The lack of Neu5Gc expression attenuated erythrocyte loss but did not prevent profound early onset thrombocytopenia or platelet activation, although TXB2 levels were decreased in the presence of Neu5GcKO.

We conclude human NK cell activation contributes significantly to GalTKO.hCD46 pig endothelial injury and lung inflammation and show that expression of HLA-E is associated with physiologically meaningful protection of GalTKO.hCD46 cells and organs exposed to human blood.

Selectin blockade may be useful as part of an integrated strategy to prevent neutrophil-mediated organ xenograft injury, especially during the early time points following reperfusion.

Background Specific blockade of T cell costimulation pathway is a promising immunomodulatory approach being developed to replace our current clinical immunosuppression therapies. The goal of this study is to compare results associated with 3 monoclonal antibodies directed against the CD40/CD154 T cell costimulation pathway. Methods Cynomolgus monkey heterotopic cardiac allograft recipients were treated with either IDEC-131 (humanized αCD154, n=9), 5C8H1 (mouse-human chimeric αCD154, n=5), or 2C10R4 (mouse-rhesus chimericαCD40, n=6) monotherapy using a consistent, comparable dosing regimen for 3 months after transplant. Results Relative to the previously reported IDEC-131 treated allografts, median survival time (MST 35±31 days) was significantly prolonged in both 5C8H1 (142±26, p<0.002) and 2C10R4 (124±37, p<0.020) treated allografts. IDEC-131 treated grafts had higher CAV severity scores during treatment relative to either 5C8H1 (p=0.008) or 2C10R4 (p=0.0002). Both 5C8H1(5 of 5 animals, p=0.02) and 2C10R4 (6/6, p=0.007), but not IDEC-131 (2/9), completely attenuated IgM antidonor alloAb production during treatment;5C8H1 (5/5) more consistently attenuated IgG alloAb production compared to 2C10R4 (4/6) and IDEC-131 (0/9). All evaluable explanted grafts experienced antibody-mediated rejection. Only 2C10R4 treated animals exhibited a modest, transient drop in CD20+ lymphocytes from baseline at d14 after transplant (-457±152 cells/μL) compared to 5C8H1 treated animals (16±25, p=0.037), and the resurgent B cells were primarily of a naïve phenotype. Conclusion In this model, CD154/CD40 axis blockade using IDEC-131 is an inferior immunomodulatory treatment than 5C8H1 or 2C10R4, which have similar efficacy to prolong graft survival and to delay CAV development and antidonor alloAb production during treatment.

Galactosyl transferase knock‐out pig lungs fail rapidly in baboons. Based on previously identified lung xenograft injury mechanisms, additional expression of human complement and coagulation pathway regulatory proteins, anti‐inflammatory enzymes and self‐recognition receptors, and knock‐down of the β4Gal xenoantigen were tested in various combinations. Transient life‐supporting GalTKO.hCD46 lung function was consistently observed in association with either hEPCR (n = 15), hTBM (n = 4), or hEPCR.hTFPI (n = 11), but the loss of vascular barrier function in the xenograft and systemic inflammation in the recipient typically occurred within 24 h. Co‐expression of hEPCR and hTBM (n = 11) and additionally blocking multiple pro‐inflammatory innate and adaptive immune mechanisms was more consistently associated with survival >1 day, with one recipient surviving for 31 days. Combining targeted genetic modifications to the lung xenograft with selective innate and adaptive immune suppression enables prolonged initial life‐supporting lung function and extends lung xenograft recipient survival, and illustrates residual barriers and candidate treatment strategies that may enable the clinical application of other organ xenografts.