Expression of human CD47 in pig glomeruli prevents proteinuria and prolongs graft survival following pig‐to‐baboon xenotransplantation

Abstract

Background Nephrotic syndrome is a common complication of pig‐to‐baboon kidney xenotransplantation (KXTx) that adversely affects outcomes. We have reported that upregulation of CD80 and down‐regulation of SMPDL‐3b in glomeruli have an important role in the development of proteinuria following pig‐to‐baboon KXTx. Recently we found induced expression of human CD47 (hCD47) on endothelial cells and podocytes isolated from hCD47 transgenic (Tg) swine markedly reduced phagocytosis by baboon and human macrophages. These observations led us to hypothesize that transplanting hCD47 Tg porcine kidneys could overcome the incompatibility of the porcine CD47‐baboon SIRPα interspecies ligand‐receptor interaction and prevent the development of proteinuria following KXTx. Methods Ten baboons received pig kidneys with vascularized thymic grafts (n = 8) or intra‐bone bone marrow transplants (n = 2). Baboons were divided into three groups (A, B, and C) based on the transgenic expression of hCD47 in GalT‐KO pigs. Baboons in Group A received kidney grafts with expression of hCD47 restricted to glomerular cells (n = 2). Baboons in Group B received kidney grafts with high expression of hCD47 on both glomerular and tubular cells of the kidneys (n = 4). Baboons in Group C received kidney grafts with low/no glomerular expression of hCD47, and high expression of hCD47 on renal tubular cells (n = 4). Results Consistent with this hypothesis, GalT‐KO/hCD47 kidney grafts with high expression of hCD47 on glomerular cells developed minimal proteinuria. However, high hCD47 expression in all renal cells including renal tubular cells induced an apparent destructive inflammatory response associated with upregulated thrombospondin‐1. This response could be avoided by a short course of weekly anti‐IL6R antibody administration, resulting in prolonged survival without proteinuria (mean 170.5 days from 47.8 days). Conclusion Data showed that transgenic expression of hCD47 on glomerular cells in the GalT‐KO donor kidneys can prevent xenograft nephropathy, a significant barrier for therapeutic applications of xenotransplantation. The ability to prevent nephrotic syndrome following KXTx overcomes a critical barrier for future clinical applications of KXTx.

Progress in Xenotransplantation: Immunologic Barriers, Advances in Gene Editing, and Successful Tolerance Induction Strategies in Pig-To-Primate Transplantation

“…On a more granular level, studies have shown that human CD47 expression in pig endothelial cells and podocytes prevented phagocytosis by correcting CD47-SIRPα species incompatibilities and enabling normal SIRPα signal transduction. Indeed, hCD47 expression on podocytes in hCD47/GalTKO pig-to-baboon kidney transplants was shown to inhibit the development of proteinuria ( 59 ).. However, our data also demonstrated that high hCD47 expression in renal tubular cells may lead to destructive inflammatory responses via the hCD47-TSP-1 pathway ( 59 ).…”

“…Indeed, hCD47 expression on podocytes in hCD47/GalTKO pig-to-baboon kidney transplants was shown to inhibit the development of proteinuria ( 59 ).. However, our data also demonstrated that high hCD47 expression in renal tubular cells may lead to destructive inflammatory responses via the hCD47-TSP-1 pathway ( 59 ). More research is needed to further refine and reliably predict gene expression in multiply modified pigs.…”

“…Over the past 5 years, we have developed strategies to prevent proteinuria, combining novel therapeutic agents (including CTLA4-Ig) with additional genetic engineering (hCD47) ( 18 , 71 , 72 ). With these new regimens, we achieved long-term survival of >6 months in multiple recipients of vascularized thymus plus kidneys ( 18 , 59 ). While hCD47 may be helpful, it is worth noting that we were able to avoid early development of proteinuria and achieve 193 days of rejection free survival using kidney+thymus from GalTKO pig without further genetic modification ( 18 ).…”

“…Both types of vascularized thymic grafts appear to be effective at inducing tolerance of co-transplanted donor kidneys across xenogeneic barriers ( 18 , 44 , 59 ), but there are advantages and disadvantages to each method. Thymokidneys ( 64 ) may be more feasible to create and thus more broadly applicable for kidney xenotransplantation; vascularized thymic lobe (VTL) ( 65 ) harvest is technically challenging and prone to ischemia due to convoluted blood supply.…”

Cellular Immune Responses in Islet Xenograft Rejection

“…This approach has been investigated in the treatment of asthma, showing reduced allergic airway inflammation ( 49 ). Human CD47 transgenic pigs have been generated, and prolonged survival of human CD47 pig-derived xenografts in NHP has been achieved by reducing macrophage activation ( 46 , 50 , 51 ). Generating pigs with human leukocyte antigens-E (HLA-E) ( 52 ) or human leukocyte antigens-G (HLA-G) ( 53 ) has also been proposed as an additional option to inhibit human macrophage-mediated porcine islet xenograft rejection.…”