Tezepelumab decreases airway epithelial IL-33 and T2-inflammation in response to viral stimulation in patients with asthma

BACKGROUND

Respiratory virus infections are main triggers of asthma exacerbations. Tezepelumab, an anti-TSLP mAb, reduces exacerbations in patients with asthma, but the effect of blocking TSLP on host epithelial resistance and tolerance to virus infection is not known.

AIM

To examine effects of blocking TSLP in patients with asthma on host resistance (IFNβ, IFNλ, and viral load) and on the airway epithelial inflammatory response to viral challenge.

METHODS

Bronchoalveolar lavage fluid (BALF, n = 39) and bronchial epithelial cells (BECs) were obtained from patients with uncontrolled asthma before and after 12 weeks of tezepelumab treatment (n = 13) or placebo (n = 13). BECs were cultured in vitro and exposed to the viral infection mimic poly(I:C) or infected by rhinovirus (RV). Alarmins, T2- and pro-inflammatory cytokines, IFNβ IFNλ, and viral load were analyzed by RT-qPCR and multiplex ELISA before and after stimulation.

RESULTS

IL-33 expression in unstimulated BECs and IL-33 protein levels in BALF were reduced after 12 weeks of tezepelumab. Further, IL-33 gene and protein levels decreased in BECs challenged with poly(I:C) after tezepelumab whereas TSLP gene expression remained unaffected. Poly(I:C)-induced IL-4, IL-13, and IL-17A release from BECs was also reduced with tezepelumab whereas IFNβ and IFNλ expression and viral load were unchanged.

CONCLUSION

Blocking TSLP with tezepelumab in vivo in asthma reduced the airway epithelial inflammatory response including IL-33 and T2 cytokines to viral challenge without affecting anti-viral host resistance. Our results suggest that blocking TSLP stabilizes the bronchial epithelial immune response to respiratory viruses.

A GIPR antagonist conjugated to GLP-1 analogues promotes weight loss with improved metabolic parameters in preclinical and phase 1 settings

Obesity is a major public health crisis. Multi-specific peptides have emerged as promising therapeutic strategies for clinical weight loss. Glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) are endogenous incretins that regulate weight through their receptors (R). AMG 133 (maridebart cafraglutide) is a bispecific molecule engineered by conjugating a fully human monoclonal anti-human GIPR antagonist antibody to two GLP-1 analogue agonist peptides using amino acid linkers. Here, we confirm the GIPR antagonist and GLP-1R agonist activities in cell-based systems and report the ability of AMG 133 to reduce body weight and improve metabolic markers in male obese mice and cynomolgus monkeys. In a phase 1, randomized, double-blind, placebo-controlled clinical study in participants with obesity ( NCT04478708 ), AMG 133 had an acceptable safety and tolerability profile along with pronounced dose-dependent weight loss. In the multiple ascending dose cohorts, weight loss was maintained for up to 150 days after the last dose. These findings support continued clinical evaluation of AMG 133.

Tezepelumab and Mucus Plugs in Patients with Moderate-to-Severe Asthma

Tezepelumab and Mucus Plugs in Patients with AsthmaMucus plugs in airways of asthma patients are associated with airway obstruction and the activity of inflammatory cytokines. This article reports prespecified and post hoc analyses of the effect of tezepelumab treatment on mucus plugs identified by computed tomography imaging in patients with moderate-to-severe asthma. At baseline, mucus plug scores correlated positively with levels of inflammatory biomarkers and negatively with lung function measures. Patients treated with tezepelumab had resolution of more mucus plugs than patients taking placebo.

Efficacy of Tezepelumab in Severe, Uncontrolled Asthma: Pooled Analysis of the PATHWAY and NAVIGATOR Clinical Trials

Rationale: Tezepelumab reduced exacerbations in patients with severe, uncontrolled asthma across a range of baseline blood eosinophil counts and fractional exhaled nitric oxide levels, and irrespective of allergy status, in the phase 2b PATHWAY (Study to Evaluate the Efficacy and Safety of MEDI9929 [AMG 157] in Adult Subjects With Inadequately Controlled, Severe Asthma; NCT02054130) and phase 3 NAVIGATOR (Study to Evaluate Tezepelumab in Adults & Adolescents With Severe Uncontrolled Asthma; NCT03347279) trials. Objectives: To examine the efficacy and safety of tezepelumab in additional clinically relevant subgroups using pooled data from PATHWAY and NAVIGATOR. Methods: PATHWAY and NAVIGATOR were randomized, double-blind, placebo-controlled trials with similar designs. This pooled analysis included patients with severe, uncontrolled asthma (PATHWAY, 18-75 years old; NAVIGATOR, 12-80 years old) who received tezepelumab 210 mg or placebo subcutaneously every 4 weeks for 52 weeks. The annualized asthma exacerbation rate over 52 weeks and secondary outcomes were calculated in the overall population and in subgroups defined by inflammatory biomarker levels or clinical characteristics. Measurements and Main Results: Overall, 1,334 patients were included (tezepelumab, n = 665; placebo, n = 669). Tezepelumab reduced the annualized asthma exacerbation rate versus placebo by 60% (rate ratio, 0.40 [95% confidence interval, 0.34-0.48]) in the overall population, and clinically meaningful reductions in exacerbations were observed in tezepelumab-treated patients with type 2-high and type 2-low disease by multiple definitions. Tezepelumab reduced exacerbation-related hospitalization or emergency department visits and improved secondary outcomes compared with placebo overall and across subgroups. The incidence of adverse events was similar between treatment groups. Conclusions: Tezepelumab resulted in clinically meaningful reductions in exacerbations and improvements in other outcomes in patients with severe, uncontrolled asthma, across clinically relevant subgroups. Clinical trials registered with www.clinicaltrials.gov (NCT02054130 [PATHWAY], NCT03347279 [NAVIGATOR]).

Pharmacokinetics and Pharmacokinetic/Pharmacodynamic Properties of Rozibafusp alfa, a Bispecific Inhibitor of BAFF and ICOSL: Analyses of Phase 1 Clinical Trials

Rozibafusp alfa (AMG 570) is a first-in-class bispecific IgG2-peptide fusion designed to inhibit inducible T-cell costimulator ligand (ICOSL) and B-cell activating factor (BAFF). The pharmacokinetics (PK) and pharmacodynamics (PD) of rozibafusp alfa were investigated in two randomized, placebo-controlled clinical studies: a phase 1a single ascending-dose study (7-700 mg subcutaneously [SC]) in healthy subjects and a phase 1b multiple ascending-dose study (70-420 mg subcutaneously every 2 weeks [Q2W]) in patients with rheumatoid arthritis. Rozibafusp alfa exhibited nonlinear PK and dose-related and reversible dual-target engagement. Maximal reduction of naïve B cells from baseline (>40%), reflective of BAFF inhibition, was achieved with rozibafusp alfa exposure (AUC_inf and AUC_tau ) above 51 and 57 days•μg/mL for the single-dose (≥70 mg) and multiple-dose studies (≥70 mg Q2W), respectively. ICOSL receptor occupancy (RO) on circulating B cells, a surrogate PD endpoint for ICOSL inhibition, was directly related to drug concentration. PK/PD analysis showed >90% RO at rozibafusp alfa ≥22.2 μg/mL (≥420-mg single dose or ≥210 mg Q2W multiple dose), with saturation occurring at higher drug concentrations. These results informed the design and dose selection of a phase 2b study assessing the safety and efficacy of rozibafusp alfa in patients with active systemic lupus erythematosus.

Safety and Biological Activity of Rozibafusp alfa, a Bispecific Inhibitor of Inducible Costimulator Ligand and B Cell Activating Factor, in Patients With Rheumatoid Arthritis: Results of a Phase 1b, Randomized, Double‐Blind , Placebo‐Controlled , Multiple Ascending Dose Study

Objective

To assess the safety and biological activity of rozibafusp alfa, a first‐in‐class bispecific antibody–peptide conjugate targeting inducible costimulator ligand (ICOSL) and B cell activating factor (BAFF), in patients with rheumatoid arthritis (RA).

Methods

This phase 1b, double‐blind, placebo‐controlled, multiple ascending dose study included 34 patients (18–75 years; 82.4% female) with active RA (Disease Activity Score of 28 joints–C‐reactive protein [DAS28‐CRP] >2.6, on stable methotrexate) randomized 3:1 to receive rozibafusp alfa (n = 26, in four ascending dose cohorts of 70, 140, 210, and 420 mg) or a placebo (n = 8) subcutaneously once every 2 weeks for 10 weeks (six total doses), with 24 weeks of follow‐up. The primary end point was the incidence of treatment‐emergent adverse events (TEAEs). Additional assessments included serum pharmacokinetics (PK), pharmacodynamics (PD), immunogenicity, and RA disease activity measures (DAS28‐CRP, Patient Global Assessment of Disease, and Physician Global Assessment of Disease).

Results

TEAEs occurred in 96.2% and 87.5% of patients receiving rozibafusp alfa and the placebo, respectively; most were mild or moderate in severity. Two (7.7%) patients treated with rozibafusp alfa reported serious TEAEs; none were considered treatment related. Multiple doses of rozibafusp alfa showed nonlinear PK (mean t_1/2 = 4.6–9.5 days) and dose‐related, reversible PD (>90% ICOSL receptor occupancy in 210‐ and 420‐mg cohorts; reduction in naïve B cells and increase in memory B cells in all cohorts). Five (20%) patients developed anti–rozibafusp alfa antibodies, with no apparent impact on safety. RA disease activity showed greater numerical improvement from baseline with rozibafusp alfa versus the placebo in the 210‐ and 420‐mg cohorts.

Conclusion

Multiple ascending doses of rozibafusp alfa were well tolerated, with PK and PD reflecting dual ICOSL and BAFF blockade. Findings support further clinical evaluation of rozibafusp alfa in autoimmune disease.

Targeting TSLP in Asthma

Thymic stromal lymphopoietin (TSLP) is an epithelial cell-derived cytokine implicated in the initiation and persistence of inflammatory pathways in asthma. Released in response to a range of epithelial insults (eg, allergens, viruses, bacteria, pollutants, and smoke), TSLP initiates multiple downstream innate and adaptive immune responses involved in asthma inflammation. Inhibition of TSLP is postulated to represent a novel approach to treating the diverse phenotypes and endotypes of asthma. Tezepelumab, the TSLP inhibitor farthest along in clinical development, is a human monoclonal antibody (IgG2λ) that binds specifically to TSLP, preventing interactions with its heterodimeric receptor. Results of recently published phase 2 and 3 studies, reviewed in this article, provide evidence of the safety and efficacy of tezepelumab that builds on initial findings. Tezepelumab is safe, well tolerated, and provides clinically meaningful improvements in asthma control, including reduced incidence of exacerbations and hospitalizations in patients with severe asthma. Clinical benefits were associated with reductions in levels of a broad spectrum of cytokines (eg, interleukin [IL]-5, IL-13) and baseline biomarkers (eg, blood eosinophils, immunoglobulin [Ig]E, fractional exhaled nitric oxide [FeNO]) and were observed across a range of severe asthma phenotypes (ie, eosinophilic and non-eosinophilic). These data strengthen the notion that anti-TSLP elicits broad inhibitory effects on pathways that are key to asthma inflammation rather than on narrower inhibition of individual downstream factors. This review presents the rationale for targeting TSLP to treat asthma, as well as the clinical effects of TSLP blockade on asthma outcomes, biomarkers of disease activity, airway inflammation, lung physiology, and patient symptoms.

Baseline type 2 biomarker levels and response to tezepelumab in severe asthma

Background

Tezepelumab is a human monoclonal antibody that blocks activity of thymic stromal lymphopoietin (TSLP). In the phase IIb PATHWAY study (NCT02054130), tezepelumab significantly reduced annualized asthma exacerbation rates (AAERs) versus placebo in adults with severe, uncontrolled asthma. We evaluated the effects of tezepelumab in reducing type 2 (T2) inflammatory biomarker levels in the PATHWAY population, and the relationship between baseline T2 biomarker levels and AAER.

Methods

Adults with severe, uncontrolled asthma (n = 550) were randomized to tezepelumab (70 mg or 210 mg every 4 weeks, or 280 mg every 2 weeks) or placebo for 52 weeks. Blood eosinophil count, fractional exhaled nitric oxide (FeNO), and serum total immunoglobulin (Ig)E, interleukin (IL)‐5, IL‐13, periostin, thymus and activation‐regulated chemokine (TARC), and TSLP were measured at baseline and over 52 weeks. AAERs were analyzed by baseline threshold (high/low) biomarker levels.

Results

Positive correlations were observed between T2 inflammatory biomarkers (blood eosinophil count, FeNO, IL‐5, IL‐13 and periostin) at baseline. At Week 52, treatment with tezepelumab 210 mg reduced all biomarker levels measured from baseline versus placebo. Exacerbations were reduced by 55–83% in the pooled tezepelumab cohort versus placebo, irrespective of baseline blood eosinophil count, FeNO, or serum total IgE, IL‐5, IL‐13, periostin, TARC, or TSLP, when these biomarkers were assessed individually.

Conclusion

At baseline, positive correlations between specific T2 inflammatory biomarkers were observed. Tezepelumab reduced multiple T2 inflammatory biomarkers, which indicates decreased airway inflammation, and reduced exacerbations irrespective of baseline T2 biomarker profiles in patients with severe asthma.

Immune Complex Formation Is Associated With Loss of Tolerance and an Antibody Response to Both Drug and Target

AMG 966 is a bi-specific, heteroimmunoglobulin molecule that binds both tumor necrosis factor alpha (TNFα) and TNF-like ligand 1A (TL1A). In a first-in-human clinical study in healthy volunteers, AMG 966 elicited anti-drug antibodies (ADA) in 53 of 54 subjects (98.1%), despite a paucity of T cell epitopes observed in T cell assays. ADA were neutralizing and bound to all domains of AMG 966. Development of ADA correlated with loss of exposure. In vitro studies demonstrated that at certain drug-to-target ratios, AMG 966 forms large immune complexes with TNFα and TL1A, partially restoring the ability of the aglycosylated Fc domain to bind FcγRIa and FcγRIIa, leading to the formation of ADA. In addition to ADA against AMG 966, antibodies to endogenous TNFα were also detected in the sera of subjects dosed with AMG 966. This suggests that the formation of immune complexes between a therapeutic and target can cause loss of tolerance and elicit an antibody response against the target.

Efficacy of Tezepelumab in Patients with Severe, Uncontrolled Asthma and Perennial Allergy

BACKGROUND

Tezepelumab is an anti-thymic stromal lymphopoietin monoclonal antibody. In the PATHWAY phase IIb study (NCT02054130), tezepelumab significantly reduced annualized asthma exacerbation rates (AAERs) versus placebo in adults with severe, uncontrolled asthma.

OBJECTIVE

This post hoc analysis assessed the efficacy of tezepelumab in PATHWAY participants with perennial allergy.

METHODS

Adults (N=550) with severe, uncontrolled asthma were randomized to receive tezepelumab (70 mg or 210 mg every 4 weeks or 280 mg every 2 weeks) or placebo, for 52 weeks. The AAER over 52 weeks was analyzed in patients grouped by sensitivity to perennial aeroallergens and by eligibility for omalizumab treatment according to the US or EU prescribing information. Change from baseline to week 52 in pre-bronchodilator forced expiratory volume in 1 second (FEV₁) and type 2 (T2) biomarkers were assessed in the perennial allergy subgroups.

RESULTS

Across doses, tezepelumab reduced the AAER versus placebo by 66-78% in patients with perennial allergy (n=254) and 67-71% in patients without perennial allergy (n=261). Tezepelumab improved pre-bronchodilator FEV₁ and reduced blood eosinophil counts and fractional exhaled nitric oxide levels over 52 weeks, irrespective of perennial allergy status. Tezepelumab reduced the AAER versus placebo by 61-82% in omalizumab-eligible patients (US, n=159; EU, n=101) and 63-70% in omalizumab-ineligible patients (US, n=372; EU, n=440), respectively.

CONCLUSIONS

Treatment with tezepelumab reduced exacerbations, improved lung function and reduced T2 biomarkers versus placebo in patients with severe, uncontrolled asthma with or without perennial allergy, further supporting its efficacy in a broad population of patients with severe, uncontrolled asthma.

Effect of tezepelumab on airway inflammatory cells, remodelling, and hyperresponsiveness in patients with moderate-to-severe uncontrolled asthma (CASCADE): a double-blind, randomised, placebo-controlled, phase 2 trial

BACKGROUND

Tezepelumab is a human monoclonal antibody that blocks the activity of thymic stromal lymphopoietin (TSLP), an epithelial cell-derived cytokine. In phase 2b and 3 studies, tezepelumab significantly reduced exacerbations versus placebo in patients with severe uncontrolled asthma, irrespective of baseline levels of type 2 inflammatory biomarkers. We investigated the mechanism of action of tezepelumab by assessing its effects on airway inflammatory cells, airway remodelling, and airway hyperresponsiveness.

METHODS

CASCADE was an exploratory, double-blind, randomised, placebo-controlled, parallel-group, phase 2 study done in 27 medical centres in Canada, Denmark, Germany, the UK, and the USA. Adults aged 18-75 years with uncontrolled, moderate-to-severe asthma were randomly assigned (1:1) to receive tezepelumab 210 mg or placebo administered subcutaneously every 4 weeks for a planned 28 weeks, extended to up to 52 weeks if COVID-19-related disruption delayed participants' end-of-treatment assessments. Randomisation was balanced and stratified by blood eosinophil count. The primary endpoint was the change from baseline to the end of treatment in the number of airway submucosal inflammatory cells in bronchoscopic biopsy samples. Eosinophils, neutrophils, CD3⁺ T cells, CD4⁺ T cells, tryptase⁺ mast cells, and chymase⁺ mast cells were evaluated separately. This endpoint was also assessed in subgroups according to baseline type 2 inflammatory biomarker levels, including blood eosinophil count. Airway remodelling was assessed via the secondary endpoints of change from baseline in reticular basement membrane thickness and epithelial integrity (proportions of denuded, damaged, and intact epithelium). Exploratory outcomes included airway hyperresponsiveness to mannitol. All participants who completed at least 20 weeks of study treatment, had an end-of-treatment visit up to 8 weeks after the last dose of study drug, and had evaluable baseline and end-of-treatment bronchoscopies were included in the primary efficacy analysis. All participants who received at least one dose of study drug were included in the safety analyses. This study is registered with ClinicalTrials.gov, NCT03688074.

FINDINGS

Between Nov 2, 2018, and Nov 16, 2020, 250 patients were enrolled, 116 of whom were randomly assigned (59 to tezepelumab, 57 to placebo). 48 in the tezepelumab group and 51 in the placebo group completed the study and were assessed for the primary endpoint. Treatment with tezepelumab resulted in a nominally significantly greater reduction from baseline to the end of treatment in airway submucosal eosinophils versus placebo (ratio of geometric least-squares means 0·15 [95% CI 0·05-0·41]; nominal p<0·0010), with the difference seen across all baseline biomarker subgroups. There were no significant differences between treatment groups in the other cell types evaluated (ratio of geometric least-squares means: neutrophils 1·36 [95% CI 0·94-1·97]; CD3⁺ T cells 1·12 [0·86-1·46]; CD4⁺ T cells 1·18 [0·90-1·55]; tryptase⁺ mast cells 0·83 [0·61-1·15]; chymase⁺ mast cells 1·19 [0·67-2·10]; all p>0·10). In assessment of secondary endpoints, there were no significant differences between treatment groups in reticular basement membrane thickness and epithelial integrity. In an exploratory analysis, the reduction in airway hyperresponsiveness to mannitol was significantly greater with tezepelumab versus placebo (least-squares mean change from baseline in interpolated or extrapolated provoking dose of mannitol required to induce ≥15% reduction in FEV₁ from baseline: tezepelumab 197·4 mg [95% CI 107·9 to 286·9]; placebo 58·6 mg [-30·1 to 147·33]; difference 138·8 [14·2 to 263·3], nominal p=0·030). Adverse events were reported in 53 (90%) patients in the tezepelumab group and 51 (90%) patients in the placebo group, and there were no safety findings of concern.

INTERPRETATION

The improvements in asthma clinical outcomes observed in previous studies with tezepelumab are probably driven, at least in part, by reductions in eosinophilic airway inflammation, as shown here by reduced airway eosinophil counts regardless of baseline blood eosinophil count. Tezepelumab also reduced airway hyperresponsiveness to mannitol, indicating that TSLP blockade might have additional benefits in asthma beyond reducing type 2 airway inflammation.

FUNDING

AstraZeneca and Amgen.

Efficacy of Tezepelumab in Patients with Severe, Uncontrolled Asthma with and without Nasal Polyposis: A Post Hoc Analysis of the Phase 2b PATHWAY Study

Background

Tezepelumab is a human monoclonal antibody that blocks thymic stromal lymphopoietin, an epithelial cytokine implicated in asthma pathogenesis, from binding to its heterodimeric receptor. In the phase 2b PATHWAY study, tezepelumab significantly reduced annualized asthma exacerbation rates (AAERs) versus placebo, irrespective of baseline disease characteristics, and improved lung function and symptom control, in adults with severe, uncontrolled asthma. This post hoc analysis assessed the efficacy of tezepelumab in adults with severe, uncontrolled asthma with and without nasal polyposis (NP).

Methods

In this post hoc analysis of the PATHWAY study (NCT02054130), participants (N=550) were randomized 1:1:1:1 to receive subcutaneous tezepelumab 70 mg every 4 weeks (Q4W), 210 mg Q4W or 280 mg every 2 weeks (Q2W), or placebo Q2W, for 52 weeks. The AAER over 52 weeks and the change from baseline to week 52 in blood eosinophil count, fractional exhaled nitric oxide (FeNO) levels and serum levels of interleukin (IL)-5 and IL-13 with tezepelumab 210 mg (the phase 3 dose) and placebo were analyzed in patients grouped by self-reported presence (NP+) or absence (NP-) of NP at screening.

Results

At baseline, NP+ patients had higher blood eosinophil counts, higher FeNO levels and higher serum IL-5 and IL-13 levels than NP- patients. Tezepelumab 210 mg reduced the AAER versus placebo to a similar extent in both NP+ and NP- patients (NP+, 75% [95% confidence interval (CI): 15, 93], n=23; NP-, 73% [95% CI: 47, 86], n=112). Patients treated with tezepelumab 210 mg demonstrated greater reductions in blood eosinophil count and levels of FeNO, IL-5 and IL-13 than placebo-treated patients, irrespective of NP status.

Discussion

Tezepelumab reduced exacerbations and reduced type 2 inflammatory biomarkers in patients with and those without NP, supporting its efficacy in a broad population of patients with severe asthma.

Pharmacokinetic and Pharmacodynamic Modeling of Tezepelumab to Guide Phase 3 Dose Selection for Patients With Severe Asthma

Tezepelumab is a human monoclonal antibody that blocks thymic stromal lymphopoietin, an epithelial cytokine involved in asthma pathogenesis. In the phase 2b PATHWAY study (ClinicalTrials.gov identifier: NCT02054130), tezepelumab significantly reduced exacerbations in adults with severe, uncontrolled asthma. We used pharmacokinetic (PK) and pharmacodynamic (PD) modeling to guide tezepelumab dose selection for phase 3 trials in patients with severe asthma. PK data from 7 clinical studies were used to develop a population PK model. Population PK-PD models were developed to characterize the relationship between tezepelumab PK and asthma exacerbation rate (AER) and fractional exhaled nitric oxide (FeNO) levels (using phase 2b PD data only). Tezepelumab PK were well described by a 2-compartment model with first-order absorption; PK parameter estimates were consistent with those of other immunoglobulin G2 antibodies. PK-PD models predicted that subcutaneous dosing at 210 mg every 4 weeks was associated with ≈90% of the maximum drug effect of tezepelumab on AER and FeNO; further dose increases were not expected to result in additional, clinically meaningful treatment benefit. No clinically significant covariates of treatment effects on AER and FeNO were identified. Population PK simulations, exposure-response relationships and safety profiles of tezepelumab at doses up to 280 mg every 2 weeks suggested that no dose adjustment based on body weight or for adolescents was required. These results support the selection of 210 mg every 4 weeks subcutaneously as the dose for phase 3 studies of tezepelumab in adults and adolescents with severe asthma.

Tezepelumab Reduces Exacerbations Across All Seasons in Patients with Severe, Uncontrolled Asthma: A Post Hoc Analysis of the PATHWAY Phase 2b Study

Introduction

Tezepelumab is a human monoclonal antibody that blocks thymic stromal lymphopoietin (TSLP), an epithelial cytokine implicated in airway inflammation in asthma, from binding to its heterodimeric receptor. In the PATHWAY phase 2b study, tezepelumab significantly reduced exacerbation rates compared with placebo in adults with severe, uncontrolled asthma, irrespective of baseline disease characteristics.

Objective

To evaluate the effect of tezepelumab on asthma exacerbations on a seasonal basis.

Methods

This was a post hoc analysis of the PATHWAY study (NCT02054130). Adults (N=550) with severe, uncontrolled asthma were randomized 1:1:1:1 to receive subcutaneous tezepelumab 70 mg every 4 weeks (Q4W), 210 mg Q4W or 280 mg every 2 weeks (Q2W), or placebo Q2W, for 52 weeks. The annualized asthma exacerbation rate (AAER), total number of days with an exacerbation, proportion of patients with at least one exacerbation or 0, 1 or ≥2 exacerbations, and proportion of patients experiencing an exacerbation per day were evaluated by season and over the year, by treatment in the overall study population and in subgroups according to baseline blood eosinophil count (≥300 cells/µL or <300 cells/µL) or atopic asthma status (fluoro-enzyme immunoassay [FEIA]+ or FEIA-).

Results

Seasonal variations in exacerbation rates were found, with peaks observed in fall and winter, and greater variations in patients with high blood eosinophil counts (≥300 cells/µL). Tezepelumab treatment consistently reduced exacerbation rates across all seasons compared with placebo. Furthermore, there was a trend, which was not significant, toward a reduction in the total number of days with exacerbations and in the proportion of patients with exacerbations during each season in patients treated with tezepelumab compared with those who received placebo, irrespective of blood eosinophil count or atopic asthma status.

Conclusion

Tezepelumab reduced exacerbations across all seasons, irrespective of evaluated baseline disease characteristics. These data support the efficacy of tezepelumab in a broad population of patients with severe, uncontrolled asthma.

Tezepelumab improves patient-reported outcomes in patients with severe, uncontrolled asthma in PATHWAY

BACKGROUND

Patients with severe, uncontrolled asthma experience frequent exacerbations and hospitalization, leading to poor health-related quality of life. In the phase 2b PATHWAY study (NCT02054130), tezepelumab reduced exacerbations by up to 71% and improved lung function, asthma control, and health-related quality of life vs placebo.

OBJECTIVE

This analysis further assessed the impact of tezepelumab on patient-reported outcomes (PROs) in PATHWAY.

METHODS

Adults with severe, uncontrolled asthma were randomized to subcutaneous tezepelumab (70 mg every 4 weeks, 210 mg every 4 weeks, or 280 mg every 2 weeks) or placebo for 52 weeks. PROs were assessed using the asthma control questionnaire-6 (ACQ-6) and the asthma quality of life questionnaire (standardized) for patients aged 12 years or older (AQLQ[S]+12). The proportions of responders (defined by improvements of ≥0.5 in ACQ-6 or AQLQ(S)+12 scores) and patients whose asthma was well-controlled, partially-controlled, or uncontrolled in the tezepelumab and placebo groups were identified. The Asthma Daily Diary questionnaire was used to assess changes in overall symptom severity.

RESULTS

Overall, 550 patients were randomized. Up to 82% and 77% of tezepelumab-treated patients were ACQ-6 and AQLQ(S)+12 responders, respectively, compared with 70% and 64% of placebo-treated patients, respectively. The proportions of patients with well-controlled or partially-controlled asthma were higher in the tezepelumab-treated group than in the placebo group. In addition, tezepelumab improved the overall symptom severity.

CONCLUSION

Tezepelumab treatment improved PROs vs placebo, as indicated by the higher proportion of ACQ-6 and AQLQ(S)+12 responders and improvements in symptom severity in the tezepelumab dose groups. These data further support the benefits of tezepelumab in patients with severe, uncontrolled asthma.

CASCADE: a phase 2, randomized, double-blind, placebo-controlled, parallel-group trial to evaluate the effect of tezepelumab on airway inflammation in patients with uncontrolled asthma

BACKGROUND

Patients with severe, uncontrolled asthma, particularly those with a non-eosinophilic phenotype, have a great unmet need for new treatments that act on a broad range of inflammatory pathways in the airway. Tezepelumab is a human monoclonal antibody that blocks the activity of thymic stromal lymphopoietin, an epithelial cytokine. In the PATHWAY phase 2b study (NCT02054130), tezepelumab reduced exacerbations by up to 71% in adults with severe, uncontrolled asthma, irrespective of baseline eosinophilic inflammatory status. This article reports the design and objectives of the phase 2 CASCADE study.

METHODS

CASCADE is an ongoing exploratory, phase 2, randomized, double-blind, placebo-controlled, parallel-group study aiming to assess the anti-inflammatory effects of tezepelumab 210 mg administered subcutaneously every 4 weeks for 28 weeks in adults aged 18-75 years with uncontrolled, moderate-to-severe asthma. The primary endpoint is the change from baseline to week 28 in airway submucosal inflammatory cells (eosinophils, neutrophils, T cells and mast cells) from bronchoscopic biopsies. Epithelial molecular phenotyping, comprising the three-gene-mean technique, will be used to assess participants' type 2 (T2) status to enable evaluation of the anti-inflammatory effect of tezepelumab across the continuum of T2 activation. Other exploratory analyses include assessments of the impact of tezepelumab on airway remodelling, including reticular basement membrane thickening and airway epithelial integrity. At the onset of the COVID-19 pandemic, the protocol was amended to address the possibility that site visits would be limited. The amendment allowed for: at-home dosing of study drug by a healthcare professional, extension of the treatment period by up to 6 months so patients are able to attend an onsite visit to undergo the end-of-treatment bronchoscopy, and replacement of final follow-up visits with a virtual or telephone visit.

DISCUSSION

CASCADE aims to determine the mechanisms by which tezepelumab improves clinical asthma outcomes by evaluating the effect of tezepelumab on airway inflammatory cells and remodelling in patients with moderate-to-severe, uncontrolled asthma. An important aspect of this study is the evaluation of the anti-inflammatory effect of tezepelumab across patients with differing levels of eosinophilic and T2 inflammation.

TRIAL REGISTRATION

NCT03688074 (ClinicalTrials.gov). Registered 28 September 2018.

Safety and efficacy of AMG 714 in adults with coeliac disease exposed to gluten challenge: a phase 2a, randomised, double-blind, placebo-controlled study

BACKGROUND

Interleukin 15 (IL-15) is implicated in the pathophysiology of coeliac disease. AMG 714 is the first anti-IL-15 monoclonal antibody to be investigated for the treatment of coeliac disease. We aimed to investigate the effects of AMG 714 in patients with coeliac disease who underwent gluten challenge.

METHODS

This randomised, double-blind, placebo-controlled, parallel-group, phase 2a trial was done at three clinical sites in Finland. Inclusion criteria included age 18-80 years, a confirmed diagnosis of coeliac disease, and adherence to a gluten-free diet for at least 12 months before screening. Patients were randomly assigned (1:1:1) to 150 mg AMG 714, 300 mg AMG 714, or placebo using permuted blocks and stratified by study site and sex. Patients and study staff were masked to treatment assignment. Treatments were administered by two subcutaneous injections every 2 weeks for 10 weeks (total six doses). Patients without severe villous atrophy at baseline received a gluten challenge (2-4 g daily) during weeks 2-12. Small bowel biopsy samples were obtained for histological assessments at baseline and week 12. The primary efficacy endpoint was the percentage change from baseline to week 12 in villous height-to-crypt depth (VHCD) ratio. Secondary endpoints were CD3-positive intraepithelial lymphocyte density; clinical symptoms measured by gastrointestinal symptom rating scale (GSRS), coeliac disease GSRS, and Bristol stool form scale (BSFS); and changes in anti-tTG and anti-DGP antibodies from baseline. The primary analysis was done in the per-protocol 1 population of patients who received at least one dose of study drug and who underwent the gluten challenge. Safety analyses were done in all patients who received at least one dose of study drug. This trial is registered at ClinicalTrials.gov, NCT02637141 and EudraCT, 2015-003647-19.

FINDINGS

Between April 13, 2016, and Nov 22, 2016, 64 patients were enrolled and randomly assigned to either the 150 mg AMG 714 group (n=22), the 300 mg AMG 714 group (n=22), or the placebo group (n=20). Two patients did not start treatment and two did not provide post-treatment biopsy samples. 49 patients underwent the gluten challenge (per-protocol 1 population) and 11 patients did not because of baseline villous atrophy. AMG 714 did not prevent mucosal injury due to gluten challenge. The least square mean difference in the relative change from baseline in VHCD ratio was -2·49% (95% CI -16·82 to 11·83; p=0·73) between 150 mg AMG 714 and placebo and 6·39% (-7·07 to 19·85; p=0·34) between 300 mg AMG 714 and placebo. Neither comparison was statistically significant. The density of CD3-positive intraepithelial lymphocytes increased in all groups, with smaller increases in the 300 mg group (-41·24% [95% CI -79·28 to -3·20] vs placebo, nominal p=0·03) but not the 150 mg group (-14·32% [-54·39 to 25·74], nominal p=0·47). Clinical symptoms were ameliorated with AMG 714 treatment between baseline and week 12, particularly diarrhoea as measured by the BSFS (nominal p=0·01 for 150 mg vs placebo, and nominal p=0·0002 for 300 mg vs placebo). Serum antibody titres for anti-tTG and anti-DGP antibodies increased in all three treatment groups, with no significant difference between AMG 714 and placebo. Treatment-emergent adverse events occurred in 21 (95%) patients in the 150 mg AMG 714 group, 0 (95%) in the 300 mg AMG 714 group, and 19 (100%) in the placebo group. The most common treatment-emergent adverse events were gastrointestinal disorders (17 [77%] participants in the 150 mg AMG 714 group, 16 [76%] in the 300 mg AMG 714 group, and 13 [68%] in the placebo group). Injection site reactions were the most common individual adverse event, reported in eight (36%) patients in the 150 mg AMG 714 group, 11 (52%) in the 300 mg group, and five (26%) in the placebo group. No serious adverse events occurred.

INTERPRETATION

The primary endpoint, change in VHCD ratio from baseline after 12 weeks of treatment in patients with coeliac disease undergoing gluten challenge, was not significantly different between placebo and AMG 714 at either 150 mg or 300 mg. Effects on intraepithelial lymphocyte density and symptoms suggest that further research of AMG 714 may be warranted in patients with non-responsive coeliac disease.

FUNDING

Celimmune and Amgen.

Safety and efficacy of AMG 714 in patients with type 2 refractory coeliac disease: a phase 2a, randomised, double-blind, placebo-controlled, parallel-group study

BACKGROUND

Refractory coeliac disease type 2 is a rare subtype of coeliac disease with high mortality rates; interleukin 15 (IL-15) is strongly implicated in its pathophysiology. This trial aimed to investigate the effects of AMG 714, an anti-IL-15 monoclonal antibody, on the activity and symptoms of refractory coeliac disease type 2.

METHODS

This was a randomised, double-blind, placebo-controlled, phase 2a study of adults with a confirmed diagnosis of refractory coeliac disease type 2. Patients were randomly assigned at a 2:1 ratio to receive seven intravenous doses over 10 weeks of AMG 714 (8 mg/kg) or matching placebo. Biopsy samples were obtained at baseline and week 12 for cellular analysis and histology. The change in the proportion of aberrant intraepithelial lymphocytes from baseline to week 12 with respect to all intraepithelial lymphocytes was the primary endpoint and was quantified using flow cytometry. Secondary endpoints were the change in aberrant intraepithelial lymphocytes with respect to intestinal epithelial cells; intestinal histological scores (villous height-to-crypt depth ratio; VHCD); intraepithelial lymphocyte counts; Marsh score; and patient-reported symptom measures, including the Bristol stool form scale (BSFS) and gastrointestinal symptom rating scale (GSRS). Main analyses were done in the per-protocol population of patients who received their assigned treatment, provided evaluable biopsy samples, and did not have major protocol deviations; only patients with non-atypical disease were included in the analyses of aberrant intraepithelial lymphocytes, including the primary analysis. Safety was assessed in all patients who received at least one dose of study drug. This study is registered at ClinicalTrials.gov (NCT02633020) and EudraCT (2015-004063-36).

FINDINGS

From April 13, 2016, to Jan 19, 2017, 28 patients were enrolled and randomly assigned to AMG 714 (n=19) and placebo (n=9). Six patients were not included in the primary analysis because of protocol deviation (one in the AMG 714 group), insufficient biopsy samples (one in the AMG 714 group), and atypical intraepithelial lymphocytes (three in the AMG 714 group and one in the placebo group). At 12 weeks, the least square mean difference between AMG 714 and placebo in the relative change from baseline in aberrant intraepithelial lymphocyte percentage was -4·85% (90% CI -30·26 to 20·56; p=0·75). The difference between the AMG 714 and placebo groups in aberrant intraepithelial lymphocytes with respect to epithelial cells at 12 weeks was -38·22% (90% CI -95·73 to 19·29; nominal p=0·18); the difference in change in Marsh score from baseline was 0·09% (95% CI -1·60-1·90; nominal p=0·92); the difference in VHCD ratio was 10·67% (95% CI -38·97 to 60·31; nominal p=0·66); and the difference in change in total intraepithelial lymphocyte count was -12·73% (95% CI -77·57-52·12); nominal p=0·69). Regarding symptoms, the proportion of patients with diarrhoea per the BSFS score decreased from ten (53%) of 19 at baseline to seven (37%) of 19 at week 12 in the AMG 714 group and increased from two (22%) of nine at baseline to four (44%) of nine at week 12 in the placebo group (nominal p=0·0008); and the difference between the groups in change in GSRS score was -0·14 (SE 0·19; nominal p=0·48). Eight (89%) patients in the placebo group and 17 (89%) in the AMG 714 group had treatment-emergent adverse events, including one (11%) patient in the placebo group and five (26%) in the AMG 714 group who had serious adverse events. The most common adverse event in the AMG 714 group was nasopharyngitis (eight [42%] patients vs one [11%] in the placebo group).

INTERPRETATION

In patients with refractory coeliac disease type 2 who were treated with AMG 714 or placebo for 10 weeks, there was no difference between the groups in terms of the primary endpoint of aberrant intraepithelial lymphocyte reduction from baseline. Effects on symptoms and other endpoints suggest that further research of AMG 714 may be warranted in patients with refractory coeliac disease type 2.

FUNDING

Celimmune and Amgen.

Pharmacokinetics, Safety, and Tolerability of Tezepelumab (AMG 157) in Healthy and Atopic Dermatitis Adult Subjects

Tezepelumab (AMG 157) is a monoclonal antibody that targets thymic stromal lymphopoietin and has shown benefits in treating asthma. We assessed the safety, tolerability, and pharmacokinetics of single-ascending and multiple-ascending doses in two randomized, double-blind, placebo-controlled phase I studies. Healthy and atopic dermatitis subjects were enrolled in the single-dose study, and healthy subjects in the multiple-dose study. Tezepelumab showed linear pharmacokinetics in both healthy and atopic dermatitis subjects. The half-life after a subcutaneous or intravenous administration ranged from 19.9 to 25.7 days. After multiple doses, the mean area under the curve accumulation ratio was 1.82, 1.64, and 1.59 for the 35 mg, 105 mg, and 210 mg monthly subcutaneous doses, respectively. The mean maximum serum concentration (C_max ) accumulation ratio was 1.59, 2.84, and 6.74 for the 210 mg dose given every 28, 14, and 7 days, respectively. Tezepelumab was well tolerated in both studies with no evidence of immunogenicity.

Tezepelumab in Adults with Uncontrolled Asthma

BACKGROUND

In some patients with moderate-to-severe asthma, particularly those with noneosinophilic inflammation, the disease remains uncontrolled. This trial evaluated the efficacy and safety of tezepelumab (AMG 157/MEDI9929), a human monoclonal antibody specific for the epithelial-cell-derived cytokine thymic stromal lymphopoietin (TSLP), in patients whose asthma remained uncontrolled despite treatment with long-acting beta-agonists and medium-to-high doses of inhaled glucocorticoids.

METHODS

In this phase 2, randomized, double-blind, placebo-controlled trial, we compared subcutaneous tezepelumab at three dose levels with placebo over a 52-week treatment period. The primary end point was the annualized rate of asthma exacerbations (events per patient-year) at week 52.

RESULTS

The use of tezepelumab at a dose of 70 mg every 4 weeks (low dose; 145 patients), 210 mg every 4 weeks (medium dose; 145 patients), or 280 mg every 2 weeks (high dose; 146 patients) resulted in annualized asthma exacerbation rates at week 52 of 0.26, 0.19, and 0.22, respectively, as compared with 0.67 in the placebo group (148 patients). Thus, exacerbation rates in the respective tezepelumab groups were lower by 61%, 71%, and 66% than the rate in the placebo group (P<0.001 for all comparisons). Similar results were observed in patients regardless of blood eosinophil counts at enrollment. The prebronchodilator forced expiratory volume in 1 second at week 52 was higher in all tezepelumab groups than in the placebo group (difference, 0.12 liters with the low dose [P=0.01], 0.11 liters with the medium dose [P=0.02], and 0.15 liters with the high dose [P=0.002]). A total of 2 patients in the medium-dose group, 3 in the high-dose group, and 1 in the placebo group discontinued the trial regimen because of adverse events.

CONCLUSIONS

Among patients treated with long-acting beta-agonists and medium-to-high doses of inhaled glucocorticoids, those who received tezepelumab had lower rates of clinically significant asthma exacerbations than those who received placebo, independent of baseline blood eosinophil counts. (Funded by MedImmune [a member of the AstraZeneca Group] and Amgen; PATHWAY ClinicalTrials.gov number, NCT02054130 .).

Effects of an anti-TSLP antibody on allergen-induced asthmatic responses

BACKGROUND

Thymic stromal lymphopoietin (TSLP) is an epithelial-cell-derived cytokine that may be important in initiating allergic inflammation. AMG 157 is a human anti-TSLP monoclonal immunoglobulin G2λ that binds human TSLP and prevents receptor interaction.

METHODS

In this double-blind, placebo-controlled study, we randomly assigned 31 patients with mild allergic asthma to receive three monthly doses of AMG 157 (700 mg) or placebo intravenously. We conducted allergen challenges on days 42 and 84 to evaluate the effect of AMG 157 in reducing the maximum percentage decrease in the forced expiratory volume in 1 second (FEV1). We also measured the fraction of nitric oxide in exhaled air, blood and sputum eosinophils, and airway hyperresponsiveness. The primary end point was the late asthmatic response, as measured 3 to 7 hours after the allergen challenge.

RESULTS

AMG 157 attenuated most measures of allergen-induced early and late asthmatic responses. The maximum percentage decrease in the FEV1 during the late response was 34.0% smaller in the AMG-157 group than in the placebo group on day 42 (P=0.09) and 45.9% smaller on day 84 (P=0.02). In addition, patients receiving AMG 157 had significant decreases in levels of blood and sputum eosinophils before and after the allergen challenge and in the fraction of exhaled nitric oxide. There were 15 adverse events in the AMG-157 group, as compared with 12 in the placebo group; there were no serious adverse events.

CONCLUSIONS

Treatment with AMG 157 reduced allergen-induced bronchoconstriction and indexes of airway inflammation before and after allergen challenge. These findings are consistent with a key role for TSLP in allergen-induced airway responses and persistent airway inflammation in patients with allergic asthma. Whether anti-TSLP therapeutics will have clinical value cannot be determined from these data. (Funded by Amgen; ClinicalTrials.gov number, NCT01405963.).

CD6 attenuates early and late signaling events, setting thresholds for T-cell activation

The T lineage glycoprotein CD6 is generally considered to be a costimulator of T-cell activation. Here, we demonstrate that CD6 significantly reduces early and late T-cell responses upon superantigen stimulation or TCR triggering by Abs. Measuring calcium mobilization in single cells responding to superantigen, we found that human T cells expressing rat CD6 react significantly less well compared with T cells not expressing the exogenous receptor. When the cytoplasmic domain of rat CD6 was removed, calcium responses were recovered, indicating that the inhibitory properties of CD6 are attributable to its cytoplasmic domain. Calcium responses, and also late indicators of T-cell activation such as IL-2 release, were also diminished in TCR-activated Jurkat cells expressing human CD6, compared with CD6-deficient cells or cells expressing a cytoplasmic deletion mutant of human CD6. Similarly, calcium signals triggered by anti-CD3 were enhanced in human T lymphocytes following morpholino-mediated suppression of CD6 expression. Finally, the proliferation of T lymphocytes was increased when the CD6-CD166 interaction was blocked with anti-CD166 Abs, but inhibited when anti-CD6 Abs were used. Our data suggest that CD6 is a signaling attenuator whose expression alone, i.e. in the absence of ligand engagement, is sufficient to restrain signaling in T cells.

Modulation of peripheral B cell tolerance by CD72 in a murine model

OBJECTIVE

B cells play a dominant role in the pathogenesis of several autoimmune diseases, including systemic lupus erythematosus. It is not well understood how B cell signaling contributes to autoantibody production. The goal of this study was to elucidate the role of CD72 in modulating B cell receptor (BCR)-mediated tolerogenic signaling and peripheral B cell tolerance.

METHODS

A mouse model utilizing hen egg lysozyme (HEL) "anergic" B cells was studied. CD72-deficient mice carrying the BCR-specific IgHEL and/or soluble HEL (sHEL) transgenes were generated by breeding IgHEL-transgenic MD4 mice and/or sHEL-transgenic ML5 mice with congenic, CD72-deficient C57BL/6J mice. Normal and anergic B cells were isolated for analyses of B cell signaling. Aged wild-type and CD72-deficient mice were also examined for autoimmune phenomena.

RESULTS

In the absence of CD72, anergic B cells inappropriately proliferated and survived in response to stimulation with self antigen. Biochemical analyses indicated that in anergic B cells, CD72 dominantly down-regulated BCR signaling to limit the antigen-induced elevation in [Ca2+]i and the activation of NFATc1, NF-kappaB, MAPK, and Akt. Mechanistically, CD72 was associated with, and regulated, the molecular adaptor Cbl-b in anergic B cells, suggesting that Cbl-b may play a role in mediating the negative effects of CD72 on BCR signaling. Moreover, in aged CD72-deficient mice, spontaneous production of antinuclear and anti-double-stranded DNA autoantibodies and features of lupus-like autoimmune disease were observed.

CONCLUSION

CD72 is required to maintain B cell anergy and functions as a regulator of peripheral B cell tolerance. Thus, altered CD72 expression may play a role during the development of systemic lupus erythematosus.

Extracellular isoforms of CD6 generated by alternative splicing regulate targeting of CD6 to the immunological synapse

The great majority of mammalian genes yield multiple transcripts arising from differential mRNA processing, but in very few instances have alternative forms been assigned distinct functional properties. We have cloned and characterized a new isoform of the accessory molecule CD6 that lacks the CD166 binding domain and is expressed in rat and human primary cells. The novel isoform, CD6Deltad3, results from exon 5 skipping and consequently lacks the third scavenger receptor cysteine-rich (SRCR) domain of CD6. Differential expression of the SRCR domain 3 resulted in a remarkable functional difference: whereas full-length CD6 targeted to the immunological synapse, CD6Deltad3 was unable to localize at the T cell:APC interface during Ag presentation. Analysis of expression of CD6 variants showed that, while being more frequent in coexpression with full-length CD6, the CD6Deltad3 isoform constituted the sole species in a small percentage of T cells. In the rat thymus, CD6Deltad3 is less represented in double-positive thymocytes but is detectable in nearly 50% of single-positive CD4 or CD8 thymocytes, suggesting that CD6 switching between full-length and Deltad3 isoforms may be involved in thymic selection. Strikingly, CD6Deltad3 is markedly up-regulated upon activation of T lymphocytes, partially substituting full-length CD6, as evaluated by RT-PCR analysis at the single-cell level, by immunoblotting, and by flow cytometry using Abs recognizing SRCR domains 1 and 3 of human CD6. This elegant mechanism controlling the expression of the CD166 binding domain may help regulate signaling delivered by CD6, through different types of extracellular engagement.

Suppressive Role of CD72 in Experimental Autoimmune Encephalomyelitis (128.22)

CD72, a type II transmembrane protein expressed predominantly on B cells, acts as a negative regulator of B cell signaling and activation, and promotes B cell apoptosis through the B-cell receptor. However, whether CD72 plays a role in autoimmunity in vivo is unknown. We found that aged CD72-deficient mice naturally developed lupus-like autoimmune disease. To examine whether CD72 might play a role in multiple sclerosis [MS], we induced experimental autoimmune encephalomyelitis (EAE), a useful animal model for MS, in both wild-type (WT) and CD72-deficient (CD72KO) mice. We found that immunization with MOG (35–55) peptide induced an earlier onset and more severe clinical disease in CD72KO mice than in WT mice. CD72KO B cells had greater capacity for antigen presentation to CD4+ T cells as determined by T cell proliferation. MOG (35–55) immunized CD72KO mice also had higher anti-MOG IgM antibody response in the late phase (Day 35) of disease compared to WT mice. The present results indicate that CD72 may play an important role in the modulation of human autoimmune diseases such as lupus and MS.

A unique CD72 epitope suggests a potential interaction with Fc gamma RII/CD32 on B lineage lymphocytes

It has long been known that ligation of the transmembrane CD72 glycoprotein delivers signals to B lymphocytes, with the outcome depending on context. Of particular interest is its ability to function as a counter-receptor/ ligand for the CD100 semaphorin protein. We have now obtained evidence that CD72 physically interacts on the lymphocyte membrane with Fcgamma receptor II (CD32). The association was first revealed with a new monoclonal antibody that recognizes polymorphic determinants on murine CD72. Although the specificity for CD72 was clear from immunoblotting, transfection and other experiments, staining with this reagent was inhibited when cells were pretreated with an Fc receptor-blocking antibody (CD16/CD32 specific). Furthermore, confocal microscopy revealed that the two molecules co-distributed on viable B cells. We also used the antibody to determine when CD72 becomes available to maturing lymphocytes. The marker is first acquired as large pre-B cells and enter the IL-7 independent phase of maturation within bone marrow. Subsequent interactions between CD72 and CD32 may cooperatively deliver negative signals that modulate humoral immune responses.

CD72 down-modulates BCR-induced signal transduction and diminishes survival in primary mature B lymphocytes

CD72, a 45-kDa type II transmembrane glycoprotein carrying an ITIM motif, is believed to be an inhibitory coreceptor of the BCR. Mature B cells lacking CD72 show enhanced Ca(2+) mobilization and are hyperproliferative in response to BCR ligation. However, the signal transduction pathways downstream of BCR signaling that transmit the inhibitory effect of CD72 in mature B cells remain unknown. To address this question, we used hen egg lysozyme-specific BCR transgenic mice to elucidate the differential cell signaling between wild-type and CD72-deficient B cells in response to hen egg lysozyme Ag stimulation. Our results demonstrate that CD72 predominantly down-regulates the major signal transduction pathways downstream of the BCR, including NF-AT, NF-kappaB, ERK, JNK, p38-MAPK, and PI3K/Akt in mature B cells. CD72 ligation with anti-CD72 Ab (K10.6), which mimics the binding of CD100 (a natural ligand for CD72) to release the inhibitory function of CD72, augments cell proliferation, Ca(2+) flux, IkappaBalpha activation, and ERK MAPK activity upon Ag stimulation in wild-type B cells. In addition, we show direct evidence that CD72 promotes cell cycle arrest and apoptosis after Ag stimulation in mature B cells. Taken together, our findings conclude that CD72 plays a dominant role as a negative regulator of BCR signaling in primary mature B lymphocytes.

Medicine on a need-to-know basis

Disease-oriented, introductory medical curricula can help overcome educational and institutional barriers that separate aspiring translational scientists in PhD programs from the world of medicine.

Long-term engagement of CD6 and ALCAM is essential for T-cell proliferation induced by dendritic cells

Interactions between T cells and antigen-presenting cells (APCs) are the first step in the induction of an adaptive immune response. Here, we show that CD6 and its ligand activated leukocyte cell adhesion molecule (ALCAM) are actively recruited to the antigen-induced dendritic cell (DC)–T-cell contact zone. Moreover, ALCAM-blocking antibodies interfere with DC–T-cell conjugate formation, demonstrating that CD6-ALCAM binding is essential for stable T-cell–APC contact. We now demonstrate that besides their role in establishing initial contacts, CD6-ALCAM interactions are also required during the proliferative phase of the T-cell response; the presence of CD6-blocking antibodies or recombinant ALCAM-Fc proteins results in a strong and sustained inhibition of T-cell proliferation. Furthermore, simultaneous crosslinking of CD6 and CD3 induces enhanced proliferation and transcriptional activity to a similar level as observed after CD3 and CD28 co-crosslinking, demonstrating that CD6 is an important costimulatory molecule. The stability of ALCAM-CD6 binding, which contrasts with transient homotypic ALCAM-ALCAM interactions, further supports the long-lasting effects observed on T-cell proliferation. Taken together, we demonstrate that CD6 and ALCAM form a key adhesive receptor-ligand pair that is not only involved in early DC-T-cell binding but also in sustaining DC-induced T-cell proliferation long after the initial contact has been established.

Mouse splenic B lymphocyte activation using different activation stimuli induces in vitro splicing of tumor necrosis factor-α nuclear pre-mRNA

The pleiotropic functions of tumor necrosis factor-alpha (TNFalpha) have brought considerable attention in the past decade to its physiological and pathological roles in inflammatory and autoimmune diseases. However, little is known about how the production of TNFalpha is regulated at the transcriptional and translational levels in immune cells such as T and B lymphocytes. Our previous study demonstrated that unspliced "pre-mRNA" of TNFalpha is present in resting T cells. Initiation of splicing of TNFalpha pre-mRNA to mature mRNA requires T cell activation, which is unique and necessary for TNFalpha production when compared to its production in mononuclear phagocytes, including different lineages of macrophages (Mvarphi) and dendritic cells (DC). In this study, we further demonstrate that resting mouse B cells also contain pre-existing TNFalpha mRNA. The physiological process of B cell activation induced by (1) either the cross-linking of the B cell receptor (BCR) or CD40, (2) treatment with LPS, or PMA plus ionomycin, induces TNFalpha mRNA splicing in vitro. The kinetic response of TNFalpha splicing in B cells is much slower when compared to that in activated T cells. Studies using well-known kinase inhibitors demonstrated that MAP kinase kinase (MEK) and protein kinase C (PKC) are required for TNFalpha splicing upon stimulation through the BCR. These studies demonstrate that the production of TNFalpha in activated B cells is regulated differently than in activated T cells, and these differences may allow for the selective inhibition of TNFalpha in various autoimmune diseases depending on the mechanism of action of the selected anti-TNFalpha therapy.

Requirement for CD100-CD72 interactions in fine-tuning of B-cell antigen receptor signaling and homeostatic maintenance of the B-cell compartment

Co-receptors on the B-cell surface regulate B-cell antigen receptor (BCR) signaling; however, it remains unclear how BCR signals are coordinated to maintain immune homeostasis. CD72, a negative regulator of B-cell responses, has immunoreceptor tyrosine-based inhibitory motifs within its cytoplasmic region, and the tyrosine phosphatase SHP-1 binds these sites. The natural ligand of CD72, CD100/Sema4D, belongs to the semaphorin family and induces the dissociation of SHP-1 from CD72, thereby switching off the negative signals of CD72. In the absence of CD100, BCR signals are significantly suppressed due to the constitutive association of SHP-1 with CD72, resulting in B-cell hyporesponsiveness. Here we show that CD100 regulates the sensitivity of the BCR by preventing the association of the CD72 with BCR, and this interaction is required for proper B-cell homeostasis. Consequently, as CD100-deficient mice age, they accumulate marginal zone B cells and develop high auto-antibody levels and autoimmunity. Collectively, our findings indicate that the strength of BCR signals is strictly tuned by the interaction of CD100 with CD72, and this interaction is essential for maintaining immunological homeostasis as well as generating a proper immune response.

Dual regulation of BCR-mediated growth inhibition signaling by CD72

CD72 has been reported to regulate BCR-mediated signals both positively and negatively. SHP-1 and Grb2 bind, respectively, to ITIM1 and ITIM2 of CD72. We generated transformed B cell lines with an immature phenotype following J2 virus infection of splenocytes from CD72(-/-) and wild-type (Wt) mice. The transformed lines were infected with retroviral vectors carrying Tyr (Y) to Phe (F) substitutions in the ITIM sequences (ITIM1 mutated: Y7/F; ITIM2 mutated: Y39/F; and both ITIM mutated: Y7,39/F). Cross-linking of the BCR induced growth inhibition in transfectants expressing Wt CD72, but this response was less sensitive in transfectants with Y7,39/F. The Y7/F transfectants demonstrated the least sensitive response. We were not able to obtain transfectants with Y39/F, suggesting that CD72 associated with SHP-1, but not with Grb2, delivers a strong negative signal. Pre-ligation of CD72, which induces dephosphorylation of the molecule, partially rescued the Wt transfectants from growth inhibition, leading to a growth response profile similar to that of Y7,39/F transfectants. These results suggest that ITIM1/SHP-1 delivers a very strong negative signal that is down-modulated by signals through ITIM2/Grb2, leading to delivery of an attenuated negative signal. Thus, pre-ligation of CD72 results in the manifestation of an ostensible positive signal.

Woodchuck interleukin-6 gene: structure, characterization, and biologic activity

Woodchuck is an important animal model for studying human hepatitis B virus (HBV) infection. Within the cytokine network, interleukin-6 (IL-6) plays an important role in immune responses that may lead to viral clearance. To further understand woodchuck IL-6 biology, we cloned and characterized the IL-6 gene from white blood cells. The complete woodchuck IL-6 gene is about 7 kb and consists of five exons and four introns. The IL-6 gene organization of the woodchuck is similar to those of the human, rat, and mouse. Also several elements are highly conserved in the 300 bp promoter region of the IL-6 gene, including a nuclear factor kappa B (NF-kappaB) binding site. The woodchuck IL-6 gene encodes a polypeptide of 207 amino acids in a precursor form and 189 amino acids in the mature form. The expressed protein was 23 kDa according to SDS-PAGE. To demonstrate biologic activity, we expressed woodchuck IL-6 and showed that the purified recombinant protein induced terminal differentiation, as reflected by upregulation of Fcgamma receptor expression, and substantially inhibited proliferation of M1 cells, a murine myeloid leukemia cell line. The inhibitory effect of woodchuck IL-6 on M1 cells was blocked by an anti-gp130 monoclonal antibody, suggesting that woodchuck IL-6 activity is specifically mediated by signaling through the IL-6 receptor complex. Cloning of the woodchuck IL-6 gene and demonstrating biologic activity of the gene product will facilitate studies of human hepatitis B virus using the woodchuck model.

OX52 is the rat homologue of CD6: evidence for an effector function in the regulation of CD5 phosphorylation

The MRC OX52 monoclonal antibody is a marker of rat T lymphocytes. We have cloned by polymerase chain reaction the rat homologue of CD6, and fluorescein-activated cell sorter analysis and immunoprecipitations using OX52 in COS7 cells transfected with rat CD6 cDNA showed that CD6 is the cell-surface molecule recognized by OX52. Immunoprecipitation analysis showed that CD6 coprecipitated with CD5, which in turn, was coprecipitated equivalently with CD2, CD6, and the T cell receptor (TCR), but the fraction of CD5 associated with CD6 was highly phosphorylated in kinase assays, in marked contrast with the low level of phosphorylation of CD5 associated with TCR or CD2. Examination of protein kinases associating with these antigens showed that paradoxically, CD2 coprecipitated the highest amount of Lck and Fyn. CD6 also associated with Lck, Fyn, and ZAP-70, although at lower levels but additionally coprecipitated the Tec family kinase Itk, which is absent from CD2, CD5, and TCR complexes. Lck together with Itk was the best combination of kinases, effectively phosphorylating synthetic peptides corresponding to a cytoplasmic sequence of CD5. Overall, our results suggest that CD6 has an important role in the regulation of CD5 tyrosine phosphorylation, probably as a result of its unique feature of associating with kinases of different families.

CD6: expression during development, apoptosis and selection of human and mouse thymocytes

CD6, a 130-kDa surface glycoprotein, is expressed primarily on cells of T lineage. A co-stimulatory role for CD6 in mature T cells has been shown, but the function of CD6 during thymocyte development is unknown. Since CD6 ligands are expressed on thymic epithelium, their interactions with CD6 could be important in thymic selection. In this report we show that CD6 is developmentally regulated in human and mouse thymocytes, and further demonstrate that increase in the level of CD6 expression correlates with expression of the selection marker CD69. We also show that activation via CD2 induces CD6 expression on mature human thymocytes and on a subset of immature human thymocytes that are resistant to apoptosis. In human and mouse thymocytes that express heterogeneous TCR, CD6 increases occur as double-positive thymocytes are selected to a single-positive stage. In contrast, in thymocytes from TCR transgenic mice, CD6 is barely increased following selection, suggesting that as functional avidity increases, requirements for CD6-dependent co-stimulation decrease. Taken together, these results indicate that during thymic development CD6-dependent signals may contribute both to thymocyte survival, and to the overall functional avidity of selection in both man and mouse.

Identification of CD72 as a lymphocyte receptor for the class IV semaphorin CD100: a novel mechanism for regulating B cell signaling

We have identified the lymphocyte semaphorin CD100/Sema4D as a CD40-inducible molecule by subtractive cDNA cloning. CD100 stimulation significantly enhanced the effects of CD40 on B cell responses. Administration of soluble CD100 markedly accelerated in vivo antigen-specific antibody responses. CD100 receptors with different binding affinities were detected on renal tubular cells (K(d) = approximately 1 x 10(-9)M) and lymphocytes (K(d) = approximately 3 x 10(-7)M). Expression cloning revealed that the CD100 receptor on lymphocytes is CD72, a negative regulator of B cell responsiveness. CD72 thus represents a novel class of semaphorin receptors. CD100 stimulation induced tyrosine dephosphorylation of CD72 and dissociation of SHP-1 from CD72. Our findings indicate that CD100 plays a critical role in immune responses by the novel mechanism of turning off negative signaling by CD72.

The class IV semaphorin CD100 plays nonredundant roles in the immune system: defective B and T cell activation in CD100-deficient mice

The class IV semaphorin CD100/Sema4D differentially utilizes two distinct receptors: plexin-B1 in nonlymphoid tissues, such as brain and kidney, and CD72 in lymphoid tissues. We have generated CD100-deficient mice and demonstrated that they have functional defects in their immune system, without apparent abnormalities in other tissues. The number of CD5(+) B-1 cells was considerably decreased in the mutant mice, whereas conventional B cells and T cells appeared to develop normally. In vitro proliferative responses and immunoglobulin production were reduced in CD100-deficient B cells. The humoral immune response against a T cell-dependent antigen and in vivo priming of T cells were also defective in the mutant mice. These results demonstrate nonredundant and essential roles of CD100-CD72 interactions in the immune system.

CD72, a negative regulator of B-cell responsiveness

The ability of lymphocytes to respond to antigenic or mitogenic stimulation is regulated not only by specific receptor proteins, but also by both positive and negative regulatory proteins that set or fine-tune the threshold for responsiveness. CD72 is one such regulatory protein on B lymphocytes. It is a member of the C-type lectin superfamily and is expressed on the surface of B cells from the pro-B through the mature B-cell stage. Studies with anti-CD72 antibodies have suggested a positive regulatory role for CD72 in B-cell activation. However, the cytoplasmic tail of CD72 contains two potential immunoreceptor tyrosine-based inhibitory motifs, one of which has been shown to recruit the tyrosine phosphatase SHP- 1. These features suggest a negative regulatory role for CD72. We have generated CD72-deficient mice to elucidate the physiological role of CD72 in B-lymphocyte development and activation. Our analyses of these mice and their B-cell compartment demonstrate that CD72 is a nonredundant regulator of B-cell development and a negative regulator of B-cell responsiveness.

CD72-deficient mice reveal nonredundant roles of CD72 in B cell development and activation

CD72, a B cell surface protein of the C-type lectin superfamily, recruits the tyrosine phosphatase SHP-1 through its ITIM motif(s). Using CD72-deficient (CD72-/-) mice, we demonstrate that CD72 is a nonredundant regulator of B cell development. In the bone marrow of CD72-/- mice, there was a reduction in the number of mature recirculating B cells and an accumulation of pre-B cells. In the periphery of CD72-/- mice, there were fewer mature B-2 cells and more B-1 cells. In addition, CD72 is a negative regulator of B cell activation, as CD72-/- B cells were hyperproliferative in response to various stimuli and showed enhanced kinetics in their intracellular Ca2+ response following IgM cross-linking.

Regulation of Mouse CD72 Gene Expression During B Lymphocyte Development

CD72 is a 45-kDa transmembrane glycoprotein that is predominantly expressed on cells of the B lineage except plasma cells. Previously, we identified the 255-bp minimal mouse CD72 promoter capable of tissue-specific and developmental stage-specific expression. DNase I footprinting analysis of the 255-bp CD72 promoter revealed three protected elements, footprint (FP) I, FP II, and FP III. FP II, which extends from nucleotide −189 to −169 of the mouse CD72 promoter, exhibited both tissue-specific and developmental stage-specific activity that was reflective of the activity of the CD72 gene in vivo. In this report, we show that FP II is specifically recognized by the transcription factor B cell-specific activator protein (BSAP). Mutations eliminating the binding of BSAP in reporter constructs also eliminated the increase of reporter activity in B cells. In addition, cotransfections with reporter constructs plus different amounts of expression plasmids for BSAP showed that CD72 promoter activity was up-regulated by BSAP in plasmacytoma cells and T cells in a dose-dependent manner. Moreover, the expression level of CD72 decreased 10-fold on normal plasma cells. Compared with the presence of BSAP binding in mature B cells, the binding of BSAP was undetectable in those plasma cells. This study strongly suggests that BSAP-FP II interaction plays a critical role in determining the cell-type specificity of the CD72 promoter. The absence of positive factors such as BSAP accounts for at least part of the loss of mouse CD72 expression in plasma cells and thus might be common for the down-regulation of many molecules at the plasma cell stage.

Regulation of mouse CD72 gene expression during B lymphocyte development

CD72 is a 45-kDa transmembrane glycoprotein that is predominantly expressed on cells of the B lineage except plasma cells. Previously, we identified the 255-bp minimal mouse CD72 promoter capable of tissue-specific and developmental stage-specific expression. DNase I footprinting analysis of the 255-bp CD72 promoter revealed three protected elements, footprint (FP) I, FP II, and FP III. FP II, which extends from nucleotide -189 to -169 of the mouse CD72 promoter, exhibited both tissue-specific and developmental stage-specific activity that was reflective of the activity of the CD72 gene in vivo. In this report, we show that FP II is specifically recognized by the transcription factor B cell-specific activator protein (BSAP). Mutations eliminating the binding of BSAP in reporter constructs also eliminated the increase of reporter activity in B cells. In addition, cotransfections with reporter constructs plus different amounts of expression plasmids for BSAP showed that CD72 promoter activity was up-regulated by BSAP in plasmacytoma cells and T cells in a dose-dependent manner. Moreover, the expression level of CD72 decreased 10-fold on normal plasma cells. Compared with the presence of BSAP binding in mature B cells, the binding of BSAP was undetectable in those plasma cells. This study strongly suggests that BSAP-FP II interaction plays a critical role in determining the cell-type specificity of the CD72 promoter. The absence of positive factors such as BSAP accounts for at least part of the loss of mouse CD72 expression in plasma cells and thus might be common for the down-regulation of many molecules at the plasma cell stage.

Distinct stage-specific cis-active transcriptional mechanisms control expression of T cell coreceptor CD8 alpha at double- and single-positive stages of thymic development

Developing thymocytes that give rise to CD8+ (cytotoxic) and CD4+ (helper) alpha beta-TCR T lymphocytes go through progressive stages of expression of coreceptors CD8 and CD4 from being negative for both (the double-negative stage), to coexpressing both (the double-positive (DP) stage), to a mutually exclusive sublineage-specific expression of one or the other (the single-positive (SP) stage). To delineate the mechanisms underlying regulation of CD8 during these developmental transitions, we have examined expression of a series of mouse CD8 alpha gene constructs in developing T cells of conventional and CD8 alpha "knock-out" transgenic mice. Our results indicate that cis-active transcriptional control sequences essential for stage- and sublineage-specific expression lie within a 5' 40-kb segment of the CD8 locus, approximately 12 kb upstream of the CD8 alpha gene. Studies to characterize and sublocalize these cis sequences showed that a 17-kb 5' subfragment is able to direct expression of the CD8 alpha gene up to the CD3intermediate DP stage but not in more mature DP or SP cells. These results indicate that stage-specific expression of CD8 alpha in developing T cells is mediated by the differential activity of multiple functionally distinct cis-active transcriptional control mechanisms. It will be important to determine the relationship of "switching" between these cis mechanisms and selection.

Distinct Stage-Specific cis-Active Transcriptional Mechanisms Control Expression of T Cell Coreceptor CD8α at Double- and Single-Positive Stages of Thymic Development

Developing thymocytes that give rise to CD8+ (cytotoxic) and CD4+ (helper) αβ-TCR T lymphocytes go through progressive stages of expression of coreceptors CD8 and CD4 from being negative for both (the double-negative stage), to coexpressing both (the double-positive (DP) stage), to a mutually exclusive sublineage-specific expression of one or the other (the single-positive (SP) stage). To delineate the mechanisms underlying regulation of CD8 during these developmental transitions, we have examined expression of a series of mouse CD8α gene constructs in developing T cells of conventional and CD8α “knock-out” transgenic mice. Our results indicate that cis-active transcriptional control sequences essential for stage- and sublineage-specific expression lie within a 5′ 40-kb segment of the CD8 locus, ∼12 kb upstream of the CD8α gene. Studies to characterize and sublocalize these cis sequences showed that a 17-kb 5′ subfragment is able to direct expression of the CD8α gene up to the CD3intermediate DP stage but not in more mature DP or SP cells. These results indicate that stage-specific expression of CD8α in developing T cells is mediated by the differential activity of multiple functionally distinct cis-active transcriptional control mechanisms. It will be important to determine the relationship of “switching” between these cis mechanisms and selection.

T cell receptor (TCR) engagement leads to activation-induced splicing of tumor necrosis factor (TNF) nuclear pre-mRNA

Inducible gene expression is primarily regulated at the level of transcription. Additional steps of "processing" pre-mRNA, involved in the regulation of induced gene expression, have not been previously reported. Here we report a novel mechanism of "activation-induced splicing" of preexisting tumor necrosis factor (TNF) message (pre-mRNA) in naive T lymphocytes after engagement of the T cell receptor (TCR), which still occurs after inhibition of transcription. Expression of TNF has been previously demonstrated to be regulated at both the transcriptional and translational levels. However, neither the large pool of TNF mRNA observed in activated T cells nor TNF protein production, which peaks very shortly after activation, can be solely attributed to increased transcription. Evidence is presented that activation-induced splicing of TNF pre-mRNA plays a significant role in the rapid production of TNF seen in activated T cells. Activation triggers processing of TNF pre-mRNA that has accumulated in naive T cells (before activation-induced transcription), and the mature TNF mRNA is translocated to the cytoplasm for rapid translation and protein production. This novel form of activation-induced splicing of TNF may allow T cells to mount an immediate response to activation stimuli under physiological conditions.

Mechanisms of CD8β-Mediated T Cell Response Enhancement: Interaction with MHC Class I/β2-Microglobulin and Functional Coupling to TCR/CD3

CD8β expression results in enhanced IL-2 production and/or altered specificity in allogeneic MHC class I-restricted T cell hybridomas. Expression of chimeric CD8β-α molecules (extracellular CD8β, transmembrane and cytoplasmic CD8α) also results in enhancement of T hybridoma responses to alloantigen, suggesting that at least part of CD8β’s ability to influence responses similar to those of mature CD8+ T cells is mediated by its extracellular domain. Current data suggest that CD8β-mediated response enhancement proceeds through mechanisms similar to those mediated by CD8α, i.e., interacting with MHC class I and stabilizing CD8-associated Lck activity. In this study we present evidence that the extracellular portion of CD8β is capable of independent interaction with MHC class I/β2m dimers in the absence of CD8α. In addition, CD8β may enhance interaction with MHC class I/β2m when associated with CD8α. We also present evidence from T hybridoma responses suggesting that the extracellular portion of CD8β is uniquely capable of efficient interaction with the TCR/CD3 complex and may couple the TCR/CD3 complex to other surface components capable of enhancing TCR-mediated signals. This represents the first evidence that a critical coreceptor function can be preferentially associated with the CD8β subunit.

Mechanisms of CD8beta-mediated T cell response enhancement: interaction with MHC class I/beta2-microglobulin and functional coupling to TCR/CD3

CD8beta expression results in enhanced IL-2 production and/or altered specificity in allogeneic MHC class I-restricted T cell hybridomas. Expression of chimeric CD8beta-alpha molecules (extracellular CD8beta, transmembrane and cytoplasmic CD8alpha) also results in enhancement of T hybridoma responses to alloantigen, suggesting that at least part of CD8beta's ability to influence responses similar to those of mature CD8+ T cells is mediated by its extracellular domain. Current data suggest that CD8beta-mediated response enhancement proceeds through mechanisms similar to those mediated by CD8alpha, i.e., interacting with MHC class I and stabilizing CD8-associated Lck activity. In this study we present evidence that the extracellular portion of CD8beta is capable of independent interaction with MHC class I/beta2m dimers in the absence of CD8alpha. In addition, CD8beta may enhance interaction with MHC class I/beta2m when associated with CD8alpha. We also present evidence from T hybridoma responses suggesting that the extracellular portion of CD8beta is uniquely capable of efficient interaction with the TCR/CD3 complex and may couple the TCR/CD3 complex to other surface components capable of enhancing TCR-mediated signals. This represents the first evidence that a critical coreceptor function can be preferentially associated with the CD8beta subunit.

PU.1/Spi-1 is essential for the B cell-specific activity of the mouse CD72 promoter

CD72 is a 45-kDa glycoprotein that is predominantly expressed on cells of the B lineage, except for plasma cells. Its expression pattern is representative of many B cell-specific proteins, which are essential for B cell development and activation but are down-regulated after B cells become terminally differentiated plasma cells. We have examined the promoter region of the mouse CD72 gene to identify sequences responsible for this regulatory pattern. The CD72 gene does not have an obvious TATAA box. Primer extension assays identified multiple transcription initiation sites. Deletion analyses have identified the 255-bp minimal promoter required for tissue-specific and developmental stage-specific expression. DNase I footprinting analysis of the CD72 minimal promoter revealed three protected elements: FP I, FP II, and FP III. Sequences corresponding to FP I or III gave increased reporter gene activity specifically in B cells, but not in T cells or NIH-3T3 cells. Sequences corresponding to FP II gave increased reporter gene activity in mature B cells, but not in plasma cells or non-B cells. Electrophoretic mobility shift assays and DNase I protection analyses revealed that FP I was bound by the transcription factor PU.1/Spi-1. Transient reporter analyses with plasmid bearing the mutated PU.1 binding site showed that binding of PU.1 is necessary for the increase in CD72 promoter activity in B cells. These results suggest that the 255-bp CD72 promoter confers both tissue specificity and developmental stage specificity, and that the B cell and macrophage-specific transcription factor PU.1 is essential for regulating the tissue specificity of the mouse CD72 promoter.