The A2A receptor agonist CGS 21680 has beneficial and adverse effects on disease development in a humanised mouse model of graft-versus-host disease

Ivy Leaf Dry Extract EA 575® Has an Inhibitory Effect on the Signalling Cascade of Adenosine Receptor A2B

Ivy leaf dry extract EA 575® is used to improve complaints of chronic inflammatory bronchial diseases and acute inflammation of the respiratory tract accompanied by coughing. Its mechanism of action has so far been explained by influencing β2-adrenergic signal transduction. In the present study, we investigated a possible influence on adenosine receptor A2B (A2BAR) signalling, as it has been described to play a significant and detrimental role in chronic inflammatory airway diseases. The influence of EA 575® on A2BAR signalling was assessed with measurements of dynamic mass redistribution. Subsequently, the effects on A2BAR-mediated second messenger cAMP levels, β-arrestin 2 recruitment, and cAMP response element (CRE) activation were examined using luciferase-based HEK293 reporter cell lines. Lastly, the impact on A2BAR-mediated IL-6 release in Calu-3 epithelial lung cells was investigated via the Lumit™ Immunoassay. Additionally, the adenosine receptor subtype mediating these effects was specified, and A2BAR was found to be responsible. The present study demonstrates an inhibitory influence of EA 575® on A2BAR-mediated general cellular response, cAMP levels, β-arrestin 2 recruitment, CRE activation, and IL-6 release. Since these EA 575®-mediated effects occur within a time frame of several hours of incubation, its mode of action can be described as indirect. The present data are the first to describe an inhibitory effect of EA 575® on A2BAR signalling. This may offer an explanation for the beneficial clinical effects of the extract in adjuvant asthma therapy.

Purinergic signalling in graft-versus-host disease

Allogeneic hematopoietic stem cell transplantation is used to treat blood cancers, but often results in lethal graft-versus-host disease (GVHD). GVHD is an inflammatory disorder mediated by donor leukocytes that damage host tissues. Purinergic signalling plays important roles in GVHD development in mice but studies of these pathways in human GVHD remain limited. P2X7 receptor activation by ATP on host antigen presenting cells contributes to the induction of GVHD, while activation of this receptor on regulatory T cells, myeloid-derived suppressor cells and possibly type 3 innate lymphoid cells results in their loss to promote GVHD progression. In contrast, A_2A receptor activation by adenosine on donor T cells serves to restrict GVHD development. These and other purinergic signalling molecules remain potential biomarkers and therapeutic targets in GVHD.

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.

Adenosine receptor 2a agonists target mouse CD11c+T-bet+ B cells in infection and autoimmunity

CD11c+T-bet+ B cells are recognized as an important component of humoral immunity and autoimmunity. These cells can be distinguished from other B cells by their higher expression of the adenosine receptor 2a. Here we address whether A2A receptor activation can affect CD11c+T-bet+ B cells. We show that administration of the A2A receptor agonist CGS-21680 depletes established CD11c+T-bet+ B cells in ehrlichial-infected mice, in a B cell-intrinsic manner. Agonist treatment similarly depletes CD11c+T-bet+ B cells and CD138+ B cells and reduces anti-nuclear antibodies in lupus-prone mice. Agonist treatment is also associated with reduced kidney pathology and lymphadenopathy. Moreover, A2A receptor stimulation depletes pathogenic lymphocytes and ameliorates disease even after disease onset, highlighting the therapeutic potential of this treatment. This study suggests that targeting the adenosine signaling pathway may provide a method for the treatment of lupus and other autoimmune diseases mediated by T-bet+ B cells.

Humanized Mouse Model to Study the P2X7 Receptor in Graft-Versus-Host Disease

Humanized mouse models of graft-versus-host disease (GVHD), where human immune cells are injected into immune deficient mice, are well established and provide opportunities to investigate pathways involved in GVHD development. This chapter provides an overview of human immune cell isolation, injection of these cells into immune deficient mice, monitoring of mice for signs of GVHD, and assessment of human cell engraftment using flow cytometry. Further, this chapter focuses on the P2X7 signaling pathway involved in GVHD, and describes a strategy to block the P2X7 receptor and examine the effect of this on GVHD development.

Purinergic Signalling in Allogeneic Haematopoietic Stem Cell Transplantation and Graft-versus-Host Disease

Allogeneic haematopoietic stem cell transplantation (allo-HSCT) is a curative therapy for blood cancers and other haematological disorders. However, allo-HSCT leads to graft-versus-host disease (GVHD), a severe and often lethal immunological response, in the majority of transplant recipients. Current therapies for GVHD are limited and often reduce the effectiveness of allo-HSCT. Therefore, pro- and anti-inflammatory factors contributing to disease need to be explored in order to identify new treatment targets. Purinergic signalling plays important roles in haematopoiesis, inflammation and immunity, and recent evidence suggests that it can also affect haematopoietic stem cell transplantation and GVHD development. This review provides a detailed assessment of the emerging roles of purinergic receptors, most notably P2X7, P2Y2 and A2A receptors, and ectoenzymes, CD39 and CD73, in GVHD.

Post-transplant cyclophosphamide limits reactive donor T cells and delays the development of graft-versus-host disease in a humanized mouse model

Graft-versus-host disease (GVHD) is a major complication of allogeneic haematopoietic stem cell transplantation (allo-HSCT) that develops when donor T cells in the graft become reactive against the host. Post-transplant cyclophosphamide (PTCy) is increasingly used in mismatched allo-HSCT, but how PTCy impacts donor T cells and reduces GVHD is unclear. This study aimed to determine the effect of PTCy on reactive human donor T cells and GVHD development in a preclinical humanized mouse model. Immunodeficient NOD-scid-IL2Rγ^null mice were injected intraperitoneally (i.p.) with 20 × 10⁶ human peripheral blood mononuclear cells stained with carboxyfluorescein succinimidyl ester (CFSE) (day 0). Mice were subsequently injected (i.p.) with PTCy (33 mg kg^-1 ) (PTCy-mice) or saline (saline-mice) (days 3 and 4). Mice were assessed for T-cell depletion on day 6 and monitored for GVHD for up to 10 weeks. Flow cytometric analysis of livers at day 6 revealed lower proportions of reactive (CFSE^low ) human (h) CD3⁺ T cells in PTCy-mice compared with saline-mice. Over 10 weeks, PTCy-mice showed reduced weight loss and clinical GVHD, with prolonged survival and reduced histological liver GVHD compared with saline-mice. PTCy-mice also demonstrated increased splenic hCD4⁺ :hCD8⁺ T-cell ratios and reduced splenic Tregs (hCD4⁺  hCD25⁺  hCD127^lo ) compared with saline-mice. This study demonstrates that PTCy reduces GVHD in a preclinical humanized mouse model. This corresponded to depletion of reactive human donor T cells, but fewer human Tregs.

P2X7 receptor antagonism increases regulatory T cells and reduces clinical and histological graft-versus-host disease in a humanised mouse model

Graft-versus-host disease (GVHD) is a severe inflammatory response arising from allogeneic haematopoietic stem cell transplantation. Previous studies revealed that antagonism of the P2X7 receptor with Brilliant Blue G (BBG) reduced liver GVHD but did not alter clinical GVHD in a humanised mouse model. Therefore, the present study aimed to trial a modified injection regime using more frequent dosing of BBG to improve outcomes in this model of GVHD. NOD-scid IL2Rγnull (NSG) mice were injected intraperitoneally (i.p.) with 10 × 106 human peripheral blood mononuclear cells (hPBMCs) (day 0), then daily with BBG (50 mg/kg) or saline (days 0-10). BBG significantly reduced clinical score, mortality and histological GVHD compared with saline treatment (endpoint). BBG significantly increased proportions of human regulatory T cells (Tregs) and human B cells and reduced serum human interferon-γ compared with saline treatment prior to development of clinical GVHD (day 21). To confirm the therapeutic benefit of P2X7 antagonism, NSG mice were injected i.p. with 10 × 106 hPBMCs (day 0), then daily with pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS) (300 mg/kg) or saline (days 0-10). PPADS increased human Treg proportions compared with saline treatment (day 21), but potential clinical benefits were confounded by increased weight loss with this antagonist. To investigate the role of P2X7 antagonism on Treg survival, hPBMCs were cultured in reduced serum conditions to promote cell death. BBG increased proportions of Tregs (and B cells) compared with saline under these conditions. In conclusion, P2X7 antagonism reduces clinical and histological GVHD in a humanised mouse model corresponding to an increase in human Tregs.