Pig-to-baboon lung xenotransplantation: Extended survival with targeted genetic modifications and pharmacologic treatments

Abstract

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.

Effects of human TFPI and CD47 expression and selectin and integrin inhibition during GalTKO.hCD46 pig lung perfusion with human blood

“…The predictive value of the ex vivo perfusion model for the hTFPI.CD47 pig genotype, and others, has recently been tested in vivo 67 ; good initial life-supporting function but early failure due to inflammation in the hTFPI.CD47 lung and in the recipient suggest that the proinflammatory and adhesive interactions seen ex vivo are associated with adverse consequences in vivo. We conclude that the ex vivo model remains mechanistically valuable even if protection from lung failure beyond 8 h is regularly observed.…”

“…11 On the other hand, survival of baboons that received a porcine lung transplant has generally been limited to a few days and a maximum of 31 days. [12][13][14] GalTKO.hCD46 porcine lungs perfused ex vivo with human blood rapidly sequester the majority of circulating platelets and neutrophils, and the majority of lungs fail within the 8 h in association with prolific activation of coagulation and inflammation. A candidate intervention to prevent coagulation dysregulation is expression of human tissue factor pathway inhibitor (hTFPI), which is a direct inhibitor of activated extrinsic coagulation pathway factors such as Va, VIIa, and Xa.…”

“…For example, the use of GalTKO.hCD46.hTBM porcine donors has enabled survival of heterotopic hearts in baboons for over 2 years, 10 and recipients of life‐supporting GalTKO.hCD46 kidneys have survived for greater than 6 months 11 . On the other hand, survival of baboons that received a porcine lung transplant has generally been limited to a few days and a maximum of 31 days 12–14 …”

Human erythrocyte fragmentation during ex‐vivo pig organ perfusion

“…Thrombocytopenia is commonly observed in organ xenograft ex-vivo perfusion models, 2,4 and in in-vivo transplant models. [24][25][26][27][28][29] To study the mechanisms contributing to thrombocytopenia, it is essential to accurately enumerate platelets and to distinguish them from cell fragments that may appear in whole blood in the context of our crossspecies organ perfusion studies. Here, we show that, in ex-vivo perfusion models, conventional platelet counting methods fail to discriminate platelets from RBC fragments.…”

Invited commentary

“…In 13 Among all these possibilities, the blockade of C5 seems important in xenotransplantation as recently shown in a pig-to-primate renal transplant model using tesidolumab. 14 A combination of those modalities together with rigorous infection prophylaxis and surveillance are likely to be necessary in the setting of clinical pig-to-human xenotransplantation.…”