Fatty Acids Play a Critical Role in Mitochondrial Oxidative Phosphorylation in Effector T Cells in Graft-versus-Host Disease.

Although the role of aerobic glycolysis in activated T cells has been well characterized, whether and how fatty acids (FAs) contribute to donor T cell function in allogeneic hematopoietic stem cell transplantation is unclear. Using xenogeneic graft-versus-host disease (GVHD) models, this study demonstrated that exogenous FAs serve as a crucial source of mitochondrial respiration in donor T cells in humans. By comparing human T cells isolated from wild-type NOD/Shi-scid-IL2rγnull (NOG) mice with those from MHC class I/II-deficient NOG mice, we found that donor T cells increased extracellular FA uptake, the extent of which correlates with their proliferation, and continued to increase FA uptake during effector differentiation. Gene expression analysis showed the upregulation of a wide range of lipid metabolism-related genes, including lipid hydrolysis, mitochondrial FA transport, and FA oxidation. Extracellular flux analysis demonstrated that mitochondrial FA transport was required to fully achieve the mitochondrial maximal respiration rate and spare respiratory capacity, whereas the substantial disruption of glucose supply by either glucose deprivation or mitochondrial pyruvate transport blockade did not impair oxidative phosphorylation. Taken together, FA-driven mitochondrial respiration is a hallmark that differentiates TCR-dependent T cell activation from TCR-independent immune response after hematopoietic stem cell transplant.

Forodesine Enhances Immune Responses through Guanosine-Mediated TLR7 Activation while Preventing Graft-versus-Host Disease.

Recent evidence indicates that specific types of nuclear acids, including guanosine and its derivatives, act as natural ligands for TLR7. This led us to hypothesize that purine nucleoside phosphorylase inhibitors not only can induce apoptosis of T cells but also can lead to TLR7 activation by accumulation of guanine nucleosides, in particular under systemic inflammation, where damaged tissues release a large amount of nucleotides. We demonstrate in the present study that a purine nucleoside phosphorylase inhibitor, forodesine, can reduce the disease severity and prolong the survival in a xenogeneic mouse model of graft-versus-host disease (GVHD). Guanine nucleosides were undetectable in mice during GVHD but increased significantly following forodesine treatment. Our in vitro experiments showed that forodesine enhanced guanosine-mediated cytokine production from APCs, including alveolar macrophages and plasmacytoid dendritic cells, through TLR7 signaling. Forodesine also enhanced Ag-presenting capacity, as demonstrated by increased CD8+ T cell proliferation and higher secretion of IFN-γ and IL-12p40 in an MLR with plasmacytoid dendritic cells. Furthermore, forodesine stimulated IFN-γ production from activated T cells in the presence of a low concentration of guanosine while inhibiting their proliferation and inducing apoptotic cell death. Although forodesine ameliorated GVHD severity, mice treated with forodesine showed significantly higher levels of multiple proinflammatory cytokines and chemokines in plasma, suggesting in vivo upregulation of TLR7 signaling. Our study suggests that forodesine may activate a wide range of immune cells, including T cells, through TLR7 stimulation while inhibiting GVHD by inducing apoptosis of T cells, after allogeneic hematopoietic stem cell transplant.

Comparison of alemtuzumab, anti-thymocyte globulin, and post-transplant cyclophosphamide for graft-versus-host disease and graft-versus-leukemia in murine models.

Graft-versus-host disease is a major complication after allogeneic hematopoietic stem cell transplantation for hematological malignancies. Immunosuppressive drugs, such as anti-thymocyte globulin, alemtuzumab, and post-transplant cyclophosphamide, have been used to prevent graft-versus-host disease in HLA-mismatched haploidentical hematopoietic stem cell transplantation. Here, we investigated whether these drugs could ameliorate graft-versus-host disease without diminishing the graft-versus-leukemia effect by using a xenogeneic transplanted graft-versus-host disease/graft-versus-leukemia model. Anti-thymocyte globulin treatment diminished graft-versus-host disease symptoms, completely depleted the infiltration of inflammatory cells in the liver and intestine, and led to prolonged survival. By contrast, improvement after post-transplant cyclophosphamide treatment remained minimal. Alemtuzumab treatment modestly prolonged survival despite an apparent decrease of Tregs. In the graft-versus-leukemia model, 1.5 to 2.0 mg/kg of anti-thymocyte globulin and 0.6 to 0.9 mg/kg of alemtuzumab reduced graft-versus-host disease with minimal loss of graft-versus-leukemia effect. Mice treated with 400 mg/kg of post-transplant cyclophosphamide did not develop graft-versus-host disease or leukemia, but it was difficult to evaluate the graft-versus-leukemia effect due to the sensitivity of A20 cells to cyclophosphamide. Although the current settings provide narrow optimal therapeutic windows, further studies are warranted to maximize the benefits of each immunosuppressant.

Mesenchymal Stromal Cells Inhibit Aerobic Glycolysis in Activated T Cells by Negatively Regulating Hexokinase II Activity Through PD-1/PD-L1 Interaction.

Mesenchymal stromal cells (MSCs) have been shown to inhibit aerobic glycolysis in activated T cells, leading to increased autophagy. Although tryptophan depletion induced by indoleamine 2,3-dioxygenase (IDO) generated by MSCs has been suggested as a potential mechanism, we found that this inhibition was completely abolished when T cells were physically separated from MSCs using the Transwell system. Instead, in the current study, we demonstrate that programmed cell death 1 receptor (PD-1) and its ligand PD-L1, the expression of which is induced on activated T cells and MSCs, respectively, in response to IFN-γ are involved in this inhibition. Blockade of PD-1/PD-L1 interaction by blocking antibodies significantly restored glucose uptake, glycolytic activity, and cluster formation of activated T cells, whereas a specific inhibitor of IDO, 1-methyl-DL-tryptophan, had no effect. Neither surface nor cytoplasmic glucose transporter-1 expression on T cells was changed by MSCs. In addition, glycolytic gene expression in activated T cells was not inhibited despite the presence of MSCs. However, we found that hexokinase II (HK2) protein expression was markedly decreased in activated T cells that had been cocultured with MSCs. PD-1 blocking antibody restored HK2 expression. Taken together, our findings indicate that the PD-1/PD-L1 axis is involved in the MSC-mediated suppression of T cell glycolysis by negatively regulating HK2 activity at the protein level, but not at the mRNA level.

Alloreactive T Cells Display a Distinct Chemokine Profile in Response to Conditioning in Xenogeneic GVHD Models.

BACKGROUND: Chemokines and chemokine receptors are potential targets for the prevention and treatment of graft-versus-host disease (GVHD). The objective of the current study is to determine the clinical relevance of xenogeneic transplantation models in terms of host and donor chemokine profiles and, if this is the case, to assess the clinical efficacy of C-C chemokine receptor (CCR) 5 antagonist maraviroc for the prevention of GVHD using this model. METHODS: Xenogeneic GVHD was induced by intravenous injection of 5 × 10 human pan T cells into NOD/Shi-scid-IL2rγ (NOG) mice or MHC class I/II-deficient NOG mice in the presence or absence of total body irradiation before transplantation. RESULTS: Extensive tissue destruction with human T-cell infiltration was observed throughout the body, particularly in lungs and liver, but relatively mild in gut. Consistent with this finding, quantitative polymerase chain reaction confirmed the upregulation of mouse CXC chemokine ligand (CXCL) 9 and CXCL10 in lungs and CCL4 in lungs and liver but not in gut. The addition of total body irradiation (1) led to the early release of mouse CCL4 and CXCL10, (2) upregulated a number of chemokine-related genes in human T cells, (3) induced higher expression of CCR5 on human CD4 and CD8 T cells and CXCR3 on human CD4 T cells, and (4) promoted their migration and proliferation in organs, resulting in more severe tissue damage. In this context, pharmacological CCR5 blockade neither ameliorated GVHD nor prolonged survival in NOG mice. CONCLUSIONS: Our experimental data do not demonstrate clinical benefit of CCR5 antagonist for the prevention of GVHD in a myeloablative setting.

Comprehensive Analysis of the Activation and Proliferation Kinetics and Effector Functions of Human Lymphocytes, and Antigen Presentation Capacity of Antigen-Presenting Cells in Xenogeneic Graft-Versus-Host Disease.

Xenogeneic graft-versus-host disease (GVHD) models in highly immunodeficient mice are currently being used worldwide to investigate human immune responses against foreign antigens in vivo. However, the individual roles of CD4+ and CD8+ T cells, and donor/host hematopoietic and nonhematopoietic antigen-presenting cells (APCs) in the induction and development of GVHD have not been fully investigated. In the present study, we comprehensively investigated the immune responses of human T cells and the antigen presentation capacity of donor/host hematopoietic and nonhematopoietic APCs in xenogeneic GVHD models using nonobese diabetic/Shi-scid-IL2rgnull mice. CD4+ T cells and, to a lesser extent, CD8+ T cells individually mediated potentially lethal GVHD. In addition to inflammatory cytokine production, CD4+ T cells also supported the activation and proliferation of CD8+ T cells. Using bone marrow chimeras, we demonstrated that host hematopoietic, but not nonhematopoietic, APCs play a critical role in the development of CD4+ T cell-mediated GVHD. During early GVHD, we detected 2 distinct populations in memory CD4+ T cells. One population was highly activated and proliferated in major histocompatibility complex antigen (MHC)+/+ mice but not in MHC-/- mice, indicating alloreactive T cells. The other population showed a less activated and slowly proliferative status regardless of host MHC expression, and was associated with higher susceptibility to apoptosis, indicating nonalloreactive T cells in homeostasis-driven proliferation. These observations are clinically relevant to donor T cell response after allogeneic hematopoietic stem cell transplantation. Our findings provide a better understanding of the immunobiology of humanized mice and support the development of novel options for the prevention and treatment for GVHD.