Anakinra is a recombinant human interleukin-1 receptor antagonist primarily administered by subcutaneous injection for the treatment of autoinflammatory conditions. Intravenous use of anakinra is only sparsely described in the literature. The aim of this study was to assess the safety of intravenous use of anakinra in a cohort of pediatric patients. This is a multicenter, retrospective cohort study. All patients who received intravenous anakinra from January 1st, 2017, to February 29th 2024 were enrolled. Collected data comprised: demographic characteristics, underlying clinical conditions, infusion-related data, anakinra-related adverse events and clinical response. The case series included 113 patients: 64 (56.6

OBJECTIVE:To assess the validity of the Patient-Reported Outcomes Measurement Information System (PROMIS) Pediatric measures in patients with chronic nonbacterial osteomyelitis (CNO). METHODS:Within the longitudinal patient registry of CNO, English-speaking patients aged 8 years and older self-reported PROMIS Pediatric measures of fatigue, pain interference (PI), pain behavior (PB), mobility, upper extremity (UE), physical activity (PA), and strength impact (SI), and external validation measures. Log-transformed linear mixed-effects models with random patient intercepts were used to assess PROMIS T-score changes. Wilcoxon signed-rank test was performed to determine the PROMIS T-score changes among the improved, worsened, and unchanged groups. Spearman rank correlation test determined the relationship of PROMIS T-scores with disease status reported by patients/families. RESULTS:More than 1,000 clinical visits from 184 patients included PROMIS Pediatric measures entries. All PROMIS T-scores correlated significantly (P < 0.01) with patient-reported variables and physician global assessment (PHGA). The correlation between function and mobility, PB, and PI was good (r = 0.4-0.6). The correlation of patient-reported disease status was strong with PHGA (r = 0.75); moderate with mobility, PB, and PI; and weak with fatigue, SI, UE, and PA. The changes of PROMIS T-scores over time for mobility, PB, PA, and PI compared with the self-reported status change were significant (P < 0.05). After effective treatment, when clinical disease activity score improved by at least three points (n = 18), the change of PROMIS T-scores for mobility, PB, PI, and UE were significant (P < 0.05). CONCLUSION:This study provided evidence supporting the use of PROMIS Pediatric mobility, PB, and PI measures for CNO clinical disease monitoring.

Objective To evaluate the prognostic utility of circulating interleukin-18 (IL-18) levels in predicting disease activity, macrophage activation syndrome (MAS), and disease course in patients with Still disease (SD) receiving first-line IL-1 inhibitors (IL-1i). Methods We retrospectively analyzed 66 biologic-naive patients with SD who received first-line treatment with IL-1i. Plasma IL-18 levels were measured at baseline and at 3, 6, and 12 months after IL-1i initiation. Associations between IL-18 levels and clinical outcomes were assessed using mixed-effects models, receiver operating characteristic (ROC) curve analysis, and multivariate logistic regression. Results Median baseline IL-18 levels were 61,425 pg/mL (interquartile range 16,194-235,746) and declined significantly after IL-1 blockade (P < 0.0001). Higher IL-18 levels persisted in patients with active disease (P < 0.0001). Baseline IL-18 >45,000 pg/mL predicted active disease at 12 months (area under the curve [AUC] 0.82; P = 0.0002), MAS development within 24 months (AUC 0.78; P = 0.01), and a chronic-persistent course (AUC 0.73; P = 0.007). In multivariate models, elevated baseline IL-18 and delayed IL-1i initiation for more than three months independently predicted adverse outcomes. Strikingly, at three months, IL-18 >15,000 pg/mL was a stronger predictor of chronic-persistent course (AUC 0.92; P < 0.0001), independent of clinical disease activity (odds ratio 25.6; P = 0.01), with the multivariate model explaining 67% of variance (AUC 0.95). Conclusion In biologic-naive patients with SD, IL-18 levels, especially reassessed three months after IL-1i initiation, robustly predict long-term disease activity, MAS risk, and chronic-persistent trajectory. Early measurement and dynamic monitoring of IL-18 may enable risk stratification and guide timely therapeutic escalation or treatment adjustment to improve outcomes.

OBJECTIVE:Systemic juvenile idiopathic arthritis (sJIA) is a chronic childhood disease classically attributed to innate immune cell dysregulation. This study aimed to elucidate the role of innate lymphoid cells (ILCs), including natural killer (NK) cells and helper-ILCs (hILCs), in sJIA during clinically inactive disease (CID) through phenotypic and functional analysis. METHODS:Peripheral ILCs from children with sJIA during CID receiving interleukin-1 (IL-1) inhibitors (n = 40) were analyzed by flow cytometry and compared to 23 healthy children (HC) and 22 patients with unrelated autoinflammatory diseases taking IL-1 inhibitors. Plasma proteomic profiling was also performed. RESULTS:Patients with sJIA showed a significant reduction in circulating NK cell frequencies compared to HC, with an increased proportion of CD56bright NK cells. Although overall hILC frequencies were comparable to HC, ILC1s were increased, whereas ILC precursors were reduced. ILC1 frequency correlated positively with IL-18 plasma levels, whereas ILC2 frequency correlated negatively. Functional assessments revealed that NK cells from patients with sJIA had variable interferon γ (IFNγ) production upon IL-18/IL-12 stimulation, inversely correlating with IL-18 levels. Additionally, hILCs from these patients showed a specific impairment in IFNγ production despite normal IL-13 production, potentially linked to decreased IL-18 receptor α expression in ILC1s. Proteomic analysis confirmed IL-18 as the most up-regulated cytokine in sJIA plasma. CONCLUSION:Patients with sJIA in CID exhibit significant innate immune abnormalities, including altered ILC subset distribution and impaired IFNγ production, strongly associated with IL-18 levels. These findings suggest ongoing immune dysregulation despite clinical remission, underscoring a potential role for ILCs and cytokine interaction in sJIA pathogenesis.

Objective The potential involvement of adaptive immunity in systemic juvenile idiopathic arthritis (sJIA) pathophysiology remains an intriguing question. Here, we investigated whether and how the inflammatory environment in sJIA versus JIA synovial fluid (SF) may differentially impact T helper (Th) cell polarization and activation. Methods SF samples from sJIA and JIA patients (both n=7) were tested in various cell culture setups, with or without recombinant cytokines or cytokine-blocking drugs, to assess their effects on healthy donor Th cell activation. We analyzed cellular surface marker, transcription factor, and effector molecule expression using flow cytometry, Luminex, ELISA, and qRT-PCR. Results Both sJIA and JIA SF revealed highly pro-inflammatory profiles. Compared to JIA, sJIA SF demonstrated markedly elevated IL-1β, IL-18, GM-CSF, S100A9, and MPO levels, while JIA SF showed trends toward higher soluble FasL and IL-17A concentrations. Notably, sJIA SF significantly increased CD4 T cell ICOS expression and expanded CXCR3posCCR6pos Th cells, whereas JIA SF favored expansion of CXCR3negCCR6pos Th cells and CCR6pos Th cell expansion was sensitive to IL-1 blockade. Systemic JIA SF selectively sustained a IFNγ/IL-21 expressing T peripheral helper (Tph) phenotype, particularly associated with IL-1β, IL-18, and GM-CSF SF levels. Spiking JIA SF with a cocktail of these cytokines recapitulated some T cellular phenotypic features observed in sJIA SF cultures. Conclusion JIA and sJIA SF drive distinct Th cell polarization, including differential and sustained Tf/ph cell activation. These findings complement our earlier observations in sJIA peripheral blood and demonstrate the impact of the SF inflammatory matrix on immune cell activation. What is already known on this topic What this study adds How this study might affect research, practice or policy ### Competing Interest Statement CB received consultancy fees from Sobi and Novartis and speaker fees from GSK. MP received consultancy fees from Sobi and Novartis. CH has received honoraria (lecture fees) from Novartis; HW has received honoraria (lecture fees) from Novartis and Takeda, and travel support from Octapharma and CSL-Behring; DF received speaker fees/honoraria from Chugai-Roche, Novartis and SOBI as well as research support from Novartis, Pfizer and SOBI. HM received honoraria (lectures fees) and travel support from Novartis. No other disclosures relevant to this article were reported. CK has received consulting fees from Novartis and Swedish Orphan Biovitrum (SOBI) (< $10,000 each) and received research support from Novartis (> $10,000). Interdisciplinary Center for Clinical Research (IZKF) Wuerzburg, Z-3/BC-13 Italian Ministry of Health Federal Ministry of Education and Research (BMBF), 01EO2108 German Research Foundation (DFG), MO 2160/4-1, KE 2026 1/3

OBJECTIVES:To evaluate diagnostic and prognostic significance of traditional laboratory parameters of hyperinflammation and of the IFNγ-related biomarkers interleukin-18 (IL-18), CXCL9 and neopterin in macrophage activation syndrome (MAS) secondary to Still's disease (SD). METHODS:Forty-one patients with MAS and 24 patients with active pediatric SD from six Italian centers were enrolled. Samples were obtained at baseline (at initiation or within 48 hours of initiation of specific treatments) for MAS or active SD and at T1 (5-15 days from baseline) only from MAS. CXCL9, IL-18 and neopterin were measured by ELISA. The MAS clinical severity score (MCSS) was developed to define MAS severity (mild: score 0-4; severe: score 5-8). RESULTS:In addition to the parameters included in the 2016 MAS criteria, lymphopenia and increased LDH reliably discriminated MAS from active SD. Levels of CXCL9, IL-18 and neopterin effectively discriminated MAS from active SD. Higher levels of the three IFNγ-related biomarkers at baseline were associated with a severe course MAS (MCSS>4). Combining levels at baseline of CXCL9 with those of ferritin, platelet count, fibrinogen and LDH, led to a prognostic score with sensitivity of 100 % and specificity of 74 % for severe MAS. Contingency analysis showed that CXCL9 >830 pg/ml and IL-18 >83,000 pg/ml at T1 had a significant risk of failing to achieve MAS remission in ≤2 months (odds ratio 9.3 and 5.4, respectively). CONCLUSIONS:These findings highlight the potential role of CXCL9 measurement in supporting the diagnosis and guiding the therapeutic management of patients with MAS in clinical practice.

Objectives To develop and validate classification criteria for paediatric chronic nonbacterial osteomyelitis (CNO) jointly supported by the European Alliance of Associations for Rheumatology (EULAR) and the American College of Rheumatology (ACR). Methods This international initiative had 4 phases: (1) candidate items were proposed in a survey of paediatric rheumatologists, (2) criteria definition and reduction by Delphi and nominal group technique exercises, (3) criteria weighting using multicriteria decision analysis, and (4) refinement of weights and threshold score in a development cohort of 441 patients and validation in another cohort of 514 patients. Results The new EULAR/ACR classification criteria for CNO require typical radiographic or magnetic resonance imaging findings and bone pain as an obligatory entry criterion and exclusion criteria of malignancy, infection, vitamin C deficiency, and hypophosphatasia, followed by additive weighted criteria in 5 clinical (site of bone lesions, pattern of bone lesions, age at onset, coexisting conditions, fever) and 4 pathology/laboratory domains (bone biopsy findings if done, anaemia, C-reactive protein level, and erythrocyte sedimentation rate). A total score ≥55 is required for classification as CNO. The new criteria had a sensitivity of 82% and specificity of 98% in the validation cohort. Conclusions These new classification criteria for paediatric CNO developed with international input reflect current views about CNO, have high specificity and good sensitivity, and provide a key foundation for future CNO research.

OBJECTIVE:To develop and validate classification criteria for pediatric chronic nonbacterial osteomyelitis (CNO) jointly supported by EULAR and the American College of Rheumatology (ACR). METHODS:This international initiative had 4 phases: (1) candidate items were proposed in a survey of pediatric rheumatologists, (2) criteria definition and reduction by Delphi and nominal group technique exercises, (3) criteria weighting using multicriteria decision analysis, and (4) refinement of weights and threshold score in a development cohort of 441 patients and validation in another cohort of 514 patients. RESULTS:The new EULAR/ACR classification criteria for CNO require typical radiographic or magnetic resonance imaging findings and bone pain as an obligatory entry criterion and exclusion criteria of malignancy, infection, vitamin C deficiency, and hypophosphatasia, followed by additive weighted criteria in 5 clinical (site of bone lesions, pattern of bone lesions, age at onset, coexisting conditions, fever) and 4 pathology/laboratory domains (bone biopsy findings if done, anemia, C-reactive protein level, and erythrocyte sedimentation rate). A total score ≥55 is required for classification as CNO. The new criteria had a sensitivity of 82% and specificity of 98% in the validation cohort. CONCLUSION:These new classification criteria for pediatric CNO developed with international input reflect current views about CNO, have high specificity and good sensitivity, and provide a key foundation for future CNO research.

Background: Chronic nonbacterial osteomyelitis (CNO) is an autoinflammatory bone disease that mainly affects children and adolescents. Disease monitoring is challenging as reported pain is not reliable and imaging is not always obtained at all clinic visits. To date, patient reported outcomes used in CNO research have not yet been validated in this population. The Patient-reported Outcomes Measurement Information System (PROMIS) questionnaires, validated in other pediatric rheumatic diseases, are administered to patients enrolled in the prospective multisite CHronic nonbacterial Osteomyelitis International Registry (CHOIR)1 since 2018. Objectives: To assess the convergent and responsive validity of the PROMIS instruments in patients with CNO. Methods: Children or young adults with CNO were consented and enrolled into CHOIR. Self-reported PROMIS questionnaires of fatigue, pain interference (PI), pain behavior (PB), mobility, upper extremity (UE), physical activity (PA) and strength impact (SI) were administered to patients 8 years and older in English or Spanish at each clinical visit. Demographic, clinical, and imaging data were prospectively collected. The T score was calculated. External validation surveys were administered to assess patients' perception of difficulty of use of limb/back/jaw, fatigue, sadness and worry on a 0-10 scale, disease status (inactive, mild, moderate, severe), and status change (unchanged, worsened, improved). Improvement of clinical disease activity score (CDAS) of 2.5 was defined as meaningful change. Descriptive statistics were used for demographic and clinical characteristics. Log-transformed linear mixed effect models with random participant intercepts were performed to assess PROMIS score changes after treatment. Wilcoxon signed-rank test with continuity correction was performed to determine the change of the PROMIS scores among the improved, worsened, and unchanged groups. Spearman rank correlation test was performed to determine the relationship between the PROMIS scores and reported disease status by patient/families. Results: More than 1,000 clinical visits from 184 patients were associated with self-reported PROMIS questionnaire entries in English. The median age at disease onset, diagnosis, and enrollment were 9.4 (IQR 7.5 – 11.3), 10.4 (IQR 8.4 -12.3), and 11.4 (IQR 9.5 – 13.8) years respectively. Seventy (38%) were males and 153 (83%) were White. All PROMIS scores correlated significantly (p<0.01) with patient reported variables and physician global assessment (PHGA). The correlation with function and PHGA was good (0.4-0.6) for Mobility, PB, and PI. All PROMIS scores, except physical activity, correlated significantly (p<0.05) with patient reported disease status. The correlation between patient-reported disease status and PHGA (0.75) was strong, moderate with Mobility (-0.53), PB (0.57), PI (0.5), and Fatigue (0.36), and weak with, SI (-0.23), UE (-0.23), and PA (-0.03). The changes of PROMIS scores over time for Mobility (p=0.015), PB (p<0.001), PA (p=0.019), and PI (p=0.011) compared to the self-reported status change (unchanged, improved, worsened) was significant. However, PROMIS score changes for Fatigue (p=0.055), SI (p=0.878), and UE (p=0.086) did not differ across various self-reported status change groups. After effective treatment when clinical disease activity score improved by at least 2.5 points (n=18), the change of PROMIS score from Mobility, PB, PI, UE was significant (p<0.05), whereas the change of PROMIS score from Fatigue, SI, and PA were not. Conclusion: PROMIS Questionnaires provide valuable information about disease status of children with CNO and correlate well with self-reported functional and other psychosocial domains. Mobility, PI, and PB show sensitivity to change after effective treatment or with disease status change. These instruments are useful for CNO clinical disease monitoring and research. REFERENCES: [1] Wu EY, Oliver M, Scheck J, et al. J Rheumatol. 2023 PMID: 37399459; PMCID: PMC10543471. Acknowledgements: The authors thank the CHOIR participants, research assistants and volunteers at all sites including Teresa Dickson, Corinne Lawler, Sumaya Aden, Thuan Bui, Kyra Shelton, Esha Mahal, Annie Xu, Kellen James, Shayla Nguyen, Zheng Xu, Ava Klein, Chessie Snider, Mabel Ho, Trang Pham, Anna Saack, Paige Trunnell, Emily Deng, Ana Park, Cailey Karshmer, Emma Leisinger, Mary Ellen Riordan, and Justine Griswold. We appreciate the help from Ingrid Goh, Mariana Correia Marques, and Min-Lee Chang for the testing of the registry database and the training material. In addition to the authors, the following CARRA CNO workgroup members participated in the February 2021 meeting: Ingrid Goh, Brian Nolan, Tzielan Lee, Annette Jansson, Aleksander Lenert, Lina Jaberi, David Cabral, Lauren Potts, Arielle Hay, Karine Toupin-April, Akaluck Thatayatikom, Ingram Chang, Piya Lahiry, Anja Schnabel, Mikhail Kostik, Nathan Rogers, Achille Marino, Dita Cebecauerova, Phillip Mease, Lindsey Bergstrom, Suzanne Li, Deborah McCurdy, Alex Theos, Matthew Hollander, Samira Nazzar, Farzana Nuruzzaman, Beverley Shea, and Chris Obrien. Statistical analysis was supported by CRMO Warriors Guild and Kaila's Komfort generous donations. Disclosure of Interests: Yongdong Zhao Bristol-Myer Squibbs, Mary Eckert: None declared, Evelyn Yawei Wu I have worked as a paid consultant for 2 pharma companies – Enzyvant Therapeutics, Inc. and Pharming Healthcare, Inc., Melissa Oliver: None declared, Joshua Scheck: None declared, Sivia Lapidus: None declared, Ummusen Kaya Akca: None declared, Shima Yasin: None declared, Aleksander Lenert: None declared, Sara Stern: None declared, Antonella Insalaco: None declared, Manuela Pardeo: None declared, Gabriele Simonini: None declared, Edoardo Marrani: None declared, Xing Wang: None declared, Bin Huang: None declared, Leonard K Kovallick: None declared, Natalie Rosenwasser: None declared, Erin Balay: None declared, Gabriel Casselman: None declared, Adriel Liau: None declared, Ava Klein: None declared, Yurong Shao: None declared, Claire Yang: None declared, Molly Briggs: None declared, Ethan Mueller: None declared, Emily Deng: None declared, Paige Rhiannon Trunnell: None declared, Iris Hamilton: None declared, Elise Machrone: None declared, Doaa Mosad Mosa: None declared, Lori Tucker: None declared, Hermann Girschick: None declared, Ronald Laxer Akros Pharmaceutical, Eli Lilly Canada, Sanofi, Novartis, Sobi all less that 5000, Georgina Tiller: None declared, Jonathan Akikusa I have been on advisory boards in the last 12 months for Pfizer and Novartis with honoraria <$5000. I am an investigator in a drug trial for Abbvie., Christian Hedrich: None declared, Karen Onel: None declared, Fatma Dedeoglu: None declared, Marinka Twilt: None declared, Seza Ozen Novartis and SOBI and Bayer, Polly Ferguson I did provide consulting services last in 2020, Laura Schanberg: None declared, Bryce Reeve: None declared.

Background Macrophage activation syndrome (MAS) is a life-threatening complication of different rheumatic diseases, particularly of systemic juvenile idiopathic arthritis (sJIA). Objectives We report the case of 17-year-old girl with sJIA complicated by recurrent severe MAS episodes. Methods Patient received emapalumab (anti-IFNg antibody) in two subsequent MAS episodes, then underwent an uncomplicated hematopoietic stem cell transplantation (HSCT) from a haploidentical donor, while receiving emapalaumab and anakinra granting complete control of inflammatory activity of the underlying disease. One year after transplant she is in complete disease remission. Results A 13-year-old Caucasian girl presented with fever, rash and hepato-splenomegaly. Laboratory parameters were consistent with full-blown MAS (tab 1). In the absence of clear evidence of an underlining condition, a diagnosis of secondary HLH was made. Treatment with high dose of intravenous (IV) methylprednisolone (mPDN) and oral cyclosporine (CYC) was started with progressive improvement. After one year, still on CYC, she presented with fever, rash and arthritis with laboratory parameters consistent with MAS (table 1), diagnosis of sJIA complicated by MAS was made. In 24 hours, her general condition rapidly worsened and she was admitted to the ICU. High dose of IV mPDN (7 pulses of 30 mg/kg/day) as well as IV CYC (5 mg/kg/day) did not yield a response. Emapalumab was started, in the NI-0501-06 trial, (6 mg/kg initial dose followed by 3 mg/kg every 3 days) for 11 infusions. Conditions progressively improved. In order to prevent flares of the underlining sJIA, anakinra (2 mg/kg/day) was started. After 2 years in clinical remission, while she receiving anakinra every other day, she presented with fever, vomiting and diarrhea. Anakinra was immediately increased to daily dosing. Stool analysis showed Salmonella infection and antibiotic therapy was started. Her condition rapidly worsened, laboratory parameters were again consistent with full-blown MAS (tab 1). She required ICU admission for multiorgan failure. Anakinra was administered IV and the dose increased up to 12 mg/kg/day. IV MPDs (8 pulses of 30 mg/kg/day) as well as IV CYC (5 mg/kg/day) were started with partial response. Based on her previous response, emapalumab was started again (compassionate use) with marked and rapid improvement. Because of recurrent MAS episodes, particularly for their rapidly progressive evolution, the patient underwent an ex-vivo T cell-depleted haploidentical HSCT from her mother. The conditioning regimen was based on a Thiotepa-Treosulfan-Fludarabine scheme. Emapalumab was continued 1 month after HSCT together with anakinra. The patient developed mild complication, achieved full donor engraftment with complete donor-derived immune reconstitution after 3 months. One year after HSCT, the patient is in excellent clinical condition on anakinra every other day, with complete remission of sJIA/MAS, also confirmed by persistently normal levels of IL-18 and CXCL9 (tab 1). Conclusion This case provides further evidence of the efficacy of emapalumab in MAS [1], of the potential benefit of HSCT in difficult sJIA patients [2]. Notably, full control of inflammatory activity with emapalumab and anakinra may help to obtain a successful HSCT and reduce the risk of rejection. References [1] De Benedetti F. Ann Rheum Dis 2022-eular.803[2] Morelle G. Pediatr Rheumatol Online J 2021 Mar 12;19(1):27 Acknowledgements: NIL. Disclosure of Interests Claudia Bracaglia Speakers bureau: SOBI, Consultant of: SOBI, Novartis, Manuela Pardeo Consultant of: SOBI, Giulia Marucci: None declared, Simona Riccio: None declared, Francesco Quagliarella: None declared, Ivan Caiello: None declared, Giusi Prencipe: None declared, Pietro Merli Consultant of: SOBI, Franco Locatelli Consultant of: SOBI, Fabrizio De Benedetti Consultant of: Abbvie, SOBI, Novimmune, Novartis, Roche, Pfizer.Table 1Laboratory parameters and cytokine levels during disease course.Laboratory parametersRangeFirst MASSecond MASThird MASHSCT1 year after HSCTGB (10^3/uL)5.5-1510.878.873.411.878.54PLT (10^3/uL)150-45080195147184327Ferritin (ng/ml)13-15013.08827.3965.92123026ALT (UI/L)<3350815051213AST (UI/L)<32891258652422LDH (UI/L)135-22517171623941175234Fibrinogen (mg/dl)190-430400500193341428TGL (mg/dl)<170197208220148106IL-18 (pg/ml)<3001897642776136606995341CXCL9 (pg/ml)<61211289522488294035050

Background MAS, a form of secondary hemophagocytic lymphohistiocytosis (sHLH), is a severe, life-threatening complication of rheumatic diseases that occurs most frequently in patients (pts) with sJIA and adult-onset Still's disease (AOSD). MAS is characterized by hyperinflammation and overproduction of interferon γ (IFNγ). Treatment with emapalumab, an anti-IFNγ monoclonal antibody, rapidly neutralized IFNγ and controlled MAS secondary to sJIA in pts with an inadequate response to high-dose glucocorticoids (GCs) in a phase 2 study (parent study).[1] Objectives To report outcomes and safety among pts with MAS treated with emapalumab after 12 months of follow-up. Methods The parent study enrolled pts with sJIA or AOSD who failed high-dose GCs (≥2 mg/kg/day). Pts who received emapalumab in the parent study (6 mg/kg on day [D] 0, followed by 3 mg/kg every 3 days until D15 and twice weekly until D28) and completed short-term follow-up (≥4 weeks) after last drug administration were invited to participate in this long-term follow-up study. Pts were assessed at follow-up Week (W) 2, W3, D30, D100, Month (M) 6 and M12. Emapalumab was not administered during follow-up. Overall MAS activity was monitored using a visual analog scale, comprehensive clinical evaluation and observation of pts' overall status. Serum samples for pharmacokinetic and pharmacodynamic analysis were collected at each study visit while serum emapalumab remained detectable. Safety was monitored throughout. Results All 14 pts (sJIA onset at <16 yrs, n=13; 1 had onset at age 16 yrs, 7 months) in the parent study participated in this long-term follow-up study. 6 pts had a history of 19 MAS episodes prior to the parent study. All prior episodes were treated with high-dose GCs; pts were also treated with anakinra (n=7) and/or cyclosporine A (n=8). 13/14 patients achieved MAS remission by W8, with rapid IFNγ neutralization during the parent study, as shown by decreased CXCL9 levels versus baseline. GCs were rapidly tapered in all pts. 13/14 pts did not present with another MAS episode; 1 MAS episode was reported 11 months after the pt stopped emapalumab (serum emapalumab was undetectable). The terminal elimination phase for emapalumab was slow and linear during follow-up (median t½, 24 days). CXCL9 and soluble interleukin-2 receptor levels remained close to, or within, the normal range. GC tapering continued during follow-up: at M12, 5 pts were off GCs and 6 pts were receiving <0.3 mg/kg/day of prednisone. 4 sJIA flares (without MAS) occurred during follow-up. In total, 37 adverse events (AEs) were reported by 12 patients, including 3 serious AEs (SAEs), all unrelated to emapalumab: 1 MAS reactivation, 1 sJIA flare and 1 ankle edema. All SAEs resolved spontaneously or with standard treatment. 10 infectious AEs (9 of viral origin) were reported during follow-up; 4 occurred when serum emapalumab levels were measurable and 6 after emapalumab became undetectable (Table 1). No new safety signals were observed. All pts were alive at M12. Conclusion Most pts with MAS who had failed high-dose GCs and responded to emapalumab remained in remission and continued GC tapering during 12 months of follow-up. Any viral infections during follow-up resolved spontaneously or with standard treatment, confirming the favorable safety profile of emapalumab. A pivotal clinical trial of emapalumab in patients with sHLH and underlying rheumatic disease is ongoing (EMERALD; NCT05001737). Reference [1] De Benedetti F, et al. Ann Rheum Dis 2022;81(Suppl 1):128 (OP0193). Acknowledgements Medical writing assistance was provided by Blair Hesp PhD CMPP of Kainic Medical Communications Ltd. (Dunedin, New Zealand), which was funded by Sobi AG (Basel, Switzerland). Disclosure of Interests Fabrizio De Benedetti Consultant of: AbbVie, Sobi, Pfizer, Roche, Sanofi, Novartis, Novimmune, Grant/research support from: AbbVie, Sobi, Pfizer, Roche, Sanofi, Novartis, Novimmune, Alexei Grom Consultant of: Novartis, AB2 Bio, Novimmune, Sobi, Paul Brogan Consultant of: Sobi, Novartis, Roche, UCB, Claudia Bracaglia: None declared, Manuela Pardeo: None declared, Giulia Marucci: None declared, Despina Eleftheriou Speakers bureau: Sobi, Charalampia Papadopoulou Speakers bureau: Sobi, Grant Schulert Consultant of: Novartis, Sobi, Novimmune, AB2 Bio, Pierre Quartier Speakers bureau: AbbVie, Chugai-Roche, Lilly, Novartis, Pfizer, Sobi, Consultant of: AbbVie, Chugai-Roche, Lilly, Novartis, Pfizer, Sobi, Jordi Antón Consultant of: Sobi, Novartis, Roche, Pfizer, AbbVie, GSK, Christian Laveille Consultant of: Sobi, Rikke Frederiksen Employee of: Former employee of Sobi, Veronica Asnaghi Employee of: Former employee of Sobi, Maria Ballabio Employee of: Former employee of Sobi, Philippe Jacqmin Consultant of: Sobi, Cristina de Min Employee of: Former employee of Sobi.Table 1N=14Emapalumab levels ≥lower limit of quantification (LLOQ)Emapalumab levels <LLOQInfection AEs, n46Pts with ≥1 infection AE, n (%)2 (14)5 (35)Cytomegalovirus (CMV) infection reactivation00CMV infection00Epstein Barr infection01Rhinovirus infection10Enterovirus infection01Viral infection01Viral upper respiratory tract infection32Nasopharyngitis00Viral test positive (CMV, adenovirus, BK polyoma virus, respirovirus)00Cestode infection01

Background Macrophage Activation Syndrome (MAS) and Secondary Hemophagocytic Lymphohistiocytosis (sHLH) are hyperinflammatory conditions, in which IFNγ plays a pivotal role. Prompt recognition and early treatment are essential to improve the outcome and the mortality rate. Objectives This is a retrospective multicenter study. We correlated traditional laboratory parameters of hyperinflammation with IL-18 and IFNγ related biomarkers. We have also evaluated the diagnostic and prognostic role of IL-18, CXCL9, CXCL10 and neopterin in patients with MAS and sHLH. Methods One hundred-six patients from 6 Italian centers were enrolled: 41 with sHLH, 41 with MAS in the context of sJIA, and 24 with sJIA without MAS. The samples were collected at three different time points: active disease (T0), 7-10 days from starting therapy (T1) and in clinical inactive disease on medication (from 1 to 3 months from onset) (T2). Serum levels of IL-18 and of the IFN-γ related biomarkers (CXCL9, CXCL10, Neopterin) were measured by ELISA. Results A total of 378 samples were collected. Laboratory features at T0 are detailed in table 1. Using the 2016 classification criteria for MAS, we can confirm that platelet count is a specific parameter, only 2 patients with sJIA had a value <181x109/liter. Instead ferritin is a sensitive parameter, 94.4% of patients with MAS had ferritin >684 mg/ml. Lactate dehydrogenase (LDH) values were statistically higher in MAS and sHLH compared to sJIA. ROC curve of LDH values in MAS showed a statistically significant area under the curve (AUC= 78.2%, p-value <0.0001). A cut-off of 683 U/L had a sensitivity of 73.6% and a specificity of 70.3%. IL-18, CXCL9, CXCL10 and neopterin levels in T0 were significantly higher in MAS and sHLH compared to sJIA. In MAS, IL-18 levels were significantly higher compared to sHLH (p<0.0001). The ROC curves performed for each biomarker showed a statistically significant AUCs (p<0.01), except for IL-18 in sHLH. We have identified a cut off value for each biomarker in MAS (CXCL9 900 pg/ml, CXCL10 260 pg/ml, neopterin 5.0 ng/ml, IL-18 82996 pg/ml) and sHLH (CXCL9 2145 pg/ml, CXCL10 270 pg/ml, neopterin 7.1 ng/ml). In T0 neopterin correlates significantly with IL-18, CXCL9 and CXCL10 in MAS group but not in sHLH. We found also strong correlation between CXCL9 and CXCL10 only in MAS group. Conclusion Platelet count and ferritin have high specificity and sensitivity, respectively, to diagnose MAS in the context of sJIA. Even if LDH is not included in 2016 classification criteria for MAS in sJIA, we have found that this parameter could help to discriminate MAS in sJIA, in addition to the others. Our results confirm that IL-18 and the IFN-γ related biomarkers are significantly higher in patients with MAS and sHLH and might be useful to diagnose MAS/sHLH. IL-18 could help to distinguish sHLH from MAS and MAS from active sJIA. References [1]Henter JI, et al. Pediatr Blood Cancer. 2007[2]Ravelli A, et al Annals of the Rheumatic Diseases 2016 Acknowledgements: NIL. Disclosure of Interests Arianna De Matteis: None declared, Denise Pires Marafon: None declared, Ivan Caiello: None declared, Manuela Pardeo: None declared, Giulia Marucci: None declared, Emanuela Sacco: None declared, Francesca Minoia: None declared, Francesco Licciardi: None declared, Angela Minaici: None declared, Ilaria Maccora: None declared, Maria Cristina Maggio: None declared, Giusi Prencipe: None declared, Fabrizio De Benedetti Consultant of: Abbvie, SOBI, Novimmune, Novartis, Roche, Pfizer, Claudia Bracaglia Consultant of: Novartis, SOBI.Table 1Laboratory parameters in T0. Values are shown as median (IQR); p-value: Mann-Whitney U test.MAS (N=54)sHLH (N=48)sJIA (N=4)MAS vs sHLHMAS vs sJIAsHLH vs sJIAFerritin (ng/ml)4755 (1816-10988)4098 (2075-16867)717 (335-2313)0.77<0.0001<0.0001Platelet count (x10^9/l)199 (107-314)97 (47-184)450 (343-570)0.0003<0.0001<0.0001AST (U/L)85 (51-146)150 (51-340)30 (22-44)0.06<0.0001<0.0001Triglycerides (mg/dl)188 (148-263)226 (166-381)105 (75-139)0.11<0.0001<0.0001Fibrinogen (mg/dl)337 (222-433)228 (137-331)572 (482-692)0.003<0.0001<0.0001LDH (U/L)965 (679-1369)1255 (701-2748)587 (365-724)0.10<0.0001<0.0001CXCL9 (pg/ml)2236 (675-9670)4159 (1880-10016)300 (300-1979)0.14<0.0001<0.0001Neopterin (ng/ml)9.4 (5.0-16.2)20.3 (9.6-35.0)4.2 (3.0-7.2)0.0018<0.0001<0.0001IL-18 (pg/ml)170338 (83277-287152)11787 (21881120)36764 (8958-82714)<0.0001<0.00010.19

ObjectivesMacrophage activation syndrome (MAS) is a severe, life-threatening complication of systemic juvenile idiopathic arthritis (sJIA) and adult-onset Still’s disease (AOSD). The objective of this study was to confirm the adequacy of an emapalumab dosing regimen in relation to interferon-γ (IFNγ) activity by assessing efficacy and safety. The efficacy outcome was MAS remission by week 8, based on clinical and laboratory criteria.MethodsWe studied emapalumab, a human anti-IFNγ antibody, administered with background glucocorticoids, in a prospective single-arm trial involving patients who had MAS secondary to sJIA or AOSD and had previously failed high-dose glucocorticoids, with or without anakinra and/or ciclosporin. The study foresaw 4-week treatment that could be shortened or prolonged based on investigator’s assessment of response. Patients entered a long-term (12 months) follow-up study.ResultsFourteen patients received emapalumab. All patients completed the trial, entered the long-term follow-up and were alive at the end of follow-up. The investigated dosing regimen, based on an initial loading dose followed by maintenance doses, was appropriate, as shown by rapid neutralisation of IFNγ activity, demonstrated by a prompt decrease in serum C-X-C motif chemokine ligand 9 (CXCL9) levels. By week 8, MAS remission was achieved in 13 of the 14 patients at a median time of 25 days. Viral infections and positive viral tests were observed.ConclusionsNeutralisation of IFNγ with emapalumab was efficacious in inducing remission of MAS secondary to sJIA or AOSD in patients who had failed high-dose glucocorticoids. Screening for viral infections should be performed, particularly for cytomegalovirus.Trial registration numberNCT02069899andNCT03311854.