Liver Xenotransplantation using CRISPR-modified Porcine Organs

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PROJECT SUMMARY / ABSTRACT Liver transplantation has failed to reach its full potential for saving lives due to the inadequate organ supply. Every year thousands of potentially salvageable patients die awaiting an allograft, hundreds of others receive a `marginal” donor organ, often in desperate circumstances, and a many times this number of potential recipients are never offered listing for lifesaving organs due to the need to ration this precious but limited resource. Liver xenotransplantation offers a potential solution to the organ shortage but clinical application has been stymied by four principle hurdles: 1) risk of zoonotic infection of humans, 2) the vigorous immune response mounted to xenogeneic tissues, and 3) physiologic incompatibilities due to species divergence arising in a rarity of protein: protein interactions, and if these obstacles can be consistently overcome, the 4) need to identify a clinically applicable IS regimen. A new tool with unprecedented potential to address these barriers to widespread application of xenotransplantation is found in technology such as CRISPR-Cas9 that dramatically increases gene editing specificity and efficiency. A powerful example is found in recent work by our industry partner, eGenesis, who used CRISPR-Cas9 to rid the pig genome of 62 copies of functional porcine endogenous retroviruses (PERVs), essentially eliminating the risk of PERV transmission to an organ recipient. In the current proposal, we explore the ability of advanced gene editing to address immunologic and physiologic barriers that cause immediate graft dysfunction of liver xenografts when transplanted into a translational baboon model. With the general goal preventing initial xenograft dysfunction (IXD) to gain long term survival of pig liver xenografts in baboon recipients, studies in Aim I will focus on two recently identified potential impediments to xenograft survival: 1) ischemia reperfusion injury, and 2) platelet consumption. Recent findings in cardiac xenotransplantation studies have exposed the critical contribution of IR injury to early heart xenograft demise. Our wealth of experience with ex vivo liver perfusion and also xeno liver perfusion with human blood and the recently reported technique for ischemia free liver transplants should yield a definitive answer to this question. Aim II will focus on understanding the impact of gene edits that: 1) eliminate expression of the three major antibody targets of preformed human anti-pig antibodies, 2) gain expression of human proteins designed to address complement and coagulation dysregulation occurring with porcine liver xenotransplants in NHP, and 3) mitigate innate and cell-mediated immunity and inflammation. To accomplish this, we will take advantage of liver transplant, ex vivo liver perfusion with human blood and in vitro assays well established in our lab and a panel of CRISPR modified pigs with varied expression of genetic edits.