Regulatory T cells contribute to the immunoregulatory effect on graft versus host reaction after liver transplantation in donor-dominant one-way MHC matching rats

OSI-027 modulates acute graft-versus-host disease after liver transplantation in a rat model

Despite its rarity (1%-2%), acute graft-versus-host disease after liver transplantation (LT-aGVHD) has a high mortality rate (85%). A gradual decrease in regulatory T cells (Tregs) correlates with disease progression in a rat LT-GVHD model, and treatments which increase Tregs exert therapeutic effects on LT-aGVHD. In this study, LT-aGVHD model rats were treated with rapamycin (RAPA), OSI-027, or an equal quantity of vehicle. Rats treated with OSI-027 survived longer (>100 days) than those in the RAPA (70 ± 8 days) or control (24 ± 3 days) groups. Flow cytometric analysis showed that the Treg ratios in peripheral blood mononuclear cells in the OSI-027 group were higher than those in the RAPA or control groups. The proportions of donor-derived lymphocytes in the OSI-027 group were lower than those in the RAPA or control groups. Hematoxylin-eosin staining of skin tissue demonstrated less severe lymphocyte infiltration in the OSI-027 group than that in the RAPA or control groups. In vitro, OSI-027 induced differentiation of CD4⁺ CD25^- T cells into CD4⁺ CD25⁺ forkhead box P3⁺ Tregs. Furthermore, injection of OSI-027-induced donor-derived CD4⁺ CD25⁺ T cells into the peripheral blood of LT-aGVHD model rats prevented LT-aGVHD. Thus, OSI-027 is implicated as a novel method for the treatment of LT-aGVHD. Liver Transplantation 23 1186-1198 2017 AASLD.

CD4(+)CD25 (+) regulatory T cells are not required for mesenchymal stem cell function in fully MHC-mismatched mouse cardiac transplantation

Although the immunomodulative properties of mesenchymal stem cells (MSCs) open up attractive possibilities in solid-organ transplantation, information concerning the optimal dose, route, timing of administration, major histocompatibility complex (MHC)-restriction and relevant mechanisms is currently lacking. Therefore, better characterization of MSC immunoregulatory activity and elucidation of its mechanisms are crucial. In this study, we confirmed that MSCs did not elicit proliferation by allogeneic CD4(+) T cells, suggesting that MSCs were not immunogenic. By using C57BL/6 mouse MSCs as donor-derived or recipient-derived or as third-party MSCs, we discovered that MSCs suppressed CD4(+) T cell proliferation and prolonged mouse cardiac allograft survival in a dose-dependent and non-MHC-restricted manner. We also found that intraperitoneal administration favored survival prolongation, although this prolongation was weaker than that via the intravenous route. Only infusion at earlier time points favored survival prolongation. Depletion of CD4(+)CD25(+) T cells did not affect the immunosuppression of MSCs on CD4(+) T cells. Moreover, MSCs did not induce regulatory T cells. The in vivo data revealed that MSCs did not increase the percentage of CD4(+)CD25(+) T cells and FoxP3 expression. More importantly, we demonstrated for the first time that depletion of CD4(+)CD25(+) T cells did not hinder MSC-induced survival prolongation, indicating that CD4(+)CD25(+) regulatory T cells were not essential for the prolongation of MSC-mediated allograft survival.

Mesenchymal stem cells administered after liver transplantation prevent acute graft-versus-host disease in rats

Acute graft-versus-host disease is a serious and life-threatening complication of liver transplantation (LT) that occurs in 1% to 2% of liver allograft recipients. It is associated with a high mortality rate, and effective therapies are lacking. In our established rat model, a relative decrease in regulatory T cells (Tregs) was previously shown to be associated with acute graft-versus-host disease after liver transplantation (LT-aGVHD). Mesenchymal stem cells (MSCs) have been used to treat graft-versus-host disease after allogeneic hematopoietic stem cell transplantation, and they have been shown to induce Tregs, which have immunomodulatory effects. In this study, when a treatment with donor- or recipient-derived MSCs was administered from day 8 to day 14 after the typical symptoms of LT-aGVHD started, the recipients were not cured, and their survival time was not prolonged. However, when MSCs of different origins were administered from day 0 to day 6 after LT, the recipients survived significantly longer than the control group, and the surviving MSC-treated rats did not show typical LT-aGVHD symptoms. In vivo tracings of carboxyfluorescein diacetate succinimidyl ester-stained MSCs did not show significant accumulations in the target organs after administration. Flow cytometry analysis showed that the Treg ratios in peripheral blood were more higher for the MSC-treated groups versus the control group. More immunohistochemically stained forkhead box P3-positive cells were also found in the intestines of the MSC-treated groups versus the control group. Further investigations of the function of MSCs showed that they could increase the Treg ratio in a mixed lymphocyte reaction (MLR) and lead to a greater reduction in MLR proliferation in vitro. In conclusion, the post-LT administration of MSCs of either donor or recipient origin could prevent the onset of LT-aGVHD in our rat model.

Correlation of Chimerism with Acute Graft-versus-Host Disease in Rats following Liver Transplantation

The accurate diagnosis of acute graft-versus-host disease following liver transplantation (LTx-aGVHD) has been hampered. Chimerism appears in the majority of recipients after LT and its significance in the diagnosis of LTx-aGVHD has not been clearly established. To demonstrate the significance of chimerism on the diagnosis of LTx-aGVHD, we compared the change of chimerism in syngeneic LT recipients, semiallogeneic LT recipients, and LTx-aGVHD induced recipients. Chimerism in PBMCs following sex-mismatched LT was identified by real-time PCR based on a rat Y-chromosome-specific primer. All recipients in semiallogeneic group grew in a normal pattern. However, when 4 × 10(8) donor splenocytes were transferred simultaneously during LT, the morbidity of lethal aGVHD was 100%. The chimerism appeared slightly higher in the semiallogeneic group than in the syngeneic LT group, but the difference was not significant. However, when the recipients developed lethal aGVHD after LT, chimerism in the PBMCs increased progressively, and even at an early time, a significant increase in chimerism was observed. In conclusion, high level chimerism correlated well with LTx-aGVHD, and detection of chimerism soon after transplantation may be of value in the diagnosis of LTx-aGVHD prior to the onset of symptoms.

Rapamycin and tacrolimus differentially modulate acute graft-versus-host disease in rats after liver transplantation

Acute graft-versus-host disease (aGVHD) is a serious complication of liver transplantation (LTx); it occurs in 1% to 2% of liver allograft recipients. The condition has a poor prognosis and poses major diagnostic and therapeutic challenges. A rat model of aGVHD after LTx has been developed, and a relative decrease in regulatory T (Treg) cells has been shown to be associated with this model. Interest has been expressed in the effects of different immunosuppressive agents on CD4+CD25+Foxp3+ Treg cell homeostasis. Rats with aGVHD after LTx were treated with tacrolimus (FK506), rapamycin (RAPA), or no immunosuppressive drug. Those that received RAPA survived longer (91.4 + or - 8.1 days) than those in the FK506 group (62.3 + or - 13.4 days) or the control group (22.9 + or - 1.2 days). Flow cytometry analysis showed that Treg cells, as a percentage of peripheral blood mononuclear cells (PBMCs), were more abundant in the RAPA group (6.8% + or - 0.8%) than in the FK506 group (1.7% + or - 0.4%) or the control group (2.0% + or - 0.4%). Immunohistochemistry demonstrated more Foxp3+ staining of intestinal cells in the RAPA group than in the FK506 group or the control group. In conclusion, the reduced mortality induced by RAPA in a rat model of aGVHD after LTx was associated with higher percentages of CD4+CD25+Foxp3+ Treg cells in PBMCs in blood and tissues than those occurring after the administration of FK506.