Xenotransplantation: the importance of the Galalpha1,3Gal epitope in hyperacute vascular rejection

In Vivo Luciferin-Luciferase Reaction in Micro-Mini Pigs Using Xenogeneic Rat Bone Marrow Transplantation

Luminescent technology based on the luciferin-luciferase reaction has been extensively employed across various disciplines as a quantitative imaging modality. Owing to its non-invasive imaging capacity, it has evolved as a valuable in vivo bioimaging tool, particularly in small animal models in fields such as gene and cell therapies. We have previously successfully generated rats with a systemic expression of the luciferase gene at the Rosa26 locus. In this study, we transplanted bone marrow from these rats into micro-mini pigs and used in vivo imaging to non-invasively analyze the dynamics of the transplanted cells. In addition, we established that the rat-to-pig transplantation system is a discordant system, similar to the pig-to-human transplantation system. Thus, rat-to-pig transplantation may provide a clinically appropriate large animal model for pig-to-human xenotransplantation.

Development of porcine skeletal muscle extracellular matrix-derived hydrogels with improved properties and low immunogenicity

Hydrogels derived from decellularized extracellular matrices (ECM) of animal origin show immense potential for regenerative applications due to their excellent cytocompatibility and biomimetic properties. Despite these benefits, the impact of decellularization protocols on the properties and immunogenicity of these hydrogels remains relatively unexplored. In this study, porcine skeletal muscle ECM (smECM) underwent decellularization using mechanical disruption (MD) and two commonly employed decellularization detergents, sodium deoxycholate (SDC) or Triton X-100. To mitigate immunogenicity associated with animal-derived ECM, all decellularized tissues were enzymatically treated with α-galactosidase to cleave the primary xenoantigen-the α-Gal antigen. Subsequently, the impact of the different decellularization protocols on the resultant hydrogels was thoroughly investigated. All methods significantly reduced total DNA content in hydrogels. Moreover, α-galactosidase treatment was crucial for cleaving α-Gal antigens, suggesting that conventional decellularization methods alone are insufficient. MD preserved total protein, collagen, sulfated glycosaminoglycan, laminin, fibronectin, and growth factors more efficiently than other protocols. The decellularization method impacted hydrogel gelation kinetics and ultrastructure, as confirmed by turbidimetric and scanning electron microscopy analyses. MD hydrogels demonstrated high cytocompatibility, supporting satellite stem cell recruitment, growth, and differentiation into multinucleated myofibers. In contrast, the SDC and Triton X-100 protocols exhibited cytotoxicity. Comprehensive in vivo immunogenicity assessments in a subcutaneous xenotransplantation model revealed MD hydrogels' biocompatibility and low immunogenicity. These findings highlight the significant influence of the decellularization protocol on hydrogel properties. Our results suggest that combining MD with α-galactosidase treatment is an efficient method for preparing low-immunogenic smECM-derived hydrogels with enhanced properties for skeletal muscle regenerative engineering and clinical applications.

Efficient Decellularization of the Full-Thickness Rat-Derived Abdominal Wall to Produce Acellular Biologic Scaffolds for Tissue Reconstruction: Promising Evidence Acquired from In Vitro Results

BACKGROUND

Functional restoration of abdominal wall defects represents one of the fundamental challenges of reconstructive surgery. Synthetic grafts or crosslinked animal-derived biological grafts are characterized by significant adverse reactions, which are mostly observed after their implantation. The aim of this study was to evaluate the efficacy of the decellularization protocol to produce a completely acellular full-thickness abdominal wall scaffold.

METHODS

Full-thickness abdominal wall samples were harvested from Wistar rats and submitted to a three-cycle decellularization process. Histological, biochemical, and DNA quantification analyses were applied to evaluate the effect of the decellularization protocol. Mechanical testing and immunogenicity assessment were also performed.

RESULTS

Histological, biochemical, and DNA analysis results showed efficient decellularization of the abdominal wall samples after the third cycle. Decellularized abdominal wall scaffolds were characterized by good biochemical and mechanical properties.

CONCLUSION

The data presented herein confirm the effective production of a rat-derived full-thickness abdominal wall scaffold. Expanding this approach will allow the exploitation of the capacity of the proposed decellularization protocol in producing acellular abdominal wall scaffolds from larger animal models or human cadaveric donors. In this way, the utility of biological scaffolds with preserved in vivo remodeling properties may be one step closer to its application in clinical studies.

Cross-linking porcine peritoneum by oxidized konjac glucomannan: a novel method to improve the properties of cardiovascular substitute material

The use of natural polysaccharide crosslinkers for decellularized matrices is an effective approach to prepare cardiovascular substitute materials. In this research, NaIO4 was applied to oxidize konjac glucomannan to prepare the polysaccharide crosslinker oxidized konjac glucomannan (OKGM). The as-prepared crosslinker was then used to stabilize collagen-rich decellularized porcine peritoneum (DPP) to construct a cardiovascular substitute material (OKGM-fixed DPP). The results demonstrated that compared with GA-fixed DPP and GNP-fixed DPP, 3.75% OKGM [1:1.5 (KGM: NaIO4)]-fixed DPP demonstrated suitable mechanical properties, as well as good hemocompatibility, excellent anti-calcification capability, and anti-enzymolysis in vitro. Furthermore, 3.75% OKGM [1:1.5 (KGM: NaIO4)]-fixed DPP was suitable for vascular endothelial cell adhesion and rapid proliferation, and a single layer of endothelial cells was formed on the fifth day of culture. The in vivo experimental results also showed excellent histocompatibility. The current results demonstrted that OKGM was a novel polysaccharide cross-linking reagent for crosslinking natural tissues featured with rich collagen content, and 3.75% OKGM [1:1.5 (KGM: NaIO4)]-fixed DPP was a potential cardiovascular substitute material.

Graphical Abstract

Biomanufacturing of Axon-Based Tissue Engineered Nerve Grafts Using Porcine GalSafe Neurons

Existing strategies for repair of major peripheral nerve injury (PNI) are inefficient at promoting axon regeneration and functional recovery and are generally ineffective for nerve lesions >5 cm. To address this need, we have previously developed tissue engineered nerve grafts (TENGs) through the process of axon stretch growth. TENGs consist of living, centimeter-scale, aligned axon tracts that accelerate axon regeneration at rates equivalent to the gold standard autograft in small and large animal models of PNI, by providing a newfound mechanism-of-action referred to as axon-facilitated axon regeneration (AFAR). To enable clinical-grade biomanufacturing of TENGs, a suitable cell source that is hypoimmunogenic, exhibits low batch-to-batch variability, and able to tolerate axon stretch growth must be utilized. To fulfill these requirements, a genetically engineered, FDA-approved, xenogeneic cell source, GalSafe® neurons, produced by Revivicor, Inc., have been selected to advance TENG biofabrication for eventual clinical use. To this end, sensory and motor neurons were harvested from genetically engineered GalSafe day 40 swine embryos, cultured in custom mechanobioreactors, and axon tracts were successfully stretch-grown to 5 cm within 25 days. Importantly, both sensory and motor GalSafe neurons were observed to tolerate established axon stretch growth regimes of ≥1 mm/day to produce continuous, healthy axon tracts spanning 1, 3, or 5 cm. Once stretch-grown, 1 cm GalSafe TENGs were transplanted into a 1 cm lesion in the sciatic nerve of athymic rats. Regeneration was assessed through histological measures at the terminal time point of 2 and 8 weeks. Neurons from GalSafe TENGs survived and elicited AFAR as observed when using wild-type TENGs. At 8 weeks postrepair, myelinated regenerated axons were observed in the nerve section distal to the injury site, confirming axon regeneration across the lesion. These experiments are the first to demonstrate successful harvest and axon stretch growth of GalSafe neurons for use as starting biomass for bioengineered nerve grafts as well as initial safety and efficacy in an established preclinical model-important steps for the advancement of clinical-grade TENGs for future regulatory testing and eventual clinical trials. Impact statement Biofabrication of tissue engineered medical products requires several steps, one of which is choosing a suitable starting biomass. To this end, we have shown that the clinical-grade, genetically engineered biomass-GalSafe® neurons-is a viable option for biomanufacturing of our tissue engineered nerve grafts (TENGs) to promote regeneration following major peripheral nerve injury. Importantly, this is a first step in clinical-grade TENG biofabrication, proving that GalSafe TENGs recapitulate the mechanism of axon-facilitated axon regeneration seen previously with research-grade TENGs.

Recent progress and remaining hurdles toward clinical xenotransplantation

BACKGROUND

Xenotransplantation has made tremendous progress over the last decade.

METHODS

We discuss kidney and heart xenotransplantation, which are nearing initial clinical trials.

RESULTS

Life sustaining genetically modified kidney xenografts can now last for approximately 500 days and orthotopic heart xenografts for 200 days in non-human primates. Anti-swine specific antibody screening, preemptive desensitization protocols, complement inhibition and targeted immunosuppression are currently being adapted to xenotransplantation with the hope to achieve better control of antibody-mediated rejection (AMR) and improve xenograft longevity. These newest advances could probably facilitate future clinical trials, a significant step for the medical community, given that dialysis remains difficult for many patients and can have prohibitive costs. Performing a successful pig-to-human clinical kidney xenograft, that could last for more than a year after transplant, seems feasible but it still has significant potential hurdles to overcome. The risk/benefit balance is progressively reaching an acceptable equilibrium for future human recipients, e.g. those with a life expectancy inferior to two years. The ultimate question at this stage would be to determine if a "proof of concept" in humans is desirable, or whether further experimental/pre-clinical advances are still needed to demonstrate longer xenograft survival in non-human primates.

CONCLUSION

In this review, we discuss the most recent advances in kidney and heart xenotransplantation, with a focus on the prevention and treatment of AMR and on the recipient's selection, two aspects that will likely be the major points of discussion in the first pig organ xenotransplantation clinical trials.

Emergence and significance of carbohydrate-specific antibodies

Carbohydrate-specific antibodies are widespread among all classes of immunoglobulins. Despite their broad occurrence, little is known about their formation and biological significance. Carbohydrate-specific antibodies are often classified as natural antibodies under the assumption that they arise without prior exposure to exogenous antigens. On the other hand, various carbohydrate-specific antibodies, including antibodies to ABO blood group antigens, emerge after the contact of immune cells with the intestinal microbiota, which expresses a vast diversity of carbohydrate antigens. Here we explore the development of carbohydrate-specific antibodies in humans, addressing the definition of natural antibodies and the production of carbohydrate-specific antibodies upon antigen stimulation. We focus on the significance of the intestinal microbiota in shaping carbohydrate-specific antibodies not just in the gut, but also in the blood circulation. The structural similarity between bacterial carbohydrate antigens and surface glycoconjugates of protists, fungi and animals leads to the production of carbohydrate-specific antibodies protective against a broad range of pathogens. Mimicry between bacterial and human glycoconjugates, however, can also lead to the generation of carbohydrate-specific antibodies that cross-react with human antigens, thereby contributing to the development of autoimmune disorders.

A Phase I Study of Alpha-1,3-Galactosyltransferase-Expressing Allogeneic Renal Cell Carcinoma Immunotherapy in Patients with Refractory Metastatic Renal Cell Carcinoma

LESSONS LEARNED

HyperAcute Renal immunotherapy was well tolerated and demonstrated antitumor activity in patients requiring salvage-line treatment for metastatic renal cell carcinoma (mRCC). HyperAcute Renal immunotherapy was safely administered with concomitant salvage-line treatments for mRCC, and it may be a candidate for inclusion in novel combinations for salvage treatment of mRCC because of its unique mechanism of action.

BACKGROUND

HyperAcute Renal (HAR) immunotherapy exploits a naturally occurring barrier to xenotransplantation and zoonotic infections in humans to immunize patients against metastatic renal cell carcinoma (mRCC) cells. HAR consists of two allogeneic renal cancer cell lines genetically modified to express α(1,3)Gal, to which humans have an inherent pre-existing immunity.

METHODS

Patients with refractory mRCC were eligible for this phase I dose-escalation trial. Concomitant treatment was permitted after the initial 2 months of HAR monotherapy. HAR was injected intradermally weekly for 4 weeks then biweekly for 20 weeks, totaling 14 immunizations. The primary endpoint was safety and determination of a maximum tolerated dose (MTD).

RESULTS

Among 18 patients enrolled, two grade 3 adverse events (AEs) were attributed to HAR, lymphopenia and injection site reaction, and no grade 4/5 AEs occurred. The recommended phase II dose (RP2D) was 300 million cells. One patient had a partial response and eight patients had stable disease, for a disease control rate of 50% (9/18). Median overall survival with low-dose HAR was 14.2 months and was 25.3 months with high-dose HAR.

CONCLUSION

In pretreated mRCC, HAR immunotherapy was well tolerated and demonstrated antitumor activity. HAR immunotherapy may be a candidate for inclusion in novel combinations for salvage treatment of mRCC.

hNTCP‑expressing primary pig hepatocytes are a valuable tool for investigating hepatitis B virus infection and antiviral drugs

Primary human hepatocytes (PHHs) are the 'gold standard' for investigating hepatitis B virus (HBV) infection and antiviral drugs. However, poor availability, variation between batches and ethical issues regarding PHHs limit their applications. The discovery of human sodium taurocholate co‑transporting polypeptide (hNTCP) as a functional HBV receptor has enabled the development of a surrogate model to supplement the use of PHHs. In the present study, the evolutionary distance of seven species was assessed based on single‑copy homologous genes. Based on the evolutionary distance and availability, PHHs and primary rabbit hepatocytes (PRHs) were isolated and infected with hNTCP‑recombinant lentivirus, and susceptibility to HBV infection in the two cell types was tested and compared. In addition, HBV infection efficiency of hNTCP‑expressing PPHs with pooled HBV‑positive serum and purified particles was determined. The potential use of HBV‑infected hNTCP‑expressing PPHs for drug screening was assessed. The results demonstrated that pigs and rabbits are closer to humans in the divergence tree compared with mice and rats, indicating that pigs and rabbits were more likely to facilitate the HBV post‑entry lifecycle. Following hNTCP complementation and HBV infection, PPHs and Huh7D human hepatocellular carcinoma cells, but not PRHs, exhibited increased hepatitis B surface antigen and hepatitis B e‑antigen secretion, covalently closed circular DNA formation and infectious particle secretion. hNTCP‑expressing PPHs were susceptible to infection with HBV particles purified from pooled HBV‑positive sera, but were poisoned by raw HBV‑positive sera. The use of HBV‑infected hNTCP‑expressing PPHs for viral entry inhibitor screening was revealed to be applicable and reproducible. In conclusion, hNTCP‑expressing PPHs may be valuable tool for investigating HBV infection and antiviral drugs.

From Friend to Enemy: Dissecting the Functional Alteration of Immunoregulatory Components during Pancreatic Tumorigenesis

Pancreatic ductal adenocarcinoma (PDAC) is a lethal disease with a 5-year survival rate of approximately 8%. More than 80% of patients are diagnosed at an unresectable stage due to metastases or local extension. Immune system reactivation in patients by immunotherapy may eliminate tumor cells and is a new strategy for cancer treatment. The anti-CTLA-4 antibody ipilimumab and anti-PD-1 antibodies pembrolizumab and nivolumab have been approved for cancer therapy in different countries. However, the results of immunotherapy on PDAC are unsatisfactory. The low response rate may be due to poor immunogenicity with low tumor mutational burden in pancreatic cancer cells and desmoplasia that prevents the accumulation of immune cells in tumors. The immunosuppressive tumor microenvironment in PDAC is important in tumor progression and treatment resistance. Switching from an immune tolerance to immune activation status is crucial to overcome the inability of self-defense in cancer. Therefore, thoroughly elucidation of the roles of various immune-related factors, tumor microenvironment, and tumor cells in the development of PDAC may provide appropriate direction to target inflammatory pathway activation as a new therapeutic strategy for preventing and treating this cancer.

Gal epitope expression and immunological properties in iGb3S deficient mice

The Gal antigen is synthesized by glycoprotein galactosyltransferase alpha 1, 3 (GGTA1) or (and) isoglobotrihexosylceramide 3 synthase (iGb3S). However, whether iGb3S deletion changes Gal epitope expression and immunological properties in animals is still not clear. The objective of this study was to develop iGb3S deficient mice, and characterize their Gal epitope expression and Gal epitope-related immunological properties. iGb3S gene knockout mice were generated on the C57BL/6 background using the bacterial artificial chromosome homology region recombination technique. Gal epitope expression in the iGb3S deficient mice was determined by using a monoclonal anti-Gal antibody. Immunological properties were analyzed by enzyme linked immune sorbent assay. It was found that Gal epitope expression was decreased from 5.19% to 21.74% in the main organs of iGb3S deficient mice, compared with that of C57BL/6 wild type mice, suggesting that the iGb3S gene participated to Gal epitope expression. However, iGb3S deletion alone did not cause significant changes in the immunological properties of iGb3S deficient mice with or without exogenous Gal antigen (Rabbit Red Blood Cell) stimulation. The data from this study suggest that the iGb3S gene likely contributes to Gal epitope expression, but may have a very weak effect on immunological properties of the iGb3S deficient mice.

A standardized quantitative method for detecting remnant alpha-Gal antigen in animal tissues or animal tissue-derived biomaterials and its application

Alpha-Gal (Gal) epitopes present in animal tissues are known to be the key xenoantigens that elicit xenorejection. However, a standardized method to determine Gal epitope in animal tissue-derived biomaterials does not exist. Herein, a standardized method for quantitative detection of Gal antigen was established based on an ELISA inhibition assay with Gal antibody. In this method, the key optimized experimental conditions were: (1) Gal-antigen positive and negative reference materials were developed, and used as positive and negative control in the test system, respectively; (2) A mixture of artificial Gal-BSA antigen plus Gal-negative matrix was used as the calibration standard sample, making it has similar composition with test sample; and (3) The lysis buffer was combined with the homogenate to expose the Gal antigen as much as possible. The results from validation and application experiments showed that the standardized method had good reproducibility (RSD = 12.48%), and the lower detection limit (LDL) is ~7.1 × 10¹¹ Gal epitopes/reaction. This method has been further developed into a detection Kit (Meitan 70101, China), and it has been developed as a standard method for detecting remnant immunogen of animal tissue derived medical devices, and as the industry standard has been released in China. (YY/T 1561–2017).

Adjuvant therapeutic strategies for resectable pancreatic adenocarcinoma

Of all patients diagnosed with pancreatic adenocarcinoma, only 15-20% present with resectable disease. Despite curative-intent resection, the prognosis remains poor with the majority of patients recurring, prompting the need for adjuvant therapy. Historical data support the use of adjuvant 5-fluorouracil (5-FU) or gemcitabine, but recent data suggest either gemcitabine plus capecitabine or modified FOLFIRINOX can improve overall survival when compared to gemcitabine alone. The use of adjuvant chemoradiation therapy remains controversial, primarily due to limitations in study design and mixed results of historical trials. The ongoing Radiation Therapy Oncology Group (RTOG)-0848 trial hopes to further define the role of adjuvant chemoradiation therapy. Intraoperative radiation therapy (IORT) and adjuvant immunotherapy represent additional possibilities to improve outcomes, but evidence supporting their use is limited. This article reviews adjuvant therapeutic strategies for resectable pancreatic adenocarcinoma, including chemotherapy, chemoradiation therapy, IORT and immunotherapy.

Rational combinations of immunotherapy for pancreatic ductal adenocarcinoma

The complex interaction between the immune system, the tumor and the microenvironment in pancreatic ductal adenocarcinoma (PDA) leads to the resistance of PDA to immunotherapy. To overcome this resistance, combination immunotherapy is being proposed. However, rational combinations that target multiple aspects of the complex anti-tumor immune response are warranted. Novel clinical trials will investigate and optimize the combination immunotherapy for PDA.

Eliminating Xenoantigen Expression on Swine RBC

BACKGROUND

The rapidly improving tools of genetic engineering may make it possible to overcome the humoral immune barrier that prevents xenotransplantation. We hypothesize that levels of human antibody binding to donor tissues from swine must approximate the antibody binding occurring in allotransplantation. It is uncertain if this is an attainable goal. Here we perform an initial analysis of this issue by comparing human antibody binding to red blood cells (RBC) isolated from knockout swine and to allogeneic or autologous human RBC.

METHODS

Human sera were incubated with RBC isolated from various genetically engineered swine or from humans. The level of IgG and IgM binding to these cells were compared using either flow cytometry or a novel mass spectrometric assay.

RESULTS

Mass spectroscopic quantitation of human antibody binding demonstrated that as few as 3 gene inactivations can reduce the levels human antibody binding to swine RBC that is as low as autologous human RBC. Flow cytometry showed that RBC from 2-gene knockout swine exhibited less human antibody binding than human blood group O allogeneic RBC in 22% of tested sera. Deletion of a third gene from pigs resulted in 30% of human samples having less IgG and IgM RBC xenoreactivity than alloreactivity.

CONCLUSIONS

Xenoantigenicity of swine RBC can be eliminated via gene disruption. These results suggest that the gene knockout approach may be able reduce antigenicity in other pig tissues to levels that enable the xenotransplantation humoral barrier to be overcome.

Molecular immunology profiles of monkeys following xenografting with the islets and heart of α-1,3-galactosyltransferase knockout pigs

Effective immunosuppression strategies and genetically modified animals have been used to prevent hyperacute and acute xenograft rejection; however, the underlying mechanisms remain unknown. In this study, we evaluated the expression of a comprehensive set of immune system-related genes (89 genes, including five housekeeping genes) in the blood of cynomolgus monkeys (~5 yr old) used as graft recipients, before and after the xenografting of the islets and heart from single and double α-1,3-galactosyltransferase (GalT) knockout (KO) pigs (<6 weeks old). The immunosuppressive regimen included administration of cobra venom factor, anti-thymocyte globulin, rituximab, and anti-CD154 monoclonal antibodies to recipients before and after grafting. Islets were xenografted into the portal vein in type 1 diabetic monkeys, and the heart was xenografted by heterotopic abdominal heart transplantation. Genes from recipient blood were analyzed using RT(2) profiler PCR arrays and the web-based RT(2) profiler PCR array software v.3.5. Recipients treated with immunosuppressive agents without grafting showed significant downregulation of CCL5, CCR4, CCR6, CD4, CD40LG, CXCR3, FASLG, CXCR3, FOXP3, GATA3, IGNG, L10, IL23A, TRAF6, MAPK8, MIF, STAT4, TBX21, TLR3, TLR7, and TYK2 and upregulation of IFNGR1; thus, genes involved in protection against viral and bacterial infection were downregulated, confirming the risk of infection. Notably, C3-level control resulted in xenograft failure within 2 days because of a 7- to 11-fold increase in all xenotransplanted models. Islet grafting using single GalT-KO pigs resulted in upregulation of CXCL10 and MX1, early inflammation, and acute rejection-associated signals at 2 days after xenografting. We observed at least 5-fold upregulation in recipients transplanted with islets grafts from single (MX1) or double (C3, CCR8, IL6, IL13, IRF6, CXCL10, and MX1) GalT-KO pigs after 77 days; single GalT-KO incurred early losses owing to immune attacks. Our results suggest that this novel, simple, non-invasive, and time-efficient procedure (requiring only 1.5 ml blood) for evaluating graft success, minimizing immune rejection, and blocking infection.

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

BACKGROUND

Despite the development of α1,3-galactosyl transferase-knockout (GTKO) pigs, acute humoral xenograft rejection caused by antibodies against non-Gal antigens, along with complement activation, are hurdles that need to be overcome. Among non-Gal antigens, N-glycolylneuraminic acid (Neu5Gc) is considered to play an important role in xenograft rejection in human.

METHODS

We generated human embryonic kidney 293 (HEK293) cells that expressed xenogeneic Neu5Gc (HEK293-pCMAH) or α1,3Gal (HEK293-pGT) antigen and investigated the degree of human antibody binding and complement-dependent cytotoxicity (CDC) against these antigens using 100 individual human sera.

RESULTS

Both IgM and IgG bound to α1,3Gal, while only IgG bound to Neu5Gc. Of the ABO blood groups, the degree of IgG binding to α1,3Gal was highest for blood group A. The degree of CDC against HEK293-pCMAH cells was significantly lower than that against HEK293-pGT cells. However, CDC against HEK293-pCMAH cells was significantly higher than that against control HEK293 cells. In addition, the severity of CDC against HEK293-pCMAH cells positively correlated with that against GTKO pig aortic endothelial cells (PAECs), suggesting that Neu5Gc is the main antigen in GTKO PAECs. Similar to antibody-binding activity, only IgG binding correlated with CDC against HEK293-pCMAH cells. The most common subclass of IgGs against Neu5Gc was IgG1, which typically induces strong complement activation.

CONCLUSIONS

We showed that IgG-mediated CDC was detected in Neu5Gc-overexpressed HEK293 cells incubated with human sera; however, this antibody reactivity to Neu5Gc was highly variable among individuals. Our results suggest that additional modifications to the CMAH gene should be considered for widespread use of pig organs for human transplants.

Inclusion of homologous DNA in nuclease-mediated gene targeting facilitates a higher incidence of bi-allelically modified cells

BACKGROUND

Recent advancements in gene editing techniques have increased in number and utility. These techniques are an attractive alternative to conventional gene targeting methods via homologous recombination due to the ease of use and the high efficiency of gene editing. We have previously produced cytidine monophosphate-N-acetylneuraminic acid hydroxylase (CMAH) knockout (KO) pigs in a Minnesota miniature pig genetic background. These pigs were generated using zinc-finger nucleases (ZFNs) in combination with donor DNA containing a total homology length of 1600 bp (800-bp homology on each arm). Our next aim was to introduce the targeted disruption of alpha-1,3-galactosyltransferase (GGTA1) in the CMAH KO genetic background and evaluate the effect of donor DNA homology length on meganuclease-mediated gene targeting.

METHODS

Zinc-finger nucleases from a previous CMAH KO experiment were used as a proof of concept to identify a correlation between the length of donor DNA homology and targeting efficiency. Based on those results, experiments were designed to use transcription activator-like effector nucleases (TALENs) to generate bi-allelically modified GGTA1 cells using donor DNAs carrying various lengths of homology. Donor DNA was designed to symmetrically flank the predicted cleavage sites in CMAH and GGTA1 for both ZFN and TALEN cleavage sites, respectively. For both genes, the length of total homology ranged from 60 to 1799 bp. Sialyltransferase gene expression profiles were evaluated in CMAH and GGTA1 double KO pig cells and were compared to wild-type and CMAH KO cells.

RESULTS

Introduction of donor DNA with ZFNs demonstrated that small amounts of homology (60 bp) could facilitate homology-directed repair during ZFN-mediated targeting of CMAH; however, donor DNA with longer amounts of homology resulted in a higher frequency of homology-directed repair. For the GGTA1 KO experiments that used TALENs and donor DNA, donor DNA alone did not result in detectable bi-allelic conversion of GGTA1. As the length of donor DNA increased, the bi-allelic disruption of GGTA1 increased from 0.5% (TALENs alone, no donor DNA present) to a maximum of 3% (TALENs and donor DNA with total homology of 1799 bp). Inclusion of homologous donor DNA in TALEN-mediated gene targeting facilitated a higher incidence of bi-allelically modified cells. Using the generated cells, we were able to demonstrate the lack of GGTA1 expression and the decrease in gene expression sialyltransferase-related genes.

CONCLUSIONS

The approach of using donor DNA in conjunction with a meganuclease can be used to increase the efficiency of gene targeting. The gene editing methods can be applied to other genes as well as other mammalian systems. Additionally, gene expression analysis further confirms that the CMAH/GGTA1 double KO pigs can be a valuable source for the study of pig-to-human xenotransplantation.

Alpha-1,3-galactosyltransferase-deficient miniature pigs produced by serial cloning using neonatal skin fibroblasts with loss of heterozygosity

Objective

Production of alpha-1,3-galactosyltransferase (αGT)-deficient pigs is essential to overcome xenograft rejection in pig-to-human xenotransplantation. However, the production of such pigs requires a great deal of cost, time, and labor. Heterozygous αGT knockout pigs should be bred at least for two generations to ultimately obtain homozygote progenies. The present study was conducted to produce αGT-deficient miniature pigs in much reduced time using mitotic recombination in neonatal ear skin fibroblasts.

Methods

Miniature pig fibroblasts were transfected with αGT gene-targeting vector. Resulting gene-targeted fibroblasts were used for nuclear transfer (NT) to produce heterozygous αGT gene-targeted piglets. Fibroblasts isolated from ear skin biopsies of these piglets were cultured for 6 to 8 passages to induce loss of heterozygosity (LOH) and treated with biotin-conjugated IB4 that binds to galactose-α-1,3-galactose, an epitope produced by αGT. Using magnetic activated cell sorting, cells with monoallelic disruption of αGT were removed. Remaining cells with LOH carrying biallelic disruption of αGT were used for the second round NT to produce homozygous αGT gene-targeted piglets.

Results

Monoallelic mutation of αGT gene was confirmed by polymerase chain reaction in fibroblasts. Using these cells as nuclear donors, three heterozygous αGT gene-targeted piglets were produced by NT. Fibroblasts were collected from ear skin biopsies of these piglets, and homozygosity was induced by LOH. The second round NT using these fibroblasts resulted in production of three homozygous αGT knockout piglets.

Conclusion

The present study demonstrates that the time required for the production of αGT-deficient miniature pigs could be reduced significantly by postnatal skin biopsies and subsequent selection of mitotic recombinants. Such procedure may be beneficial for the production of homozygote knockout animals, especially in species, such as pigs, that require a substantial length of time for breeding.

Immunotherapy for pancreatic ductal adenocarcinoma: an overview of clinical trials

Pancreatic ductal adenocarcinoma (PDAC) is the fourth leading cause of cancer-related death and current therapeutic strategies are often unsatisfactory. Identification and development of more efficacious therapies is urgently needed. Immunotherapy offered encouraging results in preclinical models during the last decades, and several clinical trials have explored its therapeutic application in PDAC. The aim of this review is to summarize the results of clinical trials conducted to evaluate the future perspective of immunotherapy in the treatment of PDAC.

Four-dimensional characterization of thrombosis in a live-cell, shear-flow assay: development and application to xenotransplantation

Background

Porcine xenografts are a promising source of scarce transplantable organs, but stimulate intense thrombosis of human blood despite targeted genetic and pharmacologic interventions. Current experimental models do not enable study of the blood/endothelial interface to investigate adhesive interactions and thrombosis at the cellular level under physiologic conditions. The purpose of this study was to develop and validate a live-cell, shear-flow based thrombosis assay relevant to general thrombosis research, and demonstrate its potential in xenotransplantation applications.

Methodology/Principal Findings

Confluent wild-type (WT, n = 48) and Gal transferase knock-out (GalTKO, which resist hyperacute rejection; n = 11) porcine endothelia were cultured in microfluidic channels. To mimic microcirculatory flow, channels were perfused at 5 dynes/cm² and 37°C with human blood stained to fluorescently label platelets. Serial fluorescent imaging visualized percent surface area coverage (SA, for adhesion of labeled cells) and total fluorescence (a metric of clot volume). Aggregation was calculated by the fluorescence/SA ratio (FR). WT endothelia stimulated diffuse platelet adhesion (SA 65 ± 2%) and aggregation (FR 120 ± 1 a.u.), indicating high-grade thrombosis consistent with the rapid platelet activation and consumption seen in whole-organ lung xenotransplantation models. Experiments with antibody blockade of platelet aggregation, and perfusion of syngeneic and allo-incompatible endothelium was used to verify the biologic specificity and validity of the assay. Finally, with GalTKO endothelia thrombus volume decreased by 60%, due primarily to a 58% reduction in adhesion (P < 0.0001 each); importantly, aggregation was only marginally affected (11% reduction, P < 0.0001).

Conclusions/Significance

This novel, high-throughput assay enabled dynamic modeling of whole-blood thrombosis on intact endothelium under physiologic conditions, and allowed mechanistic characterization of endothelial and platelet interactions. Applied to xenogeneic thrombosis, it enables future studies regarding the effect of modifying the porcine genotype on sheer-stress-dependent events that characterize xenograft injury. This in-vitro platform is likely to prove broadly useful to study thrombosis and endothelial interactions under dynamic physiologic conditions.

Lung xenotransplantation: recent progress and current status

Xenotransplantation has undergone important progress in controlling initial hyperacute rejection in many preclinical models, with some cell, tissue, and organ xenografts advancing toward clinical trials. However, acute injury, driven primarily by innate immune and inflammatory responses, continues to limit results in lung xenograft models. The purpose of this article is to review the current status of lung xenotransplantation--including the seemingly unique challenges posed by this organ-and summarize proven and emerging means of overcoming acute lung xenograft injury.

New Approaches in Immunotherapy for the Treatment of Lung Cancer

Despite the several advances in the last few years into treatment of advanced lung cancer, the 5-year survival remains extremely low. New therapeutic strategies are currently under investigation, and immunotherapy seems to offer a promising treatment alternative. In the last decade, therapeutic cancer vaccines in lung cancer have been rather disappointing, mainly due to the lack of efficient predictive biomarkers. A better refinement of the patient population that might respond to treatment might finally lead to a success story. For the first time, the immune checkpoint inhibitors are demonstrating sustained antitumor response and improved survival and they may be the first immunotherapeutics available for patients with lung cancer.

Addition of algenpantucel-L immunotherapy to standard adjuvant therapy for pancreatic cancer: a phase 2 study

BACKGROUND

Despite continued investigation, limited progress has been made in the adjuvant treatment of resected pancreatic cancer. Novel or targeted therapies are needed.

METHODS

Multi-institutional, open-label, dose-finding, phase 2 trial evaluating the use of algenpantucel-L (NewLink Genetics Corporation, Ames, IA) immunotherapy in addition to chemotherapy and chemoradiotherapy in the adjuvant setting for resected pancreatic cancer (ClinicalTrials.gov identifier, NCT00569387). The primary outcome was 12-month disease-free survival. Secondary outcomes included overall survival and toxicity.

RESULTS

Seventy patients were treated with gemcitabine and 5-fluorouracil-based chemoradiotherapy as well as algenpantucel-L (mean 12 doses, range 1-14). After a median follow-up of 21 months, the 12-month disease-free survival was 62 %, and the 12-month overall survival was 86 %. The most common adverse events were injection site pain and induration.

CONCLUSIONS

The addition of algenpantucel-L to standard adjuvant therapy for resected pancreatic cancer may improve survival. A multi-institutional, phase 3 study is ongoing (ClinicalTrials.gov identifier, NCT01072981).

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.

The αGal HyperAcute(®) Technology: enhancing immunogenicity of antiviral vaccines by exploiting the natural αGal-mediated zoonotic blockade

The αGal HyperAcute(®) Technology exploits a robust zoonotic blockade to enhance potency of antiviral vaccines. Naturally acquired immunity against the common αGal epitope [galactose-alpha(1,3)-galactose-beta(1,4)N-acetylglucosamine-R (Gal-α(1,3)-Gal-β(1,4)-GlcNAc-R)] is facilitated by the loss of a key enzyme in the epitope's biosynthetic pathway. As human cells are devoid of this epitope, chronic stimulus from gut flora leads to high levels of circulating anti-αGal antibodies and the development of a robust immune pathway. As the αGal epitope is immediately recognized as foreign, the naturally acquired αGal immune pathway in humans serves as a strong barrier to zoonotic infection. The αGal HyperAcute(®) Technology takes advantage of this natural process to facilitate the rapid presentation of modified antigens to antigen-presenting cells, leading to a strong immune response. The evolutionary immunity to αGal ensures that the presence of αGal epitopes on antigens will lead to a robust immune response involving cross-activation of T(H)1 immunity, characterized by cytokine secretion and increased phagocytic activity, and T(H)2 immunity characterized by high antibody titres. αGal epitopes can be applied to antiviral vaccines by biological, enzymatic or chemical means. Several detection methods that directly and indirectly verify αGal addition are discussed. Enhanced immunogenicity (humoral and cellular) of αGal-modified vaccines is shown for several antiviral vaccine candidates. αGal modification of antiviral vaccine components leads to enhanced immunogenicity. The existing body of literature describing the utility of αGal epitopes as a safe and robust immunostimulatory and -modulatory agent in humans supports the basis for applying the αGal HyperAcute(®) Technology to the improvement of antiviral vaccines, both new and currently approved.

Structural basis of UDP-galactose binding by alpha-1,3-galactosyltransferase (alpha3GT): role of negative charge on aspartic acid 316 in structure and activity

alpha-1,3-Galactosyltransferase (alpha3GT) catalyzes the transfer of galactose from UDP-galactose to form an alpha 1-3 link with beta-linked galactosides; it is part of a family of homologous retaining glycosyltransferases that includes the histo-blood group A and B glycosyltransferases, Forssman glycolipid synthase, iGb3 synthase, and some uncharacterized prokaryotic glycosyltransferases. In mammals, the presence or absence of active forms of these enzymes results in antigenic differences between individuals and species that modulate the interplay between the immune system and pathogens. The catalytic mechanism of alpha3GT is controversial, but the structure of an enzyme complex with the donor substrate could illuminate both this and the basis of donor substrate specificity. We report here the structure of the complex of a low-activity mutant alpha3GT with UDP-galactose (UDP-gal) exhibiting a bent configuration stabilized by interactions of the galactose with multiple residues in the enzyme including those in a highly conserved region (His315 to Ser318). Analysis of the properties of mutants containing substitutions for these residues shows that catalytic activity is strongly affected by His315 and Asp316. The negative charge of Asp316 is crucial for catalytic activity, and structural studies of two mutants show that its interaction with Arg202 is needed for an active site structure that facilitates the binding of UDP-gal in a catalytically competent conformation.

Site-directed mutagenesis of glutamate 317 of bovine alpha-1,3Galactosyltransferase and its effect on enzyme activity: implications for reaction mechanism

Bovine alpha1,3galactosyltransferase (alpha1,3GalT) transfers galactose from UDP-alpha-galactose to terminal beta-linked galactosyl residues with retention of configuration of the incoming galactose residue. The epitope synthesized has been shown to be critical for xenotransplantation. According to a proposed double-displacement reaction mechanism, glutamate-317 (E317) is thought to be the catalytic nucleophile. The proposed catalytic role of E317 involves an initial nucleophilic attack with inversion of configuration and formation of a covalent sugar-enzyme intermediate between E317 and galactose from the donor substrate, followed by a second nucleophilic attack performed by the acceptor substrate with a second inversion of configuration. To determine whether E317 of alpha1,3GalT is critical for enzyme activity, site-directed mutagenesis was used to substitute alanine, aspartic acid, cysteine and histidine for E317. If the proposed reaction mechanism for the alpha1,3GalT enzyme is correct, E317D and E317H would produce active enzymes since they can act as nucleophiles. The non-conservative mutation E317A and conservative mutation E317C are predicted to produce inactive or very low activity enzymes since the E317A mutant cannot engage in a nucleophilic attack, and the E317C mutant would trap the galactose residue. The results obtained demonstrate that E317D and E317H mutants retained activity, albeit significantly less than the wild-type enzyme. Additionally, both E317A and E317C mutant also retained enzyme activity, suggesting that E317 is not the catalytic nucleophile proposed in the double-displacement mechanism. Therefore, either a different amino acid may act as the catalytic nucleophile or the reaction must proceed by a different mechanism.

Conformational changes induced by binding UDP-2F-galactose to alpha-1,3 galactosyltransferase- implications for catalysis

Alpha-1,3 galactosyltransferase (alpha3GT) catalyzes the transfer of galactose from UDP-galactose to beta-linked galactosides with retention of its alpha configuration. Although several complexes of alpha3GT with inhibitors and substrates have been reported, no structure has been determined of a complex containing intact UDP-galactose. We describe the structure of a complex containing an inhibitory analogue of UDP-galactose, UDP-2F-galactose, in a complex with the Arg365Lys mutant of alpha3GT. The inhibitor is bound in a distorted, bent configuration and comparison with the structure of the apo form of this mutant shows that the interaction induces structural changes in the enzyme, implying a role for ground state destabilization in catalysis. In addition to a general reduction in flexibility in the enzyme indicated by a large reduction in crystallographic B-factors, two loops, one centred around Trp195 and one encompassing the C-terminal 11 residues undergo large structural changes in complexes with UDP and UDP derivatives. The distorted configuration of the bound UDP-2F-galactose in its complex is stabilized, in part, by interactions with residues that are part of or near the flexible loops. Mutagenesis and truncation studies indicate that two highly conserved basic amino acid residues in the C-terminal region, Lys359 and Arg365 are important for catalysis, probably reflecting their roles in these ligand-mediated conformational changes. A second Mn(2+) cofactor has been identified in the catalytic site of a complex of the Arg365Lys with UDP, in a location that suggests it could play a role in facilitating UDP release, consistent with kinetic studies that show alpha3GT activity depends on the binding of two manganese ions. Conformational changes in the C-terminal 11 residues require an initial reorganization of the Trp195 loop and are linked to enzyme progress through the catalytic cycle, including donor substrate distortion, cleavage of the UDP-galactose bond, galactose transfer, and UDP release.

Modified acellularization for successful vascular xenotransplantation

The purpose of this study was to estimate the possibilities of an acellular matrix using a modified acellularization protocol, which circumvents immunological, microbiological, and physiological barriers. We treated porcine subclavian arteries with various reagents to construct acellular grafts. Afterwards, these grafts were interposed in a mongrel dogs' abdominal aorta. Six dogs underwent interposition with fresh porcine grafts (control group), and seven had interposed acellular grafts (acellular group). The control and acellular group dogs were sacrificed at 1, 3, 5 (n=2 in each group) and 12 months (n=1 in acellular group) after the operation. Histopathological examinations were then performed, to assess the degree to which re-endothelialization, inflammation, thrombus formation, and calcification occurred. The entire acellular group, but none of the control group, exhibited re-endothelialization. The degrees to which inflammation, thrombosis, and calcification occurred were found to be lower in the acellular group. We also discovered many smooth muscle cells in the medial layer of the xenograft that had been implanted in the dog sacrificed 12 months after the operation. These results suggest that the construction of xenografts using our modified acellularization protocol may offer acceptable outcomes as a vascular xenograft.

Glycoengineering of alphaGal xenoantigen on recombinant peptide bearing the J28 pancreatic oncofetal glycotope

In human pancreatic adenocarcinoma, alterations of glycosylation processes leads to the expression of tumor-associated carbohydrate antigens, representing potential targets for cancer immunotherapy. Among these pancreatic tumor-associated carbohydrate antigens, the J28 glycotope located within the O-glycosylated mucin-like C-terminal domain of the fetoacinar pancreatic protein (FAPP) and expressed at the surface of human tumoral tissues, can be a good target for anticancer therapeutic vaccines. However, the oncodevelopmental self character of the J28 glycotope associated with the low immunogenicity of tumor-associated carbohydrate antigens may be a major obstacle to effective anti-tumor vaccine therapy. In this study, we have investigated a method to increase the immunogenicity of the recombinant pancreatic oncofetal J28 glycotope by glycoengineering Galalpha1,3Galss1,4GlcNAc-R (alphaGal epitope) which may be recognized by natural anti-alphaGal antibody present in humans. For this purpose, we have developed a stable Chinese hamster ovary cell clone expressing the alphaGal epitope by transfecting the cDNA encoding the alpha1,3galactosyltransferase. These cells have been previously equipped to produce the recombinant O-glycosylated C-terminal domain of FAPP carrying the J28 glycotope. As a consequence, the C-terminal domain of FAPP produced by these cells carries the alphaGal epitope on oligosaccharide structures associated with the J28 glycotope. Furthermore, we show that this recombinant "alpha1,3galactosyl and J28 glycotope" may not only be targeted by human natural anti-alphaGal antibodies but also by the mAbJ28, suggesting that the J28 glycotope remains accessible to the immune system as vaccinating agent. This approach may be used for many identified tumor-associated carbohydrate antigens which can be glycoengineered to carry a alphaGal epitope to increase their immunogenicity and to develop therapeutic vaccines.

Functionally important glycosyltransferase gain and loss during catarrhine primate emergence

A glycosyltransferase, alpha1,3galactosyltransferase, catalyzes the terminal step in biosynthesis of Galalpha1,3Galbeta1-4GlcNAc-R (alphaGal), an oligosaccharide cell surface epitope. This epitope or antigenically similar epitopes are widely distributed among the different forms of life. Although abundant in most mammals, alphaGal is not normally found in catarrhine primates (Old World monkeys and apes, including humans), all of which produce anti-alphaGal antibodies from infancy onward. Natural selection favoring enhanced resistance to alphaGal-positive pathogens has been the primary reason offered to account for the loss of alphaGal in catarrhines. Here, we question the primacy of this immune defense hypothesis with results that elucidate the evolutionary history of GGTA1 gene and pseudogene loci. One such locus, GGTA1P, a processed (intronless) pseudogene (PPG), is present in platyrrhines, i.e., New World monkeys, and catarrhines but not in prosimians. PPG arose in an early ancestor of anthropoids (catarrhines and platyrrhines), and GGTA1 itself became an unprocessed pseudogene in the late catarrhine stem lineage. Strong purifying selection, denoted by low nonsynonymous substitutions per nonsynonymous site/synonymous substitutions per synonymous site values, preserved GGTA1 in noncatarrhine mammals, indicating that the functional gene product is subjected to considerable physiological constraint. Thus, we propose that a pattern of alternative and/or more beneficial glycosyltransferase activity had to first evolve in the stem catarrhines before GGTA1 inactivation could occur. Enhanced defense against alphaGal-positive pathogens could then have accelerated the replacement of alphaGal-positive catarrhines by alphaGal-negative catarrhines. However, we emphasize that positively selected regulatory changes in sugar chain metabolism might well have contributed in a major way to catarrhine origins.

α1,3-Galactosyltransferase-Gene Knockout in Cattle using a Single Targeting Vector with loxP Sequences and Cre-Expressing Adenovirus

BACKGROUND

Gene targeting in large animals has the potential to be useful in medicine as well as in agriculture. Previously, we reported the first successful targeting of the bovine alpha1,3-galactosyltransferase (alpha1,3GT) gene and establishment of a heterozygous knockout cell line. In this report, we generated both heterozygous and homozygous knockout bovine cell lines, and alpha1,3GT-gene knockout cattle.

METHODS

alpha1,3GT gene-disruption was accomplished using primary fetal fibroblasts with a single targeting vector, a promoter-less positive selection vector containing IRES (internal ribosome entry site)-antibiotic-resistance gene (neo) cassette and loxP sequences. At each step in establishing heterozygous and homozygous knockout cell lines, the antibiotic-resistance gene cassette in the targeted allele was removed by a Cre-loxP recombination system that utilizes an adenovirus with transient Cre recombinase expression. A nuclear transfer was performed using alpha1,3GT fetal fibroblasts, and one alpha1,3GT knockout calf was generated but died shortly after birth (day 287).

RESULTS

Necropsy revealed normal morphology in all organs. The calf weighed 22.3 kg at birth and this value is within the normal range.

CONCLUSION

The alpha1,3GT knockout- and antibiotic-resistance gene free (alpha1,3GT(-/-)neo-) cells could be cloned normally. Thus, cloned cattle from alpha1,3GT(-/-) neo- cells are potentially safer for human use. Additionally, our strategy is faster and more economical than backcrossing to produce homozygous knockouts. This method should be useful for future production of knockouts of multiple genes in livestock.

Effective treatment of preexisting melanoma with whole cell vaccines expressing alpha(1,3)-galactosyl epitopes

The hyperacute immune response in humans is a potent mechanism of xenograft rejection mediated by complement-fixing natural antibodies recognizing alpha(1,3)-galactosyl epitopes (alphaGal) not present on human cells. We exploited this immune mechanism to create a whole cell cancer vaccine to treat melanoma tumors. B16 melanoma vaccines genetically engineered to express alphaGal epitopes (B16alphaGal) effectively treated preexisting s.c. and pulmonary alphaGal-negative melanoma (B16Null) tumors in the alpha(1,3)-galactosyltransferase knockout mouse model. T cells from mice vaccinated with B16alphaGal recognized B16Null melanoma cells measured by detection of intracellular tumor necrosis factor-alpha. We showed successful adoptive transfer of immunity to recipient mice bearing lung melanoma metastasis. Mice receiving lymphocytes from donors previously immunized with B16alphaGal had reduced pulmonary metastases. The transfer of lymphocytes from mice vaccinated with control vaccine had no effect in the pulmonary metastasis burden. This study unequivocally establishes for the first time efficacy in the treatment of preexisting melanoma tumors using whole cell vaccines expressing alphaGal epitopes. Vaccination with B16alphagal induced strong long-lasting cell-mediated antitumor immunity extended to B16Null. These data formed the basis for the testing of this therapeutic strategy in human clinical trials currently under way.

Endothelial cell protection in xenotransplantation: looking after a key player in rejection

The endothelium, as an organ at the interface between the intra- and extravascular space, actively participates in maintaining an anti-inflammatory and anti-coagulant environment under physiological conditions. Severe humoral as well as cellular rejection responses, which accompany cross-species transplantation of vascularized organs as well as ischemia/reperfusion injury, primarily target the endothelium and disrupt this delicate balance. Activation of pro-inflammatory and pro-coagulant pathways often lead to irreversible injury not only of the endothelial layer but also of the entire graft, with ensuing rejection. This review focuses on strategies targeted at protecting the endothelium from such damaging effects, ranging from genetic manipulation of the donor organ to soluble, as well as membrane-targeted, protective strategies.

Iminosugars as glycosyltransferase inhibitors: synthesis of polyhydroxypyrrolidines and their evaluation on chitin synthase activity

Chitin synthase is an enzyme involved in the biosynthesis of chitin, a major structural component of the cell wall of many fungi. Since chitin is absent in vertebrates, chitin synthase has been envisaged as a valuable target in the search for new antifungal agents. In this report, a series of C-2 substituted polyhydroxypyrrolidines were designed and synthesized with the aim of mimicking the glycosylation involved at the transition state of the enzymatic reaction governed by chitin synthase. Some of these models displayed chitin synthase inhibition in the millimolar range. However, no significant antifungal activity was noted on a panel of fungal strains.

Complete protection against melanoma in absence of autoimmune depigmentation after rejection of melanoma cells expressing alpha(1,3)galactosyl epitopes

The major barrier for xenotransplantation in humans is the presence of alpha(1-3) Galactosyl epitopes (alphaGal) in xenogeneic tissue and the vast quantities of natural antibodies (Ab) produced by humans against this epitope. The binding of anti-alphaGal Ab to cells expressing alphaGal triggers a complement-mediated hyperacute rejection of target cells. The hyperacute rejection of whole cancer cells, modified to express alphaGal epitopes, could be exploited as a new cancer vaccine to treat human cancers. We tested this hypothesis in alphaGalactosyltransferase knockout (alphaGT KO) mice which, like humans, do not express alphaGal on their cell surfaces and can produce anti-alphaGal Ab. Forty-five percent of mice with preexisting anti-alphaGal Ab rejected alphaGal positive melanoma cells (B16alphaGal). These mice remained tumor-free for more than 90 days. The majority of control mice injected with B16Null, alphaGal negative cells succumbed to melanoma. The rejection of B16alphaGal induced strong long-lasting antitumor immunity against B16Null measured by the expansion of cytotoxic T lymphocytes. In addition, mice rejecting B16alphaGal were protected against melanoma since they survived a second rechallenge with B16Null. Protected mice developed antitumor immunity in the absence of autoimmune depigmentation (vitiligo). These results show that rejection of alphaGal positive melanoma cells can efficiently boost the immune response to other tumor associated antigens present in alphaGal negative melanoma cells. This study supports the concept of a novel anticancer vaccine to treat human malignancies.

Capillary electrophoresis method for the enzymatic assay of galactosyltransferases with postreaction derivatization

Glycosyltransferases are key enzymes in glycoconjugate biosynthesis, which make them important targets for biomedical research. Among the different methodologies developed to analyze glycosyltransferase activities, fluorophore-assisted capillary electrophoresis (FACE) emerges as a powerful technique in carbohydrate analysis. Its application to monitor glycosyltransferase activity has been limited to reactions with derivatized sugars as acceptor substrates in which a charged fluorophore/chromophore must be introduced, thus requiring tedious preparative synthesis and purification for each single acceptor substrate. Here we describe a novel and general glycosyltransferase assay based on FACE using underivatized acceptor substrates. Enzyme activity is monitored by a discontinuous assay with postreaction derivatization by reductive amination with 8-aminonaphthalene-1,3,6-trisulfonic acid. The reaction mixture is directly analyzed by HPCE (high-performance capillary electrophoresis) under inverted electroosmotic conditions at pH 2.5 and 30 degrees C. After method validation, it was applied to the kinetic characterization of an alpha-1,3-galactosyltransferase, the enzyme responsible for the biosynthesis of alphaGal epitope involved in the hyperacute rejection in xenotransplantation. The absence of a label on the acceptor during the GT reaction avoids any interference of the label with the enzyme, and the postreaction derivatization does not require any purification step.

Relationship between ?Gal epitope expression and decrease of tumorigenicity in pancreatic adenocarcinoma model

The alphaGal epitope is a carbohydrate structure, Galalpha1,3Galbeta1,4GlcNAc-R, synthesized on glycoconjugates in many mammals by alpha1,3galactosyltransferase. Humans do not express this epitope and present in serum large amounts of naturally occuring antibodies, which recognize the alphaGal epitopes and participate in the hyperacute rejection of xenograft. Studies indicated that the fundamental mechanism of hyperacute rejection involving the alphaGal epitope expression can be used in cancer therapy. We have previously suggested that the alphaGal epitope expression by human pancreatic tumoral cells could decrease the tumorigenic behavior of these cells. To determine whether the expression of the alphaGal epitope can modify the tumorigenicity of pancreatic cancer cells, we used a Syrian golden hamster pancreatic adenocarcinoma experimental model. The expression of alphaGal epitopes in the Syrian golden hamster pancreatic cancer cell line HaP-T1 was obtained by selecting stable cell clones transfected with murine alpha1,3galactosyltransferase gene. The alphaGal epitope expression resulted in a delay in the tumoral development of HaP-T1 cells in vivo after allograft transplantation of Syrian golden hamsters (2.5-fold, P < 0.05) and of nude mice. This result is associated with an 100% increase in survival time of nude mice bearing tumors expressing the alphaGal epitope. Our results confirm that the cell surface expression of alphaGal epitope decreases the tumorigenic behavior of pancreatic cancer cells. This novel property may be useful for the development of cancer gene immunotherapy strategy.

Decrease of human pancreatic cancer cell tumorigenicity by alpha1,3galactosyltransferase gene transfer

The enzyme alpha1,3galactosyltransferase synthesizes the alphaGal epitope, a carbohydrate structure (Galalpha1,3Galbeta1,4GlcNAc-R), on glycoconjugates in lower mammals. The enzyme is absent in humans but large amounts of natural antibodies that recognize alphaGal epitopes are present in human serum. It is likely that these antibodies contribute to the host defense and participate in the hyperacute rejection of xenograft. Previous studies indicated that the glycosyltransferase gene transfer into tumoral cells can modify the structure of glycoconjugates at the cell surface and, as a consequence, modulates the metastatic and tumorigenic behaviors of these cells. The aim of our study was to determine whether the expression of alphaGal epitope can modify the tumorigenicity of human pancreatic cancer cells. The expression of alphaGal epitopes in the human pancreatic cancer cell lines BxPC-3 and Panc-1 was obtained by selecting stable cell clones transfected with murine alpha1,3galactosyltransferase gene. The expression of the enzyme activity in BxPC-3 and Panc-1 cells resulted in the formation at the cell surface of alphaGal epitopes that are recognized by human anti-alphaGal antibodies. alphaGal epitope expression at the surface of pancreatic cancer cells was associated with the fixation of complement 1q to human anti-alphaGal antibodies. The alphaGal epitope expression also resulted in a delay in the tumoral development of BxPC-3 and Panc-1 cells in vivo after xenograft transplantation of nude mice. In addition to the impairment of the metastatic potential of murine tumor cell lines and the activation of immune response, our study provides evidence that the cell surface expression of alphaGal epitopes also modulates the tumorigenic behavior of human pancreatic cancer cells.

Red blood cell antigens responsible for inherited types of polyagglutination

The three described types on inheritable polyagglutination are related to altered carbohydrate structures in glycoproteins or/and glycolipds on the erythrocyte surface. HEMPAS, a condition causing anemia and other pathological symptoms, is characterized by impaired biosynthesis of N-glycans, mostly those carried by band 3 and band 4.5 erythrocyte membrane proteins. Cad erythrocytes have abnormal glycophorin O-glycans, structurally related to the more common human Sd(a) and murine CT determinants, and accumulate an Sd(a)-like ganglioside. NOR erythrocytes express recently detected abnormal alpha-galactose-terminated glycosphingolipids, which strongly react with G. simplicifolia IB4 isolectin, but do not react with human anti-Galalpha1-3Gal antibodies.