Proteomic identification of non‐Gal antibody targets after pig‐to‐primate cardiac xenotransplantation

Abstract

Background-Experience with non-antigenic galactose α1,3 galactose (αGal) polymers and development of αGal deficient pigs has reduced or eliminated the significance of this antigen in xenograft rejection. Despite these advances, delayed xenograft rejection (DXR) continues to occur most likely due to antibody responses to non-Gal endothelial cell (EC) antigens.

Immune responses to α1,3 galactosyltransferase knockout pigs

“…Our own unpublished data, showing the absence of both immunoglobulin M (IgM) anti-Gal and IgM anti-non-Gal antibodies in cord blood samples, together with the abovementioned data of Cooper's group [16 ] suggest that xenotransplantation of GalT-KO pig organs and cells could be carried out in early infancy as for ABO-incompatible heart transplantation [21]. On the contrary, several reports following xenotransplantation of GalT-KO organs in preclinical pig-to-baboon models indicate the induction of non-Gal antibodies that are relevant for humoral rejection [2 , [22][23][24]25 ].…”

“…They showed antibody deposition in small and large vessels shortly after transplantation that increased over time [2 ,22-24,25 ,31]. Byrne et al [25 ] analysed the serum of baboons transplanted with GalT-KO pig hearts by western blotting using GalT-KO cells and identified several proteic potential xenoantigens ranging from 50 to more than 250 kDa. Further proteomic analysis revealed binding of baboon-induced non-Gal antibodies to 14 intracellular proteins, probably not relevant for rejection mechanisms, as well as weak binding to pig fibronectin, which is not only a major component of the extracellular matrix but also exists as a soluble form in the plasma [25 ].…”

“…Byrne et al [25 ] analysed the serum of baboons transplanted with GalT-KO pig hearts by western blotting using GalT-KO cells and identified several proteic potential xenoantigens ranging from 50 to more than 250 kDa. Further proteomic analysis revealed binding of baboon-induced non-Gal antibodies to 14 intracellular proteins, probably not relevant for rejection mechanisms, as well as weak binding to pig fibronectin, which is not only a major component of the extracellular matrix but also exists as a soluble form in the plasma [25 ]. Another group reported the induction of anti-nonGal antibodies of both IgM and IgG subtype following transplantation of human decay-accelerating factor transgenic pig organs into cynomolgus monkeys treated with GAS914 (a poly-L-lysine derivative shown to bind and neutralize anti-Gal antibodies) [31].…”

Immunological Challenges and Therapies in Xenotransplantation

“…In particular, most recipients' elicited antixenograft repertoire included antibodies directed against fibronectin, several stress response and inflammation proteins, and also proteins involved in key endothelial cell functions (Byrne et al 2008. These included proteins involved in regulating inflammation (e.g., annexin A2), hemostasis (e.g., CD9 and endothelial cell protein C receptor), or the complement cascade (e.g., CD46 and CD59), all potentially important functions in the context of AHXR.…”

Xenotransplantation-Progress and Problems: A Review

“…Using multitransgenic pigs and antibody depletion, HAR, once considered the most vexing problem for xenotransplantation, was thought to be overcome. However, meanwhile new carbohydrate non-Gal epitopes have been identified, which may play a role in HAR [57]. Nevertheless, when genetically modified pig hearts were transplanted heterotopically in baboons, a significantly reduced HAR and a survival of up to 8 months was observed.…”