Blockade of 4-1BB/4-1BB ligand interactions prevents acute rejection in rat liver transplantation

Background Blocking the 4-1BB/4-1BB ligand （4-1BBL） signal may modulate the secretion of Th1/Th2 cytokines and prolong the survival of the grafts, which play a key role in organ transplantation tolerance. The aim of this study was to investigate the role of blockade of the 4-1BB/4-1BBL co-stimulatory pathway with 4-1BBL monoclonal antibody （mAB） in acute rejection of rat orthotopic liver transplantation. Methods The orthotopic liver transplantation model was set up, while male Lewis rats were used as liver donors and Brown-Norway rats as recipients. The recipient rats were intravenously injected with anti 4-1BBL mAB or isotype control antibody. Groups were monitored for graft survival after transplantation. Plasma chemistry, including aspartate transaminase （AST）, alanine aminotransferase （ALT）, and bilirubin （BIL）, was assayed. The concentrations of interleukin （IL）-2, IL-10 and interferon （IFN）-γ in plasma were also measured by enzyme-linked immunosorbent assay. Allograft histology images were collected under light microscope and electron microscope. Results Isotype antibody treated recipients exhibited elevated plasma levels of liver injury markers including AST, ALT and BIL, progressive portal and venous inflammation and cellular infiltration of the liver ailografts, and a mean graft survival time （MST） of 10.9 days. Administration of anti 4-1BBL mAB resulted in a decrease in plasma levels of liver injury markers and the concentrations of IL-2, IL-10 and IFN-γ. The histological grade of rejection on day 7 decreased and MST （17.3 days） increased substantially. Conclusions These results demonstrate that attenuation of acute rejection follows the blockade of the 4-1BB/4-1BBL co-stimulatory pathway with 4-1BBL monoclonal antibody and strongly suggest it is a promising strategy to prevent progression of graft rejection by suppressing T cell-mediated immunity.

Transplantation Expression of 4-1BB molecule on peripheral blood T cells in liver transplanted patients and its clinical implication

OBJECTIVE: To investigate the gene expression of 4-1BB in peripheral blood mononuclear cells (PBMCs) and its possible significance in clinical liver transplantation. METHODS: Reverse transcription-polymerase chain reaction (RT-PCR) was used to determine the gene expression of 4-1BB in PBMCs from 22 patients receiving liver transplantation, 13 patients with primary liver carcinoma (PLC), and 12 healthy controls. To determine whether 4-1BB molecule is also expressed on the surface of CD4^+ and CD8^+ T cell, flow cytometry was used to analyse the phenotype of T cell subsets from the blood of liver transplantation patients. RESULTS: 4-1BB mRNA was detected in PBMCs from stable survivors after liver transplantation, but almost not deteeted in PBMCs from PLC patients and healthy controls. Meanwhile, 4-1BB was almost not expressed on the surface of CD4^+ and CD8^+ T cells in healthy controls and PLC patients. A low level of 4-1BB expression, however, was found on the surface of CD4^+ and CD8^+ T cells from the stable survivors after liver transplantation. CONCLUSIONS: This study demonstrates that although patients are stable after liver transplantation, effector T-cells can also be activated through the signal of 4-1BB molecule and persistent irmmune response to grafts. Blockage of 4-1BB/4-1BBL pathway may benefitially reduce the clinical dosage of immunosuppressive agents and prolong the survival of grafts.

4-1BB gene expression in peripheral blood mononuclear cells from orthotopic liver transplant recipients with graft acceptance

Objective To investigate the gene expression of 4-1BB in peripheral blood mononuclear cells (PBMCs) and the possible significance of the 4-1BB pathway after clinical orthotopic liver transplantation (OLT). Methods 4-1BB mRNA levels in PBMCs from 22 OLT patients were analyzed by RT-PCR. 4-1BB protein expressed on the surface of CD 4 + and CD 8 + T cells were detected by flow cytometry, and visualized with direct immunofluorescence and confocal fluorescence microscopy. Patients with primary liver cancer (PLC) and healthy volunteers served as controls. Six cases of recently performed liver transplantation were also observed in this study. Results 4-1BB mRNA was detected in PBMCs from both liver transplant patients with long-term graft acceptance (22 cases) and from transplant patients on day 1 to day 3 post-transplantation (6 cases), but was not found in PBMCs from transplant patients on day 7 to day 30 post-transplantation (6 cases). 4-1BB mRNA was also not found in samples from 8 of the healthy controls and 7 of the PLC patients, though very low expression was detected in the other 4 healthy volunteers and 6 PLC patients. Simultaneously, 4-1BB protein was expressed at nearly undetectable levels on CD 4 + and CD 8 + T cells from healthy controls, PLC patients, as well as OLT patients within the first month post-transplantation (6 cases). However, 4-1BB expression was found on the surface of CD 4 + and CD 8 + T cells from liver transplant patients with long-term graft acceptance. Direct immunofluorescent staining and confocal fluorescence microscopy clearly revealed evidence of 4-1BB protein on cell membranes of CD 4 + and CD 8 + T cells from liver transplant patients with long-term graft acceptance. Simultaneously, a significantly higher percentage of CD 3 + CD 25 + T cells were found in liver transplant patients with long-term graft acceptance group as compared with the healthy control group (P<0.05). The expression of 4-1BB protein on T cells did not correlate with the survival time of OLT patients postoperation. Conclusions This study demonstrates that although patients remain in stable condition after liver transplantation under the treatment of immunosuppressants, activated T cells are present to some extent and 4-1BB protein may be involved in this process. Effector T-cells can exert permanent immunoresponses against grafts under these circumstances. Therefore, we conclude that a new immune response balance is established under the combination of both treatment with immunosuppressants and natural immune responses against alloantigens. Manipulation of the 4-1BB/4-1BBL pathway may provide a therapeutic technique for prolonging graft survival.