Cyclophosphamide-induced tolerance in rat orthotopic liver transplantation

The protective effects of Cichorium glandulosum seed and cynarin against cyclophosphamide and its metabolite acrolein-induced hepatotoxicity in vivo and in vitro

Cyclophosphamide (CP) is a widely utilized chemotherapy drug. CP and its metabolite, acrolein, could induce hepatotoxicity. In this study, Cichorium glandulosum seed (CGS) effectively mitigated CP-induced hepatotoxicity in mice. Protection of cynarin, the major compound of CGS, against acrolein cytotoxicity in HepG2 cells was studied. Pretreatment with cynarin could improve cell survival against acrolein cytotoxicity. Cynarin restored the balance of glutathione (GSH) and reactive oxygen species (ROS), and inhibited mitochondrial depolarization. The kinetics of Nrf2 expression in cytosolic and nuclear fractions were observed after acrolein exposure. Intracellular Nrf2 expression was triggered within 6 h of exposure but did not translocate to the nucleus. Cynarin pretreatment ameliorated the expression and activity of GSH S-transferase and triggered Nrf2 nuclear translocation. In conclusion, treatment with CGS and cynarin protects liver injury against CP and acrolein hepatotoxicity via improvement of GSH activity and activation of the Nrf2 pathway.

Cyclophosphamide-induced tolerance in kidney transplantation avoids long-term immunosuppressive therapy

There has recently been remarkable progress in immunosuppressive agents, such as tacrolimus and cyclosporine. Therefore, the rate of organ establishment has improved in transplantation. However, immunosuppressive agents generally suppress the function of T cells. Thus, opportunistic infections, such as cytomegalovirus infection, are still a major problem in kidney transplantation. Induction of specific tolerance to avoid immunosuppressive drug therapy after kidney transplantation is considered as the ultimate goal of transplantation. Various factors induce tolerance that involves establishment of hematopoietic chimerism and various cell subsets. In particular, we have carried out various studies regarding the cyclophosphamide-induced tolerance system. Tolerance is induced after establishment of hematopoietic chimerism after donor bone marrow transplantation. At the clinical stage, kidney transplantation before administration of cyclophosphamide after transfusion of bone marrow to create hematopoietic chimera is considered to be one of the most successful protocols. Furthermore, recent studies have shown the involvement of multiple populations of immune cells in preserving immunological tolerance and promoting long-term renal grafts. The present review focuses on how cyclophosphamide and other immune factors induce tolerance in kidney transplantation.

Ultrastructurural picture of cyclophosphamide-induced damage to the liver

We studied the ultrastructural reorganization of hepatocytes and other populations of liver cells after cyclophosphamide treatment. Single administration of cyclophosphamide was followed by significant ultrastructural changes in two major populations of liver cells (hepatocytes and sinusoidal endothelial cells). This treatment was also accompanied by reactive changes in Kupffer cells, lymphocytes, and plasma cells migrating into the spaces of Disse. Cyclophosphamide-induced spatial reorganization of hepatocytes was associated with a progressive decrease in the structural density of mitochondria, significant reduction of the smooth endoplasmic reticulum, and increase in autophagocytosis (e.g., sequestration of glycogen). Intracellular reorganization of endothelial cells was related to the following two factors: damage (necrobiosis) of some cells; and increase in metabolic processes, phagocytosis, and regenerative reactions in other cells.

Provision of continuous maturation signaling to dendritic cells by RIG-I-stimulating cytosolic RNA synthesis of Sendai virus

Dendritic cell (DC)-based immunotherapy has potential for treating infections and malignant tumors, but the functional capacity of DC must be assessed in detail, especially maturation and Ag-specific CTL priming. Recent reports suggest that DC that are provided with continuous maturation signals in vivo after transfer into patients are required to elicit the full DC functions. We demonstrate in this study that the rSendai virus vector (SeV) is a novel and ideal stimulant, providing DC with a continuous maturation signal via viral RNA synthesis in the cytosol, resulting in full maturation of monocyte-derived DC(s). Both RIG-I-dependent cytokine production and CD4 T cell responses to SeV-derived helper Ags are indispensable for overcoming regulatory T cell suppression to prime melanoma Ag recognized by T cell-1-specific CTL in the regulatory T cell abundant setting. DC stimulated via cytokine receptors, or TLRs, do not show these functional features. Therefore, SeV-infected DC have the potential for DC-directed immunotherapy.

The critical role of Fas-Fas ligand interaction in donor-specific transfusion-induced tolerance to H-Y antigen

BACKGROUND

Donor-specific transfusion (DST) has been clinically used to enhance the survival of transplanted organs, and it has been shown in mice to induce tolerance to male (H-Y) antigen (Ag). Although the biologic mechanisms that initiate and maintain DST-induced tolerance involve clonal deletion, induction of anergy, and generation of regulatory cells, the molecules essential to tolerance induction are still unclear. In this study, we investigated the role of Fas-FasL interaction in DST-induced tolerance to H-Y Ag.

METHODS

C57BL/6 (B6) or B6-Fas(lpr) (lpr) female mice were intravenously injected with B6, lpr, or B6-FasL(gld) (gld) male spleen cells (SC). B6 male skin grafts, mixed lymphocyte reaction (MLR) assay, and cytotoxicity assay (CTL) were performed 7 days after DST. In some experiments, purified B-cells were used as transfused cells.

RESULTS

B6 female mice treated with B6 male SC permanently accepted B6 male skins, whereas untreated B6 or lpr female mice rejected B6 male skins. On the other hand, B6 female mice treated with gld male SC acceleratingly rejected male skin, as did lpr female mice treated with B6 or gld male SC. The recipient mice in the experimental groups, in which DST resulted in the accelerated rejection of the skin grafts, had strong allo-responses to H-Y Ag in MLR and CTL. Further, B6 female mice treated with gld male B-cells acceleratingly rejected male skins, whereas B6 female mice treated with B6 or lpr male B-cells from mice accepted male skins.

CONCLUSIONS

These findings suggest that the interaction between FasL upon infused SC, especially upon B-cells and Fas in a recipient, is essential in DST-induced tolerance to H-Y Ag.

Influence of intrauterine injection of rat fetal hepatocytes on rejection of rat liver transplantation

AIM: To investigate the influence of immune tolerance induced by intrauterine exposure to fetal hepatocytes on liver transplantation in the adult rat.

METHODS: LOU/CN rat fetal hepatocytes were injected into the fetuses of pregnant CHN rats (14-16 days of gestation). At 7-9 weeks of age, the surviving male rats received orthotopic liver transplantation (OLT) from male LOU/CN donors and the survival period was observed and monitered by mixed lymphocyte reaction assay and cytotoxicity test.

RESULTS: (1) A total of 31 pregnant CHN rats with 172 fetuses received fetal hepatocytes from LOU/CN rats via intrauterine injection. Among them, thirteen pregnant rats showed normal parturition, with 74 neonatal rats growing up normally. (2) The mean survival period after OLT in rats with fetal exposure to fetal hepatocytes was 32.1 ± 3.7 days, which was significantly different from the control (11.8 ± 2.3 days, P < 0.01) in rats without fetal induction of immune tolerance. (3) Mixed lymphocyte proliferation assays yielded remarkable discrepancies between the groups of rats with- or without fetal exposure to fetal hepatocytes, with values of 8411 ± 1361 and 22473 ± 1856 (CPM ± SD, P < 0.01) respectively. (4) Cytotoxicity assays showed values of 21.2 ± 6.5% and 64.5 ± 7.2% (P < 0.01) in adult rats with or without fetal induction of immune tolerance.

CONCLUSION: Intrauterine injection of fetal hepatocytes into rat fetuses can prolong the survival period of liver transplant adult male rats recipients, inducting immune tolerance in OLT.

Promotion of skin graft tolerance across MHC barriers by mobilization of dendritic cells in donor hemopoietic cell infusions

Flt3 ligand (FL) dramatically increases the number of immunostimulatory dendritic cells (DC) and their precursors in bone marrow (BM) and secondary lymphoid tissues. Herein we tested the ability of FL-mobilized donor hemopoietic cells to promote induction of skin graft tolerance across full MHC barriers. C57BL/10 (B10; H2(b), IE(-)) mice were given 10(8) spleen cells (SC) from normal or FL-treated, H-2-mismatched B10.D2 (H2(d), IE(+)) donors i.v. on day 0, 200 mg/kg i.p. cyclophosphamide on day 2, and 10(7) T cell-depleted BM cells from B10.D2 mice on day 3. B10.D2 skin grafting was performed on day 14. Indefinite allograft survival (100 days) was induced in recipients of FL-SC, but not in mice given normal SC. Tolerance was associated with blood macrochimerism and was confirmed by second-set skin grafting with donor skin 100 days after the first graft. In tolerant mice, peripheral donor-reactive T cells expressing TCR Vbeta11 were deleted selectively. Immunocompetence of tolerant FL-SC-treated mice was proven by rapid rejection of third-party skin grafts. To our knowledge this is the first report that mobilization of DC in donor cell infusions can be used to induce skin graft tolerance across MHC barriers, accompanied by specific deletion of donor-reactive T cells.

Normal donor bone marrow is superior to Flt3 ligand-mobilized bone marrow in prolonging heart allograft survival when combined with anti-CD40L (CD154)

Flt3 ligand (FL) administration markedly increases bone marrow (BM) stem cells and immature dendritic cells. We investigated the influence of CD40-CD40Ligand (CD154) pathway blockade on antidonor immunity, cytokine production, microchimerism and heart graft survival in BALB/c (H2d) recipients of fully allogeneic C57BL/10 (H2b) FL-mobilized BM (FL-BM) or normal BM. Anti-CD40L mAb strongly suppressed anti-donor T-cell proliferative responses in recipients of either normal or FL-BM, but was less efficient in inhibiting antidonor cytolytic T-cell (CTL) activity, especially in recipients of FL-BM. Interestingly, CD40L blockade was more effective in recipients of multiple compared with single donor BM infusions. Anti-donor cytokine responses revealed complete impairment of IFN-gamma, IL-4 and IL-10 production in recipients of normal BM and CD40L mAb. By contrast, and in agreement with the CTL data, mice given FL-BM retained ability to produce IFN-gamma CD40-CD40L blockade did not promote microchimerism, as evidenced by immunohistology and real time polymerase chain reaction. Nevertheless, anti-CD40L mAb enhanced heart allograft survival in recipients of FL-BM, but the effect was inferior to that achieved with normal BM. These data provide insight into the influence of growth factor-expanded donor BM and costimulation blockade on antidonor immune reactivity and transplant outcome. The comparatively poor outcome obtained using FL-BM plus anti-CD40L mAb in this model may be ascribed to the failure of effectively interdicting antidonor CTL activity.

Induction of apoptosis and modulation of activation and effector function in T cells by immunosuppressive drugs

Immunosuppressive drugs (ISD) are used for the prevention and treatment of graft rejection, graft-versus-host-disease (GVHD) and autoimmune disorders. The precise mechanisms by which ISD interfere with T cell activation and effector function or delete antigen-specific T cells are defined only partially. We analysed commonly used ISD such as dexamethasone (DEX), mycophenolic acid (MPA), FK506, cyclosporin A (CsA), rapamycin (RAP), methotrexate (MTX) and cyclophosphamide (CP) for apoptosis-induction and modulation of activation and effector function in human peripheral T cells, cytotoxic T cell lines (CTL) and Jurkat T cells. Of all drugs tested only CP and MTX prevented antigen-specific proliferation of T cells and decreased cytotoxicity of alloantigen specific CTL lines by direct induction of apoptosis. MTX and CP also slightly increased activation-induced cell death (AICD) and CD95-sensitivity. In contrast, all other drugs tested did not induce T cell apoptosis, increase CD95-sensitivity or AICD. CsA and FK506 even prevented AICD by down-modulation of CD95L. DEX, MPA, CsA, FK506 and RAP inhibited activation of naive T cells, but were not able to block proliferation of activated T cells nor decrease cytotoxic capacity of CTL lines. These results show that ISD can be classified according to their action on apoptosis-induction and inhibition of proliferation and would favour a rational combination therapy to delete existing reactive T cells and prevent further T cell activation.

Liver transplantation for hepatocellular carcinoma

The surgical management for hepatocellular carcinoma (HCC) is multiplicity. In Japan, liver resection has generally been considered to be the only curative treatment for HCC. The resectability of a tumor in cirrhotic patients, however, is limited by the diminished functional reserve of the cirrhotic liver and the attendant risk for intraoperative bleeding and postoperative liver failure. In cirrhotic patients, liver transplantation has been considered as the indication for HCC in many countries except Japan. Although the survival rate of patients with HCC who received liver transplants was poor in the early period, it later moved to the same level as for patients with other liver diseases. In 1993, living donor adult liver transplantation was started in Japan and it became an additional option for the treatment of HCC. A shortage of liver donors means that new methods of liver procurement must be explored. Domino liver transplantation using the livers of patients with familial amyloid polyneuropathy was also another option for advanced HCC. For the prevention of a recurrence of HCC, pre-, intra-, and postoperative chemotherapy have been performed after both liver resection and liver transplantation. We should also try to minimize intraoperative dissemination by surgical manipulation. Recently, potential gene therapies for HCC have been studied. Electroporation-mediated IL-12 gene therapy for HCC was found to be effective for both mIL-12-transferred HCC and for distant HCC. For patients with HCC accompanied by liver cirrhosis, liver transplantation remains the ultimate curative therapy. Immunologic and oncologic approaches to HCC can help prevent tumor recurrence and also help us to obtain better results after liver transplantation.