The A2A adenosine receptor (A2AR)-mediated immunosuppression is firmly implicated in the life-saving down-regulation of collateral tissue damage during the anti-pathogen immune response and in highly undesirable protection of cancerous tissues during anti-tumor immune response. Therefore, depending on specific clinical situation there is a need to either weaken or strengthen the intensity of A2AR signal. While the A2AR-mediated immunosuppression was shown to be T cell autonomous in studies of effector T cells, it was not clear how A2AR stimulation affects regulatory T cells (Treg). Here we show in parallel assays that while A2AR stimulation on T cells directly inhibits their activation, there is also indirect and longer-lasting T cell inhibitory effect through modulation of Treg. A2AR stimulation expanded CD4+ CD25hi FoxP3+ cells, which also express CD39, CD73, and CTLA-4. Treg cultured with A2AR agonist showed increased expression of CTLA-4 and stronger immunosuppressive activity. There was a significant increase of Treg cell number after A2AR stimulation. The CD4+ FoxP3+ population contained those induced from CD4+ CD25− cells, but CD4+ FoxP3+ cells predominantly derived from CD4+ CD25+ natural Treg. Thus, A2AR stimulation numerically and functionally enhanced Treg-mediated immunosuppressive mechanism. These data suggest that the A2AR-mediated stimulation of lymphocytes using A2AR agonists should be considered in protocols for ex vivo expansion of Treg before the transfer to patients in different medical applications.

ATX-101 is a safe and efficacious, first-in-class, injectable drug for SMF reduction.

Immunosuppressive signaling via the A2A adenosine receptor (A2AR) provokes a mechanism that protects inflamed tissues from excessive damage by immune cells. This mechanism is desirable not only for preventing uncontrolled tissue destruction by overactive immune responses, but also for protecting tumor tissues from antitumor immune responses. In aforementioned circumstances, T cell priming may occur in an environment containing high concentrations of extracellular adenosine. To examine qualitative changes in T cells activated in the presence of adenosine, we asked whether different functional responses of T cells are equally susceptible to A2AR agonists. In this study, we demonstrate that A2AR signaling during T cell activation strongly inhibited development of cytotoxicity and cytokine-producing activity in T cells, whereas the inhibition of T cell proliferation was only marginal. Both CD8+ and CD4+ T cells proliferated well in the presence of A2AR agonists, but their IFN-γ-producing activities were susceptible to inhibition by cAMP-elevating A2AR. Importantly, the impaired effector functions were maintained in T cells even after removal of the A2AR agonist, reflecting T cell memory of the immunoregulatory effect of adenosine. Thus, although the adenosine-rich environment may allow for the expansion of T cells, the functional activation of T cells may be critically impaired. This physiological mechanism could explain the inefficiency of antitumor T cells in the tumor microenvironment.

Activation of immune cells is under control of immunological and physiological regulatory mechanisms to ensure adequate destruction of pathogens with the minimum collateral damage to “innocent” bystander cells. The concept of physiological negative regulation of immune response has been advocated based on the finding of the critical immunoregulatory role of extracellular adenosine. Local tissue oxygen tension was proposed to function as one of such physiological regulatory mechanisms of immune responses. In the current study, we utilized in vivo marker of local tissue hypoxia pimonidazole hydrochloride (Hypoxyprobe-1) in the flowcytometric analysis of oxygen levels to which lymphocytes are exposed in vivo. The level of exposure to hypoxia in vivo was low in B cells and the levels increased in the following order: T cells < NKT cells < NK cells. The thymus was more hypoxic than the spleen and lymph nodes, suggesting the variation in the degree of oxygenation among lymphoid organs and cell types in normal mice. Based on in vitro studies, tissue hypoxia has been assumed to be suppressive to T cell activation in vivo, but there was no direct evidence demonstrating that T cells exposed to hypoxic environment in vivo are less activated. We tested whether the state of activation of T cells in vivo changes due to their exposure to hypoxic tissue microenvironments. The parallel analysis of more hypoxic and less hypoxic T cells in the same mouse revealed that the degree of T cell activation was significantly stronger in better-oxygenated T cells. These observations suggest that the extent of T cell activation in vivo is dependent on their localization and is decreased in environment with low oxygen tension.

ATX-101 (deoxycholic acid injection; Kythera Biopharmaceuticals, Inc. [an affiliate of Allergan plc, Dublin, Ireland]) was approved in 2015 in the United States (Kybella) and Canada (Belkyra) for submental fat reduction. As expected, injection-site reactions such as pain, swelling, and bruising, which were mostly mild or moderate and transient, were common adverse events (AEs) reported in clinical trials. An exploratory Phase 3b study investigating interventions for management of injection-site AEs associated with ATX-101 treatment was recently completed. Based on its results, literature review, and our clinical experiences, we have put forward considerations for management of AEs associated with ATX-101 treatment in clinical practice. Pretreatment with oral ibuprofen and/or acetaminophen an hour before treatment and preinjection with epinephrine-containing buffered lidocaine 15 minutes before treatment can help with management of pain and bruising. Cold application to the treated area before and immediately after the procedure may help to reduce pain (if local anesthetic preinjection is not performed) and swelling. Discontinuing medications/supplements that result in increased anticoagulant or antiplatelet activity 7 to 10 days before ATX-101 treatment, when possible, can reduce the risk of bruising. In summary, injection-site AEs associated with ATX-101 treatment can be effectively managed with commonly used interventions.

The γ-secretase complex is a major therapeutic target for the prevention and treatment of Alzheimer's disease. Previous studies have shown that treatment of young APP mice with specific inhibitors of γ-secretase prevented formation of new plaques. It has not yet been shown directly whether existing plaques would be affected by γ-secretase inhibitor treatment. Similarly, alterations in neuronal morphology in the immediate vicinity of plaques represent a plaque-specific neurotoxic effect. Reversal of these alterations is an important endpoint of successful therapy whether or not a treatment affects plaque size. In the present study we used longitudinal imaging in vivo with multiphoton microscopy to study the effects of the orally active γ-secretase inhibitor LY-411575 in 10-11 month old APP:PS1 mice with established amyloid pathology and neuritic abnormalities. Neurons expressed YFP allowing fluorescent detection of morphology whereas plaques were labelled with methoxy-XO4. The same identified neurites and plaques were followed in weekly imaging sessions in living mice treated daily (5 mg/kg) for 3 weeks with the compound. Although LY-411575 reduced Aβ levels in plasma and brain, it did not have an effect on the size of existing plaques. There was also no effect on the abnormal neuritic curvature near plaques, or the dystrophies in very close proximity to senile plaques. Our results suggest that therapeutics aimed at inhibition of Aβ generation are less effective for reversal of existing plaques than for prevention of new plaque formation and have no effect on the plaque-mediated neuritic abnormalities, at least under these conditions where Aβ production is suppressed but not completely blocked. Therefore, a combination therapy of Aβ suppression with agents that increase clearance of amyloid and/or prevent neurotoxicity might be needed for a more effective treatment in patients with pre-existing pathology.

Tissue hypoxia plays a key role in establishing an immunosuppressive environment in vivo by, among other effects, increasing the level of extracellular adenosine, which then signals through A2A adenosine receptor (A2AR) to elicit its immunosuppressive effect. Although the important role of the adenosine--A2AR interaction in limiting inflammation has been established, the current study revisited this issue by asking whether hypoxia can also exert its T-cell inhibitory effects even without A2AR. A similar degree of hypoxia-triggered inhibition was observed in wild-type and A2AR-deficient T cells both in vitro and, after exposure of mice to a hypoxic atmosphere, in vivo. This A2AR-independent hypoxic T-cell suppression was qualitatively and mechanistically different from immunosuppression by A2AR stimulation. The A2AR-independent hypoxic immunosuppression strongly reduced T-cell proliferation, while IFN-γ-producing activity was more susceptible to the A2AR-dependent inhibition. In contrast to the sustained functional impairment after A2AR-mediated T-cell inhibition, the A2AR-independent inhibition under hypoxia was short lived, as evidenced by the quick recovery of IFN-γ-producing activity upon re-stimulation. These data support the view that T-cell inhibition by hypoxia can be mediated by multiple mechanisms and that both A2AR and key molecules in the A2AR-independent T-cell inhibition should be targeted to overcome the hypoxia-related immunosuppression in infected tissues and tumors.

Results from this study support the safety of ATX-101 for SMF reduction, and demonstrate that pain and bruising associated with ATX-101 treatment can be mitigated by a series of simple measures.