Transgenic Expression of Human CD47 Markedly Increases Engraftment in a Murine Model of Pig-to-Human Hematopoietic Cell Transplantation

Abstract

Mixed chimerism approaches for induction of tolerance of solid organ transplants have been applied successfully in animal models and in the clinic. However, in xenogeneic models (pig-to-primate), host macrophages participate in the rapid clearance of porcine hematopoietic progenitor cells, hindering the ability to achieve mixed chimerism. CD47 is a cell-surface molecule that interacts in a species-specific manner with SIRPα receptors on macrophages to inhibit phagocytosis and expression of human CD47 on porcine cells has been shown to inhibit phagocytosis by primate macrophages. We report here the generation of human CD47 (hCD47) transgenic GalT-KO miniature swine that express hCD47 in all blood cell lineages. The effect of hCD47 expression on xenogeneic hematopoietic engraftment was tested in an in vivo mouse model of human hematopoietic cell engraftment. High-level porcine chimerism was observed in the bone marrow of hCD47 progenitor cell recipients and smaller but readily measurable chimerism levels were observed in the peripheral blood of these recipients. In contrast, transplantation of WT progenitor cells resulted in little or no bone marrow engraftment and no detectable peripheral chimerism. These results demonstrate a substantial protective effect of hCD47 expression on engraftment and persistence of porcine cells in this model, presumably by modulation of macrophage phagocytosis.

Prolonged Survival of Pig Skin on Baboons After Administration of Pig Cells Expressing Human CD47

“…A likely reason for this clearance is that inhibition of phagocytosis through macrophage SIRPα receptor binding of CD47 on HC does not occur in the pig/primate combination 16;17 . Consistent with this hypothesis, we have previously demonstrated that transgenic expression of human CD47 (hCD47) substantially increases HC engraftment in a murine model of pig-to-human cell transplantation 18 .…”

“…We previously reported the generation of a cloned transgenic miniature swine (18286) on an α-1,3-galactosyltransferase null (GalT-KO) background by recloning from a transgenic fetus (846-2) 18 . Both the fetus and 18286 demonstrated uniform expression of hCD47 on HC and fibroblasts.…”

“…All recipients were selected for low pre-transplant anti-non-Gal cytotoxic antibody levels. The derivation of cloned hCD47 transgenic pig 18286 was previously described 18 ; transgenic pig 18289 was derived in an identical fashion and the genotype confirmed also as described. All animal work was conducted in accordance with NIH and USDA guidelines and with approval from the MGH Institutional Animal Care and Use Committee.…”

Advances in the immunology of heart transplantation

“…CD47 expression has prolonged the duration of porcine hematopoietic chimerism in baboons by inhibiting the phagocytosis of donor cells by primate macrophages. 80 Encouragingly, such prolongation has been associated with markedly prolonged donor swine skin xenografts. 81 …”

Characterization of the cellular infiltrate in bioprosthetic heart valves explanted from patients with structural valve deterioration

“…In a fresh "live" pig aortic valve, macrophage infiltration could possibly be inhibited by transgenic expression of human CD47 [17,18], and pigs expressing human CD47 are now available in several centres. However, if the ultimate pig valve used for human heart valve surgery does need some glutaraldehyde fixation, then this may negate the biological activity of human CD47, and thus, alternative approaches may need to be investigated.…”