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.

Solid-phase extraction treatment is required for measurement of active glucagon-like peptide-1 by enzyme-linked immunosorbent assay kit affected by heterophilic antibodies

AIMS/INTRODUCTION

It is reported that interfering substances in the blood might influence the value for measurement of active glucagon-like peptide-1 (GLP-1) in human plasma. Solid phase extraction (SPE) pretreatment is recommended to reduce their influence, but it requires a lot of cost and time. However, there is little investigation about causative inhibitory substances and about methods that can replace solid phase extraction. In the present study, we aimed to seek the candidate of the substances that might interfere with an active GLP-1 enzyme-linked immunosorbent assay (ELISA).

MATERIALS AND METHODS

Two kinds of active GLP-1 ELISA kits using different antibodies, plural extraction carriers and elution solutions were used to evaluate the SPE method. Active GLP-1 concentration was compared with or without SPE, and with or without a heterophilic blocking tube.

RESULTS

Active GLP-1 values were often higher without SPE compared with those with SPE pretreatment. This difference was eliminated by pretreatment with a heterophilic blocking tube or ELISA kits that did not use a mouse monoclonal antibody, and was independent of SPE.

CONCLUSIONS

Substances absorbed to a heterophilic blocking tube carrier might interfere with an active GLP-1 immunoassay. Solid-phase extraction treatment is required for measurement of active GLP-1 by an ELISA kit affected by heterophilic antibodies.

What makes D-dimer assays suspicious-heterophilic antibodies?

BACKGROUND

Heterophilic antibodies are still an important source of interference in immunoassays, but reports of interference with D-dimers are rare. Are D-dimer level abnormalities, found in the clinic, caused by heterophilic antibodies as well, or are other mechanisms involved? We will elaborate on this issue through two different examples in this article.

METHODS

Serum from two patients with significantly elevated levels of D-dimers were measured and compared by different methods, diluted, and dealt with heterophilic antibody blockers. At the same time, to retrieve the interference, we focused on the cause of D-dimer false positives and made a systematic review of the literature.

RESULTS

The D-dimer values were normal (0.49 and 0.15 μg/mL) detected with different testing method and decreased after addition of heterophilic antibody blocking reagent. According to literature data, there were 66.7% (4/6) references showed the interference were heterophilic antibody.

CONCLUSIONS

The influence of heterophilic antibodies on the measurement of D-dimers remains a big challenge. Different measuring instruments and methods may have significant differences in the measurement of D-dimers. By using a combination of instrumental methods for measuring, incorporating heterophilic antibody blockers, and combining with clinical performance and imaging data, most of the interference can be eliminated.

Falsely elevated thyroglobulin and calcitonin due to rheumatoid factor in non-relapsing thyroid carcinoma: A case report

RATIONALE

Thyroglobulin (Tg) is an accurate indicator of clinical outcome after total thyroidectomy in patients with differentiated thyroid carcinoma. Usually, Tg levels agree with whole body scan. However, in some patient, discordant results were found, often because of Tg immunoassay interference. Several reports indicated that 2-site immunoassay interference with heterophile antibodies (HAb) can lead to misinterpretation of the laboratory test result.

PATIENT CONCERNS

We report a case of a 46-year-old woman referred to our endocrine clinic for markedly increased calcitonin (CT) without the associated clinical picture. The measurement was repeated with the same patient sample on a different analytical platform and the result was an undetectable CT level. The measurement of Tg was repeated on 3 different analytical platforms using chemiluminescence and electrochemiluminescence immunoassays and the results were different on each platform. HAb blocking tubes resulted in a different level of both CT and Tg, suggesting the presence of a heterophile substance in the serum sample. Further characterization showed reactivity to several animal species antibodies and an elevated level of the rheumatoid factor (RF).

DIAGNOSES

She was diagnosed as papillary thyroid carcinoma.

INTERVENTIONS

She had undergone thyroidectomy with lymph node dissection and radioactive therapy.

OUTCOMES

She was found not to have recurrence despite a high serum Tg level.

LESSONS

Our report illustrates a rare case of falsely elevated tumor markers levels due to assay interference caused by RF. This finding pointed out the importance of close communication between the clinician and laboratory staff in order to bring to light discordance between laboratory test results and clinical picture and avoid unnecessary diagnostic procedures and overtreatment.

High-level expression of Camelid nanobodies in Nicotiana benthamiana

Nanobodies (or VHHs) are single-domain antigen-binding fragments derived from Camelid heavy chain-only antibodies. Their small size, monomeric behaviour, high stability and solubility, and ability to bind epitopes not accessible to conventional antibodies make them especially suitable for many therapeutic and biotechnological applications. Here we describe high-level expression, in Nicotiana benthamiana, of three versions of an anti-hen egg white lysozyme (HEWL) nanobody which include the original VHH from an immunized library (cAbLys3), a codon-optimized derivative, and a codon-optimized hybrid nanobody comprising the CDRs of cAbLys3 grafted onto an alternative 'universal' nanobody framework. His6- and StrepII-tagged derivatives of each nanobody were targeted for accumulation in the cytoplasm, chloroplast and apoplast using different pre-sequences. When targeted to the apoplast, intact functional nanobodies accumulated at an exceptionally high level (up to 30% total leaf protein), demonstrating the great potential of plants as a nanobody production system.

Purification and partial characterization of vitellogenin from shorthead redhorse (Moxostoma macrolepidotum) and copper redhorse (Moxostoma hubbsi) and detection in plasma and mucus with a heterologous antibody

Vitellogenin (VTG), the egg yolk precursor protein, was purified from plasma of estradiol-3-benzoate (E2B)-treated male shorthead redhorse (Moxostoma macrolepidotum) and immature copper redhorse (Moxostoma hubbsi) by a two-step chromatographic procedure without precipitation. Intact VTGs appeared as dimers with apparent molecular masses, determined by gel filtration, of approximately 425 kDa (copper redhorse) and approximately 450 kDa (shorthead redhorse). In native polyacrylamide gel electrophoresis (PAGE), dimeric redhorse VTGs appeared as a 520 kDa band. Both VTGs were reduced to a single monomer of approximately 150 kDa in sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) under reducing and nonreducing conditions, indicating that monomers are not linked by disulfide bonds in the dimer form. The purified proteins were characterized as phospholipoglycoproteins. Isoelectric focusing of both VTGs revealed components with isoelectric points ranging from 5.3 to 6.0, suggesting charge heterogeneity. The amino acid composition of both VTGs contains a high proportion of nonpolar amino acids and was similar to those of other teleosts. An antibody developed against carp (Cyprinus carpio) VTG showed cross-reactivity with VTG from both redhorse species. Using this antibody, VTG was detected in plasma and surface mucus of E2B-treated redhorse. This is the most extensive report on purification and characterization of vitellogenin from catostomidid species.

Antibody-mediated xenograft injury: mechanisms and protective strategies

The use of porcine organs for clinical transplantation is a promising potential solution to the shortage of human organs. Preformed anti-pig antibody is the primary cause of hyperacute rejection, while elicited antibody can contribute to subsequent "delayed" xenograft rejection. This article will review recent progress to overcome antibody mediated xenograft rejection, through modification of the host immunity and use of genetically engineered pig organs.

Characterization of natural human anti-non-gal antibodies and their effect on activation of porcine gal-deficient endothelial cells

BACKGROUND

The generation of Galalpha1-3Gal (Gal) transferase deficient pigs has increased the interest in non-Gal antigens potentially representing important targets for xenoreactive antibody binding leading to xenograft rejection. The present study addressed the levels and immunoglobulin isotypes of preformed human anti-non-Gal antibodies and their potential to activate porcine endothelial cells.

METHODS

Porcine endothelial cells lacking the Gal epitope (Gal-/-) were used to measure immunoglobulin (Ig) M and IgG subclass anti-non-Gal antibodies, using sera from 80 blood donors and pooled human AB serum. Antibodies specific for the non-Gal Hanganutziu-Deicher (HD) xenoantigen were measured by enzyme-linked immunosorbent assay. Activation of Gal-/- and Gal+/+ endothelial cells by human serum was measured, in the presence or absence of complement inhibitors, by E-selectin cell-surface expression using flow cytometry.

RESULTS

Anti-non-Gal antibody levels varied considerably among individual sera and comprised approximately 10% of total anti-porcine antibodies without sex or age differences. Among the IgG subclasses only IgG1 and IgG2 were detected. Human serum-induced E-selectin expression on Gal-/- cells was less than 20% compared with Gal+/+ cells, correlated with anti-HD IgM and IgG antibody levels (P=0.027 and 0.032, respectively), and was largely complement-independent in accordance with the lack of IgG3 anti-non-Gal antibodies. In contrast, E-selectin upregulation on Gal+/+ cells was reduced in complement blocking experiments.

CONCLUSION

Preformed anti-non-Gal antibodies, in particular anti-HD antibodies, were present in all human sera samples, activated porcine endothelial cells, and may therefore play a role in xenograft rejection using organs from GalT-/- pigs.

The xenoantibody response and immunoglobulin gene expression profile of cynomolgus monkeys transplanted with hDAF-transgenic porcine hearts

BACKGROUND

Recent work has indicated a role for anti-Gal alpha 1-3Gal (Gal) and anti-non-Gal xenoantibodies in the primate humoral rejection response against human-decay accelerating factor (hDAF) transgenic pig organs. Our laboratory has shown that anti-porcine xenograft antibodies in humans and non-human primates are encoded by a small number of germline IgV(H) progenitors. In this study, we extended our analysis to identify the IgV(H) genes encoding xenoantibodies in immunosuppressed cynomolgus monkeys (Macaca fascicularis) transplanted with hDAF-transgenic pig organs.

METHODS

Three immunosuppressed monkeys underwent heterotopic heart transplantation with hDAF porcine heart xenografts. Two of three animals were given GAS914, a poly-L-lysine derivative shown to bind to anti-Gal xenoantibodies and neutralize them. One animal rejected its heart at post-operative day (POD) 39; a second animal rejected the transplanted heart at POD 78. The third monkey was euthanized on POD 36 but the heart was not rejected. Peripheral blood leukocytes (PBL) and serum were obtained from each animal before and at multiple time points after transplantation. We analyzed the immune response by enzyme-linked immunosorbent assay (ELISA) to confirm whether anti-Gal or anti-non-Gal xenoantibodies were induced after graft placement. Immunoglobulin heavy-chain gene (V(H)) cDNA libraries were then produced and screened. We generated soluble single-chain antibodies (scFv) to establish the binding specificity of the cloned immunoglobulin genes.

RESULTS

Despite immunosuppression, which included the use of the polymer GAS914, the two animals that rejected their hearts showed elevated levels of cytotoxic anti-pig red blood cell (RBC) antibodies and anti-pig aortic endothelial cell (PAEC) antibodies. The monkey that did not reject its graft showed a decline in serum anti-RBC, anti-PAEC, and anti-Gal xenoantibodies when compared with pre-transplant levels. A V(H)3 family gene with a high level of sequence similarity to an allele of V(H)3-11, designated V(H)3-11(cyno), was expressed at elevated levels in the monkey that was not given GAS914 and whose graft was not rejected until POD 78. IgM but not IgG xenoantibodies directed at N-acetyl lactosamine (a precursor of the Gal epitope) were also induced in this animal. We produced soluble scFv from this new gene to determine whether this antibody could bind to the Gal carbohydrate, and demonstrated that this protein was capable of blocking the binding of human serum xenoantibody to Gal oligosaccharide, as had previously been shown with human V(H)3-11 scFv.

CONCLUSIONS

DAF-transgenic organs transplanted into cynomolgus monkeys induce anti-Gal and anti-non-Gal xenoantibody responses mediated by both IgM and IgG xenoantibodies. Anti-non-Gal xenoantibodies are induced at high levels in animals treated with GAS914. Antibodies that bind to the Gal carbohydrate and to N-acetyl lactosamine are induced in the absence of GAS914 treatment. The animal whose heart remained beating for 78 days demonstrated increased usage of an antibody encoded by a germline progenitor that is structurally related, but distinct from IGHV311. This antibody binds to the Gal carbohydrate but does not induce the rapid rejection of the xenograft when expressed at high levels as early as day 8 post-transplantation.

Intrinsic Resistance of Hepatocytes to Complement-Mediated Injury

When activated on or in the vicinity of cells, complement usually causes loss of function and sometimes cell death. Yet the liver, which produces large amounts of complement proteins, clears activators of complement and activated complexes from portal blood without obvious injury or impaired function. We asked whether and to what extent hepatocytes resist injury and loss of function mediated by exposure to complement. Using cells isolated from porcine livers as a model system, we found that, in contrast to endothelial cells, hepatocytes profoundly resist complement-mediated lysis and exhibit normal synthetic and conjugative functions when complement is activated on their surface. The resistance of hepatocytes to complement-mediated injury was not a function of cell surface control of the complement cascade but rather an intrinsic resistance of the cells dependent on the PI3K/Akt pathway. The resistance of hepatocytes to complement might be exploited in developing approaches to the treatment of hepatic failure or more broadly to the treatment of complement-mediated disease.

Survival of adult islet grafts from transgenic pigs with N-acetylglucosaminyltransferase-III (GnT-III) in cynomolgus monkeys

BACKGROUND

Because of a severe shortage of human donor pancreases, pig islets are considered to be an attractive donor source. Our previous in vitro study revealed that adult pig islets have strong non-Galalpha1-3Galbeta1-4GlcNAc-R (alpha-Gal) antigenicity, including the Hanganutziu-Deicher (H-D) antigen, especially in N-linked sugars. In this study, the issue of whether islets from N-acetylglucosaminyltransferase-III (GnT-III) transgenic pigs can prolong their survival in cynomolgus monkeys was examined.

METHODS

Adult pig islets were isolated from transgenic pigs with GnT-III and wild-type genes. GnT-III enzyme activity in pig islets was measured by high performance liquid chromatography (HPLC). The antigenicity of the islets to human natural antibodies was examined by flow cytometry. Pig islets were transplanted under the kidney capsule of streptozotocin-induced diabetic monkeys. After transplantation, blood samples were obtained and plasma insulin levels were monitored on a daily basis.

RESULTS

While GnT-III was barely expressed in wild-type islets, it was expressed at high levels in islets from transgenic pigs, and xenoantigenicity was significantly reduced. There was a trend for islets isolated from GnT-III-transgenic pigs to survive longer than those from wild-type pigs in cynomolgus monkeys (wild type: 1, 1, and 3 days; GnT-III: 1, >3, 4 and 5 days). Humoral and histological studies indicated up-regulated anti-pig islet antibodies and a relatively high deposition in islet grafts from wild-type pigs, respectively.

CONCLUSION

A reduction in xenoantigenicity by GnT-III may have prolonged the survival of porcine islets, suggesting the importance of non-alpha-Gal and non-H-D antigens, as they relate to N-linked sugars in the early rejection of porcine islets in the monkey. This approach may be useful in the clinical xenotransplantation of islets in the future.

Lack of Galactose-α-1,3-Galactose Expression on Porcine Endothelial Cells Prevents Complement-Induced Lysis but Not Direct Xenogeneic NK Cytotoxicity

The galactose-alpha-1,3-galactose (alphaGal) carbohydrate epitope is expressed on porcine, but not human cells, and therefore represents a major target for preformed human anti-pig natural Abs (NAb). Based on results from pig-to-primate animal models, NAb binding to porcine endothelial cells will likely induce complement activation, lysis, and hyperacute rejection in pig-to-human xenotransplantation. Human NK cells may also contribute to innate immune responses against xenografts, either by direct recognition of activating molecules on target cells or by FcgammaRIII-mediated xenogeneic Ab-dependent cellular cytotoxicity (ADCC). The present study addressed the question as to whether the lack of alphaGal protects porcine endothelial cells from NAb/complement-induced lysis, direct xenogeneic NK lysis, NAb-dependent ADCC, and adhesion of human NK cells under shear stress. Homologous recombination, panning, and limiting dilution cloning were used to generate an alphaGal-negative porcine endothelial cell line, PED2*3.51. NAb/complement-induced xenogeneic lysis of PED2*3.51 was reduced by an average of 86% compared with the alphaGal-positive phenotype. PED2*3.51 resisted NK cell-mediated ADCC with a reduction of lysis ranging from 30 to 70%. However, direct xenogeneic lysis of PED2*3.51, mediated either by freshly isolated or IL-2-activated human NK cells or the NK cell line NK92, was not reduced. Furthermore, adhesion of IL-2-activated human NK cells did not rely on alphaGal expression. In conclusion, removal of alphaGal leads to a clear reduction in complement-induced lysis and ADCC, but does not resolve adhesion of NK cells and direct anti-porcine NK cytotoxicity, indicating that alphaGal is not a dominant target for direct human NK cytotoxicity against porcine cells.

Efficacy of antibodies against a chimeric synthetic peptide encompassing epitopes of bonnet monkey (Macaca radiata) zona pellucida-1 and zona pellucida-3 glycoproteins to inhibit in vitro human sperm-egg binding

Immunocontraception achieved by immunization with zona pellucida (ZP) glycoproteins is invariably associated with ovarian dysfunction. Use of ZP glycoprotein-based synthetic peptides as immunogens has been proposed to overcome adverse side effects on ovaries. In the present study, a chimeric peptide encompassing the epitopes of bonnet monkey (Macaca radiata) ZP glycoprotein-1 (bmZP1; amino acid residues 251-273) and ZP glycoprotein-3 (bmZP3; amino acid residues 324-347), separated by a tri-glycine spacer, was synthesized and conjugated to diphtheria toxoid (DT). Immunization of female BALB/cJ mice and bonnet monkeys with the chimeric peptide led to generation of antibodies that reacted with the chimeric peptide, individual bmZP1 & bmZP3 peptides, and also recombinant bmZP1 and bmZP3 proteins expressed by E. coli in an ELISA. Indirect immunofluorescence studies revealed that the immune serum also recognized human as well as bonnet monkey ZP. A significant inhibition of human sperm binding to ZP was observed with antibodies generated against the chimeric peptide in mice (P = 0.0001) as well as monkeys (P = 0.0002) in a hemizona assay (HZA). The inhibition efficacy was significantly higher than that observed by using antibodies against the individual bmZP1 and bmZP3 peptides. Interestingly, no ovarian pathology was observed in female bonnet monkeys immunized with the chimeric peptide. These studies have demonstrated that the chimeric peptide encompassing peptides of multiple ZP glycoproteins may be a promising candidate antigen for designing immunocontraceptive vaccines.

Generation of antibodies against prion protein in wild-type mice via helix 1 peptide immunization

We present here the development of antibodies against prion protein in BALB/C mice using as antigen human helix 1 of PrP. This sequence is suggested to be involved in protein pathological conformational changes, and is distinguished from that of mice by one amino acid. The immune tolerance to an 'almost-self' epitope and the poor immunogenicity of short peptides was overcome by using Multiple Antigen Peptide displaying eight copies of helix 1. The generated antibodies recognize the whole prion protein with a high binding constant and the established protocol may lead to an active immunization towards therapeutics of prion disease.

Vaccinia virus complement control protein inhibits hyperacute xenorejection in a guinea pig-to-rat heterotopic cervical cardiac xenograft model by blocking both xenoantibody binding and complement pathway activation

Vaccinia virus complement control protein (VCP) binds the activated third and fourth complement components and inhibits both alternative and classical pathways of activation. The ability of VCP to bind heparan sulfate allows the protein to attach itself to the cell surface, enabling it with many additional activities. Altogether, the many functions of VCP have been shown to suppress the inflammatory response of the host, helping the vaccinia virus to evade immune destruction. VCP has recently been shown to inhibit human anti-Gal alpha1-3 Gal antibody attachment to cultured porcine endothelial cells and reduce human neutrophil and NK killing of pig aortic endothelial cells through its ability to bind heparan sulfate. Here we demonstrate that in an in vivo guinea pig-to-rat heterotopic cervical cardiac xenograft model, recombinant VCP (rVCP) is able to block hyperacute xenograft rejection, significantly prolonging graft survival. Histopathological examination of transplanted hearts from rats receiving rVCP revealed a significant reduction in cardiac tissue damage as compared to control hearts. Finally, rVCP treated recipients demonstrated marked rVCP deposition on the endothelium and significantly less C3, IgG and IgM deposition in the tissue. rVCP is therefore able to inhibit hyperacute xenorejection by binding the endothelial surface, blocking complement fixation and activation, and preventing xenoantibody attachment.

Paul-Bunnell antigen and a possible mechanism of formation of heterophile antibodies in patients with infectious mononucleosis

Sera of patients with infectious mononucleosis contain heterophile anti-Paul- Bunnell (PB) antibodies to erythrocytes of numerous mammalian species. Evidence is presented that the corresponding antigen of bovine erythrocytes is not, as previously described, a single molecule, but a series of glycoproteins with glycans terminated with N-glycolylneuraminic acid (Neu5Gc). The latter compound should be an important part of the PB epitope because, in agreement with the results of others, we found that desialylation of the PB antigen abolishes almost completely its activity. We examined three different preparations of GM3 ganglioside for their capacity to bind anti-PB and found that only GM3 from horse erythrocytes containing Neu5Gc exhibited a low although ELISA measurable PB activity. The other two GM3 preparations, from bovine milk and dog erythrocytes, containing N-acetylneuraminic acid (Neu5Ac) bound little if any anti-PB antibodies. This finding confirms a previous report that human erythrocyte Neu5Ac containing sialoglycoprotein with similar O-linked glycans as the PB-antigen of bovine erythrocytes exhibits only very low PB activity (Patarca & Fletcher, 1995, Crit Rev Oncogen., 6: 305). In conclusion, we present a hypothesis that anti-PB antibodies in patients with infectious mononucleosis are formed against infection-induced cell membrane glycoconjugates containing highly immunogenic Neu5Gc.

Immune complex formation after xenotransplantation : evidence of type III as well as type II immune reactions provide clues to pathophysiology

Rejection of renal and cardiac xenografts is initiated when natural antibodies of the recipient bind to donor endothelium, activating complement on the surface of endothelial cells. Pulmonary xenotransplants, however, reveal less evidence of antibody binding and complement activation and, in contrast to other xenografts, fare worse when the complement of the graft recipient is depleted. Accordingly, we asked whether distinct immunochemical reactions might occur after xenotransplantation of the lung and what implications such reactions might have for pulmonary pathophysiology. Analysis of serum from baboons after transplantation with porcine lungs revealed complexes containing baboon IgM and porcine von Willebrand factor. The baboon IgM in these complexes was specific for Galalpha1-3Gal. Immune complexes were also seen, albeit to a lesser extent, in the serum of kidney and heart xenotransplant recipients. Deposits of porcine von Willebrand factor and baboon C3 were detected in livers and spleens of transplanted baboons. These results indicate pulmonary xenotransplantation eventuates in formation of immune complexes and in the deposition of those complexes at distant sites. Immune complex formation could explain the peculiar fate of xenoreactive antibodies after pulmonary xenotransplantation and might contribute to the pathophysiology of the lung and systemic changes not previously considered a complication of xenotransplantation.

Prolongation of xenograft survival using monoclonal antibody CD45RB and cyclophosphamide in rat-to-mouse kidney and heart transplant models

BACKGROUND

Intrigued by the finding that a monoclonal antibody (mAb) directed against the B exon of restricted CD45 (CD45RB mAb) induced renal allograft tolerance in the mouse model, we hypothesized that CD45RB mAb may prevent xenograft rejection. We explored the role of CD45RB mAb in preventing xenograft rejection in rat-to-mouse kidney and heart transplant models.

METHODS

Mice with rat kidney and heart xenografts were treated with a short course of mAb, cyclosporine, cyclophosphamide, or mAb + cyclophosphamide combination therapy. Untreated heart and kidney xenografts served as controls.

RESULTS

Untreated controls developed acute vascular and cellular rejection rapidly with a median survival time of only 6 days. Long-term kidney (median survival time = 70 days) and heart xenograft survival (median survival time = 65 days) was achieved using the combination therapy of mAb + cyclophosphamide. One-third of the kidney recipients with combination therapy survived 100 days. Immunohistochemistry and xenospecific-antibody analysis demonstrated that combination therapy remarkably reduced IgG and IgM deposition and also inhibited CD4+, CD8+, and Mac-1+ cell infiltration at early stages. This therapy, however, did not induce tolerance in this model as evoked xenoreactive antibodies and cellular responses may be the cause of late xenograft failure.

CONCLUSION

A short course of CD45RB mAb combined with cyclophosphamide effectively inhibits cellular and humoral immunoresponses and remarkably prolongs xenograft survival in rat-to-mouse heart and kidney transplant models.

Removal of xenoreactive antibodies by protein-A immunoadsorption: experience in 22 patients

The presence of naturally occurring anti-Galalpha1-3Gal (antialphaGal) Ab in human serum is believed to be a major factor in the pathogenesis of hyperacute rejection of discordant organ xenografts such as the pig-to-human combination. Galalpha1-3Gal epitopes are expressed on pig tissues and the binding of anti-Galalpha1-3Gal leads to endothelial cell activation and complement-mediated hyperacute graft rejection. Several strategies have been suggested in donor animals or in the xenograft recipient to overcome the anti-alphaGal barrier. Protein-A immunoadsorption (PAIA) was developed for the in vivo removal of circulating Ab and it has been shown to be effective in cases where pathogenic auto or alloAb are present. The aim of our study was to analyze the effect of PAIA on total and xenoreactive serum anti-alphaGal immunoglobulin levels in a group of patients treated with this technique for different diseases. After three consecutive sessions of PAIA, total and xenoreactive IgG and IgM immunoglobulin levels were decreased by more than 50% of pre-treatment levels. So we conclude that PAIA is an effective method to significantly reduce circulating Ab, including xenogeneic IgM and IgG Ab. This mode of therapy might be considered as a tool to overcome hyperacute xenograft rejection. PAIA combined with other therapeutic approaches may well protect the xenograft.

Differential inhibition of B-cell development and xenoreactive natural antibody production by administration of anti-mu or anti-delta monoclonal antibodies in adult rats

BACKGROUND

Given the role of xenoreactive natural antibodies (XNA) in the pathogenesis of xenograft rejection, we tested whether the administration of anti-mu or anti-delta monoclonal antibodies (mAbs) in adult rats would suppress the generation of XNA.

METHODS

Adult LOU/C (Igkappa-1a) rats were treated with anti-mu or anti-delta mAbs after nonlethal total body irradiation and bone marrow transplantation from congenic LOU/C (Igkappa-1b) rats. The differentiation of donor bone marrow (BM)-driven Igkappa-1b+ B cells and XNA production were analyzed.

RESULTS

Both anti-mu and anti-delta mAbs arrested B-cell differentiation in the BM. In anti-mu-treated rats, there was a total depletion of donor-driven, peripheral Igkappa-1b+ B cells, secreting cells, and circulating XNA of the Igkappa-1b allotype. In anti-delta-treated rats, a significant number of Igkappa-1b+ B cells, which did not express membrane IgD, "escaped" deletion and partially repopulated peripheral lymphoid organs. This B-cell population was active in the production of XNA, as revealed by the high serum levels of XNA in these animals.

CONCLUSIONS

Anti-mu administration resulted in arrest of B-cell differentiation and in down-regulation of IgM and IgG XNA production in adult rats. These data suggest that the use of anti-mu mAbs may be a useful approach to suppress the production of XNA and prevent xenograft rejection. Furthermore, we suggest that the B-cell population responsible for the production of XNA in adult rats belongs to a B-cell lineage expressing low levels of membrane IgD and "escaping" deletion in the BM upon anti-delta treatment.

Establishment of a concordant xenogeneic splenocyte injection model for the dynamic study of the marginal zone in the spleen

BACKGROUND

This study was undertaken to establish a simple technique with which we could investigate the relationship between the marginal zone (MZ) in the spleen and antispecies antibody production, as well as to estimate the efficacy of various immunosuppressive treatments in xenotransplantation.

METHODS

With a concordant xenogeneic combination (hamster-to-rat), the early phase reaction of the MZ was studied by use of quantitative histologic analysis, and complement-dependent cytotoxic antibody titers were determined in both a heart transplantation model and the splenocyte injection model. Furthermore, changes in the MZ were examined with isogeneic and allogeneic combinations with the splenocyte injection model. Next, the effect of cyclophosphamide, a promising immunosuppressant for concordant xenotransplantation, was examined by use of the splenocyte injection model.

RESULTS

With a concordant xenogeneic combination, the MZ enlarged, and antihamster immunoglobulin M antibody synthesis increased after immunization in both models. On the other hand, with an isogeneic combination, the MZ did not expand, and with an allogeneic combination the MZ enlargement was not as great as that with a concordant xenogeneic combination. Cyclophosphamide suppressed the MZ expansion in a dose-dependent manner and effectively diminished antibody production in the splenocyte injection model.

CONCLUSION

Dynamic studies of the MZ in the spleen with the splenocyte injection model are useful for the elucidation of the mechanisms of reaction and for estimating the efficacy of various immunosuppressive treatments in concordant xenotransplantation.

Effects of DL-penicillamine on cytotoxic reaction between baboon performed xenoantibodies and pig endothelial cells

The purpose of this study was to evaluate effects of DL-Penicillamine (DLP), a compound interrupting S-S bonds (IgM pentamers) on binding and cytotoxicity of adult baboon performed xenoantibodies to pig endothelial cells. Pooled baboon serum was treated with different concentrations of DLP during various periods of time. Complement-mediated cytotoxicity assay was used to determine the reactivity of baboon xenoantibodies to pig aortic endothelial cells (PAEC). To assess IgM and IgG binding to PAEC, ELISA method was applied. Serum treated with DLP revealed significant reduction of cytotoxicity in a dose dependent manner. Cytotoxicity was also reduced during time prolongation of DLP exposure to PAEC. Results indicate that baboon performed IgM and IgG xenoantibodies bind to pig endothelial cells, but only IgM is able to cause degradation of the complement. DLP significantly reduces cytotoxicity and eliminates binding of IgMs to PAEC in spite of continued binding of IgG xenoantibodies to the surface of endothelium.

Preferential association of V lambda x light chains with gamma 2a heavy chains in naturally occurring human myelin basic protein reactive antibodies

Active immunization with myelin basic protein (MBP) induces experimental allergic encephalomyelitis (EAE) in a variety of animal species, including rats and mice. We have previously described the ability of the newly described mouse lambda (lambda) variable (V) region V lambda x, to confer MBP reactivity to an Ab. In this report, we have evaluated the heavy (H) chain isotype distribution of V lambda x-bearing Abs in normal mouse serum. We demonstrate a biased H chain isotype association with V lambda x light (L) chains with a skewing towards gamma 2a and 2b isotypes. The IgG2a restriction in normal mouse Igs is even more evident in V lambda x-containing Abs that bind MBP. This was confirmed by the ability of purified polyclonal IgG2a Abs to bind MBP and the finding that most or all of the IgG2a Abs that bind MBP seem to harbor a V lambda x L chain. The specificity of naturally-occurring V lambda x-bearing Abs with MBP can be localized to a particular epitope encompassing residues 25-34 of the MBP molecule. Furthermore, virtually all of the reactivity of V lambda x-containing Abs with MBP peptide 25-34 is associated with the gamma 2a isotype. Collectively, these results suggest that the interaction of V lambda x with MBP seems to be facilitated by an association with gamma 2a which may reflect preferred VH usage by this isotype. Such unique pairing of particular H chains with V lambda x L chains in Abs that bind MBP may be indicative of a new B-cell component involved in the pathogenesis of EAE.

Pig alpha1, 3galactosyltransferase: a major target for genetic manipulation in xenotransplantation

Terminal carbohydrate residues of glycolipids and glycoproteins display polymorphism among as well as within various species. With the exception of Old World monkeys, great apes and man, the Gala1,3Gal structure is widely expressed in all mammals examined so far. The lack of expression of the glycosyltransferase responsible for the synthesis of Gala1,3Gal leads to the production of high titers of natural antibodies (NAb) against the Gala1,3Gal of other species. The inactivation of this gene occurred during early evolution of primates. Neutralization of viruses (e.g. retroviruses) carrying the epitope, by the pre-formed human NAb, indicates one possible evolutionary reason for the polymorphism of terminal carbohydrates among as well as within species. It has been shown that this epitope constitutes the major target, on pig endothelial cells (EC), for the pre-formed human NAb resulting in a hyperacute rejection (HAR) response. This currently makes transplantation of e.g. pig organs to humans impossible. Efforts are currently underway to prevent or to eradicate the expression of this epitope in transgenic pigs. Such pigs are likely to display a greatly increased resistance to the HAR.

Suppression of experimental crescentic-type anti-glomerular basement membrane (GBM) nephritis by FK506 (tacrolimus hydrate) in rats

The effect of FK506 (tacrolims hydrate), an immunosuppressive agent produced by Streptomyces tsukubaensis, on crescentic-type anti-glomerular basement membrane (GBM) nephritis in rats was investigated. When rats were treated with FK506 from 1 or 20 days after the anti-GBM serum injection, FK506 inhibited the increase in urinary protein excretion. Histological observation demonstrated that FK506 suppressed glomerular alterations. In the FK506-treated rats, antibody production and rat-IgG and C3 deposits on the GBM were significantly less than those in the nephritic control group. FK506 treatment suppressed the accumulation of ED-1-positive cells, CD4-positive cells, CD8-positive cells, interleukin-2 (IL-2)-receptor-positive cells, leukocyte-function-associated antigen-1 (LFA-1)-positive cells and intercellular adhesion molecule-1 (ICAM-1)-expression in nephritic glomeruli. However, in the in vitro study, FK506 failed to inhibit the up-regulated ICAM-1 expression on endothelial cells in response to tumor necrosis factor (TNF)-alpha. On the other hand, IL-2 production from the spleen cells isolated from nephritic rats treated with FK506 was lower than that in the nephritic control rats. These results suggest that FK506 is effective against crescentic-type anti-GBM nephritis and that the antinephritic mechanisms of FK506 is due to the inhibition of intraglomerular accumulation and activation of leukocytes through the suppression of ICAM-1 expression and IL-2 production.

Butein ameliorates experimental anti-glomerular basement membrane (GBM) antibody-associated glomerulonephritis in rats (1)

Effects of butein on crescentic-type anti-glomerular basement membrane (GBM) nephritis in rats were investigated. When rats were treated with butein from 1 day after i.v. injection of anti-GBM serum, it inhibited the elevation of protein excretion into urine. In the butein-treated rats, cholesterol content in plasma was lower than that of the nephritic control rats. Histological observation demonstrated that this agent suppressed the incidence of crescent formation, adhesion of capillary wall to Bowman's capsule and fibrinoid necrosis in the glomeruli. Furthermore, butein suppressed the accumulation of leukocytes, including CD4-positive cells and CD8-positive cells in the glomeruli. However, butein failed to suppress the production of the antibody against rabbit gamma-globulin and the deposition of rat-IgG on the GBM. These results suggest that butein may be a useful medicine against rapidly progressive glomerulonephritis, which is characterized by severe glomerular lesions with diffuse crescents.

Abrogation of baboon natural xenoantibody to pig splenocytes by DL-penicillamine

Natural xenoantibodies are believed to be IgM in nature and are known to play a critical role in the hyperacute rejection of distantly related xenografts. The purpose of this study was to determine whether the reducing agent DL-penicillamine could inactivate baboon natural xenoantibodies to pig splenocytes. Pooled baboon serum was treated with varying concentrations of DL-penicillamine over different lengths of time and a complement-mediated cytotoxicity assay was used to determine the reactivity of baboon natural xenoantibodies to pig splenocytes. A whole-cell ELISA assay was used to assess the binding of both IgG and IgM xenoantibodies to pig splenocytes. In addition, DL-penicillamine-treated serum was dialyzed to assess its potential clinical application. These in vitro experiments indicate that both IgM and IgG baboon natural xenoantibodies bind to pig splenocytes, but only IgM xenoantibody is cytotoxic. The binding of baboon natural IgM xenoantibody can be eliminated, and the cytotoxicity of IgM xenoantibody markedly reduced by DL-penicillamine treatment despite continued binding of IgG xenoantibody to pig splenocytes. In addition, DL-penicillamine can be dialyzed, suggesting that it may be an efficacious clinical treatment, the toxicity of which can be regulated with hemodialysis.

The effect of xenoreactive antibody and B cell depletion on hyperacute rejection of guinea pig-to-rat cardiac xenografts

Xenotransplantation between phylogenetically distant species is prevented by hyperacute rejection (HAR), a process that is thought to be initiated by the binding of naturally occurring xenoreactive antibodies (NAb) to the endothelium of the xenograft (Xg) with subsequent activation of the classical pathway of C. The relative role of direct alternative pathway C activation in HAR is controversial. To evaluate the role of NAb in HAR of discordant rodent Xg, LEW rats were treated from the day of birth with i.p. injections of rabbit anti-rat IgM antiserum (RARM), or with mAb specific for rat kappa-light chain (OX12) or rat class II MHC (14-4-4S, Y-3P, or 10-2.16), in an effort to deplete B cells and NAb. These rats then underwent xenotransplantation with discordant guinea pig hearts. RARM was effective in depleting rats (n = 5) of B cells, serum IgM, and rat NAb directed against guinea pig cells, but guinea pig cardiac Xg survival was not prolonged compared with PBS-treated controls (n = 5), possibly due to the rabbit NAb specific for guinea pig cardiac tissue that were passively transferred in the RARM preparation. Of the anti-B cell mAb used to avoid this passive transfer of NAb, mAb 14-4-4S was highly effective (n = 9) in depleting the peripheral blood and spleen of B cells and the serum of IgM and NAb. Guinea pig cardiac Xg survival, however, was again not prolonged (n = 5), and rejected Xg from the B cell- and NAb-depleted recipients demonstrated rat C3 deposition in the absence of rat IgM and IgG. This study demonstrates that while neonatal anti-B cell antibody treatment can effectively deplete B cells and NAb in the rat, such treatment does not significantly prolong cardiac Xg survival in this well-established guinea pig to rat xenotransplantation model. These findings suggest that in addition to NAb depletion, inhibition of alternative C pathway activation and other humoral mechanisms may be necessary to prevent HAR and allow successful xenotransplantation.

Binding of preformed xenoantibodies to porcine bioprosthetic valves

We have investigated whether preformed antibodies against xenoantigens bind to cellular elements remaining on porcine bioprosthetic valves after various methods of preservation. Fresh porcine valves treated with either acetone, 4% formaldehyde, or 0.625% glutaraldehyde, as well as an unfixed valve, were incubated with antiserum against porcine xenoantigens. This serum was prepared using the affinity purification method with porcine lymphocytes as the target. The valves were stained with secondary fluorescein-conjugated antibody against immunoglobulin M or immunoglobulin G and examined under fluorescent microscopy. Intense binding of immunoglobulin M to the endocardium was observed in the unfixed valve as well as in valves fixed in acetone and formaldehyde. Glutaraldehyde fixation eliminated binding of antibody. Binding was not noted within the connective tissue. No binding of antiimmunoglobulin G was noted on the endocardium of any of the sections. Examination of three glutaraldehyde-treated porcine valves explanted from the aortic position after 10 years in situ showed no immunoglobulin deposition. These results demonstrate the elimination of antigenicity to preformed antibodies in the endocardium and connective tissue of glutaraldehyde-preserved porcine valves. The findings may, in part, explain the poor performance of formaldehyde-preserved bioprosthetic xenograft valves in the past and support the use of glutaraldehyde as a preferred agent for preservation of bioprosthetic endovascular materials.

The clearance of heterologous antibodies in experimental antibasement membrane antibody mediated glomerulonephritis

A study of the clearance of anti GBM antibodies is important for an understanding of the pathogenesis of Goodpasture's syndrome. This paper reports a study of the sequential clearance of heterologous anti-glomerular basement membrane antibodies in the neonatal rat. A single intraperitoneal injection was followed by rapid and linear binding of injected antibodies to glomerular basement membranes, particularly to those glomeruli in the corticomedullary region. GBM bound antibodies were cleared gradually through the mesangium and significant amounts of antibodies still remained bound after 6 months. Subsequent injections of antibodies failed to provoke morphological abnormalities. These experiments have shown that the glomerular basement membrane of neonatal and adult rats possesses similar antigenic sites. The mesangium plays a major role in the clearance of injected heterologous antibodies. The slow clearance of antibodies from the GBM indicates a strong affinity of antibodies to antigenic sites and that the removal of antibodies is intimately related to the slow metabolic turnover of the glomerular basement membrane. The findings help to explain some of the observations in human antibasement membrane antibody mediated disease of the Goodpasture's type.

Xenogeneic antibodies and atopic disease

Xenogeneic antibodies can survive food processing procedures with their biological activity intact and even enhanced. These antibodies can be absorbed from the human gut, and will function both as antigens and antibodies in the human immune system. Antibodies to bovine gamma globulins (BGG) have been detected in human sera and the family of anti-BGG antibodies must include anti-idiotypic antibodies, very low doses of which can influence the immune response. The hypothesis is that the human immune system may be primed by low-level exposure to xenogeneic antibodies specific for those human allergens which are ubiquitous in the farm environment, such as pollens, mites, and moulds, the result being a deleterious and inappropriate response on subsequent exposure to these allergens. Dairy products are the most important source of xenogeneic antibodies in the western diet, and the hypothesis may partly explain the association between cow's milk and allergies to substances other than milk proteins.

Aberrant expression of Forssman and Paul-Bunnell antigens on lymph node cells of MRL/Mp-lpr/lpr mice

Lymph node cells (LNC) of MRL/Mp-lpr/lpr mice (MRL/1) and congeneic MRL/Mp-+/+ (MRL/n) mice were studied by means of flow fluorocytometry for the expression of heterophile Forssman (F) and Paul-Bunnell (P-B) antigens. The level of F antigen on LNC of MRL/1, but not on those of MRL/n mice, increased progressively with age and reached its maximum at 4 mo of age. No such increase in F antigen on LNC of age-matched C3H/HeJms, C57BL/6, and AKR mice was observed. In contrast, the level of P-B antigen on LNC of MRL/1 mice was significantly lower than that of MRL/n and the normal mice. F-positive LNC of MRL/1 mice were shown to be T cells with Thy-1.2 and Lyt-1 markers; those cells expanded in the lymph nodes and were responsible for the development of the massive lymphadenopathy. Studies on LNC of F1 hybrids between MRL/1 and MRL/n mice, and animals of the subsequent F2 generation provided evidence that the aberrant expression of F and P-B antigens was under the influence of the autosomal recessive lpr gene and was segregated together with the lymphadenopathy into the F2 generation. The aberrant expression of F and P-B antigens reflects the alteration of terminal carbohydrate structure of glycolipids and glycoproteins on the membrane of the LNC. It is tempting, therefore, to speculate that such alterations in the membrane structure might represent disturbances in cellular recognition resulting in unusual expansion of the T cells in the early life of MRL/1 mice.