Anticarbohydrate Antibody Repertoires in Patients Transplanted with Fetal Pig Islets Revealed by Glycan Arrays

Abstract

Ten patients with type I diabetes were transplanted with porcine fetal islet-like cell clusters (ICC) between 1990 and 1993. A significant rise in the anti-a -Gal antibody titers was seen posttransplant, but also nona -Gal-specific antibodies were detected in some patients. We have reanalyzed the carbohydrate specificity of antibodies in the sera from seven of these patients taken before transplantation, 1, 6 and 12 months posttransplantation using a glycan array with 200 structurally defined glycans. The main findings were: (i) prepig ICC transplantation patients had antibodies reactive with terminal a -GalNAc (e.g. the Forssman antigen, but not the blood group A determinant in blood group A patients), a -Gal (except blood group B determinants in B individuals), b 3-linked Gal especially Galb 1,3GlcNAc even if terminally sulfated or sialylated, b -GlcNAc except if b 1,3-linked and oligomannosyl compounds; (ii) the titers of all carbohydrate-specific antibodies detected before transplantation rose after transplantation; (iii) the kinetics of the antibody responses differed between patients; (iv) in some patients antibodies reacting with Gala 1,3Lex and several structures terminated with Neu5Gc appeared after transplantation. In conclusion, anti-a -Gal antibodies are the predominant anticarbohydrate antibodies detected after porcine ICC transplantation, with some patients also developing Neu5Gc-specific antibodies. Their clinical significance needs to be established.Key words: Anticarbohydrate antibodies, blood groups, glycan arrays, islet transplantation, xenotransplantation Abbreviations: a 1,3Gal-T, a 1,3-

Identification of New Carbohydrate and Membrane Protein Antigens in Cardiac Xenotransplantation

“…We do not know the precise structure of the glycan(s) displayed by HEK cells expressing the porcine B4GALNT2 product or by GTKO PAECs, but it seems likely to include a sialylated Gal or a ␤-linked terminal GalNAc structure similar to the SD a carbohydrate. A carbohydrate of this type would be consistent with recent reports of induce non-Gal antibody to terminal GalNAc glycans and of baboon reactivity to acidic glycolipids (11,12). Targeted inactivation of the porcine B4GALNT2 gene in combination with the existing ␣-galactosyltransferase (GGTA-1) mutation may be useful to further reduce the antigenicity of porcine xenografts.…”

“…The induced non-Gal antibody response may also react with carbohydrate or glycolipid epitopes. Consistent with this an induced primate response to an undefined acidic cardiac glycolipid has recently been reported (11,12). In this report, we used retrovirus-encoded expression libraries, produced from GT ϩ :CD46 and GTKO PAECs, to identify the target antigens detected by induced non-Gal antibody after pig-to-primate cardiac xenotransplantation.…”

Recent investigations into pig antigen and anti-pig antibody expression

“…Induced antibody from diabetic patients treated with porcine fetal islets was initially reported to be only anti-Gal antibody (42). Subsequent studies initially failed to find evidence for a general induced anti-Neu5Gc response (43) but more recently have detected induced anti-Neu5Gc specific antibody in some patients (44). A dominant anti-Gal immune response was also seen in the two patients participating in an ex vivo pig kidney perfusion trial (45) and one individual produced anti-ganglioside antibodies (46).…”

Immunological Challenges and Therapies in Xenotransplantation

“…Natural anti-Neu5GC antibodies are predominantly IgG (Padler-Karavani et al 2008), but may be IgM and IgA too, albeit to a lesser extent. Anti-Neu5GC can be induced in humans after exposure to porcine tissues (Blixt et al 2009;Scobie et al 2013). Nonhuman primates express Neu5GC antigens, however, and are unable to elicit a humoral response against this epitope, making their use in relevant preclinical studies unfeasible; hence the development of surrogate rodent models, such as double-KO mice that lack both aGal and Neu5GC epitopes as a consequence of GalT and cytidine monophospho-N-acetylneuraminic acid hydrolase (CMAH) inactivation .…”