The Structural Complexity and Animal Tissue Distribution of N-Glycolylneuraminic Acid (Neu5Gc)-Terminated Glycans. Implications for Their Immunogenicity in Clinical Xenografting

Abstract

N -Glycolylneuraminic acid (Neu5Gc)-terminated glycans are present in all animal cells/tissues that are already used in the clinic such as bioprosthetic heart valves (BHV) as well as in those that potentially will be xenografted in the future to overcome end stage cell/organ failure. Humans, as a species lack this antigen determinant and can react with an immune response after exposure to Neu5Gc present in these products/cells/tissues. Genetically engineered source animals lacking Neu5Gc has been generated and so has animals that in addition lack the major αGal xenoantigen. The use of cells/tissues/organs from such animals may improve the long-term performance of BHV and allow future xenografting. This review summarizes the present knowledge regarding structural complexity and tissue distribution of Neu5Gc on glycans of cells/tissue/organs already used in the clinic or intended for treatment of end stage organ failure by xenografting. In addition, we briefly discuss the role of anti-Neu5Gc antibodies in the xenorejection process and how knowledge about Neu5Gc structural complexity can be used to design novel diagnostics for anti-Neu5Gc antibody detection.

Glycosylated Biotherapeutics: Immunological Effects of N-Glycolylneuraminic Acid

“…Hence, Neu5Gc is foreign in humans and mediates production of a complex anti-Neu5Gc antibodies response, or "Xeno-autoantibodies" (47,51,57,76). Neu5Gc is a 325 Dalton molecule and cannot by itself fill the paratope of an antibody, yet Neu5Gc-containing glycan-epitopes are highly diverse (58)(59)(60) and are recognized by polyclonal anti-Neu5Gc IgM, IgA, and mostly IgG antibodies that make up 0.1-0.2% of total circulating antibodies in humans (47,49,(77)(78)(79). Anti-Neu5Gc antibodies in humans arise already in infants, soon after the introduction of dietary Neu5Gc (e.g., cow milk in baby formula, meat-containing grinded foods), and have been suggested to be induced through uptake of dietary Neu5Gc by non-typeable Haemophilus influenzae (NTHi) during infection in infants (80), and through micropinocytosis of Neu5Gcglycoproteins into human cells followed by recycling into the cells surface glycoproteins and glycolipids (71)(72)(73)(74).…”

“…By contrast, murine myeloma cell lines (e.g., NS0 and Sp2/0) are known to produce Neu5Gc at significantly higher levels (2,97,98). Drugs produced in animals (non-human mammals that are known to synthesize Neu5Gc intrinsically; e.g., cow, pig, goat, sheep, and rabbit) are also likely to contain Neu5Gc, since they were shown to express high amounts of Neu5Gc (50,60). For example, antithrombin produced in goat milk and antithymocyte globulin derived from rabbit, are known to contain high levels of Neu5Gc (2,62,63).…”

“…This immune-conflict may be further complicated with exposure to Neu5Gc-containing biotherapeutics, biodevices or xenografts. Indeed, recent studies have suggested that Neu5Gc-glycans have an enormous diversity (58)(59)(60), and predicted to be widely found on various approved and marketed biotherapeutics (2,61), such as Cetuximab ( 61) and anti-thymocyte globulin (62)(63)(64)(65). Although biotherapeutics provide effective treatment for a variety of clinical conditions, suboptimal efficacy and safety are major concerns for many of these products.…”

Immunogenicity of decellularized extracellular matrix scaffolds: a bottleneck in tissue engineering and regenerative medicine

“…Neu5Gc expression level is a tissuedependent issue. Despite the detrimental effects of these epitopes on the immunogenicity of decellularized heart valves [137,138,142], and dermal grafts, neurons are privileged of Neu5Gc expression [131,137,143].…”

The Possible Role of Anti-Neu5Gc as an Obstacle in Xenotransplantation

“…The transcriptome of human endothelial cells exhibiting "physiological" amounts of Neu5Gc is differentially affected by diet-derived and elicited anti-Neu5Gc antibodies (109). Of note, the involvement in xenotransplantation of elicited antibodies specific for Neu5Gc will be probably different depending on the individual as animal products, cells, tissues and organs do not induce anti-Neu5Gc antibodies in all treated humans and these antibodies show an individual-related variable affinity and specificity for the multiple Neu5Gc-containing antigens (74,75,92,101,110).…”