Alum adjuvant is more effective than MF59 at prompting early germinal center formation in response to peptide-protein conjugates and enhancing efficacy of a vaccine against opioid use disorders.

Opioid use disorders (OUD) and fatal overdoses are a national emergency in the United States. Therapeutic vaccines offer a promising strategy to treat OUD and reduce the incidence of overdose. Immunization with opioid-based haptens conjugated to immunogenic carriers elicits opioid-specific antibodies that block opioid distribution to the brain and reduce opioid-induced behavior and toxicity in pre-clinical models. This study tested whether the efficacy of a lead oxycodone conjugate vaccine was improved by formulation in either aluminum hydroxide or the squalene-based oil-in-water emulsion MF59 adjuvant, which was recently FDA-approved for influenza vaccines in subjects 65+ years old. In adult BALB/c mice, alum formulation was more effective than MF59 at promoting the early expansion of hapten-specific B cells and the production of oxycodone-specific serum IgG antibodies, as well as blocking oxycodone distribution to the brain and oxycodone-induced motor activity. Alum was also more effective than MF59 at promoting early differentiation of peptide-specific MHCII-restricted CD4+ Tfh and GC-Tfh cells in adult C57Bl/6 mice immunized with a model peptide-protein conjugate. In contrast, alum and MF59 were equally effective in promoting hapten-specific B cells and peptide-specific MHCII-restricted CD4+ T cell differentiation in older C57Bl/6 mice. These data suggest that alum is a more effective adjuvant than MF59 for conjugate vaccines targeting synthetic small molecule haptens or peptide antigens in adult, but not aged, mice.

Adenosine 2a Receptor Signal Blockade of Murine Autoimmune Arthritis via Inhibition of Pathogenic Germinal Center-Follicular Helper T Cells.

OBJECTIVE: CD4 germinal center (GC)-follicular helper T (Tfh) cells are important in the pathogenesis of autoimmune arthritis. Previous studies have shown that adenosine 2a receptor (A2aR; Adora2a) signaling can divert CD4 T cells away from the GC-Tfh cell lineage during the primary response to foreign antigens. This study was undertaken to examine the effects of A2aR signaling on CD4 T cells during the recognition of self antigen in a murine model of autoimmune arthritis. METHODS: Wild-type and Adora2a-deficient mouse KRN T cell receptor-transgenic CD4 T cells specific for glucose-6-phosphate isomerase (GPI)/I-Ag7 were transferred into immunodeficient Tcra-/- I-Ag7 -expressing mice to induce arthritis. Recipients were then treated with either the selective A2aR agonist CGS-21680 (CGS) or phosphate buffered saline alone. Severity of disease, autoantibody titers, KRN T cell numbers and phenotype, and GPI-specific isotype class-switched plasmablasts were tracked. RESULTS: CGS treatment inhibited the development of arthritis and differentiation of KRN GC-Tfh cells, blocked the appearance of high-affinity GPI-specific and IgG1 isotype class-switched polyclonal plasmablasts, and led to a reduction in serum titers of anti-GPI IgG1. In addition, therapeutic administration of CGS after the onset of arthritis blocked further disease progression in association with reductions in the number of KRN GC-Tfh cells and anti-GPI IgG1 serum titers. CONCLUSION: Strong A2aR signaling diverts autoreactive CD4 T cell differentiation away from the GC-Tfh cell lineage, thus reducing help for the differentiation of dangerous autoreactive B cells that promote arthritis. These data in a mouse model of autoimmune arthritis suggest that A2aR and its downstream signaling pathways in CD4 T cells may be promising therapeutic targets for interfering with potentially dangerous autoreactive GC-Tfh cell differentiation.

Cutting Edge: Adenosine A2a Receptor Signals Inhibit Germinal Center T Follicular Helper Cell Differentiation during the Primary Response to Vaccination.

Adenosine A2a receptor (A2aR) signaling acts as a barrier to autoimmunity by promoting anergy, inducing regulatory T cells, and inhibiting effector T cells. However, in vivo effects of A2aR signaling on polyclonal CD4 T cells during a primary response to foreign Ag has yet to be determined. To address this problem, we immunized mice with peptide Ag 2W1S coupled to PE in CFA and treated with the selective A2aR agonist CGS-21680 (CGS). 2W1S:I-Ab-specific tetramer-binding CD4 T cells did not become anergic or differentiate into Foxp3+ regulatory T cells. Additionally, CGS treatment did not inhibit Th1 or Th17 differentiation. However, CGS did abrogate germinal center T follicular helper cells, and blunted PE-specific germinal center B cell responses. The use of A2aR-deficient CD4 T cells established that this CGS effect was T cell intrinsic. Therefore, this study has identified a unique role for A2aRs in regulating CD4 T cell differentiation during vaccination.

CD4(+) T cell anergy prevents autoimmunity and generates regulatory T cell precursors.

The role of anergy, an acquired state of T cell functional unresponsiveness, in natural peripheral tolerance remains unclear. In this study, we found that anergy was selectively induced in fetal antigen-specific maternal CD4(+) T cells during pregnancy. A naturally occurring subpopulation of anergic polyclonal CD4(+) T cells, enriched for self antigen-specific T cell antigen receptors, was also present in healthy hosts. Neuropilin-1 expression in anergic conventional CD4(+) T cells was associated with hypomethylation of genes related to thymic regulatory T cells (Treg cells), and this correlated with their ability to differentiate into Foxp3(+) Treg cells that suppressed immunopathology. Thus, our data suggest that not only is anergy induction important in preventing autoimmunity but also it generates the precursors for peripheral Treg cell differentiation.

Increased susceptibility to Salmonella infection in signal regulatory protein α-deficient mice.

Recent studies have shed light on the connection between elevated erythropoetin production/spleen erythropoiesis and increased susceptibility to Salmonella infection. In this article, we provide another mouse model, the SIRPα-deficient (Sirpα⁻/⁻) mouse, that manifests increased erythropoiesis as well as heightened susceptibility to Salmonella infection. Sirpα⁻/⁻ mice succumbed to systemic infection with attenuated Salmonella, possessing significantly higher bacterial loads in both the spleen and the liver. Moreover, Salmonella-specific Ab production and Ag-specific CD4 T cells were reduced in Sirpα⁻/⁻ mice compared with wild-type controls. To further characterize the potential mechanism underlying SIRPα-dependent Ag-specific CD4 T cell priming, we demonstrate that lack of SIRPα expression on dendritic cells results in less efficient Ag processing and presentation in vitro. Collectively, these findings demonstrate an indispensable role of SIRPα for protective immunity to Salmonella infection.