Organ transplantation is a routine clinical procedure for patients with end-stage organ failure. Allograft rejection remains one of major complications after organ transplantation. Although successfully preventing acute rejection episodes , current immunosuppressive regimens are unable to control chronic rejection , which is the primary cause of long-term graft loss. Next, they cause a global immunodeficiency predisposing to opportunistic infections ,diabetes , hypertention , renal failure and malignancy. In addition, patients have been burdened by heavy medical fee because they must endure a lifelong immunosuppression regimens in order to prevent graft rejection . Therefore, the induction of transplantation tolerance remains a goal in organ transplantation .IL-10, first identified as cytokine synthesis inhibitory factor , is produced by different cell types , including T cells , monocytes and B cells after all activation . IL-10 negatively regulates a variety of immune responses. In vitro studies have shown that IL-10 indirectly prevents antigen-specific T cell proliferation by reducing the antigen-presenting capacity of APCs through down-regulation of class II major histocompatibility and B7 molecules expression. In addition, IL-10 directly suppresses T cell proliferation by specific inhibition of IL-2 production by T cells. IL-10 acts directly on CD4+Tcells, leading to the production of a negative regulatory T cell subset and inducing a long-term anergic state in T cells in vitro.IL-10 also inhibits the production of monokines such as IL-1, IL-6,IL-8,TNF-a and GM-CSF. Viral interleukinlO (vIL-10), encoded by the Esptein Barr virus , is highly homologous to mouse IL-10 (mIL-10) and human IL-lO(hlL-lO) at both the nucleoside acid and ammino acid levels. It shares many immunosuppressive properties of both them, and lacks most of the immunostimulatory properties of the T cells and B cells, which potentially makes it a more potent immunosupressant. Therefore, vIL-10 is an ideal candidate cytokine inhibiting alloreaction.Hematopoietic stem cells (HSCs) are an ideal target cells for gene therapy because of their self-renew and multilineage differentiation ability. Theoretically, the long-term therapeutic effect will be achieved by gene being transduced into HSCs because a small of engineered genetically HSCs can give rise to a variety of blood cells with therapeutic gene.Moloney virus based retroviral vectors can permanently integrate transferred gene intotarget cell genomic DNA and permits therapeutic gene to be deliveried to their progenitor during their proliferation and differentiation. It's safe to host because of its low immunogenicity.The present study based on the properties of vIL-10 immunosuppression, HSCs self-renew and multilineage differentiation ability and retroviral vector biological activities. The MSCVneo-vIL-10 recombinant was constructed with MSCVneo and vIL-10 cDNA. The HSCs were transfected by the combinant of MSCVneo-vIL-10 in vitro and injected in syngeneic mice after experienced lethal dose irradiation at the same day. And then , vIL-10 expression in vivo was monitored by ELISA. The mice with vIL-10 positive in serum were used as recipients for heterotopic allo-heart transplantation eight weeks after HSCs transplantation. It is investigated that the mechanism to induce tolerance to allo-heart transplants through the assassment of heart graft survival, histopathology , cytokines expression and lymphocytes infiltration in the grafts.The present study is divided into three parts:The first part is that mouse's heterotopic heart transplantation was developed. CBA(H-2k) mice with 8-12 weeks old and 25g-30g weigh were used as recipients and donors in the experimentns. Isoflurane anesthesia was used in all of the surgical procedures. Heart transplantation was performed using Ono' method under 16~25x magnification by one person. The donor hearts remained ascending aorta and pulmonary artery, which were cut before their bifurcation. The aorta of the donor heart was anastomosed end-to side