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The induction of transplantation tolerance and the improvement of immune reconstitution after allogeneic bone marrow transplantation are the main research fields in the clinic organ transplantation and transplantation immunology. Over the past 5 years serial studies have been performed in our lab to induce robust transplantation tolerance by using combined strategies and improve the immune reconstitution of mice following allogeneic bone marrow transplantation by using gene-engineered bone marrow stromal cells. The results are encouraging. (1) The long-term survival of allografts was received by blockade of both CD28/B7 and CD40/CD40L or CD28/B7 and OX40/OX40L costimulation signals. In the case of blockade of both CD28/B7 and OX40/OX40L, the islet allograft survival was over 150 days compared to the control 14 days. (2) The CTLA4Ig-FasL fusion molecule expressed by adenoviral vector containing CTLA4Ig-FasL gene can prevent the autoimmune diabetes of mice and significantly prolong the survival time of cardiac allografts in rats, indicating that Fas-FasL-mediated apoptosis is able to enhance CTLA4Ig-induced transplantation tolerance. (3) In the time-window of peripheral tolerance induced by various methods, the systemic infusion of donor bone marrow cells and spleen cells obtained stable allogeneic mixed chimerism and robust transplantation tolerance. In the case of CTLA4Ig-FasL treatment combined with donor bone marrow cells more than 20% donor-origin blood cells chimerism, and more than 200 days prolonged skin allograft survival were obtained or received. (4) The murine bone marrow stromal cell line QXMSC1 transfected with IL-6 gene or IL-2+IL-3 genes significantly improved the immune reconstitution of mice following allogeneic bone marrow transplantation. Furthermore, It was observed that the mesenchymal stem cells transfected with IL-7 gene suppressed 90% of GVHD and expressed antileukemic effect, while accelerating immune reconstitution in mice following allogeneic bone marrow transplantation, which might be valuable in the clinic setting.

It has been demonstrated that prolonged graft survival can be achieved through inhibiting the activation of T cells, and addition of soluble CTLA4Ig and OX40Ig proteins to mixed lymphocyte reactions can effectively inhibit T cell proliferation. To explore the potential of this type of treatment in xenotransplantation, we infected streptozotocin-induced diabetic BalB/c mice (H-2d) (200 mg/kg, IV) with 5 x 10(8) pfu AdCTLA4Ig-IRES-OX40Ig on day 1 before islets transplantation through the tail vein. The results showed that this treatment prolonged the islet xenografts survival significantly. The reaction to exogenous glucose stimulation was normal and the cytokine secretion of the type Th1 cells was inhibited. The AdCTLA4Ig-IRES-OX40Ig-mediated treatment effectively induced the T cells into anergy and the Th1/Th2 cells into deviation. These results strongly supported the therapeutic potential of blockade of costimulation by AdCTLA4Ig-IRES-OX40Ig genes transfer in inducing the organ transplantation tolerance.

T-cell costimulatory blockade combined with donor bone marrow transfusion may induce mixed chimerism, rendering robust tolerance in transplanted organs and cells. However, most protocols entail high doses of donor bone marrow cells (BMCs) or repeated administration of costly agents that block costimulatory pathways, thus delaying clinical development. To circumvent these shortcomings, we developed a strategy in which the dosage of donor BMCs was reduced but compensated by donor splenocytes (SPLCs). Furthermore, repeated administration of costly agents was replaced with a single injection of adenovirus expressing a gene of interest. In rat cardiac transplantation models, cardiac allografts from DA (RT-1a) rats were transplanted heterotopically into the abdomen of LEW (RT-11) recipient rats. Immediately after cardiac transplantation, an adenovirus vector (AdCTLA4Ig; 5 x 10(9) plaque-forming units) containing the gene for CTLA4Ig was administered to recipients (n = 6) simultaneously with a low dose of donor BMCs (1 x 10(8)/rat) and SPLCs (5 x 10(7)/rat) via the portal vein. The treated LEW recipient rats developed long-lasting mixed chimerism (>10% at >100 days) and exhibited long-term cardiac allografts (mean survival time of > 200 days) compared with control recipients. Moreover, recipients displaying long-lasting mixed chimerism accepted subsequent donor skin allografts while promptly rejecting third-party skin allografts. These results suggest that blockade of the CD28-B7 pathway, using adenovirus-mediated CTLA4Ig gene transfer, in concert with a low dosage of donor BMCs and SPLCs, may represent a feasible strategy to induce stable mixed chimerism and permit long-term survival of cardiac allografts.

Mixed hemopoietic chimerism is capable of inducing donor specific tolerance, thus eliminating the chronic immunosuppressive therapy following organ transplantation. As yet no safe and effective tolerance protocol is available for clinical implementation. Here we describe an alternative nonmyeloablative based strategy of using a single injection of recombination adenovirus vector encoding CTLA4.FasL fusing gene and donor bone marrow cells to promote durable mixed macrochimerism (>20% on 140 d). Chimeras exhibited robust donor-specific tolerance, as evidenced by acceptance of fully allogeneic skin grafts (the mean survival time (MST)>200 d) and rejection of third-party skin grafts in a normal manner (MST<10 d). In this model, the frequencies of helper T lymphocyte precursor (HTLp) and cytotoxic T lymphocyte precursor (CTLp) were greatly reduced on day 14 after transplantation, suggesting that CTLA4-FasL led to rapid systemic peripheral tolerance to facilitate the bone marrow engraftment, while both HTLp and CTLp remained at low level only in recipient mice with mixed chimerism on day 140 after transplantation, demonstrating that long-term skin grafts tolerance was associated with stable mixed chimerism, and central deletion of donor specific T cell may be the main mechanism for tolerance maintenance. [ABSTRACT FROM AUTHOR]