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ObjectivesTo assess the efficacy and safety of abatacept, a selective T-cell costimulation modulator, in a phase III study in psoriatic arthritis (PsA).MethodsThis study randomised patients (1:1) with active PsA (~60% with prior exposure to a tumour necrosis factor inhibitor) to blinded weekly subcutaneous abatacept 125 mg (n=213) or placebo (n=211) for 24 weeks, followed by open-label subcutaneous abatacept. Patients without ≥20% improvement in joint counts at week 16 were switched to open-label abatacept. The primary end point was the proportion of patients with ≥20% improvement in the American College of Rheumatology (ACR20) criteria at week 24.ResultsAbatacept significantly increased ACR20 response versus placebo at week 24 (39.4% vs 22.3%; pConclusionsAbatacept treatment of PsA in this phase III study achieved its primary end point, ACR20 response, showed beneficial trends overall in musculoskeletal manifestations and was well tolerated. There was only a modest impact on psoriasis lesions.Trial registration numberClinicalTrials.gov number, NCT01860976 (funded by Bristol-Myers Squibb).

Background Mechanistic differences between biologics are poorly understood. HLA-DRB1 alleles containing the shared epitope (SE), which are strongly associated with RA, are present in 85% of anti-cyclic citrullinated protein 2 (anti-CCP2) + patients (pts) with RA (Jiang et al. Arthritis Rheumatol 2015). In a prior retrospective exploratory analysis, abatacept (ABA) was more effective in SE+ vs SE- pts (Oryoji et al. Ann Rheum Dis 2017). Head-to-head (H2H) comparisons with other agents are lacking. Objectives This H2H, single-blinded trial (NCT02557100) in biologic-naive pts with early, active RA prospectively explored the relationship between HLA-DRB1 SE and the clinical efficacy of ABA or adalimumab (ADA). Methods Adults with early (=12 mths from symptom onset), moderate-to-severe RA (ACR/EULAR 2010 criteria) seropositive for anti-CCP2 (>3x ULN) and RF, were randomised 1:1 to SC ABA 125mg wkly or SC ADA 40mg every 2 wks (both with stable, oral MTX wkly) for 24 wks. Pts were grouped by SE status (+/-) based on HLA-DRB1 genotype (-: no SE allele; +: =1 SE allele). Safety was analysed throughout the trial and up to 8 wks post last study drug dose. Clinical efficacy was assessed at Wk24 to determine the proportion of ACR20/50/70 responders in ABA vs ADA arms, and the adjusted mean changes from baseline in DAS28 (CRP), SDAI and CDAI. Treatment (tmt) differences between ABA and ADA in SE+ and SE– pts were assessed for ACR20/50/70 responders and DAS28 (CRP) remission at Wk24. Results 80 pts were treated: 40 ABA (9 SE-, 30 SE+, 1 SE unknown) and 40 ADA (9 SE-, 31 SE+). Baseline characteristics were balanced. Mean (SD) age, disease duration and DAS28 (CRP) were 46.0 (14.4) years, 5.5 (2.6) mths and 5.2 (1.1), respectively; 75% were female. No new safety signals were identified. In each arm, related AEs (ABA: 12 [30%]; ADA: 11 [27.5%]) and related serious AEs (ABA: 0; ADA: 1 [2.5%]) were similar. Numerically higher efficacy responses were seen with ABA vs ADA at Wk24 (Table 1). Similar results were observed for DAS28 (CRP), SDAI and CDAI. In SE+ pts, numerically higher efficacy responses were seen with ABA vs ADA at Wk24; 95% CI for estimated tmt differences for ACR20/50/70 responses and DAS28 (CRP) remission did not cross 0 (Figure 1). Conclusion In this seropositive early RA population, numerically higher efficacy responses were seen with abatacept vs adalimumab after 24wks of tmt, with more pronounced tmt differences in SE+ pts. Results are consistent with a previous study in which greater efficacy was seen with abatacept, but not TNF inhibitors, in anti-CCP2+ vs anti-CCP2- pts with RA (Harrold et al. J Rheumatol 2018). Acknowledgement Marianne Peluso (protocol manager); medical writing: Lola Parfitt (Caudex; funding: BMS) Disclosure of Interests William Rigby Consultant for: AbbVie, BMS, Genentech and Pfizer, Jane Buckner Grant/research support from: Janssen, Bristol-Myers Squibb (current); Novo Nordisk, Pfizer, Eli Lilly (past), Consultant for: Bristol-Myers Squibb, Eli Lilly, Lou Bridges: None declared, Marleen Nys Shareholder of: Bristol-Myers Squibb, Employee of: Bristol-Myers Squibb, Sheng Gao Shareholder of: Bristol-Myers Squibb, Employee of: Bristol-Myers Squibb, Martin Polinsky Shareholder of: Bristol-Myers Squibb, Employee of: Bristol-Myers Squibb, Alyssa Johnsen Shareholder of: Bristol-Myers Squibb, Employee of: Bristol-Myers Squibb, Neelanjana Ray Shareholder of: Bristol-Myers Squibb, Employee of: Bristol-Myers Squibb, Vivian Bykerk Grant/research support from: Mallinckrodt, BMS, Crescendo Biosciences, Sanofi/Regeneron., Consultant for: Amgen, Pfizer, UCB, Scipher, Sanofi/Genzyme/Regeneron

Background In the placebo (PBO)-controlled Phase III aSTRAEA study (ClinicalTrials.gov, NCT01860976) in psoriatic arthritis (PsA), abatacept (ABA) 125 mg SC weekly significantly increased the aCR20 response rate at Week 24 versus PBO (39.4% vs 22.3%, respectively; p Objectives To assess aBA safety up to 2 years in patients (pts) enrolled in aSTRAEA. Methods Pts with active PsA were randomised 1:1 to aBA or PBO for 24 weeks followed by 28 weeks’ open-label (OL) aBA (total time on study: 52 weeks); pts without ≥20% improvement in joint counts at Week 16 (early escape) were switched to OL aBA (total time on study: 44 weeks).1 Pts could subsequently receive OL aBA in a 52-week long-term extension (LTE; Year 2) for the collection of safety data. The proportions of pts in the cumulative aBA population (all pts who received ≥1 dose of aBA at any time in the study) with aEs (all aEs, serious aEs [SAEs], deaths, aEs leading to discontinuation), laboratory marked abnormalities and anti-ABA antibodies over the cumulative aBA period (date of first treatment dose to end of LTE) were recorded in 1-year and 6-month intervals. Results Overall, 398 pts were included in the analysis of the cumulative aBA period (213 received aBA from study Day 1; 185 completed initial randomisation to PBO and received aBA thereafter). Of these, 322 pts entered the LTE (initial randomisation: aBA, n=162; PBO, n=160) and continued to receive OL aBA beyond the 28-week OL period. Of 162 and 160 pts initially randomised to aBA and PBO, respectively, 19 (11.7%) and 21 (13.1%) pts discontinued aBA in the LTE. Median (range) number of aBA injections in the cumulative aBA period to end of LTE was 80 (1–133). Safety during the cumulative aBA period over 2 years is shown (Table 1); 6-month interval safety data will be available at time of presentation. In the LTE, there were 3 SAEs of infection (osteomyelitis, intervertebral discitis and cellulitis) and 3 pts discontinued due to infection (hepatitis a, Epstein-Barr virus, intervertebral discitis). No malignancies or deaths were reported, and no autoimmune events were reported as serious or led to aBA discontinuation during the LTE. AEs, SAEs and aEs of special interest occurred with a similar frequency regardless of concomitant MTX or prior TNF inhibitor (TNFi) use. The proportion of pts with anti-ABA antibodies during the cumulative aBA period was higher during the post-treatment period (≥22 days after last dose; 37.1% [91/245]) than in the on-treatment period (first treatment dose date to ≤21 days after last dose; 7.1% [28/392]). No apparent relationship between anti-ABA antibodies and efficacy in the on-treatment period or aEs suggestive of systemic immune reactions was seen. Conclusion Abatacept was well tolerated up to 2 years with no new safety signals during the LTE in this Phase III study in PsA. There was no impact of concomitant MTX use or prior TNFi exposure on the safety profile of abatacept. The occurrence of anti-abatacept antibodies had no impact on abatacept efficacy or safety. References [1] Mease PJ, et al. Ann Rheum Dis2017;76:1550–8. Acknowledgement Professional medical writing: andrea Plant, PhD, Caudex; funding: Bristol-Myers Squibb. Disclosure of interests Philip J Mease Grant/research support from: abbVie, amgen, BMS, Celgene, Janssen, Lilly, Novartis, Pfizer, SUN and UCB, Consultant for: abbVie, amgen, BMS, Galapagos, Gilead Sciences, inc., Janssen, Lilly, Novartis, Pfizer, SUN and UCB, Speakers bureau: abbVie, amgen, BMS, Celgene, Genentech, Janssen, Lilly, Novartis, Pfizer and UCB, alice B Gottlieb Grant/research support from: PI: incyte Corporation, Janssen-Ortho inc., Lilly ICOS LLC, Novartis, UCB, XBiotech, Consultant for: abbVie, Dermira, incyte Corporation, Lilly ICOS LLC, Novartis, Sun Pharmaceutical industries Ltd., avotres (unpaid), XBiotech (unpaid), Speakers bureau: abbVie, Eli Lilly and Company, Janssen Biotech; advisory board: Bristol-Myers Squibb, Celgene Corporation, Janssen Biotech, Janssen-Ortho inc., LEO Pharma, Novartis, UCB, Desiree van der Heijde Consultant for: abbVie, amgen, astellas, astraZeneca, Bristol-Myers Squibb, Boehringer ingelheim, Celgene, Daiichi, Eli-Lilly, Galapagos, Gilead, GlaxoSmithKline, Janssen, Merck, Novartis, Pfizer, Regeneron, Roche, Sanofi, Takeda, Union Chimique Belge, Oliver FitzGerald: None declared, alyssa Johnsen Shareholder of: Bristol-Myers Squibb, Employee of: Bristol-Myers Squibb, Marleen Nys Shareholder of: Bristol-Myers Squibb, Employee of: Bristol-Myers Squibb, Subhashis Banerjee Shareholder of: Bristol-Myers Squibb, Employee of: Bristol-Myers Squibb, Harris a ahmad Shareholder of: Bristol-Myers Squibb, Employee of: Bristol-Myers Squibb, Dafna D Gladman Grant/research support from: abbVie, amgen, Celgene, Lilly, Novartis, Pfizer, and UCB, Consultant for: abbVie, amgen, BMS, Celgene, Galapagos, Gilead, Janssen, Lilly, Novartis, Pfizer, and UCB

Background To explore the effect of abatacept treatment on patient-reported outcomes (PROs) in psoriatic arthritis (PsA). Methods Patients with PsA were randomised (1:1) to subcutaneous abatacept 125 mg weekly/placebo for 24 weeks with early escape (EE) to open-label abatacept (week 16). Adjusted mean changes from baseline to weeks 16 (all patients) and 24 (non-EE responders) in Health Assessment Questionnaire-Disability Index (HAQ-DI), Short Form-36 (SF-36; physical and mental component summary and domains), Dermatology Life Quality Index and Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-F) were evaluated. Subpopulations were analysed by baseline C-reactive protein (CRP) level (> vs ≤ upper limit of normal [ULN]) and prior tumour necrosis factor inhibitor (TNFi) exposure. Proportions of patients reporting improvements ≥ minimal clinically important differences (MCIDs) and ≥ normative values (NVs) in HAQ-DI, SF-36 and FACIT-F (week 16 before EE) were analysed. Results In total population, numerically higher improvements in most PROs were reported with abatacept (n = 213) versus placebo (n = 211) at both time points (P > 0.05). Higher proportions of abatacept versus placebo patients reported PRO improvements ≥ MCID and ≥ NV at week 16. At week 16, all PRO improvements were numerically greater (P > 0.05) in patients with baseline CRP > ULN versus CRP ≤ ULN (all significant [95% confidence interval] for abatacept vs placebo); improvements in SF-36 component summaries and FACIT-F were greater in TNFi-naïve versus TNFi-exposed patients (abatacept > placebo). Week 24 subgroup data were difficult to interpret due to low patient numbers. Conclusions Abatacept treatment improved PROs in patients with PsA versus placebo, with better results in elevated baseline CRP and TNFi-naïve subpopulations. Trial registration ClinicalTrials.gov number, NCT01860976 (funded by Bristol-Myers Squibb); date of registration: 23 May 2013. Electronic supplementary material The online version of this article (10.1186/s13075-018-1769-7) contains supplementary material, which is available to authorized users.

To explore antinuclear autoantibody (ANA) and anti-double-stranded DNA (anti-dsDNA) autoantibody development during abatacept and tumour necrosis factor inhibitor (TNFi) treatment, and effects of switching from TNFi to abatacept in ANA/anti-dsDNA autoantibody-positive patients.This was a post hoc analysis of biologic-naïve patients with active RA in ATTEST and AMPLE. In AMPLE, patients received subcutaneous abatacept or adalimumab (2 years). In ATTEST, patients received intravenous abatacept or infliximab (1 year), or placebo (6 months) then abatacept (6 months); at 1 year, all patients could receive abatacept (open-label long-term extension). Serum ANA/anti-dsDNA autoantibody levels were measured at baseline, Month 6 (ATTEST only), Years 1 and 2.At baseline, 25.7 and 0.9% (AMPLE), and 21.6 and 8.4% of patients (ATTEST) were ANA/anti-dsDNA autoantibody positive, respectively. More baseline ANA/anti-dsDNA autoantibody-negative patients became positive during TNFi than abatacept treatment. In ATTEST (TNFi group), 48.5% (48/99; ANA) and 48.3% (57/118; anti-dsDNA) of patients seroconverted to positive status by Year 1, falling to 22.4% (22/98 ANA) and 13.3% (15/113; anti-dsDNA) by Year 2 after switching to abatacept. Of ANA/anti-dsDNA autoantibody-positive patients at Year 1, 41.9% and 68.9%, were negative at Year 2.ANA/anti-dsDNA seroconversion was more frequent with TNFi than abatacept therapy; TNFi-associated seroconversion decreased after switching from TNFi to abatacept.

Objective To develop an objective, readily measurable pharmacodynamic biomarker of glucocorticoid (GC) activity. Methods Genes modulated by prednisolone were identified from in vitro studies using peripheral blood mononuclear cells from normal healthy volunteers. Using the criteria of a >2-fold change relative to vehicle controls and an adjusted P value cutoff of less than 0.05, 64 up-regulated and 18 down-regulated genes were identified. A composite score of the up-regulated genes was generated using a single-sample gene set enrichment analysis algorithm. Results GC gene signature expression was significantly elevated in peripheral blood leukocytes from normal healthy volunteers following oral administration of prednisolone. Expression of the signature increased in a dose-dependent manner, peaked at 4 hours postadministration, and returned to baseline levels by 48 hours after dosing. Lower expression was detected in normal healthy volunteers who received a partial GC receptor agonist, which is consistent with the reduced transactivation potential of this compound. In cohorts of patients with systemic lupus erythematosus and patients with rheumatoid arthritis, expression of the GC signature was negatively correlated with the percentages of peripheral blood lymphocytes and positively correlated with peripheral blood neutrophil counts, which is consistent with the known biology of the GC receptor. Expression of the signature largely agreed with reported GC use in these populations, although there was significant interpatient variability within the dose cohorts. Conclusion The GC gene signature identified in this study represents a pharmacodynamic marker of GC exposure.

Background Maturation of autoantibody responses has been suggested to be a proxy for disease maturation. Autoantibody responses against post-translationally modified antigens are present in autoimmune diseases and antibodies directed against carbamylated proteins (anti-CarP antibodies) are a marker of RA. Anti-CarP antibody analysis in patients with early RA offers the opportunity to estimate whether specific intervention during such early stages of autoantibody development may have an impact on the maturation of the anti-CarP antibody response. Objectives We assessed the relationship between changes in anti-CarP isotypes and rates of seroconverson to negative in patients with early RA. Methods In the Assessing Very Early Rheumatoid arthritis Treatment study (AVERT; NCT01142726), patients with early RA were treated with abatacept (ABA)+MTX, ABA monotherapy or MTX alone. 1 Patients in AVERT were anti-cyclic citrullinated peptide-2 positive at baseline for study entry. 1 In this post hoc analysis, concentrations of anti-CarP isotypes were measured using custom ELISAs. Anti-CarP ELISAs for immunoglobulin (Ig)G, IgM or IgA isotypes were performed in patient serum at baseline, and at Days 85 and 365 on treatment. Baseline levels of each anti-CarP antibody isotype and % seropositivity were comparable across the three treatment arms. Adjusted mean change from baseline was calculated using a longitudinal repeated measures model. Results At baseline, 51.3, 42.5 and 29.3% of all patients with serum available in AVERT were positive for IgG, IgM (indicative of an ongoing immunoresponse) and IgA anti-CarP isotypes, respectively. Overall, approximatly 65% of patients were positive for at least one anti-CarP antibody isotype. Median % change from baseline (25%, 75%) for anti-CarP isotypes levels from baseline to Days 85 and 365 are shown (Table). Analysing patients who were positive at baseline for each of the isotypes, we observed that 19/48 (40%), 16/43 (37%) and 11/48 (23%) of the patients positive for the IgG isotype became negative on ABA+MTX, ABA and MTX, respectively, at 1 year. For the IgM isotype, 26/48 (54%), 14/36 (39%) and 15/38 (39%) became negative on ABA+MTX, ABA and MTX, respectively. For the IgA isotype, 12/26 (46%), 10/23 (43%) and 13/31 (42%) became negative on ABA+MTX, ABA and MTX, respectively. Conclusions Concentrations of all anti-CarP isotypes (IgM, IgA, IgG) were numerically reduced by abatacept+MTX therapy compared with MTX or abatacept alone. Abatacept+MTX trended towards higher rates of seroconversion to negative for all isotypes over 1 year of treatment. These results indicate that the extent of the anti-CarP antibody response can be modulated by intervention with abatacept on background MTX in anti-citrullinated protein antibody-positive patients with early RA. References Emery P, et al. Ann Rheum Dis 2015;74:19–26. Disclosure of Interest L. Trouw: None declared, S. Connolly Shareholder of: Bristol-Myers Squibb, Employee of: Bristol-Myers Squibb, A. Johnsen Employee of: Bristol-Myers Squibb, J. Ye Shareholder of: Bristol-Myers Squibb, Employee of: Bristol-Myers Squibb, M. Maldonado Shareholder of: Bristol-Myers Squibb, Employee of: Bristol-Myers Squibb, R. Toes: None declared, T. Huizinga Grant/research support from: EU & Dutch Arthritis Foundation, Consultant for: Abbott Laboratories, Biotest AG, Bristol-Myers Squibb, Crescendo Bioscience, Inc, Novartis Pharmaceuticals Corporation, Pfizer Inc, Roche, sanofi-aventis, Schering-Plough, UCB, Inc., Eli Lilly, Speakers bureau: Abbott Laboratories, Biotest AG, Bristol-Myers Squibb, Novartis Pharmaceuticals Corporation, Pfizer Inc, Roche, sanofi-aventis, Schering-Plough

Background In the Phase III ASTRAEA trial (NCT01860976), abatacept (ABA), a selective T-cell co-stimulation modulator, significantly increased ACR20 response (primary endpoint; PE) and had an overall beneficial effect vs placebo (PBO) on musculoskeletal symptoms in patients (pts) with active psoriatic arthritis (PsA) at 24 weeks (W). 1 Objectives To analyse 1-year results from ASTRAEA. Methods Pts with active disease (≥3 swollen and ≥3 tender joints), ≥2 cm target lesion of plaque psoriasis and inadequate response/intolerance to ≥1 non-biologic DMARD were randomized (1:1) to SC ABA 125 mg weekly or PBO for 24W, followed by open-label (OL) SC ABA up to 52W. Randomization was stratified by MTX use, prior TNF inhibitor (TNFi) use and skin involvement ≥3% of body surface area. Pts without ≥20% improvement in joint counts at W16 were switched to OL ABA (early escape; EE) for 28W (total study time: 44W). Pre-specified exploratory endpoints included: ACR20/50/70 responses at W44; adjusted mean changes from baseline (BL) in DAS28 (CRP; post hoc analysis) and HAQ-DI at W44 and PsA-modified total Sharp/van der Heijde score (SHS) at W44 (EE pts)/W52 (non-EE pts); complete resolution of BL enthesitis and dactylitis at W44 (EE pts)/W52 (non-EE pts); and Psoriasis Area and Severity Index (PASI) 50/75 responses at W44. Analyses used the ITT population with non-responder imputation for missing values and actual data at each time point for all pts (denominator at each time point equal to number of pts in ITT population). All missing responses were imputed as non-responders, except if the missing value was between 2 visits for which the pt was a responder. In that case the missing value was imputed as a responder. Results Of 424 pts enrolled, 213 received ABA and 211 PBO. Most (>60%) pts had received prior TNFis. Of pts in the ABA and PBO groups, 76 (36%) and 89 (42%) were EE, 12 (6%) and 24 (11%) discontinued by PE of W24; 197 (92%) and 185 (88%) entered the OL period, of whom 165 (84%) and 162 (88%) completed. At W44, ACR responses at W24 were maintained for pts who continued ABA, and improved for those who switched from PBO to ABA (Figure). Continued improvements in DAS28 (CRP) and HAQ-DI after W24 were seen for ABA and PBO/ABA groups, with mean (SE) changes from BL to W44 of –1.81 (0.09) and –1.84 (0.10) in DAS28 (CRP) (changes to W24 were –1.35 [0.10] and –0.94 [0.11]) and –0.37 (0.04) and –0.38 (0.04) in HAQ-DI (changes to W24 were –0.33 [0.04] and –0.20 [0.05]), respectively. There was minimal progression based on mean (SE) change from BL in PsA-modified total SHS at W44/52 in the ABA and PBO/ABA groups: 0.18 (0.12) vs 0.30 (0.12). Complete resolution of BL enthesitis occurred in 48.6% and 43.9% and BL dactylitis in 68.9% and 60.0% of pts with ABA and ABA/PBO, respectively, at W44/52. At W44, for ABA and PBO/ABA, PASI 50 responses were 30.1% and 34.5%; PASI 75 responses were 19.9% and 16.9%. There were no new safety signals. Conclusions Responses were maintained across musculoskeletal endpoints up to 1 year in a relatively refractory population of pts continuing on SC abatacept. Abatacept was well tolerated. References Mease P, et al. Arthritis Rheumatol 2016;68(Suppl 10):Abstract 1041. Disclosure of Interest P. Mease Grant/research support from: AbbVie, Amgen, Bristol-Myers Squibb, Celgene, Janssen, Lilly, Novartis, Pfizer, Sun, UCB, Consultant for: AbbVie, Amgen, Bristol-Myers Squibb, Celgene, Crescendo Bioscience, Corrona, Demira, Janssen, Lilly, Novartis, Pfizer, Sun, UCB, Zynerba, Speakers bureau: AbbVie, Amgen, Bristol-Myers Squibb, Celgene, Crescendo Bioscience, Genentech, Janssen, Novartis, Pfizer, UCB, A. Gottlieb Grant/research support from: Centocor (Janssen), Amgen, Abbott (AbbVie), Novartis, Celgene, Pfizer, Lilly, Coronado, Levia, Merck, Xenoport, Dermira, Baxalta, Consultant for: Amgen Inc.; Astellas, Akros, Centocor (Janssen), Inc.; Celgene Corp., Bristol-Myers Squibb Co., Beiersdorf, Inc., Abbott Labs. (AbbVie), TEVA, Actelion, UCB, Novo Nordisk, Novartis, Dermipsor Ltd., Incyte, Pfizer, Canfite, Lilly, Coronado, Vertex, Karyopharm, CSL Behring Biotherapies for Life, GlaxoSmithKline, Xenoport, Catabasis, Meiji Seika Pharma Co., Ltd, Takeda, Mitsubishi Tanabe Pharma Development America, Inc, Genentech, Baxalta, D. van der Heijde Consultant for: AbbVie, Amgen, Astellas, AstraZeneca, Bristol-Myers Squibb, Boeringer Ingelheim, Celgene, Daiichi, Eli-Lilly, Galapagos, Gilead, Janssen, Merck, Novartis, Pfizer, Regeneron, Roche, Sanofi, UCB, O. FitzGerald: None declared, A. Johnsen Employee of: Bristol-Myers Squibb, M. Nys Shareholder of: Bristol-Myers Squibb, Employee of: Bristol-Myers Squibb, S. Banerjee Shareholder of: Bristol-Myers Squibb, Employee of: Bristol-Myers Squibb, D. Gladman Grant/research support from: AbbVie, Amgen, Celgene, Janssen, Novartis, Pfizer, UCB, Consultant for: AbbVie, Amgen, BMS, Celgene, Eli Lilly, Janssen, Novartis, Pfizer, UCB

Background In the Phase III ASTRAEA study (NCT01860976), abatacept (ABA) significantly increased ACR20 responses, with benefits on other musculoskeletal symptoms in patients (pts) with active psoriatic arthritis (PsA). 1 As PsA impacts HRQoL, assessing treatment (tmt) effect using patient-reported outcomes (PROs) is important. Objectives To explore the effect of ABA tmt using PROs in intent-to-treat and post hoc analyses of ASTRAEA. Methods Pts were randomized (1:1) to SC ABA 125 mg weekly or placebo (PBO) for 24 weeks (W). At W16, pts without ≥20% improvement in joint counts started open-label ABA. Adjusted mean changes from baseline (BL) to W16 (all pts) and W24 (responder analysis) in Short Form-36 (SF-36; physical and mental component summary [PCS, MCS] and individual domains using spydergrams), pain VAS and HAQ-DI scores, Dermatology QoL Index (DLQI) and FACIT-Fatigue scale (FACIT-F) were evaluated in the total population and subgroups stratified by BL CRP level and prior TNFi use. Proportions of pts reporting improvements ≥minimal clinically important difference (MCID) in SF-36 summary (≥2.5) and domain (≥5.0), FACIT-F (≥40) and HAQ-DI ( Results In the total population, improvements in all PROs were numerically greater for ABA (n=213) vs PBO (n=211) at W16 and W24 and significant for SF-36 PCS at W16 and HAQ-DI at W24 (Table). At W16, improvements in all SF-36 domains were numerically greater with ABA, and significant for physical function, bodily pain and vitality. A higher proportion of pts receiving ABA vs PBO reported improvements ≥MCID in SF-36 PCS, MCS, SF-36 domains, FACIT-F, HAQ-DI (Fig) and DLQI (not shown) at W16. The proportion of pts whose scores were ≥normative values at W16 was higher with ABA vs PBO in SF-36 PCS, MCS, FACIT-F and HAQ-DI scores. At W24, improvements in SF-36 domain scores accrued in both groups, with numerical differences in favour of ABA except in social function. Improvements in PROs were greater with ABA tmt in BL CRP>upper limit of normal (ULN) vs CRP≤ULN and in TNFi-naive vs -exposed subpopulations. Conclusions Abatacept treatment improved many PROs in pts with active PsA, with larger benefits in the CRP>ULN and TNF-naive subpopulations. References Mease P, et al. Arthritis Rheumatol 2016;68(suppl 10): [Abstract 1041]. Disclosure of Interest V. Strand Consultant for: AbbVie, Amgen Corporation, AstraZeneca, Biogen Idec, Bristol-Myers Squibb, Boehringer Ingelheim, Celgene, Celltrion, Corrona, Crescendo/Myriad Genetics, EMD Serono, Genentech/Roche, GlaxoSmithKline, Janssen, Lilly, Merck, Novartis, Pfizer, Regeneron, Samsung, Sandoz, Sanofi, UCB, E. Alemao Shareholder of: Bristol-Myers Squibb, Employee of: Bristol-Myers Squibb, T. Lehman Shareholder of: Bristol-Myers Squibb, Employee of: Bristol-Myers Squibb, A. Johnsen Employee of: Bristol-Myers Squibb, S. Banerjee Shareholder of: Bristol-Myers Squibb, Employee of: Bristol-Myers Squibb, H. Ahmad Shareholder of: Bristol-Myers Squibb, Employee of: Bristol-Myers Squibb, P. Mease Grant/research support from: AbbVie, Amgen, Bristol-Myers Squibb, Celgene, Janssen, Lilly, Novartis, Pfizer, Sun, UCB, Speakers bureau: AbbVie, Amgen, Bristol-Myers Squibb, Celgene, Crescendo Bioscience, Genentech, Janssen, Novartis, Pfizer, UCB

Background Abatacept, a selective T-cell co-stimulation modulator, significantly increased ACR20 response and had an overall beneficial effect on musculoskeletal symptoms in patients (pts) with active psoriatic arthritis (PsA) in the Phase III Active pSoriaTic athritis RAndomizEd triAl (ASTRAEA, NCT01860976). 1 Factors that may predict responses to abatacept were explored in this post hoc analysis. Objectives To evaluate the relationship between baseline characteristics and abatacept response in a post hoc analysis of ASTRAEA. Methods Pts were randomized (1:1) to SC abatacept 125 mg weekly or placebo for 24 weeks in this trial. Pts without >20% improvement in joint counts at Week 16 were switched to open-label abatacept (early escape). ACR20 response rate in pts stratified by baseline variables was investigated in a multivariate analysis and odds ratios (ORs) generated to identify differences in response. Using a cut-off of OR 1.2, indicating pt subgroups in whom abatacept appeared to have a meaningful treatment benefit, baseline variables were further investigated in a univariate analysis and estimated differences calculated. Results Of 424 pts enrolled, 213 received abatacept and 211 placebo. In abatacept-treated pts, the multivariate model showed a difference in ACR20 response (OR >1.2) for baseline CRP (>upper limit of normal [ULN] vs ≤ULN; OR 1.346 [95% CI 0.668, 2.712]), DAS28 (CRP) (>5.1 vs ≤5.1; 1.489 [0.782, 2.836]), dactylitis (>0 vs 0; 1.372 [0.708, 2.659]), and median baseline erosions (≥3 vs 1.2 for dactylitis only (1.406 [0.619, 3.193]). These factors, which have been identified previously as indicating poor prognosis in PsA, were balanced between treatment arms at baseline. In the univariate model by poor prognostic factors, the differences in ACR20 response rates with abatacept treatment vs placebo in distinct subgroups were numerically greater in pts who were positive for these prognostic factors at baseline than in those who were not (Figure). Conclusions These findings identified subgroups of pts with PsA with certain baseline characteristics in whom abatacept is most likely to be effective. The predictive factors identified are aligned with poor prognostic factors in the EULAR and Group for Research and Assessment of Psoriasis and Psoriatic Arthritis (GRAPPA) guidelines, 2,3 and may indicate pts with the highest unmet medical need. References Mease P, et al. Arthritis Rheumatol 2016;68(Suppl 10):[Abstract 1041]. Gossec L, et al. Ann Rheum Dis 2016;75:499–510. Coates L, et al. Arthritis Rheumatol 2016;68:1060–71. Disclosure of Interest P. Mease Grant/research support from: AbbVie, Amgen, Bristol-Myers Squibb, Celgene, Janssen, Lilly, Novartis, Pfizer, Sun, UCB, Consultant for: AbbVie, Amgen, Bristol-Myers Squibb, Celgene, Crescendo Biosciences, Corrona, Demira, Janssen, Lilly, Novartis, Pfizer, Sun, UCB, Zynerba, Speakers bureau: AbbVie, Amgen, Bristol-Myers Squibb, Celgene, Crescendo Biosciences, Genentech, Janssen, Novartis, Pfizer, UCB, I. McInnes Grant/research support from: Bristol-Myers Squibb, Celgene, Janssen, UCB, Consultant for: Bristol-Myers Squibb, Celgene, Janssen, Novartis, Pfizer, AbbVie, UCB, V. Strand Consultant for: AbbVie, Amgen Corporation, AstraZeneca, Biogen Idec, Bristol-Myers Squibb, Boehringer Ingelheim, Celgene, Celltrion, Corrona, Crescendo Biosciences/Myriad Genetics, EMD Serono, Genentech/Roche, GlaxoSmithKline, Janssen, Lilly, Merck, Novartis, Pfizer, Regeneron, Samsung, Sandoz, Sanofi, UCB, O. FitzGerald Grant/research support from: AbbVie, Pfizer, Bristol-Myers Squibb, Consultant for: AbbVie, Pfizer, Bristol-Myers Squibb, Celgene, Janssen, Novartis, UCB, Lilly, H. Ahmad Shareholder of: Bristol-Myers Squibb, Employee of: Bristol-Myers Squibb, A. Johnsen Employee of: Bristol-Myers Squibb, Celgene, Janssen, Novartis, Pfizer, AbbVie, UCB, J. Ye Shareholder of: Bristol-Myers Squibb, Employee of: Bristol-Myers Squibb, S. Banerjee Shareholder of: Bristol-Myers Squibb, Employee of: Bristol-Myers Squibb

ObjectivesTo examine whether baseline anti-cyclic citrullinated peptide-2 (CCP2) antibody status and concentration correlated with clinical outcomes in patients treated with abatacept or adalimumab on background methotrexate (MTX) in the 2-year AMPLE (Abatacept versus adaliMumab comParison in bioLogic-naïvE rheumatoid arthritis subjects with background MTX) study.MethodsIn this exploratory analysis, anti-CCP2 antibody concentration was measured at baseline, and antibody-positive patients were divided into equal quartiles, Q1–Q4, representing increasing antibody concentrations. Clinical outcomes analysed by baseline anti-CCP2 status and quartile included change from baseline in disease activity and disability and remission rates.ResultsBaseline characteristics were generally comparable across quartiles and treatment groups. In both treatment groups, anti-CCP2 antibody-negative patients responded less well than antibody-positive patients. At year 2, improvements in disease activity and disability and remission rates were similar across Q1–Q3, but were numerically higher in Q4 in the abatacept group; in contrast, treatment effects were similar across all quartiles in the adalimumab group.ConclusionsIn AMPLE, baseline anti-CCP2 positivity was associated with a better response for abatacept and adalimumab. Patients with the highest baseline anti-CCP2 antibody concentrations had better clinical response with abatacept than patients with lower concentrations, an association that was not observed with adalimumab.Trial registration numberNCT00929864.

In humans and in animal models, susceptibility to arthritis is under complex genetic control, reflecting influences on the immunological processes that initiate autoimmunity and on subsequent inflammatory mechanisms in the joints. The effector phases are conveniently modeled by the K/BxN serum transfer system, a robust model well suited for genetic analysis where arthritis is initiated by pathogenic Ig. Here, we mapped the genetic loci distinguishing the high-responder BALB/c vs. low-responder SJL strains. After computational modeling of potential breeding schemes, we adapted a stepwise selective breeding strategy, with a whole-genome scan performed on a limited number of animals. Several genomic regions proved significantly associated with high sensitivity to arthritis. One of these regions, on distalchr2, was centered on the interleukin 1 gene family. Quantitation of transcripts of theIl1aandIl1bcandidate genes revealed a 10-fold greater induction ofIl1bmRNA in BALB/c than in SJL splenocytes after injection of LPS, whereasIl1ashowed much less difference. The differential activity of theIl1bgene was associated with a particular sequence haplotype of noncoding polymorphisms. The BALB/c haplotype was found in 75% of wild-derived strains but was rare among conventional inbred strains (4/33 tested, one of which is DBA/1, the prototype arthritis-susceptible strain) and was associated with vigorousIl1bresponses in a panel of inbred strains. Inbred strains carrying this allele were far more responsive to serum-transferred arthritis, confirming its broad importance in controlling arthritis severity.

Processing of exogenous antigens and microbes involves contributions by multiple different endocytic and phagocytic compartments. During the processing of soluble antigens, different endocytic compartments have been demonstrated to use distinct antigen-processing mechanisms and to process distinct sets of antigenic epitopes. Processing of particulate and microbial antigens involves phagocytosis and functions contributed by phagocytic compartments. Recent data from our laboratory demonstrate that phagosomes containing antigen-conjugated latex beads are fully competent class II MHC (MHC-II) antigen-processing organelles, which generate peptide:MHC-II complexes. In addition, phagocytosed antigen enters an alternate class I MHC (MHC-I) processing pathway that results in loading of peptides derived from exogenous antigens onto MHC-I molecules, in contrast to the cytosolic antigen source utilized by the conventional MHC-I antigen-processing pathway. Antigen processing and other immune response mechanisms may be activated or inhibited by microbial components to the benefit of either the host or the pathogen. For example, antigen processing and T-cell responses (e.g. Th1 vs Th2 differentiation) are modulated by multiple distinct microbial components, including lipopolysaccharide, cholera toxin, heat labile enterotoxin of Escherichia coli, DNA containing CpG motifs (found in prokaryotic and invertebrate DNA but not mammalian DNA) and components of Mycobacterium tuberculosis.

Background Anti-TNF therapy is associated with the induction of antinuclear antibodies (ANAs) and anti-double-stranded DNA (anti-dsDNA) antibodies in patients (pts) with RA.1,2 The effect of subsequent biologic therapy on such pts has not been explored. Objectives To compare the development of ANA and anti-dsDNA antibodies during treatment with abatacept (ABA) and anti-TNFs in the ATTEST and AMPLE trials, and to evaluate the effect of switching to ABA in pts with RA who developed anti-TNF-induced ANA/anti-dsDNA antibodies in the ATTEST trial. Methods In the 1-year double-blind (DB) ATTEST trial, pts were randomized to IV ABA (∼10 mg/kg every 4 weeks), infliximab (IFX; 3 mg/kg every 8 weeks) or placebo, all on background MTX. At Mth 6, placebo-treated pts were reallocated to ABA (blinding maintained); pts initially randomized to ABA or IFX continued treatment. Pts completing the 1-year DB period were eligible to receive ABA in an open-label long-term extension (OLE). In the head-to-head AMPLE trial, pts were randomized to SC ABA (125 mg weekly) or SC adalimumab (ADA; 40 mg biweekly), on background MTX for 2 years. Pts in both trials were biologic naive, with an inadequate response to prior MTX and active RA. Blood samples were collected for the measurement of ANA and anti-dsDNA at baseline, Mth 6, Year 1 (end of DB period) and Year 2 (OLE) in the ATTEST trial, and at baseline, Year 1 and Year 2 in the AMPLE trial. Results In the ATTEST DB period, 156 pts received IV ABA and 165 received IFX; 132 ABA- and 136 IFX-treated pts continued into the OLE and received IV ABA. In AMPLE, 318 pts received SC ABA and 328 received ADA. At baseline in the ATTEST trial, 69 pts on active treatment (32 IV ABA, 37 IFX) were ANA positive and 26 pts (11 IV ABA, 15 IFX) were anti-dsDNA positive. In the AMPLE study, the respective numbers at baseline were: 166 ANA-positive pts (72 SC ABA, 94 ADA) and 6 anti-dsDNA-positive pts (1 SC ABA, 5 ADA). The % of pts with seroconversion for ANA or anti-dsDNA in the active treatment arms of each trial are shown in the [Table][1]. In both ATTEST and AMPLE, a higher % of pts receiving anti-TNF therapy seroconverted from baseline negative to positive during Year 1 of treatment, compared with those receiving ABA. This difference in autoantibody induction for anti-TNF versus ABA continued during the second year of AMPLE. In ATTEST, 48.5% (ANA) and 48.3% (anti-dsDNA) of IFX-treated pts who entered the OLE seroconverted from baseline ANA or anti-dsDNA negative to positive at Year 1; this dropped to 22.4% and 13.3%, respectively, at Year 2 after switching to ABA. The % of pts who converted from baseline positive to negative status increased from 12.1% in the IFX group to 20.6% on switching to ABA ([Table][1]). ![Figure][2] Conclusions In the ATTEST trial, switching from infliximab to abatacept seemed to reverse the autoantibody induction observed with anti-TNF treatment. Anti-TNF therapy was associated with greater autoantibody (ANA and anti-dsDNA) induction than abatacept in the ATTEST and AMPLE trials. These data provide additional insights into differences in the mechanism of action of anti-TNFs and abatacept, and imply an effect of T-cell co-stimulation blockade on B-cell function and autoantibody production. References 1. Charles PJ, et al. Arthritis Rheum 2000;43:2383–90. 2. Eriksson C, et al. Ann Rheum Dis 2005;64:403–7. Disclosure of Interest M. H. Buch Grant/research support from: Pfizer, Bristol-Myers Squibb, Speakers bureau: AbbVie, Bristol-Myers Squibb, Roche-Chugai, Pfizer, A. Johnsen Employee of: Bristol-Myers Squibb, D. A. Wong Shareholder of: Bristol-Myers Squibb, Employee of: Bristol-Myers Squibb, M. Schiff Grant/research support from: UCB, Consultant for: AbbVie, Amgen, Antares, Bristol-Myers Squibb, Eli Lilly, Horizon, Johnson and Johnson, Novartis, Novo Nordisk, Pfizer, Roche, UCB, Speakers bureau: AbbVie [1]: #F1 [2]: pending:yes

Objective Susceptibility to inflammatory arthritis is determined by a complex set of environmental and genetic factors, but only a portion of the genetic effect can be explained. Conventional genome-wide screens of arthritis models using crosses between inbred mice have been hampered by the low resolution of results and by the restricted range of natural genetic variation sampled. The aim of this study was to address these limitations by performing a genome-wide screen for determinants of arthritis severity using a genetically heterogeneous cohort of mice. Methods Heterogeneous stock (HS) mice derive from 8 founder inbred strains by serial intercrossing (n > 60), resulting in fine-grained genetic variation. With a cohort of 570 HS mice, we performed a genome-wide screen for determinants of arthritis severity in the K/BxN serum–transfer model. Results We mapped regions on chromosomes 1, 2, 4, 6, 7, and 15 that contain quantitative trait loci influencing arthritis severity at a resolution of a few megabases. In several instances, these regions proved to contain 2 quantitative trait loci: the region on chromosome 2 included the C5 fraction of complement known to be required for K/BxN serum–transfer arthritis but also contained a second adjacent quantitative trait locus, for which an intriguing candidate is Ptgs1 (Cox1). Interesting candidates on chromosome 4 included the Padi family, encoding the peptidyl arginine deiminases responsible for citrulline protein modification; suggestively, Padi2 and Padi4 RNA expression was correlated with arthritis severity in HS mice. Conclusion These results provide a broad overview of the genetic variation that controls the severity of K/BxN serum–transfer arthritis and suggest intriguing candidate genes for further study.

Objective It has been suggested that polymorphisms in IL1 are correlated with severe and/or erosive rheumatoid arthritis (RA), but the implicated alleles have differed among studies. The aim of this study was to perform a broad and well-powered search for association between allelic polymorphism in IL1A and IL1B and the susceptibility to or severity of RA. Methods Key coding and regulatory regions in IL1A and IL1B were sequenced in 24 patients with RA, revealing 4 novel single-nucleotide polymorphisms (SNPs) in IL1B. These and a comprehensive set of 24 SNPs tagging most of the underlying genetic diversity were genotyped in 3 independent RA case–control sample sets and 1 longitudinal RA cohort, totaling 3,561 patients and 3,062 control subjects. Results No fully significant associations were observed. Analysis of the discovery case–control sample sets indicated a potential association of IL1B promoter region SNPs with susceptibility to RA (for RA3/A, odds ratio [OR] 1.27, P = 0.0021) or with the incidence of radiographic erosions (for RA4/C, OR 1.56, P = 0.036), but these findings were not replicated in independent case–control samples. No association with rheumatoid factor, anti–cyclic citrullinated peptide, or the Disease Activity Score in 28 joints was found. None of the associations previously observed in other studies were replicated here. Conclusion In spite of a broad and highly powered study, we observed no robust, reproducible association between IL1A/B variants and the susceptibility to or severity of RA in white individuals of European descent. Our results provide evidence that, in the majority of cases, polymorphism in IL1A and IL1B is not a major contributor to genetic susceptibility to RA.

Mast cells are immune sentinels that participate in the defense against bacteria and parasites. Resident within the joint, mast cells become activated in human rheumatoid arthritis and are implicated in the pathogenesis of experimental murine synovitis. However, their arthritogenic role remains undefined. Using a model of autoantibody-induced arthritis, we show that mast cells contribute to the initiation of inflammation within the joint by elaboration of IL-1. Mast cells become activated to produce this cytokine via the IgG immune complex receptor FcγRIII. Interestingly, mast cells become dispensable for the perpetuation of arthritis after delivery of IL-1, highlighting the contribution of this lineage to arthritis induction. These findings illuminate a mechanism by which mast cells can participate in the pathogenesis of autoimmune inflammatory arthritis and provide insights of potential relevance to human rheumatoid arthritis.

Background Anti-citrullinated protein antibodies (ACPA) are a marker of RA, and the presence of the immunoglobulin M (IgM) isotype indicates an ongoing immune response involving the recruitment of naive B cells.1 Abatacept (ABA) modulates T-cell co-stimulation and has been shown to impact ACPA maturation, including seroconversion of IgM, in the AVERT (Assessing Very Early Rheumatoid arthritis Treatment) trial.2 Objectives To assess the efficacy of treatment with ABA+MTX, ABA monotherapy or MTX alone in patients (pts) from the AVERT trial based on their anti-cyclic citrullinated peptide 2 (CCP2; a surrogate for ACPA) IgM serostatus at baseline (BL), and seroconversion (anti-CCP2 IgM positive to negative) through 1 year. Methods The AVERT trial has been described previously.3 In this post hoc analysis, pt samples were analysed by ELISA to determine anti-CCP2 IgM serostatus. Efficacy outcomes analysed by BL anti-CCP2 IgM serostatus included remission rate at 12 mths (CDAI, SDAI, Boolean and DAS28 [CRP] Results In the ABA+MTX treatment arm, a higher proportion of pts who were anti-CCP2 IgM positive at BL achieved remission by all indices compared with pts who were BL IgM negative (Figure). This trend was most clearly observed in the stringent indices of CDAI, SDAI and Boolean remission, compared with DAS28 (CRP)-defined remission. This trend was not observed in either the ABA monotherapy or MTX alone arms. Mean improvement in DAS28 (CRP) and HAQ-DI over time was also greatest in BL anti-CCP2 IgM-positive pts treated with ABA+MTX. A numerically higher proportion of pts who seroconverted from anti-CCP2 IgM positive at BL to negative at Mth 12 achieved Boolean remission versus pts who remained seropositive in the ABA+MTX and ABA monotherapy arms (Table). Conclusions Abatacept in combination with MTX had greater clinical efficacy in pts who were anti-CCP2 IgM positive at BL than in those who were anti-CCP2 IgM negative at BL, and in those who seroconverted over time than those who did not, suggesting that the impact on ACPA is associated with clinical benefit. References Verpoort KN, et al. Arthritis Rheum 2006;54:3799–808. Huizinga TWJ, et al. Arthritis Rheum 2014;66:S666. Poster 1515. Emery P, et al. Ann Rheum Dis 2015:74:19–26. Disclosure of Interest T. W. J. Huizinga Grant/research support from: EU & Dutch Arthritis Foundation, Consultant for: Abbott Laboratories, Biotest AG, Bristol-Myers Squibb, Crescendo Bioscience, Inc, Novartis Pharmaceuticals Corporation, Pfizer Inc, Roche, sanofi-aventis, Schering-Plough, UCB, Inc., Eli Lilly, Meteor Board, Speakers bureau: Abbott Laboratories, Biotest AG, Bristol-Myers Squibb, Novartis Pharmaceuticals Corporation, Pfizer Inc, Roche, sanofi-aventis, Schering-Plough, S. E. Connolly Shareholder of: Bristol-Myers Squibb, Employee of: Bristol-Myers Squibb, A. Johnsen Employee of: Bristol-Myers Squibb, J. Zhu Employee of: Bristol-Myers Squibb, D. E. Furst Grant/research support from: AbbVie, Actelion, Amgen, Bristol-Myers Squibb, Gilead, GSK, NIH, Novartis, Pfizer, Roche/Genentech, UCB, Consultant for: AbbVie, Actelion, Amgen, Bristol-Myers Squibb, Cytori, Janssen, Gilead, GSK, NIH, Novartis, Pfizer, Roche/Genentech, UCB, Speakers bureau: (CME only) AbbVie, Actelion, UCB, V. P. Bykerk Grant/research support from: Amgen, Pfizer, Bristol-Myers Squibb, Janssen, UCB, Roche/Genentech, Consultant for: Amgen, Pfizer, Bristol-Myers Squibb, UCB, Roche, G. R. Burmester Grant/research support from: Bristol-Myers Squibb, AbbVie, Pfizer, Medimmune, Novartis, Roche, UCB, Lilly, Consultant for: Bristol-Myers Squibb, AbbVie, Pfizer, MSD, Medimmune, Roche, UCB, Speakers bureau: Bristol-Myers Squibb, AbbVie, Pfizer, MSD, Roche, UCB, B. G. Combe Grant/research support from: Pfizer, Roche-Chugai, Speakers bureau: Bristol-Myers Squibb, Merck, Pfizer, Roche-Chugai, UCB, D. A. Wong Shareholder of: Bristol-Myers Squibb, Employee of: Bristol-Myers Squibb, L. A. Trouw: None declared, R. E. M. Toes: None declared, P. Emery Grant/research support from: Abbvie, Merck, Pfizer, Roche, Consultant for: Abbvie, Bristol-Myers Squibb, Merck, Pfizer, Roche, Lilly, Novartis

Echinomycin, a bis-intercalating, antitumor drug, has been studied for its ability to induce the deamination of cytosine to uracil (C--U) in double-stranded DNA. We have employed a sensitive lacZ alpha-complementation reversion assay to detect G.C--A.T mutations at a number of sites in M13mp2 DNA to determine the extent to which distortions of DNA structure induced by echinomycin may affect C--U rates. When double-stranded M13mp2 DNA with a 12-base target containing a CpG site was incubated at 37 degrees C, the reversion frequency of the echinomycin-treated DNA increased linearly over time, with a rate constant 3-fold greater than DNA incubated without echinomycin. Of the 11 ways that blue pseudo-revertants can occur in the target, 96% of the observed revertants arose from C--T and tandem CC--TT transitions, with 78% attributable to single-base C--T changes at three sites. Transfection into ung+ cells decreased the reversion frequencies by 85% to near background levels, indicating that the increase in C--T mutations was due to deamination of C to U. The cytosine deamination rate constants for the entire target at pH 6.0 and 37 degrees C were 1.2 x 10(-11) sec-1 for untreated DNA and 3.5 x 10(-11) sec-1 for echinomycin-treated DNA. The increase in C--T mutation rates occurred at cytosines both proximal and distal to a CpG echinomycin-binding site. We hypothesize that this increase in deamination rate is due to a more open or single-stranded DNA structure caused by the echinomycin: DNA interaction.

Mast cell-deficient W/Wv mice are resistant to K/BxN serum transfer arthritis, and this resistance may be overcome by engraftment with mast cells. However, the pathways by which mast cells participate in arthritis remain unknown. Using a candidate mediator approach, we explored IL-1 as a potentially key mediator by which mast cells promote arthritis. As expected, IL-1α/β-deficient mice were completely resistant to arthritis. Short-term administration of exogenous IL-1 restored an attenuated arthritis course in these animals, consistent with an ongoing requirement for IL-1. Surprisingly, deficient W/Wv mice treated with IL-1 at disease induction displayed a full normal course of arthritis, demonstrating that exogenous IL-1 can bypass the need for mast cells. TNF proved unable to exert a similar effect. We therefore engrafted IL-1-/- bone marrow-derived mast cells (BMMC) into W/Wv animals and found that these animals displayed resistance to arthritis equivalent to nonengrafted W/Wv mice, consistent with an obligate role for IL-1 of mast cell origin. Exploring further the mechanisms by which mast cells may become activated in this IgG1-driven model, we found that BMMC stimulated in vitro via FcγRIII elaborated IL-1, while BMMC lacking this receptor were unable to mediate arthritis upon engraftment into W/Wv recipients. While BMMC engrafted into W/Wv animals disproportionately populate the spleen, we excluded a contribution from this aphysiologic mast cell population via splenectomy and by documenting that systemic levels of IL-1 were not detectable during arthritis initiation in engrafted animals. We conclude that mast cells local to the joint and activated via FcγRIII promote K/BxN serum transfer arthritis by production of IL-1, an activity that appears delimited to the initiation of disease (the 'jump start').