Failure to deplete anti-Galalpha1-3Gal antibodies after pig-to-baboon organ xenotransplantation by immunoaffinity columns containing multiple Galalpha1-3Gal oligosaccharides

Removal of natural anti-αGal antibodies elicits protective immunity against Gram-negative bacterial infections

Antibody-dependent enhancement (ADE) of bacterial infections occurs when blocking or inhibitory antibodies facilitate the infectivity of pathogens. In humans, antibodies involved in ADE of bacterial infections may include those naturally produced against Galα1-3Galβ1-4GlcNAcβ (αGal). Here, we investigate whether eliminating circulating anti-αGal antibodies using a soluble αGal glycopolymer confers protection against Gram-negative bacterial infections. We demonstrated that the in vivo intra-corporeal removal of anti-αGal antibodies in α1,3-galactosyltransferase knockout (GalT-KO) mice was associated with protection against mortality from Gram-negative sepsis after cecal ligation and puncture (CLP). The improved survival of GalT-KO mice was associated with an increased killing capacity of serum against Escherichia coli isolated after CLP and reduced binding of IgG1 and IgG3 to the bacteria. Additionally, inhibition of anti-αGal antibodies from human serum in vitro increases the bactericidal killing of E. coli O86:B7 and multidrug-resistant Klebsiella pneumoniae and Pseudomonas aeruginosa. In the case of E. coli O86:B7, there was also an improvement in bacteria opsonophagocytosis by macrophages. Both lytic mechanisms were related to a decreased binding of IgG2 to the bacteria. Our results show that protective immunity against Gram-negative bacterial pathogens can be elicited, and infectious diseases caused by these bacteria can be prevented by removing natural anti-αGal antibodies.

Progress in pig-to-non-human primate transplantation models (1998-2013): a comprehensive review of the literature

BACKGROUND

The pig-to-non-human primate model is the standard choice for in vivo studies of organ and cell xenotransplantation. In 1998, Lambrigts and his colleagues surveyed the entire world literature and reported all experimental studies in this model. With the increasing number of genetically engineered pigs that have become available during the past few years, this model is being utilized ever more frequently.

METHODS

We have now reviewed the literature again and have compiled the data we have been able to find for the period January 1, 1998 to December 31, 2013, a period of 16 yr.

RESULTS

The data are presented for transplants of the heart (heterotopic and orthotopic), kidney, liver, lung, islets, neuronal cells, hepatocytes, corneas, artery patches, and skin. Heart, kidney, and, particularly, islet xenograft survival have increased significantly since 1998.

DISCUSSION

The reasons for this are briefly discussed. A comment on the limitations of the model has been made, particularly with regard to those that will affect progression of xenotransplantation toward the clinic.

A new generation of carbohydrate-based therapeutics: recombinant mucin-type fusion proteins as versatile inhibitors of protein-carbohydrate interactions

Cell surface carbohydrates are essential for a multitude of biomedically important interactions that take place at the cell surface. Carbohydrate-binding proteins are, therefore, significant targets for the development of carbohydrate-based inhibitors. Due to their multivalent character, monovalent low-molecular-weight sugar homologues or analogues are usually poor inhibitors of these interactions. Recent advances in organic and chemoenzymatic synthesis of carbohydrates will undoubtedly increase the pace by which new multivalent carbohydrate-based drugs are developed. Knowledge gained on the glycosyltransferases that are involved in glycan biosynthesis can be used to engineer host cells for recombinant production of proteins with tailored glycan substitution. In particular, recombinant mucin-type proteins can serve as natural scaffolds for multivalent presentation of therapeutic carbohydrate determinants.

Potential of an Injectable Polymer to Prevent Hyperacute Rejection of Ex Vivo Perfused Porcine Lungs

BACKGROUND

Removal of xenoreactive antibodies in pig-to-human lung transplantation by columns or organ perfusions proofed to be unsatisfactory and associated with adverse effects. In an ex-vivo lung perfusion model, we evaluated the potential of a soluble trisaccharide polymer (GAS914) to bind alpha-Gal antibodies and to protect a pulmonary xenograft from hyperacute rejection (HAR) and pulmonary xenograft dysfunction.

METHODS

Porcine lungs were perfused with fresh human blood for 240 min. In the GAS914 treated group (n=6) the polymer was applied in three different concentrations. The control group (n=6) received no GAS914. Survival and function of perfused xenografts were monitored, and alpha-Gal antibodies as well as cytolytic anti-porcine antibodies analyzed.

RESULTS

In the GAS-treated group survival of lungs was significantly prolonged, pulmonary vascular resistance reduced, pulmonary edema prevented, and oxygenation improved. On histopathological evaluation application of GAS resulted in minimal graft injury and significantly less deposition of the terminal complement complex C5b-9. Following application of GAS914, up to 89.8% of IgG alpha-Gal, 79.5% of IgM and 73.6% of anti-porcine antibodies in the human blood were bound by the polymer. Subsequent perfusion of porcine lungs resulted in absorption of only 3% of the baseline IgG alpha-Gal antibodies in the GAS914 group, compared to 87% in the controls.

CONCLUSIONS

In this ex-vivo lung perfusion model, a trisaccharide polymer prevented immediate HAR, due to effective removal of alpha-Gal antibodies. In combination with additional strategies GAS914 may be a valuable tool in overcoming HAR and dysfunction of pulmonary xenografts.

Characteristics of protein-carbohydrate interactions as a basis for developing novel carbohydrate-based antirejection therapies

The relative shortage of human organs for transplantation is today the major barrier to a broader use of transplantation as a means of treating patients with end-stage organ failure. This barrier could be partly overcome by an increased use of blood group ABO-incompatible live donors, and such trials are currently underway at several transplant centres. If xenotransplantation can be used clinically in the future, the human organ shortage will, in principle, be eradicated. In both these cases, carbohydrate antigens and the corresponding anti-carbohydrate antibodies are the major primary immunological barriers to overcome. Refined carbohydrate-based therapeutics may permit an increased number of ABO-incompatible transplantations to be carried out, and may remove the initial barriers to clinical xenotransplantation. Here, we will discuss the chemical characteristics of protein-carbohydrate interactions and outline carbohydrate-based antirejection therapies as used today in experimental as well as in clinical settings. Novel mucin-based adsorbers of natural anti-carbohydrate antibodies will also be described.

Anti-non-Gal porcine endothelial cell antibodies in acute humoral xenograft rejection of hDAF-transgenic porcine hearts in cynomolgus monkeys

BACKGROUND

Anti-Gal alpha 1-3Gal (Gal) antibodies play a major role in hyperacute rejection and acute humoral xenograft rejection (AHXR) in porcine-to-nonhuman primate transplantation. The role of anti-non-Gal antibodies in AHXR is less well defined.

METHODS

Eleven cynomolgus monkeys received a heterotopic heart transplant from a human decay-accelerating factor transgenic pig, and maintenance immunosuppression with cyclosporin A or tacrolimus, steroids, mycophenolate sodium or mycophenolate mofetil, and in 10 animals the Gal-containing soluble glycoconjugate GAS914. Six ended with AHXR (6 to 78 day survival) and five did not show AHXR (9 to 36 day survival). Anti-Gal antibodies were depleted in vivo with GAS914, or in vitro with Gal-coated Sepharose beads. IgM- and IgG-class anti-non-Gal antibodies in serum depleted of anti-Gal antibodies were measured by flow cytometry using porcine endothelial target cells.

RESULTS

Compared with pre-transplant values, all six recipients with AHXR showed a substantially higher level of anti-non-Gal IgM antibodies at rejection; in five animals there was also an increase in IgG-class antibodies. There was no relevant change in recipients without AHXR. AHXR at time of cessation of heart contraction could be preceeded by a steady increase in antibody level starting 2 to 3 weeks earlier.

CONCLUSIONS

AHXR is invariably associated with increased circulating anti-non-Gal antibodies. These antibodies are not observed in recipients without AHXR, and five of six recipients with AHXR were adequately depleted of anti-Gal antibodies by maintenance GAS914. This indicates that anti-non-Gal antibodies play a significant role in the pathogenesis of AHXR. Also, the assessment of these antibodies could be used as an early monitor of AHXR.