Xenotransplantation literature update, November/December 2019

Abstract

The ever-increasing disparity between the lack of organ donors and patients on the transplant waiting list is increasing worldwide. For the past several decades xenotransplantation has led the way to correct this deficit and remains clearly the only feasible option to provide a means to meet the demand for patients in need of an organ transplant. Xenotransplantation's ability to provide a specifically designed unlimited supply of organs, suited to treat the various needs for transplant organs and cells, has recently been championed by successful pre-clinical trials that have run long-term in non-human primate studies.In this review we show how these improvements have come about due to longterm dedicated research and recent advances in biomedical engineering technology, such as genome editing tools including zinc finger nucleases, TALEN, and CRISPER/ Cas9 which have paved the way for significant breakthroughs in improving xenograft outcomes through genetic modifications to the donor source pig. Other novel approaches include the development of decellularized porcine tissue, such as corneas which can now be transplanted into patients with the minimal need for immunosuppression or other side effects. Further genetic variants of the porcine genome are also now being optimized to abrogate rejection. The emergence of new modalities such as; mesenchymal stem cells, donor thymic vascularization, in vivo bioreactors, chemokine and cytokine therapies have come to show improvements in xenograft outcomes. Furthermore, new studies confirm the safety status of using porcine xenografts, verifying that with current technologies and approaches, the issue of PERV transmission is a moot point. These breakthroughs and technological advancements push the reality of xenotransplantation one step closer to the clinic. K E Y W O R D S complement regulation, CRISPR, Mesenchymal stem cells, zoonosis

A highly sensitive method for the detection of recombinant PERV-A/C env RNA using next generation sequencing technologies

“…Although xenotransplantation has been expected to serve as a potential solution to the chronic donor shortage in transplantation, its application has not progressed well due to concerns regarding immunological rejection and transmission of infectious diseases. The problem of immunological rejection has been resolved in recent years with the development of superior immunosuppressive drugs and advances in gene editing technology 35 , 36 , but there is still much uncertainty about the transmission of infectious diseases caused by known or unknown microorganisms. The prediction of the transmission of animal viruses to humans from in vitro or in vivo studies is difficult, and thus it is important to monitor the infection in the actual transplanted patients.…”

Xenotransplantation literature update, November/December 2020

“…PERVs are integrated into the pig genome and could potentially integrate into the host‐genome, although this has not been reported in any clinical or preclinical trials utilizing pig tissue. But there are limited long‐term clinical trials reported to date following xenotransplantation and as such the findings from any long‐term studies are of interest to the xenotransplant community 44 …”

Applications of CRISPR technologies in transplantation

“…However, there are still 3 major barriers preventing successful pig-to-primate (human) organ transplantations: (a) Glycans on the surface of porcine endothelial cells act like xenoantigens (α-Gal, Neu5Gc, SDa) and cause hyperacute rejection (HAR), (b) dysregulated coagulation due to the disagreement between the pig and human coagulation system (THBD, TFPI, CD39), and (c) porcine endogenous retroviruses (PERVs) in porcine genome can transfer vertically into human cells and causexenosis. Due to the efficiency and simplicity of CRISPR gene editing, researchers have tested ~40 different combinations of pig-gene knock-out and human-gene knock-in into the porcine genome with great efficiency in less than a decade 51,52. Recently, G. Church and colleagues established the most advanced transgenic pig by using CRISPR technology in which they successfully deleted 3 pig genes (GGTA1, CMAH, and B4GALNT2), and specifically inserted 9 human transgenes (CD46, CD55, CD59, B2M, HLA-E, CD47, THBD, TFB1, and CD39) in a single locus in addition to the inactivation of 25 PERV loci in pig cells 53.…”