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

Targeting the chemokines in acute graft-versus-host disease

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) constitutes a critical therapeutic approach for patients with malignant hematological disorders. Nevertheless, acute graft-versus-host disease (GVHD), one of the most prevalent complications associated with HSCT, remains a leading contributor to non-relapse mortality. In recent years, there has been an increasing focus on the interplay between chemokines and their receptors in the context of acute GVHD. Chemokines exert substantial effects across various pathological conditions, including autoimmune diseases, inflammatory processes, tumorigenesis, and metastatic dissemination. In this review, we aim to elucidate the role of chemokines in the pathogenesis of acute GVHD and further understand their potential as diagnostic biomarkers. We also present both preclinical and clinical insights into the application of chemokines in preventing and treating acute GVHD. The objective of this review is to offer novel perspectives on the clinical diagnosis and management strategies for acute GVHD.

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.

C-C chemokine receptor 5 and acute graft-versus-host disease

BACKGROUND

The C-C chemokine receptor 5 (CCR5) is mainly expressed in a variety of immune cells. It interacts with multiple chemokine ligands that mediate the trafficking and recruitment of effector cells toward sites of inflammation. CCR5 not only plays a critical role in cell growth, activation, differentiation, adhesion, and migration but also participates in the development of acute graft-versus-host disease (GVHD) after allogeneic hematopoietic cell transplantation.

METHODS

This is a literature review article. The research design method is an evidence-based rapid review. The present discourse aim is first to scrutinize and assess the available literature on CCR5 and acute GVHD. Standard literature and database searches were implemented, gathered relevant material, and extracted information was then assessed.

RESULTS

CCR5 is a marker of GVHD effector cells, and CCR5 expression is elevated when acute GVHD occurs. CCR5 blockade with maraviroc in clinical trials results in a low incidence of acute GVHD. The immune mechanism includes that CCR5 blockade inhibits donor T cell migration and recruitment toward target organs, reduces the absolute numbers of donor T cells, is capable of slightly suppressing dendritic cell maturation, and reduces the percentage of Th1 and Th17 subsets. CCR5 blockade also inhibits internalization and activation of chemokines, inhibits proliferation and chemotaxis of T cells, and decreases the production of TNF-α and IFN-γ. In addition, there may be a form of crosstalk between CCR5 and CCR2. Inconsistently, infusion of CCR5-/- Tregs into lethally irradiated mice significantly increased the infiltration of CD4+ and CD8+ T cells into the liver, resulting in earlier and more severe GVHD.

CONCLUSION

This review indicates that CCR5 plays an important role in pathogenesis and development of acute GVHD. Elucidating its role in different immune cells will aid the development of targeted therapeutic treatments.

Insights into mechanisms of graft-versus-host disease through humanised mouse models

Graft-versus-host disease (GVHD) is a major complication that occurs following allogeneic haematopoietic stem cell transplantation (HSCT) for the treatment of haematological cancers and other blood-related disorders. GVHD is an inflammatory disorder, where the transplanted donor immune cells can mediate an immune response against the recipient and attack host tissues. Despite over 60 years of research, broad-range immune suppression is still used to prevent or treat GVHD, leading to an increased risk of cancer relapse and infection. Therefore, further insights into the disease mechanisms and development of predictive and prognostic biomarkers are key to improving outcomes and reducing GVHD development following allogeneic HSCT. An important preclinical tool to examine the pathophysiology of GVHD and to understand the key mechanisms that lead to GVHD development are preclinical humanised mouse models. Such models of GVHD are now well-established and can provide valuable insights into disease development. This review will focus on models where human peripheral blood mononuclear cells are injected into immune-deficient non-obese diabetic (NOD)-scid-interleukin-2(IL-2)Rγ mutant (NOD-scid-IL2Rγ^null) mice. Humanised mouse models of GVHD can mimic the clinical setting for GVHD development, with disease progression and tissues impacted like that observed in humans. This review will highlight key findings from preclinical humanised mouse models regarding the role of donor human immune cells, the function of cytokines and cell signalling molecules and their impact on specific target tissues and GVHD development. Further, specific therapeutic strategies tested in these preclinical models reveal key molecular pathways important in reducing the burden of GVHD following allogeneic HSCT.

Improved engraftment of human peripheral blood mononuclear cells in NOG MHC double knockout mice generated using CRISPR/Cas9

Humanized mice are widely used to study the human immune system in vivo and develop therapies for various human diseases. Human peripheral blood mononuclear cells (PBMC)-engrafted NOD/Shi-scid IL2rγ^null (NOG) mice are useful models for characterization of human T cells. However, the development of graft-versus-host disease (GVHD) limits the use of NOG PBMC models. We previously established a NOG-major histocompatibility complex class I/II double knockout (dKO) mouse model. Although humanized dKO mice do not develop severe GVHD, they have impaired reproductive performance and reduced chimerism of human cells. In this study, we established a novel beta-2 microglobulin (B2m) KO mouse model using CRISPR/Cas9. By crossing B2m KO mice with I-Ab KO mice, we established a modified dKO (dKO-em) mouse model. Reproductivity was slightly improved in dKO-em mice, compared with conventional dKO (dKO-tm) mice. dKO-em mice showed no signs of GVHD after the transfer of human PBMCs; they also exhibited high engraftment efficiency. Engrafted human PBMCs survived significantly longer in the peripheral blood and spleens of dKO-em mice, compared with dKO-tm mice. In conclusion, dKO-em mice might constitute a promising PBMC-based humanized mouse model for the development and preclinical testing of novel therapeutics for human diseases.

Differential Localization and Invasion of Tumor Cells in Mouse Models of Human and Murine Leukemias

Leukemias are refractory hematopoietic malignancies, for which the development of new therapeutic agents requires in vivo studies using tumor-bearing mouse models. Although several organs are commonly examined in such studies to evaluate the disease course, the effectiveness of interventions and the localization of tumor cells in the affected organs are still unclear. In this study, we histologically examined the distribution of leukemia cells in several organs using two leukemic mouse models produced by the administration of two cell lines (THP-1, a human myelomonocytic leukemia, and A20, a mouse B cell leukemia/lymphoma) to severe immunodeficient mice. Survival of the mice depended on the tumor burden. Although A20 and THP-1 tumor cells massively infiltrated the parenchyma of the liver and spleen at 21 days after transplantation, A20 cells were hardly found in connective tissues in Glisson’s capsule in the liver as compared with THP-1 cells. In the bone marrow, there was more severe infiltration of A20 cells than THP-1 cells. THP-1 and A20 cells were widely spread in the lungs, but were rarely observed in the small intestine. These findings suggest that each leukemia model has a unique localization of tumor cells in several affected organs, which could critically affect the disease course and the efficacy of therapeutic agents, including cellular immunotherapies.