Absence of Gal epitope prolongs survival of swine lungs in an ex vivo model of hyperacute rejection

Abstract

Background Galactosyl transferase gene knock-out (GalTKO) swine offer a unique tool to evaluate the role of the Gal antigen in xenogenic lung hyperacute rejection. Methods We perfused GalTKO miniature swine lungs with human blood. Results were compared with those from previous studies using wild-type and human decay-accelerating factor-transgenic (hDAF+/+) pig lungs. Results GalTKO lungs survived 132 ± 52 min compared to 10 ± 9 min for wild-type lungs (P = 0.001) and 45 ± 60 min for hDAF+/+ lungs (P = 0.18). GalTKO lungs displayed stable physiologic flow and pulmonary vascular resistance (PVR) until shortly before graft demise, similar to autologous perfusion, and unlike wild-type or hDAF+/+ lungs. Early (15 and 60 min) complement (C3a) and platelet activation and intrapulmonary platelet deposition were significantly diminished in GalTKO lungs relative to wild-type or hDAF+/+ lungs. However, GalTKO lungs adsorbed cytotoxic anti-non-Gal antibody and elaborated high levels of thrombin; their demise was associated with increased PVR, capillary congestion, intravascular thrombi and strong CD41 deposition not seen at earlier time points. Conclusions In summary, GalTKO lungs are substantially protected from injury but, in addition to anti-non-Gal antibody and complement, platelet adhesion and non-physiologic intravascular coagulation contribute to Gal-independent lung injury mechanisms.

Lung xenotransplantation

“…Binding of preformed antibodies directed towards the α,1,3-galactose (Gal) epitope has been identified as one main trigger (7,8). Knockout of the galactosyltransferase enzyme (GalTKO) eliminates the carbohydrate antigen from porcine cells and was a key step to overcome hyperacute rejection of other organs (9–11). However, innate (mainly preformed antibody directed against other targets) and adaptive immune responses still persist in recipients of GalTKO organs and tissues (9, 12–15).…”

“…Knockout of the galactosyltransferase enzyme (GalTKO) eliminates the carbohydrate antigen from porcine cells and was a key step to overcome hyperacute rejection of other organs (9–11). However, innate (mainly preformed antibody directed against other targets) and adaptive immune responses still persist in recipients of GalTKO organs and tissues (9, 12–15). The adaptive response to lung xenotransplants has not yet been studied since they have not yet reached a relevant duration of survival; accordingly, most lung xeno research has been focused towards early inflammation.…”

“…Triggered at least in part by preformed anti-non-Gal antibodies, activation of human complement coupled with the absence of human complementary regulatory proteins lead to complement activation and contribute significantly to failure of GalTKO lungs within hours (9). These non-Gal antigens include carbohydrate, glycolipid, and perhaps protein structures.…”

Comparative biology of decellularized lung matrix: Implications of species mismatch in regenerative medicine

“…Complications of porcine lung xenografts use include hyperacute rejections mediated by anti-Gal antibodies; intravascular and alveolar macrophages that produce inflammatory cytokines, amplify procoagulant factors, and phagocytize human blood cells and platelets; and human natural killer cells (NK) that infiltrate pig organs and lyse pig endothelial cells (20, 21, 57). To mitigate these cell-based rejection limitations, research has focused the use of decellularized pig lungs as a potential platform for the construction of engineered lungs (4, 15, 17, 24).…”

“…Porcine lungs are also regarded as an ideal donor source for xenotransplantation, and considerable amounts of financial resources have been dedicated to building porcine bioengineered lungs for transplantation into human recipients (4, 15-18). Despite recent advancements in eliminating critical xenographic cellular contribution(s) to organ failure, the survival of primate recipients of porcine lungs is less than 5 days (19-21). Therefore, it is likely that in addition to cellular differences in species, there are other factors in xenographic tissues that could lead to transplantation failure.…”