The Role And Mechanism Of CD47 In Solid Organ Transplantation Immunology

Background:Organ transplantation is the most direct and effective way to treat patients with end-stage organ failure by transferring the relatively well-structured and functioning donor organs to the recipient for further effect.After transplantation,however,graft rejection occurs,function of donor is abnormal,even depleted,eventually leading to graft failure.Immunosuppressive drugs are often used to suppress the rejection of the donor after operation,but long-term use may cause various side effects and affect the patient adversely.Therefore,finding a method that can effectively induce receptors to induce immune tolerance is the key to solving the problem.CD47 is a type of transmembrane glycoprotein that ubiquitously expressed on the surface of various cells.It plays a complex role in regulation of cell survival and function.By linking with signal regulatory protein alpha(SIRP alpha),CD47 sends a "don't eat me" signal to macrophages so that cells are protected from phagocytosis.Donor CD47 cannot interact with SIRP? of recipient macrophages,eventually leading to rejection of xenogeneic cells after hematopoietic cells injection in a pig-to-mouse xenotranspantation model.However,porcine cells expressing mouse CD47,both in vivo and in vitro,can be protected from phagocytosis of macrophages of mouse.Pre-transfusion of donor-specific hematopoietic cells revealed that the absence of donor CD47 can activate innate immune responses and eventually lead to graft rejection,indicating that CD47 plays a protective role in cell transplantation.However,it is still not clear whether CD47 protects the donor as cell transplantation does in solid organ transplantation.Liver is regarded as the largest immune tolerance organ in human body.Mesenchymal cells and non-mesenchymal cells may be related to the induction of immune tolerance.In a rat heart transplantation model,donor-specific hepatocyte transfusion induces donor long-term survival and immune tolerance.However,it is still unclear whether donor immune tolerance can be induced and the role of CD47 to immune tolerance in mice cardiac transplantation by pre-infusion of donor-derived hepatocytes.Objective:To explore the role of CD47 in immunity of solid organ transplantation and to find a more effective way to induce immune tolerance.Methods:(1)CD47-deficient mice were used to observe the survival time of the graft after heart or skin transplantation,and histological examination was carried out to observe the role of CD47-deficient donor on suppressing immune rejection of homografts and MHC mismatched allografts.(2)To explore the role of CD47-TSP1 pathway in organ transplantation,Thrombospondin-1(TSP1)expression-deficient mice were used to observe the survival time of grafts after heart or skin transplantation.(3)Introsplenic transfusion of donor-derived hepatic parenchymal cells was pre-performed in a heart transplantation model to observe the prolongation of donor survival in syngeneic,allogeneic and xenogeneic heart transplantation.Results:(1)Using CD47 KO mice and mouse skin or heart transplantation models,we found that allografts of both donor CD47 KO group and control group survived long-term without rejection in syngeneic and MHC-?-mismatched allogeneic transplantation.When MHC-?-mismatch or MHC-?/?-mismatch occurred,the graft survival time of donor CD47 KO group was significantly longer than that of control group.Histological examination showed that the level of inflammatory cell infiltration in experimental group was less than that of control group when rejection occurred in control group.When histocompatibility complex fully-mismatched mice were used,donor CD47 KO was not different from that of the control group,and donor heart rejection was rapid;when anti-CD8 antibody was given,rejection of CD47 KO donor heart was similar to that of the control group;CD47 KO can prolong the survival time of donor heart in galactosyltransferase gene knockout(Gal T-KO)mice.(2)In a MHC-?/? mismatched heart transplantation model,we found that the recipient anti-TSP1 antibody can protect the graft;using TSP1 KO mice as donors and recipients respectively,we found that the survival time of heart transplants was longer than the control group.(3)Pre-transfusion of donor-derived hepatic parenchymal cells into recipients for heart transplantation resulted in prolonged graft survival;when donor-derived hepatic parenchymal cells combined with single injection of cyclosporine A(Cs A)resulted in no further prolongation of graft survival;rapamycin injection combined with donor-derived hepatic parenchymal cells cannot protect donor form rejection.Pre-transfusion of the CD47 KO liver parenchymal cells accelerated the rejection compared with wild type.In MHC-?-mismatched mice cardiac transplantation,Pre-transfusion of donor-derived hepatocytes prolonged the survival time of transplanted donor heart.The recipient spleen was found at 4,7 and 14 days after transplantation.In the rat-to-mouse xenotransplantation model,it was found that the transplanted donor heart rejected rapidly after pre-transfusion of donor-derived hepatic parenchymal cells,and the histological staining indicated that the antibody mediated rejection.Conclusions:(1)The absence of donor CD47 expression did not induce rejection in a MHC-?-mismatched allogeneic heart transplantation;In a MHC-?-mismatched or MHC-?/?-mismatched allogeneic transplantation,the absence of donor CD47 expression could protect the graft from rejection;and in syngeneic cardiac transplantation,inhibition of antibody-mediated rejection occurred in the donor of CD47 KO.(2)TSP1 accelerated the donor rejection in histocompatibility complex fully-mismatched grafts.(3)Pre-transfusion of donor-derived hepatic parenchymal cells could protect the organ graft,and the absence of CD47 expression in donor hepatic parenchymal cells could not prolong the donor survival time.