Definition and characterization of chicken Gal alpha(1,3)Gal antibodies

Precise Genome Editing in Poultry and Its Application to Industries

Poultry such as chickens are valuable model animals not only in the food industry, but also in developmental biology and biomedicine. Recently, precise genome-editing technologies mediated by the CRISPR/Cas9 system have developed rapidly, enabling the production of genome-edited poultry models with novel traits that are applicable to basic sciences, agriculture, and biomedical industry. In particular, these techniques have been combined with cultured primordial germ cells (PGCs) and viral vector systems to generate a valuable genome-edited avian model for a variety of purposes. Here, we summarize recent progress in CRISPR/Cas9-based genome-editing technology and its applications to avian species. In addition, we describe further applications of genome-edited poultry in various industries.

α-Gal-Based Vaccines: Advances, Opportunities, and Perspectives

Humans and crown catarrhines evolved with the inability to synthesize the oligosaccharide galactose-α-1,3-galactose (α-Gal). In turn, they naturally produce high quantities of the glycan-specific antibodies that can be protective against infectious agents exhibiting the same carbohydrate modification on their surface coat. The protective immunity induced by α-Gal is ensured through an antibody-mediated adaptive and cell-mediated innate immune response. Therefore, the α-Gal antigen represents an attractive and feasible target for developing glycan-based vaccines against multiple diseases. In this review article we provide an insight into our current understanding of the mechanisms involved in the protective immunity to α-Gal and discuss the possibilities and challenges in developing a single-antigen pan-vaccine for prevention and control of parasitic diseases of medical and veterinary concern.

Distribution of Bacterial α1,3-Galactosyltransferase Genes in the Human Gut Microbiome

Because of a loss-of-function mutation in the GGTA1 gene, humans are unable to synthetize α1,3-Galactose (Gal) decorated glycans and develop high levels of circulating anti-α1,3-Galactose antibodies (anti-Gal Abs). Anti-Gal Abs have been identified as a major obstacle of organ xenotransplantation and play a role in several host-pathogen relationships including potential susceptibility to infection. Anti-Gal Abs are supposed to stem from immunization against the gut microbiota, an assumption derived from the observation that some pathogens display α1,3-Gal and that antibiotic treatment decreases the level of anti-Gal. However, there is little information to date concerning the microorganisms producing α1,3-Gal in the human gut microbiome. Here, available α1,3-Galactosyltransferase (GT) gene sequences from gut bacteria were selectively quantified for the first time in the gut microbiome shotgun sequences of 163 adult individuals from three published population-based metagenomics analyses. We showed that most of the gut microbiome of adult individuals contained a small set of bacteria bearing α1,3-GT genes. These bacteria belong mainly to the Enterobacteriaceae family, including Escherichia coli, but also to Pasteurellaceae genera, Haemophilus influenza and Lactobacillus species. α1,3-Gal antigens and α1,3-GT activity were detected in healthy stools of individuals exhibiting α1,3-GT bacterial gene sequences in their shotgun data.

Development of a convenient competitive ELISA for the detection of the free and protein-bound nonhuman galactosyl-α-(1,3)-galactose epitope based on highly specific chicken single-chain antibody variable-region fragments

The presence of the nonhuman galactosyl-α-(1,3)-galactose (Gal-α-(1,3)-Gal) carbohydrate epitope on a number of recombinant therapeutic proteins has recently been reported, renewing interest in this immunogenic carbohydrate epitope. It is well-known that this motif is the primary contributing factor in hyperacute rejection of porcine organ xenograft, due to the existence of natural antibodies against this epitope in human serum. Though the number of epitopes on recombinant glycoproteins may be low when compared directly to whole tissue, circulating anti-Gal-α-R immunoglobulins can still induce anaphylaxis. Therefore, there is a need for rapid and convenient methods for detection and monitoring of this epitope in biopharmaceuticals produced in recombinant mammalian systems. To this end, we have generated immune-challenged chicken single-chain antibody variable-region fragment (scFv) libraries targeting the Gal-α-(1,3)-Gal motif and have selected a panel of scFv's that bind the target. We have used one of these antibodies to develop a competitive ELISA for both free and protein-bound Gal-α-(1,3)-Gal and have demonstrated that the ELISA is specific for the target and can be used to determine the loading of the target on glycoproteins. This competitive ELISA will provide a convenient method of detecting and quantifying Gal-α-(1,3)-Gal on therapeutic glycoproteins.

Close-up of the immunogenic α1,3-galactose epitope as defined by a monoclonal chimeric immunoglobulin E and human serum using saturation transfer difference (STD) NMR

Anaphylaxis mediated by carbohydrate structures is a controversially discussed phenomenon. Nevertheless, IgE with specificity for the xenotransplantation antigen α1,3-Gal (α-Gal) are associated with a delayed type of anaphylaxis, providing evidence for the clinical relevance of carbohydrate epitopes in allergy. The aim of this study was to dissect immunoreactivity, interaction, and fine epitope of α-Gal-specific antibodies to obtain insights into the recognition of carbohydrate epitopes by IgE antibodies and their consequences on a molecular and cellular level. The antigen binding moiety of an α-Gal-specific murine IgM antibody was employed to construct chimeric IgE and IgG antibodies. Reactivity and specificity of the resulting antibodies were assessed by means of ELISA and receptor binding studies. Using defined carbohydrates, interaction of the IgE and human serum was assessed by mediator release assays, surface plasmon resonance (SPR), and saturation transfer difference NMR analyses. The α-Gal-specific chimeric IgE and IgG antibodies were proven functional regarding interaction with antigen and Fc receptors. SPR measurements demonstrated affinities in the micromolar range. In contrast to a reference antibody, anti-Gal IgE did not induce mediator release, potentially reflecting the delayed type of anaphylaxis. The α1,3-Gal epitope fine structures of both the recombinant IgE and affinity-purified serum were defined by saturation transfer difference NMR, revealing similar contributions of carbohydrate residues and participation of both galactose residues in interaction. The antibodies generated here constitute the principle underlying α1,3-Gal-mediated anaphylaxis. The complementary data of affinity and fine specificity may help to elucidate the recognition of carbohydrates by the adaptive immune response and the molecular requirements of carbohydrate-based anaphylaxis.

Genetic parameters for levels of natural antibodies in chicken lines divergently selected for specific antibody response

The present study estimated the heritability of natural antibody (NAb) levels binding rabbit red blood cells at the day of immunization with SRBC (NAb0) and 5 d postimmunization (NAb5) in 2 chicken lines divergently selected for specific antibody levels (SpAb) against SRBC and a randombred control line. In addition, genetic correlations between the levels of NAb binding rabbit red blood cells and levels of SpAb binding SRBC were estimated. The heritability of the SpAb level against SRBC was estimated based on data from 23 generations of selection and in total 21,842 chickens. The heritability of NAb levels against rabbit red blood cells was estimated on 1,764 chickens in generations 22 and 23 using a bivariate analysis including the trait under selection (i.e., SpAb responses to SRBC). Maternal environmental effects were accounted for in the analyses. The heritability for SpAb was 0.17, the heritability for NAb0 levels was 0.23, and the heritability for NAb5 was 0.09. The genetic correlation between SpAb and NAb0 was 0.15 and the genetic correlation between SpAb and NAb5 was 0.50. The weak, though positive, genetic correlation between SpAb responses and the NAb0 levels in nonimmunized chickens, as well as the moderate genetic correlation between SpAb responses and the NAb levels 5 d postimmunization with SRBC, suggest that selection for enhanced adaptive immune system results in a positive correlated response of the innate immunity of chickens.

Decreased specific antibody responses to alpha-Gal-conjugated antigen in animals with preexisting high levels of natural antibodies binding alpha-Gal residues

High levels of natural antibodies (NAb) binding the alpha-Gal residue (Galalpha1-3Galbeta1-4GlcNAc) are found in poultry (and humans), which is probably reflected by high levels of natural agglutinating antibodies (Ab) to rabbit red blood cells (RRBC) in plasma from chickens (and humans). Recently, it was shown that alpha-Gal conjugation of proteins induced higher antiprotein Ab responses in alpha-Gal knockout mice, suggesting immune-enhancing features of preexisting Ab binding carbohydrate-protein conjugates. We challenged chickens s.c. with either alpha-Gal-conjugated human serum albumin (HuSA), beta-Gal-conjugated HuSA, or unconjugated ("native") HuSA, respectively, and measured primary and secondary Ab responses to HuSA, including isotype IgM and IgG responses, and cellular immune responses in vitro (lymphoproliferation) to HuSA or concanavalin A. alpha-Gal conjugation, but not beta-Gal conjugation, of HuSA resulted in significantly decreased primary and secondary Ab responses to HuSA, especially IgG isotype responses, as compared with Ab responses to native HuSA. Lymphoproliferation in vitro was also decreased, although not significantly, in birds challenged with alpha-Gal-conjugated HuSA. High levels of agglutinating Ab levels to RRBC and NAb binding porcine thyroglobulin were detected in all birds, as was true for (natural) Ab levels binding alpha-Gal-conjugated HuSA before immunization, whereas low levels of preexisting (natural) antibodies directed to native HuSA were present in plasma before immunization. Levels of RRBC agglutinins and Ab binding thyroglobulin were not affected by immunization with HuSA, alpha-Gal-conjugated HuSA, or beta-Gal-conjugated HuSA. Our data confirm the presence of high levels of (preexisting) NAb in the plasma of chickens directed to the alpha-Gal residue. The decreased responsiveness to alpha-Gal-bearing antigens in the current study shows that, in addition to immune-enhancing features, NAb may also have suppressive effects on specific immune responses, which substantiates the regulatory role of innate immunity (NAb) in mounting specific immune responses.

Correlated effects of selection for immunity in White Leghorn chicken lines on natural antibodies and specific antibody responses to KLH and M. butyricum

Background

The effect of selection for three general immune response traits on primary antibody responses (Ab) to Mycobacterium butyricum or keyhole limpet hemocyanin (KLH) was studied in four experimental lines of White Leghorn chicken. Birds underwent 12 generations of selection for one of three different general immune criteria; high antibody response to Newcastle disease virus 3 weeks after vaccination (ND3), high cell-mediated immune response, using the wing web response to phytohemglutinin (PHA) and high phagocytic activity, measured as carbone clearance (CC). Line ND3-L was selected on ND3, line PHA-L was selected on PHA, and line CC-L on CC, but all lines were measured for all three traits. The fourth line was a contemporary random bred control maintained throughout the selection experiment. Principal component analysis was used to distinguish clusters based on the overall set of immune measures.

Results

In the KLH immunised group, no differences were present between lines for natural antibodies binding to KLH and LPS, and, lines ND3-L and PHA-L had higher titers to LTA and anti-Gal titers measured before the immunisation protocol. The measure of ND3 was correlated positively with LPS titers measured post KLH immunisation and with the difference between LPS titers measured at day 0 and 7 post immunisation. In the M. butyricum immunised group, Line ND3-L showed significantly higher specific antibody response to M. butyricum, and this result agrees well with the hypothesis that the Th-1 pathway was expected to be selected for in this line.

Conclusion

This study has shown that the two different antigens KLH and M. butyricum gave rise to different responses in the set of selected lines, and that the response was only enhanced for the antigen associated with the same response mechanism as that for the trait (ND3, PHA or CC) for which the line was selected. Interactions between innate and acquired immunity have been observed mainly for the high antibody selected trait, indicating there was a specific interaction due to the selection criterion. Furthermore, the results confirmed the independence between the three selected traits. Finally, principal component analysis contributed to visually discriminate high and low responders to the two new antigens in the four lines.

Technology insight: Innovative options for end-stage renal disease--from kidney refurbishment to artificial kidney

The steadily growing number of patients with chronic kidney disease who will eventually develop end-stage renal disease, together with the qualitative limitations of currently available renal replacement therapies, have triggered the exploration of innovative strategies for renal replacement therapy and for salvage of renal function. Currently, new hemodialysis modalities and membranes are being used with the aim of increasing clearance of uremic toxins to afford better metabolic control. In addition to these conventional approaches, there are four innovative potential solutions to the problem of replacing renal function when kidneys fail. The first is a small, implantable device with the potential to be supplemented with human cells ('artificial kidney'). The second involves restoration of the damaged kidney by harnessing recent advances in stem-cell technology and knowledge of developmental programing ('refurbished kidney'). The third is (partially) growing a kidney in vitro with the use of therapeutic cloning ('cultured kidney'). The fourth innovative solution involves the use of other organs to replace various renal functions ('distributed kidney'). In this article we review the efforts that have been made to improve renal replacement therapies, and explore innovative approaches. We will not cover all potential solutions in detail. Rather, we aim to indicate directions of future endeavor and arouse enthusiasm in clinicians and scientists for exploration of these exciting avenues.

Gal knockout and beyond

Recently, Galalpha1-3Galbeta1-4GlcNAc (Gal) knockout (k/o) pigs have been developed using genetic cloning technologies. This remarkable achievement has generated great enthusiasm in xenotransplantation studies. This review summarizes the current status of nonhuman primate experiments using Gal k/o pig organs. Briefly, when Gal k/o pig organs are transplanted into primates, hyperacute rejection does not occur. Although graft survival has been prolonged up to a few months in some cases, the overall results were not better than those using Gal-positive pig organs with human complement regulatory protein transgenes. Gal k/o pig kidneys rapidly developed rejection which was associated with increased anti-non-Gal antibodies. Although the precise mechanisms of Gal k/o pig organ rejection are not clear, it could result from incomplete deletion of Gal, up-regulation of new antigen (non-Gal antigen) and/or production of non-Gal antibodies. Future work in xenotransplantation should place emphasis on further modification of donors, such as combining human complement regulatory genes with Gal k/o, deleting non-Gal antigens and adding protective/surviving genes or a gene that inhibits coagulation. Induction of donor-specific T- and B-cell tolerance and promotion of accommodation are also warranted.

The Role of Anti-non-Gal Antibodies in the Development of Acute Humoral Xenograft Rejection of hDAF Transgenic Porcine Kidneys in Baboons Receiving Anti-Gal Antibody Neutralization Therapy

BACKGROUND

The present study was undertaken to determine the role of preformed and induced anti-non-Gal antibodies in the rejection of hDAF pig-to-baboon kidney xenotransplants after anti-Gal antibody neutralization therapy.

METHODS

Seven baboons received life-supporting kidney transplants from hDAF transgenic pigs. Anti-Gal antibodies were neutralized by GAS914 or TPC (a Gal PEG glycoconjugate polymer). Group 1 (n=5) underwent a conventional immunosuppressive therapy with FK506, rabbit anti-thymocyte serum/immunoglobulin, mycophenolate mofetil, and steroids. Group 2 (n=2) received an anti-humoral immunity regimen with LF15-0195, Rituxan and cobra venom factor in addition to ATG, FK506 and steroids. Levels of anti-non-Gal antibodies and their mediated complement-dependent cytotoxic activities (CDC) were detected by flow cytometry using Gal knockout (k/o) pig lymphocytes (LC) or endothelial cells (EC) as targets.

RESULTS

Continuous infusion of GAS914/TPC significantly reduced anti-Gal antibodies. In Group 1, four of five baboons developed severe acute humoral xenograft rejection (AHXR) and the rejection was associated with either a high level of preformed anti-non-Gal IgG or a marked elevation in induced anti-non-Gal IgG and IgM. Sera collected at the time of AHXR had a high level of CDC to porcine LC/EC from Gal k/o animals. The intensive anti-humoral therapy in Group 2 completely inhibited both anti-Gal and non-Gal antibody production and prevented AHXR. However, this therapy was not well tolerated by the baboons.

CONCLUSION

In a pig-to-baboon kidney transplant model, both preformed and induced anti-non-Gal antibodies are strongly associated with the pathogenesis of AHXR when anti-Gal antibodies are neutralized.

Transgenic chickens as bioreactors for protein-based drugs

The potential of using transgenic animals for the synthesis of therapeutic proteins was suggested over twenty years ago. Considerable progress has been made in developing methods for the production of transgenic animals and specifically in the expression of therapeutic proteins in the mammary glands of cows, sheep and goats. Development of transgenic hens for protein production in eggs has lagged behind these systems. The positive features associated with the use of the chicken in terms of cost, speed of development of a production flock and potentially appropriate glycosylation of target proteins have led to significant advances in transgenic chicken models in the past few years.

Improvement in human decay accelerating factor transgenic porcine kidney xenograft rejection with intravenous administration of gas914, a polymeric form of alphaGAL

BACKGROUND

The present study was undertaken to determine whether intravenous administration of GAS914, a polymeric form of alphaGal, would minimize porcine kidney xenograft rejection in baboons. Human decay accelerating factor renal xenografts were transplanted into 16 baboon recipients.

METHODS

Baseline immunosuppression for all groups included cyclosporine A, cyclophosphamide, SDZ-RAD, and methylprednisolone. Group 1 received only baseline immunosuppression; group 2 animals received low-dose GAS914 with baseline immunosuppression; group 3 animals received high dose GAS914 with high-dose baseline immunosuppression; and animals from group 4 received high-dose GAS914 and low-dose baseline immunosuppression.

RESULTS

None of the animals in this study developed hyperacute rejection. Intravenous administration of GAS914 significantly reduced xenoreactive antibodies as measured by antiporcine hemolytic assays and anti-Gal (immunoglobulin [Ig] G and IgM) antibody assays. Rejection was less severe in the GAS914-treated group. Only 25% (3 of 12) of GAS914-treated animals were killed as a result of rejection, whereas 75% (three of four) of non-GAS914-treated animals were killed because of terminal rejection (P<0.01). Protocol biopsies demonstrated that the degree of acute humoral xenograft rejection (AHXR) was reduced in the GAS914-treated animals compared with non-GAS914-treated animals.

CONCLUSION

The intravenous administration of GAS914 reduces xenoreactive antibody levels and reduces the degree of porcine kidney xenograft rejection, but does not improve survival. AHXR and drug toxicity remain major barriers to the long-term success of xenotransplantation.