The GS Protein-coupled A2a Adenosine Receptor Controls T Cell Help in the Germinal Center.

T follicular helper (TFH) cells have been shown to be critically required for the germinal center (GC) reaction where B cells undergo class switch recombination and clonal selection to generate high affinity neutralizing antibodies. However, detailed knowledge of the physiological cues within the GC microenvironment that regulate T cell help is limited. The cAMP-elevating, Gs protein-coupled A2a adenosine receptor (A2aR) is an evolutionarily conserved receptor that limits and redirects cellular immunity. However, the role of A2aR in humoral immunity and B cell differentiation is unknown. We hypothesized that the hypoxic microenvironment within the GC facilitates an extracellular adenosine-rich milieu, which serves to limit TFH frequency and function, and also promotes immunosuppressive T follicular regulatory cells (TFR). In support of this hypothesis, we found that following immunization, mice lacking A2aR (A2aRKO) exhibited a significant expansion of T follicular cells, as well as increases in TFH to TFR ratio, GC T cell frequency, GC B cell frequency, and class switching of GC B cells to IgG1. Transfer of CD4 T cells from A2aRKO or wild type donors into T cell-deficient hosts revealed that these increases were largely T cell-intrinsic. Finally, injection of A2aR agonist, CGS21680, following immunization suppressed T follicular differentiation, GC B cell frequency, and class switching of GC B cells to IgG1. Taken together, these observations point to a previously unappreciated role of GS protein-coupled A2aR in regulating humoral immunity, which may be pharmacologically targeted during vaccination or pathological states in which GC-derived autoantibodies contribute to the pathology.

Germinal Center Hypoxia Potentiates Immunoglobulin Class Switch Recombination.

Germinal centers (GCs) are anatomic sites where B cells undergo secondary diversification to produce high-affinity, class-switched Abs. We hypothesized that proliferating B cells in GCs create a hypoxic microenvironment that governs their further differentiation. Using molecular markers, we found GCs to be predominantly hypoxic. Compared to normoxia (21% O2), hypoxic culture conditions (1% O2) in vitro accelerated class switching and plasma cell formation and enhanced expression of GL-7 on B and CD4+ T cells. Reversal of GC hypoxia in vivo by breathing 60% O2 during immunization resulted in reduced frequencies of GC B cells, T follicular helper cells, and plasmacytes, as well as lower expression of ICOS on T follicular helper cells. Importantly, this reversal of GC hypoxia decreased Ag-specific serum IgG1 and reduced the frequency of IgG1+ B cells within the Ag-specific GC. Taken together, these observations reveal a critical role for hypoxia in GC B cell differentiation.

Novel Biodistribution of PSMA Radiotracer in the Uvula of Patients Undergoing PSMA PET/CT.

ABSTRACT: Prostate-specific membrane antigen (PSMA) PET/CT is an imaging technique that detects primary and metastatic prostate cancer and evaluates treatment effectiveness. The radioligands for PSMA PET/CT are known to have physiological off-target uptake in various tissues. These include the well-known off-target major and minor salivary glands. We report that, in addition to this location, radioligand uptake can be seen in the uvula, which we suggest is from salivary tissue in this location. PSMA uptake in the uvula is not reported in the literature and is a rare, but normal location for tracer biodistribution in some patients.

Transcriptome and Functions of Granulocytic Myeloid-Derived Suppressor Cells Determine their Association with Disease Severity of COVID-19.

COVID-19 ranges from asymptomatic in 35% of cases to severe in 20% of patients. Differences in the type and degree of inflammation appear to determine the severity of the disease. Recent reports show an increase in circulating monocytic-myeloid-derived suppressor cells (M-MDSC) in severe COVID 19, that deplete arginine but are not associated with respiratory complications. Our data shows that differences in the type, function and transcriptome of Granulocytic-MDSC (G-MDSC) may in part explain the severity COVID-19, in particular the association with pulmonary complications. Large infiltrates by Arginase 1 + G-MDSC (Arg + G-MDSC), expressing NOX-1 and NOX-2 (important for production of reactive oxygen species) were found in the lungs of patients who died from COVID-19 complications. Increased circulating Arg + G-MDSC depleted arginine, which impaired T cell receptor and endothelial cell function. Transcriptomic signatures of G-MDSC from patients with different stages of COVID-19, revealed that asymptomatic patients had increased expression of pathways and genes associated with type I interferon (IFN), while patients with severe COVID-19 had increased expression of genes associated with arginase production, and granulocyte degranulation and function. These results suggest that asymptomatic patients develop a protective type I IFN response, while patients with severe COVID-19 have an increased inflammatory response that depletes arginine, impairs T cell and endothelial cell function, and causes extensive pulmonary damage. Therefore, inhibition of arginase-1 and/or replenishment of arginine may be important in preventing/treating severe COVID-19.

Severe COVID-19 Is Characterized by an Impaired Type I Interferon Response and Elevated Levels of Arginase Producing Granulocytic Myeloid Derived Suppressor Cells.

COVID-19 ranges from asymptomatic in 35% of cases to severe in 20% of patients. Differences in the type and degree of inflammation appear to determine the severity of the disease. Recent reports show an increase in circulating monocytic-myeloid-derived suppressor cells (M-MDSC) in severe COVID 19 that deplete arginine but are not associated with respiratory complications. Our data shows that differences in the type, function and transcriptome of granulocytic-MDSC (G-MDSC) may in part explain the severity COVID-19, in particular the association with pulmonary complications. Large infiltrates by Arginase 1+ G-MDSC (Arg+G-MDSC), expressing NOX-1 and NOX-2 (important for production of reactive oxygen species) were found in the lungs of patients who died from COVID-19 complications. Increased circulating Arg+G-MDSC depleted arginine, which impaired T cell receptor and endothelial cell function. Transcriptomic signatures of G-MDSC from patients with different stages of COVID-19, revealed that asymptomatic patients had increased expression of pathways and genes associated with type I interferon (IFN), while patients with severe COVID-19 had increased expression of genes associated with arginase production, and granulocyte degranulation and function. These results suggest that asymptomatic patients develop a protective type I IFN response, while patients with severe COVID-19 have an increased inflammatory response that depletes arginine, impairs T cell and endothelial cell function, and causes extensive pulmonary damage. Therefore, inhibition of arginase-1 and/or replenishment of arginine may be important in preventing/treating severe COVID-19.

Hypoxia and hypoxia-inducible factor (HIF) downregulate antigen-presenting MHC class I molecules limiting tumor cell recognition by T cells.

Human cancers are known to downregulate Major Histocompatibility Complex (MHC) class I expression thereby escaping recognition and rejection by anti-tumor T cells. Here we report that oxygen tension in the tumor microenvironment (TME) serves as an extrinsic cue that regulates antigen presentation by MHC class I molecules. In support of this view, hypoxia is shown to negatively regulate MHC expression in a HIF-dependent manner as evidenced by (i) lower MHC expression in the hypoxic TME in vivo and in hypoxic 3-dimensional (3D) but not 2-dimensional (2D) tumor cell cultures in vitro; (ii) decreased MHC in human renal cell carcinomas with constitutive expression of HIF due to genetic loss of von Hippel-Lindau (VHL) function as compared with isogenically paired cells with restored VHL function, and iii) increased MHC in tumor cells with siRNA-mediated knockdown of HIF. In addition, hypoxia downregulated antigen presenting proteins like TAP 1/2 and LMP7 that are known to have a dominant role in surface display of peptide-MHC complexes. Corroborating oxygen-dependent regulation of MHC antigen presentation, hyperoxia (60% oxygen) transcriptionally upregulated MHC expression and increased levels of TAP2, LMP2 and 7. In conclusion, this study reveals a novel mechanism by which intra-tumoral hypoxia and HIF can potentiate immune escape. It also suggests the use of hyperoxia to improve tumor cell-based cancer vaccines and for mining novel immune epitopes. Furthermore, this study highlights the advantage of 3D cell cultures in reproducing hypoxia-dependent changes observed in the TME.

Targeted Elimination of Immunodominant B Cells Drives the Germinal Center Reaction toward Subdominant Epitopes.

Rapidly evolving pathogens such as HIV or influenza can quickly mutate their antigenic profiles, reducing the efficacy of conventional vaccines. Despite this challenge, functionally required epitopes are highly conserved among heterologous viral strains and represent a key vulnerability that could be targeted during vaccine development. As the antigenicity of these conserved epitopes is frequently subdominant, there is a critical need for innovative vaccination strategies designed to target these neutralizing epitopes. Here, we immunized mice with antigens containing discrete immunodominant and subdominant moieties and show that treatment with soluble heterologous antigen bearing only the immunodominant epitope selectively suppresses these germinal center (GC) B cells. By exploiting this intrinsic tolerance mechanism, we promote the expansion of subdominant B cells in the GC and the subsequent long-lived components of the humoral response. We propose that this strategy may be applied to elicit preferential expansion of subdominant B cells that recognize weakly immunogenic epitopes on microbial pathogens.

Fluorinated Adenosine A2A Receptor Antagonists Inspired by Preladenant as Potential Cancer Immunotherapeutics.

Antagonism of the adenosine A2A receptor on T cells blocks the hypoxia-adenosinergic pathway to promote tumor rejection. Using an in vivo immunoassay based on the Concanavalin A mouse model, a series of A2A antagonists were studied and identified preladenant as a potent lead compound for development. Molecular modeling was employed to assist drug design and subsequent synthesis of analogs and those of tozadenant, including fluorinated polyethylene glycol PEGylated derivatives. The efficacy of the analogs was evaluated using two in vitro functional bioassays, and compound 29, a fluorinated triethylene glycol derivative of preladenant, was confirmed as a potential immunotherapeutic agent.

Immunological mechanisms of the antitumor effects of supplemental oxygenation.

Antitumor T cells either avoid or are inhibited in hypoxic and extracellular adenosine-rich tumor microenvironments (TMEs) by A2A adenosine receptors. This may limit further advances in cancer immunotherapy. There is a need for readily available and safe treatments that weaken the hypoxia-A2-adenosinergic immunosuppression in the TME. Recently, we reported that respiratory hyperoxia decreases intratumoral hypoxia and concentrations of extracellular adenosine. We show that it also reverses the hypoxia-adenosinergic immunosuppression in the TME. This, in turn, stimulates (i) enhanced intratumoral infiltration and reduced inhibition of endogenously developed or adoptively transfered tumor-reactive CD8 T cells, (ii) increased proinflammatory cytokines and decreased immunosuppressive molecules, such as transforming growth factor-ß (TGF-ß), (iii) weakened immunosuppression by regulatory T cells, and (iv) improved lung tumor regression and long-term survival in mice. Respiratory hyperoxia also promoted the regression of spontaneous metastasis from orthotopically grown breast tumors. These effects are entirely T cell- and natural killer cell-dependent, thereby justifying the testing of supplemental oxygen as an immunological coadjuvant to combine with existing immunotherapies for cancer.

Systemic oxygenation weakens the hypoxia and hypoxia inducible factor 1α-dependent and extracellular adenosine-mediated tumor protection.

UNLABELLED: Intratumoral hypoxia and hypoxia inducible factor-1α (HIF-1-α)-dependent CD39/CD73 ectoenzymes may govern the accumulation of tumor-protecting extracellular adenosine and signaling through A2A adenosine receptors (A2AR) in tumor microenvironments (TME). Here, we explored the conceptually novel motivation to use supplemental oxygen as a treatment to inhibit the hypoxia/HIF-1α-CD39/CD73-driven accumulation of extracellular adenosine in the TME in order to weaken the tumor protection. We report that hyperoxic breathing (60 % O2) decreased the TME hypoxia, as well as levels of HIF-1α and downstream target proteins of HIF-1α in the TME according to proteomic studies in mice. Importantly, oxygenation also downregulated the expression of adenosine-generating ectoenzymes and significantly lowered levels of tumor-protecting extracellular adenosine in the TME. Using supplemental oxygen as a tool in studies of the TME, we also identified FHL-1 as a potentially useful marker for the conversion of hypoxic into normoxic TME. Hyperoxic breathing resulted in the upregulation of antigen-presenting MHC class I molecules on tumor cells and in the better recognition and increased susceptibility to killing by tumor-reactive cytotoxic T cells. Therapeutic breathing of 60 % oxygen resulted in the significant inhibition of growth of established B16.F10 melanoma tumors and prolonged survival of mice. Taken together, the data presented here provide proof-of principle for the therapeutic potential of systemic oxygenation to convert the hypoxic, adenosine-rich and tumor-protecting TME into a normoxic and extracellular adenosine-poor TME that, in turn, may facilitate tumor regression. We propose to explore the combination of supplemental oxygen with existing immunotherapies of cancer. KEY MESSAGES: Oxygenation decreases levels of tumor protecting hypoxia. Oxygenation decreases levels of tumor protecting extracellular adenosine. Oxygenation decreases expression of HIF-1alpha dependent tumor-protecting proteins. Oxygenation increases MHC class I expression and enables tumor regression.

Yoga and mindfulness as therapeutic interventions for stroke rehabilitation: a systematic review.

Aim. This paper reports a systematic review and critical appraisal of the evidence on the effectiveness of behavioral therapies such as yoga and mindfulness practices for stroke rehabilitation. Background. The experience of stroke can have a negative impact on both psychological and physical health and on quality of life. Yoga and relevant practices are promising therapies that have been used with patients with a variety of conditions. In order to draw conclusions on effectiveness for stroke patients, the evidence requires systematic assessment. Methods. A comprehensive search of major biomedical and complementary medicine databases was conducted. Relevant research was categorized by study type and appraised according to study design. Results. Five randomized controlled clinical trials and four single case studies were found. Additionally, one qualitative research study was identified. Studies reported positive results, including improvements in cognition, mood, and balance and reductions in stress. Modifications to different yoga practices make comparison between studies difficult, and a lack of controlled studies precludes any firm conclusions on efficacy. Conclusion. Yoga and mindfulness could be clinically valuable self-administered intervention options for stroke rehabilitation. Further research is needed to evaluate these specific practices and their suitability in stroke rehabilitation.