and quantitative assessment of α-Gal and NeuGc in glycoprotein pharmaceuticals. The methodology offers significant potential for application in process control and optimization of glycoprotein production, aimed at minimizing immunogenicity and enhancing product quality.

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.

Knock-out of N-glycolylneuraminic acid attenuates antibody-mediated rejection in xenogenically perfused porcine lungs

BACKGROUND

Antibody-mediated rejection has long been known to be one of the major organ failure mechanisms in xenotransplantation. In addition to the porcine α1,3-galactose (α1,3Gal) epitope, N-Glycolylneuraminic acid (Neu5Gc), a sialic acid, has been identified as an important porcine antigen against which most humans have pre-formed antibodies. Here we evaluate GalTKO.hCD46 lungs with an additional cytidine monophospho-N-acetylneuraminic acid hydroxylase (CMAH) gene knock-out (Neu5GcKO) in a xenogeneic ex vivo perfusion model METHODS: Eleven GalTKO.hCD46.Neu5GcKO pig lungs were perfused for up to 6 h with fresh heparinized human blood. Six of them were treated with histamine (H) blocker famotidine and 1-thromboxane synthase inhibitor Benzylimidazole (BIA) and five were left untreated. GalTKO.hCD46 lungs without Neu5GcKO (n = 18: eight untreated and 10 BIA+H treated) served as a reference. Functional parameters, blood, and tissue samples were collected at pre-defined time points throughout the perfusion RESULTS: All but one Neu5GcKO organs maintained adequate blood oxygenation and "survived" until elective termination at 6 h whereas two reference lungs failed before elective termination at 4 h. Human anti-Neu5Gc antibody serum levels decreased during the perfusion of GalTKO.hCD46 lungs by flow cytometry (∼40% IgM, 60% IgG), whereas antibody levels in Neu5GcKO lung perfusions did not fall (IgM p = .007; IgG p < .001). Thromboxane elaboration, thrombin generation, and histamine levels were significantly reduced with Neu5GcKO lungs compared to reference in the untreated groups (p = .007, .005, and .037, respectively); treatment with BIA+H masked these changes. Activation of platelets, measured as CD62P expression on circulating platelets, was lower in Neu5GcKO experiments compared to reference lungs (p = .023), whereas complement activation (as C3a rise in plasma) was not altered. MCP-1 and lactotransferin level elevations were blunted in Neu5GcKO lung perfusions (p = .007 and .032, respectively). Pulmonary vascular resistance (PVR) rise was significantly attenuated and delayed in untreated GalTKO.hCD46.Neu5GcKO lungs in comparison to the untreated GalTKO.hCD46 lungs (p = .003) CONCLUSION: Additional Neu5GcKO in GalTKO.hCD46 lungs significantly reduces parameters associated with antibody-mediated inflammation and activation of the coagulation cascade. Knock-out of the Neu5Gc sialic acid should be beneficial to reduce innate immune antigenicity of porcine lungs in future human recipients.

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.

Multiple gene editing in porcine embryos using a combination of microinjection, electroporation, and transfection methods

Background and Aim:

Mosaicism – the presence of both wild-type and mutant alleles – is a serious problem for zygotic gene modification through gene editing using the Clustered regularly interspaced short palindromic repeats-Cas9 (CRISPR/Cas9) system. Different delivery methods, such as microinjection (MI), electroporation (EP), and transfection (TF), can be used to transfer CRISPR/Cas9 components into porcine zygotes. This study aimed to develop a method that combines MI, EP, and TF to improve mutation efficiency mediated through the CRISPR/Cas9 system for a triple-gene knockout in pigs.

Materials and Methods:

The study consisted of three groups: The MI group with three simultaneously microinjected guide RNAs (gRNAs) targeting α-1,3-galactosyltransferase (GGTA1), cytidine 32 monophosphate-N-acetylneuraminic acid hydroxylase (CMAH), and β-1,4-N-acetyl-galactosaminyltransferase 2 (B4GALNT2); the MI + EP group with two gRNAs targeting GGTA1 and B4GALNT2 genes delivered into zygotes through MI, followed by EP of gRNA targeting the CMAH 1 h later; and the MI + EP + TF group with MI of gRNA targeting GGTA1 gene into zygotes, followed by EP of gRNA targeting CMAH 1 h later, and then TF of gRNA targeting the B4GALNT2 gene into zona-free zygotes after another hour.

Results:

The rate of blastocysts carrying mutations in one or two gene(s) was significantly higher in the MI + EP + TF group than in the MI group. However, the blastocyst formation rate of zygotes in the MI + EP + TF group was lower than that of the zygotes in the other treatment groups.

Conclusion:

The combination of CRISPR/Cas9 delivery methods may improve the mutation efficiency of triple-gene edited porcine blastocysts.

Xenotransplantation becoming reality

To bridge the gap between organ demand and supply, xenotransplantation has long been considered as a realistic option for end-stage organ failure. Early this year this promise became reality for David Bennett Sr., the first patient whose own failing heart was replaced with a xeno-pig heart. To get here has been a rollercoaster ride of physiological hurdles seemingly impossible to overcome, technological breakthroughs and ethical and safety concerns. It started in 1984, with Stephanie Fae Beauclair, also known as baby Fae, receiving a baboon heart, which allowed her to survive for another 30 days. For ethical reasons primate work was soon abandoned in favour of the pig. But increased phylogenetic distance also brought with it an increased immunological incompatibility. It has been the development of ever more sophisticated genetic engineering tools, which brought down the physiological barriers, enabled humanisation of porcine organs and helped addressing safety concerns. This renewed the confidence in xenotransplantation, brought new funding opportunities and resulted finally in the first in human trial.

Are there specific antibodies against Neu5Gc epitopes in the blood of healthy individuals?

Strong discrepancies in published data on the levels and epitope specificities of antibodies against the xenogenic N-glycolyl forms of sialoglycans (Hanganutziu-Deicher Neu5Gcɑ2-3Galβ1-4Glc and related antigens) in healthy donors prompted us to carry out a systematic study in this area using the printed glycan array and other methods. This article summarizes and discusses our published and previously unpublished data, as well as publicly available data from the Consortium for Functional Glycomics. As a result, we conclude that (1) the level of antibodies referred to as anti-Neu5Gc in healthy individuals is low; (2) there are antibodies that seem to interact with Neu5Gc-containing epitopes, but in fact they recognize internal fragments of Neu5Gc-containing glycans (without sialic acids), which served as antigens in the assays used and; (3) a population capable of interacting specifically with Neu5Gc (it does not bind the corresponding NAc analogs) does exist, but it binds the monosaccharide Neu5Gc better than the entire glycans containing it. In other words, in healthy donors, there are populations of antibodies capable of binding the Neu5Gc monosaccharide or the inner core -Galβ1-4Glc, but very few true anti-Neu5Gcɑ2-3Galβ1-4Glc antibodies, i.e., antibodies capable of specifically recognizing the entire trisaccharide.

One-Step Generation of Multiple Gene-Edited Pigs by Electroporation of the CRISPR/Cas9 System into Zygotes to Reduce Xenoantigen Biosynthesis

Xenoantigens cause hyperacute rejection and limit the success of interspecific xenografts. Therefore, genes involved in xenoantigen biosynthesis, such as GGTA1, CMAH, and B4GALNT2, are key targets to improve the outcomes of xenotransplantation. In this study, we introduced a CRISPR/Cas9 system simultaneously targeting GGTA1, CMAH, and B4GALNT2 into in vitro-fertilized zygotes using electroporation for the one-step generation of multiple gene-edited pigs without xenoantigens. First, we optimized the combination of guide RNAs (gRNAs) targeting GGTA1 and CMAH with respect to gene editing efficiency in zygotes, and transferred electroporated embryos with the optimized gRNAs and Cas9 into recipient gilts. Next, we optimized the Cas9 protein concentration with respect to the gene editing efficiency when GGTA1, CMAH, and B4GALNT2 were targeted simultaneously, and generated gene-edited pigs using the optimized conditions. We achieved the one-step generation of GGTA1/CMAH double-edited pigs and GGTA1/CMAH/B4GALNT2 triple-edited pigs. Immunohistological analyses demonstrated the downregulation of xenoantigens; however, these multiple gene-edited pigs were genetic mosaics that failed to knock out some xenoantigens. Although mosaicism should be resolved, the electroporation technique could become a primary method for the one-step generation of multiple gene modifications in pigs aimed at improving pig-to-human xenotransplantation.

Efficient generation of GGTA1-deficient pigs by electroporation of the CRISPR/Cas9 system into in vitro-fertilized zygotes

BACKGROUND

Xenoantigens are a major source of concern with regard to the success of interspecific xenografts. GGTA1 encodes α1,3-galactosyltransferase, which is essential for the biosynthesis of galactosyl-alpha 1,3-galactose, the major xenoantigen causing hyperacute rejection. GGTA1-modified pigs, therefore, are promising donors for pig-to-human xenotransplantation. In this study, we developed a method for the introduction of the CRISPR/Cas9 system into in vitro-fertilized porcine zygotes via electroporation to generate GGTA1-modified pigs.

RESULTS

We designed five guide RNAs (gRNAs) targeting distinct sites in GGTA1. After the introduction of the Cas9 protein with each gRNA via electroporation, the gene editing efficiency in blastocysts developed from zygotes was evaluated. The gRNA with the highest gene editing efficiency was used to generate GGTA1-edited pigs. Six piglets were delivered from two recipient gilts after the transfer of electroporated zygotes with the Cas9/gRNA complex. Deep sequencing analysis revealed that five out of six piglets carried a biallelic mutation in the targeted region of GGTA1, with no off-target events. Furthermore, staining with isolectin B4 confirmed deficient GGTA1 function in GGTA1 biallelic mutant piglets.

CONCLUSIONS

We established GGTA1-modified pigs with high efficiency by introducing a CRISPR/Cas9 system into zygotes via electroporation. Multiple gene modifications, including knock-ins of human genes, in porcine zygotes via electroporation may further improve the application of the technique in pig-to-human xenotransplantation.

Cytokine-inducible promoters to drive dynamic transgene expression: The "Smart Graft" strategy

BACKGROUND

Ubiquitous expression of T-cell regulatory transgenes such as the cytotoxic T lymphocyte-associated antigen 4 (CTLA4) or the high-affinity variant LEA29Y improves xeno graft survival. Such donor pigs are however immunocompromised and susceptible to infection. Continous high expression of CTLA4 or LEA29Y in the graft could also compromise the health status of recipients. The novel "Smart Graft" strategy is likely to avoid these problems by controlling the expression of T-cell regulatory transgenes as and when required.

METHODS

Candidate promoters inducible by inflammatory cytokines were identified by in silico screening for potential NF-κB binding sites. Basal promoter levels and responsiveness to TNFα and IL1ß were quantified by expression of secreted embryonic alkaline phosphatase in cultured cells. Promoters were modified to increase responsiveness by removing regulatory elements or adding SP-1 or NF-κB binding sites and again tested in vitro. The most promising promoters were then assessed in vivo. Porcine cells expressing inducible Renilla luciferase constructs were transplanted into immunodeficient NOD-Scid-IL2 receptor gamma^null (NSG) mice. Following engraftment, the recipient's immune system was reconstituted by splenocyte transfer raising an immune response to the porcine xenograft. The resulting induction of promoter activity was detected by in vivo bioimaging.

RESULTS

Three human (hTNFAIP1, hVCAM1 and hCCL2), and one porcine promoter (pA20) were chosen for in vitro tests. In all experiments, the semi-synthetic and inducible ELAM promoter as well as the CAG promoter were used as references. In contrast to hTNFAIP1 and hVCAM1 the ELAM, hCCL2 and pA20 promoters showed significant induction after cytokine challenge. The hCCL2 and pA20 promoters were further optimized, resulting in increased responsiveness to TNFα and IL1ß. Cytokine-dependent upregulation of promoter activity was tested in vivo, where the ELAM and the optimized hCCL2 promoters showed a 2-fold upregulation, while one of the improved A20 promoters showed almost 10-fold upregulation. Our results also revealed more than 4-fold cytokine inducibility of the CAG promoter.

CONCLUSION

This is the first in vivo comparison of existing and newly designed cytokine-inducible promoters. Optimization of promoter structure resulted in almost 10-fold inducibility of promoter activity. Such a rapid and dynamically regulated response to inflammation and cell damage could reduce initial graft rejection, making the "Smart Graft" approach a useful means of modulating the expression of immune regulatory transgenes to avoid deleterious effects on porcine and human health. Expressing transgenes in this fashion could provide a safer organ for transplantation.

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

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

Evaluation of multiple gene targeting in porcine embryos by the CRISPR/Cas9 system using electroporation

The CRISPR/Cas9 system now allows for unprecedented possibilities of genome editing. However, there are some limitations, including achieving efficient one-step multiple genome targeting to save costs, time, and ensure high quality. In the present study, we investigated the efficiency of one-step multiple gene modification by electroporation in porcine zygotes using pooled guide RNAs (gRNAs) targeting CMAH, GHR, GGTA1, and PDX1. We first selected the best-performing gRNA from three different designs for each gene based on the effect on embryo development and mutation efficiency. The three gRNAs showed equivalent effects on the rates of blastocyst formation in each targeted gene; however, gRNAs CMAH #2, GHR #3, GGTA1 #3, and PDX1 #3 showed the highest biallelic mutation rate, although the total mutation rate of PDX1 #3 was significantly lower than that of PDX1 #1. Therefore, CMAH #2, GHR #3, GGTA1 #3, and PDX1 #1 were used as a mixture in electroporation to further clarify whether multiple genes can be targeted simultaneously. Individual sequencing of 43 blastocysts at the target sites of each gene showed mutations in one and two target genes in twenty-four (55.8%) and nine (20.9%) blastocysts, respectively. No mutation was detected in any target gene in ten (23.3%) blastocysts and no blastocysts had a mutation in three or more target genes. These results indicate that electroporation could effectively deliver multiple gRNAs and Cas9 protein into porcine zygotes to target multiple genes in a one-step process. However, the technique requires further development to increase the success rate of multiple gene modification.

Triple (GGTA1, CMAH, B2M) modified pigs expressing an SLA class Ilow phenotype-Effects on immune status and susceptibility to human immune responses

Porcine xenografts lacking swine leukocyte antigen (SLA) class I are thought to be protected from human T cell responses. We have previously shown that SLA class I deficiency can be achieved in pigs by CRISPR/Cas9-mediated deletion of β₂ -microglobulin (B2M). Here, we characterized another line of genetically modified pigs in which targeting of the B2M locus did not result in complete absence of B2M and SLA class I but rather in significantly reduced expression levels of both molecules. Residual SLA class I was functionally inert, because no proper differentiation of the CD8⁺ T cell subset was observed in B2M^low pigs. Cells from B2M^low pigs were less capable in triggering proliferation of human peripheral blood mononuclear cells in vitro, which was mainly due to the nonresponsiveness of CD8⁺ T cells. Nevertheless, cytotoxic effector cells developing from unaffected cell populations (eg, CD4⁺ T cells, natural killer cells) lysed targets from both SLA class I⁺ wildtype and SLA class I^low pigs with similar efficiency. These data indicate that the absence of SLA class I is an effective approach to prevent the activation of human CD8⁺ T cells during the induction phase of an anti-xenograft response. However, cytotoxic activity of cells during the effector phase cannot be controlled by this approach.

Viable pigs after simultaneous inactivation of porcine MHC class I and three xenoreactive antigen genes GGTA1, CMAH and B4GALNT2

BACKGROUND

Cell surface carbohydrate antigens play a major role in the rejection of porcine xenografts. The most important for human recipients are α-1,3 Gal (Galactose-alpha-1,3-galactose) causing hyperacute rejection, also Neu5Gc (N-glycolylneuraminic acid) and Sd(a) blood group antigens both of which are likely to elicit acute vascular rejection given the known human immune status. Porcine cells with knockouts of the three genes responsible, GGTA1, CMAH and B4GALNT2, revealed minimal xenoreactive antibody binding after incubation with human serum. However, human leucocyte antigen (HLA) antibodies cross-reacted with swine leucocyte antigen class I (SLA-I). We previously demonstrated efficient generation of pigs with multiple xeno-transgenes placed at a single genomic locus. Here we wished to assess whether key xenoreactive antigen genes can be simultaneously inactivated and if combination with the multi-transgenic background further reduces antibody deposition and complement activation.

METHODS

Multiplex CRISPR/Cas9 gene editing and somatic cell nuclear transfer were used to generate pigs carrying functional knockouts of GGTA1, CMAH, B4GALNT2 and SLA class I. Fibroblasts derived from one- to four-fold knockout animals, and from multi-transgenic cells (human CD46, CD55, CD59, HO1 and A20) with the four-fold knockout were used to examine the effects on human IgG and IgM binding or complement activation in vitro.

RESULTS

Pigs were generated carrying four-fold knockouts of important xenoreactive genes. In vitro assays revealed that combination of all four gene knockouts reduced human IgG and IgM binding to porcine kidney cells more effectively than single or double knockouts. The multi-transgenic background combined with GGTA1 knockout alone reduced C3b/c and C4b/c complement activation to such an extent that further knockouts had no significant additional effect.

CONCLUSION

We showed that pigs carrying several xenoprotective transgenes and knockouts of xenoreactive antigens can be readily generated and these modifications will have significant effects on xenograft survival.

Exposure of Children to Rural Lifestyle Factors Associated With Protection Against Allergies Induces an Anti-Neu5Gc Antibody Response

Rural lifestyle has been shown to be highly protective against the development of allergies. Contact to farm-animals or pets and early-life consumption of milk products turned out to be important. These exposures provide contact to N-glycolylneuraminic acid (Neu5Gc), a sialic acid naturally expressed in mammalians but not in humans or microbes although both are able to incorporate exogenously provided Neu5Gc and induce thereby an anti-Neu5Gc antibody response. Farmers' children had elevated levels of anti-Neu5Gc antibodies associated with increased contact to Neu5Gc. Farm-related exposures that were associated with protection against allergies such as exposure to farm-animals or pets and consumption of milk were also associated with an antibody response to Neu5Gc in children. Exposure to cats was associated with increased anit-Neu5Gc IgG levels at different timepoints assessed between 1 year of age and school-age. Moreover, consumption of non-pasteurized milk in the first year of life was associated with increased anti-Neu5Gc IgG levels. Neu5Gc-providing exposures that were associated with protection against allergies were reflected in an elevated anti-Neu5Gc IgG level in children. Exposure to Neu5Gc was associated with anti-inflammation and protection of asthma development in children and mice without contribution of anti-Neu5Gc antibodies.

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.

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

Background

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

Methods

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

Findings

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

Interpretation

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

Fund

None.

Phylogenetic Distribution of CMP-Neu5Ac Hydroxylase (CMAH), the Enzyme Synthetizing the Proinflammatory Human Xenoantigen Neu5Gc

The enzyme CMP-N-acetylneuraminic acid hydroxylase (CMAH) is responsible for the synthesis of N-glycolylneuraminic acid (Neu5Gc), a sialic acid present on the cell surface proteins of most deuterostomes. The CMAH gene is thought to be present in most deuterostomes, but it has been inactivated in a number of lineages, including humans. The inability of humans to synthesize Neu5Gc has had several evolutionary and biomedical implications. Remarkably, Neu5Gc is a xenoantigen for humans, and consumption of Neu5Gc-containing foods, such as red meats, may promote inflammation, arthritis, and cancer. Likewise, xenotransplantation of organs producing Neu5Gc can result in inflammation and organ rejection. Therefore, knowing what animal species contain a functional CMAH gene, and are thus capable of endogenous Neu5Gc synthesis, has potentially far-reaching implications. In addition to humans, other lineages are known, or suspected, to have lost CMAH; however, to date reports of absent and pseudogenic CMAH genes are restricted to a handful of species. Here, we analyze all available genomic data for nondeuterostomes, and 322 deuterostome genomes, to ascertain the phylogenetic distribution of CMAH. Among nondeuterostomes, we found CMAH homologs in two green algae and a few prokaryotes. Within deuterostomes, putatively functional CMAH homologs are present in 184 of the studied genomes, and a total of 31 independent gene losses/pseudogenization events were inferred. Our work produces a list of animals inferred to be free from endogenous Neu5Gc based on the absence of CMAH homologs and are thus potential candidates for human consumption, xenotransplantation research, and model organisms for investigation of human diseases.

Anti-Neu5Gc and anti-non-Neu5Gc antibodies in healthy humans

Our group previously investigated the levels of anti-Gal and anti-nonGal IgM and IgG in a cohort of 75 healthy humans of various backgrounds, and found some significant differences related to factors such as age, gender, ABO blood group, diet, vaccination history, and geographic location during childhood. We have now expanded our cohort (n = 84) to investigate the levels of anti-Neu5Gc and anti-nonGal/nonNeu5Gc antibodies in healthy humans. Anti-nonGal and anti-nonGal/nonNeu5Gc human IgM and IgG binding to pRBCs and pAECs from GTKO/CD46 and GTKO/CD46/Neu5GcKO pigs were measured by flow cytometry. Anti-Gal and anti-Neu5Gc IgM and IgG levels were measured by ELISA. In summary, (i) the great majority (almost 100%) of humans had anti-Neu5Gc IgM and IgG antibodies that bound to pAECs and approximately 50% had anti-Neu5Gc antibodies that bound to pRBCs, (ii) there was significantly less human antibody binding to pig cells that did not express either Gal or Neu5Gc compared with those that did not express Gal alone, (iii) the levels of both IgM and IgG binding to GTKO/CD46/Neu5GcKO pRBCs and pAECs were low, (iv) the level of anti-Neu5Gc IgG was higher in men than women, (v) the level did not change with age or diet, and there was some variability associated with (vi) previous vaccination history and (vii) the geographic region in which the individual spent his or her childhood. Our study confirms that human antibody binding to RBCs and AECs from GTKO/CD46/Neu5GcKO pigs is greatly reduced compared to binding to GTKO/CD46 cells. However, all humans appear to have a low level of antibody that binds to pAECs that is not directed to either Gal or Neu5Gc. Our findings require consideration in planning clinical trials of xenotransplantation.

Biochemical, Cellular, Physiological, and Pathological Consequences of Human Loss of N-Glycolylneuraminic Acid

About 2-3 million years ago, Alu-mediated deletion of a critical exon in the CMAH gene became fixed in the hominin lineage ancestral to humans, possibly through a stepwise process of selection by pathogen targeting of the CMAH product (the sialic acid Neu5Gc), followed by reproductive isolation through female anti-Neu5Gc antibodies. Loss of CMAH has occurred independently in some other lineages, but is functionally intact in Old World primates, including our closest relatives, the chimpanzee. Although the biophysical and biochemical ramifications of losing tens of millions of Neu5Gc hydroxy groups at most cell surfaces remains poorly understood, we do know that there are multiscale effects functionally relevant to both sides of the host-pathogen interface. Hominin CMAH loss might also contribute to understanding human evolution, at the time when our ancestors were starting to use stone tools, increasing their consumption of meat, and possibly hunting. Comparisons with chimpanzees within ethical and practical limitations have revealed some consequences of human CMAH loss, but more has been learned by using a mouse model with a human-like Cmah inactivation. For example, such mice can develop antibodies against Neu5Gc that could affect inflammatory processes like cancer progression in the face of Neu5Gc metabolic incorporation from red meats, display a hyper-reactive immune system, a human-like tendency for delayed wound healing, late-onset hearing loss, insulin resistance, susceptibility to muscular dystrophy pathologies, and increased sensitivity to multiple human-adapted pathogens involving sialic acids. Further studies in such mice could provide a model for other human-specific processes and pathologies involving sialic acid biology that have yet to be explored.