Development of methodology for assessing steroid-tapering in clinical trials for biologics in asthma

Background

Long-term use of oral corticosteroids (OCS) is associated with a risk of adverse events and comorbidities. As such, a goal in assessing the efficacy of biologics in severe asthma is often to monitor reduction in OCS usage. Importantly, however, OCS dose reductions must be conducted without loss of disease control.

Main body

Herein, we describe the development of OCS-sparing study methodologies for biologic therapies in patients with asthma. In particular, we focus on four randomized, placebo-controlled, parallel-group studies of varying sizes (key single-center study [n = 20], SIRIUS [n = 135], ZONDA [n = 220], VENTURE [n = 210]) and one open-label study (PONENTE [n = 598]), which assessed the effect of asthma biologics (mepolizumab, benralizumab or dupilumab) on OCS use using predefined OCS-tapering schedules. In particular, we discuss the evolution of study design elements in these studies, including patient eligibility criteria, the use of tailored OCS dose reduction schedules, monitoring of outcomes, the use of biomarkers and use of repetitive assessments of adrenal function during OCS tapering.

Conclusion

Taken together, these developments have improved OCS-sparing asthma studies in recent years and the lessons learned may help with optimization of further OCS-sparing studies, and potentially clinical practice in the future.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12931-022-01959-1.

Evaluation of sputum eosinophil count as a predictor of treatment response to mepolizumab

For patients with asthma, eosinophilic airway inflammation is associated with poor lung function, increased disease severity, reduced quality of life and increased risk of exacerbations [1, 2]. As such, several biologic therapies targeting cytokines involved in eosinophil survival and activation have been developed, with the aim of reducing eosinophilic inflammation [3]. The response to these cytokine-targeting biologics has typically been assessed by monitoring clinical outcomes. Reductions in blood eosinophils have also been monitored [2], since these cells are easily accessible and are reflective of eosinophilic airway inflammation [4, 5]. However, the utility of sputum eosinophils as a biomarker for assessing the therapeutic response to biologic therapies remains an area of ongoing scientific debate and has been largely unexplored, owing to logistical challenges associated with their collection and measurement.

In patients with severe eosinophilic asthma and sputum eosinophil counts of ≥3–<30%, sputum eosinophils may not represent a more useful biomarker than blood eosinophils for predicting clinical treatment response to mepolizumabhttps://bit.ly/3pOTw93

Eosinophils in Health and Disease: A State-of-the-Art Review

Eosinophils play a homeostatic role in the body's immune responses. These cells are involved in combating some parasitic, bacterial, and viral infections and certain cancers and have pathologic roles in diseases including asthma, chronic rhinosinusitis with nasal polyps, eosinophilic gastrointestinal disorders, and hypereosinophilic syndromes. Treatment of eosinophilic diseases has traditionally been through nonspecific eosinophil attenuation by use of glucocorticoids. However, several novel biologic therapies targeting eosinophil maturation factors, such as interleukin (IL)-5 and the IL-5 receptor or IL-4/IL-13, have recently been approved for clinical use. Despite the success of biologic therapies, some patients with eosinophilic inflammatory disease may not achieve adequate symptom control, underlining the need to further investigate the contribution of patient characteristics, such as comorbidities and other processes, in driving ongoing disease activity. New research has shown that eosinophils are also involved in several homeostatic processes, including metabolism, tissue remodeling and development, neuronal regulation, epithelial and microbiome regulation, and immunoregulation, indicating that these cells may play a crucial role in metabolic regulation and organ function in healthy humans. Consequently, further investigation is needed into the homeostatic roles of eosinophils and eosinophil-mediated processes across different tissues and their varied microenvironments. Such work may provide important insights into the role of eosinophils not only under disease conditions but also in health. This narrative review synthesizes relevant publications retrieved from PubMed informed by author expertise to provide new insights into the diverse roles of eosinophils in health and disease, with particular emphasis on the implications for current and future development of eosinophil-targeted therapies.

Response to Mepolizumab Treatment in Patients with Severe Eosinophilic Asthma and Atopic Phenotypes

Purpose

Improved understanding of characteristics that may influence treatment response across phenotypes may help guide treatment decisions.

Patients and Methods

This was a post hoc analysis of MENSA, a multicenter, randomized, double-blind, placebo-controlled trial (NCT01691521). Patients aged ≥12 years with severe eosinophilic asthma received mepolizumab (75 mg intravenously or 100 mg subcutaneously) or placebo, plus standard of care, every 4 weeks for 32 weeks. Outcomes assessed were the annualized rate of clinically significant exacerbations and change from baseline in Asthma Control Questionnaire (ACQ)-5 score. Subgroup analyses were performed by baseline blood eosinophil count (<150, ≥150–300, ≥300 cells/μL) within atopic subgroups (non-atopic [specific immunoglobulin E <0.35 kU/L], atopic [≥0.35–17.5 kU/L], strongly atopic [>17.5 kU/L]), and by house dust mite (HDM) sensitivity.

Results

Of 576 patients analyzed, 272 were non-atopic, 181 were atopic and 94 were strongly atopic; 29 had missing atopy data. In patients with blood eosinophil counts ≥300 cells/µL, mepolizumab versus placebo reduced clinically significant exacerbations by 74%, 43% and 25% in the non-atopic, atopic and strongly atopic subgroups. Similar reductions were observed in all atopic subgroups in other blood eosinophil count categories where there were sufficient patient numbers for analysis, except for non-atopic patients with baseline blood eosinophil counts of <150 cells/μL. Improvements in ACQ-5 scores of –0.75, –0.73 and –0.78 with mepolizumab versus placebo were observed in non-atopic, atopic and strongly atopic patients with blood eosinophil counts ≥300 cells/µL; consistent improvements in ACQ-5 were not observed in patients with blood eosinophil counts <150 or ≥150–300 cells/μL. Reductions in clinically significant exacerbations with mepolizumab versus placebo were also observed irrespective of sensitivity to HDMs.

Conclusion

Mepolizumab was associated with a trend for reductions in clinically significant exacerbations and improved asthma control versus placebo in patients with severe eosinophilic asthma, irrespective of atopic status or HDM sensitivity.

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Mepolizumab improves clinical outcomes in patients with severe asthma and comorbid conditions

BACKGROUND

Comorbidities can complicate the management of severe asthma; therefore, the presence of comorbid conditions or traits often need to be considered when considering treatment options for patients with severe asthma. The aim of this analysis is to investigate the efficacy of mepolizumab in patients with severe eosinophilic asthma and comorbidities.

METHODS

This was a post hoc analysis (GSK ID:209140) of data from the Phase IIb/III studies DREAM, MENSA, SIRIUS, and MUSCA. Patients aged ≥ 12 years with severe eosinophilic asthma were randomized to: mepolizumab 750, 250, or 75 mg intravenously or placebo (DREAM); mepolizumab 75 mg intravenously or 100 mg subcutaneously or placebo (MENSA); or mepolizumab 100 mg subcutaneously or placebo (SIRIUS and MUSCA) every 4 weeks for 24 weeks in SIRIUS and MUSCA, 32 weeks in MENSA or 52 weeks in DREAM. In this analysis the primary endpoint was the annual rate of clinically significant exacerbations; secondary endpoints were Asthma Control Questionnaire-5 score, St George's Respiratory Questionnaire total score, and pre-bronchodilator forced expiratory volume in 1 s at study end. Subgroups were based on comorbidities at baseline.

RESULTS

Overall, 1878 patients received placebo (n = 689) or mepolizumab (n = 1189). Across all comorbidity subgroups mepolizumab reduced the rate of clinically significant exacerbations by 44-68% versus placebo, improved Asthma Control Questionnaire-5 score by 0.27-0.59 points, and improved St George's Respiratory Questionnaire total score by 5.0-11.6 points. Pre-bronchodilator forced expiratory volume in 1 s was improved by 27.1-286.9 mL in all but one comorbidity subgroup, the diabetes mellitus subgroup.

CONCLUSIONS

Mepolizumab reduces exacerbations, and improves asthma control, health-related quality of life, and lung function in patients with severe eosinophilic asthma despite comorbid conditions, including upper respiratory conditions, psychopathologies, cardiovascular conditions, gastroesophageal reflux disease, diabetes mellitus, and obesity.

TRIAL REGISTRATION

https://clinicaltrials.gov/ DREAM, MEA112997/NCT01000506; MENSA, MEA115588/NCT01691521; SIRIUS, MEA115575/NCT01842607; MUSCA, 200862/NCT02281318.

Association of depressive symptoms with health status and markers of uncontrolled severe asthma

Background: There are limited data that describe the association between markers of asthma control and depressive symptoms in severe asthma. Objective: To evaluate the association between depressive symptoms and markers of asthma control in patients with uncontrolled severe eosinophilic asthma. Methods: Baseline data from the MENSA and SIRIUS studies (N = 681) of mepolizumab intervention in severe eosinophilic asthma was used. We analyzed the relationships between depressive symptom severity by using the Beck Depression Inventory (BDI-II) and quality of life by using the St. George's Respiratory Questionnaire (SGRQ), asthma control questionnaire-5 (ACQ-5), polypharmacy, and sleep symptoms. Results: When compared with patients with less severe depressive symptoms, patients with more severe depressive symptoms were predominantly female (81% versus 54%), had a higher mean body mass index (30.56 versus 27.67 kg/m²), were more likely to have a blood eosinophil count of ≥300 cells/uL within the previous 12 months (81% versus 68%), and to have experienced a near-fatal asthma event (16% versus 7%). The mean SGRQ score was higher in the severe BDI-II category compared with the minimal depressive symptoms category, which indicated a worse quality of life (71.6 versus 41.4, p < 0.001). Eighty-nine percent of the patients in the severe BDI-II category had poorly controlled asthma (ACQ-5 score ≥ 1.5) compared with 63% in the minimal category (p < 0.001). Conclusion: Increased severity of depressive symptoms was associated with worse respiratory-related quality of life and asthma control in the patients with severe eosinophilic asthma. These findings highlight the need for a multidimensional approach for the management of uncontrolled asthma, including timely identification of depressive symptoms. Additional research is needed to further explore the interactions between the two common conditions.Clinical trials NCT01691521 and NCT01619508, <ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="uri" xlink:href="http://www.clinicaltrials.gov">www.clinicaltrials.gov</ext-link>.

Oral corticosteroid dose changes and impact on peripheral blood eosinophil counts in patients with severe eosinophilic asthma: a post hoc analysis

BACKGROUND

An inverse relationship between oral corticosteroid (OCS) dose and peripheral blood eosinophil (PBE) count is widely recognized in patients with severe eosinophilic asthma; however, there are limited data available to quantify this relationship. This post hoc analysis of the SIRIUS study (NCT01691508) examined the impact of weekly incremental OCS dose reductions on PBE counts during the 3-8-week optimization phase of the study.

METHODS

SIRIUS was a randomized, double-blind study involving patients with severe asthma (≥12 years old), which included an initial OCS dose optimization phase prior to randomization. Regression analysis assuming a linear relationship between change in OCS dose and change in log (PBE count) during the optimization phase was used to estimate the changes in PBE count following specific decreases in OCS dose.

RESULTS

All 135 patients from the SIRIUS intent-to-treat population were included in this analysis. During the optimization period, 44% (60/135) of patients reduced their OCS dose, with an increase in geometric mean PBE count of 110 cells/μL (200 to 310 cells/μL; geometric mean ratio from beginning to end of the optimization phase: 1.52) recorded in these patients. The model estimated that reduction of daily OCS dose by 5 mg/day led to a 41% increase in PBE count (mean ratio to beginning of optimization phase: 1.41 [95% confidence interval (CI); 1.22, 1.63]).

CONCLUSION

These data confirmed and quantified the inverse association between OCS dose and PBE count. These insights will help to inform clinicians when tapering OCS doses in patients with severe eosinophilic asthma.

Role of local eosinophilopoietic processes in the development of airway eosinophilia in prednisone-dependent severe asthma

BACKGROUND

In severe asthmatics with persistent airway eosinophilia, blockade of interleukin-5 has significant steroid-sparing effects and attenuates blood and sputum eosinophilia. The contribution of local maturational processes of progenitors within the airways relative to the recruitment of mature cells from the peripheral circulation to the development of airway eosinophilia is not known. We hypothesize that local eosinophilopoiesis may be the predominant process that drives persistent airway eosinophilia and corticosteroid requirement in severe asthmatics.

OBJECTIVES

In a cross-sectional study, the number and growth potential of eosinophil-lineage-committed progenitors (EoP) were assayed in 21 severe eosinophilic asthmatics, 19 mild asthmatics, eight COPD patients and eight normal subjects. The effect of anti-IL-5 treatment on mature eosinophils and EoP numbers was made in severe eosinophilic asthmatics who participated in a randomized clinical trial of mepolizumab (substudy of a larger GSK sponsored global phase III trial, MEA115575) where subjects received mepolizumab (100 mg, n = 9) or placebo (n = 8), as six monthly subcutaneous injections.

RESULTS

Mature eosinophil and EoP numbers were significantly greater in the sputum of severe asthmatics compared with all other subject groups. In colony-forming assays, EoP from blood of severe asthmatics demonstrated a greater response to IL-5 than mild asthmatics. Treatment of severe asthmatics with mepolizumab significantly attenuated blood eosinophils and increased EoP numbers consistent with blockade of systemic eosinophilopoiesis. There was however no significant treatment effect on mature eosinophils, sputum EoP numbers or the prednisone maintenance dose.

CONCLUSIONS AND CLINICAL RELEVANCE

Patients with severe eosinophilic asthma have an exaggerated eosinophilopoeitic process in their airways. Treatment with 100 mg subcutaneous mepolizumab significantly attenuated systemic differentiation of eosinophils, but did not suppress local airway eosinophil differentiation to mature cells. Targeting IL-5-driven eosinophil differentiation locally within the lung maybe of relevance for optimal control of airway eosinophilia and asthma.

Serious Asthma Events with Fluticasone plus Salmeterol versus Fluticasone Alone

BACKGROUND

The safe and appropriate use of long-acting beta-agonists (LABAs) for the treatment of asthma has been widely debated. In two large clinical trials, investigators found a potential risk of serious asthma-related events associated with LABAs. This study was designed to evaluate the risk of administering the LABA salmeterol in combination with an inhaled glucocorticoid, fluticasone propionate.

METHODS

In this multicenter, randomized, double-blind trial, adolescent and adult patients (age, ≥12 years) with persistent asthma were assigned to receive either fluticasone with salmeterol or fluticasone alone for 26 weeks. All the patients had a history of a severe asthma exacerbation in the year before randomization but not during the previous month. Patients were excluded from the trial if they had a history of life-threatening or unstable asthma. The primary safety end point was the first serious asthma-related event (death, endotracheal intubation, or hospitalization). Noninferiority of fluticasone-salmeterol to fluticasone alone was defined as an upper boundary of the 95% confidence interval for the risk of the primary safety end point of less than 2.0. The efficacy end point was the first severe asthma exacerbation.

RESULTS

Of 11,679 patients who were enrolled, 67 had 74 serious asthma-related events, with 36 events in 34 patients in the fluticasone-salmeterol group and 38 events in 33 patients in the fluticasone-only group. The hazard ratio for a serious asthma-related event in the fluticasone-salmeterol group was 1.03 (95% confidence interval [CI], 0.64 to 1.66), and noninferiority was achieved (P=0.003). There were no asthma-related deaths; 2 patients in the fluticasone-only group underwent asthma-related intubation. The risk of a severe asthma exacerbation was 21% lower in the fluticasone-salmeterol group than in the fluticasone-only group (hazard ratio, 0.79; 95% CI, 0.70 to 0.89), with at least one severe asthma exacerbation occurring in 480 of 5834 patients (8%) in the fluticasone-salmeterol group, as compared with 597 of 5845 patients (10%) in the fluticasone-only group (P<0.001).

CONCLUSIONS

Patients who received salmeterol in a fixed-dose combination with fluticasone did not have a significantly higher risk of serious asthma-related events than did those who received fluticasone alone. Patients receiving fluticasone-salmeterol had fewer severe asthma exacerbations than did those in the fluticasone-only group. (AUSTRI ClinicalTrials.gov number, NCT01475721.).

The association between seasonal asthma exacerbations and viral respiratory infections in a pediatric population receiving inhaled corticosteroid therapy with or without long-acting beta-adrenoceptor agonist: a randomized study

BACKGROUND

A seasonal peak in asthma exacerbations in the fall has previously been reported. The association between fall exacerbations and viral respiratory tract infections (RTI) remains uncertain.

OBJECTIVE

To investigate the number of fall exacerbations and the incidence of RTIs in a pediatric asthmatic population using an at-home mucus collection methodology.

METHODS

This was a 16-week, multicenter, randomized, double-blind, parallel-group exploratory study. Children, 4-11 years of age with a clinical diagnosis of asthma requiring use of an inhaled corticosteroid, a morning peak expiratory flow ≥70% predicted and a history of ≥1 asthma exacerbation during the previous respiratory viral season were eligible for enrollment. Subjects were randomized (1:1) to receive fluticasone propionate/salmeterol (FP/SAL) 100/50 mcg or FP 100 mcg prior to starting school. Subjects collected mucus samples using an at-home kit when they experienced respiratory symptoms. Mucus samples obtained during symptomatic periods were analyzed for common respiratory viruses by multiplex polymerase chain reaction. The number of exacerbations requiring systemic corticosteroids was recorded.

RESULTS

In total, 339 (FP/SAL, n = 171; FP, n = 168) subjects were randomized and included in the intent-to-treat population; 292 (86%) completed the study. Of the 537 mucus samples collected, 64% tested positive for viruses, but only 6% of positive samples were associated with an asthma exacerbation. Exacerbations were infrequent, with only 41 subjects reporting 49 exacerbations in total. Adverse events were reported in 66% of subjects.

CONCLUSIONS

In a susceptible population, the fall asthma exacerbation rates in children were low despite frequent detection of viral RTIs. NCT01192178; GSK ID: ADA113872.

Oral glucocorticoid-sparing effect of mepolizumab in eosinophilic asthma

BACKGROUND

Many patients with severe asthma require regular treatment with oral glucocorticoids despite the use of high-dose inhaled therapy. However, the regular use of systemic glucocorticoids can result in serious and often irreversible adverse effects. Mepolizumab, a humanized monoclonal antibody that binds to and inactivates interleukin-5, has been shown to reduce asthma exacerbations in patients with severe eosinophilic asthma.

METHODS

In a randomized, double-blind trial involving 135 patients with severe eosinophilic asthma, we compared the glucocorticoid-sparing effect of mepolizumab (at a dose of 100 mg) with that of placebo administered subcutaneously every 4 weeks for 20 weeks. The primary outcome was the degree of reduction in the glucocorticoid dose (90 to 100% reduction, 75 to less than 90% reduction, 50 to less than 75% reduction, more than 0 to less than 50% reduction, or no decrease in oral glucocorticoid dose, a lack of asthma control during weeks 20 to 24, or withdrawal from treatment). Other outcomes included the rate of asthma exacerbations, asthma control, and safety.

RESULTS

The likelihood of a reduction in the glucocorticoid-dose stratum was 2.39 times greater in the mepolizumab group than in the placebo group (95% confidence interval, 1.25 to 4.56; P=0.008). The median percentage reduction from baseline in the glucocorticoid dose was 50% in the mepolizumab group, as compared with no reduction in the placebo group (P=0.007). Despite receiving a reduced glucocorticoid dose, patients in the mepolizumab group, as compared with those in the placebo group, had a relative reduction of 32% in the annualized rate of exacerbations (1.44 vs. 2.12, P=0.04) and a reduction of 0.52 points with respect to asthma symptoms (P=0.004), as measured on the Asthma Control Questionnaire 5 (in which the minimal clinically important difference is 0.5 points). The safety profile of mepolizumab was similar to that of placebo.

CONCLUSIONS

In patients requiring daily oral glucocorticoid therapy to maintain asthma control, mepolizumab had a significant glucocorticoid-sparing effect, reduced exacerbations, and improved control of asthma symptoms. (Funded by GlaxoSmithKline; SIRIUS ClinicalTrials.gov number, NCT01691508.).

Characterisation of an OCS-dependent severe asthma population treated with mepolizumab

A subpopulation of patients with asthma treated with maximal inhaled treatments is unable to maintain asthma control and requires additional therapy with oral corticosteroids (OCS); a subset of this population continues to have frequent exacerbations. Alternate treatment options are needed as daily use of OCS is associated with significant systemic adverse effects that affect many body systems and have a direct association with the dose and duration of OCS use. We compared the population demographics, medical conditions and efficacy responses of the OCS-dependent group from the DREAM study of mepolizumab with the group not managed with daily OCS.

TRIAL REGISTRATION NUMBER

NCT01000506.

Long-term treatment with fluticasone propionate/salmeterol via Diskus improves asthma control versus fluticasone propionate alone

This 52-week study was designed to assess the safety and efficacy of fluticasone propionate/salmeterol combination (FSC) 250/50 micrograms versus fluticasone propionate (FP) 250 micrograms in subjects with persistent asthma symptomatic on open-label FP 100 micrograms. The primary objective of this study was to show that FSC 250/50 micrograms was superior to FP 250 micrograms at increasing pulmonary function as measured by forced expiratory volume in 1 second over a 52-week treatment period. A secondary objective was to compare the rate of asthma attacks defined as (1) a sustained 2-day decrease in morning peak expiratory flow or increase in albuterol use for 2 consecutive days, (2) an asthma exacerbation requiring systemic corticosteroids, or (3) an unscheduled clinic or hospital visit for acute asthma symptoms. Three hundred six subjects received FSC 250/50 micrograms and 315 subjects received FP 250 micrograms. Both treatments were administered twice daily. Treatment with FSC 250/50 micrograms resulted in a significant improvement in lung function compared with FP 250 micrograms (p < 0.001). Additionally, treatment with FSC 250/50 micrograms resulted in a reduction in the rate of exacerbations of asthma (i.e., requiring systemic corticosteroids or unscheduled urgent care intervention) compared with FP 250 micrograms (0.170 versus 0.273, respectively; p = 0.017). There was no differentiation between treatments for less severe attacks of asthma. FSC 250/50 micrograms showed consistently greater improvement in lung function, symptom control, and decreased albuterol use. In addition, FSC 250/50 micrograms-treated subjects experienced fewer severe asthma exacerbations than subjects treated with FP 250 micrograms.

Controller medications and their effects on asthma exacerbations temporally associated with upper respiratory infections

BACKGROUND

Exacerbations are a major risk and a cause of asthma morbidity and healthcare utilization. Viral-induced upper respiratory tract infections are the most frequent trigger of asthma-related exacerbations. Studies have traditionally assessed exacerbations without documentation regarding exacerbation etiology. Therefore, it remains unknown whether asthma medications can alter exacerbation susceptibility based on a specific etiology.

OBJECTIVE

To examine whether treatment with inhaled corticosteroids plus long-acting beta(2)-agonists reduced the number of exacerbations associated with upper respiratory tract infections versus inhaled corticosteroids alone.

METHODS

Two large datasets comparing treatment with fluticasone propionate and fluticasone propionate plus salmeterol were analyzed, including the number of clinically reported upper respiratory tract infections, asthma-related exacerbations, and the presence of an exacerbation and concurrent report of an upper respiratory tract infection.

RESULTS

Both treatment groups had similar incidences of upper respiratory tract infections. Of those reporting an upper respiratory tract infection, statistically significantly fewer reported an asthma-related exacerbation comparing fluticasone propionate plus salmeterol with fluticasone propionate (p=0.0057).

DISCUSSION

This retrospective analysis suggests that therapy with fluticasone propionate plus salmeterol provides protection against asthma exacerbations temporally associated with upper respiratory tract infections. This retrospective analysis supports the hypothesis that specific therapeutic approaches to mitigate virus-associated exacerbations may benefit asthma care. Well-controlled prospective studies are warranted.

Dendritic cell CD83: a therapeutic target or innocent bystander?

CD83 represents an intriguing target for immunotherapy due to its preferential expression on mature DCs, the most efficient of antigen presenting cells. Based on its restricted expression pattern, structure, and the paucity of CD4+ T cells in CD83-deficient mice, multiple immunologically important functions for CD83 during immune responses have been proposed. Indeed, several studies have reported that CD83 blockade using soluble receptor constructs inhibits T cell responses in vitro and in vivo, can affect autoimmune disease development and progression, and can inhibit transplant rejection. However, others have not been able to reproduce some of these findings, and antigen presenting cells deficient in CD83 expression or expressing a mutated form of CD83 induce normal T cell responses in vitro. This review examines the controversy surrounding CD83 function, alleged CD83 ligands, the potential therapeutic utility of recombinant proteins targeting CD83 function, and the importance of soluble serum CD83. While the validity of multiple previous studies needs to be confirmed, CD83 remains a fascinating cell surface molecule with a unique pattern of expression that has multiple confirmed functions in regulating immune system development and function.

CD83 expression is a sensitive marker of activation required for B cell and CD4+ T cell longevity in vivo

CD83 is a surface marker that differentiates immature and mature human dendritic cell populations. Thymic epithelial cell expression of CD83 is also necessary for efficient CD4+ T cell development in mice. The altered phenotypes of peripheral B and CD4+ T cells, and the reduction of peripheral CD4+ T cells in CD83-/- mice, suggest additional functions for CD83. To assess this, a panel of mAbs was generated to characterize mouse CD83 expression by peripheral leukocytes. As in humans, activation of conventional and plasmacytoid murine dendritic cell subsets led to rapid up-regulation of CD83 surface expression in mice. In primary and secondary lymphoid compartments, a subset of B cells expressed low-level CD83, while CD83 was not detected on resting T cells. However, CD83 was prominently up-regulated on the majority of spleen B and T cells within hours of activation in vitro. In vivo, a low dose of hen egg lysozyme (1 microg) induced significant CD83 but not CD69 expression by Ag-specific B cells within 4 h of Ag challenge. Although B cell development appeared normal in CD83-/- mice, B and CD4+ T cell expression of CD83 was required for lymphocyte longevity in adoptive transfer experiments. Thus, the restricted expression pattern of CD83, its rapid induction following B cell and T cell activation, and its requirement for B cell and CD4+ T cell longevity demonstrate that CD83 is a functionally significant and sensitive marker of early lymphocyte activation in vivo.

CD83 influences cell-surface MHC class II expression on B cells and other antigen-presenting cells

CD83 is a member of the Ig superfamily expressed primarily by mature dendritic cells (DCs). In mice, CD83 expression by thymic stromal cells regulates CD4(+) T cell development, with CD83(-/-) mice demonstrating dramatic reductions in both thymus and peripheral CD4(+) T cells. In this study, CD83 expression was also found to affect MHC class II antigen expression within the thymus and periphery. CD83 deficiency reduced cell-surface class II antigen expression by 25-50% on splenic B cells and DCs, thymic epithelial cells and peritoneal macrophages. Reduced class II expression was a stable and intrinsic property that resulted from increased internalization of class II from the surface of CD83(-/-) B cells. Otherwise, class II antigen transcription, intracellular expression, heterodimer structure, antigen processing and antigen presentation were normal. Reduced class II antigen expression was not the primary cause of the CD83(-/-) phenotype since thymocyte and peripheral T cell development was normal in class II(+/-) mice. Comparable blocks in CD4(+) thymocyte development were also observed in CD83(-/-) and CD83(-/-)class II(+/-) littermates. TCR and CD69 expression patterns in CD83(-/-) mice further suggested that double-positive thymocytes proceed through the class II-dependent stages of positive selection in the absence of CD83. These studies further emphasize a role for CD83 in lymphocyte development and immune regulation and reveal an unexpected role for CD83 expression in influencing cell-surface MHC class II turnover.

Ag-engaged B cells express CD83, a sensitive marker for B cell activation (83.15)

CD83 is predominantly known as a surface marker that defines mature DCs. The generation of CD83−/− mice further demonstrates that thymic epithelial expression of CD83 plays a significant role in the efficient generation of CD4 single positive thymocytes. The altered phenotype and reduced number of peripheral CD4+ T cells in CD83−/− mice further suggests a role for CD83 in the peripheral lymphocyte function. With regards to the surface expression pattern of CD83, CD83 was detected in the thymic medullary compartment and was specifically detected on thymic DCs and B cells in the mouse. Peripheral CD83 expression is limited to low level expression by resting follicular B cells but is quickly upregulated and transiently expressed on nearly 90% of spleen B220+ cells within 4 h of in vivo stimulation. Additionally, the majority (&gt; 70%) of adoptively transferred B cells, expressing a BCR specific to hen egg lysozyme (HEL), expressed CD83 within 4 h of administration of a low dose of soluble HEL. At this timepoint, and low dose of antigen, less than 20% of B220+ splenocytes expressed CD69. Thus, the restricted expression pattern of CD83 and its near immediate upregulation on B cells in response to various stimuli suggest that CD83 is a sensitive, early activation marker of B cells.