Natural human antibody-mediated destruction of porcine neonatal islet cell grafts

Porcine pancreata may be considered a potential source of islets for transplantation into diabetic recipients; however, whether porcine islet grafts will be susceptible to damage by natural antibody-mediated hyperacute rejection remains unknown. In this study, we performed Western blots to determine whether membrane proteins present on porcine neonatal islet cells (NIC) are recognized by xenoreactive antibodies present in human sera. Western blots of freshly isolated porcine NICs with AB sera detected the presence of 14 antigens (MW 24-164 kDa) and 4 antigens (MW 101-150 kDa) to which antiserum against human IgM and IgG bound, respectively, The most prominent antigens with IgM reactivity had MWs of 36, 63, and 120 kDa, whereas for IgG, the most intensely reactive antigen had a MW of 120 kDa. When membrane fractions prepared from purified porcine aortic endothelial cells and LLC-PK1 cells were analyzed, the major antigens had molecular weights comparable to those seen for NICs. After culturing the NICs for 5 days, the number of detected xenoreactive antigens binding IgM or IgG decreased and the antigens present at 36, 63, and 120 kDa with IgM reactivity were shown to have a decreased intensity of binding, Incubation of cultured porcine NICs for 18 hr in the presence of human AB serum containing complement resulted in a 55% loss of cellular insulin content (P < 0.0001), a 45% reduction in recoverable DNA (P < 0.0001), and a marked reduction in insulin secretory response to an in vitro glucose challenge. Recovery and viability of porcine NICs was not affected when incubated with AB serum depleted of anti-Gal antibodies with Synsorb 90. These results demonstrate that natural human antibodies of both IgM and Ige subtypes bind to antigens present on porcine NICs and that exposure of the NICs to human AB sera and complement reduces islet cell survival and functional viability. Adsorbing serum with the alpha Gal(1-3)beta Gal(1-4)beta Glc carbohydrate removes natural human antibody-mediated destruction of porcine neonatal islet cell grafts.