Genetically engineered pig heart transplantation in non-human primates

Introduction

Clinical cardiac xenotransplantation could provide a solution for end-stage heart failure patients waiting for heart transplantation who die waiting for a suitable donor or do not otherwise qualify. Two genetically engineered (GE) pig hearts, with ten gene edits (10GE), were recently transplanted into two human recipients. One survived 60 days; the other recipient survived forty^{1, 2–3}. This is a great promise to alleviate the shortage of donor organs for transplantation. Earlier, we reported the 9-month survival of a multi-gene pig heart with 7-GE in a non-human primate ((NHP) using co-stimulation blockade-(anti-CD40 antibody) based immunosuppressive (IS) (Mohiuddin Regimen)⁴. 7GE includes the deletion of two carbohydrate antigens (i.e., GGTA1 and β4GalNT2) along with the expression of five human genes (i.e., TBM, EPCR CD46, and CD47). In addition, three additional modifications, including the deletion of growth hormone receptors and overexpression of DAF and HO1, were made in 10GE pig hearts. Längin et al. have also reported successful life-supporting porcine cardiac xenotransplantation (XTx) in NHP⁵. A combination of gene modifications of donor pigs and non-ischemic cardiac preservation (NICP) improves cardiac xenograft survival significantly and prevents xenograft rejection.

The immunobiology of cardiac xenotransplantation and justification for using each gene edit have been comprehensively reviewed elsewhere but are briefly summarized below^6,7.

Xenograft rejection occurs primarily due to endothelial cell activation by preformed antibodies against porcine donor antigens in the recipient^8,9. Preformed and elicited antibodies also promote coagulation and activate platelets, contributing to graft loss due to thrombotic microangiopathy¹⁰. Three carbohydrate antigens (i.e., α1,3-galactose (Gal), B4GALNT2KO, and CMAHKO) required knockout based on the evidence of extensive research over the past 30 years^11,12.

Studies have suggested a complex interplay between blood pressure, growth hormone receptor, and cardiac xenograft growth (or hypertrophy)^{13, 14–15}. To control the intrinsic growth of pigs and their organs (in anticipation of implantation into a non-growing chest of an adult recipient), the growth hormone receptor gene (GHR) has been knocked out⁴. Mini pigs, which naturally have a slow growth rate, have also been suggested for xenotransplantation¹⁶. We used the option of GHR knockout to improve our ability to size-match the donor hearts with...